Month: March 2026

USDA invasive species research forum 2026: tree pests

USFS Chief Tom Schultz

The US Department of Agriculture (USDA) and the North American Invasive Species Management Association (NAISMA) held the 34th annual forum on invasive species research at the end of February 2026. The agenda is available here. In this blog I summarize the  presentations about invasive alien plants (IAS); a separate blog discusses findings on invasive plants. Formal proceedings will be available in some months.

The most important information from the meeting:

  1. If NAISMA had not taken on the task of hosting the conference it would not have happened.
  2. Government leaders allowed only 1 staffer per USDA Forest Service region to participate. Not allowed to come were people who had organized the whole meeting or individual sessions, and presenters discussing several topics, including preventing IAS plant spread, and progress on controlling cogongrass (major impediment to pine plantations, affecting harvests).

What do these decisions say about the genuineness of the USDA Secretary’s recent memorandum listing invasive species as one of four priority areas for the department’s research efforts?

  • The USFS International Program is one of the few sources of support for studying potential pests before they invade the US.
  • Early detection surveillance is undermined by reliance on deploying too few traps and in a too narrow, or the wrong, timeframe. 
  • The Resistance Screening Center in Asheville, NC is no longer staffed, undermining breeding efforts in a region that reaches from Virginia to Texas.

A reminder to us all: Rebekah Wallace of the Center for Invasive Species and Ecosystem Health at the University of Georgia urged us all to provide citations for images used in informal materials – posters, presentations, outreach efforts, blogs, videos. Providing the citation increases our credibility and ensures that we avoid perpetuating mis-information!  

an ash resistance breeding plot at the Holden Arboretum, Ohio

Summary of key research reports on tree-killing arthropods and pathogens

Jennifer Koch, researcher with the USFS, described the Trees in Peril program. TiP aims to increase the pace, scale and efficiency of resistance breeding programs for American beech; eastern hemlock; and green, white, and black ash. This includes integrating genomics with other approaches and strengthening partnerships. Partners are key to finding “lingering” trees, addressing some scientific questions, and possibly screening cuttings for resistance.

Koch first explained the value of resistance breeding for producing resistant stock for restoration and reducing habitat for pests. The goal is to develop resistance, which Koch defined as the ability of a tree to survive despite the pest. Full immunity is not required. TiP participants hope that by integrating breeding with other approaches, such as biocontrol, they can create a new ecological equilibrium in which the tree species will continue to play its ecological role. As Koch asserts, the public supports breeding more than some other approaches. Also, there is a record of success; she cites the USFS Dorena Genetic Resource Center, which has developed resistant seedlings for four five-needle pines and Port-Orford cedar.

The first step is to determine whether desired traits are inherited. Genomics and other tools can test cuttings while they are still young and small – a very important advance in efficiency. Still, once cuttings with the desired traits are identified, it often takes several rounds of breeding to raise resistance levels sufficiently high. Similar testing of immature clones later in the process also can accelerate creation of seed orchards.

Breeding programs also need to incorporate genetic diversity from across the species’ ranges. TiP partners are collecting genetic material from beech, hemlock, and ash trees across their extremely large ranges – much of eastern North America.

Finally, TiP is training additional people to contribute to these breeding efforts.

Progress on each taxon:

beech grafts in a breeding experiment at the Holden Arboretum

Beech – Breeders are dealing with two diseases. A decade ago they identified genetic markers associated with beech bark disease (BBD). Their efforts had led to orchards producing seedlings of which 50% are resistant. Then beech leaf disease (BLD) showed up! Early results of a pilot study suggest BLD symptom severity is under genetic control. Even better, some trees appear to be resistant to both diseases. Koch recommends that scientists first identify BBD-resistant trees, then test those trees for BLD resistance.

Ash – the emerald ash borer (EAB) is established in 40% of the range of ash species. (Note: I am not sure whether this statement includes Canada; I am fairly certain it does not include Mexico.) Nine of the 16 US species are vulnerable, five endangered – green, white, black, blue and pumpkin.

The process by which scientists determe that resistance traits are heritable and identifying promising genotypes is described in Mason et al. (2026). The effort to develop techniques to propagate rooted cuttings is described in Merkle et al. (2022).  

Partners are helping to search for “lingering” ash. So far, 265 trees have been identified, and scion collected from 106 trees. Partners are also helping to plant cuttings for resistance testing.

The program has had to overcome several difficulties, including: 

  1. Black ash is dioecious, which complicates selection. Breeders are working on several approaches, but all are at early stages.
  2. Many of the originally collected trees turned out to be unintended crosses of white and green ashes rather than pure species. This resulted in very low seed production.

Anticipating the introduction of ash dieback disease (caused by the fungus Hymenoscyphus fraxineus), TiP is collaborating with Europeans on searching for possible resistance to this threat as well.

Hemlock – the Hemlock woolly adelgid (HWA) causes mortality of 50 – 100% of overstory trees. TiP scientists are still trying to establish a test for heritability of HWA resistance. There are additional difficulties in propagating rooted cuttings. The University of Georgia, Holden Arboretum, and others are helping to resolve these issues.

Those who want to support this program by contributing funds, knowledge, facilities, or volunteer efforts should contact Dr. Rachel Kappler, Forest Health Collaborative Coordinator, Holden Forests & Garden.   

One entity already actively helping the TiP program is the Ecological Research Institute through energizing citizen scientists. Radka Wildova described these efforts. The Monitoring and Managing Ash [MAMA] initiative has published detailed guidance on identifying “lingering” ash. For example, timing is crucial: searching too early points to trees that are not actually resistant. Searching too late means opportunities are missed (since “lingering” ash will die eventually because resistance is only partial) or a risk of confusing in-growth or regeneration for “lingering” trees.

The Institute could not create a similar action map for hemlocks because the adelgid has been present far longer. Recommends searching in sites where at least 80% of surrounding trees are dead or dying due to HWA or elongate hemlock scale. The program is also testing heritability of resistance among hemlocks on its own property, which was invaded 20-30 years ago.

[An unrelated initiative, the Hemlock Restoration Intiative, is pursuing protection and breeding efforts in the southern Appalachian mountains.]

Dutch elm disease (DED)

Avalon Miller, Pennsylvania State University, discussed new techniques to detect American elm trees tolerant of this disease.

a healthy American elm in Fairfax County, Virginia; photo by F.T. Campbell

It is important to detect elm trees’ response to infection early in the infection process because the apparent mechanism of tolerance is some trees’ ability to limit growth and proliferation of the causal fungus Ophiostoma novo-ulmi in xylem vessels. Scientists sought to use spectral analysis to detect distal leaf stress as a signal of susceptible genotypes. The USFS has developed a small stem assay that is achieving 80% accuracy in identifying disease phenotype within two months of inoculation – before symptoms appear.

Future studies will focus on determining which metabolites vary in tolerant vs. susceptible trees, and whether that information suggests useful interventions. For example, it is thought that some trees respond too aggressively to the pathogen, thereby cutting off the flow of water and nutrients and killing themselves.

Meanwhile, continuing efforts to breed resistant elm are hampered by limited greenhouse space, the tree’s complex genetics, and vast geographic range, and great variation in trees’ responses.  

Current USFS- and The Nature Conservancy-supported programs focus on the Northeast. I urge scientists in the Mid-Atlantic to engage; I have seen numerous healthy American elms in the Virginia and Maryland suburbs that could be included in a breeding program.

Managing established non-native pest species

Asian longhorned beetle (ALB)

Courtney Johnson, North Carolina State University, described efforts to determine key aspects of the ALB invasion in South Carolina. First, the bad news: a second invaded site in the Charleston region was detected in 2025.

Because Charleston is much farther south than any other ALB infestation, questions have arisen about

its phenology (timing of development). Research has confirmed that the ALB in South Carolina has ~1 year development cycle, not multiple generations as some had feared. Beetle larvae stay in the phloem through the third instar. Adult flight season is from May – Sept; the peak is in July. Unlike earlier findings, adult beetles did not exhaust their natal tree before moving to a new tree to oviposit. (This is also true in the Massachusetts outbreak.)

Some of the beetles in South Carolina are larger. Outreach materials need to be amended to reflect this fact, e.g., much larger exit holes.

typical site of ALB infestation in Charleston South Carolina; arrows indicate infested red maple trees. Photo by David Coyle

Tree dissection and dendrology studies of the principal host, red maples, show that multi-stemmed trees and smaller branches are preferred. They also preferred vertical stems or bolts, although they did oviposit on horizontal bolts raised off the ground to mimic a tree branch. There was little oviposition on bolts on the ground. In practice this means managers can leave felled trees on the ground without prolonging the infestation. This is very helpful since swamps preclude using heavy equipment.  picture

Beech leaf disease  

The disease has now been detected in Nova Scotia.

Chad Rigsby, Bartlett Tree Research Laboratory, described the results of testing the efficacy of several nematocides.  A foliar spray, Bayer’s Broadform, has received emergency approval from many states. It suppresses nematode (Litylenchus crenatae mccannii ([LCM]) numbers when applied at very low rates. Trees can be treated as long as (green) leaves are present. Rigsby recommended not spraying until a tree displays symptoms.

Since foliar sprays cannot be applied in forests, near water, or on huge trees, scientists also sought a systemic injectable fungicide. Thiabendazole [TBZ] (commercial formula Arborjet 20-S) is available. Rigsby said applicators can avoid splitting of the bark by following protocols developed by the International Society of Arboriculture. Managers should inject a tree several times in the first year to get the disease under control; then they can apply less frequently.

injection of thiobenzadole into beech; photo by Matthew Borden of The Bartlett Tree Research Laboratories

Don Grosman of Arborjet believes mortality is the result of a disease complex, not just LCM. Any of three treatments containing phosphite greatly reduces nematode numbers and canopy symptoms. Low volumes of diluted product can be injected in a few minutes. However, Thiabendazole hypophosphite requires a high volume macro trunk injection. This is expensive and takes time

Testing shows potassium phosphite PHOSPHO-jet produced dramatic improvement in 1 year. There are early indications that one treatment might be effective for two years. Arborjet will test this finding again this year. The company is also testing another chemical – the name of which cannot yet be revealed.

Andrew Miles, Ohio State, described beech response to polyphosphate (PP30). This chemical is a biostimulant, not a treatment. It is used as a disease control agent in several crops, including woody species. Field observations indicate it does reduce disease severity. Scientists are trying to understand the mode of action. Experiments are under way in Cleveland MetroParks, where BLD was first detected. Miles called for experiments within buds as well as leaves, since LCM damages tissue while in the bud.

Butternut canker

Scott Schlarbaum, University of Tennessee, collects butternuts; photo by F.T. Campbell

Anna Conrad, USFS, described ongoing efforts targetting this disease, which is present throughout the tree’s large range. A major challenge is distinguishing pure butternut from hybrids with Japanese walnut. Scientists have screened ~300 families from 22 states for possible resistance. At three sites in Indiana, the vast majority of highly resistant families are hybrids. Still, resistance was detected in up to 2.5% of pure butternuts; this level is sufficient to be enhanced through breeding. The program would benefit from genotyping across butternut’s range to identify lingering trees and confirm resistance.

Hemlock woolly adelgid

Nicholas Dietschler, Cornell University, studies the relationship between western hemlocks and HWA in their shared native ranges in the Pacific Northwest. At all sites, lower numbers of HWA (of both PWN and Japanese lineages) survived on Western hemlock – in the absence of predators. Why? Dietschler believes western hemlock has better chemical defenses. For example, hemlocks exude pitch in response to adelgid herbivory. In eastern hemlocks, this induced resin might suppress the tree’s defenses. In addition, HWA also prompts greater suppression of phenolics in eastern hemlock.  Dietschler concludes that bottom-up, tree-based defenses are a factor in the invasion and should be studied — while continuing efforts to find an effective combination of biocontrol agents.

Anne C.J. Peter, of Virginia Polytechnic Institute and State University, is comparing HWA chemical interaction with the most recent biocontrol agent, the silver fly Leucotaraxis argenticollis. (Scientists hope L. argenticollis will feed on summer populations of HWA; other biocontrol agents don’t suppress HWA at this stage.) The L. argenticollis population in the PNW feeds on HWA; however, its eastern North American relative L. rubidus feeds on pine adelgids, not the introduced HWA. It has been challenging to establish the PNW population in the East. One possibility is that the invasive HWA, which is from Japan, contain toxins that deter predators & parasitoids. Therefore, Peters is studying how both the western and eastern populations of Leucotaraxis deal with anthraquinones – compounds found in many plants and some insects, but not adelgids native to the eastern US.

Biocontrol of Emerald ash borer

Jian Duan, of the Agriculture Research Service Beneficial Insect Lab, summarized results of 15 years of biological control efforts. Over this period, four biocontrol agents have been introduced. I applaud APHIS’ rapid inclusion of this pest management approach; an egg parasitoid and two larval parasitoids were introduced before 2010, less than 8 years after the invasion was detected. Unfortunately, these agents proved less effective in northern parts of the EAB’s distribution. A fourth larval parasitoid was released in 2015. One or more of these biocontrol agents have been released in 479 counties in 34 U.S. states and three Canadian provinces.

To what degree have the wasps reduced EAB populations? Are those reductions resulting in regeneration?

Duan reported that at sites in Michigan, all four agents have spread rapidly. EAB populations crashed and recovered several times but overall numbers are lower. Ash saplings increased greatly after 2015; seedlings also increased. He concluded that the program has been successful but not spectacularly so.

Biocontrol of Spotted lanternfly

Hannah Broadley, APHIS, described developments beginning with initial searches for possible agents in China in 2015 — just one year after the lanternfly was detected in Pennsylvania. The search has focused on agents that feed on SLF eggs and nymphs. Attention has narrowed to Dryinus sinicus. This wasp both preys on and parasitizes SLF nymphs – depending on the nymphal stage. Labs are developing a third colony and conducting host specificity testing. Scientist have begun drafting a petition for release; the review process will probably take more than one year. At the same time, scientists continue exploring other possible biocontrol agents – e.g., in Vietnam. The blizzard prevented this speaker from appearing.

Xingeng Wang, of the ARS Beneficial Insect Lab, described how Dryinus sinicus attacks SLF – with a graphic video! D. sinicus attacks on third instar are often unsuccessful. When it encounters a second instar nymph, however, D. sinicus switches from predation to parasitism: it lay an egg which then develops inside the SLF nymph. This parasitism kill seven times more nymphs than predation on older nymphs.

Individual D. sinicus wasps can live up to 60 days, lay an average of 175 eggs and parasitize ~137 nymphs! Since D. sinicus is most effective against just one instar, releases will need to be carefully timed.

Asian spongy moths on a ship in Nakhodka harbor

Asian spongy moths 

Alex Wu, APHIS, discussed efforts to prevent establishment of four flighted spongy moth (Lymantria) species. APHIS seeks to improve the efficiency of trap analysis because states are submitting triple the number of trap contents of past years. The goal is to improve real-time qPCR efforts to distinguish the European species established in the East from the Asian flighted species, and to distinguish the several subspecies of latter taxon. Current qPCR results point to the wrong species ~ 5% of time. There are complexities: moths from Central Asia might be hybrids. Also Lymantria dispar japonica might be found in far southeastern corner of Korea – which is separated from Japan by a narrow strait.

Early Detection of Wood-Associated Beetles

Jiri Hulcr, University of Florida, discussed strengths and weaknesses of artificial intelligence (AI) in species identification of bark beetles. As he noted, differentiating a specific bark beetle species from among the more than 6,000 look-alike taxa is time-consuming. A properly trained AI program can help.  Furthermore, no one can keep up with publications – in 2015 there were 432 discussing just bark beetles! AI can help researchers discover papers that they otherwise would miss and empower non-English speakers to search the literature.

Hulcr has created a website that now has 63,000 images of ambrosia and bark beetles to assist identification. This work has been funded by the USFS International Program – one of the few sources of support for studying potential pests before they invade. The website will be open source once it has been copyrighted to prevent “scraping” by bots. Hulcr invited participants to send more images to continue training the algorithm on more species.

In the discussion, Alain Roques noted that scientists in Europe and probably China are developing similar AI-assisted identification tools. He urged international coordination. Hulcr replied that scientists do coordinate – as long as funding is available. Jennifer Koch noted that historic collections have many taxonomic inaccuracies. She urged people to rely on genetics when trying to identify a species.

Hulcr says AI is much faster than people in completing some tasks. But managing bioinvasions continues to require trained people (taxonomists) to collect, detect and classify new species; and execute quality control. AI cannot do science, which Hulcr defined as generating new knowledge through observation, turning that information into data, and testing hypotheses, making assumptions based on that.  

Hulcr says AI also cannot predict what the next damaging ambrosia beetle to enter the U.S. will be. He offered his predictions:

  • Euwallaceae destructans – from Indonesia – attacks live trees
  • Aggressive Platypdinae from Asia and South America (especially threatening to plantations where trees are stressed)
  • Cryphaus lipingensis (attacks pine seedlings)
  • Scolytus amygdali from the Meditteranean region – introduces pathogens during maturation feeding on living hosts; feeds on almonds and prunes – Rosaceae
  • Dryocoetes himalayensis – Asia and Europe; kills walnuts
Port of Marseille; via Wikimedia

Alain Roques, of Zoologie Forestiere in France, reported results of a beetle trapping study in France.

Since the European Union allows entry of species not listed as quarantine pests, it is vitally important to improve detection and analysis of the large percentage of detections that are “unknown” or “emerging”. Nearly 8,000 beetles have been trapped over five years; they belong to nearly 400 species, 35 non-native.

One approach is to develop more generic traps and lures. The EU is now using a blend combining 10 pheremones to trap Cerambycidae. Scientists are incorporating additional pheromones to the blend and to extend attractiveness longer than the current 10 days. There is still no generic lure for Buperstids.

Some species arrive regularly – is each detection a reintroduction? Or are these species established?

Roques asks whether we are trapping at the right sites. Half of Cerambycids are trapped only inside ports (of various types). Scolytids were trapped outside ports, at other “high-risk” locations– e.g., sawmills and recycling centers. In other words, they disperse more broadly. Roques wants to add the road network and to extend the survey to the entire European Union.

Davide Nardi, of the University of Padua, Italy, discussed results of his trapping program, which seeks to guide placement of traps. See Nardi et al. (2026) [full citation at end of this blog]. Important conclusions are:

  1. Surveillance programs are probably under-sampling species. Halving the sampling effort (from 16 to 8 traps) resulted in failure to detect ~20% of the species at the site. Cutting the sampling effort to four traps resulted in missing ~ 40% of present species. This decline in catches is particularly severe in urban landscapes – the very places where insects are most likely to be introduced.  Even when they deployed 16 traps per site almost 30% of total species richness was not detected, on average.
  2. Urban landscapes might offer a higher diversity of potential tree hosts. They also have more barriers to insects’ spread, e.g., buildings. This means urban areas require a greater sampling effort.
  3. Traps should be set near available forest patches or urban parks.

I was intrigued by Nardi’s suggestion that scientists use the data on native beetles included in the trap catches to alert countries receiving exports from these ports to which species might be transported to their shores.

Manoj Pandey, of Ohio State University, explored how environmental context shapes abundance and diversity of Scolytines caught in surveillance traps. His goal is to improve the efficacy of the USFS’ two- decade-old Early Detection Rapid Response trapping program, which targets bark and ambrosia beetles at high-risk sites. These include transit sites, destination sites, and wood waste treatment sites. Pandey analyzed program catches from 2010 through 2019.

He found that among native species bark beetles dominated catches; ambrosia beetles dominated non-native captures. Climate [minimum/maximum temperature and precipitation] was the most important factor determining which species were caught. Overall, both Scolytines and ambrosia beetles are governed more by ecological requirements than by human population levels. Among Scolytines, native species (which are adapted to stressed trees) are affected by precipitation; non-native species are favored by warmer temperatures. Ambrosia beetles – both native and non-native – are more affected by precipitation levels than bark beetles, probably because of the formers’ symbiotic relationship with fungi. Ambrosia beetles are also more likely to be generalists and to be attracted by deciduous forests.

The other influential criterion was landscape – whether forests are evergreen, deciduous, or diverse. Deciduous forests attract both types of beetles, but the influence is stronger for non-natives. Conifer (evergreen) forests attracted native species. Higher human population density was associated with higher trap catches. Propagule pressure – measured via human population density and per capita income – was less important, perhaps because the traps are always placed near population centers.

Xyleborus monographus; photo by U. Schmidt

I am concerned because this trapping program did not detect the Mediterranean oak borer (Xyleborus monographus)  before it was detected in California and Oregon. The project also did not find the greater shot hole borer Euwallaceae interjectus on the West Coast before it was detected in Santa Cruz, California. This ambrosia beetle has been established in the Southeast for years (M. Pandey, pers. comm. 12 March 2026).

Other Pests and Pathogens

Thomas G. Paul, at Ohio State, explored whether understanding the temperature regime during transit can provide early warning of which wood-associated pests might arrive. He obtained ocean surface temperature data along shipping routes from China to the U.S. West Coast and across the Atlantic. He then related those temperatures to degree-days needed for development by Xylosandrus germanus (from Asia) and Ips typographus (from Europe). At present there is still lots of uncertainty, including how to factor in the insect’s stage at the time of departure, the relationship between ocean air temperature and temperature inside a container, and possible effects of a container left to sit for several days in the port of import.

Eliana Torres Bedoya, also of Ohio State, provided an update on spore trapping for improved detection of pathogens across large landscapes. In 2024 the project developed standardized protocols for surveillance. To learn what is going on in the region, one should sample many sites across the area of interest. To find a particular pathogen, officials also need to know which season to sample. Torres Bedoya notes that few states sample in the autumn, which probably results in biased results.

In 2025, the program was expanded to 10 states. Species searched for are chosen by participating states. They include the causal agents of oak wilt, thousand cankers disease, laurel wilt, annosum root disease, and the beech leaf disease nematode (Litylenchus crenatae mccannii). Participants – including state phytosanitary officials — are now asking how to respond to a detection. For example, DNA from Bretziella fagacearum, the cause of oak wilt, was detected in several states where no disease has yet been identified (New Hampshire, Massachusetts, West Virginia, and Ohio). DNA of Geosmithia morbida, the causal agent of thousand cankers disease of walnut, was detected in New Hampshire, Massachusetts, and Maryland.  What should managers do in response to these findings?

Torres Bedoya explained that her team is now working to make the spore-trapping process more user-friendly. I noted that my poster previous blog discussed using these techniques at the interface of forests and agricultural land uses.

During other discussions, I learned that Jason Smith of the University of Mount Union is trapping for DNA from LCM in order to track the spread of BLD. 

Brown spot needle blight

Several speakers addressed this disease, which is of increasing concern to pine timber interests in the American South and around the world. New Zealand is exploring resistance breeding of Pinus radiata in advance of introduction

The disease has long been known in long-needle pine – at the “grass” stage (early seedlings). In recent years needle blight has begun damaging loblolly and other pine species – in both plantations and natural forests. Jason Smith, from the University of Mount Union, was asked for help by the industry in 2016. He found that one factor is increasing reliance on herbicides instead of fire to control ground-level vegetation. The large doses of inoculum remains in the litter, rather than being killed by periodic fire – as in the past. Smith thinks it is also possible that the pines suffer subtle damage from herbicides. Other possible factors are the widespread planting of genetically identical monocultures and climate change.

Colton Meinecke at the University of Georgia reported that Lecanostica acidola has been confirmed as the disease agent at these sites by Koch’s postulates. Scientist at the University of Georgia, University of Mississippi, and other entities are collaborating on development of a predictive model. Work includes sampling needles from both the litter and canopy, tracking tree condition, destructive sampling of dead trees, and spore trapping.

In the discussion, Smith warned that dying pines are not being detected by aerial forest health surveys because they are conducted too late in the season. This is because the surveys focus on one specific pest, the southern pine beetle. He called for a more comprehensive survey program.

Meinecke reported that the disease is more severe in western parts of the Gulf Coast regions. It is also causing problems in Christmas tree plantations, especially Scots pine.

He has found evidence of some genetic resistance. He is trying to develop a rapid test of a tree’s vulnerability using spectral wave length. Meinecke is also experimenting with stand management approaches. He praised the close cooperation with experts from around globe and New Zealand’s pro-active preparation for combatting the disease before it arrives.

Kier Klepzig, of the Jones Center at Ichauway in Georgia, described establishment of a Pine Pandemic Preparedness Plan, stimulated by awareness that a non-native pest might be introduced that attacks loblolly pine (Pinus taeda) – the foundation of the southeastern “woodbasket”. [Of course, Sirex noctilio is already established in the eastern United States. Although it is a severe pest of loblolly growing in plantations in the Southern Hemisphere, industry and federal and state agencies have dismissed concerns in North America.] The Pine Pandemic Preparedness Plan has four components: communication, detection and diagnosis, delimitation and assessment, response.

As concern about brown spot needle blight grew, the Southern Group of State Foresters ask the “P4” team to engage. Klepzig and Kamal Gandhi pulled together a working group which has the goal of developing guidance for managing the disease within two to five years. The task force is developing a website for data-sharing. The task force is also studying genetics of the host and pathogen, fungicides, the role of fire, resistance screening, and spore trapping. Industrial concerns about coordinating with competitors cause challenges.

Ashley Schulz, of Mississippi State University, has reviewed experience with biocontrol for clues on species’ traits important for facilitating invasion. She analyzed information on 394 insects introduced to North America for biocontrol of invasive plant species (see other blog) and 87 agents targeting 325 insect pests. For each species, data was recorded on whether it established, level of impact, the insect’s feeding guild, climate matching, host specialization, and evolutionary history. For the 87 entomophagous insects, she also recorded host feeding guild and host specialization.

Schulz found that entomophagous insects introduced as biocontrol agents were more likely to establish if they are a specialist. Higher impact was also associated with specialization. Parasitoids had higher impacts than predators. What does this indicate re: invasive species? Schulz said that insects which can hide or defend themselves, i.e., specialists, are likely to be more successful invaders.

Schulz recommends more analysis of what can be learned from experience with biocontrol agents. However, such studies are challenged by poor records, lack of empirical evidence and quantitative data, the lower number of biocontrol agents introduced recently, and funding shortages that preclude post-release monitoring.

Schulz also mentioned that she worries that a proposal to drop the word “harm” from definition of invasiveness could result in biocontrol agents being lumped with invasive species. This would further hamper implementation of biocontrol. She considered this loss to have particularly bad affects at a time when there are growing restrictions on pesticide use.

SOURCES

Mason, M.E., Carey, D.W., Romero-Severson, J. et al. Select genotypes of white and green ash show heritable, elevated resistance to emerald ash borer. New Forests 57, 12 (2026).  https://doi.org/10.1007/s11056-025-10158-x

Merkle, S.A., J.L. Koch, A.R. Tull, J.E. Dassow, D.W. Carey, B.F. Barnes, M.W.M. Richins, P.M. Montello, K.R. Eidle, L.T. House, D.A. Herms, K.J.K. Gandhi. 2022. Application of somatic embryogenesis for development of emerald ash borer-resistant white ash and green ash varietals. New Forests https://doi.org/10.1007/s11056-022-09903-3  

Nardi, D., D. Rassati, A. Battisti, M. Branco, C. Courtin, M. Faccoli, N. Feddern, et al. 2026. “Integrating Landscape Ecology into Generic Surveillance Plans for Bark- and Wood-Boring Beetles.” Ecological Applications 36(2): e70194. https://doi.org/10.1002/eap.70194

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

USDA invasive species research forum 2026: invasive plants

Callery/Bradford pear invasion in northern Virginia; photo by F.T. Campbell

The US Department of Agriculture (USDA) and the North American Invasive Species Management Association (NAISMA) held the 34th annual forum on invasive species research at the end of February 2026. The agenda is available here In this blog I summarize the  presentations about invasive alien plants (IAS); a separate blog discusses findings on tree-killing pests. Formal proceedings will be available in some months.

The most important information from the meeting:

  1. If NAISMA had not taken on the task of hosting the conference it would not have happened.
  2. Government leaders allowed only 1 staffer per USDA Forest Service region to participate. Not allowed to come were people who had organized the whole meeting or individual sessions, and presenters discussing several topics, including preventing IAS plant spread, and progress on controlling cogongrass (major impediment to pine plantations, affecting harvests).

What do these decisions say about the genuineness of the USDA Secretary’s recent memorandum listing invasive species as one of four priority areas for the department’s research efforts?

A reminder to us all: Rebekah Wallace of the Center for Invasive Species & Ecosystem Health at the University of Georgia urged us all to provide citations for images used in informal materials – posters, presentations, outreach efforts, blogs, videos. Images grab attention, provide context for communication, and support data cited. Providing the citation increases our credibility and ensures that we avoid perpetuating misinformation! 

Callery/Bradford pear in Kentucky; photo by Sherry Bailey via NARA archive

Two presentations focused on Callery / Bradford pear

Jess Hartshorn of ecoLogic described efforts to develop a remote sensing tool that will be as accurate as human surveyers — but faster. What scientists learned from this exercise will help build tools for other invasive plants. Hartshorn noted that while there are many no-cost sources of satellite imagery, no single source is sufficient. But integrating data from several programs, plus adding new criteria proved challenging. One setback was a surprise: the spectrum emitted from the tree’s most conspicuous feature, its early-season white blooms, is similar to that reflected from concrete! – with which the species is associated … The authors had to use data from several satellite systems to identify unique wavelengths from the leaves. Accuracy was lost when an individual pixil contain mixed “vegetation”.

Marcin Nowicki, of the University of Tennessee, explored the genetic changes that allowed a species that is rare in Asia to become a prolific continent-wide invader in North America. “Evolutionary overdrive” resulted from planting plants from several origins close together, thus promoting cross pollination. This led to exceptionally rapid diversification in nuclear and mitochondrial DNA. A bonus: once Sequencing the genomes of several cultivars have been sequenced, bans on sales of those hybrids that are most invasive can be enforced.

Becky K. Kerns, USFS Pacific Northwest Research Station reported on disturbing increases in invasive plants in forests of the Pacific Northwest. In the past, higher elevations, low light levels, and cooler temperatures appeared to protect the region’s forests from invasion. However, annual grasses, especially cheat grass (Bromus tectrorum), are now being found at unprecedented levels in forest plots that have been burned, grazed, or logged, burned, and grazed. This includes plots subjected to prescribed burns. Kern thinks the plant invasions are due to increased light, ground disturbance, changed competitive interactions, and potentially higher propagule pressure. Pyrophytic shrubs also of increasing concern; Kerns mentioned Scotch broom (Cytisus scoparius) in Douglas-fir forests. [I am uncertain how novel this threat is because academic scientists issued warnings about Scotch and other brooms in the mid-1990s.]  [run together w/ following] She is working with the staff of the National Invasive Species Council’s task force on fire and invasives to increase attention to emerging threats and to encourage managers to prioritize managing known pyrophytic species along with fire. 

Wavyleaf basketgrass infestation in closed-canopy forest in Maryland; photo by Kerry Kyde, Maryland DNR via Bugwood

Two speakers addressed aspects of the invasion by wavyleaf basket grass (Oplismenus hirtellus subsp. undulatifolius).

Wavyleaf basket grass was first detected in 1996 in Maryland. It is now widespread in the Mid-Atlantic and expected to spread along the Appalachian Trail and to other recreation sites. Thirty percent of public land in the East is considered vulnerable.

Carrie Wu of the University of Richmond is exploring the grass’ association with changes in the soil microbial community. She tested associated soil microbial communities in 12 locations with three types of soil. She found decreased fungal diversity but not homogenization of the fungal community. She is now constructing an invasion history to see how fast the changes occur, confirm the invaded range, and predict high-risk sites.

Michael Fulcher, of the USDA Agriculture Research Service’s Foreign Disease-Weed Science Lab, is concerned about the microbes associated with invasive plant species. We don’t know whether some of these microbes might be beneficial, perhaps as biocontrol agents? Or might they cause disease in desired plant species. He phenotyped 319 isolates from healthy leaves. This study detected two known crop pathogens on healthy wavy leaf basket grass plus an unknown species in a genus that includes some known pathogens. In lab tests, this organism stunted growth of wheat and tall fescue embryos

Fulcher emphasizes that even asymptomatic non-native plants can transport possible pathogens. Scientists should try to detect and analyze these as quickly as possible. I note that Eliana Torres Bedoya reported last year that healthy woody plants can also transport disease-causing fungi.

Fulcher is looking for collaborators to help collect plant samples

Other invading plants

Craig Barrett of West Virginia University seeks to answer questions related to “invasiveness” traits and whether selective pressures enhance those traits in the invasive range. To explore these topics, Barrett is mapping the invasion history of the widespread invasive species Japanese stiltgrass (Microstegium vimineum). He has found evidence of the grass’ rapid adaptation after introduction, including greater diversity in invasive populations in the Northeast than those in the Southeast. Barrett thinks it most likely that a genetic bottleneck at introduction was followed by mixing that created novel genotypes that might bridge gene transfer between larger populations. There is evidence of phenological adaptation to local climates and a genetic basis for whether a plant supports awns – which react to changes in moisture by “walking” across soil and burying themselves.

Elizabeth Ward, at the Connecticut Agriculture Experiment Station, documented how invasive plant species utilize forest gaps created by the death of ash caused by emerald ash borer (EAB). The progress of the EAB infestation across Connecticut is well-documented, so scientists can track plant responses to stages of canopy mortality. She found:

  • Larger canopy gaps contained more invasive plants and fewer native tree seedlings / reduced regeneration.
  • Higher soil nitrogen availability is also linked to higher non-native plant cover (all species) – including non-native tree seedlings.
  • Higher carbon availability led to lower non-native plant cover, including that of non-native tree seedlings.

Ward advises active management of EAB-invaded forests to reduce plant invasions and promote tree regeneration.

Ward is now comparing sites with passive management vs. salvage harvests. Early results find no difference in invasive plant cover. However, harvested sites had higher abundance of ash regeneration and and diversity of native plant species.

Jeremy Anderson, at the University of Massachusetts, discussed difficulties that have slowed the search for a biocontrol agent to control invasive knotweeds. North American scientists are collaborating with counterparts in Europe. Because knotweeds are related to rhubarb, scientists must ensure that any agent is host specific.

knotweed infestation in Maryland; photo by Will Parson, Chesapeake Bay Program

Initial surveys 20 years ago identified 180 candidate insects. However, the only speciesfound suitable for in- depth evaluation failed to establish. Why? First, there was apparently a climate mismatch: the insect is from southern Japan but the plant is from the North. Then a second difficulty was discovered: the target weeds are hybrids, not a pure species. Scientists are now testing a microbe that might overwinter on pine needles, so they are comparing needle chemistries of Japanese red pine with those of North American pines to determine whether there is a risk. In answer to a question, Anderson said scientists do not know how the microbe will respond to the warmer, wetter climate expected in New England in the future.

Ashley Schulz, of Mississippi State University, is continuing her efforts to identify clues to which newly introduced species might be most damaging. In this case she is analyzing efficacy of biocontrol agents to understand which establish and have significant impacts. Species with traits similar to successful biocontrol agents might be more successful invaders.

Schulz analyzed information from 394 insects introduced to North America to control 153 plant species and 87 agents targeting 325 insect pests. The data recorded on each species: whether it established, level of impact, insect’s feeding guild, climate matching, host specialization, and evolutionary history. For the 87 entomophagous insects, she also recorded host feeding guild and host specialization. See other blog.

Phytophagous insect biocontrol agents were more likely to establish if the insect is a generalist newly associated with the target plant species. The biocontrol agent is more likely to have a greater impact when released in environments similar to the agent’s native range. The introduced biocontrol agent will have less impact if it feeds on plant parts that the plant can easily restore (foliage, fruit/seeds).

What does this indicate re: invasive species? Schulz concluded that among phytophagous insects, generalists might be more likely to find a suitable host and survive. The “Goldilocks” premise applies: the host is sufficiently similar to the invader’s native host that it is recognizable but sufficiently distantly related to lack defenses effective against the invader. Bioinvasive phytophagous insects will have a greater impact when introduced to a similar climate and feeds on plant structures that are not easily restored – i.e., stem, root.

For traits of entomophagous insect biocontrol agents see my other blog here.

Schulz recommends more analysis of what can be learned from experience with biocontrol agents. However, such studies are challenged by poor records, lack of empirical evidence and quantitative data, the lower number of biocontrol agents introduced recently, and funding shortages that preclude post-release monitoring.

Schulz also mentioned that she worries that a proposal to drop the word “harm” from definition of invasiveness could result in biocontrol agents being lumped with invasive species. This would further hamper implementation of biocontrol. She considered this loss to have particularly bad affects at a time when there are growing restrictions on pesticide use.

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

EEICAT: improved method for assessing bioinvasion impacts

As bioinvasions and their impacts continue to expand globally, managers and decision-makers charged with developing effective management and mitigation strategies urgently need tools that can assess and rank all impacts. These start with impacts on species’ populations … but go much farther, to the assemblage, ecosystem, and abiotic levels. Impacts at the “species and assemblage” level include species extinction (locally or more broadly), changes in species range, assemblage structure, successional patterns, and the soundscape. Impacts at the “ecosystem function” and “abiotic” levels include changes to primary production, food webs, water quality, and nutrient cycles. The analysis also addresses changes that do not affect native biota directly, although they present no examples.  

For a decade, scientists studying bioinvasions have used the Environmental Impact Classification for Alien Taxa (EICAT) framework to standardize categorization of species-level impacts. One group that has not used this methodology is experts on tree pests. Why? Does the approach fail to describe the impacts of non-native arthropods and pathogens on tree species and forest ecosystems more broadly? Or is it simply because of academic silos?

Even more important: are the science and practical management of invasive species and forest pests losing valuable insights, resources, policy choices, … because of this schism? Would both groups gain from closer interactions?

In any case, the framework used by many scientists working on “invasive species” is undergoing a revision to better capture cascading and systemic effects from bioinvasion. A group of scientists has created the Extended EICAT (EEICAT) framework. (See the publication reference at the end of this blog to learn the process of development and details of the new system.) The proponents claim that the new system recognizes the functional interdependence of species in ecosystems, which means that alterations in species assemblages inevitably amplify throughout the system. E.g., alterations in physico-chemical characteristics or habitat structure. Impacts can even cross-ecosystem impacts between ecosystems that are often managed separately. An example is a change in the quality, magnitude, and novelty of resource flows between terrestrial and aquatic systems. To address these multifaceted effects, EEICAT integrates 19 impact types into the analysis. The intention is to improve communication about the complex ecological impacts caused by bioinvasions and facilitate prioritization of responses to competing bioinvasions.

While the various outcomes from bioinvasion can be positive or negative for nature and people, the EEICAT does not use value-laden distinctions. These determinations are left to stakeholders, managers, and community members, based on their own perspectives. Instead, it compiles and standardizes information about the measurable changes to species numbers (some decrease, others increase); to ecosystem processes (e.g., nutrient dynamics or hydrological regimes).

EEICAT incorporates the “reversibility concept”, which addresses the potential for a native sp (including individuals, pops, and assemblages), ecosystem function, or abiotic environmental to recover after removal of the bioinvader.  The system developers distinguish “naturally reversible changes” and “naturally irreversible changes”. In the former case, the affected spp, ecosystem processes or abiotic conditions are thought likely to return to their original state within 10 years or three generations (whichever is longer) through natural processes or human-assisted actions that do not exceed what is already being done. This does not include reintroductions or restoration efforts that require new efforts. Instances of “naturally irreversible changes” are those in which the affected species, ecosystem functions, or abiotic conditions cannot return to their original state within that timeframe without significant additional human intervention, or even after intense human intervention. The system has reached a different, stable equilibrium. These “permanent” changes are the result of one or more species’ global extinction, or persistent environmental alterations, e.g., soil modification, altered hydrology, or irreversible changes in nutrient cycling.

The proponents assert that EEICAT allows multiple impacts reported in a single study to be classified independently at each impact level. Furthermore, the EEICAT analysis does not require extensive research on the assessed species or understanding of the mechanisms through which the invasive species affects native species or the environment. EEICAT framework is applicable to any amount of info available in each study. It also explicitly assesses the adequacy / reliability of evidence [data, methods, approach] used in studies of bioinvasions that are included in the analysis.

EEICAT framework enables researchers to evaluate how “ecosystem engineer” species influence key ecological functions by explicitly accounting for changes to ecosystem processes, e.g., nutrient dynamics or hydrological regimes. For example introduced bivalves increase water clarity in certain systems, triggering cascading effects on biodiversity and ecosystem functions.

The EEICAT framework also allows separation of the mechanisms of impact vs. attribution of impact. For example, when a non-native plant species alters nutrient availability, thereby changing the microbial community, EEICAT assigns separate impact categories to the two impacts.

Regarding cross-ecosystem effects, the proponents cite rats on islands. Their predation suppresses seabird pops; reduced guano alters the nutrient dynamics of adjacent coral reef ecosystems. Thus assign impact categories not only to the changes in nutrients, but also to ecological functioning. This provides a more comprehensive view of interconnected effects.

Proponents of the proposed new framework assert that the fundamental distinction between EEICAT and the earlier EICAT is that the earlier assessment is “species-based”, whereas the new one is “impact-based”. It is broader because it focuses on specific combinations of invading species plus the affected systems. It is better able, they assert, to account for contrasting impacts in different invasions.

EEICAT can be applied to any invasion event (i.e., a specific combination of invasive species, recipient system, and context). It broadens the range of evidence that can be integrated into the assessment. Decision-makers benefit from access to more information. The information can also be provided in more easily understood form through two visualization tools:

  1. An “invasive species profile” aggregates all recorded impacts caused by a single invading species. This facilitates clear communication of the bioinvasion’s impact severity to managers and stakeholders, plus how those impacts vary by context.
  2. An “invaded ecosystem profile” compiles impacts from different species to a site or location. This is particularly useful for synthetic analyses (e.g., meta-analyses), evidence syntheses, and manager assessments.

Resulting profiles can help stakeholders prioritize species or ecosystems for responses.

https://www.dontmovefirewood.org/pest_pathogen/phytophthora-root-rot-html/to are ants. No disease agent is discussed or even named. This gap is surprising given the devastating and geographically extensive impacts of e.g., avian malaria, chitrid fungi (Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans) on amphibians, and Phytophthora cinnamomi on the flora of western Australia.

One example in Table 3 pertains to native Hawaiian forests. The underlying study analyzed changes in ecosystem functions caused by the invasive nitrogen-fixing tree Falcataria moluccana. The EEICAT proponents say their analysis of this study would supports more informed decisions in conservation planning and ecosystem management. Indeed, the principal author of the underlying study has recently published a suggested method to manage the Falcataria moluccana invasions by replacing these trees with either native species or valued crops under an agroforestry program. Neither of the articles mentions that exactly this same area (the Puna District on the “Big Island) has suffered widespread death of the native tree ʻōhiʻa lehua (Metrosideros polymorpha) as a result of the invasive disease rapid ʻōhiʻa death (ROD). The more recent article does address the fact that native plant species are extremely rare in this region.

Would integrating studies of tree-killing arthropods and pathogens into the EEICAT system provide benefits? First, let’s consider analytical methodology. Many analyses of forest pests’ impacts already discuss at least some of the wider ecological (and economic) outcomes. (To explor this, visit www.dontmovefirewood.org and read some of the species profiles under the “invasive species” tab.) Would comparing these findings to an EEICAT analysis confirm the proposed methodology? Or would it instead suggest needed adaptations? In either case, the results should improve scientists’ work.

Second, would the science and practice of managing invasive species be strengthened by bridging the differences in methods and terminology between those focused on plants and vertebrates and those focused on tree-killing invertebrates and microbes? Would greater unity result in more attention to bioinvaders from policy-makers and/or conservation practitioners and advocates? Especially since (nearly) all the major forest pest invasions would qualify as “naturally irreversible changes” or even “permanent”: the affected species, ecosystem processes or abiotic conditions are thought unlikely to return to their original state within 10 years or 3 generations (whichever is longer) in the absence of intense human-assisted actions. If joining forces might bring about greater societal efforts, is the EEICAT methodology a promising tool to achieve this goal?

Finally, would applying the EEICAT system improve the analyses of tree-pest impacts? Would this approach result in incorporation of types of effects that would otherwise be missed – either often or in specific cases? Are there relationships among forest species, or between species and ecological functions, that might be discovered? Might preparation of “invaded ecosystem profiles” that include bioinvaders from earthworms to canopy foliage feeders provide an informative perspectives that is now lacking?

SOURCE

Carneiro, L., Pincheira-Donoso, D., Leroy, B., Bertolino, S., Camacho-Cervantes, M., Cuthbert, R.N., et al. (2026) Expanding invasive species impact assessments to the ecosystem level with EEICAT. PLoS Biol 24(3): e3003665. https://doi.org/10.1371/journal.pbio.3003665

Posted by Faith Campbell

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

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

Or https://fadingforests.org/

Is this a way to overcome difficulties detecting invasive pathogens? Is APHIS applying these ideas?

SOD-infected rhododendron in a nursery; photo by Jennifer Parke, ODF

A group of scientists (See Khusnitdinova et al., 2026; full reference at the end of this blog.) contend that landscape interfaces—e.g., crop–forest edges, riparian zones, abandoned agricultural fields and orchards, and nursery–wildland transitions—are active zones of pathogen exchange. Biological and abiotic vectors collectively move pathogens from crops to wild plants, and vice versa. These exchanges create conditions speed up the evolution of pathogen aggressiveness and dispersal traits and promote the selection of generalist pathogen lineages capable of infecting both cultivated and wild hosts. In this way, crop-natural ecotones become not just passive transition zones but centers of adaptation.

The stronger or novel pathogens don’t stay in the specific local area; they are spread by a variety of human activities. Establishing large monocultures of crops and simplifying biological diversity at the landscape level boost inoculum production, limit host genetic diversity, and diminish natural regulation. Pathogens present in irrigation water can be spread during floods. Improperly sanitized green waste and compost can harbor viable oomycete propagules. Foot traffic and heavy equipment can move contaminated soil. Movement of infested plants for planting can transport the disease to a different continent. One example cited by Khusnitdinova et al. (2026) is the spread of numerous Phytophthora spp. from nurseries to forests and shrublands. A second example is rapid ʻōhiʻa death. They say it demonstrates that 1) a combination of human movement, forestry activities, and animal vectors can enable rapid local and landscape-scale spread; and 2) management measures (biobarriers, access control, restriction of animal movements, and phytosanitary inspection of planting material) can curtail that spread.

Meanwhile, the changing climate is causing shifts in the latitudinal and elevational distribution of plants and their associates; changing reproduction rates and latent periods; altering ranges and connectivity; and affecting disease incidence and severity. The direction is not always predictable; while drought or heat might reduce fungal and oomycete epidemics, the same conditions increase host stress and so might worsen disease outcomes.

Plant health scientists can use these concentrated geographic areas to focus plant disease surveillance. By integrating molecular and genomic tools with remote sensing and Geographic Information System (GIS)-based monitoring, plant health agencies can more quickly detect newly emerging diseases and implement effective action to counter the threat. 

However, Khusnitdinova et al. (2026) warn that surveillance employing these technological advances can reduce the risk that a pathogen will “spill over” from an anthropogenic to a natural ecosystem or vice versa only if pertinent sectors are transformed. Yes, they need resources: funding, staff, facilities. Also required is unification – or at least coordination. Khusnitdinova et al. (2026) advocate abandoning the compartmentalization that currently separatesforest health studies from invasive-plant and infectious-disease ecology studies. Instead, agencies should consider managed and natural systems together. They should conduct joint surveillance programs, share data standards, and coordinate management of the transition zones. In other words, apply a “One Health” landscape-based approach to the entire landscape.

Khusnitdinova et al. (2026) add that implementing such combined surveillance programs is especially vital in biodiversity-rich regions which have limited monitoring capacity. Might I suggest Hawai’i? 

ohia trees killed by ROD; photo by J.B. Friday, UH

Other facts that challenge traditional phytosanitary practices

Khusnitdinova et al. (2026) provide strong evidence that pathogens change – sometimes quickly. Is the current regulatory system sufficiently flexible and agile to effectively address these developments?

First, pathogens’ host range is not fixed. Instead, it is a trait that changes quickly under the influence of alterations in effector repertoires, plant immunity genes, and environmental conditions (including those driven by human actions). Even small genetic changes—such as mutations, gene losses or gains, or horizontal gene transfers—can enable pathogens to infect new hosts or weaken previous infection barriers. They suggest that plant pathogens with broad host ranges, e.g., Phytophthora cinnamomi, can easily move between hosts in agricultural plantings, ornamental landscapes, and semi-natural vegetation within a relatively small region. Such frequent spillovers maintain inoculum in landscape mosaics and complicating eradication or containment efforts.

Khusnitdinova et al. (2026) note that host-range expansions have especially long-term consequence in forest ecosystems, where loss of a single tree species can change understory makeup, light and moisture patterns, related fungi and invertebrate communities, and ultimately, landscape diversity and function. They cite chestnut blight and sudden oak death in North America and ash dieback in Europe as examples.

In addition, Khusnitdinova et al. (2026) maintain that genetic recombination is now recognized as a fundamental driver of innovation in plant pathogen populations. Table 2 of their publication lists pathogens exhibiting well-documented and experimentally confirmed cases of recombination, hybridization, or other forms of genome exchange. Forest-related examples include several Phytophthora hybrids and the ash decline fungus, Hymenoscyphus fraxineus.

Phytophthora dieback in Western Australia

Khusnitdinova et al. (2026) add their voices to a growing chorus decrying a global forest health crisis. They say that repeated pathogen introductions—often via trade in plants and wood—have shifted many temperate and boreal forests into states characterized by higher tree mortality, increased dominance of opportunistic or disturbance-adapted species, and reduced functional diversity. These changes lead to reduced resistance [defined as the capacity to limit damage during a new outbreak] and resilience [defined as the speed and trajectory of post-disturbance regeneration and ecosystem reorganization]. They note that increasing tree species diversity is one of the few management interventions that succeeds in strengthening both forest resistance and resilience to pathogens—by decreasing host density for specialist pathogens and reducing continuous “fuel” for epidemics.

One step toward improving scientific understanding on the scale they advocate, in their view, is the European Holistic Management of Emerging Forest Pests and Diseases (HOMED) effort. HOMED combines plant pathology, forest ecology, and biosecurity. The emphasis is on early detection, risk assessment, and management of human-mediated pathways, incl plant trade and nursery systems. The initiative aims to limit pathogen establishment and spread while strengthening forest resistance and resilience under global change. Participants also try to provide practical solutions for stakeholders to manage emerging native and non-native pests and pathogens threatening European trees not only in forests, but also in nurseries, urban and rural areas.

USDA Secretary Brooke Rollins

I am inspired by the proposals in Khusnitdinova et al. (2026). In hopes that USDA will explore how to implement them, I presented a poster presentation at the annual USDA Research Forum on Invasive Species. In that poster I suggested that these ideas complement USDA Secretary Rollins’ Memorandum on departmental research priorities. The need for research to clarify scientific puzzles is particularly acute regarding tree-killing pathogens nematodes, etc.

I suggested prioritizing research on the following issues:

  • Setting up intensive monitoring programs targetting the agriculture/natural system interfaces, as recommended by Khusnitdinova et al. (2025). These authors describe useful technologies in molecular diagnostics, genomic surveillance, environmental DNA, and remote sensing to detect fungi, oomycetes, rusts, bacteria, and viruses. Kantor et al. (2025) define techniques applicable for nematodes.
  • Rapid analysis of potentially invasive species and their pathways of entry revealed by “early warning” systems [e.g., APHIS’ “PestLens” website; “door knocker” introductions; academic studies; and “unimportant” species introduced to the U.S. (e.g., Leptosillia pistaciae in California)].  
  • Exploring ways (in addition to those suggested by Khusnitdinova et al. 2025) to shorten the time lag between introduction of a pathogen and its detection.
  • Incorporating into risk analyses information from sentinel garden program. Fund expansion of data collection and analysis to address asymptomatic plants, sampling techniques, and seasonality, as outlined by Drs. Eliana Torres Bedoya and Enrico Bonello (at the 2025 USDA Research Forum) and Raffa et al. (2023).

Over a somewhat longer-term, I suggested that research address these topics:   

  • Find techniques to speed up determination of disease causal agents – which often remain obscure for years or decades. The International Plant Protection Convention (IPPC) link requires countries to name the causal agent before regulating disease hosts and vectors.
  • Determine which components of a “systems approach” are most effective against each type of pathogen – fungi, oomycetes, rusts, bacteria, viruses, nematodes, etc.
  • With state counterparts, explore ways to better curtail domestic spread of organisms once they have established in the United States.
  • Integrate socio-economic drivers of pest introductions into studies. E.g., why do some organisms suddenly spread to numerous countries over a period of a few years?
  • Greatly expand efforts (in house and by collaborators) to breed trees resistant to established and newly detected pathogens.
  • Increase research supporting biocontrol.

As I have frequently complained in the past, the international phytosanitary system has failed to protect Earth’s forests and other natural ecosystems from non-native plant pests (or invasive plants). This failure has been documented by Weed, Ayres, and Hicke (2013), Fei et al. (2019), Quirion et al. (2021) for North America; and Gougherty (2023), Wu (2023), Sitzia et al. (2021), Martinac et al. (2025) and Khusnitdinova et al. (2025) from a global perspective.

Challenges:

  • Most microorganisms are unknown to science – “unknown unknowns”.
  • Scientists usually cannot predict the impact of known micro-organisms on new hosts under novel environmental conditions.
  • The World Trade Organization’s SPS Agreement and the International Plant Protection Convention (IPPC) demand unachievable levels of specificity re: a potential pest’s impact.
  • Most tree-killing pathogens are detected after they have entered the forest.
  • Agencies assign a low priority to protecting natural ecosystems from bioinvasion.
  • Resources (funds, staffing, etc.) are unreliable for agencies carrying out the full range of efforts, from assessing various risks to restoring pest-resistant trees to the forest.

SOURCES

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

Gougherty, A.V. (2023) Emerging tree diseases are accumulating rapidly in the native & non-native ranges of Holarctic trees. NeoBiota 87: 143–160. https://doi.org/10.3897/neobiota.87.103525

Kantor, C., Teixeira, M., Kantor, M., and Gleason, C. 2025. Tiny Invaders, Big Trouble: Emerging Nematode Threats in the United States. Phytopathology 2025   115:587-595  https://doi.org/10.1094/PHYTO-09.-24-0290-IA

Khusnitdinova, M., V. Kostyukov, G. Nizamdinova, A. Pozharskiy, Y. Kydyrbayev and D. Gritsenko. 2026. Cross-Ecosystem Transmission of Pathogens from Crops to Natural Vegetation. Forests 2026, 17, 76

Martinac, M-L., F. Ningre, A. Dowkiw, N.Le Goff, B. Marcais. 2025.  High host density favour ash dieback Preprint  Plant Pathology

Quirion BR, Domke GM, Walters BF, Lovett GM, Fargione JE, Greenwood L, Serbesoff-King K, Randall JM & Fei S (2021) Insect and Disease Disturbances Correlate With Reduced Carbon Sequestration in Forests of the Contiguous United States. Front. For. Glob. Change 4:716582.  [Volume 4 | Article 716582] doi: 10.3389/ffgc.2021.716582

Sitzia, T., T. Campagnaro, G. Brundu, M. Faccoli, A. Santini & B.L. Webber. 2021.  Routledge Handbook of Biosecurity & invasive species. Chapter 7. Forest Ecosystems. ISBN 9780367763213

Weed, A.S., M.P. Ayers, J.A. Hicke. 2013. Consequences of CC for biotic disturbances in North American forests. Ecological Monographs, 83(4), 2013, pp. 441–470

Wu, H. 2023/24. Modelling Tree Mortality Caused by Ash Dieback in a Changing World: A Complexity-based Approach MSc/MPhil Dissertation Submitted August 12, 2024. School of Geography & the Enviro, Oxford University

Posted by Faith Campbell

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

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

Or https://fadingforests.org/

A “fix” for some invaded Hawaiian ecosystems?

Falcataria moluccana tree; photo by Forest & Kim Starr via Flickr

Nitrogen-fixing tree species have been recognized as damaging to invaded ecosystems for decades. These trees increase soil N availability through increased N content in litterfall. The elevated soil N availability might persist long after the mature individuals responsible for creating such litterfall have ceased to exist. When this happens, some plant species able to exploit increases in nutrients and light, e.g., non-native grasses and forbs, might quickly dominate post-control succession.

In Hawai`i one of the worst nitrogen-fixing tree species is albizia (Falcataria falcata) [formerly Falcataria moluccana, Paraserianthes falcataria, or Albizia falcataria]. This fast-growing species has aggressively invaded across the archipelago, transforming composition, structure, and function of remnant lowland wet forests. There are an estimated four million F. falcata trees across the Hawaiian islands; 720,000 large trees (i.e., > 25 cm DBH). The trees spread rapidly once established because the small seeds remain attached to the lighweight pods, which can be blown for long distances in wind storms (J.B. Friday, University of Hawaii, pers. comm.).

Stands with contiguous overstory F. falcata canopies reduce light availability to 20% of ambient levels; adding in understory vegetation further reduces light to ~5% of ambient levels. Albizia’s abundant and persistent seedbank promotes its return to dominance after mature individuals controlled.

understory of an albizia-invaded area; invasive plants: forbs along roadside; Miconia calvescens in the shade. Photo by F.T. Campbell

Beyond the conservation threats, albizia also poses a threat to residential communities & agricultural lands. The trees are some of the fastest growing species in the world, easily growing 5 m in height annually over the first few years and reaching up to 40 m. When their brittle branches fall they crush structures and entire trees can topple during windstorms. The damage is exacerbated by trees’ widespread presence. When Tropical Storm Iselle hit Hawai‘i island in 2014, over 10,000 people were stuck in their subdivisions or on their farms because fallen albizia had blocked all their access roads (Friday, pers. comm.).   

Until recently control efforts have relied largely on clearing the land using large machinery (e.g., bulldozers). This is expensive and – worse – not very effective because the magnitude of disturbance to the soil disturbance often leads to explosive germination of the trees’ seeds.

There has been success recently through application of a target-specific herbicide (aminopyralid) at low doses (Leary et al. 2014). Hughes et al. (2025) found that herbicide-killed F. falcata quickly lost their leaves. This litterfall increased litter inputs of N and P that translated to increased soil nutrient availability that is exploited by extant understory vegetation (non-native grasses and forbs). These plants formed a continuous layer that severely limited germination of F. falcata seeds. In their study plots the number of saplings per ha after three years was only 18, despite the presence of perhaps 8 million seeds!

As an early successional pioneer species, F. falcata requires high light conditions to germinate, persist, & grow. The rapid growth & thorough occupation of the understory by other species prevents the species’ re-establishment. However, these aggressive non-native plants also prevent restoration of native Hawaiian species. There is little to no regeneration of native plants under albizia, either on stands that established on abandoned agricultural or ranch lands or under trees that spread into native forests.

Hughes et al. (2025) suggest manipulating the succession trajectory by planting desired species – either native species or species that have cultural importance to native Hawaiians – under albizia stands before herbicide treatment. If the land is to be restored to agricultural use, mechanical clearing would be used rather than herbicide used as felling the brittle dead trees is hazardous to equipment operators, and standing dead trees would pose a risk to farmers. In a forest setting, understory planting before herbicide treatment of the canopy-forming F. falcata stands would allow desired species to take maximum advantage of the increased resources (i.e., light and nutrients) (Friday pers. comm.).  

Even after invasive N-fixing trees have been physically removed, the soil legacy effects of transformed microbial communities, depleted native seedbanks, increased available soil N, and dominance by undesirable weed species are daunting barriers to restoration of native species.  With intensive management, though, these lands can be restored to agricultural production. Dozens of acres of papaya farms have been established on areas in the Puna district of Hawai‘i island on lands formerly occupied by albizia (Friday, pers. comm.).

In this case, re-establishment by native species is not expected due to their scarcity in study areas. These areas had experienced significant disturbance (i.e., fire, and/or conversion to agriculture) before albiziast and establishment. Instead, the proposal’s objective is primarily to understand whether, how, and to what extent F. falcata stands could be eliminated from areas in a manner that constrains  the species’ seedling recruitment and subsequent re-establishment leading to overstory dominance once again (Friday, pers. comm.).

Hughes et al. (2025) emphasize the need for long-term follow-up to ensure that F. falcata does not re-establish later on. The species’seeds retain 70 – 90% viability following 18 months in storage; possibly some much longer. Also, a few saplings did still establish. The non-native grass invasion  might lead to declines in soil N availability that provide opportunities for secondary invasion by N2-fixing treesin light gaps. Dr. Friday reports that practitioners revisit treated areas to kill these seedling while they are still 10 – 20 feet tall.

Conclusions

Hughes et al. (2025) assert that management of this large, fast-growing, & disruptive invasive tree is possible by exploiting its weakness of shade intolerance. Dr. Friday agrees that fast-growing timber species, e.g., Eucalyptus, could outcompete regenerating albizia. However, will there be a market for locally grown timber? Dr. Friday doubts the possibility of agro-forestry plantings of smaller or slower-growing species because of the danger that the overtopping dead F. falcate would fall on and crush agricultural workers or structures.

The fall hazard would presumably apply in other parts of the Pacific & elsewhere where F. faclata poses the same invasiveness problems.  

 ʻōhiʻa trees killed by ROD in the Puna District of Hawai`i Island; photo by F.T. Campbell

Hughes et al. (2025) do not mention that the native tree that was probably most widespread before the disturbances is ʻōhiʻa lehua (Metrosideros polymorpha). In precisely the same lowland region of the Big Island where they conducted their study,  ʻōhiʻa has been killed by a newly introduced disease, rapid ʻōhiʻa rust (ROD). This new invader greatly complicates any effort aimed at restoring native plant species.

healthy  ʻōhiʻa in Hawaii Volcanoes National Park; photo by F.T. Campbell

SOURCES

Hughes, R.F., C. Morrison, E. Bufil, J. Leary. 2025. Ecosystem response to management of an invasive N-fixing tree in Hawai`i. Trees, Forests and People 21 (2025) 100932

Leary, J., J. B. Friday, S. Kaye, and F. Hughes. 2014. Proper technique of injecting albizia (Falcataria moluccana L.) with the herbicide Milestone ® (active ingredient aminopyralid).

Dr. Friday provided the following more local references:

https://plantpono.org/high-risk-plants/falcataria-moluccana-albizia

https://dlnr.hawaii.gov/hisc/info/biocontrol/latest-biocontrol/falcataria-molucca

Posted by Faith Campbell

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

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

Or     https://fadingforests.org/

Tree-killing pests can undermine conservation programs on tropical islands

an aye-aye – one of the highly endangered lemurs dependent on moist tropical forests of Madagascar; photo by Andrew Ciscel via Wikimedia

A forthcoming study examines two important issues: interactions of pathogens’ spread and changing climate, and invasive species threats to tropical islands’ forests.

Underwood et al. (in press) analyzed how an introduced vascular wilt pathogen — Leptographium calophylli – is likely to affect a tree endemic to Madagascar’s already threatened mid-level elevation humid & subhumid forests, Calophyllum paniculatum (sorry; I can find no photographs of the tree species).

Climate change is expected to cause substantial shifts in temperature and precipitation patterns on the island. These temperature and moisture regimes in turn govern pathogen sporulation, infection efficiency, and survival. They also affect the host’s levels of stress and defenses. The direction of change is not certain, however. In some cases, warming and other changes to the climate might facilitate a pathogen’s spread, allowing it to track shifts in the host’s range and expand into previously unoccupied refugia. In other cases, these changes might erect environmental thresholds that limit the pathogen’s survival and spread, thereby creating spatial refugia for the host.

diademed lemur, courtesy of Animalia

Environmental change increases the area of suitable landscape, that is, it weakens climatic barriers to establishment. Continued anthropogenic movement of some vector (biological or not) generates multiple introductory events over time. As a result, the likelihood of a successful establishment also increases, even if the probability per individual introduction is unchanged. Underwood et al. say that invasion outcomes thus become increasingly dependent on propagule pressure.

On many other tropical islands the threat from climate change is exacerbated by deforestation. On Madagascar, clearing driven by slash-and-burn agriculture and fuelwood harvesting has already reduced natural forest cover to less than 10% of its original extent. [For more on this topic, see e.g., Mittermeier et al. (2011).]  Underwood et al. cite a determination by the ForestAtRisk model that humid forest in Madagascar could be almost entirely lost by 2100.

Loss of Madagascar’s forest has global implications. The island is one of 36 global biodiversity hotspots for both flora and fauna (e.g., lemurs). Its flora exceeds 12,000 plant species, of which 83% are endemic. In this case, the host tree species — Calophyllum paniculatum — is already considered vulnerable by the International Union for the Conservation of Nature (IUCN). Thus it is of global importance to understand the relative importance of several threats so that conservations can adopt the most effective countermeasures.

While they do not say so explicitly, it appears that Underwood et al. worry that too few of the conservationists active on Madagascar are paying attention to the possible impact of introduced pathogens. They note that pathogen-driven mortality of dominant or functionally unique trees can rapidly alter community structure and ecosystem function, potentially triggering local extinctions and cascading ecological consequences. For example, if an infection removes mature trees, their loss reduces fruit and nectar availability and so depresses populations of dependent wildlife. The trees’ death also diminishes above-ground carbon stocks and litter inputs. In combination, these impacts can shift community composition toward disturbance-tolerant states and heighten susceptibility at forest margins. These changes difficult to reverse once thresholds crossed.

red-bellied lemur in Ranomafana National Park – site of the first detection of Leptographium calphylli; via Flickr

This threat is not hypothetical. Since 2016 mature C. paniculatum at one site – a National Park – have been dying from a vascular wilt disease caused by a species in the Leptographium genus, probably Leptographium (formerly Verticillium) calophylli. While the species hasnot yet officially been recorded in Madagascar, it is established on neighboring Indian Ocean islands and across much of mainland Africa. Various species in the fungal genus are known to cause disease in other woody hosts. Underwood et al. suggest it was probably transported to Madagascar on infected wood, although they present no data.

Inside forests, Leptographium spp. are vectored by bark beetles in the Cryphalus genus. At least 25 Cryphalus species occur on the African Continent; some are vectoring disease on Seychelles and Mauritius.

The analysis by Underwood et al. indicates that future climatic conditions are likely to worsen the Leptographium calophylli infection over coming decades. The causal agent is likely to retain two-thirds of its current probable distribution and expand into previously uninhabited regions. The suitable habitat is expected to stretch across the entire north-south humid belt – the entire distribution of the host tree. Underwood et al. (in press) say it is even possible that the pathogen might remain in the forest, subsisting on other hosts, after C. paniculatum becomes functionally extinct across its range.

Meanwhile, that host – Calophyllum paniculatum – is projected to experience severe range shifts, with an overall net contraction across all climate change scenarios. It is forecast up to 67% of its current area by 2100. This range contraction will be compounded by fragmentation and dispersal limitation resulting from from deforestation. The refugia will be few and geographically isolated by late in the 21st century.

red-veined swallowtail; photographed in Ranomafana National Park by Frank Vassen, via Wikimedia

Are conservationists considering the implications of Leptographium calophylli’s probable persistence? Underwood et al. imply they are not; they say the impact of this and related pathogens on Madagascar & nearby islands is “still an unknown to the conservation community”. They urge their colleagues to conduct a set of research actions to identify, monitor, & limit the fungus’ spread – – and thereby improve the effectiveness of conservation efforts.

  1. Host range & other targets: determine whether L. calophylli infects other taxa in Madagascar – especially the endemic species and genera. They suggest systematic field sampling of multiple species across sites within the core probable range of L. calophylli. A trained pathologists should be consulted to officially identify the pathogen.
  • Determine the spread phase of the pathogen. They suggest random sampling of species & sites within & outside of the fungus’ probable distribution, mapping the possible start point & dispersal patterns, including both anthropogenic & natural spread routes.
  • Assess applicability of IPBES tools & suggestions for invasive species management to the case of a fatal pathogen in the context of tropical islands’ characteristics. How might Madagascar implement prevention, early detection & rapid response systems?

I applaud Underwood et al. for trying to alert the conservation community active on tropical islands to the simultaneous impacts of multiple global & regional change drivers on vulnerable species. Probably other host-pathogen systems are experiencing the same diverging trajectories that might intensify their biodiversity loss, particularly when compounded by deforestation.

SOURCES

Mittermeier, R.A., E.E. Louis Jr., M. Richardson, C. Schwitzer, O. Langrand, A.B. Rylands. 2010. Lemurs of Madagascar. Conservation International, Arlington, USA. ISBN 9781934151235

Underwood, E.L., K.A Brown, A. Ronnfeldt, M. Mulligan, N. Walford, R. Allgayer. In press. Climate change facilitates fungal pathogen expansion while driving endemic host range contractions in a tropical biodiversity hotspot. Research Square.

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

Horizon Scanning – 2 experiences

sorting coffee beans; photo by Niels Van Iperen via Wikimedia

 
Many have recognized that preventing introduction of invasive species is the most efficient approach to minimizing their ecological and economic impacts. Prevention requires many capacities, including control over a country’s borders, strong border biosecurity agencies and policies, and foreknowledge of probable pathways of introduction and high-impact species that might arrive.
 
Horizon scanning is one tool for gathering information about non-native species likely to enter, how they might arrive, and their probable impact. Horizon scanning involves a systematic search for potential invaders, assessment of their potential to harm BD, economic activities and human health, and opportunities for impact mitigation. It thus supports choice of prevention policies, targetting of efforts, and implementation of early identification and eradication procedures (Kenis et al. 2022; Martinou et al. 2026)
 
I have reviewed two case studies of the application of horizon scans.
 
Plant Pests in Ghana
 
One horizon scanning exercise aimed to identify and rank potential invasive non-native plant pest species that could be harmful to agriculture, forestry, and the environment in Ghana. The ultimate objective was to enable prioritization of actions aimed at preventing their introduction. As the participants in this exercise note (Kenis et al. 2022), the resource-poor farmers of Sub-Saharan Africa are particularly vulnerable to invasive pests that attack their crops, both those grown for subsistence e.g., maize and sorghum, and those grown for the international market, e.g., cacao and tomatoes. The continent’s vulnerability is increased by porous borders, weak cross border biosecurity, and inadequate capacity to limit or stop invasions. This exposes Africa both to repeated invasions and to continued spread across the continent once they have arrived.
 
Marc Kenis and 21 others assessed 110 arthropod and 64 pathogenic species using a simplified pest risk assessment. This set had been winnowed from an initial list of 1486 arthropods, nematodes and pathogens. Unfortunately, assessors were unable to agree on confidence levels for the assessments.
 
Sixteen of the assessed species – 14 arthropods and two pathogens – were thought at the time to not be on the African continent. Another 19 arthropod and 46 pathogenic species had been reported established in the neighboring countries of Burkina Faso, Côte d’Ivoire, and Togo. Seventy-seven species [62 of them pathogens] were recognized as established elsewhere in Africa.
 
Ninety-five percent of the arthropods were considered likely to arrive as contaminants on commodities, i.e. on their host plants; 23% were also likely to arrive as stowaways; some good fliers already present in neighboring countries could also enter unaided.

The 64 pathogen species included 14 bacteria, 16 fungi, 14 nematode, seven water moulds (Kingdom: Chromista), and 13 viruses. Sixty-two of these species have been detected on the African continent; 46 are reported in neighboring countries. Thirty-one (48.4%) of the pathogenic organisms were considered likely to arrive both as contaminants on commodities and/or as stowaways; Twenty-six (40.6%) probably arrive only as contaminants; five could arrive exclusively as stowaways. Kenis et al. (2022) specify which of the fungi, nematodes, viruses, bacteria, and water moulds fall into which category.
 
The most important input in the threat scoring process was likelihood of entry. The unsurprising result was that species known to be in neighboring countries or spreading rapidly in Africa received the highest overall scores. The likelihood of establishment was less important because the assessors had already excluded species they thought would encounter an unsuitable climate or absence of host plants. The impact score played an important role in the overall score; it was based primarily through their potential economic impact. There is little information about or attention to the potential threat of non-native plant pest species to non-commercial plants. Kenis et al. (2022) cite well-known examples to remind us that invasive plant pest species have had “huge impacts” on native tree species and biodiversity in North America and Europe. On the African continent, most non-native pests attack mostly concern exotic trees. They note one exception, Euwallacea fornicatus, DMF a wood-boring beetle from Asia killing many native trees in South Africa.

Bemisia tabaci; one of the arthropod pests in a country bordering Ghana; photo courtesy of INCTELUNI


Kenis et al. (2022) state that some of the several alien arthropods and pathogens identified in neighboring countries might already be present in Ghana although not yet recorded or identified to the species level. They say it is essential to clarify these species’ status by enhanced surveillance and applying morphological and molecular methods. Some of these possibly introduced species received high scores in the assessment. They threaten cocoa, a key crop in Ghana, and vegetable crops.
 
I am disappointed that Kenis et al. (2022)’s main actions suggested for both arthropod and pathogenic species that scored highly are to ramp up surveys and to conduct full pest risk analyses. It is true, as thy point out, that such assessments are required by international regulations before a country may implement phytosanitary measures. [See discussion of the requirements of the International Plant Protection Convention here.]  
 
To some extent, the horizon scan echoed the obvious: most of species ranked high are already on the African continent, including 19 arthropod and 46 pathogenic species known to be established in neighboring countries. Plus, the recommended actions are minimal. Since Kenis et al. (2022) is essentially the scan itself, it provides no information on whether Ghana has implemented the recommendations. Still, given what I assume is lagging preparation across most of Africa, the horizon scan might be useful in encouraging countries to set priorities and take some action.
 
Cyprus
 
The second case study of applying horizon scanning is more encouraging. Scientists on Cyprus tried to assess the efficacy of their own horizon scanning exercise. I applaud their decision to do so. The horizon scan itself might have been undertaken on their own initiative? Or it might have been taken on in response to European Union regulations, which oblige Member States to enact measures to prevent or manage introduction and  spread of invasive species designated as of Union Concern. The Union also encourages development of national invasive species lists and provides a legal basis for emergency measures in response to a detection.
 
Scientists carried out two horizon scan workshops in 2017 and 2019. The two workshops evaluated 225 and 352 species, respectively, to predict which are most likely to arrive and the level of provable impact to Cyprus’ biodiversity, human health, and economy. In 2023, four to six years after the workshops, scientists evaluated the listed species to reveal the accuracy of the predictions and actions taken so far (Martinou et al. 2026).
 
During the period 2017 – 2023 there were 183 Martinou et al. (2026) found publications naming 183 non-native species not previously officially detected in Cyprus. (As I will discuss later, a significant number of these species had been present on the island in 2017 but knowledge of their presence did not reach the assessors.) Of the 183 newly reported species, 31 had been included on some list of invasive species (e.g., EPPO or European Union list of species “of Concern”) or predicted by the horizon scanning exercises to rank amongst the top 100 riskiest species.
 
Cyprus’ horizon scans highlighted the risk posed by 10 of these 26 species. Martinou et al. (2026) focused on seven of them as having been ranked as high risk to the nation’s BD, human-health or economy. They added an eighth species, a venomous marine fish.
 
A further 10 species that were detected in the country had received lower impact scores, so they had not been included on the high priority lists of the horizon scans.
 
One of the species allotted a lower impact score, Spodoptera frugiperda, is under eradication, although it is widely distributed on the island. This action might be in response to the species’ inclusion on the EPPO A2 list.
 
As I noted above, scientists learned that 17 of the species had been present in Cyprus before the scanning exercises were undertaken but since their presence was then unknown to the participants, they were assessed as if still had not been introduced. This points to the country’s non-native species checklists not being fully up to date at the time.
 
Nine plant species common in the plant trade were most certainly present on Cyprus before the horizon scans (2017), but there were no published reports of their escape from cultivation. Nevertheless, they might have already been present in the wild. It is also possible that at least some escaped since the scans. Always tricky; always depends on who looking where.
 
Actions upon detection of specific taxa
 
Detection of the common myna (Acridotheres tristis) – a species widely recognized as invasive – occurred in January 2022, close to a port. Eradication measures were implemented by the wildlife agency. Martinou et al. (2026) believe the introduction was facilitated by shipping. They think there is an extremely high risk of repeated introductions of mynas.

Aedes aegypti; photo by James Gathany via Flickr


Two mosquitoes were detected in 2022. A pilot project to eradicate The yellow fever mosquito, Aedes aegypti, was begun in 2023. There is no information about its success.  The Asian tiger mosquito, Aedes albopictus, has been documented by citizen scientists as spreading rapidly in the suburbs of Limassol and Nicosia. To date the proposed interventions have been unsuccessful, possibly due to focusing on public land while the mosquitoes can also breed on private properties.
Detection of the little fire ant Wasmannia auropunctata (in 2022) was not surprising since it had already invaded other regions of the Mediterranean. Martinou et al. (2026) believe the introduction was probably facilitated by the plant trade. The scientists note that ant management and eradication efforts are both challenging and costly, but do not report whether any has been initiated.
Detection of several marine invasive species was reported, some by citizens, e.g., divers or fishermen.
Among the 17 species determined to have been present on the island since before 2017 were some fairly conspicuous vertebrates: brown rat (Rattus norvegicus), raccoon Procyon lotor, two tortoise species, house crow (Corvus splendens) ruddy duck (Oxyura jamaicensis). Also two more ant species, Solenopsis geminata and Trichomyrmex destructor. There were also several non-native plant species, including the notorious seaweed Caulerpa taxifolia.
 
Value of the Horizon Scan
 
I am surprised that Martinou et al. (2026) do not explore why so many detections were published in 2022 since they assert that horizon scanning helped raise awareness amongst the authorities, scientists and the public. They do note that this awareness led, in some cases, to a rapid response by the competent authorities. Martinou et al. (2026) assert further that the exercise facilitated communication between invasive species experts, policy makers and society, encouraged active engagement and raised awareness regarding the importance of early warning, rapid response, and management of IAS. They therefore propose that the horizon scanning process for the island of Cyprus be repeated regularly – every five to 10 years – since new introductions continue. These efforts should include development pathway management plans and contingency planning that would be shared with local authorities and stakeholders.

 Martinou et al. (2026) note two detections that have not, apparently, resulted in establishment. A dead specimen of brown marmorated stink bug (Halyomorpha halys) was reported in luggage in May 2022, the result of ‘Bug Alert Cyprus’ awareness campaign.  The Colorado potato beetle (Leptinotarsa decemlineata) was detected in 2010 by Department of Agriculture inspectors in a consignment of potatoes. The agency ordered immediate destruction. Imports of potatoes are subject to special phytosanitary requirements for protected zones. It is not clear that this measure was implemented by Cyprus or is a European Union decree.

brown marmorated stinkbug; courtesy of Oregon Department of Agriculture


Martinou et al. (2026) are worried that no introductions have been reported at border crossings across the ‘Green Line’ [the United Nations-controlled buffer zone between Greek and Turkish portions of the island]. They call for enhanced cross-community collaboration and improved information and data sharing for border control staff and customs officers about invasive species. They suggest that border order inspections and pathway monitoring could be supported by local experts offering identification services for a variety of taxa. They suggest that the horticultural industry is a major pathway for the introduction of plants and insects such as ants.
 
Martinou et al. (2026) also advocate efforts to improve communication among the various institutions and authorities that discover bioinvasions and are responsible for taking action. While researchers + experts from government departments involved in the horizon scans are informed, the findings of the horizon scanning needs to be provided to e.g., customs officers, fishers, ship crews, pet shop owners, and school teachers. Much of this information might be exchanged through informal networks and through a growing body of web-based databases and other resources.
 
Early detection and rapid response depends increasingly on efforts by citizen scientists to report observations of IAS of concern. Martinou et al. (2026) note that six of the invasive species identified in the horizon scanning exercise were reported by citizen scientists. They express the hope that artificial intelligence and deep learning models could help identify species from photographs collected by citizen scientists on platforms such as iNaturalist. Such platforms also facilitate rapid dissemination of information to decision-makers who can take appropriate action. Martinou et al. (2026) also hope eDNA can help detect cryptic bionvaders, including freshwater or marine taxa.

 As I blogged earlier, Mark Hoddle had endorsed several components of prevention programs:
* Early research to identify natural enemy species that might “self-introduce” along with the invading host.
* Collaborating with non-U.S. scientists to identify and mitigate invasion bridgeheads. 
* Sentinel plantings. These plantings can also support research on natural enemies of key pests. [A year ago, Eliana Torres Bedoya of Ohio State alerted participants in the annual USDA research forum on invasive species that fungi, including potential pathogens, were isolated from asymptomatic plants;
Detection of the full range of fungal pathogens requires that samples must be collected throughout the growing season; microbes present differ.
Need to expand surveillance beyond symptomatic plants – at both sentinel gardens and plant health border inspection stations.
*Integrating online platforms, networks, professional meetings, and incursion monitoring programs into “horizon scans” for potential invasive species. He mentions specifically PestLens, (https://pestlens.info/); online community science platforms, e.g., iNaturalist; international symposia; and official pest surveillance, e.g., U.S. Forest Service’s bark beetles survey and surveys done by the California Department of Food and Agriculture and border protection stations. 
 
That blog also cites Weber et al.’s support for sentinel plant nurseries because accidental plant and herbivore invasions often occur at the same points of entry.
 
At the 2026 meeting of the annual USDA Research Forum on Invasive Species, Ashley Schulz (Mississippi State) reported findings of study analyzing establishment of insects imported deliberately as biocontrol agents as clues to bioinvasion. She found that generalist phytophagous insects might be more likely to find a suitable host and survive after introduction. The “goldilocks” standard applies: the host must be sufficiently closely related to the insect’s native host to be recognizable but sufficiently distant so that it lacks defenses. Considering impact, phytophagous insects that feed on structures not easily restored – e.g., main stem or root, cause more damage than those that feed on easily replaced leaves. Entomopagous insect, on the other hand, must be able to find hosts that can hide or defend themselves. This means that highly specialized insects might be more likely to establish.
      
SOURCE
 
Hoddle. M.S. 2023. A new paradigm: proactive biological control of invasive insect pests. BioControl https://doi.org/10.1007/s10526-023-10206-5
 
Kenis et al. 2022. Horizon scanning for prioritizing invasive alien species with potential to threaten agriculture and biodiversity in Ghana. Neobiota 71: 129-148 (2022) doi: 10.3897
 
Martinou, A.F., J. Demetirou, I. Angelidou, N. Kassinis, A. Melifronidou, J.M. Peyton, H.E. Roy, A.N.G. Kirschel. 2026. Multiple introductiions of invasive alien species on a Mediterranean Island predicted by horizon scanning. Biological Invasions (2026) 28:41 https://doi.org/10.1007/s10530-025-03729-8
 
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
Or
https://fadingforests.org/
 

Tree-Killing Pests = Existential Threats to U.S. National parks

black bears in a whitebark pine (Pinus albicaulis) in Yellowstone National Park; tree species is vulnerable to white pine blister rust. Public image

America’s national parks protect some of Earth’s most unique and valued species, ecosystems, geologic features, and cultural sites. These values are under threat from multiple interacting climatic changes. Over the last 100 years, national park units have experienced a disproportionate degree of warming and precipitation change relative to the United States in general. These changes are projected to continue.

The types of change are not limited to temperature and precipitation. These alterations bring multiple cascading impacts such as extreme weather events, forest insect outbreaks, more frequent and severe wildfires, and other novel disturbance regimes. Furthermore, the new events occur both individually and simultaneously. Michalak et al. (2026) fear that these disturbances and stressors might trigger irreversible ecological transformations in our national parks. The authors hope to prompt park managers to evaluate park-specific threats and plan how to respond.

Michalak et al. (2026) analyzed threats from the multiple interacting forces to determine which parks are greatest at risk. They limited their analysis to 259 parks in the continental states (including Alaska) and to parks recognized by the agency as possessing natural resource values. Some historic or cultural sites are included; I am somewhat confused about the criteria applied.  I regret that they lacked sufficient data to include parks on the Hawaiian and Caribbean islands.

Hawaiian birds threatened by avian malaria; picture via Flickr

Their analysis defined potentially transformative impacts as heightened risk of fire, drought, sea-level rise, and forest insects and pathogens (not limited to non-native species). An example of such impacts is a prediction that a significant proportion of the park’s area would be inundated during storm surge.

Michalak et al. (2026) identified 174 parks (67% of the units analyzed) as most exposed to one or more of these potentially transformative impacts.  The number of parks facing cumulative vulnerability across multiple dimensions was highest in the Midwest and East. Their peril is due to high physical exposure to the transformational change, exacerbation of existing stressors, and high surrounding land-use intensity. Parks in the West were partially protected by less intense human land-use and the varied topography, which might provide climate refugia. However, those western parks tended to be the most exposed to multiple transformative impacts (as defined above).

At the national level (excluding the islands), 28% of the parks have a high fire hazard now; this rises to 38% of parks by an unspecified future time. They provided no estimate of the proportion of parks facing a risk in the future from the other factors. Current levels of risk are 25% at risk to summer drought; 36% (92 parks) at risk to forest pests; and 11% to sea-level rise. Again, across all parks analyzed, 174 – or 67% of the total – face one or more of these threats.

The authors conclude that the 60-old goal of conserving National parks as a “vignette of primitive America” – as stated by Leopold et al. (1963) – is no longer possible. Instead, park managers should now seek to steward resources “for continuous change that is not yet fully understood” as advocated by Colwell et al. (2014).

Michalak et al. (2026) found that the National parks are not prepared. Only 10% have had park-specific assessments; 37% had no assessment at any level. For individual National parks, likelihood of climate impacts and potential transformational changes remains uncertain. Determining where more in-depth, park- specific assessments are warranted is essential for allocating resources.

Michalak et al. (2026) define climate change vulnerability as the combined effects of exposure, sensitivity, and adaptive capacity. Exposure is the intensity of changes a location might experience. This includes changes in the climate itself (e.g., temperature or precipitation) plus changes in climate-exacerbated disturbances (e.g., fire, drought, and sea-level rise). Sensitivity is the extent to which a location or resource is affected – or existing stressors are amplified – by the changing climate, which can be either adversely or beneficially. For example, imperiled species might be further threatened if new conditions are more conducive to bioinvasion. Adaptive capacity is the ability of a system to adapt to the climate change impacts. For example, does human development impede species’ dispersal to new regions that support more suitable climate regimes. I appreciate that the authors note the importance of ensuring continuation of evolutionary processes.

A Subset of Threats: Invasive Species and Forest Pests

 According to Michalak et al. (2026), National parks with the highest cumulative vulnerability scores were in the Midwest, Washington, DC, and along the Gulf Coast. The threats were high levels of human development, poor air quality, high proportions of non-native species, and low environmental diversity.

mountain pine beetle in Rocky Mountain National Park; photo by Bchemicoff via Wikimedia

National parks that scored high for forest pest risks are concentrated in the mountainous West and Northeast. While Michalak et al. (2026) do not say so, I assume this refers to widespread mortality of pines due to outbreaks of the native mountain pine beetle (Dendroctonus ponderosae). Thirteen parks in the West scored high for a “trifecta” of fire, drought, and forest pests. The consequences for these parks’ natural resources might be rapid, dramatic, and irreversible transformation of ecosystems. Michalak et al. (2026) mention specifically Rocky Mountain and Yellowstone National parks. Other parks facing a threat from forest insects or pathogens include all the crown jewels of the West: Grand Teton National Park, Crater Lake National Park, Glacier National Park, Great Basin National Park, Kings Canyon-Sequoia National Park, Yosemite National Park, and Mount Rushmore National Memorial.

limber pine (Pinus flexilis) at Haiyaha Lake, Rocky Mountain National Park. Species is vulnerable to white pine blister rust. Photo by F.T. Campbell

Another example is Mojave National Preserve, which has experienced increased fire risk linked to the presence of invasive annual grasses.

I know that in the Northeast, more than a dozen species of introduced insects and pathogens threaten forest resources in the parks, including hemlock woolly adelgid, emerald ash borer, spongy moth, and – most recently – beech leaf disease. Parks mentioned in  supplementary material provided by Michalak etal. (2026) include Delaware Water Gap National Recreation Area, New River Gorge National River, Harpers’ Ferry National Historical Park, and the homes of Eleanor and Franklyn Roosevelt. See blog 356a and underlying article by Miller et al. (2023).

mature Fraser fir killed by balsam woolly adelgid in Great Smoky Mountains; photo by F.T. Campbell

Many other National parks in the East and Midwest also are reported to be impacted by introduced forest pests, among them Great Smoky Mountains National Park, Blue Ridge Parkway, Shenandoah National Park, Appalachian National Scenic Trail, Prince William Forest Park, Cumberland Gap National Historical Park, Gauley River National Recreation Area, Mammoth Cave National Park, Ozark National Scenic Riverways, Pictured Rocks National Lakeshore, Sleeping Bear Dunes, St Croix National Scenic Riverway, and Big Thicket National Preserve.          

There are some odd omissions. The supplementary data list the Chesapeake and Ohio Canal National Historical Park as facing a threat from tree pests, but does not so list Rock Creek Park. The two parks are a few miles apart and share the same invasive forest pests! The supplementary data do not mention Gettysburg National Military Park, although Miller et al. (2023) say that more than half of the seedlings and a quarter of the saplings in the park are ashes. These trees are likely to be killed by the emerald ash borer. Perhaps the explanation is that canopy trees threatened by pests in these parks do not occupy more than 80% of the parks’ cover.

I appreciate the effort to compile a nationwide analysis of threats to our national treasures. By focusing on one of those threats, I do not intend to downplay the others. Specific to climate changes, the Trump Administration has told the National Park Service to remove educational signs describing the impact of climate change on, for example, the glaciers at Glacier National Park. An earlier Executive Order https://climate.law.columbia.edu/content/trump-issues-executive-order-climate-change-0 reversed President Obama’s 2015 memorandum that required Interior and other departments to “avoid and then minimize harmful effects to land, water, wildlife, and other ecological resources (natural resources) caused by land- or water-disturbing activities, and to ensure that any remaining harmful effects are effectively addressed, consistent with existing mission and legal authorities.” In February 2026, the Environmental Protection Agency revoked the “endangerment finding” for greenhouse gases, which is the foundation for all regulations governing emissions of those substances. Clearly we cannot hope for federal efforts to address these threats to the National parks during this Administration’s tenure.

I hope, nevertheless, that this study gets wide attention and stimulates renewed campaigns to counter all threats to our natural heritage.

shrunken glacier in Glacier National Park; photo by F.T. Campbell

SOURCES

Colwell, R. S. Avery, J. Berger, G.E. Davis, H. Hamilton, T. Lovejoy, S. Malcom, A. McMullen, M. Novacek, R.J. Roberts, R. Tapia,  and G. Machlis. Revisiting Leopold: Resource Stewardship in the National Parks. Parks 2014 Volume 20.2

Leopold, A. et al. 1963. Wildlife Management in the National Parks. available here: chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://static-gcs.edit.site/users-files/30eb6df2212095e14d89a611f0f8f0f1/leopold-report-wildlife_management_in_the_national_park-1963.pdf?dl=1

Michalak, J.L., C.E. Littlefield, J.E. Gross, T.G. Mozelewski, J.J. Lawler. 2026. Relative Vulnerability of US National Parks to Cumulative and Transformational Climate Impacts. Conservation Letters, 2026 Vol 19, Issue 1; 19:e70020

Miller, K.M., S.J. Perles, J.P. Schmit, E.R. Matthews, M.R. Marshall. 2023. Overabundant deer and invasive plants drive widespread regeneration debt in eastern United States national parks. Ecological Applications. 2023; 33:e2837. https://onlinelibrary.wiley.com/r/eap

Posted by Faith Campbell

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

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

Or

https://fadingforests.org