The Washington Post has summarized data on the number of container ships travelling from China to U.S. west coast ports for the first half of 2025. It compares those numbers to the same period in 2024.
For the first four months, the trips exceeded 2024 levels, often by considerable amounts, as importers sought to get their goods before President Trump imposed high tariffs. Thus, the number of container ships arriving at Los Angeles, Long Beach, Oakland, Seattle, and Tacoma during each month:
January: 17% increase
February: 32% increase
March: 14% increase
April: 5% increase
In May, landings from China decreased by 33%! Those ships arriving also carried fewer containers.
When measured by the value of imported goods, imports from China fell 20% nationwide when we compare April 2024 to April 2025. This decrease was seen at four of the five west coast ports; the exception was Tacoma.
When President Trump “paused” the 145% increase in tariffs on Chinese goods, the prices shippers charge for transporting containers doubled – from less than $3,000 per container to $6,000. This change probably portends a rebound in import volumes.
I always worry about containers from China (see Haack et al. 2022; full citation at the end of this blog; and this blog). For more than 30 years they have too often been the means by which wood-boring insects are introduced to North American forests. I fret even more when import volumes are rising – especially when importers are in a rush. I suspect that neither exporters nor importers pay much attention to whether the crates and pallets have been treated properly.
ash tree killed by EAB — the risk of woodborers introduced in wood packaging; photo courtesy of John Hieftje, former mayor of Ann Arbor, Michigan
I have asked the Bureau of Customs and Border Protection for comment, but have not yet received a reply.
Please note that these data do not include information about imports from other Asian countries … or shipments destined for U.S. ports in the Gulf or Atlantic (via the expanded Panama Canal) or to Canadian ports.
SOURCE
Haack RA, Hardin JA, Caton BP and Petrice TR (2022) Wood borer detection rates on wood packaging materials entering the United States during different phases of ISPM#15 implementation and regulatory changes. Frontiers in Forests and Global Change 5:1069117. doi: 10.3389/ffgc.2022.1069117
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
In June I visited Shenandoah National Park (SHNP) (above) for the first time in years. The Park’s forests are mostly mature secondary forests, having recovered over the 90 years since establishment from earlier logging and clearing for small-scale farms and pasture.
While I loved the forest and the vistas, I was aware of which species are missing …
Five years ago I blogged about a study by Anderson-Teixeira et al. (full citation at the end of this blog) that reported on the changes in the forests of SHNP and the neighboring Smithsonian Conservation Biology Institute (SCBI). This is important because, as Fei et al. (2019) (full citation at the end of this blog) documented, nine of the 15 most damaging introduced forest pests grow in eastern forests. In fact, the greatest increase in biomass loss has occurred in Eastern forests. Seven are found specifically in SHNP (Potter et al. 2019; full citation at the end of the blog).
Anderson-Teixeira et al. report that non-native forest pests caused a loss of about a quarter of ecosystem above-ground biomass between 1991 and 2013 across 66 sites. These invasions occurred after the worst impacts of chestnut blight, which entered the country ~120 years ago – before “modern” phytosanitary programs were instituted. Still, total above-ground biomass has largely recovered through germination and growth by trees in other genera. Greatest increases have been by tulip poplar (Liriodendron); oaks (Quercus); ash (Fraxinus) – but see below; birch (Betula); and maples (Acer). And while several taxa were lost from monitoring plots in SHNP and SCBI, a-diversity also remained steady.
So what does that look like on the ground?
American chestnut used to dominate many Eastern forests, composing more than one-third of the pollen assemblage in some stands (Fei et al.) According to Anderson-Teixeira et al., chestnut trees larger than 10 cm DBH disappeared by 1910, killed by chestnut blight. In past decades I frequently saw chestnut root sprouts when hiking. The National Park Service now urges visitors to hike to low elevation sections of the South River Trail to see such sprouts.
In the 1980’s, groves of eastern hemlocks occupied about 9,800 acres in SHNP, primarily in shaded valleys and along streams. Invasion by the hemlock woolly adelgid killed 95% of these hemlocks. Anderson-Teixeira et al. document the species’ disappearance from their study plots by 2007. Park staff treated more than 20,000 hemlocks using injections of imidacloprid. In 2015, the Park began partnering with Virginia Polytechnic Institute and State University in releasing predatory biocontrol beetles (Laricobius spp.) While the beetles have shown promising establishment and spread, it is now recognized that additional biocontrol agents will be needed to suppress the adelgid. The Park plans to allow releases of predatory silver flies (Leucotaraxis spp.) in remaining hemlock sites and will begin to phase out the imidacloprid treatments.
I remember the hemlocks! But this year, at least in the creek valleys where I hiked, I saw almost no remnants – not even fallen logs.
fallen hemlock; all photos by F.T. Campbell in Shenandoah NP in June 2025
And I remember the flowering dogwoods. They are almost gone now from the Appalachian chain, killed by dogwood anthracnose. Their status in SHNP is unclear. Anderson-Teixeira et al. report flowering dogwoods only from the Smithsonian property. There, they declined by almost 90% from the study plots from 2008 to 2019. The Park’s list of tree and shrub species reports that flowering dogwood is still “abundant”; my visit was too late in the season to observe how visible flowering dogwoods still are. Certainly the species survives the disease better in open settings, e.g., meadows and roadsides. I don’t know how the three other native Cornus species were affected.
Dead ash are still visible. Ash trees made up about 5% of the Park’s forest cover. Anderson-Teixeira et al. report that ash aboveground biomass was increasing in SHNP and stable on the SBCI property before arrival of the emerald ash borer (EAB). EAB-caused mortality was first detected in 2016. In just three years — by 2019 – 28% of green, white, and black ash had died; this meant a loss of 30% of ashes’ aboveground biomass. Ninety-five percent of remaining live trees were described as “unhealthy’’. In an effort to retain ash trees for visitor enjoyment, reduce threats to visitors from hazard trees, and to preserve a portion of the park’s ash tree communities until host-specific biological controls become available, SHNP staff – supported by specially trained volunteers and interns, Virginia Department of Forestry and Fairfax County – began treating high-value ash with emamectin benzoate. They began at Loft Mountain Campground, a location (elevation 3,300 feet) where ash trees make up most of the forest. Three hundred forty three trees were treated there — exceeding expectations for what could be accomplished in a single year. The park hopes to treat an additional 200-400 trees. They will target ash trees around campgrounds, picnic areas, overlooks and other areas frequently used by visitors. These efforts were supported by the Shenandoah National Park Trust and here.
I saw many dead oaks – probably the result primarily of repeated attacks by the spongy moth link beginning in 1982. Oak-dominated study plots in SHNP lost on average 25% of individuals and 15% of above-ground biomass. After 1995, when spraying of Bacillus thuringiensis var. curstaki improved control efforts (at the expense of native moths), oak aboveground biomass increased gradually, driven by individual tree growth rather than recruitment. Oak abundance continues to decline due to oak decline and absence of management actions to promote regeneration (Anderson-Teixeira et al.). These authors do not mention oak wilt although a decade-old map shows the disease to be present just to the west of the Blue Ridge (visible here).
Fortunately Shenandoah National Park has relatively few American beech, so it will be less affected by beech leaf disease (BLD). The Blue Ridge is also far from large waterbodies — which promote the disease. However, I did see some beech sprouting in creek valleys – probably in gaps opened when the hemlocks died. These valleys with higher humidity are the type of ecosystem most conducive to the disease! Anderson-Teixeira et al. note that they did not analyze the impact of beech bark disease – which was the disease of concern before arrival of BLD and continues to be present.
They also did not evaluate the impacts of balsam woolly adelgid, described as having decimated high-elevation populations of firs (Abies balsamea); white pine blister rust on eastern white pine; or EAB on fringetree (Chionanthus virginicus) in SCBI. Nor did they document the impact of thousand cankers disease (TCD) on walnuts or butternuts. This concerns me because they report that the disease “appears to be affecting Juglans spp. in our plots.” Furthermore, butternut (J. cinera) had been ‘‘common’’ in 1939, but had disappeared from SHNP by 1987. On the Smithsonian property, the four individuals found originally had declined by half – to two living individuals. Butternut has suffered high levels of mortality throughout its range from butternut canker.
The understory tree redbud (Cercis canadensis) also declined precipitously – by almost76% from 1995 to 2018 in SCBI plots. While Anderson-Teixeira et al. do not speculate why, a few years ago a wider decline was reported.
Of course, Shenandoah also has been invaded by non-native plants! So I saw some plants that should not be there. At least the mid- and high-elevations that I visited appear to be much less abundant in the Park than in coastal and piedmont regions of Virgina. Ailanthus is listed as “common” in the Park. I didn’t see Japanese stiltgrass but it is clearly present at lower elevations. I was particularly disturbed to see oriental bittersweet along trails located in all three sections of the Park.
Anderson-Teixeira, K.J., V. Herrmann, W.B. Cass, A.B. Williams, S.J. Paull, E.B. Gonzalez-Akre, R. Helcoski, A.J. Tepley, N.A. Bourg, C.T. Cosma, A.E. Ferson, C. Kittle, V. Meakem, I.R. McGregor, M. N. Prestipino, M.K. Scott, A.R. Terrell, A. Alonso, F. Dallmeier, & W.J. McShea. 2021. Long-Term Impacts of Invasive Insects & Pathogens on Composition, Biomass, & Diversity of Forests in Virginia’s Blue Ridge Mountains. Ecosystems
Fei, S., R.S. Morin, C.M. Oswalt, & A.M. Liebhold. 2019. Biomass losses resulting from insect & disease invasions in United States forests. Proceedings of the National academy of Sciences.
Potter, K.M., M.E. Escanferla, R.M. Jetton, G. Man, & B.S. Crane. 2019. Prioritizing the conservation needs of United States tree spp: Evaluating vulnerability to forest insect & disease threats. Global Ecology & Conservation.
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
whitebark pine in Glacier National Park killed by white pine blister rust
The Kunming-Montreal Global Biodiversity Framework (KMGBF) is a major global policy driver around the world for more effective action to preserve biodiversity from current and future threats. (However, the United States has not joined the underlying treaty, the Convention on Biological Diversity (CBD). So its importance is probably less in the United States than in countries that take part.) This relatively new Framework was adopted at the 15th Conference of the Parties (COP) of the CBD in December 2022 after four years of negotiations. However, cynics note that the 196 countries that are parties to the CBD have rarely met previous ambitious goals set at earlier COP.
Hulme et al. have just published a paper [full reference at the end of this blog] addressing how invasive species and this Framework’s target may interact. They note that conserving biodiversity costs money. Many of the countries hosting diverse and relatively intact ecosystems lack sufficient resources, capability, or robust governance structures for this conservation.
The Kunming-Montreal Global Biodiversity Framework sets out ambitious global targets to reduce biodiversity loss by 2030 so as to maintain the integrity of ecosystems and their constituent species. Of the 23 targets, one – Target 6 – addresses bioinvasion. Countries endorsing the CBD have committed to eliminating, minimizing, reducing and/or mitigating invasive species’ impacts on biodiversity and ecosystem services. This is to be accomplished by identifying and managing introduction pathways; preventing introduction and establishment of priority invasive species; reducing rates of introduction and establishment of known or potential invasive species by at least 50% by 2030; and eradicating or controlling invasive species, especially in priority sites.
I rejoice that the CBD parties have recognized invasive species as a major driver of biodiversity loss in terrestrial and marine ecosystems. I wish conservation organizations’ and funders’ activities clearly reflect this finding.
This is the challenge raised by Hulme et al.: countries must integrate efforts to counter bioinvasions into overall conservation programs. Success in curbing bioinvasion depends upon achieving almost all other KMGBF targets. And this is a two-way street: the more holistic approach offers greater likelihood of successful biodiversity conservation.
The same authors point out that some of the 22 other targets address rapidly evolving introductory pathways e.g.,
Target 15 – increasing international and domestic tourism;
Target 12 – encroachment of urban areas near protected areas;
Target 10 – development of intensive agriculture or aquaculture systems near protected areas;
Target 7 – species rafting on plastic marine pollutants; and
Target 8 – growing risk from species shifting ranges in response to climate change.
pallet graveyard behind camp store & snack bar art Lake MacDonald, Glacier National Park; photo by F.T. Campbell
Other targets relate to management of established invasive species, e.g.,
Target 1 – planning and priority-setting for allocation of limited resources among the various threats to biodiversity;
Identifying factors that pose risks to highly-valued species, e.g., threatened species (Target 4) and species that provide important ecosystem services (Target 11);
A final group of targets are intended to guide all conservation efforts. These goals include integrating biodiversity concerns in decision-making at every level (Target 14); reducing harmful economic incentives and promoting positive incentives (Target 18); and several targets addressing issues of equity, benefit sharing, and access to information. Hulme et al. assert that the threat posed by bioinvasions must be incorporated into policies, regulations, planning and development processes and environmental impact assessments across all levels of government.
Hulme et al. decry an imbalance as to which KMGBF targets have been the focus of attention from governments, conservation organizations, and media. These stakeholders have concentrated on
Target 3, which calls for extending legal protection to 30% of lands and waters by 2030;
Target 4, which promotes maintaining genetic diversity within and among populations of all species;
Target 7, which encourages reducing harmful pollution;
Target 15, which urges businesses to decrease biodiversity risks arising from their operations; and
Target 21, which advocates ensuring equitable and effective biodiversity decision-making.
Even when stakeholders have looked at Target 6, they have focused primarily on how to quantify the numbers of species being introduced to novel ecosystems. Hulme et al. argue that conservationists should instead concentrate on the challenge of achieving the target. They note that bioinvasion is worsening despite implementation of many long-term management programs. As they note, numbers of introduced species globally have increased, these species are occupying larger geographic areas, and the species’ measured impacts have risen to astounding levels (see my previous blog about new cost estimates). This same point was made two years ago by Fenn-Moltuet al. (2023) [full citation at the end of this blog]; they found that the number of invasive species-related legislation and treaties to which a country adheres did not relate to either the number of insect species detected at that country’s border or the number of insect species that had established in that country’s ecosystems.
As conservationists, Hulme et al. remind us that not all damages are monetary: invasive species threaten more than half of all UNESCO World Heritage Sites.
Hulme et al. say achieving Target 6 presents several scientific challenges – most of which have been discussed by numerous other authors. Introduction pathways are changing rapidly. There is great uncertainty regarding current and especially future propagule pressures associated with various pathways. Information about particular species’ impacts and where they are most likely to be introduced is insufficient. Management costs are routinely underestimated. Perhaps most challenging is the need to judge programs’ effectiveness based not simply on outputs (e.g., number of acres cleared of weeds) but on outcomes in relation to reducing the subsequent impact on biodiversity and ecosystem services.
I note that several environmental organizations endorsed a “platform” that discussed this last point a decade ago. [I have rescued the NECIS document from a non-secure website; if you wish to obtain a copy, contact me directly through the “comment” option or my email.] Unfortunately, the coalition that prepared this document no longer exists. Even when conservation organizations have invasive species efforts, they are no longer attempting to coordinate their work.
APHIS inspecting imported plants
I greatly regret that Hulme et al. continue a long-standing misrepresentation of international border biosecurity controls as consisting primarily of inspections — of imported commodities, travellers, and associated transport conveyances. I have argued for decades that inspections are not effective in preventing introductions. See Fading Forests II Chapter 3 (published in 2003); Fading Forests III Chapter 5 (published in 2014); “briefs” describing pathways of introduction prepared for the Continental Dialogue on Non-Native Forest Insects and Diseases – in 2014 and in 2018.
The weaknesses of visual inspection are especially glaring when trying to prevent introductions via wood packaging material and living plants — also here.
Hulme et al. propose a politically astute approach to finding the resources to strengthen countries’ efforts to curtail invasive species’ spread within their borders. Recognizing that no country has unlimited resources to allocate to managing invasive species, they suggest concentrating slow-the-spread efforts on preventing damage to legally protected areas. Furthermore, authorities should avoid designating as new “protected areas” places that are already heavily invaded – or at risk of soon becoming so. As they note, programs aimed at protecting these areas often engage conservation stakeholders, decision-makers, even potential non-governmental donors. In other words, there is a foundation on which to build.
To buttress their argument, Hulme et al. cite evidence that bioinvasions threaten these areas’ integrity. For example, Cadotte et al. (2024) found that bioinvasion is one of most frequently identified threats identified in a survey of 230 World Heritage sites; and that they pose a greater degree of concern than other threats to biodiversity. They reiterate that managing invasive species is one of the most effective interventions aimed at protecting biodiversity.
The task remains complex. Hulme et al. note that accurate information about pressure caused by invasive species is not easily quantified using remote sensing. It requires expensive on-the-ground data collection. Even current methods for ranking invasive species have crucial gaps regarding species’ potential impact and the feasibility of their control. Choosing management strategies also requires assessing potential unintended effects on biodiversity and other GBF Targets, e.g., pollution from pesticides (Target 7).
Still, the context remains: successful management of bioinvasions to support the integrity of protected areas depends on the integrative approach described above.
Hulme et al. note a contradiction within the Kunming-Montreal Global Biodiversity Framework: Target 10 calls for the agriculture, aquaculture, and forestry industries to adopt sustainable practices, but doesn’t raise the issue of these sectors’ role in the introduction and spread of invasive species. They say guidelines have been developed for sustainable forestry production. These guidelines recommend that commercial plantation forests not plant non-native tree species within 10 km of a protected area. Hulme et al. also suggest applying a “polluter pays” fine or bond to forestry businesses that use invasive species without sufficient safeguards to prevent escape. These funds could be accessed to support invasive species management in protected areas, particularly surveillance. (Target 19 mandates obtaining more funds for this purpose). They add that these aquaculture, agriculture, horticulture and forestry sectors should take action to prevent the local feralization of alien crops and livestock.
Target 8 calls for minimizing the impacts of climate change on biodiversity. Hulme et al. note numerous scientific challenges here, including understanding how specific ecosystems’ and native species’ are vulnerable to altered climates, along with how specific invasive species’ are responding to an altered climate regime.
These same authors provide specific recommendations to the global conservation community to put in place a more holistic perspective. Some recommendations deal with data integration. Others call for major undertakings: i.e., developing a protected area management toolkit at a global scale. This action will require significant investment in capacity-building of protected area managers plus international cooperation and technology transfer (Target 20). Hulme et al. suggest funding this effort should be a priority for any resources leveraged from international finance (Target 19).
Hulme et al. also propose changes in the conservation approaches advocated by the CBD and IUCN. Specifically, they call for more explicit consideration of current and future impacts of bioinvasions and their management — on protected areas. The needed activities fall into six areas:
(1) reduce risks associated with various pathways;
(2) plan for range-shifting invasive species;
(3) mitigate invasive species’ impacts on biodiversity and (4) on ecosystem services;
(5) ensure new protected areas (including urban green spaces and infrastructure corridors) are largely free of established (“legacy”) invasive species; and
(6) provide managers sufficient resources to take effective action.
SOURCES
Fenn-Moltu, G., S. Ollier, O.K. Bates, A.M. Liebhold, H.F. Nahrung, D.S. Pureswaran, T. Yamanaka, C. Bertelsmeier. 2023. Global flows of insect transport & establishment: The role of biogeography, trade & regulations. Diversity & Distributions DOI: 10.1111/ddi.13772
Hulme, P.E., Lieurance, D., Richardson, D.M., Robinson, T.B. 2025 Multiple targets of Global Biodiversity Framework must be addressed to manage invasive species in protected areas. NeoBiota 99: 149–170. https://doi.org/10.3897/neobiota.99.152680
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
In early May I posted a blog about the Trump Administration’s proposed budget – saying that it would eliminate funding for nearly all USFS research & Forest Health Protection.
I can now provide some additional information.
The Administration has released a supplemental document providing a few details about the severe cuts it is proposing for USFS programs vital to countering bioinvasion in the coming fiscal year (FY2026), which starts October 1st. You can download this document at https://www.whitehouse.gov/wp-content/uploads/2025/05/appendix_fy2026.pdf
Congress has the final say on appropriations – so please!!! inform your representative & senators about why these cuts are disastrous.
USFS [See pages 162-168 of the Appendix]
Research & Development
The Administration requests $0 for R&D. It says it will strategically use existing carryover balances to responsibly terminate research programs & close research stations. Thus, funding for R&D will decrease from the $301 million in FY24 to $44 million in FY26. The Forest Inventory & Analysis will be shifted to the National Forest System and funded at $21.5 million – less than program supporters are seeking.
The proposal does contain an “additional amount” of $26 million for dealing with the consequences of wildfires, hurricanes & other natural disasters that occurred in calendar years 2022, 2023, and 2024. I am confused about this funding.
State, Private, and Tribal Forests
The Administration requests $0 for S,P&T. Again, the proposal says the agency will use existing carryover balances to effectively & responsibly terminate these programs. The number of employees would be cut from 520 employees in FY24 to 37.
Again, the proposal contains an “additional amount” of $208 million for Forest Health Management to deal with the consequences of wildfires, hurricanes & other natural disasters that occurred in calendar years 2022, 2023, and 2024. $14 million of this sum is earmarked for assistance to states in the Northeast that are anticipating an outbreak of eastern spruce budworm (which has been spreading from Canada). In a highly unusual move, the proposal says this funding is not subject to a requirement that grant recipients provide matching funds from non-federal sources. [Is it a coincidence that Maine Senator Susan Collins chairs the Senate Appropriations Committee?]
National Forest System
Total funding for NFS would be $1.5 billion. This includes an “additional amount” of nearly $2.5 billion for expenses related to the consequences of wildfires, hurricanes & other natural disasters that occurred in calendar years 2022, 2023, and 2024. $75 million of this amount is earmarked for construction or maintenance of shaded fuel breaks in the Pacific Northwest.
As I noted above, the Forest Inventory and Analysis program would be placed under the NFS.
I am particularly concerned that the budget proposal provides explicitly for $20 million to improve or maintain landscape & watershed conditions by preventing invasive plant infestations and installing aquatic organism passages, etc. There is no mention of programs intended to address damage caused by non-native insects and pathogens. It appears that the Administration proposes to drop all programs re: these organisms.
The overall objective of NFS programs is defined as managing the forests for productive use & resilience to catastrophic wildfire & provide broad range of ecosystem services. The budget allegedly prioritizes funding of programs designed to increase health & resilience of National Forests & Grasslands – including meeting multiple use requirements for resources on these lands.
The prose no longer says that timber production is the sole purpose of Nation forests – as the original budget stated.
APHIS appears to have survived – although the supplement provides minimal information (on pp. 85 – 87 of the Appendix).
The supplement contains a lengthy description of APHIS’ purpose — to protect America’s agricultural and natural resources from introduced pests. It requests $1.1 billion for FY2026. The only plant pest listed as a priority is exotic fruit flies. Personnel would be cut from 6,142 in FY24 to 5,092. I could find no specifics regarding funding for programs of interest – tree & wood pests, specialty crops, pest detection, and methods development.
Implications for Non-native Insects and Pathogens
Remember that USFS’s research and development program is intended to improve forest managers’ understanding of ecosystems, including human interactions and influences, thereby enabling improvements to the health and use of our Nation’s forests and grasslands. Most importantly to me, this program provides foundational knowledge needed to develop effective programs to prevent, suppress, mitigate, and eradicate the approximately 500 non-native insects and pathogens that are killing America’s trees.
The Forest Health Program provides technical and financial assistance to the states and other forest-management partners to carry out projects (designed based on the above research) intended to prevent, suppress, mitigate, and eradicate those non-native insects and pathogens. The program’s work on non-federal lands is crucial because introduced pests usually start their incursions near cities that receive imports (often transported in crates, pallets, or imported plants).
[FIA might inform all about where such pests are found — but it doesn’t address how to contain their spread, suppress their impacts, or restore the affected tree species.]
Eliminating either or both programs will allow these pests to cause even more damage to forest resources – including timber.
Both supporting research and on-the-ground management must address pest threats across all U.S. forests, including the more than 69% that are located on lands managed by others than the USFS. Already, the 15 most damaging of these pests threaten destruction of 41% of forest biomass in the “lower 48” states. This is a rate similar in magnitude to that attributed to fire (Fei et al. 2019). [This estimate does not include loss of beech beech leaf disease.] It is ironic that the Administration considers the fire threat to be so severe that it has proposed restructuring the government’s fire management structure.
I remind you that the existing USFS R&D budget allocates less than 1% of the total appropriation to studying a few of the dozens of highly damaging non-native pests. I have argued that this program should be expanded, not eliminated. Adequate funding might allow the USFS to design successful pest-management programs for additional pests (as suggested by Coleman et al.).
As a new international report (FAO 2025) notes, genetic resources underpin forests’ resilience, adaptability, and productivity. Funding shortfalls already undercut efforts to breed trees able to thrive despite introduced pests and climate change (the latter threat is still real, although the Administration disregards it). I have frequently urged the Congress to increase funding for USFS programs – which are sponsored primarily by the National Forest System and State, Private, and Tribal, although some are under the R&D program.
I repeat: Please ask your Member of Congress and Senators to oppose these proposed cuts. Ask them to support continued funding for both USFS R&D and its State, Private, and Tribal Programs targetting non-native insects and pathogens. America’s forests provide resources to all Americans – well beyond only timber production and they deserve protection.
Contacting your Representative and Senators is particularly important if they serve on the Appropriations committees.
House Appropriations Committee members:
Republicans: AL: Robert Aderholt, Dale Strong; AR: Steve Womack; AZ: Juan Ciscomani; CA: Ken Calvert, David Valadao, Norma Torres; FL: Mario Diaz-Balart, John Rutherford, Scott Franklin; GA: Andrew Clyde; ID: Michael Simpson; IA: Ashley Hinson; KY: Harold Rogers; LA: Julia Letlow; MD: Andy Harris; MI: John Moolenaar; MO: Mark Alford; MS: Michael Guest; MT: Ryan Zinke; NC: Chuck Edwards; NV: Mark Amodei; NY: Nick LaLota; OH: David Joyce; OK: Tom Cole, Stephanie Bice; PA: Guy Reschenthaler TX: John Carter, Chuck Fleishmann, Tony Gonzales, Michael Cloud, Jake Ellzey; UT: Celeste Maloy; VA: Ben Cline; WA: Dan Newhouse; WV: Riley Moore
Democrats: CA: Pete Aguilar, Josh Harder, Mike Levin; CT: Rosa DeLauro; FL: Debbie Wasserman Schultz, Lois Frankel; GA: Sanford Bishop; HI: Ed Case IL: Mike Quigley, Lauren Underwood; IN: Frank Mrvan; MD: Steny Hoyer, Glenn Ivey; ME: Chellie Pingree; MN: Betty McCollum; NJ: Bonnie Watson Coleman NY: Grace Meng, Adriano Espaillat, Joseph Morelle; NV: Susie Lee; OH: Marcy Kaptur; PA: Madeleine Dean; SC: James Clyburn; TX: Henry Cuellar, Veronica Escobar; WA: Marie Gluesenkamp Perez; WI: Mark Pocan
Senate Appropriations Committee members:
Republicans: AK: Lisa Murkowski; AL: Katie Britt; AR: John Boozman (AR); KS: Jerry Moran; KY: Mitch McConnell; LA: John Kennedy; ME: Susan Collins; MS: Cindy Hyde-Smith; ND: John Hoeven; NE: Deb Fischer; OK: Markwayne Mullin; SC: Lindsey Graham; SD: Mike Rounds TN: Bill Hagerty; WV: Shelley Moore Capito;
Democrats: CT: Chris Murphy; DE: Chris Coons; GA: Jon Ossof; HI: Brian Schatz; IL: Richard Durbin; MD: Chris van Hollen; MI: Gary Peters; NH: Jeanne Shaheen; NM: Martin Heinrich; NY: Kirsten Gillibrand; OR: Jeff Merkley; RI: Jack Reed; WA: Patty Murray; WI: Tammy Baldwin
Addendum
Maintaining the USFS State, Private, and Tribal (SPT) programs is essential to
complying with laws adopted by the Congress (see second page).
meeting the USFS mission of sustaining“the health, diversity, and productivity of the nation’s forests and grasslands to meet the needs of present and future generations.”
ensuring future economic and ecological benefits to Americans.
More than two-thirds of U.S. forests are privately owned or managed by state, local, or tribal governments. These forests provide many benefits, including 89% of America’s timber harvest.[i] SPT is the only federal program providing technical, financial, & educational assistance to these non-federal landowners.
Among the many threats to American forests, the Center for Invasive Species Prevention (CISP) focuses on the threat from insects and pathogens introduced from abroad. More than 41% of forest biomass in the “lower 48” states is at risk to non-native pests already established in the country.[ii] From 2011 to 2020, sap feeders, e.g., hemlock woolly adelgid, killed trees on 635,000 acres; foliage feeders, e.g., spongy moth, killed trees on 948,884 acres.[iii] Additional pests will be introduced and kill more trees.
Non-native pests are introduced primarily in crates, pallets or other packaging made of wood; and in imported plants. These imports – and the pests – usually land in cities or suburbs and establish there. Initially they cause widespread death of urban trees and impose high costs on local governments and property owners who must remove dying trees. The pests also spread. Hemlock woolly adelgid, emerald ash borer, polyphagous and Kuroshio shot hole borers, goldspotted oak borer, sudden oak death, and beech leaf disease have all spread to National forests from cities or suburbs.
The most effective way to protect America’s forests is to find and kill the pests where they first appear – usually in city trees. Waiting to act until a pest reaches National Forest boundaries means failure. Instead, we should expand the Forest Health Management (FHM) Cooperative Lands program to quickly detect, contain, and – if possible – eradicate the pests. With higher appropriations, the STP FHM program could tackle more of the 53 tree species under threat. At present, only four of these species benefit from 95% of FHM projects – eastern oaks, loblolly and ponderosa pines, and hemlocks.[iv]
USFS Research and Development (R&D) program
FHM adopts strategies based on knowledge of pests’ life histories and traits gained through research conducted or sponsored by the USFS R&D program. CISP urges you to support continued funding for the USFS Research and Development (R&D) program. However, we advocate a realignment: raise the proportion of research funding allocated to invasive species from the current paltry level of 1% to 5%. Funding for studying non-native pests has decreased 70% since FY2010 despite new pests attacking our forests. As a result, the Forest Service is hampered from developing effective programs to prevent, suppress, and eradicate most non-native pests.
Another crucial strategy for reducing loss of tree species to non-native pests is breeding trees able to thrive despite introduced pests. Currently these projects are supported – inadequately – by all three USFS divisions: R&D, SPT, and National Forest System (NFS).
The model program is the Dorena Genetic Resource Center. The Center has bred Western white pine and Port-Orford-cedar trees resistant to introduced pathogens; these trees are now being planted. Promising projects target the pathogens killing whitebark pine, American chestnut, American elm, and Hawaiian koa. Projects at earlier stages address ash, beech, and ʻōhiʻa.
Lesson: federal dollars, wisely invested, can mitigate the damage caused by invasive species. CISP asks you to support continuing these programs so that America can restore threatened trees to our forests.
Complying with the Law
The Cooperative Forestry Assistance Act of 1974
Section 2 (a) Findings …—
(1) most of the productive forest land of the United States is in private, State, and local governmental ownership, and the capacity of the United States to produce renewable forest resources is significantly dependent on such non-Federal forest lands;
(b) Purpose.—… authorize[s] the Secretary …, with respect to non-Federal forest lands … to assist in—
…
(3) the prevention and control of insects and diseases affecting trees and forests;
(c) Priorities.—In allocating funds … , the Secretary shall focus on the following national private forest conservation priorities, …:
…
(2) Protecting forests from threats, including … invasive species, insect or disease outbreak, … and restoring appropriate forest types in response to such threats.
(e) Policy. … it is in the national interest for the Secretary to work through and in cooperation with State foresters, or equivalent State officials, nongovernmental organizations, and the private sector …
Healthy Forests Restoration Act of 2003
Sec. 401(a) FINDINGS.—(1) high levels of tree mortality resulting from insect infestation (including the interaction between insects and diseases) may result in — (A) increased fire risk; … (E) degraded watershed conditions; (F) increased potential for damage from other agents of disturbance, including exotic, invasive species; and (G) decreased timber values;
…
(3) the hemlock woolly adelgid is— (A) destroying streamside forests throughout the midAtlantic and Appalachian regions; (B) threatening water quality and sensitive aquatic species; and (C) posing a potential threat to valuable commercial timber land in northern New England;
(4)(A) the emerald ash borer … has quickly become a major threat to hardwood forests …; and (B) … threatens to destroy more than 692,000,000 ash trees in forests in Michigan and Ohio alone, and between 5 and 10 percent of urban street trees in the Upper Midwest;
…
(11)(A) often, there are significant interactions between insects and diseases; (B) many diseases (such as white pine blister rust, beech bark disease, and many other diseases) can weaken trees and forest stands and predispose trees and forest stands to insect attack; and (C) certain diseases are spread using insects as vectors (including Dutch elm disease and pine pitch canker); …
(b) … The purposes of this title are— (1) to require the Secretary to develop an accelerated basic and applied assessment program to combat infestations by forest-damaging insects and associated diseases; (2) to enlist the assistance of colleges and universities …, State agencies, and private landowners to carry out the program; and (3) to carry out applied silvicultural assessments.
Sec. 402 Definitions
…
(3) FOREST-DAMAGING INSECT. … means … (D) a gypsy moth; (E) a hemlock woolly adelgid; (F) an emerald ash borer; … and (I) such other insects … identified by the Secretary.
[i] Oswalt, S.N., .W.B. Smith, P.D. Miles, & S.A. Pugh. Forest Resources of the United States, 2017 Uport WO-97SDA Forest Service Gen. Tech. Report WO-97. March 2019
[ii] Fei, S., R.S. Morin, C.M. Oswalt, and A.M. 2019. Biomass losses resulting from insect and disease invasions in United States forests. PNAS August 27, 2019. Vol. 116 No. 35 17371–17376
[iii] Coleman, T.W, A.D. Graves, B.W. Oblinger, R.W. Flowers, J.J. Jacobs, B.D. Moltzan, S.S. Stephens, R.J. Rabaglia. 2023. Evaluating a decade (2011–2020) of integrated forest pest management in the United States. Journal of Integrated Pest Management, (2023) 14(1): 23; 1–17
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 https://treeimprovement.tennessee.edu/
Scientists at the University of Minnesota have begun a project to assess the usefulness of remote sensing to detect the presence of emerald ash borer (EAB) earlier in the invasion. Previous studies had suggested that EAB infestation reduces leaf photosynthesis and transpiration before the yellowing of leaves. Scientists can monitor these changes from space. The project is now testing whether such monitoring can reliably detect EAB infestations at an early stage … The project began in April 2025 and is scheduled to end in December 2028.
Specific research questions to be addressed are:
How effective is remote sensing in detecting EAB years ahead of crown dieback?
Do changes in photosynthesis and transpiration caused by climate stresses (e.g. droughts and floods) differ from those caused by EAB infestation?
How quickly does an EAB infestation progress and spread spatially?
If remote sensing proves to be useful, land managers will have a new tool allowing them to intervene early enough to treat ash trees, before it is too late. The project team will build on existing detection protocols in collaboration with the USDA Forest Service, Minnesota Department of Agriculture (MDA), and Minnesota Department of Natural Resources (DNR).
I note that the Pacific coast states would benefit greatly from being able to identify satellite EAB outbreaks.
ash-dominated swamp in the Ankeny National Wildlife Refuge along the Willamette River in Oregon; photo by Wyatt Williams, Oregon Department of Forestry
I hope that this tool might also be tested for efficacy re: the non-native wood-borers attacking oaks and other trees in the Pacific coast states, e.g.goldspotted oak borer, Mediterranean oak borer, and three species of invasive shot hole borers.
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 https://treeimprovement.tennessee.edu/
Coast live oak killed by GSOB at William Heise State Park, San Diego County; photo by F.T. Campbell
Forest entomologists in southern California have organized the first of what they intend to be annual an annual “GSOB blitz”. The goldspotted oak borer has established widely in the region and has killed tens of thousands of California black and coast live oaks.
The goal of the “blitz” is to train community members & organizations in detecting and reporting presence of this beetle. Survey events are scheduled in six Southern California Counties between June 1-June 15, 2025. Participants are welcome from the general public, private business, public or community organizations, etc.
We have already seen threats to the Clean Air Act of 1970, the Clean Water Act of 1972 from the Trump Administration. Now the Endangered Species Act of 1973 (16 U.S.C. 1531-1544) faces severe risks.
The Washington Post has reported that the Trump Administration is saying that scientists’ ability to revive extinct species through biotechnology justifies relaxing legal protections. The Post quoted Interior Secretary Doug Burgum as saying that innovation – not government regulation — will save species. He has already met with Dallas-based Colossal Biosciences about using its animals in federal conservation efforts, as well as for potential species restoration. I note that having a few “engineered” specimens living in a zoo is not the goal of the Act or sensible biodiversity conservation programs.
This is just the Administration’s latest maneuver aimed at reducing the Act’s protections, which have been in place since adoption of the Endangered Species Act in 1973. The Fish and Wildlife Service — an agency in the Interior Department — has sought White House comments on a proposed redefinition of “harm” under the act. The term is not defined in the text of the Act, so a rule change could allow for significant reductions in protections, especially regarding listed species’ habitats.
Already, President Trump and his administration have overridden endangered species protections. First, he demanded that the Bureau of Reclamation open water transfer systems to drain water from a Northern California river system to southern California. Ostensibly the action was to protect the area from the devastating wildfires, although scientists declared that a lack of water for firefighters was not the reason the fires caused so much damage. The water had been stored, in part, to protect the habitat of the delta smelt.
President Trump also has revived the long-dormant “God Squad.” a federal committee that can override protections for endangered species. Members include Secretary Burgum and five other high-level officials. It was created by Congressional amendment in the late 1970s, during the fight over whether to build the Tellico Dam on the Tennessee River. It is empowered to approve projects even if they result in the extinction of a species.
In February, Interior Secretary Burgum also rescinded guidance adopted by the Biden Administration aimed at minimizing ship strikes on the Rice’s whale, one of the most endangered marine mammals. He has also ordered staff to consider economic factors when deciding habitat protections.
Other threats came earlier. Elon Musk’s SpaceX launch site is only about 10 miles from Aransas National Wildlife Refuge, which provides winter habitat for one of the “iconic” endangered species, whooping cranes. The Midwestern population of piping plovers is also listed as endangered; it winters along the Gulf coast, including at Aransas. The Refuge is home to 400 bird species, primarily ducks, herons, egrets, ibises, and roseate spoonbills. The few studies of noise impacts on birds focus on nesting – which neither whoopers nor plovers engage in while at Aransas … Still ….
Another refuge — in the middle of the Pacific Ocean – is also under threat from rocket activities. The Post reports that the U.S. Space Force – a branch of the U.S. Air Force – will soon publish an Environmental Assessment regarding plans to build two landing pads on Johnston Atoll. The facilities are intended to expedite movement of military cargo around the globe – by transporting it on large commercial rockets. Johnson Atoll is an unincorporated U.S. territory consisting of four tiny islands about 800 miles southwest of Honolulu. Although tens of thousands of red-tailed tropicbirds, red-footed boobies and sooty terns nest on the atoll, the Space Force said in its notice of intent that it expects the construction and operation of the demonstration project will have no significant environmental impact. This finding has been criticized by several organizations, including the Conservation Council for Hawaii, National Wildlife Refuge Association, and Union of Concerned Scientists. See also this statement by the American Bird Conservancy.
red-footed booby adult & nestling on Johnson Atoll; photo by Jordan Akiyama, USFWS via Flickr
One concern is that construction and operation could re-introduce various invasive species. The Post mentions yellow crazy ants; their acids can cause deformities in birds and, in some cases, deadly infections. The U.S. Fish and Wildlife Service spent a decade eradicating the ants. I note that rats very often are introduced to remote islands by cargo ships and are a significant threat to ground-nesting birds.
red-tailed tropic bird swarmed by yellow crazy ants – on Johnson Atoll; photo by Sheldon Plentovich USFWS via Flickr
Congressional Republicans – who now control both houses of the legislature — are preparing amendments to the Endangered Species Act that would slash protections for at-risk species that are – or might later be – qualified for listing under the Act. One approach is to legislatively remove, or “delist,” those species that have gotten in the way of various activities. The Post names gray wolves and grizzly bears, which ranchers say prey on livestock; plus a lizard in Texas oil country; and the northern long-eared bat, which lives in forests that the timber industry wants to log.
range of northern long-eared map in US & Canada
Citing the fact that only 3% of listed species have recovered, Representative Bruce Westerman of Arkansas, Chairman of the House Committee on Natural Resources, wants to amend the Act to give more power to states. He also plans to limit courts’ power to review agencies’ decisions to remove protections for plants and animals.
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 https://treeimprovement.tennessee.edu/
Erythrina caffra one of the native tree species in South Africa killed by PSHB. photo by Coana/Riti via Flickr
Introductions of bark and ambrosia beetles (Coleoptera: Curculionidae, Scolytinae) have significantly increased over the past century. Surveys conducted at borders and ports of entry around the world have shown the majority of beetles intercepted were scolytines. These insects are highly destructive on their own. Also, they can carry pathogenic fungal symbionts that can have devastating effects on the trees they attack.
One or more species in a complex in the Euwallacea genus have become established in countries around the world. One of these, the polyphagous shot hole borer (Euwallacea fornicatus; PSHB) and its associated fungus (renamed from Fusarium euwallaceae to Neocosmospora euwallaceae) is threatening havoc in South Africa about a decade after its establishment (Townsend, Hill, Hurley, and Roets. 2025).
Over this brief period PSHB/Fusarium disease has spread from two introduction sites – Pietermaritzburg, in KwaZulu-Natal Province, and Cape Town, in Western Cape Province – to all but one of the country’s nine provinces. It has become established in four of five forest types studied – Afrotemperate, coastal, sand, and swamp forests. It has not established in mangrove forests. (The Western Cape Province is home to its own “floral kingdom”. The kingdom’s charactersitic fynbos flora is a heathland habitat, not a forest one.)
Townsend and colleagues established a network of 78 monitoring plots in the Western Cape and KwaZulu-Natal provinces. The sites reflected a variety of natural and human impacts.
tree infested by PSHB/Fusarium disease in KwaZulu-Natal Botanical Garden, Pietermaritzburg. Photo from website of Greenpop.org
By monitoring these plots over five years (2019 – 2024), Townsend and colleagues have demonstrated that the beetle/fungus complex and resulting “Fusarium disease” is spreading and intensifying. The number of infected trees rose from 100 to 176 over the five years – a mean increase of 0.6% per year. The number of PSHB entry holes increased by over 10% annually. The number of plots containing infected trees roughly doubled from 23 in 2019 (29% of the 78 plots) to 48 (60%) in 2023.
By the end of the study, 29% of the 148 species sampled had been infected. This represented 43 species and 7 unidentified trees infected. Trees of eight native species died, , although one — Diospyros glabra (Ebenaceae) – resprouted after the main bole died.
In addition to the eight species known to suffer mortality, another 18 species were found to be able to support PSHB reproduction. Townsend and colleagues worry that, as the infestation spreads and intensifies, some of these species might also succumb. They mention specifically Erythrina caffra (coral tree), which is prevalent in coastal forest ecosystems across South Africa.
Most of the hosts are in the same families as those identified earlier by Lynch et al. (2021), e.g., Ebenaceae, Fagaceae, Fabaceae, Malvaceae, Podocarpaceae, Rutaceae, Sapindaceae and Stilbaceae.
Disease progress, speed of death, and visibility of symptoms varied not only between species, but sometimes among individuals of the same species. Some trees died rapidly. Townsend and colleagues say it is impossible to predict which individuals will succumb to infection.
There is, though, a clear frequency-dependent relationship between trees and beetles. Sites with higher relative abundance of host trees also had a higher proportion of infected trees, on average. The number of PSHB holes per species and per plot both increased to a larger extent at these same sites.
Individual trees’ traits influenced the severity of infestations (measured by the number of PSHB entry holes). Larger trees, those with a less healthy canopy, and those farther from a water source suffered more attacks. (This last finding differs from others’; Townsend et al. speculate that in the absence of flood-stressed trees, drought-stressed trees might be more attractive to ambrosia beetles.)
native tree in Tsitsikama National Park; photo by F.T. Campbell
Characteristics of the monitoring plots also affected disease progression. Higher proportions of trees became infected when they grew in plots that were closer to source populations, or that contained a higher proportion of host species as distinct from non-host species. The proportion of trees infected decreased in plots with higher tree densities or tree species richness.
As of 2023, “Fusarium disease” is more widespread and intense in KwaZulu-Natal than in the Western Cape. In KwaZulu-Natal 0.11% of monitored trees are infected compared to 0.06% in the Western Cape. The number of infected trees rose twice as fast over the five years in KwaZulu-Natal – ~6%, than in Western Cape – 3%. While all KwaZulu-Natal plots contained infected trees, three of 11 monitoring sites in the Western Cape did not. Townsend and colleagues believe that the most likely explanation is that PSHB arrived in KwaZulu-Natal earlier (as far back as 2012 as opposed to 2017 in Western Cape). Another possible factor is that source populations of infected trees are indigenous trees within the forest in KwaZulu-Natal whereas, in the Western Cape, they are often non-native trees planted in urban areas far from the study plots. Also, forests in KwaZulu-Natal are fragmented while, in Western Cape, the study forests are nearly contiguous. Townsend et al. conclude that the disease will spread and intensify in Western Cape as additional source populations become established in the forest.
locations of PHSB/Fusarium disease in Cape Town, South Africa – West of the study sites; map from City of Cape Town
As of 2023, the proportion of trees infected appears to be small — 7.6% of the 2,313 trees monitored. Only 11 trees in the monitored plots have died. However, the longer PSHB is active in the environment the more trees it will infest, the higher its impact will be on hosts, and the higher the number of dispersing individuals produced. This will substantially increase the chances and rates of additional areas becoming infected, especially in areas close to infestations – e.g., cities. They fear that in the future impacts will increase as progressively more competent host individuals are infected. Therefore, they emphasize the importance of mitigating PSHB increase in natural ecosystems, even in already infected areas.
Townsend and colleagues urge phytosanitary officials and resource managers to prioritize surveillance and management on the families containing several host species (above) and within plant communities in which they predominate. Managers must also be alert to new reproductive hosts for the beetle that appear as the infestation spreads and intensifies.
The situation could be worse than described; the Townsend et al. study did not examine how the invasion might affect eco-regions outside these two provinces. Because the PSHB has such a broad host range, hosts can die quickly, and South Africa provides ideal climatic conditions, this bioinvader could cause severe ecological effects on most indigenous forest types as well as agriculture and urban trees throughout Africa.
SOURCES
Lynch, S.C., A. Escalen, and G.S. Gilbert. 2021. Host evolutionary relationships explain tree mortality caused by a generalist pest-pathogen complex. Evol Appl 14:1083 – 1094. https://doi.org/10.1111/eva.13182
Townsend, G., M. Hill, B.P. Hurley, and F. Roets 2025. Escalating threat: increasing impact of the polyphagous shot hole borer beetle, Euwallacea fornicatus, in nearly all major South African forest types. Biol Invasions (2025) 27:88 https://doi.org/10.1007/s10530-025-03551-2
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 https://treeimprovement.tennessee.edu/
results of invasion by emerald ash borer (photo courtesy of Nathan Siegert, USFS ); one of the woodboring beetles found to be so damaging to hardwood trees
Over the last nine years scientists have made significant progress in identifying aspects of insect-plant host relationships that play important roles in determining how much damage an introduced, non-native pest is likely to cause within forest ecosystems in the United States. Predicting which introductions will probably cause the greatest damage is vitally important because scientists, phytosanitary officials, and resource managers cannot address all the hundreds of established insects, much less the thousands which might be introduced. This shortfall increases with each surge in import volumes (see my previous blogs about wood packaging by scrolling down the website below the “Archives” to “Categories”, then find “SWPM”), proliferation of goods types and source areas, and cutbacks in funding.
I hope USDA APHIS and Forest Service are adjusting their procedures to apply the scientists’ path-breaking findings.
Their progress will help protect our forests. I apologize if I seem ungrateful — but we need similar progress in managing plant pathogens. Consider the damage caused by chestnut blight, white pine blister rust, Dutch elm disease, sudden oak death, beech leaf disease … (All these and other pathogens are described briefly here.) Understanding the universe of introduced fungi, water molds, nematodes, viruses, etc., is per se much more challenging. Ashley Schulz points out that among the complications are pathogens’ complex life cycles, and possible new relationships with vectors.
Undertaking this analysis will be set back decades if agencies’ resources – funds and staffs – are decimated during the current “downsizing” of government. We must speak up!!
At least regarding non-native insects that attack North American tree species, scientists’ analyses promise a new ability to set priorities. This should improve the efficacy of phytosanitary programs – if government downsizing is not allowed to destroy USDA’s scientific, regulatory, and resource management programs.
We must speak up!!
What science tells us now
Schulz et al. (2025) summarize current findings. (Full citation to all references appear at the end of the blog.)
Earlier, scientists sought to find commonalities associated with introduced insects that caused high impacts on North American conifer trees [Mech et al. (2019)] and hardwoods (angiosperms) [Schulz et al. (2021)] (Full citations at the end of the blog; earlier blogs posted here and here.) Both studies found that the time elapsed since tree species in North America diverged from the host plants of the insects in their native range (i.e., host evolutionary history) is a diagnostic factor. This factor best predicted non-native insect impact compared to the other factors that were significant for conifer and hardwood specialists. For conifers, the other significant factors included the shade and drought tolerance of the North American host plants and whether there was a related insect native to North America on the same hosts that the non-native insect impacted. For hardwoods, another important factor explaining a specialist insect’s impact is if the insect is a wood borer, especially a scolytine beetle. The wood density of the North American host plant was also considered a significant factor when predicting impact of the non-native insect.
In 2022, Uden et al. applied the divergence time method to insect species not yet introduced to North America that might attack conifer species. They hoped to identify both insects posing the greatest hazard and tree species most vulnerable to introduced pests.
Now, a new team again led by Ashley Schulz and Angela Mech (see Schulz et al. 2025) has applied a similar approach to a more comprehensive range of pest-host relationships, including the pests that specialize on host plants and pests that feed on a broader array of hosts. Some feed on both conifers and hardwoods. They found that:
It is possible to quantify insect host breadth and identify the cutoff where “specialists” and “generalists” diverge. Specifically, the split occurs around 2,250 cumulative million years, where insects that feed on hosts that add up to less than that have narrow host breadth (i.e., “specialists”) and insects that feed on hosts that add up to more than that have broad host breadth (i.e., “generalists”). This technique also helps categorize insects that fall within the middle range of host breadth and are traditionally difficult to classify as either specialists or generalists based on differing qualitative definitions of the terms.
Insects that use more hosts in their native range also tend to use more hosts in the introduced range (North America). However, many of these insects utilized fewer hosts in the introduced range compared to the native range. This shrinkage was not universal, however; about 30% of insects increased their host breadth in the introduced range. Most of these fed on a single species in their native range but attacked additional species in the same family in North America. The corresponding i-Tree Pest Predictor tool uses the list of hosts in the insect’s native range and these models to determine the insect’s likelihood that it would cause high impact, as well as each North American tree species’ susceptibility to the insect entered into the tool.
Certain feeding guilds had – on average — a significantly narrower host breadth in North America than in their native ranges. These were gall makers (13 species analyzed); sap feeders (120 species); and wood borers (35 species). In contrast, host ranges did not differ for folivores (68 species), reproductive feeders (7 species), and root feeders (5 species). Still, we know that wood borers, as a group, have caused enormous damage to a range of North American tree taxa (see emerald ash borer, redbay ambrosia beetle, invasive shot hole borers (all described briefly here). Again, the i-Tree Pest Predictor tool can help identify the threat to particular tree species.
Of course, APHIS should not disregard pests with narrow host ranges; several have caused enormous damage.
red spruce (Pikea rubens) in Great Smoky Mountains National Park; photo by famartin via Wikipedia. Red spruce is the species found to be most vulnerable by the Uden et al. study
Schulz et al. (2025) developed models for three groups of introduced herbivorous insects that feed on trees:
1) conifer specialists (based on analysis of 69 species);
2) hardwood specialists (based on analysis of 141 species);
3) hardwood generalists (based on analysis of 30 species).
Because of their quantification of host breadth, they defined the “specialist” group more broadly than is commonly done, e.g., an insect that feeds on the three families Betulaceae, Fagaceae, and Juglandaceae would be considered “specialists” because all three host families are in the Fagales clade.
Tree relatedness was the only significant explanatory factor for all three host breadth categories. As determined in the previous studies, North American host tree species that were too closely or distantly related to the insect’s hosts in its native range were less impacted than hosts that diverged somewhere in the middle – the “Goldilocks” range. The divergence period differs among the three pest-risk categories: 3–4 million years ago for conifer specialists, 5–9 million years ago for hardwood specialists, ~1–2 million years ago for hardwood generalists. Schulz et al. suggest that the reason why the peak probability of high impact differs among these groups is that different feeding guilds cause the most damage to the specific host category, and each feeding guild is challenged by different tree host defenses. Bark and wood boring beetles (the hardwood specialists with the greatest impact) must overcome lethal constitutive and induced tree defenses in order to survive for long periods in the cambial layer. These insects have adapted the ability to locate and select poorly defended individuals in the host population. Folivores (i.e., the generalists with the highest impact) adapt to plant chemistry and trichomes (hair-like or scale-like outgrowths), or can avoid host defenses by moving off the foliage. Sap feeders (which include many high impact conifer specialists) are usually tolerated by trees, unless they stimulate hypersensitive reactions or vector pathogens.
Of course, scientists’ estimates of how long ago tree taxa diverged from common ancestors differ. Fortunately, Uden et al. (2022) found that these differences only rarely affect the predicted impact of a non-native insect – at least in the case of the 62 European insects and 47 North American conifer species they analyzed. In only 1.37% of the 2,914 pairs analyzed did the predicted risk differ depending on which source phylogeny was used. These cases were associated with 27 conifer-specialist insects and 9 conifer hosts. The article does not tell us which pest/host pairs these are but, overall, this paper demonstrates that the estimate differences in the phylogenetic trees does not differ enough to be problematic when forecasting insect impact.
Changes Needed in the Way Agencies Set Priorities
Schulz et al. (2025) urged agencies to stop relying only on insect traits as the basis for developing models & phytosanitary regulations. The only insect trait that predicted impact is the insect’s feeding guild. Considering hardwoods, they found that wood borers pose the greatest risk among specialists to hardwoods; folivores among generalists. While sap feeders do not cause statistically higher damage on hardwood tree species, four of the seven high-impact conifer specialists are sap feeders (hemlock woolly adelgid, balsam woolly adelgid, red pine scale, and spruce aphid). Therefore, the i-Tree Pest Predictor tool incorporates consideration of whether a pest of conifers is a sap feeder.
Schulz et al. (2025) also caution agencies against relying on just the number of hosts an insect might exploit. Assessors must consider the range of underlying plant chemistry / host defenses that the insect encounters. They found that hosts that are shade tolerant are more susceptible to high impact from conifer specialists and hosts that have intermediate to no shade tolerance are more susceptible to high impact from generalists.
Uden et al. (2022) identified a possible weakness in USDA efforts to prioritize pest prevention targets. They found that APHIS’ Prioritized Offshore Pest List included only 12 conifer specialists from Europe among the 150 species listed. They go on to note that while sap feeders constitute 53% of tree pest species established in the U.S., APHIS listed none. The models applied by Uden, Schulz, and Mech do not consider whether the insect is likely to become established. Improving our understanding of the many factors influencing an insect’s likelihood of being transported to North America or becoming established requires additional research. This might eventually lead to a usable tool for predicting this aspect of bioinvasion by forest pests.
There is an urgent need for such a tool. As Uden et al. noted, they found that 66% of the insect species they analyzed fell into the “high impact” category. This is a much higher proportion than estimates based on earlier studies, so identifying which of these insects are likely to establish versus not establish in North America can provide more resolution and help identify which insects are going to be most problematic.
Mature Fraser fir killed by balsam woolly adelgid; Clingman’s Dome; photo by Ben Ramsey via Flickr
Tree species at risk
The analysis undertaken by Uden et al. determined that three conifer species face a high level of hazard from European insects if they are introduced. They identified particularly high threats to two species, Fraser fir (Abies fraseri) and Carolina hemlock (Tsuga caroliniana). The fir is determined to be vulnerable to 17 insect species which are predicted to have high likelihood of a high impact. The hemlock is highly vulnerable to one of the insect species they sampled. They note that both of these conifers have a limited geographic range and ecological habitat, so they likely have a relatively narrow genetic pool. A third species said to be at elevated risk is red spruce (Picea rubens) – which, although more widespread, is also under attack by a non-native insect. All three species fit earlier finding by Mech et al. that conifer trees with high shade tolerance but low drought tolerance more vulnerable to non-native pests. In none of these cases do Uden et al. mention that the tree species have already been severely diminished by established non-native insects – i.e., balsam woolly adelgid on the fir (above), hemlock woolly adelgid on the Carolina hemlock. The Schulz/Mech team is working to refine methods for identifying tree species and regions at greatest risk.
Meanwhile, Uden et al. have suggested that phytosanitary authorities and forest managers apply their findings to identify the European herbivorous insects that pose the greatest threat to North American conifer species. They should identify Palearctic tree species that fall within the high-impact “Goldilocks” zone of divergence times in relation to specific North American tree species, then identify the insects that feed on those Palearctic trees. These insects would presumably pose the highest predicted hazard to those North American tree species. They suggest that species so identified should be added to the USFS’ list of species targetted by its wood borer early detection program. To address likelihood of introduction, they suggest incorporating data on insect species commonly intercepted at ports – an indication of high propagule pressure. There will always be exceptions though. For example, Ips typographus feeds on spruce and has been frequently detected at the ports, but it has not established in North America.
For those focused on identifying species or ecoregions at greatest risk, Uden et al. suggest scientists use several sources to identify vulnerable vegetation communities. Sources suggested include USFS Forest Inventory and Analysis (FIA) and NatureServe Explorer plant community descriptions) that have relatively high-value tree species predicted to be at risk from introduced species.
SOURCES
Aukema, J.E., D.G. McCullough, B. Von Holle, A.M. Liebhold, K. Britton, and S.J. Frankel. 2010. Historical Accumulation of Nonindigenous Forest Pests in the Continental United States. BioScience 60(11): 886-897. https://doi.org/10.1525/bio.2010.60.11.5
Mech, A.M., K.A. Thomas, T.D. Marsico, D.A. Herms, C.R. Allen, M.P. Ayres, K.J. K. Gandhi, J. Gurevitch, N.P. Havill, R.A. Hufbauer, A.M. Liebhold, K.F. Raffa, A.N. Schulz, D.R. Uden, & P.C. Tobin. 2019. Evolutionary history predicts high-impact invasions by herbivorous insects. Ecology and Evolution 9(21): 12216–12230. https://doi.org/10.1002/ece3.5709
Schulz, A.N., A.M. Mech, M.P. Ayres, K. J. K. Gandhi, N.P. Havill, D.A. Herms, A.M. Hoover, R.A. Hufbauer, A.M. Liebhold, T.D. Marsico, K.F. Raffa, P.C. Tobin, D.R. Uden, K.A. Thomas. 2021. Predicting non-native insect impact: focusing on the trees to see the forest. Biological Invasions 23: 3921-3936. https://doi.org/10.1007/s10530-021-02621-5
Schulz, A.N., N.P. Havill, T.D. Marsico, M.P. Ayres, K.J.K. Gandhi, D.A. Herms, A.M. Hoover, R.A. Hufbauer, A.M. Liebhold, K.F. Raffa, K.A. Thomas, P.C. Tobin, D.R. Uden, A.M. Mech. 2025. What Is a Specialist? Quantifying Host Breadth Enables Impact Prediction for Invasive Herbivores
Uden, D.R., A.M. Mech, N.P. Havill, A.N. Schulz, M.P. Ayres, D.A. Herms, A.M. Hoover, K.J.K. Gandhi, R.A. Hufbauer, A.M. Liebhold, T.D. Marsico, K.F. Raffa, K.A. Thomas, P.C. Tobin, C.R. Allen. 2022. Phylogenetic risk assessment is robust for forecasting the impact of European insects on North American conifers. Ecological Applications 33(2): e2761. https://doi.org/10.1002/eap.2761
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 https://treeimprovement.tennessee.edu/
Scientists in New Zealand are saying explicitly that a forest’s unique mixture of species matters when considering the future. This mixture is the result of the forest’s evolutionary history. Losing members of the biological community reduces the forest’s ability to respond to current and future stresses – its resilience.
New Zealand’s forests are part of the broader legacy of the ancient supercontinent of Gondwanaland – the island nation’s plants have close relatives in South America, the Pacific Ocean islands, and Australia. Still, these forests are unique: 80% of New Zealand’s plant species are endemic. The forests are also species-rich. The warm temperate evergreen rain forests of the North Island are home to at least 66 woody plant species that can reach that reach heights above six meters (Simpkins et al. 2024).
These forests have been severely changed by human activity. In just ~ 750 years people have cut down approximately 80% of the original forest cover! (Simpkins et al. 2024) Of the eight million hectares of surviving native forest, a little over five million hectares is managed for the conservation of biodiversity, heritage, and recreation. Another 2 million hectares are plantations of non-native species.
sites in New Zealand where pine plantations are “wilding”
All these forests are challenged by introduced mammals – from European deer to Australian possums. Climate change is expected to cause further disturbance, both directly (through e.g., drought, extreme weather) and indirectly (e.g., by facilitating weed invasion and shifting fire regimes) (Simpkins et al. 2024).
Pathogen threats are also common threats to the native trees of the Pacific’s biologically unique island systems. For example, Ceratocystis lukuohia and C. huliohia (rapid ‘ōhi‘a death, or ROD). The latter is killing ‘ōhi‘a (Metrosideros polymorpha) on the Hawaiian Islands. More than 40% of native plant species in Western Australia are susceptible to Phytophthora cinnamomi. Here I focus on two pathogens, kauri dieback and myrtle rust, now ravaging New Zealand’s native flora. No landscape-level treatment is available for either pathogen.
When considering this suite of challenges, Simpkins et al. focus on these two pathogens’ probable impact on forest carbon sequestration. They worry in particular about erosion of the forests’ resilience due to loss of “ecological memory” – the life-history traits of the species (e.g., soil seed banks) and the structures left behind after individual disturbances.
one of the largest remaining kauri trees, “Tane Mahuta”, in Waipoua Kauri Forest; photo by F.T. Campbell
Kauri Dieback
The causal agent of Kauri dieback, Phytophthora agathidicida, is a soil-borne pathogen that spreads slowly in the absence of animal or human vectors. The disease affects a single species, Agathis australis (kauri, Araucariaceae). However, kauri is a long-lived, large tree that is a significant carbon sink. It probably modifies local soil conditions, nutrient and water cycles, and associated vegetation. Also, kauri has immense cultural significance.
Simpkins et al. note that kauri dieback threatens stand-level loss of A. australis – that is, local extinctions. In the absence of disturbance Kauri trees can grow to awe-inspiring size. In the 19th Century, before widespread logging, some were measured at 20 meters or more in circumference. Consequently, kauri dieback might cause a decline in aboveground live carbon storage of up to 55%. This loss would occur over a period of hundreds of years, not immediately.
Huge kauri are not likely to be replaced by other long-lived emergent conifers (based on an analysis of one species, Dacrydium cupressinum). Instead, kauri are probably going to be replaced by late-successional angiosperms. The authors discuss the ecological implications for levels of carbon storage and proportions of trees composed of Myrtaceae – exacerbating damage caused by myrtle rust (see below).
The expectation of Simpkins et al. that kauri will suffer at least local extinctions is based on an assumption that no kauri trees are resistant to the pathogen. Fortunately, this might not be true: different Agathis populations show various levels of tolerance to Agathis dieback. Identification and promotion of some levels of resistance could enable A. australis to retain a diminished presence in the landscape.
However, Lantham, et al. make clear that containing kauri dieback remains “challenging,” despite its discovery nearly 20 years ago (in 2006). Scientists and land managers have little information on the distribution of symptomatic trees, much less of the pathogen itself. This means they don’t know where infection foci are or how fast the disease is spreading.
As is often true, the pathogen is probably present in a stand for years, possibly a decade or more, before symptoms are noticed. This means that the current reliance on public reports of diseased trees, or targetting surveillance on easy-to-access sites (e.g., park entrances and along existing track networks), or at highly impacted areas readily identified through aerial methods, fails to detect early stages of infection. Indeed, it seems probable that P. agathidicida had been present in New Zealand’s ecosystems for decades before its formal identification.
The Waipoua forest is one of the largest areas of forest with old kauri stands in the country. A new analysis of aerial surveys done between 1950 and 2019, shows how the forest is changing. The number of dead trees increased more than four-fold and the number of unhealthy-looking trees increased 16-fold over these 70 years. Kauri dieback is now widespread in this forest, especially in areas near human activities like clearing for pasture or planting commercial pine plantations).
Lantham et al. have developed a model which they believe will help identify areas of higher risk so as to prioritize surveillance and inform responses. These could delimit the disease front and help implement quarantines or other measures aimed at limiting the spread of P. agathidicida to uninfected neighboring sites.
I hope New Zealand devotes sufficient resources to expand surveillance and management to levels commensurate with the threat to this ecologically and culturally important tree species.
Leptospermum scoparia; photo by Brian Gatwicke via Flickr
Myrtle Rust
Myrtle rust is a wind-borne disease that affecting numerous species in the Myrtaceae, including some of the dominant early successional species (e.g., Leptospermum spp.). Simpkins et al. expect that myrtle rust might hasten the decline of two such tree species (L. scoparium and Kunzea ericoides). However, these trees’ small size and rapid replacement by other species during succession minimizes the effect of their demise on carbon storage.
Because I am concerned about the irreplaceable loss to biodiversity, I note that Simpkins et al. also feared immediate threats to some trees in the host Myrtaceae family, specifically highly susceptible species such as Leptospermumbullata.
As I reported in a recent blog, a second group of scientists (McCarthy et al.) explored the threat from myrtle rust more broadly. Austropuccinia psidii has spread through Myrtaceae-dominated forests of the Pacific islands for about 20 years.
Trees in the vulnerable plant family, Myrtaceae, are second in importance (based on density and cover) in New Zealand’s forests. Successional shrub communities dominated by the two species named above, Kunzea ericoides and Leptospermum scoparium, are widespread in the northern and central regions of the North Island and in northeastern and interior parts of the South Island. These regions’ vulnerability is exacerbated by the area’s climate, which is highly suitable for A. psidii infection (Simpkins et al. 2024).
McCarthy et al. concluded that ifLeptospermumscoparium and Kunzea ericoides prove to be vulnerable to myrtle rust, their loss would cause considerable change in stand-level functional composition across these large areas. They probably would be replaced by non-native shrubs, which are already common on the islands. Any resulting forest will differ from that formed via Leptospermeae succession.
These authors also worry that the risk to native ecosystems would increase if more virulent strains of the myrtle rust pathogen were introduced or evolved. They note that A. psidii is known to have many strains and that these strains attack different host species.
SOURCES
Latham, M.C., A. Lustig, N.M. Williams, A. McDonald, T. Patuawa, J. Chetham, S. Johnson, A. Carrington, W. Wood, and D.P. Anderson. 2025. Design of risk-based surveillance to demonstrate absence of Phytophthora agathidicida in New Zealand kauri forests. Biol. Invasions (2025) 27, no. 26
McCarthy, J.K., S.J. Richardson, I. Jo, S.K. Wiser, T.A. Easdale, J.D. Shepherd, P.J. Bellingham. 2024. A Functional Assessment of Community Vulnerability to the Loss of Myrtaceae from Myrtle Rust. Diversity and Distributions, https://doi.org/10.1111/ddi.13928
Simpkins, C.E., P.J. Bellingham, K. Reihana, J.M.R. Brock, G.L.W. Perry. 2024. Evaluating the effects of two newly emerging plant pathogens on North Aotearoa-New Zealand forests using an individual-based model. Ecological Modelling, www.elsevier.com/locate/ecolmodel
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 https://treeimprovement.tennessee.edu/
