forest pests – Page 8 – Center for Invasive Species Prevention

Restoring American chestnut: importance of Phytophthora root rot

TACF back-crossed chestnut growing in southern Fairfax County, Virginia

same chestnut, dying in 2021; probably from *Phytopthora* root rot

In the first half of the 20^th Century, American chestnut (Castanea dentata) was functionally extirpated from US forests east of the Mississippi River by chestnut blight, caused by a fungus from Asia, Cryphonectria parasitica. Today, only 10% of the pre-blight chestnut population remains, most as root sprouts less than 2.5 cm dbh (Dalgleish et al. 2015; full citation at the end of the blog).

Volunteer organizations — with recent help from federal and state agencies – have worked for more than a century to develop chestnut trees resistant to the blight. Their aim is to restore the species to the forest. Their decades of hybridization efforts now appear unlikely to produce a highly blight-resistant chestnut with a genome that is predominantly American, so TACF now plans to incorporate the use of transgenic techniques to enhance resistance to the blight fungus.

However, restoration of chestnut requires addressing a second Asian pathogen: Phytophthora cinnamomi, which causes a fatal root disease. Several studies indicate that up to 80% of seedlings are killed. The pathogen is widespread in soils south of 40^oNorth Latitude, which falls just north of the Maryland-Pennsylvania line. Thus, P. cinnamomi occupies the southern half of American chestnut’s former range. Scientists expect this pathogen to move north in response to the warming climate; indeed, some project that the root disease could reach throughout the entire current chestnut range by 2080.

Gustafson et al. 2022 modelled chestnut’s vulnerability to P. cinnamomi to current and expected environmental conditions in two state forests in the Appalachians of western Maryland to evaluate the probable impact of the root disease on efforts to restore the tree species.

They found that root rot greatly reduced chestnut biomass on the landscape, even when resistance to root rot was at the target level for selection of root rot-resistant chestnut families using traditional breeding methods.

Gustafson et al. 2022 recommend that chestnut restoration apply the following strategies:

Locate restoration plantings at latitudes, elevations, and sites where root rot is not expected to be present well into the future. This probably means sites in the Northeastern US and Canada (Burgess et al. 2017)
Enhance the planting stock’s resistance to P. cinnamomi through breeding.
Identify soil conditions, including soil microbes, that suppress the pathogen or protect tree roots.
Since planting stock – both bareroot and containerized – can transmit P. cinnamomi, either raise seedlings in nurseries located outside the pathogen’s current range or rely on direct seeding. These strategies have their own downsides. Restricting locations of nurseries might complicate efforts to ensure seedlings are adapted to local conditions in the restoration area and seeds would need to be protected from seed predators.

The authors specify these additional important conditions:

Planting locations: while Canada is currently outside the range of American chestnut, the same climatic warming that will facilitate northward spread of P. cinnamomi will probably allow the tree to thrive farther north (Barnes and Delborne 2019). Perhaps the tree’s range will shift farther north than the pathogen’s.
Breeding: some resistance to Phytophthora root rot has been found in families providing blight resistance used in The American Chestnut Foundation (TACF) breeding program. TACF now plans to cross individuals from those families with transgenic blight-resistant chestnut to combine both resistances.
Soils: P. cinnamomi is favored by compacted soils with poor aeration or that tend to remain saturated. These include heavy clay soils and those highly disturbed by agriculture or mining. Restoration sites should be non-disturbed, well-drained sites. (This recommendation contradicts others’ proposals that chestnuts be planted on reclaimed mining sites.) Silvicultural management should also minimize environmental stresses.

that dying chestnut trying to reproduce!

Restoring chestnut will be challenging in any case: successful restoration requires chestnut trees that can compete successfully in the forest and adapt to conditions which are now quite different from those a century ago when the species was dominant. These include abiotic factors, e.g., climate and atmospheric CO₂levels; and biotic factors, e.g., different forest pests and invasive plant species.

In an earlier publication, Gustafson and colleagues (Gustafson et al. 2018) modelled the effects of warmer temperature and elevated atmospheric CO₂ levels on chestnut’s growth and competition and the tree’s adaptation to natural and anthropogenic disturbances. They concluded that aggressive restoration programs – involving clearcutting, then planting chestnuts – could restore chestnut as an important component of forested ecosystems in the Appalachian Mountains.

However, this earlier study did not consider the effects of Phytophthora root rot. The 2022 study demonstrates that these recommendations are probably applicable only to the northernmost portion of former chestnut range, outside the areas infested by Phytophthora root rot, unless breeding is successful in substantially increasing resistance to root rot.

Several studies indicate American chestnut is highly susceptible to P. cinnamomi; rates of root rot induce mortality of 80% or higher have been documented. TACF has found that hybrid chestnut families selected for root rot resistance have a mortality rate of about 45%. Even with this level of tolerance, the model shows that chestnut could not regain anything approaching its former abundance on the landscape. Since the threat of P. cinnamomi to chestnut restoration has become evident, TACF is assessing how to integrate increased tolerance to root rot into their larger blight resistance breeding program (Westbrook et al. 2019).

Soil properties – texture, land use, drainage, waterlogging, drought, temperature, and water-holding capacity – influence infection. So does weather: a single heavy rain event might saturate soil sufficiently to facilitate a P. cinnamomi infection. For these reasons, climate change is expected to exacerbate its geographic spread and pathogenicity.

The sites used in both studies are at the center of chestnut’s former range, which is also at the northern edge of the root rot pathogen’s range. However, the two sites differ in important ways, especially in rainfall and soils. The researchers considered one a mesic site and the other, xeric.

Their 2022 model showed that root rot caused a dramatic reduction in chestnut biomass on both the mesic and xeric sites. Apparently temperature and wetness levels offset each other. That is, higher soil temperatures intensified P. cinnamomi virulence at the xeric site sufficiently to overcome its relative soil dryness. At the mesic site, soil temperature sometimes dropped to levels that are lethal to Phytophthora. On the whole, then, climate change is expected to intensify P. cinnamomi infection rates on both sites and reduce the number of sites where the pathogen is absent.

Gustafson et al. (2022) discuss several assumptions and data gaps that require further study.

SOURCES

Barnes, J.C. and Delborne, J.A., 2019. Rethinking restoration targets for American chestnut using species distribution modeling. Biodiversity and Conservation, 28(12), pp.3199-3220.

Burgess, T.I., Scott, J.K., Mcdougall, K.L., Stukely, M.J., Crane, C., Dunstan, W.A., Brigg, F., Andjic, V., White, D., Rudman, T. and Arentz, F., 2017. Current and projected global distribution of Phytophthora cinnamomi, one of the world’s worst plant pathogens. Global Change Biology, 23(4), pp.1661-1674.

Dalgleish, H.J., Nelson, C.D., Scrivani, J.A. and Jacobs, D.F., 2015. Consequences of shifts in abundance and distribution of American chestnut for restoration of a foundation forest tree. Forests, 7(1), p.4.

Gustafson, E.J., B.R. Miranda, T.J. Dreaden, C.C. Pinchot, D.F. Jacobs. 2022. Beyond blight: Phytophthora root rot under climate change limits populations of reintro Am chestnut Ecosphere. 2022;13:e3917.

Gustafson, E.J., A.M.G. De Bruijn, N. Lichti, D.F. Jacobs, B.R. Sturtevant, D.M. Kashian, B.R. Miranda, and P.A. Townsend. 2018. “Forecasting Effects of Tree Species Reintroduction Strategies on Carbon Stocks in a Future without Historical Analog.” Global Change Biology 24: 5500–17. https://doi.org/10.1111/gcb.14397

Westbrook, Jared W., et al. “Resistance to Phytophthora cinnamomi in American chestnut (Castanea dentata) backcross populations that descended from two Chinese chestnut (Castanea mollissima) sources of resistance.” Plant disease 103.7 (2019): 1631-1641.

Posted by Faith Campbell

[An earlier version of this blog has now been corrected, with additional sources added. I think Cornelia Pinchot, USFS, for the corrections.]

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

www.fadingforests.org

Plants for Planting – Major Pathway, Too Little Attention

*Phytopthora cinnamomi* on manzanita in California; photo courtesy of Ted Swiecki/Phytosphere

While I blog often about wood packaging the fact is that imports of live plant [= “plants for planting” in USDA’s terms] have historically posed a higher risk of introducing tree-killing pests. In 2012, Liebhold et al. found that nearly 70% of 455 damaging pests introduced to the continental U.S. as of 2006 had probably been introduced via plant imports. These included 95% of sap feeding and 89% of foliage feeding insects and about half of the pathogens. Imported plants not only carry a greater variety of pests than wood packaging; they also carry many more.

Introductions on imported plants for planting is not a rare event. An analysis of data in the Agriculture Quarantine Inspection Monitoring (AQIM) during 2009 found that the approach rate of pests on imported plants was apparently 12% (Liebhold et al. 2012) — more than 100 times higher than the 0.1% approach rate found by Haack et al. (2014) for wood packaging. This alarming statistic receives less attention than warranted because APHIS objected to the accuracy of other aspects of the study.

APHIS has adopted changes to its phytosanitary system for plants for planting in the decade since 2009. The question is, have these changes reduced the known risks associate with live plant imports – especially given skyrocketing imports? Are more measures necessary? Current data and analyses cannot provide a scientifically valid answer.

ohia rust on endangered Hawaiian native plant *Eugenia koolauensis*

First, most studies focus on insects – they even exclude pathogens. Among pathogens introduced in recent decades, probably by the plant trade, are several Phytophthoras, rapid ‘ōhi‘a death, beech leaf disease, boxwood blight. (I am assuming that the Fusarium dieback disease vectored by Euwallacea beetles was introduced via wood packaging.) There have been repeated detections of the Ralstonia solanacearum Race 3 biovar 2, a bacterium that attacks a range of herbaceous plants, despite APHIS requiring specific integrated pest management programs in producing nurseries located in Central America. Examples of recently introduced leaf feeders include the European beech leaf-mining weevil and elm zigzag sawfly.

I concede that it is difficult to study introduced pathogens. It is nearly impossible to compile a complete list of introduced fungi and related organisms since only the most damaging are typically detected and their native ranges are frequently undeterminable. However, European forest pathologists are much more active on these questions. Why? What can we do to focus Americans on the threats these organism pose?

Second, most studies analyzing the pest risk associated with plant imports use port inspection data. However, port inspection data are not reliable indicators of the pest approach rate – as explained by Liebhold et al. 2012 and Haack et al. 2014 (as it pertains to wood packaging). Thus, most of the analyses carried out by Liebhold et al. and MachLachlan et al. (2022) are based on the pests found by APHIS inspectors: actionable pests were detected on only 2.6% of the incoming plants that they inspected.

Here I discuss two recent discussions of the risk associated with imported plant for planting. One is an analysis of establishments of one order of insects in the United States over 200 years (MacLachlan et al. 2022; full citation at the end of the blog). Again, the focus is on insects! The other is a discussion of the pathway during the recent annual meeting of the Continental Dialogue on Non-Native Forest Insects and Diseases. link to posting of presentations This discussion raised some of the key questions, although no answers were provided.

U.S. imports of plants have increased by more than 400% since the 1960s; 35% in just the last 15 years (in 2007 the U.S. imported approximately 3.7 billion plants [Liebhold et al. 2012]; in 2021 it was about 5 billion [MacLachlan et al. 2022]. Yet establishments of new non-native insects associated with this pathway have not risen commensurately. MacLachlan et al. (2022) attempt to answer why this is so. However, pests are often not detected for several years or a decade after their introduction. Furthermore, I doubt that an analysis based on inspection data, not the more reliable AQIM data, can provide an accurate assessment.

To clarify the pest risk associated with plant imports, studies of some insect types, excluding pathogens, is not sufficient. Again, APHIS should update the Liebhold et al. study to determine the approach rate for all types of organisms that threaten North American tree species. Any such study should include trees on Hawai`i, Guam, Puerto Rico, and other U.S possessions and territories. These islands are usually excluded from analyses of imported pests, including Liebhold et al. 2012. I concede that there are probably scientific and data-management challenges but these islands are immensely important from a biodiversity point of view, and they are parts of the United States!

*Cycas micronesica* endemic to Guam; threatened by cycad scale & cycad blue butterfly; photo courtesy A. Gawel

MacLachlan et al. (2022) focused their analysis on the insect order Hemiptera, including the so-called true bugs, including cicadas, aphids, planthoppers, and leafhoppers. This is the insect order most frequently transported with imported plants. In addition, establishments of Hemiptera can be attributed to plant imports rather than to wood or other vectors. Of the 3,500 species of non-native insects established in North America (including the contiguous U.S. states, Alaska, and Canada), about 27% are Hemiptera. Many are serious pests, e.g., hemlock woolly adelgid and balsam woolly adelgid). Complicating the analysis, however, is the fact that some Hemiptera are inconspicuous so they are difficult to detect. In fact, MacLaughlan et al. 2022 estimate the median delay between introduction and detection to be 80 years! They believe that many introduced species remain undiscovered, ranging from 21% for Eurasian regions to 38% for the Neotropics and 52% for Australasia.

eastern hemlocks killed by hemlock woolly adelgied; Linville Gorge, NC; photo by Steven Norman, USFS

MacLachlan et al. (2022) compare the relationship between plant imports and discoveries of Hemiptera from 1800 to the present in an attempt to answer the puzzle of why new Hemiptera establishments have remained relatively steady despite quadrupled plant imports. Perhaps the pool of novel insect species in the source region has been depleted. Or other factors might have changed, such as

the commodities imported (plant species or types; or geographic source)
phytosanitary measures applied by the U.S.

MacLachlan et al. (2022) tracked plant imports since 1854 from seven ecological regions: Afrotropic, Asian Palearctic, Australasia, European Palearctic, Indomalaya, Nearctic, Neotropic. In the early decades, both imported plants and introduced Hemiptera detected in the U.S., came predominantly from European and Asian Palearctic regions. Now, however, almost no new Hemiptera species are being introduced on plants imported from the European and Asian Palearctic regions. Since the 1950s, estimated establishments from the Indomalaya region have remained relatively stable. Establishments from the Neotropic and Afrotropic regions rose following World War II and have remained relatively high. After also declining in the first half of the 20th century, establishments of new species from Australasia have recently increased.

Generally, the regions associated with declining establishments of new species (Eurasia) are experiencing relatively gradual increases in their exports to the U.S. Those regions which contribute relatively steady or increasing establishments (Neotropics, Indomalaya, Australasia, and Afrotropic) have each undergone rapid increases in exports to the U.S.

Establishment Risk Among Regions

Source regions vary in the type of plants they export (e.g., rootless cuttings v. whole plants) and in the volume of exports. They also differ in the composition of their indigenous and introduced insect populations. Imports from areas with an abundance of species capable of establishing and adapted to environmental conditions in North America pose greater establishment risk, although it is challenging to determine the risk associated with individual species.

Establishment risk of shipments from a particular region also changes over time. The number of potential new species of invaders might shrink as more and more arrive in North America. (This situation has no effect on the continued introduction of insect species already established in North America. These reintroductions might arrive in new areas – so expanding the area at risk; or their increasing number contributes to propagule pressure at establishment sites.) Another factor might be phytosanitary policies. Strengthening of phytosanitary measures might suppress the number of organisms that travel with the plant shipment, enter North America, and establish. The opposite might happen if phytosanitary measures are relaxed or if the sourcing or type of imports diversifies in ways that connect additional species in source regions with trade pathways.

Considering all regional plant sources, MacLachlan et al. (2022) estimate that establishments per unit of additional imports – of Hemipterans – have shrunk because of a combination of increased imports, accumulated introductions associated with past imports, and the passage of time. These decreases are substantial – between 75.2% and 99.8% for the various regions from 1962 to 2012. For the Asian Palearctic and Neotropic regions, MacLachlan et al. (2022) determined that depletion of species pools is a contributing factor. Other factors are thought to explain the substantial decline in establishment likelihood for the other regions. However, note the caveats above re: lag times in detecting introductions.

However, despite that significant decrease in risk per unit of imports, the number of establishments has remained relatively constant over the past century. MacLachlan et al. (2022) attribute this pattern to the decreases in marginal risk from additional imports being offset by substantial increases in overall import levels and diversification of the origins of imports across regions, which exposed the U.S. to new source species pools.

MacLachlan et al. (2022) suggest that APHIS should target biosecurity resources to the specific commodity-country pairs associated with a demonstrated higher relative risk of introducing additional insect species.

MacLachlan et al. (2022) are unable to evaluate the efficacy of APHIS’ most important policy change: creation of the “Not Authorized for Importation Pending Pest Risk Assessment” (NAPPRA) program because it was adopted in 2011 and they analyzed data only through 2012. A decade later this policy restricts imports of about 250 taxa (Regelbrugge to Continental Dialogue). It is certainly time to evaluate its efficacy through a new study of pest approach rates in the “plants for planting” trade.

I do not think that U.S. phytosanitary policy should be based on an analysis of just one of at least three types of pests that travel via the pathway. We need analysis of the risk from pathogens, nematodes, viruses … and other orders of arthropods.

The Continental Dialogue on Non-Native Forest Insets and Pathogens

The Continental Dialogue on Non-Native Forest Insects and Pathogens hosted a discussion of the risk of pest introduction via the plant trade during its recent annual meeting. Participants asked: How can the international phytosanitary system curtail introductions of unknown organisms when it is based on risk assessments that address only species that are fully known and – usually – have proven to be invasive elsewhere.

*Rhodomyrtos psidioides* in eastern Australia killed by myrtle rust; photo by Peter Entwistle

In recent decades, tens of species of Phytophthora have been introduced to countries around the world. Myrtle rust (Austropuccinia psidii) has been introduced to 27 countries from the U.S. to Australia and South Africa. The two causal agents of boxwood blight has been introduced to at least 24 countries in three geographic areas: Europe and western Asia; New Zealand; and North America. The ash decline fungus has been introduced across Europe. Most of these species were unknown to science at the time of their introduction. Other species were known – but not believed to pose a threat because, in their native regions, their co-evolved hosts are not harmed.

For more than a decade, scientists have noted that the international phytosanitary system has failed to prevent this rapid worldwide spread of significant pathogens via the international nursery trade. Examples include Brasier 2008; Liebhold el. al. 2012; Santini et al. 2013; Roy et al. 2014; Eschen et al. 2015; Jung et al. 2015; Meurisse et al. 2019; O’Hanlon et al. 2021.

During the Continental Dialogue discussion, Craig Regebrugge, Vice President of AmericanHort (the principal nursery trade association) noted the economic importance of greenhouse and nursery production and the importance of offering novel plants to their customers. Also, he noted that U.S. retail nurseries import primarily unrooted plant cuttings. In so doing, they have a strong incentive to ensure that they are pest-free in order to avoid delays arising during inspections. Those delays would probably kill these highly perishable products. Most U.S. imports of “finished” plants come from Canada. There have been pest problems; one of the most recent examples is a moth that attacks boxwoods (Buxus), which is the top-selling shrub crop in the U.S. Earlier there was confusion over whether plants shipped from British Columbia had been infected by the sudden oak death pathogen.

Regelbrugge noted that the industry’s voluntary integrated pest management program – Systems Approach to Nursery Certification (SANC) – currently has about two dozen participating nurseries. Hoped-for adoption by more of the hundreds of production nurseries in the country has been delayed by COVID-related travel restrictions, but he hopes to restore momentum. The industry is looking for opportunities to strengthen the program through marketing messages.

Regelbrugge and a second speaker, Rebecca Epanchin-Niell of the University of Maryland, warned that prohibitions on imports will stimulate smuggling. Both raised concerns about direct-to-consumer sales by e-commerce vendors and sought ideas on how to change the behavior of both exporters and consumers.

Later Sarah Green of British Forest Research asked the APHIS representative whether the agency’s import procedures are working to prevent introductions. She pointed to the issues raised by the scientific sources I cited above: pest risk analyses address only known organisms, so this process cannot protect importers from unknown organisms. She noted that the United Kingdom is struggling to contain a number of introductions of previously unknown pathogens. Gary Lovett of the Cary Institute noted that this weakness of pest risk assessments also hampers U.S. attempts to prevent introductions – especially of pathogens. He called on the Dialogue to focus on the resource at risk – native and urban forests – and change our phytosanitary programs on this basis. He has advocated halting imports of plants that are congenerics of important North American tree species, in order to minimize the risk that pests that damage those genera will be introduced.

an American elm that has survived DED – at Longwood Gardens; photo by F.T. Campbell

Jiri Hulcr of the University of Florida tried to reassure Dialogue participants by stating that recent research has substantially reduced the threat from “unknown unkowns”. I applaud Dr. Hulcr’s efforts to reduce scientific uncertainty about the invasive potential of pathogens native to regions other than North America. His study might be the largest attempted by U.S.-based scientists. However, I note that his study assessed the threat posed by 55 insect-vectored fungi to two species of oak and two species of pines. The forests of the southeastern U.S. comprise many other tree genera! He also set a very high bar for defining a threat as serious: the damage to the host must be equivalent to that caused by Dutch elm disease or laurel wilt. Both have devastated their respective hosts. I believe U.S. phytosanitary policy must aim at protecting the full range of native species. Furthermore, levels of damage that affect the host’s role in the ecosystem – not just rapid mortality — should not be acceptable.

SOURCES

Epanchin-Niell, R., M. Springborn, an A. Lindsay. 2016. Resources No. 193 Fall 2016. http://www.rff.org/files/document/file/RFF_Resources_193_Web.pdf

Li, Y. C. Bateman, J. Skelton, B. Want, A. Black, Y-T. Huang, A. Gonzalez, M.A. Jusino, Z.J. Nolen, S. Freemen, Z. Mendel, C-Y. Chen, H-F. Li, M. Kolarik, M. Knizek, J-H. Park, W. Sittichaya, P.H. Thai, S-I. Ito, M. Torii, L. Gao, A.J. Johnson, M. Lu, J. Sun, Z. Zhang, D.C. Adams, J. Hulcr. 2021. Pre-invasion assessment of exotic bark beetle-vectored fungi to detect tree-killing pathogen. Phytopathology. https://doi.org/10.1094/PHYTO-01-21-0041-R

Liebhold, A.M., E.G. Brockerhoff, L.J. Garrett, J.L. Parke, and K.O. Britton. 2012. Live Plant Imports: the Major Pathway for Forest Insect and Pathogen Invasions of the US. www.frontiersinecology.org

MacLachlan, M.J., A. M. Liebhold, T. Yamanaka, M. R. Springborn. 2022. Hidden patterns of insect establishment risk revealed from two centuries of alien species discoveries. Sci. Adv. 7, eabj1012 (2021).

Posted by Faith Campbell

www.fadingforests.org

West Coast Steps Up Efforts to Protect Ash

Oregon-ash dominated swamp in the Ankeny National Wildlife Refuge, Willamette Valley, Oregon; photo by Wyatt Williams, Oregon Department of Forestry

In April 2022 I blogged about efforts on the West Coast to prepare for arrival of the emerald ash borer (EAB).

That blog focused on Oregon ash (Fraxinus latifolia), which is an important component of riparian forests. I alerted you to the availability of ODA/ODF EAB 2018 Response Plan.

I also mentioned Oregon’s active participation in “don’t move firewood” campaigns.

California has long inspected incoming firewood. In 2021 it establishment of a state quarantine in response to APHIS ending the federal quarantine. Washington State operates a statewide trapping program for invasive insects but does not regulate firewood.

Contributions from the Tualatin Soil and Water Conservation District enabled the USDA Forest Service Dorena Genetic Resource Center to begin testing Oregon ash for resistance to EAB and related genetics work. Other funding came from the USFS Forest Health Protection program.

EAB has now been detected in Oregon — in the Willamette Valley! (See photo above, by Wyatt Williams) Concerned stakeholders have established a new newsletter to keep people informed and promote cooperative efforts.

The newsletter is “Ash across the West”.

The first issue of the newsletter provides the following information:

there are eight ash species in the West; all are vulnerable to the emerald ash borer (EAB)

Single-leaf ash (Fraxinus anomala) CA, NV, AZ, UT, NM, CO, WY

Fragrant ash (Fraxinus cuspidata) NV, AZ, NM, UT

Calif ash (Fraxinus dipetala) CA, NV, AZ, UT

Fresnillo (Fraxinus gooddingii) AZ

Gregg’s ash (Fraxinus greggii) AZ

OR ash (Fraxinus latifolia) WA, OR, CA

Chihuahuan ash (Fraxinus papillosa) AZ, NM, TX

Velvet ash (Fraxinus velutina) CA, NV, AZ, UT, NM, TX

EAB Risk Map for OR: based upon known occurrences of ash & corresponding human activities associated with known pathways of EAB introduction and establishment.
2022 status of the two field trials
- the Dorena Genetic Resource Center (DGRC): planted 600 seedlings from 27 families; 85% survival in 2022; controlling competing vegetation
- Washington State University Puyallup Research Center: planted seedlings from 26 of these families; 95% survival rate. Possible complication from a foliar disease.
Seedlings from 17 Oregon ash families (including 14 of those in the DGRC field trial) sent to Dr. Jennifer Koch (USFS) in Ohio) for EAB resistance/susceptibility testing.
Seed collections began in 2019; interrupted by COVID-19 in 2020 but resumed in 2021 and continue in 2022. Several consortia are involved in Oregon and Washington. In California and the other states, The Huntington Botanical Gardens will lead the collecting effort. Funding is from USFS Forest Health Protection. Seeds are stored for gene conservation; some are used for the field trials in Oregon and Washington and the initial EAB-resistance studies going on in Ohio.
Penn State Ash Genomic Project: Dr. Jill Hamilton is trying to create a ‘genomic passport’ for Oregon ash populations for use in establishing genotype-environment associations to inform seed transfer guidelines. If you would like to help Dr. Hamilton collect leaves for sampling, contact: Dr. Jill Hamilton at jvh6349@psu.edu

To help with seed collection, ash monitoring, documenting the importance of ash to various communities, and other activities; or to get on the mailing list for the newsletter, contact Richard Sniezko at Richard.sniezko@usda.gov

A video explaining the campaign to save Oregon ash is at https://youtu.be/uZmfLrxEA7g

Posted by Faith Campbell

www.fadingforests.org

APHIS: Release Study of Pest Approach Rates!

I have posted nearly 40 blogs about wood packaging (SWPM) since 2015. [You can view these by scrolling below archives to find category “wood packaging”.]

I first raised the need for APHIS to authorize Robert Haack to update his study analyzing pest “approach rates” in wood packaging in July 2018.

Why?

SWPM has delivered our worst forest pests.

SWPM has been recognized as a major pathway of introduction of wood-boring insects for 30 years. Examples include the Asian longhorned beetle, emerald ash borer, redbay ambrosia beetle, and, possibly, the invasive shot hole borers.

For decades, pest-infested wood packaging has come primarily from the same countries: Mexico, Italy, China, and, more recently, Turkey. Many of our most damaging invaders have come from Asia so growing import volumes from Vietnam and other Asian countries also raise concern.

2) The U.S. and Canada have required that wood be treated to kill pests for at least 16 years.

The U.S. and Canada fully implemented the international standard on wood packaging (ISPM#15) in early 2006 – nearly 17 years ago. They had earlier (1999) required treatment of SWPM from China – nearly 24 years ago.

3) Even old analyses concluded that more than 11,000 incoming containers harbored wood pests each year.

The U.S., Canada, and Mexico import more than 31 million shipping containers per year (see “Background” below). Applying decade-old estimates to this number, we conclude that 11,600 of these containers are probably transporting a quarantine wood-boring pest. About 80% of the containers – and probably the pests! – come to U.S. ports. This pest risk is not limited to the West Coast; expansion of the Panama Canal and congestion at West Coast ports mean that an increasing number of ships are travelling directly to ports on the East and Gulf coasts. These region have already been demonstrated to be highly vulnerable to pests from Asia (ranging from Dutch elm disease and Asian longhorned beetle to laurel wilt and beech leaf disease.)

dead redbay trees – killed by redbay ambrosia beetle + laurel wilt fungus – introduced from Asia to Savannah, Georgia

4) Efforts to reduce the pest “approach rate” have not worked yet.

Meantime, administrative efforts to reduce the numbers of containers carrying pests have not been successful. The Bureau of Customs and Border Protection (CBP) has tried. CBP began penalizing individual shipments that are not in compliance with ISPM#15 in 2017 — 5 years ago.

As of the first three-quarters of Fiscal Year 2022 (John Sagle pers. comm. and Crenshaw-Nolan of CBD to Continental Dialogue on Non-Native Forest Insects and Diseases, September 2022), CBP has issued 510 Emergency Action Notifications (EAN) for noncompliant SWPM. About 38% (194) were issued because actionable pests had been discovered. The rest were issued because the ISPM#15 stamp (attesting to the wood having been treated) was either missing or fraudulent. The full-year interception rate will probably be comparable to interceptions in recent years: in FY2021, 548 EANs; in FY2020, 509; in FY2019, 746. CBP staff are disappointed that interceptions have not declined.

5) APHIS has avoided stricter enforcement.

APHIS has not adopted an enforcement stance. It has not stiffened penalties. The agency did not raise these phytosanitary issues when it negotiated a major agriculture trade agreement with China in 2020. The agency continued to insist that ISPM#15 is working – but agreed to work with Robert Haack to re-evaluate the approach rate only in 2021.

Correction: I became alarmed when the study had not been released four months after the analysis was completed (in May). I have since learned that the findings had not yet been completely written up and that internal reviews were proceeding. I apologize for the criticism in the original version of this blog. I impatiently await the study’s release, which I hope will be in a few weeks or months.

In the meantime, APHIS has also hired the Entomological Society to carry out an extensive study that includes analysis of interception data from five ports over a period of five years and rearing insects extracted from incoming wood packaging. I don’t want to postpone action aimed at curtailing introductions via this pathway for another five years!

APHIS has instead tried to improve foreign suppliers’ and phytosanitary agencies’ compliance with ISPM#15 through education. In partnership with Canada and Mexico, APHIS has supported two regional education workshops sponsored by the North American Plant Protection Organization (NAPPO). APHIS is now expanding its outreach to smaller companies, industry associations, and foreign suppliers. APHIS and CBP are now collaborating with an industry initiative to train inspectors that insure other aspects of foreign purchases. In addition, the International Plant Protection Convention (IPPC) is developing a “guidance document”. These educational efforts are supported by the U.S. pallet trade association, National Wooden Pallet and Container Association.

For all of these reasons we urgently need the updated data on the pest approach rate in the analysis by Haack and colleagues. Until we see these results, we can’t know the current level of risk associated with growing volumes of imports or assess the effectiveness of new policies. For example, CBP incorporated compliance with ISPM#15 into its government-importer partnership aimed at ensuring cleanliness of supply chains (C-TPAT) in February 2021. Only by comparing the results of the “approach rate” study with future data collected using the same techniques will it be possible to know how effective this action has been. I greatly appreciate CBP’s efforts.

There is still the issue of untrustworthy stamps.

Past data indicate a high proportion – 87% – 95% — of the SWPM found to be infested bore the ISPM#15 stamp. The same proportion was found in a narrower study in Europe (Eyre et al. 2018). Nor are all problems associated with Asia – importers in Houston have complained that stamps on dunnage from Europe also cannot be trusted.

While there are questions about whether this breakdown results from treatment inadequacy (i.e., 56^oC for 30 minutes does not kill the larvae), failure of application, or of fraud –

What matters is that neither regulators nor importers can rely on the stamp to identify pest-free wood packaging.

infested wood packaging bearing ISPM#15 mark; photo courtesy of Oregon Department of Agriculture

(True: ISPM#15 was never intended to prevent pest introductions, only to “reduce the risk of introduction and spread of quarantine pests associated with the movement in international trade of wood packaging material made from raw wood.” Still, we should be trying to minimize pest introductions which threaten our wildland, rural, and urban forests.)

CPB’s experience indicates that cracking down on individual shipments will not be sufficient.

Immediate actions to hold foreign suppliers responsible

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 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.

APHIS and CFIA have the authority to take these actions under the “emergency action” provision (Sec. 5.7) of the World Trade Organization’s Agreement on the Application of Sanitary and Phytosanitary Standards (WTO SPS Agreement). (For a discussion of the SPS Agreement, go to Fading Forests II, here.)

APHIS should also release the findings of the 2021-2022 study of approach rates by Haack and colleagues. Then the agency should invite stakeholders to discuss the implications, then develop and implement protective strategy reflecting its findings.

Longer-term Actions

APHIS and CFIA should cite their need for setting a higher “level of protection” to minimize introductions of pest that threaten our forests (described inter alia here.) They should then prepare a risk assessment to justify adopting more restrictive regulations that would prohibit use of packaging made from solid wood – at least from the countries with records of high levels of non-compliance.

Michigan champion green ash killed by emerald ash borer

APHIS and CFIA should also undertake the studies needed to determine the cause of the continuing issue of the wood treatment mark’s unreliability, then act to resolve it. Preferably, this work should be conducted with other countries and such international entities as the IPPC & International Forest Quarantine Research Group (IFQRG). However, if attempting such collaboration causes delays, they should begin unilaterally. Upcoming opportunities to address this issue include:

FAO International Day of Forests in 2023
FAO global assessment of forests & health – pest & disease outbreaks

Of course, these steps should be based on the findings of Haack and colleagues.

Meanwhile, what can we do?

Urge Congress to conduct oversight on APHIS’ failure to protect America’s natural resources from continuing introductions of nonnative insects and diseases.
- These hearings should be in the context of drafting the 2023 Farm Bill.
Raise the issue with local, state, and federal candidates for office;
Urge Congress to include provisions of H.R. 1389 in the 2023 Farm Bill;
Ask any associations of which we are members to join in communicating these concerns to Congressional representatives and senators. These include:
- if you work for a federal or state agency – raise to leadership; they can act directly or through National Plant Board, National Association of State Departments of Agriculture, National Association of State Foresters, National Governors Association, National Association of Counties
- scientific membership societies – e.g., Society of American Foresters, Entomological Society of America, American Phytopathological Society;
- individual conservation organizations, either with state chapters or at the national level;
- woodland owners’ organizations, e.g., National Woodland Owners Association, National Alliance of Forest Owners (NAFO) and their state chapters
- urban tree advocates
- International Forest Quarantine Research Group
Write letters to the editors of your local newspaper or TV news station.

BACKGROUND: Calculation of the Number of Infested Containers Entering U.S.

As of 2020 (when trade was greatly depressed by the COVID-19 pandemic), nearly 31 million TEUs [a standardized measure for containerized shipment; defined as the equivalent of a 20-foot long container] entered North America. Ports in the U.S. received 80% (24.5 million); Canada 11.5% (3.5 million); Mexico ~9% (2.7 million). U.S. imports have grown substantially since 2020; during the first quarter of 2022 U.S. imports from Asia each month were 20 to 30% higher than in 2019 before COVID-19 disrupted supply chains (blog #292). The U.S. is projected to handle ~26 million TEUs in 2022 [sources here and here.

A “TEU” equals a 20-feet container. Most containers now are twice as large – 40-feet. Several steps are involved in applying findings of Haack et al. 2014 and Meissner 2009 estimates:

divide estimated number of containers (26 million) in half = 13 million.
Assume that three-quarters of that number (13 million) contain wood packaging (based on Meissner) = 9.75 million.
If 1 out of each thousand of these containers with wood packaging is transporting a pest = 9,750 containers / year.

I performed the same calculation for North America-wide estimate of 31 million TEUs discussed at the beginning of the blog.

container being offloaded at Savannah harbor; photo by F.T. Campbell

A separate study (Hudgins et al. 2022) projected that introduction of a new woodboring insect pest that attacks maples or oaks it could kill 6.1 million trees and cost American cities $4.9 billion over 30 years. The risk would be highest if this pest were introduced via a port in the South. I have blogged often about the rising rate of shipments coming directly from Asia to the American South.

An analysis of fungi associated with Eurasian bark and ambrosia beetles reached a conclusion that the authors consider to be more optimistic. Li et al. (2021) found that none of the 111 fungi was sufficiently virulent to trigger tree mortality after a single-point inoculation. This level of lethality was considered analagous to Dutch elm disease DMF or laurel wilt DMF. Thirty-eight percent of the fungi were considered to be weak or localized pathogens that could kill trees under certain conditions. However, they tested the fungi against only two oak and two pine species. They did not evaluate fungi that might be lethal when the vector beetle engages in mass attacks. Finally, I think phytosanitary agencies should act promptly when a pathogen threatens levels of mortality somewhat below Dutch elm disease and laurel wilt!

SOURCES

Hudgins, E.J., F.H. Koch, M.J. Ambrose, B. Leung. 2022. Hotspots of pest-induced US urban tree death, 2020–2050. Journal of Applied Ecology 59(5): 1302-1312.

Li, Y., C. Bateman, J. Skelton, B. Wang, A. Black, Y-T. Huang, A. Gonzalez, M.A. Jusino, Z.J. Nolen, S. Freeman, Z. Mendel, C-Y. Chen, H-F. Li, M. Kolařík, M. Knížek, J-H. Park, W. Sittichaya, P.H. Thai, S-I. Ito, M. Torii, L. Gao, A.J. Johnson, M. Lu, J. Sun, Z. Zhang, D.C. Adams, J. Hulcr. 2021. Pre-invasion assessment of exotic bark beetle-vectored fungi to detect tree-killing pathogens Phytopathology. 112(2): 261–270. https://doi.org/10.1094/PHYTO-01-21-0041-R

Posted by Faith Campbell

www.fadingforests.org

Invasive shot hole borers: global threat; will international phytosanitary system prevent further spread?

ISHB-infested California sycamore; photo by Beatriz Nobua-Behrmann, University of California Cooperative Extension

Numerous ambrosia beetles have become introduced species. Their invasions are facilitated by their cryptic habits and ecologies, wide host ranges, and specialized breeding systems – all of which allow extremely low populations to start an infestation. The way they breed often results in low genetic diversity in their introduced ranges, but this has not hampered their success. [Bierman et al. 2022]

Also, ambrosia beetles carry fungi, which provide food needed by their larvae. While most of these fungi don’t harm living trees, some do. The United States has been invaded by three damaging ambrosia beetle-fungal complexes: laurel wilt in the Southeast, and Fusarium dieback disease, carried to southern California with polyphagous and Kuroshio shot hole borers.

These shot hole borers and their fungi represent an especially high risk to our forests because they can be transported in both living and dead wood. So not only massive U.S. imports of live plants but also the global movement of goods enclosed in solid wood packaging offer ready pathways for them to arrive and spread here. Neither pathway is regulated effectively enough to prevent either pest imports or interstate spread.

Invasive ambrosia beetles in California and Hawai’i

The invasive ambrosia beetles introduced to California are in the genus Euwallacea. This genus has undergone several taxonomic revisions. Now, the Euwallacea are divided into four species (Stouthammer 2017), of which three are in the U.S.:

Euwallacea fornicatus s.s. – common name polyphagous shot hole borer; first came to attention in southern California in 2012; formerly known as E. whitfordiodendrus.
E. perbrevis – common name tea shot hole borer; formerly known as E. fornicatus s.l.
E. kuroshio – unchanged nomenclature since detected in California in 2013;
E. fornicatior — apparently has not invaded outside of its native range in Asia.

Those now in the U.S. have been introduced to naïve habitats here and elsewhere, often with dire consequences. E. perbrevis, and possibly other species in the complex, are established on the Hawaiian islands.

For an extensive discussion of their introduction history go here

The Fungi: U.S. and Worldwide

Several fungal associates are vectored by the polyphagous shot hole borer (PSHB) and Kuroshio shot hole borer (KSHB). The most important are Fusarium euwallacea and Fusarium kuroshium, respectively. These fungi were only described after they appeared in California in the 2010s. They cause Fusarium dieback disease.

Because the two beetle species are difficult to distinguish and the associated diseases cause very similar impacts, Californians studying them and educating stakeholders now speak of the two beetle-fungus complexes as one unit, “invasive shot hole borers”.

Both PSHB and KSHB have numerous genetic strains, or haplotypes. For PSHB, the greatest haplotype diversity is in Asia – Thailand, Vietnam and China. Remember that these same regions are also a center of diversity for the huge genus Phytophthora, blog a genus widely recognized as containing many plant pathogens. https://www.dontmovefirewood.org/pest_pathogen/sudden-oak-death-syndrome-html/ One of the PSHB haplotypes, H33, has invaded many more regions than the others, including Israel, California, and South Africa. It has also been detected in several tropical plant greenhouses in Europe (where it has been eradicated). H33apparently is native to Vietnam – near Hanoi and Ho Chi Minh City – the country’s major ports (Rugman-Jones et al 2020 and pers. comm.). Does this haplotype’s spread to three continents reflect circumstances, such as the proximity of its native range to major ports and a “bridgehead effect” from its multiple introductions (the insects can be introduced to new regions on shipments from invaded regions established earlier)? Or does it point to an unknown genetic superiority (Bierman et al. 2022). This issue seems worth exploring.

I have blogged about the rising volume of imports from Vietnam, including to ports on the Gulf Coast –a region that has climatic similarities to Vietnam and known host species, so it seems quite vulnerable to invasion by either PSHB or KSHB.

A second species in the genus, KSHB, was detected in southern California in 2012; it has now spread to Mexico. So far, only one haplotype of this species has been detected in North America; this haplotype is widespread in Taiwan.

Finally, E. perbrevis (formerly known as E. fornicatus s.l.) has been detected in Florida, Hawai`i (island of Maui), and West Australia (to which it is probably native). This species has also been detected in nurseries in the Netherlands, where authorities report that it has been eradicated (Rugman-Jones et al. 2020).

Akacia koa – native tree in Hawai“i attacked by Euwallaceae; photo by David Eckhoff, via Flickr

Some species or haplotypes have been detected in only one introduced location: E. fornicatus H35 and E. kuroshio (H20) in California; H38 in South Africa; H43 on Oahu and the Big Island of Hawai`i; and an unnamed haplotype in West Australia (Rugman-Jones et al. 2020).

This is a brief guide to worldwide invasions by one or more Euwallacea-fungus complexes (Rugman-Jones et al. 2020):

Southern California — two haplotypes of E. fornicatus s.s. (H33 & H35) and E. kuroshio (one haplotype).
Hawai`i – a unique haplotype of E. fornicatus s.s. (H43) on Oahu, the Big Island, and possibly other islands; E. perbrevis on Maui and possibly other islands.
Israel — E. fornicatus s.s. haplotype H33 only.
South Africa — E. fornicatus s.s. haplotype H33 and a unique haplotype (H38).
Western Australia — a unique haplotype of E. fornicatus s.s. and E. perbrevis (which is probably native in northern Queensland).
Greenhouses in Europe – both E. fornicatus s.s. (haplotype not specified) and – in the Netherlands — E. perbrevis; both reported eradicated.

When a location has been invaded by two or more species or haplotypes, this is probably an indication of separate introductions. Multiple introductions thus are suspected in California (Stouthamer et al. 2017; Bierman et al. 2022); South Africa (Bierman et al. 2022); and Hawai`i (Bierman et al. 2022).

As is true of other pathogens, e.g., Phytophthoras, there appears to have been a spurt of introductions in recent decades, to, e.g., California, South Africa, and the second species in Hawai`i. Bierman et al 2022 note the constantly growing number of locations with introductions.

*Indigofera jucuna* – reproductive host of PSHB in South Africa; photo by Giardano de Barcelona

Impact and Spread

As is common in the case of forest pests, especially pathogens, detection occurred only years after the initial introduction. In South Africa this delay was five years – from 2012 to 2017 or 2018. In California, identification of the species as PSHB in 2012 was nine years after the organism was first detected in the state (2003).

Over the decade since 2012, PHSB, KSHB, and the pathogens they transmit have spread through large portions of southern California. KSHB has spread through “jumps” to distant locations in Orange, Los Angeles, and as far as Santa Barbara and Ventura counties. There have also been detections in even more distant San Luis Obispo and Santa Clara. These latter apparently have not become established.

A likely explanation for this pattern is the movement of firewood. (Rugman-Jones et al 2020 and pers. comm.) See the map here The two beetles and the plant pathogens they carry are expected to spread throughout much of California wherever their many host plants occur.

On Hawai`i, PSHB is attacking several endemic species including one of the largest forest trees, Acacia koa, as well as Pipturus albidus and Planchonella sandwicensis. Numerous non-native species growing on the Islandsare also attacked, including crops (Macadamia and Mangifera) and invasive species

In South Africa, PSHB has spread faster and farther. It has been present since at least 2012 (Stouthamer et al. 2017), although it was not identified until 2018. In about a decade it has spread to every province except Limpopo – PSHB’s largest geographical outbreak of this beetle [Bierman et al. 2022]

Hosts and Areas at Greatest Risk

Hundreds of plant species in at least 33 plant families support successful reproduction of both beetle and fungus. These include many species widespread in southern California, other parts of the U.S., and South Africa. Some California ecosystems are at particular risk because they are dominated by susceptible tree or shrub species. These vulnerable ecosystems are mixed evergreen forests, oak woodlands, foothill woodlands, and riparian habitats. In San Diego County alone, more than 58,000 acres of riparian woodlands are at risk (California Forest Pest Council).

Experience with the Kuroshio shot hole borer (KSHB) in the Tijuana River valley along the California-Mexico border demonstrates the importance of ecological factors in determining disease outcomes. Following introduction, the KSHB killed a high proportion of the willows near the main river channel. However, beginning in 2016, these trees have regrown to almost pre-infestation sizes. Lead researcher John Boland is not certain why these new, fast-growing trees have not been attacked by the KSHB which remains in the area. See links to the Boland studies below.

riparian forest in Tijuana River Valley after recovery from KSHB attack; photo by John Bolton

Urban forests are at particular risk. For example, in South Africa, conservative estimates were that 25% of urban trees would be lost (Bierman et al. 2022). In California, a model developed by Shannon Lynch found the cities at greatest jeopardy are San Diego, Los Angeles, the San Francisco Bay area, and Sacramento. In other areas in the state that lack data on city tree composition, Lynch applied climate models; this approach extended the list of threatened areas to the eastern half of southern California and other parts of the Central Valley. (Lynch presentation to ISHB webinar April 2022; 2^nd day.) In my view, this model should also be applied to cities in Arizona and Nevada with similar climates.

Management

Symptoms of PSHB attack and fungus infection differ among tree species. For illustrations of the symptoms on various species, visit here.

Most important, prevent the beetles’ spread through movement of dead or cut wood, e.g., green waste, firewood, and even large wood chips or mulch. Websites provide information on managing these sources.

Where the beetles have already established, California scientists recommend focusing management on heavily infested “amplifier trees”. On these trees, dead limbs should be pruned; dying trees and those with beetles infesting the main trunk should be removed. The wood must be disposed of properly.

Sources

Bierman, A., F. Roets, J.S. Terblanche. 2022. Population structure of the invasive ambrosia beetle, Euwallacea fornicatus, indicates multiple introductions into South Africa. Biol Invasions (2022) 24:2301–2312 https://doi.org/10.1007/s10530-022-02801-x

Boland, J.M. — all of Boland’s reports and articles on the KSHB are available at: The Ecology and Management of the Kuroshio Shot Hole Borer in the Tijuana River Valley — Tijuana Estuary : TRNERR]

California Forest Pest Council. 2015. 2015 California Forest Pest Conditions. http://bofdata.fire.ca.gov/hot_topics_resources/2015_california_forest_pest_conditions_report.pdf

Eskalen, A., Stouthamer, R., Lynch, S. C., Twizeyimana, M., Gonzalez, A., and Thibault, T. 2013. Host range of Fusarium dieback and its ambrosia beetle (Coleoptera: Scolytinae) vector in southern California. Plant Dis. 97:938-951.

Stouthamer, R., P. Rugman-Jones, P.Q. Thu, et al. 2017. Tracing the origin of a cryptic invader: phylogeography of the Euwallacea fornicatus (Coleoptera: Curculionidae: Scolytinae) species complex. Agric For Entomol 19:366-375. https://doi.org/10.1111/afe.12215

recordings of April 2022 webinar posted at https://youtu.be/RyqJYyLkshk day 1; and https://youtu.be/kWmtcbjTczw day 2

Posted by Faith Campbell

www.fadingforests.org

Hundreds of U.S. Tree Species Endangered, Most due to Non-Native Pests

Horton House on Jekyll Island, Georgia before laurel wilt killed the giant redbay trees; photo by F.T. Campbell

Close to four hundred tree species native to the United States are at risk of extinction. The threats come mainly from non-native insects and diseases – a threat we know gets far too little funding, policy attention, and research.

As Murphy Westwood, Vice President of Science and Conservation at the Morton Arboretum, which led the U.S. portion of a major new study, said to Gabriel Popkin, writing for Science: “We have the technology and resources to shift the needle,” she says. “We can make a difference. We have to try.”

Staggering Numbers

More than 100 tree species native to the “lower 48” states are endangered (Carrero et al. 2022; full citation at the end of this blog). These data come from a global effort to evaluate tree species’ conservation status around the world. I reported on the global project and its U.S. component in September 2021. This month Christina Carrero and colleagues (full citation at the end of this blog) published a summary of the overall picture for the 881 “tree” species (including palms and some cacti and yuccas) native to the contiguous U.S. (the “lower 48”).

This study did not address tree species in Hawai`i or the U.S. Pacific and Caribbean territories. However, we know that another 241 Hawaiian tree species are imperiled (Megan Barstow, cited here).

Assessing Threats: IUCN, NatureServe, and CAPTURE

Carrero and colleagues assessed trees’ status by applying methods developed by IUCN and NatureServe. (See the article for descriptions of these methods.) These two systems consider all types of threats. Meanwhile, three years ago Forest Service scientists assessed the specific impacts of non-native insects and pathogens on tree species in the “lower 48” states and Alaska in “Project CAPTURE” (Conservation Assessment and Prioritization of Forest Trees Under Risk of Extirpation). All three systems propose priorities for conservation efforts. For CAPTURE’s, go here.

Analyses carried out under all three systems (IUCN, NatureServe, and CAPTURE) concur that large numbers of tree species are imperiled. Both IUCN and CAPTURE agree that non-native insects and pathogens are a major cause of that endangerment. While the overall number of threatened species remained about the same for all three systems, NatureServe rated threats much lower for many of the tree species that IUCN and CAPTURE considered most imperiled.

This difference arises from the criteria used to rate a species as at risk. IUCN’s Criterion A is reduction in population size. Under this criterion, even extremely widespread and abundant species can qualify as threatened if the population declines by at least 30% over three generations in the past, present, and/or projected future. NatureServe’s assessment takes into account rapid population decline, but also considers other factors, for example, range size, number of occurrences, and total population size. As a result, widespread taxa are less likely to be placed in “at risk” categories in NatureServe’s system.

In my view, the IUCN criteria better reflect our experience with expanding threats from introduced pests. Chestnut blight, white pine blister rust, dogwood anthracnose, emerald ash borer, laurel wilt disease, beech leaf disease, and other examples all show how rapidly introduced pathogens and insects can spread throughout their hosts’ ranges. (All these pests are profiled here . ) They can change a species’ conservation status within decades whether that host is widespread or not.

Which Species Are at Risk: IUCN

Carrero and colleagues found that under both IUCN and NatureServe criteria, 11% to 16% of the 881 species native to the “lower 48” states are endangered. Another five species are possibly extinct in the wild. Four of the extinct species are hawthorns (Crataegus); the fifth is the Franklin tree (Franklinia alatamaha) from Georgia. A single specimen of a sixth species, an oak native to Texas (Quercus tardifolia),was recently re-discovered in Big Bend National Park.

Franklinia (with Bachman’s warbler); both are extinct in the wild; painting by John Jacob Audubon

The oak and hawthorn genera each has more than 80 species. Relying on the IUCN process, Carrero and colleagues found that a significant number of these are at risk: 17 oaks (20% of all species in the genus); 29 hawthorns (34.5% percent). A similar proportion of species in the fir (Abies), birch (Betula), and walnut (Juglans) genera are also threatened.

Other genera have an even higher proportion of their species under threat, per the IUCN process:

all species in five tree genera, including Persea (redbay, swampbay) and Torreya (yews);
two-thirds of chestnuts and chinkapins (Castanea), and cypress (Cupressus);
almost half (46.7%) of ash trees (Fraxinus).

Pines are less threatened as a group, with 15% of species under threat. However, some of these pines are keystone species in their ecosystems, for example the whitebark pine of high western mountains.

Carrero et al. conclude that the principal threats to these tree species are problematic and invasive species; climate change and severe weather; modifications of natural systems; and overharvest (especially logging). Non-native insects and pathogens threaten about 40 species already ranked by the IUCN criteria as being at risk and another 100 species that are not so ranked. Climate change is threatening about 90 species overall.

Considering the invasive species threat, Carrero and colleagues cite specifically ash trees and the bays (Persea spp.). In only 30 years, the emerald ash borer has put five of 14 ash species at risk. All these species are widespread, so they are unlikely to be threatened by other, more localized, causes. In about 20 years, laurel wilt disease threatens to cause extinction of all U.S. tree species in the Persea genus.

Carrero and colleagues note that conservation and restoration of a country’s trees and native forests are extremely important in achieving other conservation goals, including mitigating climate change, regulating water cycles, removing pollutants from the air, and supporting human well-being. They note also forests’ economic importance.

As I noted above, USFS scientists’ “Project CAPTURE” also identified species that deserve immediate conservation efforts.

Where Risk Assessments Diverge

All three systems for assessing risks agree about the severe threat to narrowly endemic Florida torreya and Carolina hemlock.

With three risk ranking systems, all can agree (as above), all can disagree, or pairs can agree in four different ways. Groups of trees fall into each pair, with various degrees of divergence. Generally, only two of the three systems agree on more widespread species:

black ash: IUCN and Project CAPTURE prioritize this species. NatureServe ranked it as “secure” (G5) as recently as 2016.
whitebark pine: considered endangered by IUCN, “vulnerable” (G3) by NatureServe. The US Fish and Wildlife Service has proposed listing the species as “threatened” under the Endangered Species Act. https://www.fws.gov/species-publication-action/endangered-and-threatened-wildlife-and-plants-threatened-species-18 However, Project CAPTURE does not include it among its highest priorities for conservation. Perhaps this is because there are significant resistance breeding and restoration projects already under way.
tanoak: considered secure by both IUCN and NatureServe, but prioritized by Project CAPTURE for protection.

dead tanoak in Curry County, Oregon; photo by Oregon Department of Forestry

Carrero notes the divergence between IUCN and NatureServe regarding ashes. Four species ranked “apparently secure” (G4) by NatureServe (Carolina, pumpkin, white, and green ash) are all considered vulnerable by IUCN. They are also prioritized by Project CAPTURE. I have described the impact of the emerald ash borer on black ash. Deborah McCullough, noted expert on ash status after invasion by the emerald ash borer, also objects to designating this species as “secure” (pers. comm.).

This same divergence appears for eastern hemlock.

Port-Orford cedar is currently ranked as at risk by IUCN and Project CAPTURE, but not NatureServe. Growing success of the restoration breeding project has prompted IUCN to change the species’ rank from “vulnerable” to “near threatened”. IUCN is expected to reclassify it as of “least concern” in about a decade if breeding efforts continue to be successful (Sniezko presentation to POC restoration webinar February 2022).

While these differing detailed assessments are puzzling, the main points are clear: several hundred of America’s tree species (including many in Hawai`i, which – after all – is our 50^th state!) are endangered and current conservation and restoration efforts are inadequate.

Furthermore, a tree species loses its function in the ecosystem long before it becomes extinct. It might still be quite numerous throughout its range – but if each individual has shrunken in size it cannot provide the same ecosystem services. Think of thickets of beech root sprouts – they cannot provide the bounteous nut crops and nesting cavities so important to wildlife. Extinction is the extreme. We should act to conserve species much earlier.

YOU CAN HELP!

Congress is considering the next Farm Bill – which is due to be adopted in 2023. Despite its title, this legislation has often provided authorization and funding for forest conservation (for example, the US Forest Service’ Landscape Scale Restoration Program).

There is already a bill in the House of Representatives aimed at improving the US Department of Agriculture’s prevention and early detection/rapid response programs for invasive pests. Also, it would greatly enhance efforts to restore decimated tree species via resistance breeding, biocontrol, and other strategies. This bill is H.R. 1389.

The bill was introduced by Rep. Peter Welch of Vermont, who has been a solid ally and led on this issue for several years. As of August 2022, the bill has seven cosponsors, most from the Northeast: Rep. Mike Thompson [CA], Rep. Chellie Pingree [ME], Reps. Ann M. Kuster and Chris Pappas [NH], Rep. Elise Stefanik [NY], Rep. Deborah K. Ross [NC], Rep. Brian Fitzpatrick [PA].

Please write your Representative and Senators. Urge them to seek incorporation of H.R. 1389 in the 2023 Farm Bill. Also, ask them to become co-sponsors for the House or Senate bills. (Members of the key House and Senate Committees are listed below, along with supporting organizations and other details.)

Details of the Proposed Legislation

The Invasive Species Prevention and Forest Restoration Act [H.R. 1389]

Expands USDA APHIS’ access to emergency funding to combat invasive species when existing federal funds are insufficient and broadens the range of actives that these funds can support.
Establishes a grant program to support research on resistance breeding, biocontrol, and other methods to counter tree-killing introduced insects and pathogens.
Establishes a second grant program to support application of promising research findings from the first grant program, that is, entities that will grow large numbers of pest-resistant propagules, plant them in forests – and care for them so they survive and thrive.
[A successful restoration program requires both early-stage research to identify strategies and other scientists and institutions who can apply that learning; see how the fit together here.]

Mandates a study to identify actions needed to overcome the lack of centralization and prioritization of non-native insect and pathogen research and response within the federal government, and develop national strategies for saving tree species.

Incorporating the provisions of H.R. 1389 into the 2023 Farm Bill would boost USDA’s efforts to counter bioinvasion. As Carrera and colleagues and the Morton Arboretum study on which their paper is based demonstrate, our tree species desperately need stronger policies and more generous funding. Federal and state measures to prevent more non-native pathogen and insect pest introductions – and the funding to support this work – have been insufficient for years. New tree-killing pests continue to enter the country and make that deficit larger –see beech leaf disease here. Those here, spread – see emerald ash borer to Oregon.

For example, funding for the USDA Forest Service Forest Health Protection program has been cut by about 50%; funding for USFS Research projects that target 10 high-profile non-native pests has been cut by about 70%.

H.R. 1389 is endorsed by several organizations in the Northeast: Audubon Vermont, the Maine Woodland Owners Association, Massachusetts Forest Alliance, The Nature Conservancy Vermont, the New Hampshire Timberland Owners Association, Vermont Woodlands Association, and the Pennsylvania Forestry Association.

Also, major forest-related national organizations support the bill: The American Chestnut Foundation (TACF), American Forest Foundation, The Association of Consulting Foresters (ACF), Center for Invasive Species Prevention, Ecological Society of America, Entomological Society of America, National Alliance of Forest Owners (NAFO), National Association of State Foresters (NASF), National Woodland Owners Association (NWOA), North American Invasive Species Management Association (NAISMA), Reduce Risk from Invasive Species Coalition, The Society of American Foresters (SAF).

HOUSE AND SENATE AGRICULTURE COMMITTEE MEMBERS – BY STATE

STATE	Member, House Committee	Member, Senate Committee	Key members * committee leadership # forestry subcommittee leadership @ cosponsor of H.R. 1389
Alabama	Barry Moore
Arizona	Tom O’Halleran
Arkansas	Rick Crawford	John Boozman*
California	Jim Costa Salud Carbajal Ro Khanna Lou Correa Josh Harder Jimmie Panetta Doug LaMalfa
Colorado		Michael Bennet #
Connecticut	Jahana Hayes
Florida	Al Lawson Kat Cammack
Georgia	David Scott * Sanford Bishop Austin Scott Rick Allen	Raphael Warnock Tommy Tuberville
Illinois	Bobby Rush Cheri Bustos Rodney Davis Mary Miller	Richard Durbin	Note that the report was led by scientists at the Morton Arboretum – in Illinois!
Indiana	Jim Baird	Mike Braun
Iowa	Cindy Axne Randy Feenstra	Joni Ernst Charles Grassley
Kansas	Sharice Davids Tracey Mann	Roger Marshall#
Kentucky		Mitch McConnell
Maine	Chellie Pingree @
Massachusetts	Jim McGovern
Michigan		Debbie Stabenow *
Minnesota	Angie Craig Michelle Fischbach	Amy Klobuchar Tina Smith
Mississippi	Trent Kelly	Cindy Hyde-Smith
Missouri	Vicky Hartzler
Nebraska	Don Bacon	Deb Fischer
New Hampshire	Ann McLane Kuster @
New Jersey		Cory Booker
New Mexico		Ben Ray Lujan
New York	Sean Patrick Maloney Chris Jacobs	Kristen Gillibrand
North Carolina	Alma Adams David Rouzer
North Dakota		John Hoeven
Ohio	Shontel Brown Marcy Kaptur Troy Balderson	Sherrod Brown
Pennsylvania	Glenn Thompson
South Dakota	Dusty Johnson	John Thune
Tennessee	Scott DesJarlais
Texas	Michael Cloud Mayra Flores
Vermont		Patrick Leahy
Virginia	Abigail Spanberger #
Washington	Kim Schreir

SOURCES

Christina Carrero, et al. Data sharing for conservation: A standardized checklist of US native tree species and threat assessments to prioritize and coordinate action. Plants People Planet. 2022;1–17. wileyonlinelibrary.com/journal/ppp3

Washington Post: Sarah Kaplan, “As many as one in six U.S. tree species is threatened with extinction” https://www.washingtonpost.com/climate-environment/2022/08/23/extinct-tree-species-sequoias/

Popkin, G. “Up to 135 tree species face extinction—and just eight enjoy federal protection”, Science August 25, 2022. https://www.science.org/content/article/135-u-s-tree-species-face-extinction-and-just-eight-enjoy-federal-protection

Posted by Faith Campbell

www.fadingforests.org

Posted by Faith Campbell

www.fadingforests.org

Firewood – How to Change Risky Behavior

The Nature Conservancy (TNC) and Clemson University have analyzed how to persuade people not to move firewood – and the tree pests that can accompany it. (Full citation at the end of this blog) Their study is based on five surveys conducted by TNC between 2005 and 2016. These surveys guided TNC’s “Don’t Move Firewood” campaign and its outreach efforts since the beginning in 2008

As Solano et al. note, wood-boring pests continue to enter the country and spread, causing immense damage. Firewood transport by campers is a significant contributor to that spread. Millions of individuals decide whether to move firewood. Yet the scientific literature is quite limited regarding their behavior and TNC’s survey data has never been published.

The patchwork of state and federal quarantines is largely reactive and has failed to prevent continuing spread. The regulatory regime has been further fragmented by APHIS’ deregulation of the emerald ash borer. As a consequence, limiting the spread of pests depends even more on educating campers to behave responsibly – voluntarily.

The TNC’s surveys each focused on different geographic areas and asked different questions in each. So their compilation cannot show trends in awareness or other measures. Nevertheless, the authors find:

Most people in the United States don’t know firewood can harbor invasive forest insects and diseases, but when targeted by effective education they can learn and are likely to change their behavior.
The two best ways to reach the public is through emails confirming campsite reservations and flyers handed out at parks. Web-based information seemed less effective. However, most of the surveys were done before 2011, the year when 50% of adults reported using internet media.
Forestry-related public agencies (especially state forestry departments) are the most trusted sources of information about forest health issues.
It works better to “push” information, not expect people to seek it on their own.
Messages should focus on encouraging the public to make better choices, including how they, themselves, will benefit. Positive, empowering calls to action, like “Buy it Where You Burn It” or “Buy Local, Burn Local” are better than negative messages, such as “Don’t Move Firewood”.
People respond to messages that emphasize protecting forest resources, e.g., ecosystem services like clean water. They response less to messages about forest threats.

Hungerford Lake Recreation Area at Equestrian Campground. Original public domain image from Flickr

Solano et al. describe the ways that different socioeconomic groups differ in their awareness of forest pests and in how they respond to various statements about forests, pests, and messengers. The focus is on how to overcome four psychological barriers to changing behavior that had been identified in a study of climate change. In the firewood context, those barriers were: 1) lack of awareness; 2) mistrust and negative reactions to the messengers; 3) habit; and 4) social comparison, norms, conformity, and perceived poor quality of purchased firewood.

From this work, the authors suggested further work::

Development of education and outreach programs that target those with lower education levels, since, on average, ~60% of people who camp did not graduate from college. Further research is probably needed to identify the most effective messengers and messages.
While 80% of the survey respondents were over 40, the proportion of campers made up of Gen X and millennials is increasing. Managers need to improve outreach for younger audiences. This includes engaging the messengers they trust: scientists, environmentalist politicians, peer networks, and social media.
While women trust the USDA Forest Service and conservation organizations, 55% of campers in a given year are men. Further research is needed to clarify the most effective messengers and messages for men. The outreach agencies should select the messengers that both sexes trust.
Levels of awareness should be assessed both before and after implementing new educational strategies so that the strategies’ effectiveness can be determined.

Since 80% of the respondents were white, determining the most effective messages and messengers for other ethnic groups also seems necessary, although the authors did not address this.

SOURCE:

Solano, A., Rodriguez, S.L., Greenwood, L., Rosopa, P.J., and Coyle, D.R. 2022. Achieving effective outreach for invasive species: firewood case studies from 2005-2016. Biological Invasions.
https://link.springer.com/article/10.1007/s10530-022-02848-w

You can read the article – but not download it – at https://rdcu.be/cRRVH

To request a copy of this study from the author, contact the lead author at Clemson University.

Posted by Faith Campbell

www.fadingforests.org

Invasive Species Costs Point to Inadequate Effort – especially Prevention

EAB-killed ash tree falls before it can be taken down; photo courtesy of former Ann Arbor mayor John Hieftje

Concerned by growing impacts of bioinvasion and inadequate responses by national governments worldwide and by international bodies, a group of experts have attempted to determine how much invasive species are costing. They’ve built the global database – InvaCost. See Daigne et al. 2020 here.

Several studies have been based on these data. In two earlier blogs, I summarized two of these articles, e.g., Cuthbert et al. on bioinvasion costs, generally, and Moodley et al. on invasive species costs in protected areas, specifically. Here, I look at two additional studies. Ahmed et al. focusses on the “worst” 100 invasives affecting conservation — as determined by the International Union of Conservation and Nature (IUCN). The second, by Turbelin et al., examines pathways of introduction. Full citations of all sources appear at the end of this blog.

It is clear from all of these papers that the authors (and I!) are frustrated by the laxity with which virtually all governments respond to bioinvasions. Thus more robust actions are needed. The authors and I also agree that data on economic costs influence political decision-makers more than ecological concerns. However, InvaCost – while the best source in existence — is not yet comprehensive enough to generate the thoroughly-documented economic data about specific aspects of bioinvasion that would be most useful in supporting proposed strategies.

Scientists working with InvaCost recognize that the data are patchy. At the top level, these data demonstrate high losses and management costs imposed by bioinvasion. The global total – including both realized damage and management costs – is estimated at about $1.5 trillion since 1960. In fact, these overall costs are probably substantially underestimates (Cathbert et al.). [For a summary of data gaps, go to the end of the blog.] Furthermore, they recognize that species imposing the highest economic costs might not cause the greatest ecological harm (Moodley et al).

citrus longhorned beetle exit hole in bonsai tree; USDA APHIS photo

Comparing estimated management costs to estimated damage, the authors conclude that countries invest too little in bioinvasion management efforts and — furthermore — that expenditures are squandered on the wrong “end” of bioinvasion – after introduction and even establishment, rather than in preventive efforts or rapid response upon initial detection of an invader. While I think this is true, these findings might be skewed by the fact that fewer than a third of countries reporting invasive species costs included data on specifically preventive actions. Cuthbert et al. notes that failing to try to prevent introductions imposes an avoidable burden on resource management agencies. Ahmed et al. developed a model they hope will overcome the perverse incentives that lead decision-makers to either do nothing or delay.

Why Decision-Makers Delay

Citing the InvaCost data, the participating experts reiterate the long-standing call for prioritizing investments at the earliest possible invasion stage. Ahmed et al. found that this was the most effective practice even when costs accrue slowly. They ask, then, why decision-makers often delay initiating management. I welcome this attention because we need to find ways to rectify this situation.

They conclude, first, that invasive species threats compete for resources with other threats to agriculture and natural systems. Second, Cuthbert et al. and Ahmed et al. both note that decision-makers find it difficult to justify expenditures before impacts are obvious and/or stakeholders demand action. By that time, of course, management of invasions are extremely difficult and expensive – if possible at all. I appreciate the wording in Ahmed et al.: bioinvasion costs can be deceitfully slow to accrue, so policy makers don’t appreciate the urgency of taking action.

Cuthbert et al. also note that impacts are often imposed on other sectors, or in different regions, than those focused on by the decision-makers. Stakeholders’ perceptions of whether an introduced species is causing a “detrimental” impact also vary. Finally, when efficient proactive management succeeds – prevents any impact – it paradoxically undermines evidence of the value of this action!

Ahmed et al. point out that in many cases, biosecurity measures and other proactive approaches are even more cost effective when several species are managed simultaneously. They cite as examples airport quarantine and interception programs; Check Clean Dry campaigns encouraging boaters to avoid moving mussels and weeds; ballast water treatment systems; and transport legislation e.g., the international standard for wood packaging (ISPM#15) [I have often discussed the weaknesses in ISPM#15 implementation; go to “wood packaging” under “Categories” (below the archive list)].

pallet “graveyard”; photo by Anand Prasad

Pathways of Species’ Introduction

Tuberlin et al. focus on pathways of introduction, which they say influence the numbers of invaders, the frequency of their arrival, and the geography of their eventual distribution. This study found sufficient data to analyze arrival pathways of 478 species – just 0.03% of the ~14,000 species in the full database. They found that intentional pathways – especially what they categorized as “Escape” – were responsible for the largest number of invasive species (>40% of total). On the other hand, the two unintentional pathways called “Stowaway” and “Contaminant” introduced the species causing the highest economic costs.

Tuberlin et al. therefore emphasize the importance of managing these unintentional pathways. Also, climate change and emerging shipping technologies will increase potential invaders’ survivability during transit. Management strategies thus must be adapted to countering these additive trends. They suggest specifically:

eDNA detection techniques;
Stricter enforcement of ISPM#15 and exploring use of recyclable plastic pallets (e.g., IKEA’s OptiLedge); [see my blog re: plastic pallets, here]
Application of fouling-resistant paints to ship hulls;
Prompt adoption of international agreements addressing pathways (they cite the Ballast Water Management Treaty as entered into force only in 2017 — 13 years after adoption);
Ensuring ‘pest free status’ (per ISPM#10) before allowing export of goods—especially goods in the “Agriculture”, “Horticulture”, and “Ornamental” trades; and
Increasing training of interception staff at ports.

What InvaCost Data say re: Taxa of greatest concern to me

Two-thirds of reported expenditures are spent on terrestrial species (Cuthbert et al.). Insects as a Class constitute the highest number of species introduced as ‘Contaminants’ (n = 74) and ‘Stowaways’ (n = 43). They also impose the highest costs among species using these pathways. Forest insects and pathogens account for less than 1% of the records in the InvaCost database, but constitute 25% of total annual costs ($43.4 billion) (Williams et al., in prep.). Indeed, one of 10 species for which reported spending on post-invasion management is highest is the infamous Asian longhorned beetle (Tuberlin et al.)

ALB pupa in wood packaging; Pennsylvania Dept. of Natural Resources via Bugwood

Mammals and plants are often introduced deliberately – either as intentional releases or as escapes. Plant invasions are reported as numerous but impose lower costs.

Tuberlin et al. state that intentional releases and escapes should in theory be more straightforward to monitor and control, so less costly. They propose two theories: 1) Eradication campaigns are more likely to succeed for plants introduced for cultivation and subsequently escaped, than for plants introduced through unintentional pathways in semi-natural environments. 2) Species introduced unintentionally may be able to spread undetected for longer; they expect that better measures already exist to control invasions by deliberate introductions. I question both. Their theories ignore that constituencies probably like the introduced plants … and the near absence of attention to the possible need to control their spread. This is odd because elsewhere they recognize conflicts over whether to control or eradicate “charismatic” species.

Geographies of greatest concern to me

North America reported spending 54% of the total expenditure in InvaCost. Oceania spent 30%. The remaining regions each spent less than $5 billion. (Cuthbert et al.)
North America funded preventative actions most generously than other regions. Cuthbert suggests this was because David Pimentel published an early estimate of invasive species costs. I doubt it. The Lacey Act was adopted in 1905. USDA APHIS was formed in 1972 – based on predecessor agencies — because officials recognized the damage by non-native pests to agriculture. APHIS began addressing natural area pests with discovery of the Asian longhorned beetle in 1996. Of course, most of APHIS’ budget is still allocated to agricultural pests. I conclude that North America’s lead in this area has not resulted in adequate prevention programs.

Oregon ash swamp before attack by EAB (photo by Wyatt Williams, Oregon Dept. of Forestry)

Equity Issues

Tuberlin et al and Moodley et al. address equity issues of who causes introductions vs. who is impacted. This is long overdue.

More than 80% of bioinvasion management costs in protected areas fell on governmental services and/or official organizations (e.g. conservation agencies, forest services, or associations). With the partial exception of the agricultural sector, the economic sectors that contribute the most to movement of invasive species are spared from carrying the resulting costs (Moodley et al.)
A lack of willingness to invest might represent a moral problem when the invader’s impacts are incurred by regions, sectors, or generations other than those that on whom management action falls (Ahmed et al.)
People are perhaps more inclined to spend money to mitigate impacts that cause economic losses than those that damage ecosystems (Tuberlin et al.)

Data deficiencies

Only 41% of countries (83 out of 204) reported management costs; of those, only 24 reported costs specifically associated with pre-invasion (prevention) efforts (Cuthbert et al.).
Reliable economic cost estimates were available for only 60% of the “worst” invasive species (Cuthbert et al.)
Only 55 out of 266,561 protected areas reported losses or management costs (Moodley et al.).
Information on pathways of introduction was available for only three species out of 10,000 (Turbelin et al).
Taxonomic and geographic biases in reporting skew examples and possibly conclusions (Cuthbert et al.).

SOURCES

Ahmed, D.A., E.J. Hudgins, R.N. Cuthbert, .M. Kourantidou, C. Diagne, P.J. Haubrock, B. Leung, C. Liu, B. Leroy, S. Petrovskii, A. Beidas, F. Courchamp. 2022. Managing biological invasions: the cost of inaction. Biol Invasions (2022) 24:1927–1946 https://doi.org/10.1007/s10530-022-02755-0

Cuthbert, R.N., C. Diagne, E.J. Hudgins, A. Turbelin, D.A. Ahmed, C. Albert, T.W. Bodey, E. Briski, F. Essl, P. J. Haubrock, R.E. Gozlan, N. Kirichenko, M. Kourantidou, A.M. Kramer, F. Courchamp. 2022. Bioinvasion costs reveal insufficient proactive management worldwide. Science of The Total Environment Volume 819, 1 May 2022, 153404

Moodley, D., E. Angulo, R.N. Cuthbert, B. Leung, A. Turbelin, A. Novoa, M. Kourantidou, G. Heringer, P.J. Haubrock, D. Renault, M. Robuchon, J. Fantle-Lepczyk, F. Courchamp, C. Diagne. 2022. Surprisingly high economic costs of bioinvasions in protected areas. Biol Invasions. https://doi.org/10.1007/s10530-022-02732-7

Turbelin, A.J., C. Diagne, E.J. Hudgins, D. Moodley, M. Kourantidou, A. Novoa, P.J. Haubrock, C. Bernery, R.E. Gozlan, R.A. Francis, F. Courchamp. 2022. Introduction pathways of economically costly invasive alien species. Biol Invasions (2022) 24:2061–2079 https://doi.org/10.1007/s10530-022-02796-5

Williams, G.M., M.D. Ginzel, Z. Ma, D.C. Adams, F.T. Campbell, G.M. Lovett, M. Belén Pildain, K.F. Raffa, K.J.K. Gandhi, A. Santini, R.A. Sniezko, M.J. Wingfield, and P. Bonello 2022. The Global Forest Health Crisis: A Public Good Social Dilemma in Need of International Collective Action. Submitted

Posted by Faith Campbell

www.fadingforests.org

Hemlock biocontrol – need summer parasitoids

healthy hemlocks in Cook Forest, Pennsylvania; photo by F.T. Campbell

I blogged recently about North Carolina’s multi-pronged hemlock conservation program. As noted there, scientists are putting considerable hope in biological control as the most promising strategy to protect eastern (Tsuga canadensis) and Carolina hemlocks (T. caroliniana) from the hemlock woolly adelgid (HWA; Adelges tsugae). For a more detailed discussion of the adelgid’s life cycle, go here.

A new study by Crandall, Lombardo and Elkinton (full citation at end of blog) cheers us by supporting the probable efficacy of this approach – as long as a complete suite of biocontrol agents is deployed. The study points to the need to introduce additional biocontrol agents, specifically those that feed in the summer.

The study analyzed the relative importance of two different mechanisms to protect plants from herbaceous insects: do some hemlock species have an enhanced ability to fend off the adelgid (bottom-up protection); or do predators apply sufficient pressure (top-down protection) to reduce adelgid populations to levels that the tree can withstand? The study simultaneously analyzed

(1) the relative importance of summer-active and winter-active native predators;

(2) whether HWA colonization and abundances differed on western and eastern hemlock species;

(3) the relative importance of top-down and bottom-up forces on HWA feeding on western and eastern hemlocks in the adelgid’s native range;

4) tested whether the adelgid is ubiquitous at low densities across the Pacific Northwest (PNW) and compared HWA abundance in PNW to invaded range in New England.

The study was carried out in Washington State, where both western hemlock (Tsuga heterophylla) and HWA are native. They were able to compare adelgid impacts on eastern hemlock because the tree is planted in parks and gardens in the PNW.

Eastern hemlock infested by HWA; USDAFS via Bugwood

In an earlier study, (Crandall et al. 2020) found that L. nigrinus was not able to reduce HWA densities in the east. Laricobius spp have their greatest impact on HWA by larval feeding on the progrediens eggs produced by the sistens. However, 90% of hatching progrediens die naturally because there are a finite number of needles for them to settle on. To have an impact on HWA populations, Laricobius spp would have to prey on more than 90% of progrediens eggs. The solution appears to be summer-active predators – e.g., silver flies — which feed on the progrediens eggs and the sistens eggs which the progrediens generation lays.

western hemlock in British Columbia; photo by F.T. Campbell

KEY FINDINGS

Western hemlock is a native host of the adelgid. Crandall, Lombardo, and Elkinton found no evidence that western hemlock’s structure, chemistry, or other attributes help it fend off adelgid attack. The proportion of branches colonized by HWA was significantly higher on western than on eastern hemlock. Indeed, HWA populations were able to reach levels similar to those in eastern North America and were able to persist on western hemlock for multiple generations. Thus there is no evidence for bottom-up control of HWA on western hemlock.

HWA survival was significantly lower on branches of western hemlock when predators were allowed access. Crandall assumes that the smaller, non-significant, decrease in HWA densities on eastern hemlocks in the Pacific Northwest is also attributable to predation, although the data are too few to support a definitive conclusion. These predators included a species that has been released as a biocontrol agent in the east, Laricobius nigrinus. More important, apparently, was the presence of summer-active predators, including Leucotaraxis spp. and generalists. These summer-active predators are active from the progrediens nymph stage in April through the aestivating sistens nymph stage until about October. Laricobius nigrinus doesn’t become active until September. These results support the hypothesis that predator-caused mortality is responsible for suppressing HWA during rare and localized outbreaks on western hemlock in the PNW. In the east there are no native natural enemies that attack HWA – which is introduced to the region.

Effective control of HWA on the eastern naïve hosts will require establishment of a suite of predators which – together — attack the adelgid during both summer and winter.While several possible biocontrol agents have been introduced in the region, and at least some – e.g., Laricobius nigrinus – have established self-sustaining populations, are spreading, and have high predation rates, they have had very limited success in reducing HWA populations. Crandall, Lombardo and Elkinton say these data support the recent decision by the USDA Forest Service to augment the HWA biocontrol effort by introducing two species of silver flies, Leucotaraxis argenticollis and Le. piniperda, that feed on both the sistens and progrediens generations in PNW.

Tree-adelgid interactions are probably significantly affected by the lineage of both – whether the tree species has co-evolved with the specific lineage of the adelgid with which it is interacting. Crandall, Lombardo and Elkinton think evaluation of any Tsuga species’ resistance to HWA or any potential biocontrol agent needs to be studied in relation to the appropriate lineage of the adelgid.

When they compared HWA abundance (in 2021) on hemlock forests in western Washington with HWA abundance at introduced HWA range in New England, Crandall, Lombardo and Elkinton found that HWA abundance was higher in New England. They note that these comparisons are between two different linages of HWA – the lineage native to PNW and the introduced Japanese lineage in the East.

The authors note that HWA densities in the PNW are higher at the urban site (Seattle) than rural sites. Perhaps the reason is lower densities of HWA predators in non-forest settings because some, e.g., La. nigrinus, require a duff layer for pupation. Duff layers are rarely permitted to accumulate in urban areas. The authors call for studies to assess the relative abundance and identify factors affecting the abundance of HWA predators in rural and urban settings.

SOURCES

Crandall R.S., Jubb C.S., Mayfield A.E., Thompson B., McAvoy T.J., Salom S.M. and J.S. Elkinton. 2020. Rebound of Adelges tsugae spring generation following predation on overwintering generation ovisacs by the introduced predator Laricobius nigrinus in the eastern United States. Biological Control 145, 104-264. https://doi.org/10.1016/j.biocontrol.2020.104264

Crandall, R.S., J.A. Lombardo, and J.S. Elkinton. 2022. Top-down regulation of hemlock woolly adelgid (Adelges tsugae) in its native range in the Pacific Northwest of North America. Oecologia 199, 599-609. https://doi.org/10.1007/s00442-022-05214-8

Posted by Faith Campbell

www.fadingforests.org

Funding APHIS & USFS in FY23 – Senate Recommendations

The Senate Appropriations Committee has adopted its recommendations for funding APHIS and the US Forest Service in Fiscal Year 2023, which begins on October 1. The full Senate has not yet acted; most people expect that it will not act before October, so the agencies will have to operate under a “continuing resolution” for at least the first several months. Under a “CR”, funding is maintained at the current level.

SOD-infected rhododendron plants detected by state officials in Indiana in 2019

Funding for APHIS in FY23

The Senate Appropriations Committee issued a report [available here] that recognizes APHIS’ objective of protecting the animal and plant resources of the Nation from diseases and pests. These objectives are carried out through, inter alia, Safeguarding and Emergency Preparedness/Response and Safe Trade and International Technical Assistance.

The Committee recommends the following funding for specific APHIS programs (in $millions)

PROGRAM	FY22 FUNDING	FY23 ADMIN REQ	HOUSE $	SENATE COMM RECOMM	CISP ASK
Border inspections (AQI appropriated)	33.849	36.725		36.650	X
Pest Detection	28.218	29.137	29.825	29.075	30
Methods Development	21.217	21.854	31.807	23.557	23
Specialty Crops	209.533	219.533	219.698	222.072	219
Tree & Wood pests	61.217	62.854	62.562	62.719	70
Subtotal, Plant health	379.144	385.560		397.603	X
Emerg. Prepare & Response	42.021	44.242		44.317	X

Specific programs mentioned:

Northern (~~Asian)~~ giant hornet eradication: $1.75 million to continue cooperation with Washington State to eradicate this pest; also to improve monitoring methods and lures, and build a rapid response platforms
sudden oak death (SOD): recognize that the EU1 and NA1 strains of this pathogen threaten Douglas-fir / tanoak forests and lead foreign governments to impose quarantines on U.S. timber exports. So APHIS should spend no less that FY22 funding to better understand threat and treatment methods in wildlands. This earmark disappoints because it focuses on APHIS’ role as certifying timber exports as pest-free rather than the spread of the pathogen within the U.S. via the nursery trade. The same language appears in the report’s discussion of the Agriculture Research Service (see below).

Pertinent action re: Agriculture Research Service

The Senate Committee report sets several priorities, including the following:

Invasive Pests: The Committee is concerned about the threats invasive pests pose to agriculture, the economy, environment, human health, and national security of the Pacific region. The Committee directs ARS to continue working with stakeholders in the region to assess options for combatting invasive species, including biocontrol research facilities, containment facilities, additional laboratory space.
Sudden oak death: the same language as for APHIS. Again, I wish the language referred to the pathogen’s spread via the nursery trade.

These numbers are disappointing; the increase for “specialty crops” demonstrates the lobbying clout of the nursery and berry industries! I appreciate the attention to sudden oak death – with the caveat I mentioned.

SOD-infected tanoaks in southern Oregon; photo by Oregon Department of Forstry

Forest Service

The Senate Appropriations Committee issued a report [available here] . The Senate Appropriations Committee recommends the following funding levels for USFS programs that address non-native forest pests and other invasive species (in $millions):

PROGRAM	FY22 FUNDING	FY ADMIN REQUEST	HOUSE $	S COMM RECOMM	CISP ASK
Research	296.616	317.733	$360.4	$302.773	317.733
State & Private Forest Health Protection TOTAL	48	59.232	$52.232	50	83
S&P FHP Federal lands	16,000	22,485	?	17,000	51
S&P FHP non-federal lands	32,000	36,747	?	33,000	32

R&D

The Senate wants to retain the current structure of five regional stations, International Institute of Tropical Forestry, and Forest Products Laboratory.

The Senate listed several research priorities. Two pertain to forest health: 1) needle pathogens, and 2) Northeastern States Research Cooperative working to sustain the health of northern forest ecosystems and biological diversity management. I am disappointed that no mention is made of the need to respond to 400 introduced tree-killing insects and pathogens.

planting to test ash trees’ resistance to emerald ash borer; photo courtesy of Jennifer Koch, USFS

S&P

The Senate Committee recommends a significant increase in S&P overall ($8 million above FY22 level), but not for Forest Health Management. This is disappointing.

The Committee is concerned about high tree mortality on National Forests due to bark beetle infestations and instructs USFS to work with states and tribes to prioritize insect prevention, suppression & mitigation projects.

The Committee expects the Forest Service and Bureau of Land Management (BLM) to continue efforts to treat sudden oak death in California and Oregon. It provides $3 million for this purpose, including for partnerships with private landowners.

Posted by Faith Campbell