Science continues to provide new hope for management of some of the tree-killing insects introduced to North America.
searching for ALB; photo by USDA
Asian longhorned beetle
USDA Forest Service and APHIS scientists have developed an Asian Longhorned Beetle (ALB; Anoplophora glabripennis) Eradication and Risk Tracking (ALBERT) 1.0 toolkit. Trotter et al. (2024) believe that the toolkit will improve the efficiency of ALB eradication programs by better estimating changing infestation risk in real time and comparing efficacy of various management strategies in those circumstances. Managers can thus set priorities for surveys and eradication efforts, optimize surveys, and improve eradication outcomes. Improved efficiency will also reduce long-term management costs.
Data on dispersal and infestation risk are analyzed at the hectare level. Inputs are contemporary, so they reflect hectare-scale changes in risk level and ALB detectability simultaneously with program implementation. Managers and stakeholders can track and visualize the distribution of risk on the landscape. In the example, the risk of infestation is shown by the color and height of the surface on the landscape.
I note that the research was completed two years ago. I wish the USFS “Rooted in Research” brief had discussed whether programs managing extant ALB infestations are using the tool – and finding it useful.
Suppressing emerald ash borer populations
black ash swamp via Flickr
Minnesota authorities and scientists wish to protect the expansive black ash (Fraxinus nigra) swamps located mostly in the central & northern portions of the state. There, the emerald ash borer (EAB; Agrilus planipennis) has not yet spread to all vulnerable locations. They consider that use of pesticides is not concerned feasible in these locations. And two of the introduced biocontrol agents have limited efficacy. One of the wasps—Tetrastichus planipennisi— can oviposit in EAB larvae only in trees with thin bark, that is trees smaller than 16 cm dbh. A second wasp, Spathius agrili, doesn’t persist in northern regions – i.e., northern Minnesota! Therefore they are seeking additional management tactics workable in natural mature ash stands across northern North America.
Peters, Rajtar, & Blanchette (2025) are testing whether useful levels of suppression can be provided by release of entomopathogenic fungi (EPF). They are building on earlier studies link? that determined that one entomopathogenic fungus isolate, Beauveria bassiana, showed promise in reducing EAB population growth. This fungus is available as a commercial product.
Peters, Rajtar, & Blanchette (2025) tested isolates from five genera = Beauveria, Purpureocillium, Metarhizium, Clonostachys, & Samsoniella. They found that Beauveria pseudobassiana, Beauveria bassiana GHA, Metarhizium sp. Meta, & Purpureocillium sp. consistently reduced EAB mean survival time (MST) and probability of survival over time.
They also tested use of an inoculation method different from that used in the earlier studies: autodissemination devices (ADDs). The devices expose adult EAB to the fungal spores using baited Lindgren funnels with non-stick surfaces hung in the canopy of an infested ash tree. Infected beetles transmit the fungus to others during mating. In a Canadian study, this method of infecting EAB adults with an isolate of B. bassiana CFL-A caused rates of infection up to 40% and a significant decrease in EAB pop growth rate over a 3-year period.
Scientists have isolated and identified 1,126 fungal isolates associated with EAB larval galleries from trees growing across Minnesota. Eight percent of these isolates are entomopathogens. Some of these isolates have been proved to kill EAB eggs. In this study Peters, Rajtar, & Blanchette (2025) tested the fungi’s efficacy against adults and whether the ADDs system inoculates sufficient numbers of beetles.
They found that five of the fungal isolates significantly decreased the mean survival time of EAB adults post-exposure and the probability of EAB survival over time. These were Beauveria bassiana GHA, B. pseudobassiana EAB 16.8 & B. pseudobassiana EAB 53-5, Metarhizium sp. Meta, and Purpureocillium sp. EAB 59-16-2. They are most promising isolates for future study. Peters, Rajtar, & Blanchette (2025) discourage further consideration of isolates in the genera Samsoniella and Clonostachys because of disappointing reductions in adult beetle survival.
The probability of survival of beetles in the negative control groups differed significantly between the two experiments. The authors say they can only speculate about the reason because many external factors influence EAB adult lifespan. Among such factors are a) the longer storage period for insects used in the first experiment; b) differences in nutrient quality or microbiomes of ash leaves provided during incubation; or c) health of trees from which the beetles had been collected.
Peters, Rajtar, & Blanchette (2025) say the effectiveness of these fungi and this inoculation method must now be tested under field conditions. One concern: the fungal inoculum can degrade due to exposure to the environment while it is in the trap. A second concern is that the fungus might grow across the inoculum pouch unevenly, thereby undermining equal delivery of conidia to each beetle. They call for research to optimize the type and/or formulation of inoculum used in ADDs to prolong fungal viability in the field.
an ash in a suburban setting; photo by F.T. Campbell
While I am cheered by the prospect of conservationists having new tools to counter the EAB infestation, I am concerned by how slowly work pursuing possible use of entomopathogens is proceeding. Peters, Rajtar, & Blanchette (2025) refer to several past studies that reached similar findings. Why has this knowledge not been applied in the field already? Is it due to the intrinsic difficulty of detecting and working with the fungi? Lack of funding for non-commercial approaches? Leaders’ narrow focus on strategies already in use? Some other complication?
SOURCES
Peters, C.J.; Rajtar, N.N.; Blanchette, R.A. Entomopathogenic Fungi from MN Are Virulent Against Emerald Ash Borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), Adults in a Laboratory Autodissemination Device Assay. Forests 2025, 16, 1742. https:// doi.org/10.3390/f16111742
Trotter, R.T., III; Warden, M.L.; Vazquez, R.J.; Ryan, J.K.; Pfister, S. 2024. ALB Hazard Management and Monitoring Version 1.0: an assessment and tracking tool for Asian longhorned beetle eradications in the United States. Gen. Tech. Rep. NRS-222. Madison, WI: U.S. Department of Agriculture, Forest Service, Northern Research Station. 24 p. https://doi.org/10.2737/NRS-GTR-222.
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
Tillandsia utriculata; photo courtesy of Teresa Cooper
Florida has 16 native species of bromeliads. Up to 15 invertebrates depend on bromeliads, especially the water that collects at the bases of the leaves. See Frank (1983) and Frank and Fish (2008) for more information about bromeliads’ ecological importance.
Eight species had been listed as threatened or endangered in the state (visit here) (Frank and Cave 2005) before arrival of the Mexican bromeliad weevil. The Florida Endangered Plant Advisory Council added two of its hosts – Tillandsia utriculata and Tillandsia fasciculata. The website now lists 12 species as threatened by the weevil.
Twelve species are believed to be vulnerable to the weevil. T. utriculata is at most immediate risk. Before arrival of the Mexican bromeliad weevil, some populations of this species were described by Teresa Cooper as “giant” and dense, containing very large mature plants and producing huge volumes of of seed.
One such population — in the Enchanted Forest Sanctuary in Brevard County – succumbed to the weevil quickly: 87% died in six months. At 27 months after arrival of the weevil, less than 3% of the original population remained. It is now rare to see large T. utriculata plants. Medium-sized plants put out inflorescences. The weevil persists at low levels, so is able to feed on and reproduce on medium and small plants. Several endemic wildlife species that inhabit the water pooled in T. utriculata’s base face global extinction (T.M. Cooper pers. comm. 2026).
damage to a bromeliad caused by the weevil; photo courtesy of Teresa Cooper
The first reason T. utriculata is at higher risk is that each plant can support many weevil larvae. Its leaves are softer (so more easily consumed) and its large stems contain lots of nutrients — for a bromeliad). More important is the plant’s very slow reproduction in contrast to the weevil’s rapid attack. T. utriculata plants do not produce seed until after they have grown for up to 20 years. Furthermore, an extremely small fraction of the ~ 10,000 seeds released by a mature plant make it to reproductive age. A plant that after 18 years begins growing an inflorescence — which then takes ~ a year to flower and produce seed – can be killed by a weevil within a few months. In addition, T. utriculata is monocarpic – it doesn’t produce offshoots. T.M. Cooper asserts that if the bromeliad weevil extirpates T. utriculata from Florida, it will not be because the weevil ate the very last plant, it will be because T. utriculata seed output has fallen below a sustainable level.
Teresa Cooper demonstrating the size of a T. utricuclata flower spike; photo courtesy of T. Cooper
A second host, Tillandsia fasciculata, had large and dense population in Loxahatchee National Wildlife Refuge (Palm Beach County) in 2002 to 2005. Almost every tree had multiple T. fasciculata plants; many were huge with multiple pups. When Teresa Cooper revisited about 10 years later, T. fasciculata plants were very sparse, large plants very rare; none was really large (T.M. Cooper pers. comm. 2026).
T. fasciculata is expected to decline more slowly than T. utriculata. First among several advantages is that its leaves are tougher and stems smaller, so they provide less nutrition to the weevil. Probably more important, T. fasciculata is polycarpic (it produces both seed and offshoots). A large T. fasciculata plant can sprout up to a dozen blooming rametes at a time. If the weevil kills one, other rametes will bloom and seed. At the same time, the plant might produce numerous up to 20 offshoots which come detatched from the “mother” plant and start a new individual. Still, as the weevil kills these rametes year after year the plant shrinks in size and eventually dies (T.M. Cooper pers. comm. 2026).
Teresa Cooper has documented damage on Tillandsia paucifolia, T. simulate, and T. variabilis (T.M. Cooper pers. comm. 2026). She has no funding to continue studying these species. I have been unable to find any more recent information about the status of the Tillandsia species. The Florida Department of Agriculture and Consumer Services does not have an active program addressing the weevil (Patrick Gordon, FDACS, pers. comm. June 2026).
There is considerably more information about another endangered bromeliad, Guzmania monostachia. This species has the broadest distribution of any species in the genus, stretching across northern South America, Central America, the Caribbean, as well as southern Florida. As the northernmost population, the Florida population might harbor unique genetics important for the species’ adaptation to climate change (Krupar et al. 2023).
Formerly more common, G. monostachia is now found in six fragmented and disjunct populations in five areas in Florida. The species has apparently been extirpated from four other sites by habitat loss, not depredations by the weevil. One set of habitats is in wetland sloughs on the peninsula’s west coast on the peninsula’s west coast. These forests comprise pond apple (Annona glabra) and Florida ash (Fraxinus caroliniana); Kupar et al. (2023) don’t mention whether this species is vulnerable to the emerald ash borer, which has not yet been detected in Florida. The largest of the bromeliad populations is in Fakahatchee Strand State Preserve, in Collier County in Southwest Florida. Fakahatchee Strand Preserve is Florida’ oldest and largest state park. The bromeliad’s population was previously estimated to exceed two million individuals. Their number has been halved by weevil attack. Also, since M. callizona prefers larger plants, the proportion of reproductively mature individuals had been reduced from roughly 50% to only 10–20% by 2021. T.M. Cooper reports (pers. comm. 2026) fears this species might also be extirpated eventually.
Guzmania monostachia; photo courtesy of Teresa Cooper
The adjacent Big Cypress National Preserve is home to two populations of G. monostachia; they are separated by ~2,900 km2 so there is no interaction between them. The southern population consists of ~ 1000 individuals, the northern population comprises only~ 200 individuals.
Guzmania monostachia is in an even more precarious situation on the eastern side of the peninsula: tiny populations of two or three plants are found in three locations: Everglades National Park, Fuchs (formerly Sykes) Hammock Preserve, and Meissner Hammock Preserve.
The Mexican bromeliad weevil Metamasius callizona (Chevrolat) is native to southern Mexico, Guatamala, (Frank and Thomas 1994; Frank and Cave 2005) and Belize (Cooper, Cave and Frank 2023). Its presence in Florida was detected in a nursery in Ft. Lauderdale, Broward County, in 1989. Probably introduced on a shipment of ornamental bromeliads from Mexico. The nursery treated the infested plants, but the weevil had already established on native bromeliad species in the natural environment. By 1991, it was detected in four counties in southern Florida; by 1999, it was found in 12 more. It is now in most counties of peninsular Florida from Daytona (Volusa County) south to Miami-Dade (Patrick Gordon, Florida Department of Agriculture and Consumer Services, pers. comm. June 2026).
While chemical control is feasible in nurseries and display plantings, it can’t be used in natural areas, where the epiphytes are not accessible from the ground and stakeholders fear likely non-target effects.
Therefore, scientists initially focused on classical biocontrol. They made 16 expeditions to Mexico and Central and South America from 1992 to 2010 searching for natural enemies of the weevil. The chose parasitoid tachinid fly, Lixadmontia franki. A colony was established in the University of Florida’s quarantine laboratory and research on fly-weevil interactions was conducted for several years. Releases into the environment were begun under Federal and State permits in 2007. Although more than 3,100 flies were released, the species failed to establish. So this approach is no longer being pursued (Cooper, Cave, and Frank (2024); T.M. Cooper pers. comm. June 2026).
Meanwhile, in 2010, Dr. Frank and D. Giardina of the Florida Fish and Wildlife Conservation Commission observed that in one location in Belize the weevils had no apparent detrimental effect on bromeliads identified as Tillandsia utriculata (although there is some disagreement on this classification). Cooper, Cave, and Frank (2024) undertook a study to determine how the bromeliad could coexist with Metamasius callizona in Belize while being so vulnerable in Florida. They compared life cycle parameters (oviposition and pupation rates, egg hatch rate, adult emergence and size, and developmental time) of weevils from Florida and Belize. They also observed how populations of the weevil from Florida fared on three hosts: pineapple (Ananas comosus), T. utriculata collected from Florida, and T. utriculata collected from Belize. Finally, they quantified the hosts’ nutritional content using two measures (percent soluble solids and leaf toughness).
Their most important finding is that weevil larva from Florida could not develop past the third instar on leaves of the T. utriculata from Belize. The weevil larvae starved because the Belize bromeliad’s leaves had fewer nutrients and were tougher than the leaves from T. utriculata collected in Florida.
bromeliads seen in Big Cypress National Preserve in the early 1980s; photo by F.T. Campbell
Based on this finding, Cooper, Cave, and Frank (2024) recommend that authorities introduce T. utriculata plants from Belize into Florida’s forests and allow them to colonize and/or hybridize naturally with Florida’s remaining plants. An alternative would be to breed hybrid Tillandsia in the lab and release them into Florida’s forests. I note that the American Chestnut Foundation pursued a similar strategy for decades to develop American chestnuts (Castanea dentata) able to tolerate the chestnut blight fungus (Cryphonectria parasitica).
Sources
Cave, R.D. 1997. Admontia sp., a potential biological control agent of Metamasius callizona. J Brom Soc. 47:244-249.
Cave, R.D. 2008. Biological control of the MEXICO bromeliad weevil. Biocontrol News and Information 29(1):1N-2N.
Cooper T.M. 2006. Ecological and demographic trends and patterns of Metamasius callizona (Chevrolat), an invasive bromeliad-eating weevil, and FLORIDA’s native bromeliads [Master’s thesis]. [Gainesville (FLORIDA)]: University of FLORIDA. 69 p.
Cooper, T.M., R.D. Cave, and J.H. Frank. 2023. Potential bottom-up control of Metamasius callizona in Florida, USA. Entomologia Experimentales et Applicata. 2024. 172;4090421
Frank, JH. 1983. Bromeliad phytotelmata and their biota, especially mosquitoes. In: Frank J.H., Lounibos, L.P., editors. Phytotelmata: terrestrial plants as hosts for aquatic insect communities. Medford (NJ): Plexus. p. 101-128.
Frank, J.H. and R.D. Cave. 2005. Metamasius callizona is destroying FLORIDA’s native bromeliads. In: Hoddle MS, editor. USDA Forest Service Publication FHTET-2005-08. Vol 1. Second International Symposium on Biological
Control of Arthropods; 2005 Sep 12-16; Davos, Switzerland. Washington D.C.: USDA Forest Service. p. 91-101.
Frank, J.H. and D. Fish. 2008. Potential biodiversity loss in Florida bromeliad phytotelmata due to Metamasius callizona (Coleoptera: Dryophthoridae), an invasive species. Florida Entomol. 91(1):1-8.
Frank, J.H. and M.C. Thomas. 1994. Metamasius callizona (Chevrolat) (Coleoptera:Curculionidae), an immigrant pest, destroys bromeliads in FLORIDA. Can Entomol.126(1):673-682.
Krupar, S., A.A. Naranjo, G. Godden, N. Cellinese. The Fate of Guzmania monostachia in Florida Rests with Humans. Diversity 2023, 15, 525. https://doi.org/10.3390/d15040525
Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S., Prioritizing the conservation needs of US tree species: Evaluating vulnerability to forest insect and disease threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/
Salas, J. and J.H. Frank. 2001. Development of Metamasius callizona (Coleoptera:Curculionidae) on pineapple stems. Florida Entomol. 84(1):123-126.
Wood, D.M. and R.D. Cave. 2006. Description of a new genus and species of weevil parasitoid from Honduras (Diptera: Tachinidae). Florida Entomol. 89(2):239-24.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
ash trees (Fraxinus spp.) killed by EAB along Mattawoman Creek, Prince Georges County, Maryland; photo by Leslie A. Brice
I report here on action so far on funding vital agencies in Fiscal Year 2047 (which begins on October 1, 2026). I describe the various programs roles in addressing the invasive species threat briefly in my earlier blog.
USDA Forest Service
The House Appropriations Committee approved the FY27 Interior Appropriations bill (which includes the USFS) in early June. I greatly appreciate Congress’ continued support for two USFS programs that are vitally important in protecting resilience of the Nation’s forests in the face of invasions by non-native pests and plants: Research and Development and Forest Health Management (in the State, Private, and Tribal lands division). The Trump Administration had – for the second year in a row – called for ending these programs’ specific appropriations.
Research and Development
In my testimony I had asked the Subcommittee to maintain funding for R&D at the Fiscal Year 2026 Continuing Resolution level of $308 million. Instead the Subcommittee ignored the Administration’s request and provided $295 million – a fairly small reduction under the circumstances. Funding for the Forest Inventory and Analysis (FIA) program continues to see small increases — to $34 million.
While there is no specific line item for invasive species in the R&D budget, the report does encourage the USFS to address high priority invasive species, pests, and diseases, including the emerald ash borer, an unspecified “bark beetle”, spotted lanternfly, and Spruce Budworm. The list also includes three invasive plant species: buckthorn, Amur honeysuckle, and Callery pear. This language is not tied to a specific program, so it is unclear what will actually result.
In the R&D section of the report, the Committee “recognizes the significant damage invasive species can cause throughout forests, including urban forests, and encourages the USFS to continue reforestation efforts, including through the management of woody invasive species & tree planting in urban areas.” Again, the wording seems somewhat misplaced since the R&D program does not carry out tree planting.
State, Private, and Tribal forests
I had asked the Interior Appropriations Subcommittee to maintain funding for State, Private, and Tribal forests program at the FY26 Continuing Resolution level of $310.6 million. Again, appropriators ignored the Administration’s request and provided $283,500,000 – a fairly small reduction. The Forest Health Management program was funded at $58 – of which $16 million is specified for efforts on federal lands, $42 million for helping state and tribal agencies and private landowners to manage pests on their lands.
The Subcommittee report emphasized the importance of working with Colorado to curtail spread of mountain pine beetle d associated wildfire risk. Music to my ears is the Committee’s statement encouraging the USFS to work with state & local agencies to counter the high rate of tree mortality due to the goldspotted oak borer infestation in Southern California. It advised prioritizing insect research, prevention, suppression, & mitigation projects that support community wildfire protection & State forest action plans. Since none of the members of the House Interior Appropriations Subcommittee is from California, I am pleasantly puzzled.
coast live oak (Quercus agrifolia) killed by goldspotted oak borer; Heisey County Park, San Diego County, California. Photo by F.T. Campbell
The Interior Appropriations Subcommittee expressed continued concern about poor regeneration of eastern white oak (Quercus alba). (Of course, several other tree species are also regenerating poorly but a strong lobby is tied to oaks due to their economic importance.
i’iwi – a formerly common Hawaiian honeycreeper badly suppressed by avian malaria; photo by by James Petruzzi
Hawaii’s endangered birds
I am very pleased that the House Interior Appropriations Committee has provided $1,250,000 is for continuing research to protect Hawaiian forest birds from the dire extinction threat arising from non-native mosquitoes carrying avian malaria & other pathogens.
USDA Animal and Plant Health Inspection Service
APHIS is responsible for preventing the introduction and spread of pests and invasive plants that harm agriculture, including forests. APHIS policy guides port inspections carried out by the DHS CBP. APHIS inspects imported live plants. Unlike the USFS, APHIS has the support of the Trump Administration, so funding levels have remained steady. Of course, continuing introductions of new pests and spread of established ones – and inflation – have increased the cost of countering invasions, so the agency continues to fall behind despite its relatively privileged position.
The House of Representatives adopted the FY27 Agriculture Appropriations Bill in early June. I apologize for the obscurity of the FY26 funding levels. Figures are in millions of dollars.
FY2025 enacted FY27
APHIS total $1,148 $1,157
Plant health subtotal $387.5 $387.6
Agric. quarantine $35.5 $35.5
Field crop and rangeland $12 $10
Pest detection $29 $29
Methods development $21.5 $21
Specialty crops $206.5 $209
Tree and wood pests $59 $58.6
In its report, the Subcommittee on Agriculture Appropriations did not express concern about the issues that I had raised in my testimony. Instead, it mentioned several agricultural pests, e.g., citrus greening, fruit flies, a non-native beetle threatening nut orchards, and spotted lanternfly (Lycorma delicatula). The Subcommittee also urged APHIS to work with the USDA Forest Service to counter the spread of two native wood-borers, mountain pine beetle (Dendroctonus ponderosae) in Colorado and southern pine beetle (Dendroctonus frontalis). Since both are native, APHIS’ role is unclear. The Subcommittee mentioned two invasive plants: glossy buckthorn (Frangula alnus) – saying it threatens biodiversity, especially in the Allegheny National Forest in Pennsylvania; and Carizzo cane (Arundo donax), saying it contributes to tick invasions in addition to hampering detection of human immigrants along the Rio Grande.
sounder graphic by Jack Mayer, Savannah River National Laboratory
The bill increases funding for the national feral swine management program by $500,000. (I cannot determine total the appropriation). The Agriculture Appropriations Subcommittee had urged APHIS Wildlife Services to prioritize states with the largest invasive populations – although this choice contradicts standard advice for managing invasive species, including feral swine.
In one action linked to our concerns about wood-borer introductions via wood packaging, the Subcommittee encouraged APHIS to recognize sulfuryl fluoride as a treatment for logs, wood products, & wood packaging. This fumigant has been accepted under the international (ISPM#15) since 2013.
wooden pallets discarded next to wooded border in Glacier National Park, Montana; photo by F.T. Campbell
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
Photo of infested cactus at Cabo Rojo National Wildlife Refuge, Puerto Rico. Taken August 20, 2018 by Yorelyz Rodríguez-Reyes
For 15 years I have maintained a profile of the Harrisia cactus mealybug Hypogeococcus pungensbecause it threatens columnar cacti in the subfamily Cactoideae from the Caribbean basin and possibly in the American Southwest and Mexico. My recent attempts to clarify the current situation have been frustrated by the apparent collapse of funding support for scientists trying to conserve these cactus species.
The dry regions of the Caribbean Islands are home to about 100 native cacti, 75% of which are endemic. According to the Center for Plant Conservation, 20 species are listed as threatened by the IUCN. Puerto Rico specifically is home to 14 cactus species, at least three of which are endemic.
How and when the mealybug first invaded the Caribbean and North America is unknown. The presence of the insect now known as H. pungens Hyp-C on Puerto Rico was detected in the Guánica Commonwealth Forest and Biosphere Reserve on the island’s southern coast in 2005 (Zimmerman et al. 2010). However, the actual introduction probably occurred about ten years earlier, in about 1996 (Poveda-Martinez et al. 2022). See map of locations below.
In the 20 years since then, the mealybug has spread across the island’s dry districts. By 2010, it was estimated to be present on about 1,400 km2. By 2014 – nine years after detection — the mealybug had reached the small island of Caja de Muertos. The most recent survey of which I am aware (date unclear) detected the mealybug on 268 out of 445 cactus plants examined (60%) in 12 out of 39 sites examined (Poveda-Martinez et al. 2022). The mealybug is also killing native cacti on the nearby U.S. Virgin Islands (Poland et al. 2019), although I have found no data on this invasion or its impact.
Below – columnar cacti on St. John, US Virgin Islands; photos by F.T. Campbell
H. pungens Hyp‑C threatens seven of 14 native cactus species in Puerto Rico. Three of the cacti are endemic; two are federally listed as endangered species: Harrisia portoricensis and Leptocereus grantianus (USDA ARS). Since the mealybug’s detection in Puerto Rico, it has caused extensive damage to Pilosocereus royenii (Royen’s tree cactus), Leptocereus qaudricostatus (pitaya), Melocactus intortus (turk’s cap), and an introduced cultivar, Cereus hexagonus. It has caused minor damage to Stenocereus fimbriatus (Zimmerman et al. 2010). These cacti provide food or shelter for endemic bats, birds, moths and other pollinators (Segarra and Ramirez; USDA ARS).
The insect’s attack promotes abnormal gall-like growth on the stem and deformed flowers. These deformations severely affect infested plants’ reproduction and eventually survival (Poveda-Martinez et al. 2022).
Biological Control
When the mealybug was first detected Commonwealth and federal agencies tried to counter it. A search for possible biocontrol agents in the insect’s native range in Argentina began the 2010. While no funds have ever been appropriated for this activity, for several years the U.S. Department of Agriculture supported the work by allocating funds to the Agriculture Research Service Insect Behavior and Biocontrol laboratory in Gainesville, Florida, from broader programs. Dr. Stephen Hight took the lead, working with colleagues in South America. According to Dr. Hilda Diaz-Soltero, then a USDA official, these funds came primarily from the USDA Invasive Species Coordination Program and APHIS Eastern Region. In fiscal years 2017 and 2019, an additional ~$550,000 came in the form of grants under APHIS’ Plant Pest and Disease Management and Disaster Prevention Program. Link Scientists at the Center for Excellence in Quarantine and Invasive Species at the University of Puerto Rico devoted at least a decade to the search.
Scientists focused on two parasitoid wasps, Anagyrus cachamai and A. lapachosus (Hymenoptera: Encyrtidae). A third candidate, the predator Hyperaspis conclusa, was also assessed (Aguire et al.).
Research on the mealybug-wasps interaction uncovered troubling patterns. First, it has long been known that some mealybugs believed to be belong to the species Hypogeococcus pungens feed on columnar cacti while others feed on plants in two unrelated families, Amaranthaceae and Portulacaceae (USDA ARS; Zimmerman et al. 2010). Would the introduced wasps attack the cactus-feeding mealybug in sufficient numbers?
The confusion over how many mealybug species have been introduced – and where – severely hampered development of a program. (The mealybug has been introduced to control invasive cactus in Australia and South Africa. Most sources say it has been highly effective – prompting the initial concern when it appeared on Puerto Rico.) I have been unable to find any information about the status of the candidate biocontrol agents more recent than 2022.
Genetic Conservation
The USDA also partnered with the Naples (Florida) Botanical Garden to collect fruits and vegetative material for ex situ conservation. Rigorous phytosanitary procedures were followed to ensure the absence of the mealybug. Collections of fruits and vegetative material provided 1,298 cacti samples from 13 species, representing 1,173 maternal lines from 91 sites throughout Puerto Rico. A total of 90,720 seeds representing 8 species are banked at the NBG for long-term storage. Propagation of the vegetative material has 56% success, and plants are incorporated into the NBG’s living collections. (These figures include Opuntia cacti that are hosts of a second invasive insect, Cactoblastis cactorum.)
Genetic Concerns
Scientists now consider Hypogeococcus pungens (Hemiptera: Pseudococcidae) to be a species complex composed of at least five putative species. The species are separated in part by the plants they use as hosts. Two of the complex have apparently been introduced to Puerto Rico: H. pungens Hyp‑C feeds on cacti; H. pungens Hyp‑AP feeds on hosts in the Portulacaceae & Amaranthaceae. Both evolved from putative source populations in Brazil (Poveda-Martinez et al. 2022).
The two species H. pungens Hyp-C and Hyp-AP are currently separated on Puerto Rico by host preferences and climatic niches. They also occupy different geographic areas. Scientists fear that ongoing climate change could allow H. pungens Hyp-C to establish farther into the island’s interior and in a large area in the north. Such range expansion would end the geographic separation. Overlapping of the two species is likely to exacerbate the threat to Puerto Rico’s cacti. Most directly, it would complicate implementation of management strategies, especially biological control. Intermixing of the two species could also facilitate hybridization which might result in more vigorous attacks or a broadened host range. Hybridization is frequent in closely related species (Poveda-Martinez et al. 2022).
The Mealybug is Frequently Introduced
Mealybugs that feed on cacti and believed to be in the species Hypogeococcus pungens made multiple appearances in southern California between 2000 and 2018 – in gardens and in nurseries. Confusingly, CDFA reports interception of the mealybug on alternanthera and ludwigia plants shipped from Florida (CDFA 2018). I have no more recent data. The population in Florida was reported to be present in 16 counties in 2009); it might be the species that feeds on plants other than cacti (Poveda-Martinez et al. 2022). Other populations has been reported in the Dominican Republic (no date) (CDFA 2018); and in Hawai`i in 2005 (Hawaii Department of Agriculture new pest report). A mealybug that feeds on Amaranthaceae and Portulacaceae was detected in 2000 in San Juan, Puerto Rico (Poveda-Martinez et al. 2022).
In the absence of control measures, scientists expect H. pungens Hyp-C to continue decimating Puerto Rican cactus diversity and threaten other cactus rich ecosystems across the Caribbean islands, Central America and, potentially, North America (Poveda-Martinez et al. 2022).
saguaro and organ pipe cacti in Organ Pipe Cactus National Monument; photo by F.T. Campbell
North America has more than 500 columnar cactus species in the Cactoideae (Zimmerman et al. 2010). Some of these cacti are already endangered, e.g., several Pediocactus. Others are totems of the desert, e.g., the saguaro (Carnegiea gigantea) and organ pipe (Stenocereus thurberi) cacti. Picture The larger ones, particularly, play important ecological roles. It is not known how vulnerable individual species are to the mealybug (Golubov pers. comm. January 2011). In Mexico several mealybugs in the same genus are already present. The natural enemies of these mealybugs might be able to attack H. pungens Hyp-C if it invades the country (Zimmerman et al. 2010). Despite the well-founded concern, apparently no funds have been allocated by governments or conservation organizations to studying the vulnerability of these cacti to one or more mealybugs in the Hypogeococcus genus.
The most likely pathway by which the mealybug is spread is the trade in plants for planting (the horticultural trade) (Zimmerman et al. 2010). A decade ago APHIS reported intercepting mealybugs on cactus (primarily on roots) imported from Germany, Peru, and Puerto Rico. APHIS has also intercepted several other mealybugs in the same genus – on plants (including orchids and bromeliads as well as cacti) from Belize, Costa Rica, Ecuador, Guatemala, Honduras, Mexico, Panama, Peru, and Venezuela (USDA APHIS alert).
A decade ago NatureServe and IUCN found that 31% of Earth’s cactus species were threatened with extinction. They named overharvesting (often for the illegal horticultural trade) and destruction of habitat by smallholder livestock ranching and farming. Did not mention predation by introduced insects – although that is now manifest not only in the cactus mealybug but also the cactus moth.
Sources
Aguirre, M. G. Logarzo, S. Triapitsyn, H. Diaz-Soltero, S. Hight, O. Bruzzone. 2023? Effect of egg production dynamics on the functional response of parasitoids
California Plant Pest and Disease Report. 2005. Vol. 22 No. 1. Covering Period from July 2002 through July 2005.California Department of Food and Agriculture. 2018.California Pest Rating for Hypogeococcus pungens Granara de Willink | Harrisia cactus mealybug Hemiptera: Pseudococcidae Pest Rating: A California Pest Rating for Hypogeococcus pungens Granara de Willink | Harrisia cactus mealybug Hemiptera: Pseudococcidae Pest Rating: A
Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector. Springer Verlag.
Poveda-Martinez, D. N.A. Salinas, M. Belen Aguirre, A.F. Sanchez-Restrepo, S. Hight, H. Diaz-Soltero, G. Logarzo, and E. Hasson. 2022 Geonomic & ecol evidence shed light on the recent demographic history of two related invasive insects. Scientific Reports.
Segarra-Carmona, A.E., A. Ramirez-Lluch. No date. Hypogeococcus pungens (Hemiptera: Pseudococcidae): A new threat to biodiversity in fragile dry tropical forests.
Segarra-Carmona, A.E., A. Ramírez-Lluch, I. Cabrera-Asencio and A.N. Jiménez-López. 2010. First Report of a New Invasive Mealybug, the Harrisia Cactus mealybug Hypogeococcus pungens (Hemiptera: Pseudococcidae). J. Agrie. Univ. RR. 94(1-2):183-187 (2010)
Srivastava, M., P. Srivastava, R. Karan, A. Jeyaprakash, L. Whilby, E. Rohrig, A.C. Howe, S.D. Hight, and L. Varone. 2019. Molecular detection method developed to track the koinobiont larval parasitoid Apanteles opuntiarum (Hymenoptera: Braconidae) imported from Argentina to control Cactoblastis cactorum (Lepidoptera: Pyralidae). Florida Entomologist 102(2): 329-335.
Triapitsyn, Aguirre, Logarzo, Hight, Ciomperlik, Rugman-Jones, Rodriguez. 2018. Complex of primary and secondary parasitoids (Hymenoptera: Encyrtidae and Signiphoridae) of Hypogeococcus species. mealybugs (Hemiptera: Pseudococcidae) in the New World. Florida Entomologist Volume 101, No. 3 411
USDA Agriculture Research Service, Research Project: Biological Control of the Harrisia Cactus Mealybug, Hypogeococcus pungens (Hemiptera:pseudococcidae) in Puerto Rico Project Number: 0211-22000-006-10 Project Type: Reimbursable
Zimmermann, H.G., M.P.S. Cuen, M.C. Mandujano, and J. Golubov. 2010. The South American mealybug that threatens North American cacti. Cactus and Succulent Journal. 2010 Volume 82 Number 3
The Trump Administration proposes (again!) to end all funding for USFS Research and State, Private, and Tribal Forestry programs. The budget document claims that these cuts are necessary “to ensure fiscal responsibility w/ taxpayer dollars & appropriate alignment of resources w/ USFS’s responsibility to appropriately steward National Forest System lands.” Ending the SP&T programs is justified as “better balance[ing] the appropriate roles of federal & State governments. … and [restoring] federalism …] The document claims that the federal component of Forest Health Management [currently receiving $16 million] duplicates programs managed by the National Forest System; yet the actions listed under this second budget category all relate to water management, not insects or pathogens. The document says states should manage pests on non-federal lands [currently receives $42 million]. I think this approach ignores the need for coordinated management for each of hundreds of pest species, from detection to eradication or development of host resistance. Eliminating the Research program will deprive all forest managers of a scientific foundation for management efforts.
The Trump Administration’s proposed budget would hold funding for key APHIS programs steady. This is great news compared to the extreme cuts proposed for the Forest Service. The budget document says that it is essential to continue APHIS programs success; any stoppages or reductions would potentially cause catastrophic consequences for environmental health. Contrary to this statement, holding funding steady actually results in cuts due to continuing introductions of new pests and inflation.
Item
2024 Actual
2025 Actual
2026 Estimated
2027 Estimated
Field Crop & Rangeland Ecosystems Pests (incl cogongrass)……….
12,000
12,000
11,000
9,026
Pest Detection ………………………………………………..
29,000
29,000
29,000
29,000
Plant Protection Methods Development ………………….
21,500
21,500
21,500
21,500
Specialty Crop Pests …………………………………………
215,000
215,000
214,000
217,339
Tree & Wood Pests …………………………………………..
59,000
59,000
58,650
58,650
Subtotal, Plant Health …………………………………….
387,500
387,500
385,150
386,515
USDA Forest Service
Two USFS programs w/ vital roles in protecting resilience of the Nation’s forests in the face of invasions by non-native pests and plants: R&D program and FHM within SPT division
The many economic & ecological benefits from our forests are under growing threats from a variety of disturbances, ranging from fires & hurricanes to non-native pests. ~ 60% of forests owned by non-feds; USFS must address threats to forests outside NFS to achieve its mission of sustaining “health, diversity, & productivity of the nation’s forests & grasslands to meet the needs of present & future generations.”
Research & Development
The Continuing Resolution for FY26 funded Research at $308 million for the year. Ask Congress to maintain this level. + increase research on invasive species from the current level of 1% to 5%.
The area of our forests & woodlands that is threatened by alien pests is similar to that attributed to fire or western bark beetles. More than 41% of forest biomass in the “lower 48” states is at risk to established non-native pests.[1] If able, add reference to pests on Hawai`i or Caribbean islands. Since additional introductions almost guaranteed, even greater proportion of US’ forest resources at risk in future. If possible, name example, e.g., Phytophthora austrocedri.Forest managers cannot counter these threats without understanding how these P&P kill trees & what actions are effective counter measures. This knowledge is obtained by research.
At least 53 tree species in forests across America are already under attack by non-native pests and pathogens. Yet as of FY23, Research stations spent just 1% of appropriation studying a few of the dozens of NIS pests. Funding for alien pests has decreased 70% since FY2010 even as new pests enter our forests. This inadequate research effort means USFS cannot develop effective programs to prevent, suppress, & eradicate the majority of alien pests. One crucial strategy suffers particularly = efforts to breed trees able to thrive despite NIS pests. R&D currently supports only a few such projects.
Forest Health Management: Supporting the Full Continuum of Pest Management
The Continuing Resolution for FY26 funded State, Private, and Tribal forests program at $310.6 million. I have not found specifics for the FHM program. This was an increase over the $281 million level in FY25.
Non-native pests and pathogens arrive as contaminants or hitchhikers on imported goods, especially on wood packaging and plants. These imports usually arrive in cities or suburbs, so the pests establish there first. They immediately cause enormous damage to urban forests, forcing local governments and property owners to absorb high tree removal costs. They then spread to rural forests, including National forests. Examples include hemlock woolly adelgid, emerald ash borer, invasive shot hole borers, goldspotted oak borer, sudden oak death, and beech leaf disease.
The most effective approach is to kill the pests where they first appear – usually in those urban or semi-rural forests. This response is led by FHM Cooperative Lands subprogram. We urge maintain funding for this subprogram at the FY26 level (possibly $42 million) so that the agency’s experts can continue to assist the states and other partners in countering these pests. As these pests spread to rural areas – including to National forests, National parks, and other public lands, responsibility for their management involves FHM Federal Lands subprogram. So much maintain funding for this subprogram at FY26 levels.
A recent analysis[2] determined that the natural resource values of 92 National parks are threatened by forest pests. Western parks are threatened primarily by outbreaks of the native mountain pine beetle (Dendroctonus ponderosae). Those in the East face threats from more than a dozen species of non-native pests, including hemlock woolly adelgid, emerald ash borer, spongy moth, laurel wilt, and – most recently – beech leaf disease.
Again, combatting these pests requires understanding their life histories & traits – understanding gained through the research program mentioned above.
Funding reductions over the past decade have already shrunk the number of FHM projects & areas treated each year. While 53 tree species are threatened, only four [eastern oaks, loblolly & ponderosa pines, & hemlocks] are targeted by 95% of projects. To counter the threats to 50 additional tree taxa, FHM needs additional resources.[3]
Investing in urban forestry is key to addressing both parties’ priorities & advancing flexible & cost-effective solutions to a wide range of issues impacting American communities, businesses, & families. The USFS SPT division’s Urban & Community Forestry Program efficiently distributes funds to shovel-ready projects for improving communities by maintaining a healthy tree canopy. Federal “seed” money provides resources necessary to initiate & stabilize these local programs.
A surprisingly high proportion of the (inadequate) funding for breeding trees to mitigate the damage caused by non-native pests is from FHM or the NFS, rather than R&D. These programs should receive substantial increases. The model program is the Dorena Genetic Resource Center. It provides decades-long commitment, skilled staff, necessary facilities; these result in breeding successes, i.e., western white pines and Port-Orford cedar.
Invasive Plants
Invasions of forests by non-native plant species erode forest productivity & provision of the full range of ecosystem services, hinder forest uses, degrade biodiversity & habitat, and impose substantial financial costs. A recent analysis[4] documents that this threat is growing: the number of FIA inventory plots containing invasive plant species rose in 58.9% of surveyed counties. Furthermore, in 73.2% of the counties the plots experienced an increase in species richness of invading plants. Increases occurred in all regions, but were greater in the East: from 46% to 52.3%. In the Rocky Mountains, the proportion of invaded plots rose from 6% to 11%. In Hawai`i, this proportion grew from 70% to 83.2%. Again, USFS Research and FHM programs, working together, are key to making progress in countering these bioinvasions.
[1] Fei, S., R.S. Morin, C.M. Oswalt, and A.M. 2019. Biomass losses resulting from insect and disease invasions in United States forests. PNAS August 27, 2019. Vol. 116 No. 35 17371–17376
[2] Michalak, J.L., C.E. Littlefield, J.E. Gross, T.G. Mozelewski, J.J. Lawler. 2026. Relative Vulnerability of US National Parks to Cumulative & Transformational Climate Impacts. Conservation Letters, 2026 Vol 19, Issue 1; 19:e70020
[3] Coleman, T.W, A.D. Graves, B.W. Oblinger, R.W. Flowers, J.J. Jacobs, B.D. Moltzan, S.S. Stephens, R.J. Rabaglia. 2023. Evaluating a decade (2011–2020) of integrated forest pest management in the United States. Journal of Integrated Pest Management, (2023) 14(1): 23; 1–17
[4] Potter, K.M., B.V. Iannone III, K.H. Riitters, Q. Guo, K. Pandit, C.M. Oswalt. 2026. US Forests are Increasingly Invaded by Problematic NIS Plants. Forest Ecology & Management 599 (2026) 123281
USDA Animal and Plant Health Inspection Service
APHIS is responsible for preventing intro and spread of pests and invasive plants that harm agric, including forests. APHIS policy guides port inspections carried out by the DHS CBP. APHIS inspects imported live plants.
Introductions of pests and pathogens have continued to occur. APHIS funding has remained steady – which means it is not growing to match the rising threat. At minimum, maintain current levels.
FY2025 enacted FY26 House FY26 Senate
APHIS total $1,148 $1,146 $1,168
Plant health subtotal $387.5 $388.6
Agric. quarantine $35.5 $35.5 $35.5
Field crop and rangeland $12 $11 $11.5
Pest detection $29 $28.5 $29
Methods development $21.5 $21.5 $21.5
Specialty crops $206.5 $216.3 $208.5
Tree and wood pests $59 $59 $58.6
Emergency preparedness and response* $44.5 $44.5 $44.3
* this fund is apparently for both animal and plant emergencies
Rationale
Already introduced pests threaten the many forest products and services benefitting all Americans. Just 15 of the worst pests threaten 41% of forest biomass in the “lower 48” states – comparable to fire.[1] A significant proportion of the resulting costs are imposed on municipal governments and homeowners. Fifteen years ago, it was estimated[2] that the municipal governments were spending more than $1B / year, primarily on removing and replacing trees on public property killed by these non-native pests. Homeowners faced costs of $1B plus loss of another $1.5B in property value. A more recent study estimated that cities will have to spend $30M per year to remove and replace ~ 1.4M street trees by 2050. Additional trees in parks and on homeowners’ properties also die.[3]
A new pattern has appeared in recent years: more newly-introduced pests are being detected in the Pacific Coast states rather than in the East and Midwest. Two southern California counties are projected to pay $150M – $1B[4] to remove and replace trees killed by invasive shot hole borers. The emerald ash borer threatens 9,000 ash on the streets of Portland, Oregon and millions more in parks and the forested wetlands of Willamette Valley, including in Ankeny National Wildlife Refuge. The Mediterranean oak borer has already killed thousands of oak trees in the San Francisco Bay area; it also threatens urban forests and valued oak savannahs in Oregon.
Additional introductions of highly damaging wood-borers are likely because we continue to receive inadequately treated crates, pallets, and other forms of packaging made of wood. For 20 years, all countries shipping goods to North America must treat their wooden packaging per prescribed protocols. To address this risk, we urge a modest $1M increase in APHIS’ “Tree and Wood Pest” account. We also suggest that the Subcommittee inquire of APHIS what steps it will take to improve compliance with the treatment requirement. You should focus your inquiry on China; wood packaging from this country is three times more likely to harbor a tree-killing pest than the global average.[5]
Other pests—especially plant diseases and sap sucking insects—enter on imported plants. Pathogens introduced recently via this pathway include rapid ohia death in Hawai`i (threatening the species that constitutes 80% of the Islands’ forest biomass) and beech leaf disease (thin a dozen years has spread across much of the East).
All assessments of APHIS’ plant import programs’ effectiveness use data from 2009; at that time, plant imports were more than 100 times more likely to transport pests than was wood packaging.[6] APHIS has amended its regulations several times since 2009. We urge the Subcommittee to call for APHIS to facilitate independent analysis of the efficacy of its current phytosanitary programs in order to understand whether the updated regulations have reduced the risk of additional introductions.
Again, pests introduced via this pathway proliferate and spread – often facilitated by movement of firewood, plants, and outdoor household goods. APHIS’ programs have suffered severe failures to prevent such spread, for example in the cases of the emerald ash borer and sudden oak death. We suggest that the Subcommittee inquire of APHIS what steps it will take to improve containment efforts regarding damaging plant pests, including through collaboration with its state partners.
We ask for small increases to the Pest Detection and Methods Development programs. The first enables prompt detection of newly introduced pests … which is critical to successful pest eradication or containment. The second empowers APHIS to improve essential detection and eradication tools.
The current emergency fund of is far below the level needed to respond when a new pest is discovered. We thank both the House and the Senate for clearly recognizing that these appropriations are inadequate by including in their bills language reiterating the Agriculture Secretary’s power to access funds from other Departmental programs (usually the Commodity Credit Corporation) to respond to emergencies.
[1] Fei, S., R.S. Morin, C.M. Oswalt, and A.M. 2019. Biomass losses resulting from insect and disease invasions in United States forests. PNAS August 27, 2019. Vol. 116 No. 35 17371–17376
[2] Aukema, J.E., B. Leung, K. Kovacs, C. Chivers, K. O. Britton, J. Englin, S.J. Frankel, R. G. Haight, T. P. Holmes, A. Liebhold, D.G. McCullough, B. Von Holle.. 2011. Economic Impacts of Non-Native Forest Insects in the Continental United States PLoS One September 2011 (Volume 6 Issue 9)
[3] Hudgins, E.J., F.H. Koch, M.J. Ambrose, and B. Leung. 2022. Hotspots of pest-induced US urban tree death, 2020–2050. Journal of Applied Ecology
[4] Jetter, K. A. Hollander, B.E. Nobua-Behrmann, N. Love, S. Lynch, E. Teach, N. Van Dorne, J. Kabashima, and J. Thorne. 2022. Bioeconomic modeling of invasive species management in urban forests: final report.
[5] Haack RA, Hardin JA, Caton BP and Petrice TR (2022) Wood borer detection rates on wood packaging materials entering the United States during different phases of ISPM#15 implementation and regulatory changes. Front. For. Glob. Change 5:1069117. doi: 10.3389/ffgc.2022.1069117
[6] Liebhold, A.M., E.G. Brockerhoff, L.J. Garrett, J.L. Parke, and K.O. Britton. 2012. Live Plant Imports: the Major Pathway for Forest Insect and Pathogen Invasions of the US. www.frontiersinecology.org
Congressional Committees with Jurisdiction … & how to submit testimony
FUNDING APHIS
House Committee on Appropriations, Subcommittee on Agriculture, Rural Development, Food and Drug Administration, and Related Agencies
Chairman: Andy Harris (R-MD)
Members: Robert Aderholt, David Valadao, John Moolenaar, Dan Newhouse, Julia Letlow, Ben Cline, Ashley Hinson, Scott Franklin
Democrats à Sanford Bishop, Jr., Chellie Pingree, Lauren Underwood, Marie Gluesenkamp Perez, Marcy Kaptur, Debbie Wasserman Schultz
deadline: May 1; email to ag.approp@mail.house.gov
instructions: 5 pages, double-spaced in Times New Roman, 12 Point Font; single-sided; PDF attachment to your email. At top of 1st page, clearly indicate your name, title, & institutional affiliation (if any); In 1st paragraph, clearly state agency, program, & amount of funding in the request
Senate Committee on Appropriations, Subcommittee on Agriculture, Rural Development, Food and Drug Administration, and Related Agencies
Chairman: John Hoeven (R-ND)
Members: Republicans à Mitch McConnell, Susan Collins, Jerry Morn, Cindy Hyde-Smith, Deb Fischer, Mike Rounds
Democrats à Jeanne Shaheen, Jeff Merkley, Tammy Baldwin, Martin Heinrich, Gary Peter, Kirsten Gillibrand, Jon Ossof
deadline: not clear; might be 22 May; email to agri@appro.senate.gov
instructions: 4 pages.. At top of 1st page, clearly indicate your name, title, & institutional affiliation; state agency, program, & amount of funding in the request
FUNDING USFS
House Committee on Appropriations, Subcommittee on Interior, Environment and Related Agencies
Chairman: Mike Simpson (R-WY)
Members: Republicans à Mark Amodei, Guy Reschenthaler, Michael Cloud, Ryan Zinke, Jake Ellzey, Celeste Maloy
Democrats à Chellie Pingree (D-ME), Betty McCollum, Josh Harder, James E. Clyburn
deadline: 22 April; email to IN.Approp@mail.house.gov
instructions: 4 pages, single-spaced in 12 Point Font; single-sided; prefer PDF but other formats OK. At top of 1st page, clearly indicate your name, title, & institutional affiliation (if any); In 1st paragraph, clearly state agency, program, & amount of funding in the request
Senate Committee on Appropriations, Subcommittee on Interior, Environment and Related Agencies
Chairman: Lisa Murkowski (R- AK)
Members: Republicans à Mitch McConnell, Shelly Moore Capito, John Hoeven, Deb Fischer, Mike Rounds
Democrats à Jeff Merkley, Chris van Hollen, Martin Heinrich, Tammy Baldwin, Kirsetn Gillibrand, Jon Ossof
deadline: unclear; possibly mid-June; email to int@appro.senate.gov
instructions: 4 pages, single-spaced in Microsoft Word or Word Perfect; do NOT send PDF. At top of 1st page, clearly indicate your name, title, & institutional affiliation (if any); In 1st paragraph, clearly state agency, program, & amount of funding in the request
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:
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
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.
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
A decade ago I posted a blog reporting that 39% of forests surveyed under the Forest Inventory and Analysis (FIA) system were invaded by one or more invasive plants (Oswald et al. 2015). By regions, Hawai`i had the highest invasion intensity – 70%. The second highest density was in the eastern forests – 46%. Forests in the West ranked third, with 11% of plots containing at least one of the monitored invasive plant species. Finally, forests in Alaska and the Intermountain regions both had 6% of plots invaded.
I rejoice that US Forest Service scientists have continued to analyze their data on plant invasions. Analysis of the most recent data shows alarming increases in invasions everywhere since 2015. However, the scientists could not determine a nation-wide percentage because many areas in the West had not yet been surveyed anew. They did determine that the number of inventory plots containing invasive plant species rose in 58.9% of surveyed counties. Furthermore, in 73.2% of the counties the plots experienced an increase in species richness of invading plant species. While increases were observed in all regions, they were greater in the East than in the West — and in the USFS Southern region compared to the Northern region. Specifically, the proportion of forest plots in the East (USFS Southern and Northern regions) invaded has risen from 46% to 52.8%. In the Rocky Mountains they rose from 6% to 11%. In Hawai`i plots having invasive plants grew from 70% to 83.2%. Surveys in the Pacific Coast states have not yet been completed so this region is not included in the analysis (Potter et al. 2026). It is not clear to me how the current boundaries of the western regions – which are based on Bailey’s ecosystem boundaries relate to the 2015 boundaries, which were based on USFS official regions. Hawai`i is clearly the same.
Porter et al. (2026) concluded that in the forests of the East plant invasions are so extensive that elimination of their impacts is practically impossible. Their spread to new areas is unhindered now and, I would add, is likely to remain so without heroic counter measures.
Forests in the East have a greater mean richness of invasive plant species than do western forests. In particular, there is a profusion of shrubs and vines as well as trees. The West has a greater diversity of invasive forbs. The diversity of invasive grasses is high in both regions.
kudzu (Pueraria montana) spreading from edge into forest in Virginia; photo by F.T. Campbell
Potter at al. (2026) worry that the apparently lower level of plant invasions in the West might be an artifact of a higher proportion of plant species being at an earlier stage of invasion. That is, the species have not yet established sufficiently widely to be classified as invasive.
thicket of guava (Psidium cattleianum ) replacing ohia killed by ROD; Hawai`i Island; photo by F.T. Campbell
Of course, the situation in Hawai`i is much worse. Another, more detailed, discussion of invasive plant species in Hawai`i pointed out that relying on data reflecting canopy-level trees obscures the real picture. While “only” 29% of large trees across the Islands are non-native, about two-thirds of saplings and seedlings are. Potter et al. (2023) expected that plant succession will result in non-native tree species taking over the canopy. This likelihood exists regardless of the impact of rapid ‘ohi’a death since ‘ohi’a lehua (Metrosideros polymorpha) is not reproducing even when seed sources are plentiful and people remove invasive forbs and grasses Potter et al. (2023).
The nation-wide analysis of Potter et al. (2026) does not include forests on U.S. Caribbean islands, i.e., Puerto Rico and the Virgin Islands. See here for a description of this situation. In summary, 33 of 57 (58%) of non-native tree species tallied by FIA surveyors are actual or potential high-impact bioinvaders. Furthermore, 21 (38%) of the non-native species occurred on at least 2% of the FIA plots – far above the seven species fitting this description in the continental U.S.
As these sources, and those with a broader perspective, demonstrate that we should not ignore invasions of our forests by non-native plants. These species erode forest productivity and provision of the full range of ecosystem services, hinder shifting (?) forest uses, and degrade biodiversity and habitat.
These invasions also impose extensive financial costs from lost or damaged resources (Potter et al. ( 2022). Potter et al. (2026) note that these negative outcomes depend on interactions between the traits of the non-native plants and the biomes being invaded. These impacts are greatly exacerbated in Hawai`i because more than 95% of native species on the Islands are endemic. This includes 67% of the large trees still present in the forests. As Potter et al. (2023) point out, extirpation of any of these species is a global loss.
ʻōhiʻa lehua (Metrosideros polymorpha); photo by F.T. Campbell
Data issues
Potter et al. (2026) note that in the Northern region only about 20% of plots were surveyed for invasive plants. They state that these difference in sampling intensity does not affect statistical analyses across broad scales.
The regional lists of invasive plants were developed by experts. They include those species thought at the time to be most damaging. Of course, there are other non-native plant species that might be present – and some might prove to be invasive over time (Potter et al. 2026). I have been unable to determine whether the regional lists are updated periodically. Because of this structure of the FIA system, these surveys can assess only spread of already-established species. It is not suitable for early detection of new species entering the forest.
For all these reasons, the analyses in Porter et al. (2026) probably underestimate the total abundance of non-native plant species in U.S. forests. Indeed, the time lag between introduction or even identification of invasive species and their eventual ecological and economic impact obscures their full impact. This ever-increasing invasion debt probably contributes to decisions not to implement effective countermeasures.
Recommendations
How do we set priorities for responding to nearly unmanageable situations? We sharpen our focus on the most damaging pathways of introduction, the most vulnerable regions, and the most at-risk species.
The high-risk pathways are imports of plants for planting and wood – including but not limited to crates, pallets, and other forms of packaging.
Vulnerable regions start with the Hawaiian Islands, Puerto Rico, and the Virgin Islands; and include many biodiversity-rich areas on the continent. We should enhance monitoring of these vulnerable regions by federal, state, and tribal agencies, conservation organizations, citizen scientists, and others. Surveys must report all non-native plant present, not just those already known to be invasive. These data will improve detection of new species and better inform us about factors affecting species’ spread.
Also, I support Potter et al.’s (2026) emphasis on the wildland-urban interface as an area of high human-environment conflict.These include, but are not limited to, plant invasions. The authors point out that we need new policy, management, and scientific tools to address threats in these vulnerable and too-often ignored social and ecological zones.
This increase in available information must be paired with management of the factors that facilitate invasion. Some of these are associated with ecosystems. But the key target must be plant species being brought into the region by people for various purposes. This is often for ornamental horticulture.
lesser celandine (Ficaria verna) dominating herb layer in a Virginia forest; photo by F.T. Campbell
We must ask state legislatures and Congress to empower regulatory agencies – e.g., their state departments of agriculture and USDA’s Animal and Plant Health Inspection Service – to be far more more assertive and pro-active. For example, they must give higher priority to the full range of ecological and economic impacts of invading plants, not just damage to agriculture.
Evans et al. (2024) urged prioritizing for state regulation those species in the ornamental trade that are projected to remain or become abundant under evolving climate conditions. Beaury et al. (2023) called for regulating the nursery trade at the national level – reflecting the scope of sales.
SOURCES
Beaury, E.M., J.M. Allen, A.E. Evans, M.E. Fertakos, W.G. Pfadenhauer, B.A. Bradley. 2023. Horticulture could facilitate invasive plant range infilling and range expansion with climate change. BioScience 2023 0 1-8 https://doi.org/10.1093/biosci/biad069
Evans, A.E., C.S. Jarnevich, E.M. Beaury, P.S. Engelstad, N.B. Teich, J.M. LaRoe, B.A. Bradley. 2024. Shifting hotspots: Climate change projected to drive contractions and expansions of invasive plant abundance habitats. Diversity and Distributions 2024;30:4154
Potter, K.M., C. Giardina, R.F. Hughes, S. Cordell, O. Kuegler, A. Koch, E. Yuen. 2023. How invaded are Hawaiian forests? Non-native understory tree dominance signals potential canopy replacement. Landsc Ecol 2023 https://doi.org/10.1007/s10980-023-01662-6
Potter, K.M., B.V. Iannone III, K.H. Riitters, Q. Guo, K. Pandit, C.M. Oswalt. 2026. US Forests are Increasingly Invaded by Problematic Non-Native Plants. Forest Ecology and Management 599 (2026) 123281
Potter K.M., K.H. Riitters, and Q Guo. 2022. Non-native tree regeneration indicates regional and national risks from current invasions. Frontiers in Forests & Global Change Front. For. Glob. Change 5:966407. doi: 10.3389/ffgc.2022.966407
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
garlic mustard (Alliaria petiolata); photo by Katja Schulz via Wikimedia
I welcome a recent series of studies documenting the extent of plant invasions in forests of the eastern United States and the socio-economic conditions that contribute to a state of affairs increasingly recognized as a crisis. I wish, however, that the authors had devoted more attention to the role of deliberate planting of non-native species and the resulting propagule pressure.
I summarize here findings of two studies written by largely the same scientists and relying on the same underlying data: surveys of forest plots conducted under the Forest Inventory and Analysis (FIA) program. In this blog, if focus on the extent of invasive plant presence in the forests of the eastern United States. In an accompanying blog I will summarize the status of plant invasions in forests nation-wide.
As I have noted in earlier blogs, link a decade ago one or more invasive plant species had already invaded 46% of FIA plots in the eastern U.S. (Oswald et al. 2015). This situation has worsened. Updated data show that 52.8% of these plots contain invasive plants. In the USFS Southern Region, invasive plants have been documented on 55.3 million ha. In the Northern Region, they are found on 36.9 million ha. (Only ~20% of FIA plots in the Northern Region were surveyed for invasive plants.) In some counties of the 37 states constituting these two USFS regions, 80% of inventoried forest plots contain invasive plants. Areas with lower levels of invasion are found in parts of New England, the Great Lakes states, southern Appalachians, southeastern coastal plain, and western Texas and Oklahoma (Potter et al. 2026). Spread of these bioinvaders is largely unchecked – either throughout the East or “just” in the South. In any case, the extent and intensity of these invasions are so great that their complete removal – or elimination of their impacts – is “practically impossible” (Potter et al., 2024; Potter et al. 2026). [It is not clear whether the scientists mean “nearly” or “in practice”. Or that this difference is important.]
[In comparison, in the West less than 30% of FIA plots are invaded, on average. In Hawai`i, more than70% are (Potter et al. 2026).]
The scientists analyzing the FIA data warn that the extent and impact of plant invasions in eastern forests is undoubtedly worse than these data indicate. The records include only some of the non-native plant species present — those considered to be the worst invaders at the time regional lists were compiled – apparently in the first years of the 21st Century (Potter et al. 2026).
Japanese honeysuckle (Lonicera japonica) photo by Chuck Bargeron
The scientists emphasize the role of disturbance in promoting plant invasions. They cite various studies as well as the FIA data to document that forest edges facilitate non-native plant establishment and spread into forests. They stress various aspects of suburban development, including roads and other transportation corridors. It follows that invasion rates are highest in the “wildland-urban interface (WUI).” [The wildlife-urban interface is the zone of transition between unoccupied land and human development; the zone where structures meet or intermix with undeveloped land and its vegetation.] They worry that the WUI is growing faster than any other land use type in the country – and especially rapidly in the East. As a result, the scientists expect more and worse invasions in the future (Potter et al., 2024 and Potter et al. 2026).
I appreciate that they highlight the uniqueness of WUI ecosystems. Housing development in the WUI has numerous effects on natural ecosystems, including habitat modification and fragmentation followed by diffusion of the direct and indirect effects of anthropogenic activities into neighboring ecosystems at different scales. As regards specifically non-native plants, this transmission occurs through a combination of (1) human-driven disturbances to native ecosystems that promote plant invasion and (2) providing a source of non-native plant propagules in their yards and gardens. These plants can then spread into and establish in nearby ecosystems (in this case, forests). [I note that tree-killing arthropods and pathogens also can be introduced in the WUI.] (Scroll below “Archives” to “Categories”, click on “forest pests” and “wood packaging”.)
They also found that plant invasions are more strongly related to older, than more recent, land-cover changes. Survey plots that have been located in the WUI since 1990 or earlier had on average 2.6% more invasive plant cover and 0.33 more invasive plant species than those that were classified as being in the WUI in 2000 or 2010. Their explanation is that the WUI forests experienced decreased spatial integrity, increased forest-developed area edges, and falling proportions of forest in the surrounding landscapes. In addition, the human population in the vicinity might have grown. All these factors that would increase forest fragmentation and the plots’ susceptibility to invasion.
The other side of the coin is propagule pressure. Both Potter et al (2024) and Potter et al. (2026) note that the flora of residential landscapes – rural as well as suburban – is typically dominated by non-native plant species. Still, I think these studies downplay the impact of this ubiquity of non-native plants in all anthropogenic landscapes.
In discussing the higher invasion rates found in survey plots located in WUIs dating from the 1990s they made no mention of human activities that promote plant invasions. There are several. Plants growing in those older yards had one or two more decades to flower – and for their fruits and seeds to be transported into the forest by birds, wind, or water. Residents might have decided to beautify their neighborhood by planting shrubs or flowers in the woods. Maybe they succumbed to the temptation to dump yard waste in the woods – thinking it would be absorbed by “nature”. Since plant invasions take time to unfold, these additional years of human-mediated exposure are highly relevant. Another factor is that people who choose to live in wooded surroundings probably choose horticultural plants that thrive under such conditions – exactly those best able to establish beyond the property line.
Another opportunity to discuss these factors came from the discovery that plant invasion rates are higher in association with “interface” rather than “intermix” WUI forests. [“WUI interface forests” are those where settled areas abut wildlands. In “WUI intermix forests” the structures are scattered.] They speculate about reasons. Potter, et al. (2024) mention that invasions originating from older housing developments have had more time to establish (or at least to be detected) given the well-known lag associated with plant invasions.
I wish they had focused more on the probable difference in suburban development across time. While I was growing up in expanding suburbs in the 1950s, I observed that the earlier housing developments were either built on land that had been cleared to support agriculture or the builders cleared the forest to make construction easier and cheaper. More recently, wealthier buyers have sought residences on more wooded sites – so creating an “intermix” WUI. Potter et al. (2024) speculate that locations in the “interface” WUI are closer to high-density urbanization so have higher exposure to non-native plants. They do not discuss whether the “interface” WUIs are older, thus giving associated plantings longer years to proceed through the stages of bioinvasion.
burning bush (Euonymus alatus) invading a forest in Virginia; photo by F.T. Campbell
The Role of Deliberate Planting?
I recognize that these authors analyzed mountains of data. However, I wish they had incorporated the findings of numerous scientists who have analyzed the role of deliberate planting – especially ornamental horticulture – in facilitating introduction and spread of invasive plants. (Scroll below “Archives” to “Categories” and click on “invasive plants”. Also See Reichard and White 2001 and Mack 2000).
As I hope USFS scientists are aware, recent studies confirm the continuing role of ornamental horticulture in plant invasions. Kinlock et al. (2025) blog 440 found that more than 1,600 plant species sold by nursery and seed catalogs over 200 years had “naturalized” somewhere in the continental 48 states. They do not discuss what proportion of these species are truly damaging invaders. Fertakos and Bradley (2024) found that species were likely to establish if they were introduced to as few as eight locations. Beaury et al. (2024) found that half of 89 plant species recognized as invasive are sold in the same locations where they are invasive. Another 25 species are sold by one or more nurseries located in an area that is currently unsuitable for those species, but that will become more suitable for invasion as temperatures warm.
Potter et al. (2026) acknowledge that the ornamental plant trade is likely to continue introducing new plant species into U.S. forests. However, they recommend only updating the lists of invasive plants to be included in future surveys. Apparently these lists have not been updated since 2004.
Potter et al. (2024) go farther, urging efforts to encourage homeowners to plant more native and environmentally friendly private landscapes. They note that such advocacy is complicated by the fact that non-native – even invasive – species provide valued ecosystem and cultural services.
I add that the nursery industry and their customers enjoy enormous lobbying clout.
Many associations – native plant societies, regional or state invasive plant councils, etc. – are pursuing this approach. To research these efforts, visit the websites for the state native plant societies and the Southeast Exotic Pest Plant Council, Mid-Atlantic Invasive Plant Council, and Midwest Invasive Plant Network. These voluntary efforts have yielded some success. But they have not resulted in adequate protection for our ecosystems. Dr. Douglas Tallamy points out that even non-invasive, non-native plants disrupt food webs.
The insufficient attention to the role of the plant trade in articles intended to be comprehensive has crucially important impacts. As both Potter, et al. (2024) and Potter et al. (2026) affirm, determining which factors are most important in facilitating plant invasions of eastern American forests is the necessary foundation for identifying and implementing the most efficient and effective counter measures.
These scientists are employees of the U.S. Department of Agriculture. If departmental leadership interpret their studies as justifying inaction on regulating plant sales, USDA’s regulatory agencies will not respond. And we will continue failing to curtail introduction and spread of damaging plant invasions.
I agree with the authors on the need for enhanced monitoring and management of WUI zones in the East to detect new species or new locations of invasion and the need to develop better tools for these purposes. However, I ask all stakeholders to follow Evans et al. (2024), who urge prioritizing for state regulation those species in the ornamental trade that are projected to remain or become abundant under evolving climate conditions. Or, more aggressively, follow Beaury et al. (2023)’s call for regulating the nursery trade in a manner consistent with the scope of the horticultural trade at the national level. That would require legislation, since the Federal Noxious Weed Act does not currently address long-established, widespread species. Beaury et al. (2023) also note that existing state restrictions are outdated, tend to include only a few weeds that plague agriculture rather than those that invade natural systems, and are irregularly enforced.
orchids in Everglades National Park; photo by F.T. Campbell
I conclude by agreeing with the scientists that managing the disturbance component of plant invasions points to protecting particularly forests of high conservation value. They suggest adoption of land-use planning rules aimed at this goal. However, as they point out, such action will be extremely unlikely given the magnitude of predicted land-use changes in the country and powerful demographic factors driving them. I would add other barriers: the lobbying clout of the real estate industry and homeowners plus the local nature of zoning decisions.
SOURCES
Beaury, E.M., J.M. Allen, A.E. Evans, M.E. Fertakos, W.G. Pfadenhauer, B.A. Bradley. 2023. Horticulture could facilitate invasive plant range infilling and range expansion with climate change. BioScience 2023 0 1-8 https://doi.org/10.1093/biosci/biad069
Evans, A.E., C.S. Jarnevich, E.M. Beaury, P.S. Engelstad, N.B. Teich, J.M. LaRoe, B.A. Bradley. 2024. Shifting hotspots: Climate change projected to drive contractions and expansions of invasive plant abundance habitats. Diversity and Distributions 2024;30:4154
Fertakos, M.E. and B.A. Bradley. 2024. Propagule pressure from historic U.S. plant sales explains establishment but not invasion. Ecology Letters 2024;27:e14494 doi: 10.1111/ele.14494
Kinlock, N.L., D.W. Adams, W. Dawson, F. Essl, J. Kartesz, H. Kreft, M. Nishino, Jan Pergl, P. Pyšek, P. Weigelt and M. van Kleunen. 2025. Naturalization of ornamental plants in the United States depends on cultivation and historical land cover context. Ecography 2025: e07748 doi: 10.1002/ecog.07748
Oswalt, C.M., S. Fei, Q. Guo, B.V. Iannone III, S.N. Oswalt, B.C. Pijanowski, K.M. Potter. 2016. A subcontinental view of forest plant invasions. NeoBiota. 24:49-54 http://www.srs.fs.usda.gov/pubs/48489
Potter, K.M., K.H. Riitters, B.V. Iannone III, Q. Guo and S. Fei. 2024. Forest plant invasions in the eastern United States: evidence of invasion debt in the wildland‑urban interface. Landsc Ecol (2024) 39:207 https://doi.org/10.1007/s10980-024-01985-y
Potter, K.M., B.V. Iannone III, K.H. Riitters, Q. Guo, K. Pandit, C.M. Oswalt. 2026. US Forests are Increasingly Invaded by Problematic Non-Native Plants. Forest Ecology and Management 599 (2026) 123281
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
Alaska yellow cedar (Chamaecyparis nootkatensis); one of the species vulnerable to Phytophthora austrocedri; APHIS has determined it is too late to try to slow its spread. Photo by Nucatum amygdalarum via Wikimedia
On 30 December 2025, US Department of Agriculture Secretary Brooke L. Rollins issued a Secretary’s Memorandum setting five new priorities for research and development. One is to protect agriculture from invasive species. Another is to resolve longstanding trade barriers due to sanitary and phytosanitary concerns.
The Secretary’s intention is to strengthen US agriculture to benefit both farmers and consumers. He justifies the action by claiming that President Lincoln’s original purpose in establishing USDA was to acquire and diffuse useful information on subjects connected with agriculture. According to this interpretation, Lincoln recognized that working to improve agriculture and secure the nation’s food supply would benefit everyone. The emphasis on research and development was reiterated by the almost simultaneous adoption of the Morrill Act of 1862, which created the system of land-grant universities and development of the Cooperative Extension System via the Smith-Lever Act of 1914.
The memorandum specifies five priority areas of research to be pursued by all USDA agencies and offices – to the maximum extent permitted by law and in accordance with any applicable regulations and procedural requirements.
Increasing Profitability of Farmers & Ranchers — especially reducing volatility in profitability. Goals include reducing inputs or increasing mechanization and automation.
Expanding Markets for US agricultural products. Two approaches are mentioned: generating science and data to resolve longstanding sanitary and phytosanitary trade barriers; and expanding use of agricultural commodities in novel biobased products and bioenergy.
Protecting the Integrity of American agriculture from Invasive Species. The memorandum lists four examples of current invasive pest and pathogen threats: new world screwworm in Mexico; continued westward expansion of spotted lanternfly; persistence of highly pathogenic avian influenza in poultry flocks; and citrus greening. It notes that invasive species threaten both agriculture and natural resources. The research is to focus on new and effective methods for preventing, detecting, controlling,and eradicating these threats.
Promoting Soil Health to Regenerate Long-Term Productivity of Land. The research is to promote soil health practices, increase water-use efficiency, & reduce the need for inputs.
Improving Human Health through Precision Nutrition and Food Quality. Research on “precision nutrition” is said to improve understanding of how healthy dietary patterns impact individuals. Research will also focus on increasing foods’ nutritional content and quality.
Vaccinium myrtillus (photo by Anneli Salo via WikiMedia); one of several species in genera shared with North America that are infected by Phytophthora spp in the Italian alps
The memorandum also instructs USDA’s Office of the Chief Scientist (that is, the Under Secretary for Research, Education, & Economics) to coordinate these priorities within USDA and among key partners in other federal agencies.
Does This Policy Mean Substantially Stronger USDA Efforts to Counter Bioinvasions?
Can we expect new energy in USDA’s programs aimed at managing non-native forest pests and invasive plants that damage forests, wetlands, grasslands, and other natural systems? The first paragraph of the memorandum states that it is USDA policy to reaffirm a focus on the Department’s original objectives of maximizing and promoting American agriculture; ensuring a safe, nutritious, and secure food supply; enhancing rural prosperity; and protecting our National Forests & Grasslands. That is promising.
The explicit recognition that invasive species pose severe threats to both agriculture and natural resources is also promising. I welcome the inclusion of two plant pests among the examples. Livestock diseases usually receive far more attention in USDA pronouncements.
I note three caveats:
The prominence of enhancing markets for US agricultural exports (# 2). In the past, this longstanding emphasis has led to undercutting phytosanitary agencies’ ability to counter suspected — but incompletely understood — pest risks. I discussed the impracticality of determining a newly detected species’ probable impacts in Chapter 3 of my report, Fading Forests II.
The memorandum makes no reference to implementing stronger sanitary or phytosanitary policies. In my view, the Animal and Plant Health Inspection Service has sufficient knowledge to support adoption of a more assertive regulatory stance with regard to both new introductions and spread within the country? Does the memorandum signal support for such a stance by high-ranking USDA officials?
These officials have often reminded APHIS that it is not a research agency. However, its staff do “methods development” and it funds considerable research through the Plant Pest and Disease Management and Disaster Prevention Programs – Section 7721 of the Plant Protection Act and a matching program for animal diseases.
The US Forest Service does have a research division – although the Trump Administration proposed its virtual elimination in early 2025. The Congressional appropriators have provided funding for USFS R&D – but those bills have not yet been enacted into law. I have complained for years that USFS R&D allocates too few resources (about 1% of the total budget) to research on introduced pests and disease pathogens. Might this new directive help fix this problem?
I hope the emphasis on protecting National Forests & Grasslands does not result in narrowing the types of invasive pests addressed.
Posted by Faith Campbell
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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
