December 2019 – Center for Invasive Species Prevention

New USFS Report on Forest Health – Confusing Differences from Other Studies

ash killed by emerald ash borer
photo by Nate Siegert

USDA Forest Service has issued its annual summary of the nation’s forest health, based on various data sources.

The report seeks to provide status and trends at the national and regional levels as of 2017. It analyzes drivers of tree mortality including insects and pathogens, fire, and weather (especially drought). The report also discusses plant invasions in forests in the East. There is considerable discussion of emerging methods to improve data collection and analysis. Finally, it includes three case studies to illustrate the power of these approaches for analyzing forest health issues at specific sites:

• Decline of bishop pine (Pinus muricata) stands in California’s northern coastal areas;

• Impacts on naio (Myoporum sandwicense) on Hawaii’s Big Island of the myoporum thrips; and

• Impacts of increasing temperatures on Great Basin bristlecone pine (Pinus longaeva) communities.

Tree-Killing Insects and Pathogens

In 2017, the USFS Forest Health Protection (FHP’s) national Insect and Disease Survey (IDS) covered 55.1% of the total forested area of the lower 48 states. In Alaska, surveys covered about 7.3% of the total forested area. In Hawai`i, the surveys covered about 80.1 %.

The FHP program and partners in State agencies identified 63 mortality-causing agents and complexes that cumulatively affect 3.27 million hectares in the lower 48 states – 1.3% of the total 252 million hectares of forested land in these states. They also identified 50 defoliating agents and complexes affecting approximately 2.34 million hectares.

Most of the analyses focus on ecoregions developed by USFS scientists based on concepts put forward by Bailey (1995). Ecoregions are made up of regions with similar geology, climate, soils, potential natural vegetation, and natural communities. The area of the lower 48 states is divided into 190 ecoregions (see Chapter 1, esp. page 7).

Their damage, by type and level, was not evenly spread. Geographic hot spots of forest mortality were associated with bark beetle infestations in the West, and with emerald ash borer and southern pine beetle in the East. Hot spots of defoliation were associated with European gypsy moth and several native insects. Several native insects were the principal agents of defoliation in Alaska. In Hawai`i, about 37,000 hectares of mortality were listed officially as caused by an unknown agent, but the report attributes this mortality to rapid ‘ōhi‘a death.

The emerald ash borer was the most widespread single mortality agent in 2017, causing measurable tree mortality on 1.42 million hectares. In the program’s North Central region, 91% of the area suffering tree mortality was associated with the EAB. In one ecoregion – the Lake Whittlesey Glaciolacustrine Plain ecoregion (on the Ohio-Michigan border), about 73% of the mortality was caused by insects, especially the EAB. In a second, the Southwestern Great Lakes Morainal ecoregion (along the western shore of Lake Michigan in Wisconsin and Illinois), a quarter of the surveyed forest was experiencing exacerbated mortality due to EAB. The EAB also is causing mortality across 10,346 ha in the Northeast and more than 5,000 ha in the South.

However, heightened mortality (rates above 1%) in several Great Plains ecoregions were attributed largely to drought – even in the elm-ash-cottonwood forest type. However, such biological factors as oak decline, bur oak blight (Tubakia iowensis), Dutch elm disease, and native pests of ash were also significant. Emerald ash borer is mentioned rarely. I am confused by this finding – perhaps it reflects the fact that EAB has not yet been detected in North Dakota?

Other non-native pests that affect more than 5,000 ha in the lower 48 states were the Balsam woolly adelgid (20,758 hectares, primarily in the Northeast), beech bark disease (12,222 ha, primarily in the North Central region), oak wilt (9,573 ha, primarily in the North Central region), and sudden oak death (6,335 ha, in California). (All are described here.)

Still, despite the numerous and widespread presence of EAB and other non-native tree-killing insects and pathogens in the Central and Eastern States, in most areas, tree mortality is low relative to tree growth. Indeed, in nearly all the other North Central ecoregions, as well as those in the Northeast and South, 1% or less of the forested area was exposed to mortality agents. Hot spots associated with EAB were detected in Connecticut and eastern Kentucky.

Oak wilt was reported as a mortality agent in Michigan and Texas.

I am confused by the discrepancy between the findings of the Forest Health Protection (FHP’s) national Insect and Disease Survey and studies by other USFS scientists – as reported in earlier blogs. Thus, Randall Morin, speaking at the 81^st Northeastern Forest Pest Council in March 2019, reported detecting an approximate 5% increase in mortality – measured by tree volume – nation-wide. The greatest increases in mortality above the background rate was the four-fold increase for redbay and the three-fold increase for ash trees (from 0.8% to 2.7%), beech (from 0.7% to 2.1%), and hemlock (from 0.5% to 1.7%). (The increase for ash was incorrectly stated in my earlier blog).

Other studies by, among others, Guo et al. 2019 and the Potter studies discussed the threat – present and future – rather than current changes in mortality levels. See my blog here.

All note that their estimates are probably underestimates.

All the studies agree that EAB, European gypsy moth, and oak wilt threaten the greatest number of species (Potter et al. 2091b).

However, these reports also note the widespread presence of other damaging invaders – several of which don’t appear in the FHP survey. These include white pine blister rust (present in 94% of the potential hosts’ ranges; 955 counties); and dogwood anthracnose (in 609 counties in the East; plus uncalculated number of counties in the West) (Morin and the western counties were not calculated) (FIA “dashboards”).

whitebark pine in Crater Lake National Park killed by white pine blister rust
photo by F.T. Campbell

Data available from the West are less suited to the kind of analysis the FHP report used (for an explanation, see chapter 5). In the FHP West Coast and Interior West regions, principal mortality agents were bark beetles, drought, and fire. Some ecoregions suffered up to 5% mortality. Using a different measurement tool — annual mortality volume to gross annual volume growth (MRATIO) – the Southern California Mountain and Valley Ecoregion had the highest damage – at 2.50. This was attributed to a combination of prolonged drought, bark beetles, and fire.

Of 50 defoliation agents and complexes across the lower 48, the most widespread was the European gypsy moth. Across the continent, its impacts were detected on 39% of the total forested area of the lower 48 states (913,000 ha). Defoliation was particularly severe in the Northeast Region — again primarily by the European gypsy moth (869,000 ha). Other non-native defoliation agents affecting more than 5,000 ha in the lower 48 were the larch casebearer (25,891 ha in the North Central region, another 7,400 ha in the West Coast region) and winter moth (12,760 ha in the Northeast region). (The last is described here.)

The report concedes that death of tree species that are scattered in multi-species forests, such as most of the victims of non-native forest pests in the East, are not easily detected by the methodology the USFS uses. Examples cited by the report include emerald ash borer, hemlock woolly adelgid, laurel wilt, Dutch elm disease, white pine blister rust, and thousand cankers disease. (All are described here.)

Hence the authors advise decision-makers to use other forest health indicators in addition to this report.

I have already reported on studies by Morin, Liebhold, and colleagues and Kevin Potter and colleagues. Each finds ways to analyze Forest Inventory and Analysis (FIA) data to provide more detail on mortality caused by non-native insects and pathogens.

Invasive Plants

Invasive plants have already invaded a large proportion of rural forest in the East. Christopher Oswalt and colleagues used FIA data to assess the plant invasion status in 13 bioregions covering most of the temperate and boreal forests in the Eastern U.S. I blogged about Oswalt’s studies previously. Their findings are also reported here, in chapter 6:

Data were analyzed on 71 invasive plant species;
Half of the total area of 74 forest types was found to be invaded;

Plant invasions are almost twice as likely on privately than publicly owned land. Ownership alone was the deciding factor for the most-invaded forest types.)

The types of forest most heavily invaded were loblolly-shortleaf pine (61%), elm-ash-cottonwood (59%) oak-pine and oak-hickory (each 58%). The forest types least invaded were northern types: spruce-fir (20%), aspen-birch (32%), and maple-beech-birch (34%).

However, several forest type groups were excluded from the study; these included other eastern softwoods; pinyon-juniper; exotic softwoods; other hardwoods; woodland hardwoods; tropical hardwoods; and exotic hardwoods, and Fraser fir.

One-third of publicly owned (federal, state, and local) forest land was invaded, compared to 46% of private corporate forest and 59% of private non-corporate forest.

SOURCES

Bailey, R.G.. 1995. Descriptions of the ecoregions of the United States. 2d ed. Miscellaneous Publication No. 1391. Washington, D.C.: U.S. Department of Agriculture Forest Service. 108 p.

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. 2019. Biomass losses resulting from insect and disease invasions in United States forests

Guo, Q., S. Feib, K.M. Potter, A.M. Liebhold, and J. Wenf. 2019. Tree diversity regulates forest pest invasion. PNAS. www.pnas.org/cgi/doi/10.1073/pnas.1821039116

Morin, R.S., K.W. Gottschalk, M.E. Ostry, A.M. Liebhold. 2018. Regional patterns of declining butternut (Juglans cinerea L.) suggest site characteristics for restoration. Ecology and Evolution.2018;8:546-559

Morin, R. A. Liebhold, S. Pugh, and S. Fie. 2019. Current Status of Hosts and Future Risk of EAB Across the Range of Ash: Online Tools for Broad-Scale Impact Assessment. Presentation at the 81^st Northeastern Forest Pest Council, West Chester, PA, March 14, 2019

Potter, K.M., B.S. Crane, W.W. Hargrove. 2017. A US national prioritization framework for tree species vulnerability to climate change. New Forests (2017) 48:275–300 DOI 10.1007/s11056-017-9569-5

Potter, K.M., M.E. Escanferla, R.M. Jetton, and G. Man. 2019a. Important Insect and Disease Threats to United States Tree Species and Geographic Patterns of Their Potential Impacts. Forests. 2019 10 304.

Potter, K.M., M.E. Escanferla, R.M. Jetton, G. Man, and B.S. Crane. 2019b. Prioritizing the conservation needs of United States tree species: Evaluating vulnerability to forest insect and disease threats. Global Ecology and Conservation. (2019)

USDA Forest Service. Forest Health Monitoring: National Status, Trends, and Analysis 2018. General Technical Report SRS-239. June 2019. Editors Kevin M. Potter Barbara L. Conkling

Will Chaos Replace International Trade Rules?

The United Nations has designated 2020 as the International Year of Plant Health. I welcome the possibility of heightened awareness – although it could result in promises that are more optimistic than facts warrant.

APHIS and probably other national and international phytosanitary bodies have planned events to draw attention to the importance protecting of plant health. For example, the APHIS website lists numerous meetings, some of which are special events, e.g., Safeguarding 2020: North American Safeguarding and Safe Trade Conference in Washington, DC, in August. Another event is a continuation of the Entomological Society of America’s Grand Challenges event, “Pre-border Prevention: A New Conversation on Invasive Pest Pathways Through Trade” – which will take place in Orlando in November.

I repeat that we should support the international phytosanitary community’s efforts to raise political leaders’ awareness of the importance of preventing phytosanitary disasters.

However, at the same time, the international system that, for more than two decades, has governed trade, with all its associated phytosanitary risks and regulations, is falling apart.

The World Trade Organization – which is the basis for international trade rules – is under unprecedented threat. United States has blocked nomination of individuals to the World Trade Organization’s Dispute Panel. As of December 10, 2019 the Panel no longer has a quorum. As a result, experts expect countries to revert to the pre-WTO practice of bullying trade “partners” with whom they have a quarrel. They will probably erect tariffs and other barriers in order to force other parties to concede. Phytosanitary requirements might again be governed by individual countries’ bilateral agreements, leading to confusion and perhaps a “race to the bottom” in the name of facilitating trade.

Collapse of the WTO rules alarms me – despite my having criticized WTO restrictions on strong national phytosanitary measures over the past 25 years. (The restrictions were imposed by the WTO’s Agreement on the Application of Sanitary and Phytosanitary Measures – the SPS Agreement). For more details, see Fading Forests II. All-out country vs. country trade battles seldom put a priority on preventing the movement of pests. At least under WTO SPS, there has been a process for addressing pest problems.

Most phytosanitary issues – including development of international standards – are addressed under the International Plant Protection Convention. The IPPC is a separate organization from the WTO, so it might continue to function with fewer disruptions. Still, much of its clout comes from its recognition by the WTO SPS as the standard-setting body for plant health matters.

Of course, there are benefits associated with individual countries’ acting independently. Might the current collapse of trade rules allow the U.S. to adopt more stringent regulations governing introduction pathways of concern to us — for example, wood packaging? Can we hope that an administration focused on “America First” take aggressive phytosanitary actions to protect our agriculture and environment?

Unfortunately, I see no indications that the U.S. Department of Agriculture – much less other agencies – might seize this opportunity.

The United Kingdom has an even greater opportunity to act independently, since it is “Brexiting” the European Union in January 2020. In theory, the UK is now free to adopt its own phytosanitary measures. A House of Lords committee held extensive hearings to explore options in 2018.

While eminent plant pathologist Clive Brasier and others urged the UK to adopt more stringent rules based on a precautionary approach – for example, by banning imports of semi-mature trees with large root balls – the committee noted that the British government has often said that it wants to maintain “seamless” trade with the EU. It therefore seems unlikely that the UK will seize this opportunity to erect more effective phytosanitary barriers to prevent pest introductions to the islands.

Meantime, the European Union is making some mildly encouraging changes. Europe (including the UK) has the highest number of introduced tree-killing non-native pathogens of any continent – five times more than North America (Ghelardini 2017). Europe has a much more leaky phytosanitary system for plant imports than does the United States. See also Jung et al. (2015), Roy et al. (2014), the Montesclaros Declaration.

participants at the Montesclaros negotiation

In response to growing awareness of the plant pest threat, EU officials have gone through a multi-year process to strengthen phytosanitary rules governing movement of plants for planting (living plants, such as nursery stock). The process was described in Klapwijk et al. (2016) and discussed in my blog in October 2016. The new rules took effect in December 2019. The new European Commission regulation simplifies and harmonizes the “plant passport” system, under which plants are moved among EU member states. Plant imports that pose the greatest risk – called “priority pests” – are subject to enhanced measures concerning surveys, action plans for their eradication, contingency plans and simulation exercises. Plants for planting and plant products being imported into the EU will be subject to varying levels of restrictions, including prohibition of importation of those posing the highest risk. Less risky plants must be accompanied by a phytosanitary certificate issued by the phytosanitary agency of the exporting country (House of Lords report). The new system no longer depends on a list of harmful plant pests, but instead “sets out the conceptual nature of quarantine pests” and empowers the Commission to adopt measures to control certain pests (Klapwijk et al. (2016)).

Three years ago, Klapwijk et al. (2016) praised the new approach as a significant step forward. However, they note that the new rules still don’t provide for precautionary assessments of high-risk commodities. Nor do they actually restrict import of the highest-risk commodities, such as imports of large plants or plants in soil (my emphasis). Such restrictions still must be enacted separately. Organisms whose pest status is unknown will continue to be allowed into the EU. (See discussions of the impact of failing to curtail imports of “unknown unknowns” by Brasier (2008) and in Fading Forests II.

(While the U.S. also does not address organisms with unknown pest potential, it is much more stringent regarding sizes of plants, presence of soil or other growing media, and other issues. Furthermore, it has the NAPPRA process, which facilitates a more rapid response to emerging pest threats.)

Posted by Faith Campbell

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

SOURCES

Brasier CM. 2008. The biosecurity threat to the UK and global environment from international trade in plants. Plant Pathology 57: 792–808.

Ghelardini, L., Luchi, N., Pecori, F., Pepori, A.L., Danti, R., Della Rocca, G., Capretti, P., Tsopelas, P. , Santini, A. 2017. Ecology of invasive forest pathogens. Biological Invasions. June 2017

Jung, T. et al. 2015 “Widespread Phytophthora infestations in European nurseries put forest, semi-natural and horticultural ecosystems at high risk of Phytophthora disease” Forest Pathology. November 2015;

Klapwijk, M., Hopkins, A.J.M., Eriksson, L. Pettersson, M., Schroeder, M., Lindelo¨w, A., Ro¨nnberg, J. Keskitalo, E.C.H., Kenis, M. 2016. Reducing the risk of invasive forest pests and pathogens: Combining legislation, targeted management and public awareness. Ambio 2016, 45(Suppl. 2):S223–S234 DOI 10.1007/s13280-015-0748-3

Roy, B.A., Alexander, H.M., Davidson, J., Campbell, F.T., Burdon, J.J., Sniezko, R., and Brasier, C. 2014. Increasing forest loss worldwide from invasive pests requires new trade regulations. Frontiers in Ecology https://cpb-us-e1.wpmucdn.com/blogs.uoregon.edu/dist/1/11561/files/2018/07/Roy-et-al-2014-Frontiers-12p4898.pdf

APHIS seeks comments on NAPPRA proposals

APHIS proposes to place numerous plant taxa on its list of plants for planting whose importation is “not authorized pending pest risk analysis” (NAPPRA). Unfortunately, the proposal comes too late for some pests; doesn’t apply to at least one significant pathway of entry; excludes some highly damaging newly detected pathogens; and too often applies only to agricultural pests. Nevertheless, the proposal is worth supporting – while mentioning those caveats.

APHIS is accepting comments on the data sheets justifying the proposed listings until 24 January. The Data sheets can be obtained here. We encourage you to comment.

APHIS’ Regulatory Framework

Under APHIS’ regulations in ‘‘Subpart— P4P’’ (7 CFR 319.37 through 319.37–14 …), APHIS prohibits or restricts the importation of “plants for planting” – living plants, plant parts, seeds, and plant cuttings – to prevent the introduction of “quarantine pests” into the US. A “quarantine pest” is defined in § 319.37–1 as a plant pest or noxious weed that is of potential economic importance to the United States and not yet present in the country, or is present but not widely distributed and is being officially controlled.

§ 319.37–2a authorizes APHIS to identify those plant taxa whose importation is not authorized pending pest risk analysis (NAPPRA) in order to prevent their introduction into the United States. If the plant taxon has been determined to be a probable invasive species, its importation is restricted from all countries and regions. If the taxon has been determined to be a host of a plant pest, the list includes (1) names of affected taxa, (2) the foreign places from which these taxa’s importation is not authorized, and (3) the quarantine pests of concern.

APHIS finalized a rule giving itself the authority to place plant taxa in the NAPPRA program in 2011; it has previously used this process twice to restrict imports of plant taxa – most recently in 2017.

Plant Taxa that Host a Damaging Pest or Pathogen

The proposed restrictions would apply to two plant families — Myrtaceae taxa (when destined to Hawai`i), and the subfamily Bambusoideae (bamboo); plus 43 other taxa that are likely to transport damaging insects, pathogens, or viruses.

`ohi`a in bloom; National Park Service photo

1) All plants in the family Myrtaceae that are destined for Hawai`i.

The proposed restriction is intended to counter the risk that additional strains of the `ohi`a rust pathogen Austropuccinia psidii might be introduced and prove more damaging to native Hawaiian vegetation than the strain already present on the islands. (See description of `ohi`a rust here.

`Ohi`a rust was detected in Hawai`i in 2005. Detection was followed by scientific studies to determine whether different strains exist and, if so, whether they posed a threat to Hawaiian vegetation. Under the circumstances, the proposed action is disturbingly tardy.

Worse, the pathogen was probably introduced to Hawai`i on imports of flower and foliage cuttings, rather than entire plants or propagules. Unfortunately, the section of APHIS’ regulations that governs imports of plants that can be grown (“plants for planting”) does not apply to imports of cuttings (including flowers). In the Federal Register notice, APHIS says it will issue a separate proposal to tighten regulations on imports of cuttings and flowers. I hope they move expeditiously on this rulemaking – which will be more cumbersome in even the best case because it requires a full rulemaking, not the expedited notice and comment process allowed under the NAPPRA program.

It is disturbing that the proposal does not include the two Ceratocystis species that are killing millions of `ohi`a trees in Hawai`i link to DMF writeup. It is true that these were identified relatively recently – in 2017. However, other plant taxa proposed for inclusion in the NAPPRA category were also detected or determined to be the cause of a disease as recently as 2017.

`ohi`a trees killed by Ceratocystis; Island of Hawai`i; photo by J.B. Friday, University of Hawai`i

2) APHIS proposes to include another pest that might attack a native Hawaiian plant, Phyllanthus distichus. Another species in the genus, P. saffordii is endemic to Guam; it is listed as endangered under the federal Endangered Species Act. Other Asian gooseberries in the Phyllanthus genus are grown in backyards in Hawai`i and other semitropical areas and there is some interest in expanding commercial uses.

3) APHIS proposes to include several plant taxa important in tropical agriculture because of the threat that imports of those plants will transport diseases or pests. These include two pathogens that threaten production of macadamia nuts (Neopestalotiopsis macadamiae and Pestalotiopsis macadamiae); and pests of breadfruit, lychee, and durian.

4) Some of the plant taxa that APHIS hopes to protect from new pests or pathogens by placing hosts in the NAPPRA category are invasive. These include – in Hawai`i – Syzygium jambos (rose apple). It is named as a host of two pests targetted by the proposed action – the `ohi`a rust pathogen Austropuccinia psidii and armored scale insect Myrtaspis syzygii.

Euonymus bungeanus (winterberry euonymus) is in the same genus as several plant species invasive across the continent. APHIS proposes to restrict its importation in order to prevent introduction of the Euonymus yellow mottle associated virus (EuYMaV), which has only that plant species as a known host.

5) APHIS also proposes to add to the NAPPRA category several plant taxa that could transport the Elm mottle virus (EMoV) because of the threat the virus poses to several European elm species – and presumably also to North American elms. The virus also attacks hydrangea and lilac.

In several cases, some of the primary hosts of the target pest or pathogen are already in NAPPRA for other reasons from some origins. Nearly all the woody hosts are already required to undergo post-entry quarantine – which presumably APHIS now considers to provide inadequate protection.

6) Also proposed are diseases or pests that threaten grapevines and tomatoes.

Several of the proposed taxa are already present in the US (including `ohi`a rust). Other proposed listings appear to be precautionary actions to protect plant taxa that USDA expects to be increasingly important economically in the future.

Plant Taxa Proposed Because They Appear Likely to be Invasive

APHIS has proposed 26 plant taxa for inclusion in the NAPPRA category because they might themselves be invasive. Of greatest ecological concern are two taxa of mangroves which had been introduced by early 20^th century plant explorer David Fairchild and have since been detected to be spreading in South Florida. These are Bruguiera gymnorhiza and Lumnitzera racemose. Also of concern is a vine that grows in Asian and Indian Ocean mangrove forests, Derris trifoliate.

Several proposed species are aquatic plants that can form dense mats.

Other taxa proposed appear to possibly threaten pastures or other agricultural uses.

Posted by Faith Campbell