Category: resistance breeding

Ambrosia Beetles: Not All the Same (laurel wilt v. shot hole borers)

Horton House on Jekyll Island, Georgia – when the redbays were still alive!
photo by Faith Campbell

A recent USFS book on invasive species reports that at least 58 species of bark and ambrosia beetles have been established in the US.  Recent studies highlight very different situations due to two invasive ambrosia beetles. Here are summaries of each.

1. Laurel Wilt: Unmitigated Disaster in Atlantic and Gulf Coastal Plains – and Possibly More Widely

The disease laurel wilt, caused by the pathogen Raffaelea lauricola and vectored primarily by the redbay ambrosia beetle (Xyleborus glabratus) presents a dire contrast. (For this section, see Olatinwo, Fraedrich & Mayfield. 2021; full reference at end of the blog.) In the nearly 20 years since its first detection near Savannah, Georgia in 2002, laurel wilt has spread across more than 100 counties and parishes in 11 states from North Carolina south through Florida, west to eastern Texas, and as far northward as Kentucky.

Laurel wilt has killed hundreds of millions of trees in the plant family Lauraceae. Approximately 13 Lauraceae species in eight genera (depending on taxonomic proclivities!) are indigenous to the U.S. Individual species’ vulnerability appears to depend largely on size; the beetle is attracted to vertical stems of a certain diameter. As a result, the native tree species redbay (Persea borbonia), swampbay (Persea borbonia var. pubescens or P. palustris), and more recently sassafras (Sassafras albidum) have experienced the most damaging attacks. Also heavily attacked has been the commercial avocado (Persea americana)  which is native to Central America.

sassafras photo by David Moynihan

While redbay is widespread in a defined geographic area – a long the Atlantic and Gulf Coastal Plain from North Carolina to Texas, sassafras is subcontinental: it is found in 28 states, 53 ecoregions, and 69 forest types. Approximately 80% of sassafras in affected areas have been killed. In recent years, spread has proceeded by many “jumps” to disjunct areas where sassafras occurs in isolation from other hosts. At present, approximately 52% of the range of sassafras might experience winter temperatures sufficiently cold to cause significant mortality of the redbay ambrosia beetle. However, this temperature protection is likely to decline to about10% of sassafras’ range as a result of even modest climate change (a 1.4 °C increase in winter minimum temperatures).

The ecological impact of loss of redbay and sassafrass are not clear. Both are sources of wildlife food. The principal specialist on redbay is the Palamedes swallowtail butterfly (Papilio palamedes), which is also the primary pollinator of a rare plant, yellow-fringed orchid. The rapid loss of swampbay on tree islands in the Everglades could facilitate establishment of even more individuals of the already widespread invasive plant species Brazilian pepper (Schinus terebinthifolius) or Melaleuca quinquenervia.

Other U.S. native plant species in the Lauracea family are apparently partially protected by the small diameter of their stems, which the beetle doesn’t find acceptable. These include – in the Southeast — the federally listed pondberry (Lindera melissifolia), “species of interest” pondspice (Litsea aestivalis), bog spicebush (Lindera subcoriacea), pepperleaf sweetwood (Licaria trianda), lancewood (Ocotea coriacea), and love-vine (Cassytha filiformis). The common shrub spicebush (Lindera benzoin) might be protected by its possession oflower quantities of the primary host volatile attractant. On the other hand, the widespread Pacific state shrub California laurel or Oregon myrtle (Umbellularia californica) is considered highly vulnerable, should laurel wilt be moved there in wood, mulch, or nursery plants.

Laurel wilt poses an unknown threat to the many plant species in the Lauraceae in Central and South America (750 species), Australia (125 species), Madagascar (135 species), and the Macaronesian Islands off the coasts of Europe and Africa – the Azores, Canary Islands, and Madeira. The commercial spice bay laurel (Laurus nobilis) is native to the Mediterranean region (and planted elsewhere, including in the US). However, its small size, discontinuous distribution and isolation from other lauraceous host species might prevent development of a widespread epidemic.

The authors note the absence of effective measures to manage laurel wilt 20 years after its detection. They recommend restricting long-distance movement of infested wood, associated public awareness efforts, development and deployment of resistant hosts, silviculture (sanitation), targeted application of preventive chemical treatments for protecting high-value trees, and severing root grafts in avocado orchards and sassafras clones. They note that success will be dependent on sustained funding and a commitment to long-term area-wide implementation.

[As I noted in past blogs about APHIS deregulating the emerald ash borer, it is now up to the states to regulate movement of firewood. The lead will continue to be the non-governmental “Don‘t Move Firewood” campaign. The message will continue to encourage the public to buy firewood where they burn it and to refrain from moving firewood from areas that are under Federal quarantine for other pests of firewood (e.g., Asian longhorned beetle). This campaign and the new National Plant Board guidelines stress that firewood is a high-risk pathway for many pests of national or regional concern; they do not focus on any particular species. Leigh Greenwood, director of Don’t Move Firewood, thinks this is a good approach.]

Mayfield adds that the spread northwards on sassafras means that state diagnostic pathology labs should familiarize themselves with protocols for isolating the laurel wilt pathogen.

As to developing resistant varieties of redbay, I note that Potter et al. 2019 ranked redbay as fifth species highest in priority for genetic conservation and restoration breeding efforts. However, it is my impression that few federal resources have been allocated to such an effort on behalf of redbay.

2. Ambrosia beetles in California

At least 22 of the recently-established ambrosia and bark beetles are in California. Heavily urbanized southern California appears to be particularly vulnerable to such introductions. The proximity of ship traffic and associated cargo, as well as the great diversity of potential hosts in the area’s urban forests, are likely to blame.

Two such pests are the polyphagous (PSHB) and Kuroshio (KSHB) shot hole borers [collectively, invasive shot hole borers (ISHB)]. John Boland has studied the KSHB outbreak in the Tijuana River estuary intensively since 2015. Two recent studies – 2019 and 2021– demonstrate the importance of ecological and tree-related factors in determining the severity of attack by this ambrosia beetle. See references at the end of the blog.

The most susceptible site is wet and nutrient enriched (in the case of the Tijuana River, due to pollution).

The most susceptible trees are young, fast growing, and have thin bark (allowing KSHB access) and wood of low density and high moisture content (providing ideal conditions for KSHB and associated fungi).

willows killed by KSHB in Tijuana River estuary; photo by John Boland

As Boland has noted, all of these conditions occurred in the “wet” forests close to perpetual streams in the Tijuana River delta in 2015. These factors led to dramatic levels of mortality, which have not been equaled in other southern California deltas. In the five years from 2015 to 2020, the beetle/fungus complex infested an estimate 350,000 willows and killed an estimated 123,000 in a boom-and-bust cycle. Since 2016, the trees in the Tijuana River estuary have regrown to almost pre-infestation dimensions.  (Boland is not certain why these new, fast-growing trees have not been attacked by the KSHB that remain in the area. He suggests that a local pathogen, parasite, parasitoid or predator is keeping the KSHB in check – although this has not been verified.)

Willows near the main river channel (“Wet Forest” units) cumulatively had a fatality rate of 39%. Strikingly, more distant “Dry Forest” units had a combined fatality rate of only 9%.

The 2019 study linked the higher rates of infestation, damage, and mortality that occurred in trees near the main river channel to the presence of year-round water that was often enriched by a heavy load of sewage. The trees respond by growing rapidly, resulting in thinner bark and less dense wood. The KSHB attacked in much higher numbers, impeding water transport and weakening the trees’ structure so that they were more easily broken during windstorms.

The 2021 study provided further detail. By comparing bark samples cut from 27 infested trees at the height of the infestation, in 2016 – 17, Boland and Woodward demonstrated thicker bark on the “Dry Forest” trees protected the trees by limiting the density of KSHB entry points. The fewer holes reduced internal structural damage to the trees, which allowed them to survive. Boland notes that the protection might arise from either the bark thickness itself, or higher quantities of protective chemicals.

Repercussions

  • The results suggest that a KSHB individual actively searches for a suitable tree and then searches for the thinnest bark on that tree in which to drill its hole. 
  • Trees can recover from KSHB attack, indicating that the fungal symbionts are only moderately pathogenic at worst.
  • The ISHB are likely to cause much less damage than indicated by the one early model developed before these factors were understood. We need new models for ISHB spread and impact that incorporate these factors of site characteristics and host tree condition.

SOURCES

Boland, J.M. 2019. The Ecology and Management of the Kuroshio Shot Hole Borer in the Tijuana River Valley Final Report. (Year 5) https://trnerr.org/wp-content/uploads/2020/05/KSHB-TRValley2020.pdf

Boland J.M. and D.L. Woodward. 2021. Thick bark can protect trees from a severe ambrosia beetle attack. PeerJ 9:e10755 https://peerj.com/articles/10755/

[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]

Olatinwo, R.O., S.W. Fraedrich & A.E. Mayfield III. 2021. Forests 2021, 12, 181.  Laurel Wilt: Current and Potential Impacts and Possibilities for Prevention and Management

Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S.  2019. Prioritizing the conservation needs of US tree spp: Evaluating vulnerability to forest P&P threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/ j.gecco.2019.e00622.

Posted by Faith Campbell

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

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

APHIS Deregulates Emerald Ash Borer – Now it is up to the States

APHIS formally proposed to stop regulating movement of firewood, nursery stock, and other articles that can transport the emerald ash borer (EAB) in 2018; I blogged in opposition to this proposal at the time.  Now APHIS has evaluated the 2018 comments on its proposal and has decided to proceed with its plans.

I recently blogged about the current and probable future status of ash. A study confirmed that robust regeneration of ash seedlings and saplings seen in various invaded areas will not result in recovery of mature ashes that can perform their ecological role. 

APHIS received 146 comments on the proposal. Twenty-five supported the proposal as written; 121 raised concerns. Many of the latter were a few sentences without supporting information. These comments and the final rulemaking can be read here.

How has APHIS responded to the serious questions raised? Dismissively.

I certainly concede that EAB has been difficult to manage and has spread rapidly. However, I continue tobelieve that maintaining the quarantine serves important purposes and the analysis APHIS provides does not justify terminating of the regulatory program. I remain concerned.

Neither the proposal nor the final regulation tells us how much money and staff resources have been dedicated to detection or enforcement of the regulations in recent years. Therefore we don’t know how many resources are now available for supporting other activities that the agency thinks are more effective. APHIS also refuses to provide specific information on how it will allocate the freed-up resources among its (minimal) continuing efforts. For example, APHIS has supported resistance-breeding programs. Will it help them expand to additional species, e.g., black and Oregon ash?

How Does APHIS Propose to Curtail EAB Spread?

APHIS states in the final rule that it is ending the domestic quarantine regulation so that it can allocate resources to more effective strategies for managing and containing EAB. The agency wants to reallocate funds “to activities of greater long-term benefit to slowing the spread of EAB … These activities include further development and deployment of EAB biocontrol organisms; further research into integrated pest management of EAB that can be used at the local level to protect an ash population of significant importance to a community; and further research, in tandem with other Federal agencies, into the phenomenon of “lingering ash … ”

However, APHIS has not funded detection efforts since 2019. (Detection methods were only partially effective, but they gave us some information on where EAB had established.) APHIS is now ending regulation of the movement of vectors. APHIS concedes that biocontrol agents cannot be effective in preventing pest spread. So – what efforts – other than continued support for the “Don’t Move Firewood” campaign – will APHIS make to slow the spread of EAB?

Environmental and Economic Impacts: Not Adequately Assessed

Second, APHIS still has not analyzed the economic or environmental impact of the more rapid spread of EAB to the large areas of the country that are not yet infested – especially the West Coast – that are likely to result from deregulation. As even APHIS concedes, the EAB is currently known to occupy only 27% of the range of native Fraxinus species within conterminous US. There are additional large ash populations in Canada and Mexico – although neither country commented on the proposal — unfortunately!

Instead, APHIS largely restates its position from the proposal that it is too difficult to calculate such impacts. Furthermore, that it is APHIS’ “experience that widely prevalent plant pests tend, over time, to spread throughout the geographical range of their hosts …” In other words, APHIS denies the value of delaying invasions – yet that has always been a premise underlying any quarantine program.

The final regulation refers to an updated economic analysis, but no such document is posted on the official website. The rule does not mention costs to homeowners, property owners, municipal governments, etc. I believe it would not be so difficult to estimate costs to these entities by applying costs of tree removal in the Midwest to tree census data from major West Coast cities. Also, it might have been possible to provide some estimate of the ecological values in riparian forests by analogy to data from the Midwest developed by Deborah McCullough and others.

Biological Control: Effective – or Not

In the final regulation, APHIS concedes that the biocontrol agents currently being released have geographic and other limitations. However, APHIS does not address concerns raised by me and others about their efficacy. APHIS does say explicitly that it has not [yet?] begun efforts to find biocontrol agents that might be more effective in warmer parts of the ash range, especially the Pacific Northwest and  riparian areas of the desert Southwest. However, APHIS has conceded that these areas are almost certain to be invaded – so should it not take precautionary action?  

APHIS states several times that it cannot promise specific funding allocations among program components or strategies – such as resistance breeding – that might be pursued in the future. The agency stresses the value of flexibility.

U.S. Forest Service biologists have higher expectations; see their podcast here.

I wish to clarify that I do not oppose use of biocontrol; I strongly supported then APHIS Deputy Administrator Ric Dunkle’s decision to initiate biocontrol efforts for EAB early in the infestation. My objections are to overly optimistic descriptions of the program’s efficacy.

Firewood: Outreach Only, No National Regulation

As noted, APHIS has promised to continue support for public outreach activities, especially the “Don ‘t Move Firewood” campaign. The program’s message will continue to encourage the public to buy firewood where they burn it and to refrain from moving firewood from areas that are under Federal quarantine for other pests of firewood (e.g., Asian longhorned beetle). This campaign and the new National Plant Board guidelines link stress that firewood is a high-risk pathway for many pests of national or regional concern; they do not focus on any particular species. Leigh Greenwood, director of Don’t Move Firewood, thinks this is a good approach.

In 2010, the National Firewood Task Force recommended that APHIS regulate firewood at the national level. APHIS does explain why the agency did not do so. The agency says national regulations would be overly restrictive for some states and that requiring heat treatment would not be feasible in the winter for producers in Northern states. Finally, a Federal regulation would not address a significant non-commercial pathway – campers. [I have serious questions about APHIS’ assertion that it can regulate only commercial movement of vectors across state lines. Contact me directly for details on this.]

Perhaps APHIS is not required to analyze the probable overarching efficacy of the several efforts of 50 states. Given the states’ many perspectives and obvious difficulty in coordinating their actions on phytosanitary and other policies, I fear a scattered approach that will result in faster spread of EAB. I hope the National Plant Board guidelines on firewood regulation and outreach can overcome the history.

Most federally-managed recreation areas adopted an education campaign on firewood in autumn 2016; I blogged about it then.

Imported Wood Will be Minimally Regulated

APHIS clarifies that it will take enforcement actions against imports of ash wood only if inspectors detect larvae but can identify them just to family level and not below. APHIS will allow the importation if the larvae can be identified as EAB specifically. This policy reflects international standards, which do not allow a country to erect restrictions targetting a pest from abroad if that pest is also present inside the country and is not under an official control program. (See my discussion of the WTO Agreement on Sanitary and Phytosanitary Standards in Chapter 3 and Appendix 3 of Fading Forests II, available here.) 

APHIS does not discuss how it will react to pests identified to the genus – several other Agrilus also pose pest risks. (See here and here.)

APHIS recommends that states leery of accepting yet more EAB-infested wood from abroad petition the agency under the Federally Recognized State Managed Phytosanitary Program (FRSMP) program, under which APHIS would take action to prevent movement of infested material to that particular state.

Lessons Learned

Finally, one commenter asked whether APHIS would analyze the program to learn what could have improved results. APHIS replies that the agency “tend[s] to reserve such evaluations for particular procedures or policies in order to limit their scope …” I hope APHIS is serious about “considering” doing a “lessons learned” evaluation. It is important to understand what could have been done better to protect America’s plant resources.

My take: the EAB experience proves, once again, that quarantine zones must extent to probable locations – beyond the known locations. The pest is almost always more widely distributed than documented. This has been true for EAB, sudden oak death, ALB, citrus canker … Failure to regulate “ahead” of the pest guarantees failure. I recognize that adopting this stance probably requires a change in the law (or at least understanding of it) and of current international standards adopted by the International Plant Protection Convention (IPPC). However, absent a more aggressive approach, programs are doomed to be constantly chasing the pest’s posterior.

Finally, let us mourn the loss of ash so far, the future losses … and opportunities missed.

Posted by Faith Campbell

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

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

Let’s shape the Biden Administration’s & New Congress’ Policies on Non-Native Forest Pests!

We have a great opportunity to shape future efforts to counter non-native forest pests and diseases. Administration officials are most open to new ideas when they first take office. The same is true of new Congressional leadership.

So now is the time to suggest needed changes!

The USDA Secretary-designate is Tom Vilsack. Of course, he was USDA Secretary during the Obama Administration … so he is not entirely “new” to the issues. However, perspectives and priorities have changed, so now is a good time to urge him to consider new approaches.  Furthermore, the Senate Agriculture Committee will hold confirmation hearings for him; we can ask the Senators to advocate for our views during this proceeding.

The House Agriculture Committee has a new Chair, David Scott – from the suburbs of Atlanta, Georgia. Again, this provides an opportunity to suggest new approaches and topics for hearings. 

I assume you all are knowledgeable about the numbers and impacts of non-native forest insects and pathogens in the United States, and of the pathways by which they are introduced and spread. If you are not, peruse my blogs about wood packaging or plants as vectors (click on the appropriate “categories” listed at the bottom of the archive of blogs). Or read Fading Forests III (see the link at the end of this blog) and the article I coauthored early this year on improving forest pest management programs.

On the basis of my long experience, I suggest that you encourage USDA Secretary-designate Vilsack, Senators on the Agriculture Committee, and House Agriculture Committee Chair David Scott to consider the following recommendations:

Actions Congress could take

  1. Congress could amend the Plant Protection Act [7 U.S.C. §7701, et seq. (2000)] to prioritize the protection of natural and agricultural resources over the facilitation of trade.  This might be done by amending the “findings” section of the statute to give higher priority to pest prevention.
  2. The Agriculture Committees of both the House and Senate could hold hearings on the importation of forest pests. They could determine if the USDA is doing an adequate job protecting the country from insect pests and diseases, and how our defenses could be strengthened. One component of the hearings could focus on whether current funding levels and mechanisms are adequate to support vigorous responses to new pest incursions.
  3. Congress could commission a study of the feasibility, costs and benefits of establishing a “Center for Forest Pest Control and Prevention” to coordinate research and policy on this issue.
  4. Congress could increase funding for the appropriate USDA APHIS and Forest Service programs and activities to enable vigorous containment and eradication responses targeting introduced forest pests and diseases.    
  5. Congress could increase funding for USDA research on detection of insects and pathogens in shipping; insect and disease monitoring/surveillance; biological control; alternatives to packaging made from wooden boards; management of established pests; and resistance breeding to enable restoration of impacted tree species.

Actions Secretary-designate Vilsack could initiate without legislative action (once he is confirmed)

Introductions of pests in the wooden crates, pallets, etc., goods come in

  1. APHIS could take emergency action to prohibit use of wood packaging by importers of goods from countries with a record of poor compliance with ISPM#15. This action is allowed under authority of the Plant Protection Act [7 U.S.C. §7701, et seq. (2000)] and Article 5.7 of the World Trade Organization’s Agreement on the Application of Sanitary and Phytosanitary Measures.
  2. APHIS could strengthen enforcement of current regulations by aggressively prosecuting repeat offenders.  For instance, APHIS could begin imposing administrative financial penalties on importers each time their wood packaging is non-compliant with ISPM#15.
  3. APHIS could work with Department of Homeland Security Bureau of Customs and Border Protection (CBP) to improve information available to U.S. importers about which foreign suppliers of SWPM and shippers have good vs. bad records of compliance with ISPM#15.
  4. DHS CBP could release information on country of origin and treatment facility for ISPM#15-stamped SWPM that is found to be infested with pests.
  5. USDA APHIS could begin a phased transition from solid wood packaging to alternative materials that cannot carry wood-boring pests. APHIS could initiate a pest risk assessment to justify making such an action permanent. Imports could be packaged in alternative materials, e.g., manufactured wood products (e.g. plywood), metal, or plastic.

Nursery Plant (“Plants for Planting”) Pathway

  1. APHIS could apply authorities under NAPPRA and other existing authorities to curtail imports of plants that pose a high risk of introducing insects and pathogens that would threaten tree species that are important in natural and urban forests in the U.S. At a minimum, APHIS should restrict imports of live plants that are in the same genus as native woody plants of the U.S.
  2. APHIS could work with the Agriculture Research Service and National Institute of Food and Agriculture to determine which taxa of woody vegetation native to the U.S. are vulnerable to pathogens present in natural systems of trade partners. Particularly important would be the many Phytophthora species found by Jung and colleagues in Vietnam, Taiwan, Chile, and other countries. Once the studies are sufficiently complete, APHIS could utilize authority under NAPPRA to prohibit importation of plants from those source countries until effective phytosanitary measures can be identified and adopted.

Other Actions

  1. APHIS could develop procedures to ensure the periodic evaluation of pest approach rates associated with wood packaging and imports of “plants for planting” and highlight areas of program strengths and weaknesses. A good place to start would be to update the study by Haack et al. (2014), which estimated the approach rate in wood packaging a decade ago.
  2. The USDA could expand early detection systems for forest pests, such as the APHIS CAPS program and the Forest Service EDRR program. These programs should be better coordinated with each other and should make better use of citizen observations collected through smartphone apps, professional tree workers such as arborists and utility crews, and university expertise in pest identification and public outreach.  An effective program would survey for a broad range of pests as well as for suspicious tree damage, and would be focused on high-risk areas such as forests around seaports, airports, plant nurseries, and facilities such as warehouses that engage in international trade.
  3. The USDA could initiate a “Sentinel Plantings“ network of US tree species planted in gardens abroad and monitored for potential pests and diseases. 

Posted by Faith Campbell

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

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

Ash Mortality Accelerates – Population Regeneration Will Not Reverse Collapse

dead ash along Accotink Creek, Fairfax County, Virginia photo by F.T. Campbell

As we all know, the emerald ash borer (EAB) has killed millions of ash trees in its invaded range across eastern North America. However, field studies have detected robust regeneration of ash seedlings and saplings in various invaded areas. Ward et al. 2021 (full citation at end of blog) set out to determine whether this regeneration will result in recovery of mature ashes that can perform their ecological role. They conclude that it will not. Instead, they say, the EAB invasion will probably alter successional patterns and composition of large areas of naturally regenerating forests, causing a cascade of ecological impacts in ash-containing ecosystems

Ward and colleagues used USDA Forest Service Forest Inventory and Analysis (FIA data) to quantify ash recruitment and regeneration across the entire eastern United States. Theirs is the first study to evaluate trends across the region, rather than specific locations or stands. They related the FIA recruitment data to EAB spread, as measured by USDA Animal and Plant Health Inspection Service’ (APHIS) record of the first EAB detection in each county.

FIA inventories in 2002-2007 and 2013-2018 show large numbers of ash seedlings and saplings in counties invaded in the first wave of invasion, 2002–2006. These areas had higher densities of both seedlings and saplings than plots in other counties. The earliest-invaded counties were in areas that had extraordinarily high densities of ash before the EAB invasion, so the numbers of seedlings and saplings probably reflected that abundant seed source.

However, by the 2013-2018 inventory ash trees in the smallest overstory class (12.7 cm dbh) were dying at faster rates than they were recruited from seedlings or saplings in all 362 counties recorded by APHIS as EAB-infested before 2013. Ward and colleagues found these negative population trajectories on plots that have been invaded for more than about 10 years. This trend suggests that ash will continue to decline in abundance and may become functionally extinct across the invaded range.

Some U.S. Forest Service biologists are more optimistic about ash recovery in response to biocontrol of the EAB. See their podcast here.

In the risk of functional extinction, ash trees are unfortunately not unique. The authors note similar impacts from the invasion of the hemlock woolly adelgid and beech bark disease.

Data Reveal History of Invasion (spread)

Ward and colleagues focused on the risk of mortality for young ashes as they developed from seedlings to saplings, and, eventually, to overstory trees. The youngest “overstory” trees are 12.7 to 17 cm dbh. FIA data show that even the largest trees in this class are 3 cm smaller than trees that produce seeds.

Mortality was initially uniformly low – less than 2.1% — as measured by the first FIA inventory (2002–2007). This is not surprising because EAB was detected only in 2002, and then in only few counties. (EAB had probably been present for a decade before it was detected.)

By the 2013-2018 FIA inventory, mortality had quadrupled to 8–11% in counties invaded during the 2002–2006 period. In the counties invaded during the 2007–2012 period, morality also rose to 3-5%. Both measurements included all diameter classes. Annual mortality rates in the FIA 2013-2018 inventory were still highest for the counties invaded during 2002–2006 except for the largest trees (those greater than 40 cm dbh). By the time of the 2013-2018 FIA survey, overstory ash densities near the epicenter had since declined substantially. They had been nearly eliminated in some counties in southeastern Michigan. There were still sufficient numbers of smaller trees in the region to exhibit an elevated mortality rate – more than 10% per year in several counties in Michigan, Indian, and Ohio. By contrast, in the most recently invaded areas – those counties recorded by APHIS as infested after 2013 – there was very little change in ash densities compared to the 2002-2007 period. This is hardly surprising since it takes years for mortality to reach levels observable by the FIA process.

dead ash on edge of Pohick Bay, Fairfax County, Virginia photo by F.T. Campbell

Considering trees just entering the overstory category (those with diameters of 12.7 cm dbh), annual mortality increased substantially across the region. Between the first FIA inventory (conducted in 2002-2007) and the second inventory (conducted in 2013-2018), their average annual mortality rose more than four-fold, from 0.08 trees per ha to 0.37 trees per ha. By 2013-2018, recruitment in the 2002–2006 invasion cohort was about 50% less than tree mortality levels; recruitment and mortality were about equivalent for the counties invaded in the 2007–2012 period. Recruitment was [still] significantly higher than mortality for the counties recorded as invaded in 2013–2018. However, Ward and colleagues expect mortality rates of this cohort to accelerate over the next five to 10 years – even in areas with lower ash densities.

Ward and colleagues note that many of the young ash trees were dying before they could reach reproductive age – which they estimated to be about 20 years with a dbh of about 20 cm.

As the invasion progresses and hosts are depleted, mortality rates could slow, but, for ash to persist, it is critical that sufficient numbers of trees reach reproductive age before succumbing to residual EAB populations.

Other factors that might influence ash include competition with trees in other genera. The biocontrol agents now becoming established in young ash forests might increase the likelihood of ash persistence. Still, seed production and seedling survival will need to be frequent and widespread if they are to offset expected mortality. Resilience might also vary depending on individual species’ vulnerability to changes in the climate and to EAB (green and black ash are more vulnerable than white ash).

SOURCE

Ward, S.F., A.M. Liebhold, R.S. Morin, S. Fei. 2021. Population dynamics of ash across the eastern USA following invasion by emerald ash borer. Forest Ecology and Management 479 (2021) 118574

Posted by Faith Campbell

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

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

Hope for eastern hemlocks – IF funding can be obtained

eastern hemlocks in Great Smoky Mountains National Park

As we all know, eastern (Tsuga canadensis) and Carolina (T. caroliniana) hemlocks have suffered huge losses due primarily to the introduced hemlock woolly adelgid (Adelges tsugae – HWA). In New England, there has been more than a 60% decrease in total hemlock basal area since 1997 and a virtual absence of hemlock regeneration in HWA-infested areas. HWA continues to spread – most recently into western Michigan and Nova Scotia (all information, unless otherwise indicated, is from Kinahan et al. 2020; full citation at end of this blog). [However, Morin and Liebhold (2015) found that hemlock basal volume continued to increase for the first 20 years or so after invasion by the adelgid, due to ingrowth of immature hemlocks. See “results” in Morin et al., full citation at the end of the blog.]

This loss deprives us of a gorgeous tree … and unique habitats. Hemlock-dominated forests were characterized by deep shade, acidic and slowly decomposing soil, and a cool microclimate. They provided unique and critical habitat for many terrestrial and aquatic species.

A team of scientists based at the University of Rhode Island has carried out an experiment comparing cuttings from eastern hemlocks apparently resistant to HWA to susceptible ones. Matching sets of resistant and susceptible trees were planted at eight sites in seven states – Ithaca and Bronx, NY; Boston; southern CT; Lycoming County, PA; Thurmont, MD; southern WV; and Waynesville, NC. All plantings were within or adjacent to forests containing HWA-infested hemlocks.

After four years, 96% of the HWA-resistant hemlocks had survived, compared to 48% of the control plants. The HWA-resistant plants were 32% taller, put out 18% more lateral growth, had 20% longer drip lines, and were in 58% better condition. HWA was found on trees at only three out of the eight plots. HWA density on resistant eastern hemlocks was 35% lower than on HWA-susceptible hemlocks, although this difference was not statistically significant.

Trees in all eight plots were infested with elongate hemlock scale (Fiorinia externa – EHS), a second insect damaging hemlocks in eastern North America. However, the HWA-resistant hemlocks had EHS densities 60% lower than those of the controls.

Kinahan et al. note that identification and use of host tree populations’ potential for pest resistance has played a role in other programs managing non-native pests and pathogens, including Dutch elm disease and chestnut blight.  

The same scientists note that significant effort has been put into biocontrol or insecticides for management of hemlock woolly adelgid, but without achieving the desired improvement of forest health. Attempts to cross eastern hemlocks with HWA-resistant hemlocks unfortunately produced no viable offspring. However, Kinahan et al. were inspired to explore possible genetic resistance within natural populations of eastern hemlocks by the 1) evidence of resistance in Asian and western hemlocks; 2) the different foliar terpene profiles in those species; and 3) the presence of apparently healthy mature hemlock trees growing in proximity to heavily infested trees.

They asked forest managers and other concerned groups to help locate stands with trees that were mature and apparently completely healthy, were located within HWA-devastated hemlock stands, and had not been chemically treated. They chose a small stand of eastern hemlocks growing within the Walpack Fish and Wildlife Management Area in northern New Jersey. This stand was called the “Bulletproof Stand”. They evaluated HWA resistance in five of these trees, then chose two for propagation and planting in the test.

New Jersey’s “bullet-proof stand” on the left
photo by Richard Casagrande

The trees were planted in September 2015. Due to funding gaps, they were not revisited for four years. Thus, Kinahan et al. re-evaluated the resistant and vulnerable trees in Autumn 2019 – with the results I reported above.

Does this study prove that clonal propagation of apparently resistant hemlocks is an effective strategy to restore the species?

It is not that simple.

The difference in survival and condition was striking, but the authors note several caveats:

1) they had not recorded pre-experiment data on plant height or other variables, so they cannot be certain that variation in initial plant height or dripline did not contribute to current treatment-level differences in these variables.

2) they cannot distinguish between the impacts of HWA and EHS on plant growth.

3) since they could not monitor the planting sites for four years, they cannot definitively link increased mortality of HWA-susceptible trees to higher pest densities. However, the lower pest densities and higher survival of HWA-resistant hemlocks are consistent with herbivore-driven tree mortality.

They also cannot assess the impact of other environmental stressors (drought, cold, etc.) on their results.

4) The small number of trees planted at each site prevented detailed site-level analyses.

The scientists conclude that their work is most appropriately viewed as a ‘proof of concept’ experiment highlighting the need for future research exploring how HWA-resistant eastern hemlocks might best be integrated into existing HWA management.

Unfortunately, the Rhode Island researchers report they cannot persuade the US Forest Service to support continuing this effort. Will these promising hints not result in action?

Kinahan et al. stress the importance of the reduced pest densities (both HWA and EHS) on the putatively resistant hemlocks. They think this might be a result of the higher terpene concentrations in the twigs and needles. Finally, they note that lower densities of sap-feeding herbivores may also indirectly provide protection against other consumers, including gypsy moth (Lymantria dispar) and hemlock looper (Lambdina fiscellaria).

SOURCE

Kinahan, I.G., G. Grandstaff, A. Russell, C.M. Rigsby, R.A. Casagrande, and E. L. Preisser. 2020. A four-year, seven-state reforestation trial with eastern hemlocks (Tsuga canadensis) resistant to hemlock woolly adelgid (Adelges tsugae). Forests 11: 312

Morin, R.S. and A.M. Liebhold. 2015. Invasions by two non-native insects alter regional forest species composition and successional trajectories. Forest Ecology and Management 341 (2015).

Posted by Faith Campbell

P.S. I have been working with colleagues to promote a more coordinated and well-funded program to combat non-native forest pests – including much greater reliance on identifying and breeding resistance to the pest. Visit here to see this effort.

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.

New Study: Non-Native Pests Threaten 2/5ths of 48 States’ Forest Biomass

redbay in Georgia killed by laurel wilt
photo by Scott Cameron

In August I posted a blog summarizing information on pest introductions and impacts gleaned over my nearly 30 years of engagement. Already, I need to post an update, with an alarming estimate of introduced pests’ impacts across the continent.

Fei et al. 2019 (see the full citation is at the end of this blog) estimate that the 15 most damaging introduced species threaten 41.1% of the total live forest biomass in the 48 conterminous states.

In fact, this might be an underestimate of the pests’ impacts on biomass loss. Fei et al. (2019) note several limitations in their data that might result in such an underestimate. These include:

1) Mortality rates – and impacts – may increase over several decades following the initial invasion.

2) For pests already established throughout nearly all their potential ranges, pest-induced biomass loss could be substantially underestimated because most of their hosts died long ago, before the FIA data began to be collected. Consequently, the actual loss of these tree species from the forest is much greater than has been measured by the study’s methods.

3) Mortality rates vary among species and regions, which might introduce errors. They cite European gypsy moth, in which relatively small areas of heightened mortality due to repeated defoliations are swamped by lower mortality rates across the chosen measurement area. 

4) They considered only tree mortality, not crown or root dieback or reductions in tree growth.

5) They did not estimate carbon release to the forest floor as a result of defoliation.

6) Pest-related mortality rates may be underestimated due to salvage – although the authors did not observe evidence of substantial salvage efforts for most of these pests.

7) The data did not include losses from urban tree mortality.

Fei et al. estimate that more than 450 pests are established in the 48 conterminous states. This study excluded pests attacking palms; trees on U.S. Pacific and Caribbean islands; and pests native to portions of North America that are causing severe damage in naïve hosts – e.g., goldspotted oak borer. I did include the latter groups in my slightly larger estimate laid out in my August blog.

Fei et al. base their analysis on 83 of the introduced pest species considered to cause substantial effects on tree health and productivity and sometimes extensive tree mortality. (In my August blog, I described findings by another study by Guo et al (2019) that counted 91 species in that category.)

Fei et al. build on studies by a group of USDA Forest Service (USFS) scientists that I described in an earlier blog.

This team found that, nation-wide, non-native forest pests are causing an approximate 5% increase in total annual mortality by tree volume. They based their studies on analysis of 92,978 long-term plots maintained by the USDA Forest Inventory and Analysis program.

As noted above, the article cannot capture the full range of mortality in species affected by pests introduced decades ago. Chestnut blight, white pine blister rust, Port-Orford-Cedar root disease, beech bark disease, butternut canker, dogwood anthracnose, and European gypsy moths had all killed millions of trees before the USFS forest inventory plots were established. Fei et al. do form a solid basis for measuring some of the current impacts and projecting future ones.

The focus of the new article is on the amount of carbon being transferred from live biomass to dead organic matter as a result of the increased mortality caused by the 15 species with the highest impacts. This is arguably a more quantifiable measure of pests’ impacts than others’ approaches.  Here, I focus more narrowly on the documentation of exacerbated mortality as measured by the loss of biomass. Added together, these 15 species have caused an additional (i.e., above background levels) tree mortality rate of 5.53 TgC per year [defined as terragrams of carbon]. This estimate of annual conversion of live biomass to dead wood is similar in magnitude to that attributed to fire (5.4 to 14.2 TgC per year) (Fei et al. 2019). Yet the fire threat gets much more attention – for both prevention and management.

It is important to remember that conversion of living biomass to dead wood does not result in an immediate release of carbon to the atmosphere. Atmospheric releases take place through decomposition which is both gradual and takes place at varying rates. Some of the carbon will remain in the soil. And, over time, some of the carbon storage capacity will be restored by compensatory growth in unaffected trees and the recruitment of new regeneration – although this faster growth is delayed by as much as two or more decades after pest invasions begin (Fei et al. 2019).

American elm being killed by “Dutch” elm disease
photo by Cheryl Kaiser, University of Kentucky; bugwood.org

The 15 species of introduced pests used in this analysis are laurel wilt disease, chestnut blight, butternut canker, dogwood anthracnose, emerald ash borer (EAB), Dutch elm disease, red pine scale, beech bark disease, hemlock woolly adelgid, balsam woolly adelgid, European gypsy moth, white pine blister rust, green spruce aphid, sudden oak death, and Port-Orford cedar root disease. Of these, the highest elevation in biomass loss – as measured by FIA plot data – was caused by EAB, Dutch elm disease, beech bark disease, and hemlock woolly adelgid. We know that elms and beech, at least, began dying decades before the FIA data began to be collected. So the reported mortality rates are an underestimate. This is especially true because beech mortality is highest in the first decade after invasion by beech bark disease.

Annual levels of biomass loss are virtually certain to increase. First, pests will spread to new host ranges and infestations in already-invaded ranges will intensify. As a result, substantial amounts of the hosts’ biomass are at risk of exacerbated mortality. As I noted at the top of the blog, the total amount of host biomass at risk from these 15 species is estimated to be 5,197 TgC – or 41.1% of the total live forest biomass in the 48 conterminous states. Further exacerbating future losses is the likelihood that additional pests will be introduced. I would add that pests not included in this analysis – e.g., polyphagous and Kuroshio shot hole borers and possibly the spotted lanternfly – are also likely to contribute to losses of live forest biomass.

Fei et al. (2019) did not attempt to determine the economic value of this biomass loss or to address other types of losses to ecosystem services.

Remember that a separate set of studies reported by Potter et al. (2019) (the CAPTURE project) also relied on data from the FIA plots to evaluate the impact of introduced pests. These studies focused on identifying the host species at greatest risk rather than highest-impact pests or biomass loss. I find it reassuring that the Fei and Potter studies – using different approaches – resulted in very similar species rankings. See my discussion of the Potter studies here.

Together, the teams led by Potter and Fei set clear priorities for addressing the threats from non-native pests. What we need now is action! See my recommendations in my recent “solutions” blog.

U.S. Capitol – inform your representatives that you want action to protect trees!

SOURCES

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

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)

Solutions Suggested by 30 Years’ Work

Faith Campbell receives award for activism from National Association of State Foresters; 2016

For nearly 30 years I have documented bioinvasion threats and gaps, first in three Fading Forests reports (available here), then in five years of blogging. Here I pull together that information and suggest — in most cases reiterate — steps to address these threats and gaps. I list sources of discussion of the underlying issues – other than my reports and blogs – in references at the end of this blog.

My first premise is: robust federal leadership is crucial:

  1. The Constitution gives primacy to federal agencies in managing imports and interstate trade.
  2. Only a consistent approach can protect trees (and other plants) from non-native pests.
  3. Federal agencies have more resources than state agencies individually or in any likely collective effort — despite decades of budget and staffing cuts.

My second premise is: success depends on a continuing, long-term effort founded on institutional and financial commitments commensurate with the scale of the threat. This requires stable funding; guidance by research and expert staff; and engagement by non-governmental players and stakeholders. Unfortunately, as I discuss below, funding has not been adequate or stable.

My third premise is that programs’ effectiveness needs to be measured, not just effort (see the NECIS document referenced at the end of the blog).

SPECIFICS 

Preventing new introductions continues to be the most effective action. Mitigating options decrease and damages increase once a non-native pest has entered the country – much less become established (see Lovett et al. 2016 and Roy et al. 2014). I recognize that preventing new introductions poses an extremely difficult challenge given the volume and speed of international trade and the strong economic forces supporting free trade. These challenges have been exacerbated over several decades by the political zeitgeist – the anti-regulatory ideology, the emphasis on “collaborating” with “clients” rather than imposing requirements through regulations. Although the current “America First” policy might reduce import volumes and therefore reduce the invasive species threat to some extent, the anti-regulatory stance has only strengthened.

containers at the Port of Long Beach, California

Decades of cutting key agencies’ budgets and personnel are another factor. However, the damage to America’s natural systems is so great that we must try harder to find more effective strategies (See the Fading Forest reports; my previous blogs; Lovett et al. 2016; and APHIS annual reports – e.g., the 2019 report here)

Prevention

  1. Despite adoption and implementation of new international and national regulations to stem pest introductions, introductions continue – although probably at a lower level than would otherwise be the case. Delays in adoption of regulations (documented in Fading Forests II and III and my two recent 30-years-in-review blogs have facilitated damaging introductions and spread.

Solutions 

  1. Stakeholders press USDA leadership to initiate rules intended to strengthen phytosanitary protection and expedite their completion
  2. APHIS promote and facilitate analysis of current programs and policies by non-agency experts to ensure the agency is applying most effective strategies (Lovett et al. 2016).
  • Adoption of insufficiently protective regulations (documented in FFII, FFIII, two 30-years-in-review blogs) – adopted in part because APHIS is trying to “balance” trade facilitation and phytosanitary protection – has further contributed to damaging pests’ introduction and spread.

Solutions:

  1. Boost priority of preventing pest introductions by amending the Congressional finding in the Plant Protection Act [7 USC 7701(3)] as follows

Existing language: “[I]t is the responsibility of the Secretary [of Agriculture] to facilitate exports, imports and interstate commerce in . . . commodities that pose a risk of harboring plant pests or noxious weeds in ways that will reduce, to the extent practicable, as determined by the Secretary, the risk of dissemination of plant pests and noxious weeds .… “

Amend to read as follows: “…. in ways that will reduce prevent, to the greatest extent practicable feasible, as determined by the Secretary, …” [emphasis added]

  • Adopt several actions to strengthen phytosanitary protections at the point of origin (Lovett et al. 2016)
  • Expand pre-clearance partnerships — as authorized for plants under Q-37 regulations and ISPM-36
  • Expand sentinel tree programs
  • Promote voluntary substitution of packaging made from materials other than solid wood.
  • APHIS doesn’t use the enforcement powers that it has under Plant Protection Act (see several of my past blogs)

Solutions:

CBP inspectors search for pests in a pallet; CBP photo
  1. APHIS follow the lead of Customs and Border Protection and begin penalizing importers on the first instance of their wood packaging not being in compliance with ISPM#15 (see blog here).
  2. APHIS prohibit use of wood packaging by countries and importers of categories of imports that – over the 13 years since implementation – have developed a record of frequent violations of ISPM#15.
  3. APHIS use its authority per revised Q-37 regulations to negotiate with countries that export plants to the U.S. to establish “integrated measures” programs aimed at minimizing the risk of associated pests being transported to the U.S.
  4. APHIS use its authority per revised Q-37 to place in the “Not Authorized for Import Pending Pest Risk Assessment (NAPPRA) “limbo” category genera containing North American “woody” plants  (see Roy et al. 2014; Lovett et al. 2016).

Spread within the U.S.

  1. The United States lacks a coordinated system to prevent pest spread within the country (see Fading Forests III Chapter 5). Even our strictest methods, like APHIS’s quarantines regulating interstate movement of goods, have failed to curtail spread of significant pests. The most obvious example is the emerald ash borer.

The regulations governing movement of the sudden oak death pathogen in the nursery trade have also failed: there have been periodic outbreaks in which the pathogen has been spread to nurseries across the country. Between 2003 and 2011, a total of 464 nurseries located in 27 states tested positive for the pathogen, the majority as a result of shipments traced from infested wholesalers. In 2019, plants exposed to the pathogen were again shipped to 18 states; eight of those states have confirmed that their plant retailers received infected plants (see my blog from summer here).

Another serious gap is the frequent failure of APHIS and states to adopt official programs targetting bioinvaders that will be difficult to control because of biological characteristics or cryptic natures – even when severe impacts are demonstrated. Recent examples include the laurel wilt disease complex, goldspotted oak borer, polyphagous and Kuroshio shot hole borers and associated pathogens, and even the spotted lanternfly (although the last has received significant funds from APHIS.)

redbay killed by laurel wilt disease, Georgia; photo by Scott Cameron

Solutions:

  1. APHIS apply much more stringent regulations to interstate movement, based on a heightened priority for prevention in contrast to facilitating interstate trade. E.g., prohibit nurseries on the West Coast from shipping P. ramorum hosts to states where the pathogen is not established.
  2. APHIS encourage states to adopt quarantines and regulations aimed at preventing spread of invasive pests to regions of the state that are not yet infested. For example, the sudden oak death pathogen in California and Oregon; the borers in southern California.
  3. APHIS abandon plans to deregulate emerald ash borer and step up its support for state  regulations on firewood.
  4. APHIS stop dumping pests it no longer wants to regulate onto the states through the “Federally Recognized State Manage Phytosanitary (FRSMP) program”.
  5. APHIS revise its policies so that the “special needs exemption” [7 U.S.C. 7756] actually allows states to adopt more stringent regulations to prevent introduction of APHIS-designated quarantine pests (see Fading Forests III Chapter 3).

To help fill the gaps, the states are trying to coordinate their regulations in some important areas. The most advanced example is the voluntary Systems Approach to Nursery Certification, or SANC program. APHIS has supported this initiative, including by funding from the Plant Pest and Disease Management and Disaster Program (see below). However, it is a slow process; USDA funds first became available in 2010. The states are trying to coordinate on firewood, but we don’t yet know what the process will be.

  • Funding shortfalls (See the three Fading Forests reports, my blogs about appropriations)
  • Increase APHIS’ access to emergency funds from the Commodity Credit Corporation by  amending the Plant Protection Act [7 U.S.C. 7772 (a)] to include this new definition of “emergency”:

the term “emergency” means any outbreak of a plant pest or noxious weed which directly or indirectly threatens any segment of the agricultural production of the United States and for which the then available appropriated funds are determined by the Secretary to be insufficient to timely achieve the arrest, control, eradication, or prevention of the spread of such plant pest or noxious weed.

  • Although APHIS has the most robust prevention program of any federal agency, its funding is still inadequate. Stakeholders should lobby the Congress in support of higher annual appropriations.

The Plant Pest and Disease Management and Disaster Program (now under Section 7721 of the Plant Protection Act) has provided at least $77 million for tree-pest programs (excluding NORS-DUC & sentinel plant programs and other programs) since FY 2008. Much useful work has been carried out with these funds. However, these short-term grants cannot substitute for stable, long-term funding. I reiterate my call for stakeholders to lobby the Congress to provide larger appropriations to the APHIS Plant Protection program and Forest Service Forest Health Protection and Research programs.

Long-term Responses to Bioinvasive Challenge

More stakeholders are advocating raising the priority of – and providing adequate resources to – such long-term solutions as biocontrol and breeding trees resistant to pests and restoring them to our forests. Advocates include the state forestry agencies of the Northeast and Midwest, some non-governmental organizations, some academics, and individual USFS scientists. One effort resulted in inclusion of language in the 2018 Farm Bill (see blog here) – although this approach has apparently run into a dead end. The new emphasis on breeding has so far not been supported by agency or Congressional leaderships.

test planting of an American chestnut bred to be resistant to chestnut blight

Solutions:

  1. USFS convene workshop of the federal, state, National Academy, academic, and NGO groups promoting resistance breeding in order to develop consensus on priorities  and general structure of program.

Explicitly include evaluation of the CAPTURE Project’s (see blog here) efforts to set priorities to guide funding allocations and policies; and proposals for providing needed supportive infrastructure – facilities, trained staff in various disciplines. (See my blogs here.)

Report results of meeting to USDA leadership, Congress, and stakeholders

Then ensure implementation of the accepted approach by both Research and Development and Forest Health Protection programs. Include provisions to provide sustainable funding.

These proposed actions still do not address ways to correct the provisions of the international phytosanitary agreements (World Trade Organization and International Plant Protection Convention) that complicate – or preclude – efforts to prevent introduction of pests currently unknown to science. This  issue is discussed in Fading Forests II. A current example is beech leaf disease (described here).

Continuing inadequate engagement by stakeholders

Most constituencies that Americans expect to protect our forests don’t press decision-makers to fix the problems I have identified above: inadequate resources, weak and tardy phytosanitary measures. Some of these stakeholders are other federal agencies, or state agencies – or their staffs. They face restrictions on how “political” they can be. But where are the professional and scientific associations, representatives of the wood products industry, forest landowners, environmental NGOs and their funders, urban tree advocates Efforts by me, USDA, and others to better engage these groups have had disappointing results.

As I have documented, groups of USFS scientists have made several attempts to document the extent of invasive species threats and impacts and to set priorities. So far, they have not gained much traction. Another USFS attempt, Poland et al. in press, will appear at the end of the year. Will this be more successful?

I detect growing attention to educating citizen scientists for early detection; but if there is an inadequate – or no – official response to their efforts won’t people become discouraged?

SOURCES

Lovett, G.M., M. Weiss, A.M. Liebhold, T.P. Holmes,  B. Leung, K.F. Lambert, D.A. Orwig, F.T. Campbell, J. Rosenthal, D.G. McCullough, R. Wildova, M.P. Ayres, C.D. Canham, D.R. Foster, SL. Ladeau, and T. Weldy. 2016. NIS forest insects and pathogens in the US: Impacts and policy options. Ecological Applications, 26(5), 2016, pp. 1437–1455

National Environmental Coalition on Invasive Species “Tackling the Challenge.”

Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector.  Springer Verlag. (in press).

Roy, B.A., H.M Alexander, J. Davidson, F.T Campbell, J.J Burdon, R. Sniezko, and C. Brasier. 2014. Increasing forest loss worldwide from P&Ps requires new trade regulations. Front Ecol Environ 2014; 12(8): 457–465

30 years of Analyzing Forest Pest Issues

dead whitebark pine in Crater Lake National Park
photo by F.T. Campbell

I began studying and writing about the threat to North America’s forests from non-native insects and pathogens in the early 1990s – nearly 30 years ago. I reported my analyses of the evolving threat in the three “Fading Forests” reports – coauthored by Scott Schlarbaum – in 1994, 2003, and 2014. These reports are available here.

So what has changed over those 30 years? What remains the same? Why have both the changes and the stasis occurred? What can we do to fix the gaps, close unaddressed pathways, strengthen flabby policies? I will address these issues in this and following blogs.

experimental American chestnut planted in Fairfax County, VA
photo by F.T. Campbell

What has changed since the early 1990s:

  • Adoption and implementation of significant new international and national regulations and programs aimed at preventing introductions of non-native invasive species.
  • Despite the welter of new regulations, an alarming increase in numbers of highly damaging forest pests established in the country.  (By my count, about 50 new species have established on the continent, six on Pacific islands; see details below.)
  • Alarming spread of established pests to new geographic regions and new hosts (e.g., emerald ash borer in 35 states and 5 provinces; laurel wilt disease across the range of redbay and swamp bay; rapid ‘ōhi‘a death on three of the main Hawaiian islands).
  • Introductions via unexpected pathways and vectors far removed from phytosanitary agencies’ usual targets, e.g., ship superstructures, imported steel and stone …

What has remained the same since the early 1990s:

  • Inadequate resources provided to response and recovery efforts.
  • Available funding focused on only a few of the more than 90 species causing damage.
  • Adoption of insufficiently protective regulations that have failed to prevent introduction and spread of tree-killing pests.
  • Lengthy delays in implementing programs that tighten controls – another factor in continuing introductions and spread.
  • Continued importance of expected pathways – nursery stock and raw wood, especially crates, pallets, and other forms of wood packaging.
  • Federal and state agencies still choose not to take action on pests e.g., goldspotted oak borer, polyphagous and Kuroshio shothole borers, beech leaf disease.
  • Inadequate coordination despite several efforts to set priorities.
  • Spurts of attention by media and political decision-makers, contrasted by lengthy periods of inattention.
  • Failure of most stakeholders to support efforts to prevent and respond to introductions of tree-killing pests. 

Details: The Situations Then and Now

(Many of the individual species mentioned here are described more fully here.  Full citations of sources are at the end of blog.)

American elm on the National Mall, Washington, D.C.

photo by USDA Agricultural Research Service

In 1993:

  • The number of non-native forest pest species established in the U.S. was estimated at between 300 (Millers et al. 1993) and 380 (Mattson et al., 1994; Liebhold et al., 1995) .
  • The area suffering the greatest numbers and impacts was the Northeast.
  • Several highly damaging pests that had been established for decades, including chestnut blight, white pine blister rust, Port-Orford-cedar root disease, Dutch elm disease, hemlock woolly adelgid, butternut canker, and dogwood anthracnose were receiving some attention but continued to spread.
  • USDA Forest Service funding for management of exotic pest infestations was crisis-oriented, with “… priorities … set under political pressures for immediate answers, with too much regard for short-term problems and too little consideration for broader management objectives.” (NAS 1975)
  • Since few high-profile pests had been introduced in recent years, APHIS was not actively engaged. In FY92, APHIS spent $20 million on efforts to eradicate the Asian gypsy moth. The narrow focus is illustrated by the fact that in FY93, more than two-thirds of all USDA tree pest control funds were devoted to efforts to suppress or eradicate the European gypsy moth (See FFI).
  • Concern about possible new introductions had grown; it focused on proposals to import unprocessed wood from Siberia, New Zealand, and Chile. The USDA Forest Service, academic scientists, and therefore APHIS emphasized the risks of known Asian pests, e.g., Asian gypsy moth, to western coniferous forests (See FFI). While individual scientists had expressed concern about wood packaging material, there was little public discussion of this threat.
  • We would learn later that several of the most damaging pests were already present in the country but not yet recognized – Asian longhorned beetle, sudden oak death pathogen, probably emerald ash borer.

beech leaf disease

photo by John Pogacnik

In 2019:

  • Numbers of non-native insects and pathogens attacking trees in North America approach 500 species.  (In Fading Forests III, I calculated that by the first decade of the 21st Century, the number had risen to at least 475. Several more have been detected since 2014. More than 181 exotic insects that feed on woody plants had established in Canada. (Source: USDA APHIS. 2000. Wood packaging risk assessment.)
  • Of these, 91 are considered “serious” threats (Guo et al. 2019). This estimate excludes pests native to portions of North America that are causing severe damage in naïve hosts – e.g., goldspotted oak borer; pests of palms; and pests attacking trees on U.S. Pacific and Caribbean islands.
  • Introductions had continued.
    • Between 1980 and 2016, at least 30 non-native species of wood- or bark-boring insects (Scolytinae / Scolytidae) were newly detected in the U.S. (Haack and Rabaglia 2013; Rabaglia et al.  2019). A few of these are highly damaging, e.g. redbay ambrosia beetle, polyphagous and Kuroshio shothole borers.
    • In addition to these 30 new pests, other highly damaging tree-killing pests probably introduced since the 1980s include (on the continent):
      • Eight Cerambycids such as Asian longhorned beetle (Wu et al. 2017)
      • 7 Agrilus, including emerald ash borer and soapberry borer; plus goldspotted oak borer transported from Arizona to California (Digirolomo et al. 2019; R. Haack, pers. comm.)
      • Sirex woodwasp
      • Pests of palm trees, e.g., red palm mite, red palm weevil, South American palm weevil
      • Spotted lanternfly
      • Beech leaf disease
    • Also not included in the above estimate and lists are tree-killing pests on America’s Pacific Islands :
      • ‘ōhi‘a rust
      • Cycad scale
      • Cycad blue betterfly
      • Erythrina gall wasp
      • two Ceratocystis pathogens that cause rapid ‘ōhi‘a death
      • Coconut rhinoceros beetle
    • Authorities also carried out approximately 25 eradication programs targetting introductions of the Asian gypsy moth (USDA Pest Alert Asian Gypsy Moth plus additional outbreaks since 2014).
  • Impacts of exacerbated tree mortality rates linked to these introduced pests are seen across wide swaths of the country, and affect widespread species, genera, and families. 
dead redbay in Claxton, Georgia
photo by Scott Cameron

I will discuss the risk of continuing new introductions in a separate blog.

Trying to Develop the Big Picture and Set Priorities

In recent years, USDA Forest Service scientists have made several attempts to provide nation-wide assessments of the impact of these pests and criteria for establishing priorities.

The National Insect and Disease Forest Risk Assessment predicted the loss of basal area to various pests over the 15-year time period 2012 – 2027. The assessment predicted the following losses for specific species: 90% for redbay; 60% for whitebark pine; more than 40% for limber pine; 24% for tanoak; 11% for coast live oak; 6% for eastern and Carolina hemlock; 27% for eight species of ash; 20% for American elm; 19% for red oak; 18% for American beech (Krist et al. 2014).

A separate group of scientists found that, nation-wide, non-native forest pests are causing an approximate 5% increase in total mortality by tree volume (Randy Morin at NEFPC). For details on Dr. Morin’s findings, see my blog here.

A third approach to developing a nation-wide picture, Project CAPTURE, (and my blog here) utilized FIA data to develop priorities for conservation action. Fifteen species were placed in the highest priority category, including Florida torreya (Torreya taxifolia), American chestnut and Allegheny and Ozark chinquapins, redbay, five species of ash, two species of hemlock, Port-Orford cedar, tanoak, and butternut (Potter et al. 2019(b).

According to Project CAPTURE, the non-native pests affecting the largest number of hosts are the European gypsy moth, which attacks 65 hosts; and oak wilt (Bretziella fagacearum), which infects 61 hosts. The Asian longhorned beetle attacks 43 hosts (Potter et al. 2019(b).

I note that several other non-native pests also have high numbers of host species. In the Project CAPTURE study, these pests are ranked lower because the project limited its evaluation to the five agents with the greatest effect on any particular host. Thus, of the 18 native tree species that host one or both of the invasive shothole borers and associated Fusarium disease complex (PSHB website), the project included only six. Of the 22 tree species listed by APHIS as hosts of Phytophtora ramorum, the project included 12 (K. Potter, pers. comm. April 17, 2019).

SOD-killed tanoak on the Big Sur peninsula, California
photo by Matteo Garbelotto, University of California Berkeley

More extensive discussions of non-native pests’ impacts are provided in Lovett et al. 2006, Lovett et al. 2016, and Potter et al. 2019. A book-length discussion of invasive species impacts – ranging from feral hogs to invasive plants, is expected in December; look for Poland et al. (in press).

SOURCES

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

Digirolomo, M.F., E. Jendek, V.V. Grebennikov, O. Nakladal. 2019. First North American record of an unnamed West Palaearctic Agrilus (Coleoptera: Buprestidae) infesting European beech (Fagus sylvatica) in New York City, USA. European Journal of Entomology. Eur. J. Entomol. 116: 244-252, 2019

Guo, Q., S. Fei, K.M. Potter, A.M. Liebhold, and J. Wenf. 2019. Tree diversity regulates forest pest invasion. Proceedings of the National Academy of Sciences of the United States of America. www.pnas.org/cgi/doi/10.1073/pnas.1821039116

Haack, R.A. and R.J. Rabaglia. 2013. Exotic Bark and Ambrosia Beetles in the USA: Potential and Current Invaders. CAB International 2013. Potential Invasive Pests of Agricultural Crops (ed. J. Peña) 

Krist, F.J. Jr., J.R. Ellenwood, M.E. Woods, A. J. McMahan, J.P. Cowardin, D.E. Ryerson, F.J. Sapio, M.O. Zweifler, S.A. Romero 2014. National Insect and Disease Forest Risk Assessment. United States Department of Agriculture Forest Service Forest Health Technology Enterprise Team FHTET-14-01

Leung, B., M.R. Springborn, J.A. Turner, E.G. Brockerhoff. 2014. Pathway-level risk analysis: the net present value of an invasive species policy in the US. The Ecological Society of America. Frontiers of Ecology.org

Liebhold, A. M., W. L. MacDonald, D. Bergdahl, and V. C. Mastro.  1995.  Invasion by exotic forest pests:  a threat to forest ecosystems.  Forest Sci., Monograph 30. 49 pp.

Lovett, G.M., C.D. Canham, M.A. Arthur, K.C. Weathers, and R.D. Fitzhugh. Forest Ecosystem Responses to Exotic Pests and Pathogens in Eastern North America. BioScience Vol. 56 No. 5 (May 2006)

Lovett, G.M., M. Weiss, A.M. Liebhold, T.P. Holmes,  B. Leung, K.F. Lambert, D.A. Orwig, F.T. Campbell, J. Rosenthal, D.G. McCullough, R. Wildova, M.P. Ayres, C.D. Canham, D.R. Foster, SL. Ladeau, and T. Weldy. 2016. NIS forest insects and pathogens in the US: Impacts and policy options. Ecological Applications, 26(5), 2016, pp. 1437–1455

Mattson, W. J., P. Niemela, I. Millers, and Y. Ingauazo.  1994. Immigrant phytophagous insects on woody plants in the United States and Canada: an annotated list.  USDA For. Ser. Gen. Tech. Rep. NC-169, 27 pp.

Millers, I. United States Department of Agriculture, Forest Service Entomologist, Forest Health Protection Northeastern Area State and Private Forestry. Durham, NH. Personal communication to F.T. Campbell, 1993.

Morin, R. presentation at Northeastern Forest Pest Council 81st Annual Meeting, March 12 – 14, 2019,  West Chester, Pennsylvania

National Academy of Sciences. 1975. Forest Pest Control. Washington, D.C.

Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector.  Springer Verlag. (in press).

Polyphagous shothole borer website https://ucanr.edu/sites/pshb/overview/About_PSHB/

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

Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S. 2019. Prioritizing the conservation needs of US tree spp: Evaluating vulnerability to forest insect and disease threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/

Rabaglia, R.J., A.I. Cognato, E. R. Hoebeke, C.W. Johnson, J.R. LaBonte, M.E. Carter, and J.J. Vlach. 2019. Early Detection and Rapid Response. A Ten-Year Summary of the USDA Forest Service Program of Surveillance for Non-Native Bark and Ambrosia Beetles. American Entomologist Volume 65, Number 1 

USDA, Animal and Plant Health Inspection Service. 2014. Asian gypsy moth pest alert https://www.aphis.usda.gov/publications/plant_health/content/printable_version/fs_phasiangm.pdf and pers. comm.

U.S. Department of Agriculture, Animal and Plant Health Inspection Service.  2009.  Risk analysis for the movement of wood packaging material (WPM) from Canada into the US.

Wu,Y., N.F. Trepanowski, J.J. Molongoski, P.F. Reagel, S.W. Lingafelter, H. Nadel1, S.W. Myers & A.M. Ray. 2017. Identification of wood-boring beetles (Cerambycidae and Buprestidae) intercepted in trade-associated solid wood packaging material using DNA barcoding and morphology  Scientific Reports 7:40316

Restoring Devastated Tree Species: Let’s Get Behind H.R. 5519

Port-Orford cedar resistance trials

USFS Dorena Genetic Resource Center

 

In January I wrote about possible changes to the 2018 Farm Bill aimed at restoring tree species devastated by non-native insects and diseases. (Earlier, in July 2017, I had blogged about these and other proposed amendments to the Farm Bill. Here’s an update.

 

The House Committee on Agriculture has completed action on its version of the Farm Bill; it now awaits action by the full House. The House bill (H.R. 2) does not contain any of the proposals put forward by the Center for Invasive Species Prevention to improve both “rapid response” to introduced forest pests or long-term efforts to restore species devastated by such pests. It does contain very controversial provisions weakening the Endangered Species Act, National Environmental Protection Act, and Federal Insecticide, Fungicide and Rodenticide Act. The bill also makes major changes to the food stamp program. Most political analysists do not think the bill will become law in its current form.

 

We do not yet know what provisions will be in the Senate’s version of the Farm Bill. I am still hopeful that our proposals might be included in some form.

 

Rep. Peter Welch

Meanwhile, Representative Peter Welch from Vermont has introduced a separate House bill:  H.R. 5519. It would amend the Plant Protection Act in order to increase funding for both APHIS-led programs to eradicate or contain invasive species and for competitive grants to research specific questions related to the recovery of pest-decimated native tree species.

 

Specifically, Mr. Welch’s Invasive Species Prevention and Forest Restoration Act would:

  • Strengthen the USDA Secretary’s authority to access Commodity Credit Corporation funds to supplement appropriations to counter non-native insects and pathogens and noxious weeds that threaten agricultural production (including forest resources).
  • Create a competitive grant program to address the critical threat to numerous tree species posed by non-native plant pests and noxious weeds. The grants would provide up to $100,000 per year, over two to five years, to support research that promotes the restoration of affected tree species, including research on—

(A) biological control of plant pests or noxious weeds;

(B) exploration of genetic manipulation of plant pests or noxious weeds;

(C) enhancement of host-resistance mechanisms; and

(D) development of other strategies for restoring tree species.

These studies must be part of comprehensive forest restoration research.

The research institutions are to disseminate to the public tools and information based on the research conducted under this program.

 

Institutions eligible for funding under this program include:

(1) An agency of the Federal Government.

(2) A State cooperative institution.

(3) A college or university offering a baccalaureate or higher degree in the study of food, forestry, and agricultural sciences.

(4) A nonprofit entity described in § 501(c)(3) of IRS Code.

 

A committee of government experts would advise the Secretary of Agriculture on applying the funding criteria for the grant program. This committee would be composed of representatives of the USDA Forest Service, APHIS, and Agriculture Research Service; and State forestry agencies. This committee of experts would receive advice from a separate advisory committee composed of representatives of land-grant colleges and universities, affiliated State agriculture experiment stations, the forest products industry, recreationists, and conservation organizations.

 

Funds from the Commodity Credit Corporation (not subject to annual appropriations) are made available, beginning at $3 million in Fiscal Year 2019 and rising to $10 million in FY 2022.

 

Please ask your Representative to co-sponsor this bill. Also, ask your Senators to consider sponsoring a similar bill in the Senate (assuming that no such provisions are included in the Senate Farm Bill).

If these proposals are not included in the version of the Farm Bill that is adopted this year, there might be new opportunities to advance resistance breeding and similar programs in the future.  As I noted in the March blog, a growing number of scientists and concerned stakeholders have developed proposals to expand resistance breeding programs. I hope that the several groups can coordinate their efforts and recruit supporters for a lobbying effort that will create a coordinated program to restore native trees devastated by non-native insects and diseases.

 

Posted by Faith Campbell

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