Imports from China down slightly, but high pest risk continues

I have blogged often about the pest risk of wood packaging associated with imports from Asia – especially China – and the shift in that risk arising from import volumes and ports at which they are arriving (increasing volumes entering country at ports along Atlantic and Gulf coasts). [See blogs posted on this site, under the “wood packaging” category (listed below the archives by date).] As noted, U.S. imports from Asia are at all-time highs: in the first three months of 2022, they reached 1.62 million TEU (shipping containers measured as twenty-foot equivalents). This was 31.1% higher than in the same period in pre-pandemic 2019 (Mogelluzzo, B. April 22, 2022).

The most recent information (Szakonyi, M. 2023) confirms that U.S. importers are shifting suppliers to countries other than China, primarily because of lengthy shutdowns in Chinese factories linked to the “0 COVID” policy and some U.S. restrictions and tariffs. Over 2022 (full year), China – including Hong Kong – supplied 40.7% of U.S. imports. This is still a huge proportion, but lower than in 2021, when it was 42.4%. The Journal of Commerce calculates that the number of containers coming from China fell by 435,000. At the current rate of infestation in wood packaging from China calculated by Haack et al. 2022, that might mean about 1,200 fewer containers from China with infested wood packaging entering the U.S.

[Explanation of calculations: I divided 435,000 by 2 to convert 20-ft TEU into 40-ft containers that CBP encounters at the ports; multiplied the result by 0.75 – based on the decade-old Meissner estimate of % of containers that have SWPM; then multiplied the result by .0073 because that is infestation rate for China during 2010-2020 period]

This might be progress. China continues to have a terrible record of non-compliant wood packaging 23 years after U.S. and Canada instituted phytosanitary requirements. According to Haack et al. (2022), packaging from China made up 4.6% of all shipments inspected under the terms of their analysis, but 22% of the 180 consignments with infested wood packaging. Thus the proportion of Chinese consignments with infested wood is five times greater than expected based on their proportion of the dataset. The rate of wood packaging from China that is infested has remained relatively steady = 1.26% during 2003–2004, 0.73% during 2010 – 2020. And the insects present belong to the group that causes the greatest damage: longhorned beetles (Cerambycids). Indeed, 78% of beetles in this family that were detected were from China.

There is some good news: some types of goods likely to be enclosed in crates have decreased notably. The proportion of furniture and other home items imported from China has declined from 71.6% of all U.S. imports in 2010 to 52.6% in 2022. As Haack et al. (2022) found, crates are the type of wood packaging where wood pests are most commonly found. While crates constituted only 7.5% of the wood packaging inspected, they made up 29.4% of the infested packaging – or four times greater than their proportion of the dataset.

The pest risk might not be changing significantly, however, because some of the new suppliers are also in Asia. Vietnam’s share of U.S. imports rose from 8.2% to 8.7%. The types of goods most often imported from Vietnam included electronics, shoes, and apparel. The U.S. has already been invaded by insect-pathogen complexes native to Vietnam, Taiwan, and other parts of southeast Asia – e.g., redbay ambrosia beetle and laurel wilt; invasive shot hole borers and Fusarium disease.

U.S. imports from South Korea, mostly electronics and autoparts, climbed from 3.8% to 4.1%. Imports from India also saw a tiny increase – from 3.8% to 3.9%. These shipments were primarily apparel and iron and steel components. These goods prompt concern because wood packaging associated with heavy materials are often infested by insects (Eyre et al. 2018). The Haack et al. (2022) analysis found two interceptions of wood packaging from Vietnam, one from Korea, and three from India.

Besides, the Journal of Commerce notes that shifts in suppliers cannot go far. These countries’ manufacturing capacity and transportation infrastructure are far below those of China (Szakonyi, M. 2023).

In February 2023, U.S. imports from Asia continued to decline from record levels in 2021 and 2022 to 1.09 million TEU. This level still exceeds by 25% the 869,091 TEU recorded in March 2020, at the beginning of the COVID-19 shutdown (Mongelluzzo, March 17, 2023).

[Reminder: higher shares of imports from Asia are going to ports along the Atlantic and Gulf coasts – spreading the risk. See earlier blogs. In early March the Port of Savannah posted an advertisement to the on-line Journal of Commerce, crowing that by July it will complete straightening the river at the Garden City Terminal (the container terminal). This fix will enable Savannah to raise its annual container processing capacity by 1.5 million TEU, to 7.5 million.]

The most hopeful finding is that imports from Mexico jumped 19.2% in the first 11 months of 2022 compared to the same period in 2021. Importers have their reasons: a desire to buy from producers closer to the U.S. market. These motivations have nothing to do with the risk of forest pest introductions. However, we can rejoice because Mexico has greatly improved the pest-infestation rates of its exports since 2009. The rate fell from 0.29% in 2003-2004 to 0.04% in 2010-2020 (Haack et al. (2022).  

larval Asian longhorned beetle; Thomas Denholm, NJ Department of Agriculture; Bugwood

I remain outraged that U.S. agencies have not taken effective steps to deal with the nearly 25-year-long problem of Chinese noncompliance with our phytosanitary requirements. As I noted in my previous blog, link to blog 303 Customs and Border Protection officials are disappointed that their enhanced enforcement in 2017 and 2021 has not yet resulted in improved compliance.

I suggested that the U.S. and Canadian government agencies should penalize trade partners with high records of not complying with ISPM#15. Among steps they should consider are

  • U.S. and Canada should refuse to accept wood packaging from foreign suppliers that have a record of repeated violations – whatever the apparent cause of the non-compliance. Institute severe penalties to deter foreign suppliers from taking devious steps to escape being associated with their violation record.
  • APHIS and CBP and their Canadian counterparts should provide guidance to importers on which foreign treatment facilities have a record of poor compliance or suspected fraud – so they can avoid purchasing SWPM from them. I greatly regret that the death of Gary Lovett might put an end to the voluntary industry program he had been developing, described here.
  • Encourage a rapid switch to materials that don’t transport wood-borers. Plastic is one such material. While no one wants to encourage production of more plastic, the Earth is drowning under discarded plastic. Some firms are recycling plastic waste into pallets.

Haack et al. 2022 fully describes the methodology used, the structure of USDA’s Agriculture Quarantine Inspection Monitoring (AQIM) program, detailed requirements of ISPM#15, the phases of U.S. implementation, etc.  Also see the supplemental data sheet in Haack et al. (2022) that compares the methods used in each analysis.

SOURCES

Eyre, D., Macarthur, R., Haack, R.A., Lu, Y. and Krehan, H., 2018. Variation in inspection efficacy by member states of wood packaging material entering the European Union. Journal of Economic Entomology, 111(2), pp.707-715.

Haack RA, Hardin JA, Caton BP and Petrice TR (2022) Wood borer detection rates on wood packaging materials entering the United States during different phases of ISPM#15 implementation and regulatory changes. Frontiers in Forests and Global Change 5:1069117. doi: 10.3389/ffgc.2022.1069117

Meissner, H., A. Lemay, C. Bertone, K. Schwartzburg, L. Ferguson, L. Newton. 2009. Evaluation of Pathways for Exotic Plant Pest Movement into and within the Greater Caribbean Region. A slightly different version of this report is posted at 45th Annual Meeting of the Caribbean Food Crops Society https://econpapers.repec.org/paper/agscfcs09/256354.htm

Mongelluzzo, B. Q1 US imports from Asia show no slowing in consumer demand. Apr 22, 2022. https://www.joc.com/maritime-news/container-lines/q1-us-imports-asia-show-no-slowing-consumer-demand_20220422.html

Mongelluzzo, B. US imports from Asia hit three-year low in February: data. https://www.joc.com/article/us-imports-asia-hit-three-year-low-february-data_20230317.html

Szakonyi, M. 2023. Sourcing shift from China pulls US import share to more than a decade low. https://www.joc.com/article/sourcing-shift-china-pulls-us-import-share-more-decade-low_20230201.html

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

Protecting ash & hemlock – latest information

nearly dead ash in Shenandoah National Park; photo by F.T. Campbell

I participated in the annual USDA Interagency Invasive Species Research Forum in Annapolis in January 2023; as usual, I learned interesting developments. I focus here on updates re: efforts to protect ash and hemlock

Hopeful Developments re: countering EAB to protect ash

There are hopeful results in both the biocontrol and resistance breeding programs. The overall goal is to maintain ash as a viable part of the North American landscape.

Biocontrol

Juli Gould (APHIS) reminded us that the agency began a classical biocontrol program targetting emerald ash borer (EAB) in 2003 – only a year after EAB had been detected and much earlier than is the usual practice. [Thank you, former APHIS PPQ Deputy Administrator Ric Dunkle!] By 2007 scientists had identified, tested, and approved three agents; a fourth was approved in 2015.

Nicole Quinn (University of Florida) stressed that the egg prarasitoid, Oobius — if it is effective — could prevent EAB from damaging trees. However, it is so small that it is very difficult to sample. One small study demonstrated that Oobius will parasitize EAB eggs laid in white fringe trees (Chionanthus virginicus) as well as in ash. This is important because it means this secondary host is not likely to be a reservoir of EAB.

The numbers

According to Ben Slager (APHIS), more than 8 million parasitoids have been released at 950 sites since the program began in 2007. These releases have been in 418 counties in 31 states, DC, and four Canadian provinces. Still, these represent just 28% of infested counties. Parasitoids have been recovered in 21 states and two provinces.

Rafael de Andrade (University of Maryland) specified that these releases included more than 5 million Tetrastichus in 787 sites; ~2.5 million Oobius in 828 sites in 30 states; ~500,000 Spathius agrili – lately only north of the 40th parallel. Releases of Spathius galinae began in 2015; so far ~ 470,000 in 395 sites.

 Impact

Several presenters addressed questions of whether the agents are establishing, dispersing, and – most important – improving ash survival. Also, can classical biocontrol be integrated with other management techniques, especially use of the pesticide emamectin benzoate.

Dispersal

Several studies have shown that the four biocontrol agents disperse well (with the caveat that Oobius is very difficult to detect so its status is much less certain).

Implementation considerations

De Andrade found that the longer the delay between the date when EAB was detected and release of Oobius, the less likely Oobius will be recovered. Tetrastichus surprised because the higher the numbers released, the fewer were recovered. He could determine no association between recovery of S. agrili and variations in release regime [numbers released; delay in releasing biocontrol agents; or frequency of releases]. He said it is too early to assess Sp. galinae since releases began only in 2015, but he did see expected relationship to propagule pressure – the more wasps released, the higher the number that were recovered. Sp. galinae did surprise in one way: it seemed to perform better at lower latitudes. De Andrade noted he was working data from less than half of release sites. He asked collaborators to submit data!!!!

Initial signs of ash persistence and recovery 

Claire Rutledge (Connecticut Agriculture Experiment Station) determined that

  • More large trees were surviving in plots where the biocontrol agents were released
  • EAB density was lower at long-invaded sites
  • Parasitism rates were similar across release age treatments and release/control plots

Gould focused on protecting saplings so they can grow into mature trees which could be sources of seeds to establish future generations. She noted that there are many “aftermath” forests across the northern United States – those dominated by ash saplings.

In Michigan, at a site of green ash, as of 2015 – 2021, EAB populations are still low, parasitism rate by Tetrastichus and S. galinae high. The percentage of saplings that remained healthy was greater than 80%. There were similar findings in white ash in New York: very low EAB larval density; and more than 70% of ash saplings had no fresh galleries. Gould reported that Tetrastrichus impcts could be detected within three years of release.

So, EAB are being killed by the biocontrol agents combined with woodpecker predation; but in their fourth instar, after considerable damage to the trees.

downy woodpecker in Central Park, NYC. photo by Steven Bellovin, Columbia University

Jian Duan reported on two long-term studies in green & white ash in Michigan and New England. His team used the most labor-intensive but best approach to determine EAB larval mortality and the cause – debarking trees – to determine whether the EAB larva were parasitized, were preyed on by woodpeckers, or were killed by undetermined cause, such as tree resistance, disease, or competition. In Michigan, he linked a crash of EAB population in 2010 was caused by Tetrastichus; EAB tried to recover, but crashed again, due to S. galinae. EAB larval densities had been reduced to 10 / m2. Predation by abundant woodpeckers and the native parasitoid Atanycolus was also important.

In New England, EAB has also declined from 20-30 larvae /m2 to ~ 10 m2.

In Michigan, healthy ash with dbh of larger than 5 inches were much more plentiful in sites where parasitoids had been released. Their survival/healthy rate also was much higher in release sites but the difference declined as years passed. In New England there were growing numbers of healthy trees in 2021-22; (almost none in 2017). Duan conceded that he could not prove a direct link but the data points to recovery.

Tim Morris (SUNY-Syracuse) found that white ash saplings continued to die in large numbers, but the mortality rate was significantly below the rate in 2017. Canopy conditions varied; some trees that were declining in 2013 were recovering in 2017. Forty percent of “healthy” ash in 2013 continued recovering in 2021. Few living trees were declining; trees were either healthy or dead. He thinks probably a combination of genetics and presence of parasitoids explains which trees recover. Morris also reported some signs of regeneration.

beaver feeding on ash saplings, Fairfax County, Va;
photo by F.T. Campbell

At this point, I noted that in parts of northern Virginia, beavers have killed ash saplings. Morris reported finding the same in some sites in New York. Perhaps others have, also; my comment was greeted by laughter.

Theresa Murphy (APHIS) looked at integration of biocontrol and insecticide treatment in urban and natural sites. A study of black and green ash in Syracuse, NY Naperville, IL, and Boulder, CO found continued high parasitism by Tetrasticus and S. galinae and woodpecker attacks in trees treated with emamectin benzoate. Researchers could not detect Oobius. By 2020, most of the untreated trees had died but treated trees remained healthy.

Murphy has begun studying integration of biocontrol and pesticides in green and black ash forests. The goal is to protect large trees to ensure reproduction; the biocontrol agents do not yet protect the large trees. This is especially important for black ash because it declines very quickly after EAB invades. Sites have been established in New York, through collaboration with New York parks, Department of Environmental Conservation, and the Mohawk tribe. She is still looking for sites in Wisconsin – where EAB is spreading more slowly than expected.

1 of the infested ash in Oregon; photo by Wyatt Williams, ODF

Max Ragozzino of the Oregon Department of Agriculture reported on imminent release of biocontrol agents targetting the recently detected outbreak there. I am encouraged by the rapid response by both the state and APHIS.

EAB resistance in ash

Jennifer Koch (USFS) said the goal is not to produce populations where every seedling is fully EAB-resistant, but to develop populations of ash trees with enough resistance to allow continued improvement through natural selection while retaining sufficient genetic diversity to adapt to future stressors (changing climate, pests, diseases). The program has developed methods to quantify resistance in individuals.. Initial field selections of “lingering ash” were shown to be able to kill as many as 45 % of EAB larvae. Already green ash seedling families have been produced by breeding lingering ash parents.  This first generation of progeny had higher levels of resistance, on average, than the parent trees.  Each generation of breeding can increase the proportion of resistance. Although the bioassays to test for EAB-resistance are destructive (e.g., cutting and peeling to count numbers of surviving larvae), the potted ash seedling stumps can resprout. Once the new sprouts are big enough they are planted in field trials to correlate bioassay results with field performers.  Poor performers are culled; those with higher levels of resistance remain and become sources of improved seed.

To ensure preservation of local adaptive traits, this process must be repeated with new genotypes to develop many seed orchards from across the species’ wide range. To support this work, concerned scientists are building multi-partner collaborative breeding networks. These organizations provide ways for citizens and a variety of partners to engage through monitoring and reporting lingering ash, making land available for test planting, and helping with the work of propagation.

See Great Lakes Basin Forest Health Collaborative » Holden Forests & Gardens (holdenfg.org), Monitoring and Managing Ash (MaMA) – A citizen-science-driven program for conservation and mitigation (monitoringash.org), and TreeSnap – Help Our Nation’s Trees! for more information.

Resistance levels in some of the first generation progeny were high enough for use in horticulture, where it is important that trees can remain healthy in challenging environments (street trees, city parks, landscaping, etc.). Koch hopes to develop about a dozen cultivars comprising the best-performing trees, appropriate for planting in parts of Ohio, Michigan, Indiana, and Pennsylvania.   Local NGO partners are planting some of these promising genotypes in Detroit to see how they withstand EAB attack.

a black ash swamp; photo via Flickr

The threat to black ash is especially severe, and this species presents unique difficulties. While scientists found several seedlings from unselected seedlots had killed high levels of larvae, those deaths did not always result in better tree survival. Koch thinks the tree’s defense response becomes detrimental to tree by blocking transport of water and nutrients. She is working with experts in genomics and others, such as Kew Royal Botanic Gardens, to try to identify candidate trees for breeding programs.  The genomics work has been supported by APHIS and the UK forest research agency, DEFRA. Michigan and Pennsylvania have supported the breeding work. USFS Forest Health Protection has supported work with black and Oregon ash (see below) (J. Koch, USFS, pers. comm.).

Koch has also begun working with Oregon ash, in collaboration with the USFS Dorena Genetic Resource Center (located in Cottage Grove, Oregon) and other partners.

dead hemlock in Massachusetts; photo by Ian Kinahan,
University of Rhode Island

Hemlock woolly adelgid

Scientists are still trying to find the right combination of biocontrol, chemical treatments, and silvicultural manipulation.

For several years, hope has focused on two has been on two predatory beetles, Laricobius nigrinus and L. osakiensis. Scott Salom (Virginia Tech) reports that release of these beetles over the past 20 years has had a significant impact on HWA density and tree photosynthetic rate and growth. However, Laricobius aredifficult to rear and they attack only the sistens generation of the adelgid. Ryan Crandall (University of Massachusetts) reports it has been difficult to establish these beetles in the Northeast. He links this difficulty is caused by temporary drops in HWA populations after cold snaps.

Scientists now agree that need to find predators that attack HWA during other parts of its lifecycle. Hope now focuses on silverflies — Leucotaraxis argenticollis and Le. piniperda.  While both species are established in eastern North America, the clades in the east feed almost exclusively on pine bark adelgid, and have not begun attacking HWA. Biocontrol practitioners therefore collect flies in the Pacific Northwest for release in the east. Salom is increasing his lab’s capacity to rear silverflies and exploring release strategies.

Preliminary evidence indicates that the western clades of Leucotaraxis are establishing, although data are not yet definitive (Havill, USFS).

Detecting the presence of biocontrol agents presents several challenges. Tonya Bittner (Cornell) described efforts to use eDNA analysis for this. Some puzzles have persisted; e.g., at some sites, she detected eDNA but caught no silverflies. This raised the question of long eDNA associated with the original release might persist. Another problem is that the assay cannot separate the introduced western L. nigrinus from the native congener, L. rubus (which also does not feed on HWA). She continues efforts to improve this technique.

Others explored interactions of the biocontrol agents with insecticides. Salom is studying the impact of soil-applied insecticides on Laricobius populations, which aestivate in the soil. Preliminary results showed significant reduction in the beetle’s population under soil drench application but not under soil injection. He has not yet analyzed all the data.

Michigan is trying to prevent spread of HWA from five counties along the eastern shore of Lake Michigan (where HWA was introduced on nursery stock) to widespread hemlock forests in northern part of the state. Phil Lewis (APHIS) is studying persistence of systemic insecticides in hemlock tissues, particularly twigs and needles. The pesticides involved are imidacloprid, dinotefuran, and Olefin. He has found that pesticide levels are highest 18 – 22 months after treatment, then decline. They are significantly higher after trunk injection compared to bark spray or soil treatments. Imidacloprid had higher residues in twigs; dinotefuran in needles. This difference affects the likelihood of adelgids actually ingesting the toxin.

healthy hemlock in experimental gap; Jefferson National Forest, VA; photo by Bud Mayfield, USFS

Bud Mayfield (USFS) reported on his study of silvicultural strategies to support healthier hemlocks. While hemlocks normally thrive in shade, it has been determined that sunlight assists small trees  reducing HWA sufficiently to counter the tree’s leaf-level stress. Small sapling hemlocks grown in sunlight fix more carbon and convert it to growth in shoots and trunk diameter.

Mayfield found promising immediate suppression of HWA in large gaps in Georgia and Tennessee. By the third year the saplings were still growing, although their faster growth had attracted more HWA. These findings were less clear farther north in central Virginia and western Maryland – Mayfield thinks because HWA pressure there is lower. However, managers must maintain the gaps by cutting rapidly-growing competing woody species. He plans to test this strategy farther north in Pennsylvania. He is still trying to determine the optimal size of the gap.


Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

Plant Diversity & Invading Insects: Key Relationship has Policy Applications

spotted lanternfly; photo by Stephen Ausmus, USDA; establishment facilitated by extent of invasion by its preferred host, Ailanthus

Seven coauthors (full citation at end of blog) compared various factors associated with numbers of invasive insect species in 44 land areas.These ranged from small oceanic islands to entire continents in different world regions, Liebhold et al. determined that the numbers of established non-native insect species are primarily driven by diversity of plants, including both native and non-indigenous. Other factors, e.g., land area, latitude, climate, and insularity, strongly affect plant diversity. Through this mechanism these factors affect insect diversity as a secondary impact.

Seven coauthors (full citation at end of blog) compared various factors associated with numbers of invasive insect species in 44 land areas.These ranged from small oceanic islands to entire continents in different world regions, Liebhold et al. determined that the numbers of established non-native insect species are primarily driven by diversity of plants, including both native and non-indigenous. Other factors, e.g., land area, latitude, climate, and insularity, strongly affect plant diversity. Through this mechanism these factors affect insect diversity as a secondary impact.

At large spatial scales [greater than 10 km2], regions supporting more diverse plant communities offer greater opportunities for herbivore colonization. Thus, plant diversity promotes invasion through the “facilitation effect”. Since most insects – including most of those introduced to naïve ecosystems – are herbivores, a greater number of possible foods is a clear advantage. Those insects that prey on herbivores benefit by plant diversity indirectly.

Non-native coral tree, Erythrina, in Hawai`i; photo by Forrest and Kim Starr; did wide planting of exotic Erythrina facilitate invasion by Erythrina gall wasp?

At smaller spatial scales, plant diversity might impair the ability of insects to locate hosts because of the “dilution effect”. I have been asking for decades why so few of the Eurasian insects established in eastern North America have not also established along the Pacific coast from Oregon into British Columbia. The region has a plant-friendly climate and almost every plant species from temperate climates is grown there in cultivation. Perhaps the non-native plants – while numerous enough to become invaders themselves – are still sufficiently scarce or dispersed to impair introduced insects’ locating an familiar host?

According to the Smithsonian Institution, Hawai`i has approximately 2,499 taxa of flowering plants and 222 taxa of ferns and related groups. The native flora of the United States includes about 17,000 species of vascular plants; at least 3,800 non-native species of vascular plants are recorded as established outside cultivation. I don’t know how many non-native plant species are in cultivation.

horticultural viburnum invading riparian forest in Fairfax County, VA. photo by F.T. Campbell; did the widespread presence of many non-native viburnum species facilitate establishment of the viburnum leaf beetle?

I note that this article appeared more than four years ago. However, its important findings do not appear to have been integrated into either policy formulation governing plant introductions or pest risk analysis applied to insects or pathogens that might be introduced. (Indeed, we probably need a separate analysis of whether fungi, oomycetes, nematodes, and other pathogens show the same association with plant diversity in the receiving environment.)

How do we – government agencies, academics, conservation organizations, plant industry representatives — use this information to help curtail introductions of plant pests? Can it be integrated into APHIS’ NAPPRA process?

SOURCE

Liebhold, A.M., T. Yamanaka, A. Roques, S. August, S.L. Chown, E.G. Brockerhoff & P. Pyšek. 2018. Plant diversity drives global patterns of insect invasion. www.nature.com/scientificreports/

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

Can we work together to curtail introductions of new diseases?

Phytopthora ramorum-infected potted plants; photo by Washington State University

At this year’s USDA Invasive Species Forum I will be seeking to promote a discussion of what American and other stakeholders can do to suppress spread of forest pathogens. I have raised this issue many times before.  To see my blogs about the P4P pathway, scroll down below the archives to the “categories”.  See especially here  and here

I note that:

  • Non-native invasive pathogens and pests are decimating forests worldwide, threatening biodiversity & limiting efforts to rely on forests to alleviate impacts of climate change.
  • Many of the most damaging non-native organisms are pathogens that are especially difficult to detect at borders or to contain or eradicate once introduced.
  • A principal pathway by which pathogens are introduced is the international trade in living plants, or “plants for planting” (P4P).
  • Forest pathologists have long advocated a more pro-active approach – but national and international plant health officials have not taken up the challenge. [think Clive Brasier, Bitty Roy, Thomas Jung, Michael Winfield …]
Austropuccinia psidii on Melalecua in Australia; John Tann via Flickr

At the global level I suggest that we need:

  1. National agricultural agencies, stakeholders, FAO & International Plant Protection Convention (IPPC) to consider amending IPPC requirement that scientists identify a disease’s causal agents before regulating it. I think experience shows that this policy virtually guarantees that pathogens will continue to enter, establish, & damage natural and agricultural environments.
  2. National governments & FAO / IPPC to fund greatly expanded research to identify microbes resident in regions that are important sources of origin for traded plants, vulnerability of hosts in importing countries, and new technologies for detecting pathogens (e.g., molecular tools, volatile organic compounds [VOCs]).
  3. Researchers & agencies to expand international “sentinel plants” networks; incorporate data from forestry plantations, urban plantings, etc. of non-native trees.
  4. Application of ISPM#36 to promote use of HACCP programs for plants in trade. (See also my discussion in Fading Forests III – link at end of this blog.)
‘ohi‘a trees killed by rapid ‘ohi‘a death; photo by Richard Sniezko, USFS

We Americans need to

  1. Evaluate efficacy of current regulations – incorporating NAPPRA & Q-37 revision.  Rely on AQIM data. Include arthropods, fungal pathogens, oomycetes, bacteria, viruses, nematodes. Include threats to U.S. tropical islands (Hawai`i,  Puerto Rico, Guam, etc.) which are centers of plant endemism.
  2. Apply existing programs (e.g., NAPPRA, Clean Stock Network, post-entry quarantine) to strictly regulate trade in plant taxa most likely to transport pests that threaten our native plants; e.g., plants belonging to genera shared between North American trees & plants on other continents.
  3. Recognize that plant nurseries are incubators for microbial growth, hybridization, and evolution; require nurseries to adopt sanitary operation procedures regardless of whether they sell in inter-state or intra-state commerce

I will explain my sense of urgency by noting the many recent introductions of pathogens – most probably via P4P or cut vegetation:

  • 13 outbreaks of Phytophthora-caused disease in forests and natural ecosystems of Europe, Australia and the Americas. Three of four known strains of P. ramorum are established in U.S. forests.
  • Myrtle rust (Austropuccinia psidii) has been introduced to 27 countries, including the U.S., Australia, and South Africa.
  • Two new species of Ceratocystis (C. lukohia & C. huliohia)—causal agents of rapid ‘ohi‘a death (ROD) – spreading on the Hawaiian Islands. The former species appears to have originated in the Caribbean; the latter in Asia.
  • Since 2012, beech leaf disease has spread from northeastern Ohio to Maine.   
  • Boxwood blight (caused by 2 ascomycete fungi, Calonectria pseudonaviculata & C. henricotiae) introduced to at least 24 countries in 3 geographic areas: Europe / western Asia; New Zealand, North America.
  • ash dieback fungus (Hymenoscyphus fraxineus) has spread across Europe after introduction from Asia.

What do you think? Can we find more effective methods to curtail introductions?

beech leaf disease

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

America & Russia – Sharing the Pests

Platanus orientalis in Turkey; photo by Zeynek Zebeci

A current issue of the journal Forests (2022 Vol. 13) is a special issue focused on forest pests. This topic was chosen because of increased pest incursions. Choi and Park (full citations at the end of the blog) link this to climate change and increased international trade, as well as difficulties of predicting which pests will cause damage where.

The journal issue contains 15 papers. Several patterns appear throughout. First is the important role of international trade in living plants – “plants for planting” – in introductions. This is hardly news! A second pattern is that at least two North American species were introduced to Europe during the 1940s, probably in wood packaging used to transport military supplies during World War II.

This compilation provides the opportunity to review which organisms of North American origin have become damaging invaders in Eurasia — and sometimes other continents. For example, the journal carries four articles discussing pine wilt disease (PWD). It is caused by the North American nematode Bursaphelenchus xylophilus, and is vectored by wood-boring insects in the genus Monochamus. Beetles introduced from North America and those native to the invaded area are both involved. This disease is considered a severe threat to forest health globally. No apparent association with WWII exists for PWD.

Two fungal pathogens from North America cause serious damage in urban and natural forests of Europe and central Asia. Neither is discussed in the special issue:

  • Ceratocystis platani has devastated urban trees in the Platanus genus, especially the “London plane” hybrid, and the native European tree, Platanus orientalis. This fungus was accidentally introduced to southern Europe during WWII – as were the two insects described by Musolin et al. It was first reported in northern Italy and Mediterranean France in the early 1970s, but disease symptoms had been observed years earlier. C. platani is established across the northern rim of the Mediterranean and to the east in Armenia and Iran. The worst damage has been in Greece, especially in natural forest stands in riparian areas. Spread of the pathogen there is facilitated by root grafts and by tree wounds caused by floating wooden debris during floods (Tsopelas et al. 2017.)
Platanus orientalis along Voidomatis River in Greece; photo by Onno Zweers, via Wikimedia
  • Heterobasidion irregulare infects conifers. It has spread and killed large numbers of Italian stone pine (Pinus pinea). The disease was inadvertently introduced to central Italy in the 1940s. H. irregulare has greater sporulation potential and decays wood more quickly than the native congener H. annosum. H. irregulare appears to be replacing the European species; scientists fear it will exacerbate tree infection and mortality rates (Garbelotto, Leone, and Martiniuc. date?)

A third North American pathogen, sooty bark disease (Cryptostroma corticale) has been introduced to Europe. This disease, found on sugar maple in eastern North America, was detected in Great Britain in 1945; it is now throughout Europe (Tanney 2022). EPPO reports that it is widespread in western Europe and in some Balkan countries. The website provides no information on its impact in Europe.

Pests in Russia

A paper authored by Musolin, et al. discusses 14 species of invasive or emerging tree pests found in Russian forest and urban ecosystems. Of these, two are native to North America. Another eight pose a threat to North America if they are introduced here.

As Musolin et al. point out, Russia covers a huge territory across Europe and Asia – stretching 10,500 km, or 6,500 miles. These encompass a great variety of ecological zones. Russia is also actively involved in international trade. It is not surprising, then, numerous non-native organisms have been introduced.

As of 2011, 192 species of phytophagous non-native insects from 48 families and eight orders were documented in the European part of Russia. This number does not include the vast areas in Asian Russia. Additional introductions have probably occurred in the most recent decade. Some of these introduced species have cause significant economic losses. Still, Russia appears to rarely mount a serious control effort.

Of course, the opposite is also true: pests native to some part of Russia can be transported to new regions of Russia or beyond its borders. We North Americans have focused on various species of tussock moths (Lymantria spp., etc.). There are many others. Musolin et al. describe eight in detail. All the information in this blog are from that article unless otherwise indicated.

Two North American Species’ Damage in Eurasia

Both these introductions were detected around the year 2000. Was there some event – other than simply expanding trade – that might explain these introductions?

Leptoglossus occidentalis; photo by nutmeg66 via Flickr
  • Western Coniferous Seed Bug, Leptoglossus occidentalis

This insect from western North America has invaded Eurasia, North Africa, and Central America. The first detection in Europe was in 1999 in Italy. It spread quickly and is present now from Morocco to Japan, as well as in South Africa and South America. The seed bug is spreading northward in European Russia, including into the forest-steppe zone. Its ability to spread to the East is uncertain.

L. occidentalis attacks a wide range of Pinaceae and Cupressaceae. In the Mediterranean region it has had serious impacts on the pine nut supply (Ana Farinha, IUFRO, Prague, September 2021). In southern parts of Russia it has caused “significant damage”. L. occidentalis also vectors a pathogenic fungus Sphaeropsis sapinea (=Diplodia pinea), which causes diplodia tip blight. The cumulative damage of insect and pathogen to pines can be significant.

The introduction pathway to Russia is unknown. It might have flown from established populations in Europe, or it might have been transported on plants for planting or Christmas decorations.

  • Oak Lace Bug, Corythucha arcuata  

This insect is widespread in the United States and southern Canada. It was first detected in Europe – again, Italy – in 2000. Twenty years later it has spread to almost 20 countries.

Russia was invaded relatively recently; the first outbreak was detected in 2015 in the subtropical zone along the Black Sea coast and Caucasus. Musolin et al. expect the lace bug to spread to natural forests of Central Asia and other countries of the Caucasus. Its spread will be assisted by air currents and movement of plants for planting. The insect is causing considerable aesthetic damage, but other impacts have not been estimated.

Hosts include many species of oak (Quercus spp.), European and American chestnuts (Castanea spp.) plus trees from other botanical families: willows and maples (Salicaceae), redbay (Fagaceae), and alder (Betulaceae).  

Pests in Russia that Could Damage North America if Introduced Here

Malus sierversii; photo by Lukacz Szczurowski via Wikimedia

Threat to Apples — Apple Buprestid, Agrilus mali

This Asian beetle has caused extensive mortality of wild apple (Malus sieversii) forests in Xinjiang, China. Wild apple trees are important components of deciduous forests in the Central Asian mountains. The species is also an ancestor of the domestic apple tree. Consequently, the borer is considered a potential threat to cultivated apple trees – presumably everywhere. A. mali might also attack other fruit trees in the Rose family, i.e., Prunus (plums, cherries, peaches, apricots, almonds) and Pyrus (pears).

Unlike most of the other species described here, A. mali is a quarantine pest in Russia and across Europe and the Mediterranean regions – the region where phytosanitary policies are coordinated by the European and Mediterranean Plant Protection Organization (EPPO). Russia bans imports of apple seedlings from infested areas.

China is reported to be experimenting with a possible biocontrol agent, Sclerodermus pupariae (a parasitoid of emerald ash borer).

Threat to Pines and Firs, Already Under Invasive Species Threats

  • Small Spruce Bark Beetle, Ips amitinus

This European beetle has been considered a secondary pest of dying conifers. Over the last 100 years, it has moved farther North. The first Russian record was 100 years ago, in the region where Russia, Belarus, and Ukraine meet. (Did military action during World War I play a role? This is not discussed by the authors.) By 2022, the beetle occupies 31 million ha. It is probably spread through transport of logs by rail.

In Western Siberia, the spruce beetle has attacked a new host, Siberian pine (Pinus sibirica).

The danger to North America arises from this beetle’s preference for five-needle pines (genus Pinus section Quinquefoliae). North America’s five-needle pines are already under severe pressure from the introduced pathogen white pine blister rust (Cornartium ribicola) and the native mountain pine beetle (Dendroctonus ponderosae). 

  • Four-Eyed Fir Bark Beetle, Polygraphus proximus

This East Asian beetle feeds on firs (Abies spp.). Less commonly, it feeds on other genera in the Pinaceae: spruce (Picea ), pines (Pinus), larch (Larix), hemlock (Tsuga).

This beetle has been spreading west; the first substantiated record in European Russia was 2006 in Moscow. The beetle was probably present in western Siberia in the 1960s, although it was not detected until 2008. Again, the probable pathway of spread is movement of lumber by railroad.

P. proximus vectors an obligate symbiotic fungus, which can rapidly weaken the host. Musolin et al. comment on the beetle’s impacts – which they rarely do in this article. (Does this signify more damaging impacts, or availability of past studies?) They note significant changes in the forests’ ecosystem structure and microclimate, vegetation cover, and local insect fauna.

The danger to North America arises from this beetle’s preference for firs from the sections Balsamea and Grandis. Many North American firs are in these sections, including Fraser fir (Abies fraseri), balsam fir (A. balsamea), subalpine fir (A. lasiocarpa), grand fir (A. grandis), white fir (A. concolor), and others. Several of these firs already are challenged by the introduced balsam woolly adelgid. Firs in central and western Europe are less vulnerable since they are in the section Abies, which the beetle prefers less.

Threats to Poplars

  • Spotted Poplar Borer, Agrilus fleischeri

This boring beetle is native to northern Asia. It has caused significant mortality in native and exotic Populus plantations in China. Although there have been no reports of this beetle moving beyond its native range, many other Agrilus species have. Canada has twice intercepted adult spotted poplar borers on wood packaging. Musolin et al. fear that the adoption of non-native hosts might trigger an outbreak that would facilitate spread.

  • Poplar Leafminer, Phyllonorycter populifoliella
balsam poplar; photo by Matt Lavin via Flickr

This micromoth is widely distributed across the Palearctic. It was recently detected on introduced poplars growing in India.  

The danger to North America arises from the beetle’s preference for black and balsam poplars. Several species in these taxonomic groups are common in North America, including Populus balsamifera, P. trichocarpa, P. deltoides, and Populus × Canadensis.

Threat to Oaks — Leaf Blotch Miner Moth, Acrocercops brongniardella

This micromoth is widely distributed in Europe and expanding to the north. The pest mines the leaves of several oak species (Quercus spp.), especially English oak, Q. robur; and sometimes European chestnut (Castanea sativa). Leaf blotch miner is considered one of the most important folivore insect pests of oaks in Russia. Damage has been greater in Omsk Oblast (Siberia), where both English oak and the micromoth are introduced species, than in St. Petersburg, which is on the northern limit of their natural range. Musolin et al. fear that the warming climate will lead to the pest causing greater damage in the northern portions of its range.

Threat to Basswood — Lime Leaf Miner, Phyllonorycter issikii

This Asian moth has been moving west since the mid-1980s. It now occupies most of European Russia with some outbreaks in Siberia. In Europe, it is a conspicuous pest of Tilia species.

In these invaded regions, the leaf miner has shifted to novel hosts, including American basswood (T. americana). Basswood is a common plant in the eastern deciduous forest of North America.

Threat to Horse Chestnuts & Urban Trees — Horse-Chestnut Leaf Miner, Cameraria ohridella

This tiny moth was unknown to science before the first recorded outbreak in the late 1980s. Over the next three decades it spread to most of Europe, where horse chestnut (Aesculus hippocastanum)has been widely planted for three centuries. It has caused significant damage.

The first Russian detection was in Kaliningrad, on the shores of the Baltic Sea, in 2003. The leaf miner now occupies 69% of administrative units of European Russia. It is considered one of the Top 100 most dangerous invasive species in Russia.

In North America, the moth might attack native horse chestnuts, Ae. octandra (=flava) and Ae. glabra. Urban plantings are at particular risk because the leaf miner might attack both European horse chestnuts and two non-native maples that have been planted widely, sycamore maple (Acer pseudoplatanus) and Norway maple (A. platanoides). Data cited by Musolin et al. are contradictory regarding larval development on the maples. Once introduced, the leaf miner is difficult to contain because it spreads through natural flight of adults, wind-blown leaves, hitchhiking on vehicles, and movement of infected plants. 

Shared Pests

Russia has been invaded by two species that have been introduced in many countries (beyond pine wilt nematode). These two entered the country on plants for planting being imported to landscape venues for the XXII Winter Olympic Games – held in Sochi in 2014.

First to arrive was the Box Tree Moth, Cydalima perspectalis. This East Asian species was first detected outside its native range in Germany in 2006. By 2011 it was widespread in European and Mediterranean countries. In 2021, the boxwood moth was found in North America (first Canada, then the United States).  [I discuss the boxwood moth briefly here.]

boxtree moth; photographer unknown

In Russia, box tree moth larvae were first recorded in 2012 on the planting stock of its principal host, Buxus sempervirens. The moth quickly spread around the Black Sea region and to the North Caucasus. It spread farther, too: it reached the Kaliningrad Oblast (southeast coast of the Baltic Sea) in 2020. The main pathway of C. perspectalis invasion was the introduction of infested box-wood planting material.

Further spread of C. perspectalis is likely from Russia into the natural forests across the Caucasus (Transcaucasia) and to countries located further south. This is most distressing because the region has extensive natural forests of Buxus sempervirens. In 2015–2017, C. perspectalis almost completely destroyed the natural boxwood populationsin these regions of Russia and further eastwards in Abkhazia. Boxwood stands in Georgia and northern Iran are already suffering intensive defoliation as the result of infection by two non-native pathogens, Calonectria pseudonaviculata [synonym Cylindrocladium buxicola] and Calonectria henricotiae. Damage to these forests could lead to reductions in soil stability and subsequent declines in water quality and flood protection, changes in forest structure and composition, and declines in Buxus-associated biodiversity (at least 63 species of lichens, fungi, chromista and invertebrates might be obligate). (In December 2022, Iryna Matsiakh presented a compelling overview of threats to these forests in a webinar sponsored by the Horticulture Research Initiative; apparently no recording is available.)

The second global invader to appear was the Brown Marmorated Stink Bug, Halyomorpha halys.

This insect from southeast and east Asia invaded the United States in 1996. The first detection in Europe was in Liechtenstein in 2004. In both cases, it spread quickly across these continents.

Russia’s first detection of stinkbug was in 2014 in parks in Sochi and elsewhere along the Black Sea coast. The spread in Russia appears to have been limited to the Black Sea – Caucasus area.

The brown marmorated stinkbug is highly polyphagous, feeding on more than 300 species of plants.  In southern Russia, 107 species have been documented as hosts. At times, stinkbug feeding has caused severe losses in yields of fruit and vegetable crops.

Patterns

Musolin et al. stress the importance of the pest shifting to new hosts–usually from the same or a closely related genus. They cite several examples of these shifts occurring in the pest’s native range, including Agrilus planipennis (from local Asian ash species to introduced North American ash species); Phyllonorycter populifoliella and Agrilus fleischeri (from local poplars to widely cultivated introduced North American poplars and hybrids); Agrilus mali (from cultivated to wild apples).

As I noted above, the introduction and spread pathways are the usual ones: plants for planting (three species) and shipments of logs. There is one indication of wood packaging – Spotted Poplar Borer, Agrilus fleischeri at the Canadian border.

SOURCES

Choi, W.I.; Park, Y.-S. Management of Forest Pests and Diseases. Forests 2022, 13, 1765. https://doi.org/10.3390/f13111765

Garbelotto, M., G. Lione, and A.V. Martiniuc. date?  The alien invasive forest pathogen Heterobasidion irregulare is replacing the native Heterobasidion annosum. Biological Invasions https://doi.org/10.1007/s10530-022-02775-w

Musolin, D.L.; Kirichenko, N.I.; Karpun, N.N.; Aksenenko, E.V.; Golub, V.B.; Kerchev, I.A.; Mandelshtam, M.Y.; Vasaitis, R.; Volkovitsh, M.G.; Zhuravleva, E.N.; et al. Invasive insect pests of forests and urban trees in Russia: Origin, pathways, damage, and management. Forests 2022, 13, 521.

Tanney, J. Forest Health Challenges Exacerbated by a Changing Climate: Swiss Needle Cast and Sooty Bark Disease in B.C. 65th ANNUAL FOREST PEST MANAGEMENT FORUM (Canada). December 7, 2022.

Tsopelas, P., A. Santini, M.J. Wingfield, and Z.W. de Beer. Canker Stain: A Lethal Disease Destroying Iconic Plane Trees. Plant Disease 2017. 101-645-658 American Phytopathological Society

Climate Change + CO2 Levels – Can Scientists Include the Complexity in their Analyses?

Spruce budworm (Choristoneura fumiferana); photo by Jerald E. Dewey, USFS; via Bugwood; populations of several forest birds, including Cape May, Tennessee and Bay-Breasted warblers, become more numerous during budworm outbreaks

Now that Drs. Ziska and Aucott have educated us about the strong impact atmospheric CO2 can have on both plants and phytopagous insects, I have asked the experts whether these interactions have been incorporated in the models scientists are using to forecast pest activity in American forests as the climate changes.

The answer is no.

bay-breasted warbler; photograph by Dave Inman at Presque Isle State Park, PA; via Flickr

Dr. Bethany A. Bradley, Co-Director, Northeast Climate Adaptation Science Center at the University of Massachusetts, says empirical models of species range shifts typically only use climate and sometimes other environmental factors (like soils or topography) as predictors of potential geography. Inclusion of demographic processes like how plant growth is affected by more or less water, CO2, competition with other plants etc. would require a lot of data. It is currently impossible since there are tens of thousands of plant species interacting in the forests of eastern North America – and perhaps these factors have been analysed for only a hundred of them.

Mike Aucott points to the same difficulty: inclusion of CO2 in models of the future populations of specific plants would be difficult since the impacts vary from species to species and are compounded by other factors such as soil nitrogen levels, moisture levels, temperature, presence of competing plants, etc.  

Regarding insects, Dr. Aucott thinks it is clear that some orders, such as Lepidoptera, don’t fare as well when feeding on plants grown under elevated CO2.  He is not aware of efforts to model impacts of high CO2 on specific insects or even orders or feeding guilds. 

juniper geometer (inchworm); Dr. Tallamy says inchworms are hairless & good tasting – so sought by birds

Dr. Ziska concurs about the difficulties. Dr. Ziska asks why there is so little funding to study these issues, especially given their probable impact on human food supplies and health – as described in his blog and an opinion piece published in Scientific American two years ago.

I hope that scientists, decision-makers, readers of this blog … maybe even the media! – take into consideration these complexities, even if they cannot be defined.

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – [but do not address climate or CO2 aspects] review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

Climate Change & Habitat Disruptions: Connected by Carbon Dioxide

Wildfire: one of the widely recognized results of climate change (The Pioneer Fire located in the Boise National Forest near Idaho City, ID began on Jul. 18, 2016 and the cause is under investigation. The Pioneer Fire has consumed 96,469 acres. U.S. Forest Service photo. Original public domain image from Flickr)

A guest blog by Michael Aucott. Mike is a retired research scientist of the NJ Department of Environmental Protection. He has also taught chemistry at the College of New Jersey.  He is currently a member of the NJDEP Science Advisory Board Standing Committee on Climate and Atmospheric Sciences, and on the board of directors of the PA/NJ Chapter of the American Chestnut Foundation. If you wish to contact Mike, use the contact button on this website. You MUST include your email address; it is not recorded automatically.

Two major perturbations affect Earth and its living systems, climate change and habitat disruptions. Emerging data show that these are more closely related than previously realized; they are connected by carbon dioxide, CO2.

Climate change basics: the physics

Climate change concerns have focused on the alteration of weather and climate due to the increase in atmospheric concentrations of greenhouse gases, primarily carbon dioxide, CO2. The impact of CO2 on climate has been understood for at least 120 years. In 1896 the Nobel-Prize-winning Swedish chemist Svante Arhennius published calculations demonstrating that human emission of CO2, when combined with the positive feedback effects of water vapor, would warm the Earth (Arhennius, 1896). His equation, ΔF = α ln(C/C0), relates the change in climate “forcing” (the degree to which temperature change is forced) to the ratio of the concentration of CO2 currently in the atmosphere (C) to a previous concentration (C0). This equation is still in use today. Arhennius estimated that a doubling of CO2 would warm the Earth by about 4 degrees C. This estimate is not far off from current estimates based on much more elaborate calculations.

This warming impact is caused by the physics of CO2, water vapor, and other “greenhouse” gases. Infrared radiation causes the CO2, water, and other greenhouse gas molecules to vibrate, leading to the absorption of the energy carried by that radiation. Much of the solar energy coming from the sun is not in the infrared frequency range, so it passes through the atmosphere without being absorbed. However, when this energy is absorbed by the surfaces of the Earth and its biota, and is re-radiated as infrared radiation, it is then absorbed by greenhouse gases, warming the planet.


The amount of water vapor in the atmosphere is directly related to the atmosphere’s temperature: warm air holds more water vapor. Human activity hasn’t directly changed the concentration of water vapor in the atmosphere significantly. But by burning fossil fuels, humans have dramatically increased the atmospheric concentration of CO2 and in so doing, also indirectly increased the concentration of water vapor. Just as Arhennius predicted over 120 years ago, this increase in CO2 is warming the Earth.

Ramifications of this warming include increased heat episodes, the intensification of the hydrological cycle (greater frequency of both heavy precipitation events and of droughts), sea level rise due to the melting of land-based glaciers and the thermal expansion of ocean water, and, almost certainly, intensification of storms and an increase in extreme weather. These climate-warming- based perturbations have the potential to influence the functioning of Earth’s biota in many deleterious ways, and clearly can be associated with the many facets of habitat disruption.

Climate change amplifications: the chemistry

But there’s another aspect of CO2 that may be more important insofar as habitat disruption is concerned and that has been largely ignored: chemistry. CO2 is a trace gas as far as we humans and other animals are concerned, unnoticed by our bodies in normal life. But to plants it is a vital food. It is taken up by plants as an essential input to photosynthesis. In this chemical reaction, using the energy of sunlight, plants combine CO­2 and water vapor to make oxygen and carbohydrates, represented with a generic formula of CH2O, according to the equation CO2 + H2O → CH2O + O2.  Without this reaction, life as we know it would not exist.

The atmospheric concentration of CO2 has varied over time; some 50 million years ago it was considerably higher than today. However, for at least the last three million years, the concentration of CO2 has been in the range of 280 ppm. Over these millions of years biota have adapted to this concentration. But within the last 300 years, one ten thousandth of this period – a blink of an eye in the geological or evolutionary time scale – the concentration of CO2 has shot up to 420 ppm, a 50% increase, due to humanity’s burning of fossil fuels and forests.


Imagine what might happen to a person who had been on a tight dietary budget for most of his or her life but suddenly got access to 50% more carbohydrates, but no more protein or minerals?  We could expect major changes in the metabolism of that person. This dramatic change is what has, in effect, happened to the whole of life on Earth. Our planet’s primary biota, plants, now suddenly have the opportunity to gorge on CO2. But their access to other important substances such as nitrogen has not changed. Evidence is accumulating that CO2 at its elevated level of 420 ppm is not, as has been proclaimed by some, a healthy influence but is instead throwing Earth’s ecosystem into disarray.

Much of the recent experimental evidence on the impacts of enriched atmospheric CO2 has been assembled by Lewis Ziska and presented in his new book, Greenhouse Planet: How Rising CO2 Changes Plants and Life as We Know It (Ziska, 2022; see full citation at the end of the blog). The findings documented in this book reveal a variety of impacts of elevated CO2. These impacts include stimulation of growth of invasive plants, decreases in the nutrient content of major crops, and changes in plants’ production of insecticidal, allergenic, and other compounds. The changing chemistry of plants may be contributing to a major die-off of insects and insect-eating animals including birds. Below are some details.

Habitat Disruptions: Stimulation of Invasive Plants

The generally accepted explanation for why some plants are invasive is that they have been introduced to new regions where their historic predators and parasites aren’t present. Without these drags on their growth, they have flourished. That some alien plants are not browsed by white-tailed deer contributes significantly to their invasiveness in Eastern North America. Other factors are clearly involved as well, including changes in the temperature regime and the availability of water and other resources such as nitrogen.

But elevated CO2 is also a factor. In recent years, techniques for measuring responses of organisms in situ under elevated CO2 conditions have been developed, making possible investigations of the impacts of CO2 concentrations that could exist in the future under otherwise relatively realistic conditions. What the actual atmospheric CO2 concentration will be in 2050 or 2100 is difficult to predict; it depends on what humanity does to control emissions. Various scenarios suggest that levels could exceed 500 ppm by 2050 and might exceed 1000 ppm by 2100 (Tollefson, 2020).

cheatgrass; photo by Jaepil Cho

One study found that the invasive weed Canada thistle, Cirsium arvense, responds more strongly to elevated CO2 than soybean, a crop that it often plagues. In a high CO2 environment, this weed’s root system grows strongly enough to make it significantly more resistant to herbicides (Ziska, et al., 2004) (Ziska, 2010). The highly invasive and dangerously flammable cheatgrass (Bromus tectorum), nicknamed “grassoline” by the U.S. Forest Service because of its propensity to intensify wildfires, also responds strongly to elevated CO2 (Ziska, et al., 2005). Also found to be boosted by enriched CO2 is yellow star-thistle (Centaurea solstitialis), considered one of California’s worst weeds. In one study (Dukes, et al., 2011) this plant grew 600% larger in elevated CO2 relative to ambient, while native plants responded much less strongly or not at all. Japanese honeysuckle, Lonicera japonica, which plagues many areas in the U.S., was found to increase in biomass by 135% at a CO2 concentration of 675 ppm while a similar native plant, coral honeysuckle (Lonicera sempervirens) increased by only 40% (Sasek & Strain, 1991). In a field study also involving Japanese honeysuckle (Belote, et al., 2004), researchers found that its above ground net production (ANPP) approximately tripled under enriched CO2 while other plants in the trial showed showed lesser increases or actual decreases.

Other plants have been found to be selectively encouraged by enriched CO2 including cherry laurel (Prunus laurocerasus), invasive in the Pacific Northwest U.S. and the U.K., (Hattenschwiler & Korner, 2002); dalmation toadflax (Linaria dalmatica), invasive in much of North America (Blumenthal, et al., 2013); honey mesquite (Prosopis glandulosa) , invasive in Australia and parts of Africa (Polley, et al., 1996); and kudzu (Pueraria lobata), which afflicts the Southeast U.S. (Sasek & Strain, 1988). Three plants invasive in China or Southeast Asia, American rope (Mikania micrantha), Creeping oxeye (Wedelia trilobata), and a morning glory species (Ipomoea cairica), were found to produce 70.3% greater biomass when grown at a CO2 concentration of 700 ppm while three corresponding indigenous plants Paederia scandens, Wedelia chinensis and Ipomoea pescaprae, produced only 30.5% more biomass (Song, et al., 2009).

yellow star thistle; photo by Eugene Zelenko

The list goes on of studies showing increased growth of some plants under enriched CO2 conditions. As more in situ investigations are undertaken, it seems likely it will become clearer that today’s enriched level of CO2 is helping some plants to become invasive.

Complexities and contradictory findings exist however. Not all plants are stimulated by enriched CO2. An important difference in the response to higher levels of CO2 is whether a plant has a C3 or a C4 photosynthetic mechanism. C4 plants contain a biochemical pump that concentrates CO2, making them more adapted to low CO2 conditions (Hager, et al., 2016). At current levels of CO2, such plants’ need for CO2 is easily met. C3 plants do not have this CO2 concentrating ability, and so higher levels boost their growth. In a broad meta-analysis of literature, the average response to elevated CO2 of 365 C3 plant species and 37 C4 plant species was noted; the response was significantly increased in C3 species but was unchanged in C4 species (Robinson, et al. 2012). One striking example of such a difference was observed in the field study noted above (Belote, et al., 2004), wherein researchers found that Japanese honeysuckle (a C3 plant) was significantly encouraged by elevated CO2 relative to other plants at the same locale. The same study found that another aggressive invader, Japanese stiltgrass (Microstegium vimineum), a C4 plant, was unaffected or even slightly inhibited relative to competing plants’ growth by elevated CO2.

Habitat Disruptions: Changing of Plants’ C/N Ratio and Nutrient Content

One finding is widespread; most plants studied under enriched CO2 regimes show an increase in biomass and evince a higher ratio of carbon to nitrogen (C/N ratio) in their tissues and an overall decline in nitrogen concentrations than when grown under ambient conditions. Since nitrogen is a key component of protein, this change can be expected to lead to lowered protein content of critical food crops. Some impacts of this change are already well underway because of today’s elevated CO2 concentration. Changes since 1850 in the C/N ratio and in the estimated protein content of an important plant product, pollen, were discovered in a striking study by Lewis Ziska and colleagues (Ziska, et al., 2016). Using archived museum samples, these researchers determined the nitrogen content of pollen of Solidago canadensis (Canada goldenrod) going back to the 1850s. They estimated that the protein content of goldenrod pollen, a vital nutrient for North American bees, has declined in inverse proportion to the rise in atmospheric CO2, dropping from a concentration of approximately 18% in the mid-1800s to approximately 12% today. They pointed out that it is possible that bees are now unable to provide sufficient protein and other nutrients to larvae, and that one of the main reasons for bee declines is malnutrition caused by enriched atmospheric CO2. Other studies also indicate that elevated CO2 could cause lower nitrogen concentrations in plants and lead to less proteinaceous plant parts, including pollen, being available to plant-feeding insects (Hall, et al., 2005; Knepp, et al., 2007).

bumblebee on goldenrod; photo by Keila

The changing C/N ratio is almost certainly already affecting the human food supply. As documented in an extensive review of published findings (Soares, et al., 2019), elevated CO2 has a considerable impact on the accumulation of minerals and protein in plants, with many plant species showing declines in both quality and quantity of key nutrients. These changes have worrisome implications for human nutrition and may already be responsible for increasing incidences of dietary deficiency in some areas. Lewis Ziska discusses the likely impact of rising CO2 on the future human food supply in his recent post. A number of studies showing declines in protein and also other nutrients such as zinc in food crops important to humanity are also described in Ziska’s new book, Greenhouse Planet, noted above.

Habitat Disruptions: Other Changes in Plant Chemistry

Other changes in plants besides nutritional content may be driven by enriched CO2. Plants produce a variety of secondary metabolites. Most plants use the C3 mechanism; with 50% more available of a key input, some changes in these plants’ production of such chemicals can be expected. Some changes have been observed. Mohan et al. (2006) report that enriched CO2 in an intact forest system increased water use efficiency, growth, and population biomass of poison ivy (Toxicodendron radicans) and that high-CO2 plants also produced a more toxic form of the allergenic compound urushiol.

Quercus chapmanii; photo by Mary Keim at Seminole State Forest, Florida

Many of the phytochemicals plants produce function as defenses against insect predation, and changes in such production have been found to impact herbivore feeding. For example, Landosky and Karowe (2014) suggest that specialist herbivores may have to contend with more effective chemical defenses by plants under elevated CO2. Hall, et al. (2005), in a study involving several oak and one legume species in a scrub oak ecosystem in Florida (see photo above), found that 700 ppm CO2 levels led to decreased damage to plants by four of six insect groups investigated. They did not see increases in plants’ production of carbon-based secondary metabolites, including total phenolic compounds, condensed tannins, hydrolyzable tannins, cellulose, hemicellulose, and lignin however. They concluded that the primary driver of decreased insect predation under elevated CO2 was lower overall plant nitrogen levels. They stated that the decline of nitrogen levels in foliage under elevated CO2 indicated lower foliar quality and hypothesized that the reductions in insect feeding stemmed from the combined effects of nutrient limitation and increases in parasitism and predation on the nutrient-constrained insects. They further stated that although insects try to compensate for lower nutrient content of leaves by eating more, they did not see an increased portion of damaged leaves in their study. These researchers did not report measurements of terpenoid compounds however, which are reported to represent the largest class of secondary metabolites (Wikipedia, 2022). In another study (Hall, et al., 2005a) found that concentrations of condensed tannins were higher in oak leaf litter under elevated CO2, which suggests that enhanced production of insecticidal compounds or other changes to plant tissues could affect not only insects that consume living plant tissue, but also detritivores.

Robinson et al. (2012) also investigated plants’ production of secondary metabolites in their literature review. Looking at all plant groups, they found that under elevated CO2 the production of nitrogen-based secondary metabolites (e.g., alkaloids, cyanogenic glycosides, and glucosinolates) decreased by 16% while the carbon-based secondary metabolites total phenolics, condensed tannins, and flavonoids increased by 19%, 22%, and 27% respectively. Another carbon-based metabolite, terpenoids, declined by 13%.  They further divided plants into grasses, shrubs, herbs/forbs, and trees and found differing responses to elevated CO2. Trees, for example, showed increased production of total glycosides and total phenolics, little change in production of total flavonoids, and a decline in the production of total terpenes. Like Hall et al., (2005), Robinson et al. found a strong and significant decrease in nitrogen concentrations under elevated CO2 for C3 plants. A decrease did not show up for C4 plants.

In addition to chemical defenses, plants have physical characteristics such as surface waxes, trichomes, secretory canals, and tissue toughness-enhancing substances such as lignin. All of these features can reduce the edibility of plants for arthropod herbivores. Robinson et al. (2012) found consistent responses to these characteristics under elevated CO2; leaf toughness and specific leaf weight increased by 11% and 18%, respectively, while specific leaf area did not show a significant change. They concluded that there is an increase in general “toughness” of leaves under elevated CO2. As did Hall et al., (2005), Robinson et al. concluded that elevated CO2 will induce changes in plant chemistry, physiology, and morphology that are likely to impact the nutritional quality of host plants for insect herbivores.

Habitat Disruptions: Changes in Plant Chemistry and Insect Decline

Numerous studies have documented a recent and dramatic decline in insect populations and discussed the probable cascading impacts of such declines through the food chain, affecting spiders, lizards, birds, and other organisms (Samways, et al., 2020; Cardoso, et al., 2020; Sánchez-Bayoa & Wyckhuys, 2019; Tallamy & Shriver, 2021). It has been argued that the main drivers of insect species declines are habitat loss and conversion to intensive agriculture and urbanization; pollution, mainly by synthetic pesticides and fertilizers; biological factors, including pathogens and introduced species; and climate change.

But a puzzling aspect is that some insect declines have been observed in nature preserves (Vogel, 2017) that presumably are not greatly affected by most of the above drivers. One example is a study spanning 27 years that found a 76% decline in flying insect biomass at several of Germany’s protected areas subject to rather low levels of human disturbance (Hallmann et al., 2017). Another study in rainforests of Puerto Rico, apparently not subject to influences such as light pollution, habitat loss, pesticides, or agriculture, reported biomass losses between 98% and 78% for ground-foraging and canopy-dwelling arthropods over a 36-year period, (Lister and Garcia, 2018). This leaves climate change as the likely culprit. But although the varied impacts of climate change, including heat episodes, drought, and other episodes of extreme weather could impact insect populations in remote as well as populated areas, the trends observed appear to far exceed the magnitude of such climate-related disturbances over the last several decades.

tent caterpillars; Shiela Brown, Public Domain Pics

Another puzzling aspect is that not all insect orders or feeding guilds seem to be equally affected. Sanchez-Bayoa & Wychuys (2019) whose article reports on a review of 73 historical reports, state that Lepidoptera, Hymenoptera and dung beetles (Coleoptera) appear to be the taxa most affected in terrestrial environments. Robinson et al. (2012) found that phloem feeders such as Homoptera respond positively to elevated CO2 while foliage feeders/Lepidoptera respond negatively. Lepidoptera were among the most impacted; relative growth rate, fecundity, and abundance all declined under high CO2 conditions, while relative consumption rate, total consumption, and development time all increased.

Most Lepidoptera are herbivorous, feeding in their larval stage, caterpillars, on plants. Caterpillars are key components of the terrestrial ecology; in most forests of the world, caterpillars consume more living leaves than all other animals combined (Janzen, 1988). Insect herbivores such as caterpillars are near the hub of most terrestrial food webs, comprising essential food for insect predators and parasitoids, spiders, amphibians, lizards, rodents, bats, birds, and even higher predators such as foxes and bears (Burghardt et al., 2010). At least 310 North American bird species are known to feed extensively on caterpillars, and the majority of terrestrial birds rely on insects during reproduction and other nutrient-limited periods in the annual cycle (Narango, Tallamy & Marra, 2018). Caterpillars and moths are the largest component of nestling diets in hundreds of species of migrant bird species (Tallamy & Shriver, 2021); they are among the “little things that run the world” (Wilson, 1987).

Carolina chickadee; one of the birds Dr. Tallamy focuses on because it feeds its young on caterpillars; photo by Dan Pancamo; through Wikimedia

Habitat Disruptions and Climate Change: Connected by CO2

The apparently heightened rate of decline of insect herbivores such as caterpillars compared to some other insects, and the findings that many declines have been observed in areas relatively unimpacted by direct human influences such as light pollution, pesticides, and land-use change, point to the likelihood of a broad, perhaps ubiquitous, cause. Climate change is such a broad cause. Even broader and more ubiquitous is the main driver of climate change, CO2. Every plant in the world is constantly bathed in an enriched concentration of this gas. A conclusion seems likely: CO2 is not only causing global warming and climate change but is also affecting life on this planet in ways that, while still poorly understood, are already reducing the nutritive value of food crops, may be a significant cause of the spread of invasive plants, and may be the main driver of insect declines and the cascading impacts of such declines on insect-eating animals such as birds.

What to do? 

To mitigate climate change and, as argued here, to mitigate habitat disruption, the steady rise in the atmosphere’s burden of CO2 must be halted, and then steps must be taken to lower the current concentration to a healthier level. These are not hopeless tasks. Although what has been a relentless rise in CO2 emissions at the global level continues, increases have slowed and even stopped in some parts of the world. Accelerating the development of low- and zero-carbon energy sources and encouraging energy conservation, as will be done through the U.S.’s Inflation Reduction Act, will further this progress.

More will be needed. Putting a significant and steadily increasing price on the carbon in fossil fuels is arguably the most important next step. Fossil fuels enjoy a free ride. The byproduct of their combustion, CO2, is dumped with little or no restrictions into the world’s atmosphere. A price on carbon would end this inequity. There are ways this could be done in a revenue-neutral (“fee and rebate”) manner that would avoid harm to economies and those with low- and moderate-incomes. A major step forward in pricing carbon by the European Union, a carbon border adjustment mechanism, is close to implementation. For more on this and other developments in cutting CO2 emissions, see the analyses and insights of the Carbon Tax Center and learn more about actions you can take to influence governments with Citizens’ Climate Lobby.

Not discussed here, but another stark example of habitat disruption is the increasing acidification of the world’s oceans caused by the dissolution of atmospheric CO2 in the waters. The ocean’s average pH has dropped from 8.2 to 8.1 within the last 200 years. Because pH is a logarithmic scale, this represents an increase in hydrogen ion concentration of over 25%, a change that is already threatening some marine creatures. More on this is available from many sources; e.g., Kolbert (2014).

References

Arhennius, Svante, 1896, On the Influence of Carbonic Acid in the Air upon the Temperature on the Ground, Philosophical Magazine and Journal of Science, 41, 237-276.

Belote, R., J. Weltzin, and R. Norby, 2004, Response of an Understory Plant Community to Elevated [CO2] Depends on Differential Responses of Dominant Invasive Species and Is Mediated by Soil Water Availability, New Phytologist 161, 827-835.

Blumenthal, D., V. Resco, J. Morgan, D. Williams, D. LeCain, E. Hardy, E. Pendall, and E. Bladyka, 2013, Invasive Forb Benefits from Water Savings by Native Plants and Carbon Fertilization Under Elevated CO2 and Warming, New Phytologist 200, 1156-1165.

Burghardt, Karin T., D. W. Tallamy, C. Philips, and K. Shropshire, 2010, Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities, Ecosphere 1: 1-22.

Cardoso, P., et al. 2020, Scientists’ warning to humanity on insect extinctions, Biological Conservation 242, 108426. https://doi.org/10.1016/j.biocon.2020.108426

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Hall, M., P. Stiling, B. Hungate, B. Drake, and M. Hunter, 2005a, Effects of elevated CO2 and herbivore damage on litter quality in a scrub oak ecosystem, Journal of Chemical Ecology, 31, 2343-2356.

Hall, M., P. Stiling, D. Moon, B. Drake, and M. Hunter, 2005, Effects of elevated CO2 of foliar quality and herbivore damage in a scrub oak ecosystem. Journal of Chemical Ecology 31, 267-286.

Hallmann, C.A., Sorg, M., Jongejans, E., Siepel, H., Hofland, N., Schwan, H., Stenmans, W., Müller, A., Sumser, H., Hörren, T., Goulson, D., de Kroon, H., 2017, More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLoS One 12, e0185809.

Hattenschwiler, S. and C. Korner, 2003, Does Elevated CO2 Facilitate Naturalization of the Non-indegenous Prunus laurocerasus in Swiss Temperate Forests?, Functional Ecology 17, 778-785.

Janzen, Daniel H., 1988, Ecological Characterization of a Costa Rican Dry Forest Caterpillar Fauna, Biotropica, 20, 120-135.

Knepp, R., J. Hamilton, A. Zangeri, M. Berenbaum, and E. Delucia, 2007, Foliage of oaks grown under elevated CO2 reduces performance of Antherae Polyphemus (Lepidoptera: Saturnidae), Environmental Entomology 36, 609-617.

Kolbert, E., 2014, The Sixth Extinction, Henry Holt & Co., NY

Landosky, J., and D. Karowe, 2014, Will chemical defenses become more effective against specialist herbivores under elevated CO2? Global Change Biology, 20, 3159–3176.

Lister, B., and A. Garcia, 2018, Climate-driven declines in arthropod abundance restructure a rainforest food web, PNAS 115, E10397–E10406

Mohan, J., L. Ziska, W. Schlesinger, R. Thomas, R. Sicher, K. George, and J. Clark, 2006, Biomass and toxicity responses of poison ivy (Toxicodendron  radicans) to elevated atmospheric CO2. PNAS 103, 9086-9089.

Narango, D., D. Tallamy, and P. Marra, 2018, Nonnative plants reduce population growth of an insectivorous bird, PNAS 115: 11549–11554.

Polley, H., H. Johnson, H. Mayeux, C. Tischler, and D. Brown, 1996, Carbon Dioxide Enrichment Improves Growth, Water Relations, and Survival of Droughted Honey Mesquite (Prosopis glandulosa) Seedlings, Tree Physiology, 16, 817-823.

Robinson, E., G. Ryan, and J. Newman, 2012, A meta-analytical review of the effects of elevated CO2 on plant-arthropod interactions highlights the importance of interacting environmental and biological variables, New Phytologist 194, 321-336.

Samways, M., et al., 2020, Solutions for humanity on how to conserve insects, Biological Conservation 242, 108427. https://doi.org/10.1016/j.biocon.2020.108427

Sánchez-Bayoa, F. and K. Wyckhuys, 2019, Worldwide decline of the entomofauna: A review of its drivers, Biological Conservation 232, 8-27.

Sasek, T. and B. Strain, 1988, Effects of Carbon Dioxide Enrichment on the Growth and Morphology of Kudzu (Pueraria lobata), Weed Science 36, 28 – 36, DOI: https://doi.org/10.1017/S0043174500074415

Sasek, T. and B. Strain, 1991, Effects of CO2 Enrichment on the Growth and Morphology of a Native and Introduced Honeysuckle Vine, American Journal of Botany 78, 69-75.

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Song, L., J. Wu, C. Li, F. Li, S. Peng, and B. Chen, 2009, Different responses of invasive and native species to elevated CO2 concentration, Acta Oecologica 35, 128-135.

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Ziska, L., Shaun Falukner, and John Lydon, 2004, Changes in biomass and root: Shoot Ratio of Field-grown Canada Thistle (Cirsium arvense), a Noxious, Invasive Wed, with Elevated CO2: Implications for Control with Glyphosate, Weed Science 52, 584-588.

Ziska, L.H., J.S. Pettis, J. Edwards, J.E. Hancock, M.B. Tomecek, A. Clark, J.S. Dukes, I. Loladze, and H.W. Polley, 2016, Rising atmospheric CO2 is reducing the protein concentration of a floral pollen source essential for North American bees, Proc. R. Soc. B, 283, 20160414, http://dx.doi.org/10.1098/rspb.2016.0414

Ziska, Lewis, 2022, Greenhouse Planet: How Rising CO2 Changes Plants and Life as We Know It, Columbia University Press, NY.

Wood Packaging: Pests Still Coming, USDA Not Taking Action

photo courtesy of Oregon Department of Agriculture

As we know, wood packaging (SWPM; crates, pallets, spools, etc.) is a high-risk pathway for introduction of bark- and wood-infesting insects (borers). (To see my 40 earlier blogs about wood packaging material, scroll down below archives to “Categories,” click on “wood packaging”.) Examples of highly damaging pests introduced to North America include Asian longhorned beetle; emerald ash borer; redbay ambrosia beetle; sirex woodwasp; possibly the polyphagous and Kuroshio shot hole borers; Mediterranean oak borer; and dozens of others. (As of 2014, 58 new species of non-native wood- or bark-boring insects had been detected in the past 30 years [Leung et al. 2014]).

The Asian longhorned beetle and emerald ash borer were probably introduced before the World Trade Organization (WTO) came into effect in 1994; many of the others were detected – if not introduced – after that date. This global trade agreement not only facilitated rapid growth in trade volumes; it also imposed stringent conditions for adoption of plant health (= phytosanitary) measures aimed at preventing pest introductions. (For a review of the WTO restrictions, see my Fading Forests II report, here).

While the risk of pests travelling in raw wood was well known, U.S. and international phytosanitary agencies became aware that wood packaging fit into that category with detection of the ALB in New York and other wood-borer introductions. They acted remarkably rapidly to reduce this risk by negotiating and adopting International Standard for Phytosanitary Measures (ISPM) #15 in 2002.

The goal of ISPM#15 is to “significantly reduce” [not eliminate] the risk of pests associated with solid wood used for constructing packaging (e.g., crates, pallets), from being introduced to other countries through international trade.

This first international standard addressing a pathway of introductions was adopted 20 years ago. (The U.S. fully implemented ISPM#15 in 2006; see either article by Haack for a description of the phase-in period.) So – how great is the risk of pest introduction in wood packaging now? What proportion of these incoming containers are likely to be harboring tree-killing insects? Since it is impossible to reduce that risk to 0 while continuing trade using wood packaging, what is an acceptable level of risk? In determining that level, we must keep in mind the huge volumes of wood packaging being used in international trade, and the serious damage these wood-borers can cause. (See the pest profiles in the links provided above.)

I applaud the international phytosanitary community for acting fast and for choosing a pathway standard rather than try to differentiate the level of risk associated with any particular transaction – given that wood packaging could be made from dozens or hundreds of tree taxa, there are thousands of species of wood-boring insects, and the likelihood of an introduction depends in part on the exporting and importing countries. Plus, international trade involves huge volumes of goods. According to Haack et al. (2022), ~ 55 million TEU (shipping containers measured as twenty-foot equivalents) entered the U.S. in 2020. This is a 68% increase over the volume in 2003. Imports in the first half of 2020 were down because of the COVID epidemic. They then grew rapidly through the first half of 2022; imports from Asia in the first 10 months of 2022 were 21% higher than in the same period in 2019 (Mongelluzzo 2022). Haack et al. (2022) note that the number of countries from which SWPM originated more than doubled from 2003–2004 to 2010–2020, although it dropped after 2018.

In 2014, Haack et al. published an estimate of the pest approach rate in wood packaging as of 2009. Depending on which countries were included and how the time periods were selected to separate pre- and post-adoption of ISPM#15, they reported a 36–52% reduction in the SWPM infestation rate following ISPM#15 implementation. This resulted in an estimated infestation rate of 0.1% (1/10th of 1%). In a recent blog, I applied this estimated approach rate to find that probably 11,000 containers per year transported pests to North America in 2021; 80% of these shipments came to the United States.

Since 2009, traders have gained 13 more years of experience. More important, in 2009 the standard was changed to require that wood packaging be constructed from wood that had been debarked before treatment. There is a tolerance limit for small patches of residual bark. Given that bark provides shelter both for insects already there, and facilitates any new infestation after the treatment was performed, it was expected that this change would further reduce the pest risk.

Since more than a decade has passed since the original analysis, and wood-borers continue to be found in wood packaging – in the U.S. and elsewhere – Haack and colleagues have re-analyzed the pest approach rates (see Haack et al. 2022). Their objectives were to

(1) compare pre-and post-ISPM#15 borer-infestation rates;

(2) compare the borer detection rates individually for three kinds of imports and key US trading partners;

(3) see whether wood borer presence varies by season; and

(4) assess the diversity of borer taxa detected overall, and by cargo category and country of origin.

Over the entire 17-year period 2003 – 2020, 87,571 consignments met the conditions for the study: they contained wood packaging that bore the ISPM#15 mark (from 2006 and onwards) indicating it had been treated as required; and the shipment was not from Canada (the U.S. does not require wood packaging from Canada to comply with ISPM#15).

They analyzed the data for the entire 17-year period and separately for four phases:

1) before the U.S. implemented ISPM#15 (2003-2004);

2) phasing-in of U.S. implementation (2005 – 2006);

3) full implementation – but without any restriction on THE presence of bark (2007-2009); and

4) full implementation with restrictions on bark (2010 – 2021).

Over the period 2003– 2020, wood borers were detected in 180 of the 87,571 consignments, or 0.21%. This was 38% less than the 0.34% infestation rate in 2003-2004, before the U.S. implemented ISPM#15. Still, the US had required China to treat its wood packaging as of December 1998 because of introduction of ALB. However, the reduction was greatest in the first phase (2005-2006); in subsequent periods the pest approach rate inched back up. Detection rates have been relatively constant since 2005 despite the requirement in 2009 that bark be removed and a resulting reduction in the presence of bark (it fell from 40% or more of inspected consignments before 2009 to 15% after 2010). 

Unfortunately, the data used in the study do not indicate if borers detected on wood were located under any bark that was present. There might be some indication from the species detected: 100% of Scolytinae identified to genus or species detected before 2007 were true bark beetles (which develop primarily under bark), but only 23% in 2010–2020 period.

The data revealed no strong seasonal pattern.  

Types of Wood Packaging

The study findings indicate that crates are the type of wood packaging most likely to be infested by insects. While crates constituted only 7.5% of the wood packaging inspected, they made up 29.4% of the infested packaging – or four times greater than their proportion of the dataset. Pallets constituted 88.6% of the inspected wood packaging, but only 67.2% of the infested shipments. Dunnage and “other” wood packaging made up insignificant proportions of both total wood packaging inspected and wood packaging found to be infested. (Of course, dunnage can still pose a threat; see my blog about issues in Houston with dunnage bracing breakbulk cargo.) The Haack et al. (2022) study did not examine dunnage accompanying breakbulk shipments.  

Records of Various countries

The 180 infested consignments originated from 30 countries. For two of these countries, the percentage of wood packaging found to be infested was higher than the proportion of all wood packaging from that country that was inspected. Packaging from China made up 4.6% of all shipments inspected, but 22% of the 180 consignments with infested wood packaging. Thus the proportion Chinese consignments with infested wood is five times greater than expected based on their proportion of the dataset. The rate of wood packaging from China that is infested has remained relatively steady – as I noted above. The Chinese infestation rate was 1.26% during 2003–2004, and ranged from 0.58 to 1.11% during the next three periods.

I remind you, again, that the U.S. has required treatment of wood packaging from China since December 1998. Why does this country continue to ship pest-infested wood packaging to the United States? Why are the responsible agencies in the United States not taking action to correct this problem? (DHS Bureau of Customs and Border Protection enhanced its enforcement in 2017; see my blogs.)

A second country with a record of non-compliant wood packaging – Italy – has done better. The level of pest detection still exceeded their expected proportional level – that is, Italy constituted 12.7% of all inspected shipments, but had 15% of infested consignments. Still, Italy has reduced detection rates by almost two-thirds over the 17 years of the study. The Italian statistics would have been even better if there had not been a spike of infested wood in 2015 – 2018 – for unknown reasons.

The data indicate that a third country, Mexico, has improved the pest-free quality of wood packaging accompanying it exports.

Wood from Costa Rica and Turkey has deteriorated as regards pest infestation rates.The borer detection rate on Costa Rican shipments rose from 0.072% during all of 2003–2009 to 0.665% during 2010–2020. Pest-detection rates for Turkey were actually 0 during 2003–2004 (only 59 consignments) but rose to 1.05% during 2010– 2020.

Disturbing Trends

The data reveal other trends that I find disturbing:

  • While the pest approach rate has fallen since U.S. implementation of ISPM#15, the extent of the decline has progressively decreased during each period studied: the reduction during 2005–2006 was 61%; during 2007–2009, 47%; during 2010-2020 only 36%.
  • The 2010 – 2020 pest approach rate was calculated at 0.22%. This is more than double the rate based on 2009 data (0.1%, as stated in the 2014 paper). However, we should be cautious in making this comparison because the 2014 and 2022 studies used different methods (see below). The bottom line, however, is that the approach rate remains too high, in my view. Our forests continue to be exposed to the risk of introduction of highly damaging wood-boring pests. Furthermore, since the number of countries sending us infested wood packaging has increased, those potential pests include insects from a greater variety of countries (biomes).
  • Given the higher number of countries involved and rising proportion of wood that is infested, it is not surprising that the diversity of wood borers found in wood packaging increased. Cerambycidae were consistently the most commonly intercepted borers – making up just under half of the total for the 17 years. Scolytinae were consistently second, at 39%. Still, all major families of borers had been intercepted throughout the period.

Explanation

From the perspective of protecting our forests, what matters is whether the “current” infestation rate is significantly below the rate before ISPM#15 was implemented. As noted, the infestation rate in the 2010-2020 period (0.22%) is, on first glance, more than twice as high as the 2009 approach rate as calculated in the 2014 paper (0.1%). However, the earlier calculation excluded reports of wood packaging from China and Mexico for reasons given in the 2014 paper. Since these countries are among the top three sources of imports to the U.S., and all have had relatively high levels of infested wood packaging, this difference must have had a significant impact on the final finding.

Indeed, the supplementary materials in Haack et al. (2022) show just such a big impact. When records from China and Mexico are excluded from the calculation, the 2010-2020 approach rate appears to have been even higher — 0.272%. This is a reduction from the pre-ISPM#15 approach rate (0.299%) of only 9% — a quarter of the reduction found when data from China and Mexico were included (note the 36% reduction noted above). This difference in approach rate estimates reflects Mexico’s success in cleaning up its wood packaging (as noted above). Since China had “steady” infestation rates throughout, adding or dropping China had less of an impact.

The data do not show a significant drop in pest approach rates during the period 2010-2020 compared to pre-ISPM#15 levels, which is disappointing.  Scientists do not know why this happened. It could reflect many of the reasons discussed in the 2022 paper. Perhaps the most important factor is that reporting data on a consignment basis does not allow us to detect whether the numbers of a pest species present have decreased. [See point 5 below.]

The fact is that a pallet or crate bearing the ISPM#15 mark has not proved to be reliable as to whether the wood is pest-free. (This might be because the wood had not been treated, or that it was, but the treatment failed). All the pests detected in study (after 2006) were in wood packaging bearing the ISPM#15 mark. I have noted in past blogs [click on the “wood packaging” category to bring up blogs about wood packaging and enforcement] that Customs and Border Protection also reported that nearly all the wood packaging in which that they detected insect pests bore the mark.

Conclusions: Haack et al. (2022)

Haack et al. (2022) note that U.S. imports have risen 68% by volume from 2003 to 2020 (with additional growth since; see above); however, borer detection rates have remained rather steady. This, plus the apparently lower number of woodborers established in recent years, suggest that ISPM#15 is helping to mitigate risks. However, the reduction in detection rates is less than hoped. They discuss ten possible explanations. Six of these factors were discussed in the original analysis (Haack et al. 2014); four others are new.

(1) Pest Thermotolerance. Can pests tolerate the heat treatment schedule mandated by ISPM#15? Haack et al. (2022) note that this schedule was based on one intended to kill the pinewood nematode and that it was recognized that some pests might be able to tolerate those conditions (Haack et al. 2014).  The authors review the literature and conclude that some of the live borers found in heat-treated wood packaging in the study probably did survive the heat treatment. They note that studies are now under way to test temperatures that are lethal to various borers. I have raised the issue that standards must be based on lethal temperatures that can be achieved in practice; otherwise, they won’t protect forests from introduced pests.

(2) Unintentional non-compliance. The authors concluded that accidental treatment failures are likely. They note that the International Plant Protection Convention (IPPC) has issued guidance on handling and testing during heat treatment and fumigation.

(3) Fraud. The authors conclude that fraud is possible, but that the incidence at the global scale is unknown. Each country is responsible for their own compliance. Unfortunately, there is no effective means for independently testing whether treatments have been applied. Still, we note that all live insects evaluated in this paper were in wood package that bore the required stamp and was apparently compliant.

(4) Post-treatment colonization. Haack et al. (2022) note that adoption of the bark requirements in 2009 was intended to reduce re-infestation risk. They note that fewer true bark beetles (that develop under bark) have been detected in recent years compared w/ ambrosia beetles (that develop in wood).  As I noted above, the survey data do not reveal whether insects detected by inspectors were under any remaining bark.

(5) AQIM data collection protocols. The authors note that reporting of wood borer detections by consignment conceals the per-piece infestation rate. There might be many fewer individuals of a pest in a container now – and this is important because fewer individuals pose a lower establishment risk (lower propagule pressure).

(6) Pre-ISPM actions.  Some countries had begun requiring treatment of wood packaging before 2003, when data collection for the study began. Thus the approach rate might have already been reduced before ISPM#15 was implemented in the U.S., leading to a smaller apparent change.

(7) Level of detection. All the analyses assumed that the detection abilities of port inspectors remained the same over the 17 years of the study. However, inspectors might have improved their efficacy through improvements in training, inspection techniques, or technology. If so, the apparent impact of ISPM#15 would be lessened in recent years. Haack et al. (2022) say estimating the effectiveness of inspections is not possible in the absence of a “leakage survey” conducted on inspected goods to see how often target pests are missed.

(8) Changing trade partners. Countries have varying levels of effort and efficacy in enforcing ISPM#15.

(9) Varying trees and their associated borers. Countries and global regions are home to different tree species and associated insects. Therefore, changes in trading partners – or forest pest conditions within a country – can affect the number and species of potential pests harbored in the wood packaging approaching our borders.

(10) Practical limits on compliance. Reducing infestation levels to near zero through reliance on application of the ISPM#15 standard would require nearly universal compliance by industry, using highly effective treatments. Haack et al. (2022) note that such compliance levels might be difficult to achieve without either very strong incentives or intensive oversight and significant penalties for noncompliant exporters. I note that I have urged the U.S. to enhance both; link to blogs at least CBP has taken action to step up enforcement.

Haack et al. (2022) call for improved education and outreach by the IPPC, plus greater cooperation and information sharing among trading countries. I note that the Cary Institute is pursuing opening data on treatment facilities’ records so importers can hire the best.

Haack et al. (2022) conclude that ISPM#15 has resulted in marked decreases in rates of borer detection in wood packaging. However, problem areas remain re: some types of commercial goods and exporting countries. Given the enormous and growing volume of international trade, the relatively low risk associated with individual crates or pallets still poses a real risk for pest intro.

Still, they consider that the near global acceptance of ISPM#15 indicates a strong commitment by the world community to minimize movement of wood pests in SWPM through international trade.

Haack et al. (2022) call for several improvements. Some concern data to support analysis of the risk level. First, recording the numbers of infested pieces instead of reporting only consignments would help determine the numbers of insects reaching our borders. They also wish to learn whether when bark is present if it exceeds the current tolerance limits; and the type of treatment applied to each infested piece of wood packaging.

They also note opportunities to improve ISPM#15 implementation and enforcement through training on applying treatments, marking and repairing wood packaging, compiling the required records, and inspecting treatment facilities.

Oregon ash swamp; photo by Wyatt Williams, Oregon Department of Forestr

Faith’s Conclusions

In my view, it is less important whether the current approach rate is exactly 0.22% or somewhat less or more. What is important:

  • the pest approach rate is not acceptable given the huge and rising volume of imports, potential for introductions from new trading partners (with different insect faunas), and the great damage caused by wood-boring insects. 
  •  long-standing enforcement problems have not been resolved (i.e., Chinese wood packaging). Perhaps DHS CBP’s enhanced enforcement will bring improvements. CBP staff expressed disappointment in August 2022.

American government agencies must take more effective action to ensure that trade partners comply with ISPM#15. They should also look more aggressively at other actions to curtail introductions via this pathway, e.g.,

  • U.S. and Canada refuse to accept wood packaging from foreign suppliers that have a record of repeated violations – whatever the apparent cause of the non-compliance. Institute severe penalties to deter foreign suppliers from taking devious steps to escape being associated with their violation record.
  • APHIS and CBP and their Canadian counterparts provide guidance to importers on which foreign treatment facilities have a record of poor compliance or suspected fraud – so they can avoid purchasing SWPM from them. I am hopeful that the voluntary industry program described here will help importers avoid using wood packaging from unreliable suppliers in the exporting country.
  • Encourage a rapid switch to materials that won’t transport wood-borers. Plastic is one such material. While no one wants to encourage production of more plastic, the Earth is drowning under discarded plastic. Some firms are recycling plastic waste into pallets.

The two articles by Haack et al. – 2014 and 2022 – fully describe the methodology used, the structure of USDA’s Agriculture Quarantine Inspection Monitoring (AQIM) program, detailed requirements of ISPM#15, the phases of U.S. implementation, etc.  Also see the supplemental data sheet in Haack et al. (2022) that compares the methods used in each analysis.

SOURCES

Haack RA, Britton KO, Brockerhoff EG, Cavey JF, Garrett LJ, et al. (2014) Effectiveness of the International Phytosanitary Standard ISPM No. 15 on Reducing Wood Borer Infestation Rates in Wood Packaging Material Entering the United States. PLoS ONE 9(5): e96611. doi:10.1371/journal.pone.0096611

Haack RA, Hardin JA, Caton BP and Petrice TR (2022) Wood borer detection rates on wood packaging materials entering the United States during different phases of ISPM#15 implementation and regulatory changes. Frontiers in Forests and Global Change 5:1069117. doi: 10.3389/ffgc.2022.1069117

Leung, B., M.R. Springborn, J.A. Turner, and E.G. Brockerhoff. 2014. Pathway-level risk analysis: the net present value of an invasive species policy in the US. Front Ecol Environ. 2014. doi:10.1890/130311

Mongelluzzo, B. Trans-Pacific volume decline picks up pace in October. JOC. November 17, 2022. https://www.joc.com/maritime-news/container-lines/trans-pacific-volume-decline-picks-pace-october_20221117.html?utm_source=Eloqua&utm_medium=email&utm_campaign=CL_JOC%20Daily%2011%2F18%2F22%20NONSUBSCRIBER_PC015255_e-production_E-148476_KB_1118_0617

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

A Forest without Big Trees — Which Animals Will be Decimated?

In an earlier blog about tree extinctions, I commented that less drastic impacts by pests can also be important. I mentioned specifically that clumps of beech root sprouts cannot duplicate the quantities of nuts and cavities provided by mature beech trees.

This thought prompted me to search for information about use of tree cavities by wildlife. The articles I have found are decades old and largely focus on implications for management of forests for timber. Timber production conflicts with a goal of ensuring the presence of large (“overmature”), trees, especially those with dead branches, and completely dead trees (“snags”). These articles were written too long ago to address the possible impacts of non-native insects and pathogens – although there is some discussion of widespread mortality of pines caused by the mountain pine beetle.

These sources make clear that species that make cavities are keystone species. Many other wildlife species depend on them — birds, bats and terrestrial animals – mammals and herps. Furthermore, these cavity-associated species require forests with significant numbers of large, old, declining trees. When non-native insects or pathogens kill those trees, there might be a short-term bonanza of dying trees – suitable for nesting and foraging; and wood-feeding insects to provide food. But afterwards – for decades or longer – there will probably be small-diameter trees, and different species. Can the cavity-dependent species find habitat or food under these circumstances?

[By coincidence, the PBS program “Nature” broadcast an episode on woodpeckers on the 2nd of November! The title is “The Hole Story”. ]

Cavities provide a variety of habitats for many species – including some not usually thought of as “forest” species. Among the 85 North American bird species identified by Scott et al. as associated with cavities are seven species of ducks, two vultures, three falcons, 12 owls, two swifts, six flycatchers, two swallows, purple martin, seven chickadees, three titmice, four nuthatches, brown creeper, five wrens, three bluebirds, and two warblers. They point out that the majority of these birds are insectivores. Woodpeckers are especially important predators of tree-killing bark beetles.

Goodburn and Lorimer found that more than 40 species of birds and mammals in hardwood forests of Wisconsin and Michigan use cavities in snags and dead portions of live trees for nest sites, dens, escape cover, and winter shelter. Bunnell reported that 67 vertebrate species commonly use cavities in the Pacific Northwest. Chepps et al., Daily et al., and Wiggins focus on specific species in the Rocky Mountains. (Full citations for all sources are at the end of the blog.)

While Scott et al. (published in 1977) do not address the impact of non-native pests, their profiles of individual bird species sometimes name specific types of trees favored. Several of these tree taxa have been decimated by such non-native pests, or face such attack in the near future. Thus, concern appears warranted for:

pileated woodpecker; photo by Jo Zimni via Flickr
  • birds nesting in American elm, including two that are quite large so they require large trees to accommodate their nests: common goldeneye (a duck) and pileated woodpecker (larger than a crow).
  • the pileated woodpecker also nests in ash and beech and here
  • the yellow-bellied sapsucker nests in butternut.

How many species depended on American chestnut, which – before the blight — grew to diameters up to 5 feet, heights of 70 to 100 feet, and had hollow centers (USDA 2022)?

In the West, some nesting tree species are under imminent threat from invasive shot hole borers, goldspotted oak borer, or sudden oak death. Detection of the emerald ash borer in Oregon portends a longer-term threat. Birds likely to feel these impacts include the acorn woodpecker, ash-throated flycatcher, and purple martin. The golden-fronted woodpecker is associated with oaks in parts of Texas where oak wilt is severely affecting live oaks.

ash-throated flycatcher; photo by Mick Thompson via Flickr

At the beginning of the 21st Century – before widespread mortality caused by the emerald ash borer — densities of snags in the managed forests in the Lake States were apparently already insufficient to sustain population densities of cavity nesting birds. Pileated woodpeckers and chimney swifts both prefer snags greater than 50 cm dbh, which are significantly less abundant in harvested stands. For six of eight bird species studied, the number of breeding pairs was significantly higher in old-growth northern hardwood stands than in those under management (Goodburn and Lorimer).

Strong Primary Excavators are Keystone Species

Cavity nesters are commonly divided into:

1) primary excavators that excavate their own cavities. These are further divided into strong excavators – those species that forage by drilling, boring, or hammering into wood or soil; and weak excavators – those species that probe or glean bark, branches, and leaves to acquire prey.

2) secondary cavity users, that use holes made by primary cavity excavators (Bunnell).

Strong primary excavators tend to be large, e.g., most woodpeckers, sapsuckers, and the northern flicker. Weak excavators are mostly smaller species, such as chickadees and nuthatches; plus those woodpeckers that forage primarily by probing and gleaning, extracting seeds, or capturing insects in flight [e.g., acorn woodpecker (Melanerpes formicivorus), downy woodpecker (Picoides pubescens)] (Bunnell).

Bunnell considers strong excavators to be keystone species because so many other cavity users depend on them. Their loss would seriously disrupt forest ecosystems. For example, in the Pacific Northwest, only nine of 22 avian primary excavators are strong excavators. Another 45 species are secondary cavity users. These include waterfowl, tree swallows, and some mammals such as flying squirrels. Some cavity nesters support an even wider group of species: in the Pacific Northwest, at least 23 bird species, six mammal species, and numerous arthropods (nine orders and 22 families) feed on sap and insects collected at holes drilled by sapsuckers (Bunnell). [I discuss sapsuckers’ ecosystem role in greater detail later.]

Tree Characteristics

There is general agreement that animals dependent on tree cavities “prefer” (actually, require) trees that are large – tall, of large circumference, and sturdy – while having decayed interiors.

Size:

As Bunnell notes, larger snags provide more room and tend to stand longer without breaking, so they provide greater opportunities for cavity use. They also tend to be taller, so they offer higher nest sites that provide better protection from ground-dwelling predators. While larger-diameter trees remain standing longer regardless of the cause of mortality, snags created by fire usually fall sooner than do other snags. Beetle-killed trees are more attractive to cavity nesters that tend to excavate nest sites in trees on which they have foraged.

In the upper Midwest, cavity trees were a scare resource, even in unmanaged forests. Mean diameters for live cavity trees were twice as large as the mean diameter of the live trees in stands under a management regime. Such larger-diameter snags were more numerous in old-growth than in managed stands, especially in mixed hemlock-hardwood stands (Goodburn and Lorimer).

The Importance of Decay

Excavating a cavity demands considerable energy, so birds seek sites where a fungal infection has softened the interior wood. The exterior wood must remain strong to prevent collapse of the nest. These rots take time to develop, so they appear more often in older, even dying, trees. Bunnell, Scott et al., Chepps et al., and Goodburn and Lorimer all emphasize the role of decay in providing suitable cavity sites. Chepps et al. compared the aspen trees used by four species of cavity-nesting birds in central Arizona. Not only were nest trees softer than neighboring trees; they were softer at the spot where the nests were excavated than at other heights. [Spring (1965) provides a fun discussion of different species’ adaptations to the energy demands of hard pecking and climbing vertical trunks.]

Live v. Dead Trees

However, the need for decay does not necessarily mean birds prefer dead trees. Goodburn and Lorimer found that in Wisconsin and Michigan, a large percentage of all cavities found were in live trees.  

Bunnell found that strong excavators select trees with less visible signs of decay. Where possible, secondary users will also use live trees. However, intense competition often forces them to use dead trees.

Hardwoods v. Conifers

Bunnell states that deciduous trees more often contain internal rot surrounded by a sound outer shell than do conifers (at least this is true in the Pacific Northwest). He found that cavity nesters chose hardwoods for 80–95% of their nest sites even where hardwoods comprised only 5–15% of the available tree stems. He concluded that availability of living hardwoods had a significant influence on strong excavators in the West, although probably was less important in hardwood stands in the East.

Taxa Dependent on Other Types of Cavity

Some species depend on cavities created by forces other than bird excavations, such as decay or fire. These include most of the mammals, especially the larger ones e.g., American martens, fishers, porcupines, and black bears. These natural cavities are often uncommon. Vaux’s swifts nest and roost in hollow snags large enough that they can fly in a spiral formation to enter and leave (Bunnell).

little brown bat Myotis sp. photo by S.M. Bishop via Wikimedia Commons

Bats are a special case. Bats are unique among mammals of their size in having long lives, low reproductive rates, and relatively long periods of infant dependency. They also play a key ecological role as the major predators of nocturnal flying insects (van den Driesche 1999). Also many species are in perilous conservation status: half of the 16 bat species in British Columbia were listed as threatened or endangered as of 1998 (van den Driesche). This was before the deadly disease whitenose syndrome had been detected in North America.

Bats require larger trees. In the Pacific Northwest at least, that choice often means conifers (Bunnell). Roosts are difficult to find, so samples are small. A study on the west coast of Vancouver Island (van den Driessche), located only nine roosts despite searching during three summers. Five roosts were in large-diameter (old) western red cedar, with dead tops and extensive cracks.

Brown creepers and some amphibians and reptiles nest or seek cover under slabs of loose bark, which are typically found on dead or dying trees. The same large, mature and old-growth conifer trees also provide preferred foraging habitat, since there is a higher density of arthropod prey on their deeply furrowed bark. While Wiggins (2005) studied bird populations in the Rocky Mountains, he cited studies in the eastern United States, specifically in the Blue Ridge and Allegheny mountains, that have found similar results. Goodburn and Lorimer found that in National forests in Wisconsin and Michigan, only 15% of trees consisted of the necessary snags with loose bark plates. Suitable trees were most frequent old-growth hemlock-hardwood stands, and on larger-diameter snags. A high proportion of the snags with loose bark were yellow birch (Betula alleghaniensis).

Importance of foraging sites

As Bunnell points out, a bird must feed itself before it can nest. Foraging trees and snags are usually smaller than nesting trees. Furthermore, birds need many more foraging sites than nesting sites. The situation perhaps most pertinent to our usual focus on invasive pests concerns bird species’ response to mountain pine beetle outbreaks. Red-breasted nuthatches and mountain chickadees increasing dramatically in apparent response to the beetle epidemic. When most of the conifers had been killed, and numbers of beetles diminished, numbers of these bird species also declined–despite the increased availability of conifer snags for nesting. Indeed, the birds continued to nest primarily in aspen during the epidemic.

Bunnell reiterates that snags of all sizes are needed; they provide perching, foraging, and hawking sites for bird species beyond cavity nesters as well as sustenance for bryophytes, insects, and terrestrial breeding salamanders. He says more than 200 studies reported harvesting of standing dead trees in beetle-killed forests had negative effects on bird, mammal, and fish species.  

Other Dependencies – Food Sources

yellow-bellied flycather; photo by Dennis Church via Flickr

A few studies looked at the role of cavity-creating birds in providing food sources. The focus was on sapsuckers. They drill sapwells into trees’ phloem; sap flowing into these wells attracts many other species. In Michigan, Rissler determined that yellow-bellied sapsuckers’ sapwells attracted insects in seven orders and 20 families, especially Coleoptera, Diptera (other than Tephritidae), bald-faced hornets, and Lepidoptera. Daily et al. (1993) cites other studies showing that ruby throat and rufous hummingbirds have extended their breeding ranges by relying on these sapwells for nutrition in early spring before flowers open. [The “Nature” program covers this behavior.]

In a subalpine ecosystem in Colorado, Daily et al. found that red-naped sapsuckers support other species in two ways. First, they excavate nest cavities in fungus-infected aspens that are utilized by at least seven secondary cavity nesting bird species. When they feed, they drill sapwells that nourish more than 40 species – including hummingbirds, warblers, and chipmunks. Daily et al. called this a keystone species complex comprised of sapsuckers, willows, aspens, and a heartwood fungus. Disappearance of any element of the complex could cause an unanticipated unraveling of the community.

Goodburn and Lorimer looked at the availability of downed wood but did not discuss the implications of the presence of only small-diameter coarse woody debris.

Efforts to Accommodate Biodiversity Needs

Scott et al. reported in 1977 that the USDA Forest Service had required staff at regional and National Forest levels to develop snag retention policies. Twenty years later, Goodburn and Lorimer noted that Forest Service management guidelines for some Wisconsin and Michigan National forests since the early 1980s have called for the retention of all active cavity trees and  5-10 snags (larger than 30 cm dbh)/ha. However, as I noted above, they fear that these recommended snag retention levels might still be too limited to support cavity nesters. They found that two species that prefer snags greater than 50 cm dbh, pileated woodpeckers and chimney swifts, were significantly more abundant in old-growth than in selection stands. Furthermore, the number of breeding pairs of six species was at least 30% higher in old-growth northern hardwood than in selection stands and more than 85% higher in selection cuts than even-aged.

Goodburn and Lorimer cited others’ findings that removal of some live timber and snags in an Arizona ponderosa pine forest reduced cavity-nesting bird populations by 50%. Species affected were primarily violet-green swallows, pygmy nuthatches, and northern three-toed woodpeckers.

Female mountain bluebird by Jacob W. Frank. Original public domain image from Flickr

As I noted, none of these experts has addressed the impacts of wide-spread pest-caused tree mortality. If I may speculate, it seems likely that when the first wave of mortality sweeps through a forest, the result might be an expansion of both nesting opportunities (in dead or dying trees) and food availability for those that feed on wood borers. These would probably be more plentiful even in trees killed by pathogens or nematodes. Sapsuckers and those that depend on them might experience an immediate decline in sap sources. Over the longer term it seems likely that all cavity-dependent species will confront a much lower supply of large mature trees. I note that many deciduous/hardwood tree species are being affected by introduced pests.

Are there current studies in Michigan, where so many ash have died?

SOURCES

Bunnell, F.L. 2013. Sustaining Cavity-Using Species: Patterns of Cavity Use and Implications to Forest Management. Hindawi Publishing Corporation. ISRN Forestry. Volume 2013, Article ID 457698

Chepps, J., S. Lohr, and T.E. Martin. 1999. Does Tree Hardness Influence Nest-Tree Selection by Primary Cavity Nesters? The Auk 116(3):658-665, 1999

Daily, G.C., P.R. Ehrlich, and N.M. Haddad. 1993. Double keystone bird in a keystone species complex. Proc. Natl. Acad. Sci. USA Vol. 90, pp. 592-594, January 1993 Ecology

Goodburn, J.M. and C.G. Lorimer. 1998. Cavity trees and coarse woody debris in old-growth and managed northern hardwood forests in Wisconsin and Michigan. Can. For. Res. 28: 427.438 (1998)

Rissler, L.J., D.N. Karowe, F. Cuthbert, B. Scholtens. 1995. Wilson Bull., 107(4), 1995, pp. 746-752

Spring, L.W.  1965. Climbing and Pecking Adaptations in Some North American Woodpeckers.

Scott, V.E., K.E. Evans, D.R. Patton, C.P. Stone. 1977. Cavity-Nesting Birds of North American Forests. Agriculture Handbook 511 USDA Forest Service. https://www.gutenberg.org/files/49172/49172-h/49172-h.htm

United States Department of Agriculture, Animal and Plant Health Inspection Service. Draft Enviromental Impact Statement. 2022. State University of New York College of Enviromental Science and Forestry Petition (19-309-01p) for Determination of Nonregulated Status for Blight-Tolerant Darling 58 c’nut (Castanea dentata)

van den Driessche, R., M. Mather, T. Chatwin. 1999. Habitat use by bats in temperate old-growth forests, Clayoquot Sound, British Columbia 

Wiggins, D.A. (2005, January 27). Brown Creeper (Certhia americana): a technical conservation assessment. [Online]. USDA Forest Service, Rocky Mountain Region. Available: http://www.fs.fed.us/r2/projects/scp/assessments/browncreeper.pdf [date of access].

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

Australia Builds Capacity to Address Forest Pests

Australian Eucalypts; photo by John Turnbull via Flickr

I congratulate Australian scientists for bringing about substantial improvements of their country’s biosecurity program for forest pests. While it is too early to know how effective the changes will be in preventing new introductions, they are promising. What can we Americans learn from the Australian efforts? [I have previously praised South Africa’s efforts – there is much to learn there, too.]

Australia has a reputation of being very active in managing the invasive species threat. However, until recently biosecurity programs targetting forest pests were minimal and ad hoc. Scientists spent 30 years trying to close those gaps (Carnegie et al. 2022). Their efforts included publishing several reports or publications (listed at the end of the blog) and an international webinar on myrtle rust. Scientists are hopeful that the new early detection program (described below) will greatly enhance forest protection. However, thorough pest risk assessments are still not routinely conducted for forest pests. (Nahrung and Carnegie 2022).

The native flora of Australia is unique. That uniqueness has provided protection because fewer of the non-native insects and pathogens familiar to us in the Northern Hemisphere have found suitable hosts (Nahrung and Carnegie 2020). Also – I would argue – the uniqueness of this flora imposes a special responsibility to protect it from threats that do arise.

Only 17% of Australia’s landmass is covered by forests. Australia is large, however; consequently, these forests cover 134 million hectares (Nahrung and Carnegie 2020). This is the 7th largest forest estate in the world (Carnegie et al. 2022).

Australia’s forests are dominated by eucalypts (Eucalyptus, Corymbia and Angophora). These cover 101 million ha; or 75% of the forest). Acacia (11 million ha; 8%); and Melaleuca (6 million ha) are also significant. The forest also includes one million ha of plantations dominated by Pinus species native to North America (Carnegie et al. 2022). A wide range of native and exotic genera have been planted as amenity trees in urban and peri-urban areas, including pines, sycamores, poplars, oaks, and elms (Carnegie et al. 2022). These urban trees are highly valued for their ecosystem services as well as social, cultural, and property values (Nahrung and Carnegie 2020). Of course, these exotic trees can support establishment and spread of the forest pest species familiar to us in the Northern Hemisphere. On the positive side, they can also be used as sentinel plantings for early detection of non-native species (Carnegie et al. 2022 and Nahrung and Carnegie 2020).

Despite Australia’s geographic isolation, its unique native flora, and what is widely considered to be one of the world’s most robust biosecurity system, at least 260 non-native arthropods and pathogens of forests have established in Australia since 1885 (Nahrung and Carnegie 2020). [(This number is about half the number of non-native forest insects and pathogens that have established in the United States over a period just 25 years longer (Aukema et al. 2010).] As I noted, forest scientists have cited these introductions as a reason to strengthen Australia’s biosecurity system specifically as it applies to forest pests.

What steps have been taken to address this onslaught? For which pests? With what impacts? What gaps have been identified?

Which Pests?

Nahrung and Carnegie (2020) compiled the first comprehensive database of tree and forest pests established in Australia. The 260 species of non-native forest insect pests and pathogens comprise 143 arthropods, 117 pathogens. Nineteen of them (17 insects and 2 fungal species) had been detected before 1900. These species have accumulated at an overall rate of 1.9 species per year; the rate of accumulation after 1955 is slightly higher than during the earlier period, but it has not grown at the exponential rate of import volumes.

While over the entire period insects and pathogens were detected at an almost equal rate (insects at 1.1/year; pathogens at 0.9/year), this disguises an interesting disparity: half of the arthropods were detected before 1940; half of the pathogens after 1960 (Nahrung and Carnegie (2020). By 2022, Nahrung and Carnegie (2022) said that, on average, one new forest insect is introduced each year. Some of these recently detected organisms have probably been established for years. More robust surveillance has  just detected them recently. I have blogged often about an apparent explosion of pathogens being transported globally in recent decades.

In a more recent article (Nahrung and Carnegie, 2022), gave 135 as the number of non-native forest insect pests. The authors don’t explain why this differs from the 143 arthropods listed before.

damage to pine plantations caused by Sirex noctilio; photo courtesy of Helen Nahrung

Eighty-seven percent of the established alien arthropods are associated with non-native hosts (e.g., Pinus, Platanus, Populus, Quercus, Ulmus) (Carnegie et al. 2022). Some of these have escaped eradication attempts and caused financial impact to commercial plantations (e.g., sirex wood wasp, Sirex noctilio) and amenity forests (e.g., elm leaf beetle, Xanthogaleruca luteola) (Carnegie and Nahrung 2019).

About 40% of the alien arthropods were largely cosmopolitan at the time of their introduction in Australia (Carnegie et al. 2022). Only six insects and six fungal species are not recorded as invasive elsewhere (Nahrung and Carnegie 2020). Of the species not yet established, 91% of interceptions from 2003 to- 2016 were known to be invasive elsewhere. There is strong evidence of the bridgehead effect: 95% of interceptions of three species were from their invaded range (Nahrung and Carnegie 2022). These included most of the insects detected in shipments from North America, Europe and New Zealand. These ubiquitous “superinvaders” have been circulating in trade for decades and continue to be intercepted at Australia’s borders. This situation suggests that higher interception rates of these species reflect their invasion success rather than predict it (Nahrung and Carnegie 2021).  

I find it alarming that most species detected in shipments from Africa, South America, and New Zealand were of species not even recorded as established in those regions (Nahrung and Carnegie 2021; Nahrung and Carnegie 2022).

Arhopalus ferus, a Eurasian pine insect often detected in wood from New Zealand; photo by Jon Sullivan – in New Zealand; via Flickr

Half of the alien forest pests established in Australia are highly polyphagous. This includes 73% of Asian-origin pests but only 15% of those from Europe (Nahrung and Carnegie 2021). Nahrung and Carnegie (2022) confirm that polyphagous species are more likely to be detected during border inspections.

PATHWAYS

As in North America and Europe, introductions of Hemiptera are overwhelmingly (98%) associated with fresh plant material (e.g. nursery stock, fruit, foliage). Coleoptera introductions are predominantly (64%) associated with wood (e.g. packaging, timber, furniture, and artefacts). Both pathways are subject to strict regulations by Australia (Nahrung and Carnegie 2021).

Eradication of High-Priority Pests

Eight-five percent of all new detections were not considered high-priority risks. Of the four that were, two had not previously been recognized as threats (Carnegie and Nahrung 2019). One high-priority pest – expected to pose a severe threat to at least some of Australia’s endemic plant species – is myrtle rust, Austropuccinia psidii. Despite this designation, when the rust appeared in Australia in 2010, the response was confused and ended in an early decision that eradication was impossible.  Myrtle rust has now spread along the continent’s east coast, with localized distribution in Victoria, Tasmania, the Northern Territory, and – in 2022, Western Australia.   `

Melaleuca quinquenervia forest; photo by Doug Beckers via Wikimedia

There have been significant impacts to native plant communities. Several reviews of the emergency response criticized the haste with which the initial decision was made to end eradication (Carnegie and Nahrung 2019). (A review of these impacts is here; unfortunately, it is behind a paywall.)

A second newly introduced species has been recognized as a significant threat, but only after its introduction to offshore islands. This is Erythina gall wasp Quadrastichus erythrinae (Carnegie and Nahrung 2019). DMF Although Australia is home to at least one native species in the Erythrina genus, E. vespertilio,, the gall wasp is not included on the environmental pest watch list.

Four of the recently detected species were considered to be high impact. Therefore eradication was attempted. Unfortunately, these attempts failed in three cases. The single success involved a pinewood nematode, Bursaphelenchus hunanesis. See Nahrung and Carnegie (2021) for a discussion of the reasons. This means three species recognized as high-impact pests have established in Australia over 15 years (Nahrung and Carnegie (2021). In fact, Australia’s record of successful forest pest eradications is only half the global average (Carnegie and Nahrung (2019).

Carnegie and Nahrung (2019) conclude that improving early detection strategies is key to increasing the likelihood of eradication. They discuss the strengths and weaknesses of various strategies. Non-officials (citizen scientists) reported 59% of the 260 forest pests detected (Carnegie and Nahrung 2019). Few alien pests have been detected by official surveillance (Carnegie et al 2022). However, managing citizen scientists’ reports involves a significant workload. Futhermore, surveillance by industry, while appreciated, is likely to detect only established species (Carnegie and Nahrung 2019).

Interception Frequency Is Not an Indicator of Likelihood of Establishment

Nahrung & Carnegie (2021) document that taxonomic groups already established in Australia are rarely detected at the border. Furthermore, only two species were intercepted before they were discovered to be established in Australia.

Indeed, 76% of species established in Australia were either never or rarely intercepted at the border. While more Hemiptera species are established in Australia, significantly more species of Coleoptera are intercepted at the border. Among beetles, the most-intercepted family is Bostrichid borers (powderpost beetles). Over the period 2003 – 2016, Bostrichid beetles made up 82% of interceptions in wood packaging and 44% in wood products (Nahrung and Carnegie 2022). This beetle family is not considered a quarantine concern by either Australian or American phytosanitary officials. I believe USDA APHIS does not even bother recording detections of powderpost beetles. Nahrung and Carnegie (2021) think the high proportion of Bostrichids might be partially explained by intense inspection of baggage, mail, and personal effects. While Australia actively instructs travelers not to bring in fruits and vegetables because of the pest risk, there are fewer warnings about risks associated with wood products. 

Nahrung & Carnegie (2021) concluded that interception frequencies did not provide a good overall indicator of likelihood of risk of contemporaneous establishment.

Do Programs Focus on the Right Species?

Although Hemiptera comprise about a third of recent detections and establishments, and four of eight established species are causing medium-to-high impact, no Hemiptera are currently listed as high priority forestry pests by Australian phytosanitary agencies (Nahrung & Carnegie (2021). On the other hand, Lepidoptera make up about a third of the high-priority species, yet only two have established in Australia over 130 years. Similarly, Cerambycidae are the most frequently intercepted forest pests and several are listed as high risk. But only three forest-related species have established (Nahrung and Carnegie 2020). (Note discussion of Bostrichidae above.).

Unlike the transcontinental exchanges under way in the Northern Hemisphere, none of the established beetles is from Asia; all are native to Europe. This is especially striking since interceptions from Asia-Pacific areas account for more than half of all interceptions Nahrung and Carnegie (2021).

Interestingly, 32 Australian Lepidopteran and eight Cerambycid species are considered pests in New Zealand. However, no forest pests native to New Zealand have established in Australia despite high levels of trade, geographic proximity, and the high number of shared exotic tree forest species (Nahrung and Carnegie 2020).

STRUCTURE OF PROGRAM

The structure of Australia’s plant biosecurity system is described in detail in Carnegie et al. (2022). These authors call the program “comprehensive” but to me it looks highly fragmented. The federal Department of Agriculture and Water Resources (DAWR,[recently renamed the Department of Agriculture, Fisheries, and Forestry, or DAFF) is responsible for pre-border (e.g., off-shore compliance) and border (e.g., import inspection) activities. The seven state governments, along with DAFF, are responsible for surveillance within the country, management of pest incursions, and regulation of pests. Once an alien pest has become established, its management becomes the responsibility of the land manager. In Australia, then, biosecurity is considered to be a responsibility shared between governments, industry and individuals.

Even this fragmented approach was developed more recently than one might expect given Australia’s reputation for having a stringent biosecurity system. Perhaps this reflects the earlier worldwide neglect of the Plant Kingdom? Carnegie and Nahrung (2019) describe recent improvements. Until the year 2000, Australia’s response to the detection of exotic plant pests was primarily case-by-case. In that year Plant Health Australia (PHA) was incorporated. Its purpose was to facilitate preparedness and response arrangements between governments and industry for plant pests. In 2005, the Emergency Plant Pest Response Deed (EPPRD) was created. It is a legally-binding agreement between the federal, state, and territorial governments and plant industry bodies. As of 2022, 38 were engaged. It sets up a process to implement management and funding of agreed responses to the detection of exotic plant pests – including cost-sharing and owner reimbursement. A national response plan (PLANTPLAN) provides management guidelines and outlines procedures, roles and responsibilities for all parties. A national committee (Consultative Committee on Emergency Plant Pests (CCEPP) works with surveys to determine invaded areas (delimitation surveys) and other data to determine whether eradicating the pest is technically feasible and has higher economic benefits than costs..

Austropuccinia psidii on Melaleuca quinquenervia; photo by John Tann via Flickr

Even after creation of EPPRD in 2005, studies revealed significant gaps in Australia’s post-border forest biosecurity systems regarding forest pests (Carnegie et al. 2022; Carnegie and Nahrung 2019). These studies – and the disappointing response to the arrival of myrtle rust – led to development of the National Forest Biosecurity Surveillance Strategy (NFBSS) – published in 2018; accompanied by an Implementation Plan. A National Forest Biosecurity Coordinator was appointed.

The forest sector is funding a significant proportion of the proposed activities for the next five years; extension is probable. Drs. Carnegie and Nahrung are pleased that the national surveillance program has been established. It includes specific surveillance at high-risk sites and training of stakeholders who can be additional eyes on the ground. The Australian Forest Products Association has appointed a biosecurity manager (pers. comm.)

This mechanism is expected to ensure that current and future needs of the plant biosecurity system can be mutually agreed on, issues identified, and solutions found. Plant Health Australia’s independence and impartiality allow the company to put the interests of the plant biosecurity system first. It also supports a longer-term perspective (Carnegie et al. (2022). Leading natural resource management organizations are also engaged (Carnegie, pers. comm.).

Presumably the forest surveillance strategy (NFBSS) structure is intended to address the following problems (Carnegie and Nahrung 2019):

  • Alien forest pests are monitored offshore and at the border, but post-border surveillance is less structured and poorly resourced. Australia still lacks a surveillance strategy for environmental pests.
  • Several plant industries have developed their own biosecurity programs, co-funded by the government. These include the National Forest Biosecurity Surveillance Strategy (NFBSS).

Some pilot projects targetting high risk sites were initiated in the early 2000s. By 2019, only one surveillance program remained — trapping for Asian spongy (gypsy) moth.

  • The states of Victoria and New South Wales have set up sentinel site programs. Victoria’s uses local council tree databases. It is apparently focused on urban trees and is primarily pest-specific – e.g., Dutch elm disease. The New South Wales program monitors more than 1,500 sentinel trees and traps insects near ports. This program is funded by a single forest grower through 2022.  

Dr. Carnegie states: “With the start of the national forest biosecurity surveillance program in December 2022, the issues and gaps identified by Carnegie et al. 2022 are starting to be addressed. The program will conduct biosecurity surveillance specifically for forest pests and pathogens and be integrated with national and state biosecurity activities. While biosecurity in Australia is still agri-centric, a concerted and sustained effort from technical experts from the forest industry is changing this. And finally, the new Biosecurity Levy should ensure sustained funding for biosecurity surveillance.”

There is a separate National Environmental Biosecurity Response Agreement (NEBRA), adopted in 2012. It is intended to provide guidelines for responding, cost-sharing arrangements, etc. when the alien pest threatens predominantly the environment or public amenity assets (Carnegie et al. (2022). However, when the polyphagous shot hole borer was detected, the system didn’t work as might have been expected. While PSHB had previously been identified as an environmental priority pest, specifically to Acacia, the decision whether to engage was made under auspices of the the Emergency Plant Pest Response Deed (EPPRD) rather than the environmental agreement (NEBRA). As a result, stakeholders focused on environmental, amenity and indigenous concerns had no formal representation in decision-making processes; instead, industries that had assessed the species as a low priority (e.g., avocado and plantation forestry) did (Nahrung, pers.comm.).

Additional Issues Needing Attention

Some needs are not addressed by the National Forest Pest Strategic Plan (Carnegie et al. 2022) (Nahrung, pers. comm.):

1) The long-term strategic investment from the commercial forestry sector and government needed to maintain surveillance and diagnostic expertise;

2) Studies to assess social acceptance of response and eradication activities such as tree removal; 

3) Studies to improve pest risk prioritization and assessment methods; and

4) Resolving the biosecurity responsibilities for pests of timber that has been cut and used in construction.

In 2019, Carnegie and Nahrung (2019) called for developing more effective methods of detection, especially of Hemiptera and pathogens. They also promoted national standardization of data collection. Finally, they advocated inclusion of technical experts from state governments, research organizations and industry in developing and implementing responses to pest incursions. They note that surveillance and management programs must be prepared to expect and respond to the unexpected since 85% of the pests detected over the last 20 years—and 75% of subsequently mid-to high-impact species established—were not on high-priority pest list. See Nahrung and Carnegie 2022 for a thorough discussion of the usefulness and weaknesses of predictive pest listing.

SOURCES

Aukema, J.E., D.G. McCullough, B. Von Holle, A.M. Liebhold, K. Britton, & S.J. Frankel. 2010. Historical Accumulation of Nonindigenous Forest Pests in the Continental United States. Bioscience. December 2010 / Vol. 60 No. 11

Carnegie A.J. and H.F. Nahrung. 2019. Post-Border Forest Biosecurity in AU: Response to Recent Exotic Detections, Current Surveillance and Ongoing Needs. Forests 2019, 10, 336; doi:10.3390/f10040336 www.mdpi.com/journal/forests

Carnegie A.J., F. Tovar, S. Collins, S.A. Lawson, and H.F. Nahrung. 2022. A Coordinated, Risk-Based, National Forest Biosecurity Surveillance Program for AU Forests. Front. For. Glob. Change 4:756885. doi: 10.3389/ffgc.2021.756885

Nahrung H.F. and A.J. Carnegie. 2020. NIS Forest Insects and Pathogens in Australia: Establishmebt, Spread, and Impact. Frontiers in Forests and Global Change 3:37. doi: 10.3389/ffgc.2020.00037 March 2020 | Volume 3 | Article 37

Nahrung, H.F. and A.J. Carnegie. 2021. Border interceps of forest insects estab in AU: intercepted invaders travel early and often. NeoBiota 64: 69–86. https://doi.org/10.3897/neobiota.64.60424

Nahrung, H.F. & A.J. Carnegie. 2022. Predicting Forest Pest Threats in Australia: Are Risk Lists Worth the Paper they’re Written on? Global Biosecurity, 2022; 4(1).

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org