Category: animal invaders

Florida’s bromeliads: who will protect them?

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. 1996. Bromeliad biota: history of Metamasius callizona FLORIDA [online]. Gainesville (FLORIDA): University of FLORIDA [cited 2010 Feb 1]. Available from https://www.entnemdept.uFlorida.edu/frank/bromeliadbiota/wvbrom6.htm

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

Or

https://fadingforests.org

Factoids from recent publications

Agrilus auroguttatus

Agrilus genus

Hernández‐Gutiérrez, Nichols, and Kelly (2026) (full citation at the end of the blog) analyzed interactions between this genus of beetles and oaks (Quercus species). In this context, they report that 32 Agrilus species from Africa, Asia, Europe, and North and South America use 51 Quercus species as hosts in their native range. Eighteen (56.25%) use only Quercus hosts.

Oaks that host Agrilus species cluster in several clades, i.e., the entire Section Cerris and one clade of Section Ilex and two clades of section Lobatae. Clades where Agrilus hosts are underrepresented are Sections Cyclobalanopsis and Quercus &, surprisingly, two clades in Section Lobatae.  

Their analysis indicated that beetle-oak interactions involving all the 32 Agrilus species and 105 Quercus species in their study had a significant likelihood of being damaging. For example, northern red oak (Q. rubra) is already known to host six Agrilus species. Hernández‐Gutiérrez, Nichols, and Kelly (2026)’s analysis indicated that this tree species might be utilized by all 32 Agrilus species assessed. The tree’s wide distribution (both native and introduced) places it close to other known or probable hosts, which exacerbates the risk of an interaction. Another 26 Quercus species are predicted to host ten or more Agrilus species.

The model was not successful in predicting hosts of A. auroguttatus (goldspotted oakborer) in its introduced range in California.

black oak (Quercus kelloggii) in Cleveland National Forest killed by GSOB; photo by F.T. Campbell

It also predicted that few of China’s oak species might host Agrilus beetles. However, as Dr. Robert Haack notes (pers. comm. June 2026), larval hosts have been identified for only 13% of the nearly 1,200 Asian Agrilus.

Some Agrilus species have a very large number of predicted novel interactions. A. graminis and A. angustulus are predicted to have more than 40 novel oak hosts. Both have numerous known oak hosts; so their “polyphagous” nature is already documented.

Since two-thirds of 666 Agrilus species with known larval hosts exploit only one plant genus as a host in their native range, Hernández‐Gutiérrez, Nichols, and Kelly (2026) assert that they might spread faster if introduced to homogeneous rather than species-rich habitats. Dr. Haack believes that this statement is too broad (pers. comm. June 2026).

A. bilineatus; photo by Christina Butler via Wikimedia

Twolined chestnut borer

Haack and Blank (2024) document that the twolined chestnut borer, Agrilus bilineatus has preferentially infested apparently healthy English oak (Quercus robur) trees over healthy native oak trees in Michigan. In North America, A. bilineatus is a major pest of oaks and American chestnut (Castanea dentata)when they are stressed by drought or other factors. Infestation typically begins in the upper crown and proceeds downward; tree death often occurs within three years.

 At several sites in southern Michigan, where English oaks were intermixed with native white oaks (Quercus alba) and close to northern red oaks (Quercus rubra), A. bilineatus preferentially infested Q. robur trees that initially appeared healthy. Further study revealed that many of the English oaks attacked had low or depleted root starch levels.

Although these findings are cause for alarm, English oak is already used by 11 species of Agrilus in Europe. Perhaps the tree and ecosystem might have sufficient defenses in Europe. Meanwhile, A. bilineatus has been reported in Turkey as of 2018; I have found no recent information about the damage whether it is causing any damage there.

Data from Britain and Worldwide

Peyton et al. (2026) reviewed the effectiveness of a “horizon scanning” exercise conducted for Great Britain (England, Scotland and Wales). They report that 3,248 recognized non-native species have been detected in Great Britain, of which 2,016 have established self-sustaining populations. Some 194 (~10%) are considered invasive, that is, have negative impacts on biodiversity and wider ecosystem viability. These consist of 108 terrestrial species, 47 freshwater species, and 39 marine species. These bioinvaders cost the British economy an estimated ~£3.9 billion per year (the bulk of the damage is attributed to ash dieback, caused by the fungus Hymenoscyphus fraxineus).

In the decade between completion of the “horizon scan” and the present, 143 species were recorded as being introduced. The horizon scan predicted 31 of these species, 22%. Peyton et al. (2026) consider this to be success.

Peyton et al. (2026) report that globally, ~ 6% of non-native plant species are ranked as invasive. Among invertebrates, this proportion rises to 22%. Considering vertebrates introduced to Europe or North America, the figure is more than 50%!! I welcome global data that support my call for rethinking the “rule of tens” long relied on for estimating the proportion of non-native species that are invasive.  

Discussing bioinvaders’ role in causing extinctions, Peyton et al. (2026) report that 30 predators have been linked to declines and extinctions of 738 vertebrate species.

Peyton et al. (2026) also discuss the difficulty in predicting an introduced species’ impacts when in some cases the time lag between introduction and presence in the wild or between establishment and spread w/in the region can last decades or even a century. They cite as an example Senecio squalidus, which escaped the Oxford Botanic Gardens in the 1700s but started to spread only during mid-1900s.

Australia

More than 300 non-native insect pests, pathogens and nematodes have established on tree or shrub hosts in Australia; 20% have caused moderate to high impacts to commercial plantations, urban forests, or trees in natural ecosystems (Carnegie et al. 2026).The rate at which non-native forest pests and pathogens have been detected in Australia has doubled since 2018 compared to earlier decades: from ~ 1.5 to ~ 3 per year. Carnegie et al. (2026) attribute this rise to greatly expanded official surveillance efforts. Still, three-quarters of the most recent detections came too late for eradication to be attempted.

The Forestwatch program (inaugurated – under a different name – in 2022) includes pathogens. I rejoice!!! Still, the target species threaten primarily tree species not native to Australia but important to commercial forestry or urban forests: Asian longhorned beetle,  burnt pine longicorn (Arhopalus ferus), pine pitch canker, pine wilt disease, red turpentine beetle (Dendroctonus valens), Asian spongy moth, red needle cast, and sudden oak death. The exceptions are strains of Austropuccinia psidii not yet intro to Australia, and eucalypt leaf blight (caused by Teratosphaeria destructans) (Carnegie et al. 2026).

Austropuccinia psidii infection on Melaleuca in Australia; photo by John Tann via Flickr

Among the introduced pests causing the greatest damage to native species are

  • Phytophthora cinnamomi: this soil fungus can kill 40% of the plant species in the southern portion of Western Australia  – which is one of 36 “Biodiversity Hotspots” recognized by the Critical Ecosystem Partnership Fund.  
  • Austropuccinia psidii (cause of myrtle rust) in natural ecosystems; Members of the host family Myrtaceae occur in 11 of 13 major vegetation formations on Australia. Various authorities have identified 76 species as at risk to the rust.

I hope the Australians are developing strategies for landowners to counter damage by the polyphagous shot hole borer (Euwallacea fornicatus) and its associated fungus (Fusarium euwallaceae). DMF Outbreak detected near Perth, Western Australia, in 2021 – apparently three years after the actual introduction. By June 2025 authorities had determined that it was too widespread to be eradicated, so landowners will be responsible for any management.  (Carnegie et al. 2026) Impact is predicted to be greatest in urban landscapes, and cost up to AU$9.7 M per annum to manage.

Pherosphaera fitzgeraldii; photo from https://savingourspecies.environment.nsw.gov.au/managementsite/3752

Phytophthora pluvivora was first detected in Australia on an English oak, Quercus robur. However, it has since been recorded on native species in the Blue Mountains, including the critically endangered dwarf mountain pine (Pherosphaera fitzgeraldii) in a National Park.

SOURCES

Carnegie. A.J., B.A. Summerell, C. Trollip, F. Tovar, D.I. Smith, and J. McDonald. 2026. Sentinel trees for early detection of non-native forest pests and pathogens in Australia. Front. For. Glob. Change 9:1801183. doi: 10.3389/ffgc.2026.1801183

Haack, R.A. and R.B. Blank. 2025.  Susceptibility of English Oak (Quercus robur) to the Twolined Chestnut Borer, Agrilus bilineatus (Coleoptera: Buprestidae): Observations from Michigan. The Great Lakes Entomologist. 57: 113-125. https://doi.org/10.22543/0090-0222.2492

Hernández‐Gutiérrez, E., R.A. Nichols, and L.J. Kelly. 2026. Combined phylogenetic and geographic data can predict plant–pest interactions with high accuracy. New Phytologist (2026) doi: 10.1111/nph.71306

Peyton, J.M., S. Rorke, D.C. Aldridge, O.L. Pescott, K. Dehnen- Schmutz, D.G. Noble,  J. Sewell, A.J.A. Stewart,  T. Adriaens,  B.C. Beckmann,  J. R. Britton, J. Brodie1, P.M.J. Brown, I.C.N. Cavadino, P.F. Clark, A.M. Dunn, J.Foster, C. Harrower, M.C. Harvey, M.C. Jackson, T. Jones, C.A. Maggs, G. Martin, F. Mathews, A.C. Mill, D. Murphy,  E. Paganini, R. Payne, W. Rabitsch, T. Renals,    K. Schönrogge, R.H. Shaw, G.C. Smith, P.D. Stebbing, P.A. Stroh, H. Tidbury, E. Tricarico, J. Vallet,   K.J. Walker, L.E. Wood, C.A. Wood, B. Woodcock, H.E. Roy. 2026. Assessing the success of a horizon scanning approach in predicting invasive non- native species arrival. J Appl Ecol. 2026;63: https://doi.org/10.1111/1365-2664.70217

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

Earthworms – relationships to Pleistocene glaciers

I last blogged about bioinvasions by earthworms in September 2023. My concern was that the USDA Animal and Plant Health Inspection Service (APHIS) was refusing to regulate worms’ introduction based on an inadequate risk assessment. I complained that APHIS’ principal concern was that introduced worms or the soil they were transported in might transport pathogens. APHIS’ website did not mention introduced earthworms’ well-established ability to disrupt the soil and possibly cause undesirable impacts on plant growth and diversity.

I also cited a study by USDA Forest Service scientists regarding interactions between long-term, continuous stressors, including earthworm invasions, and short-term gap-forming events. Reed, Bronson, et al. (2025) reported finding lower earthworm biomass and density in both deer exclosures and canopy gaps. They hypothesized that in canopy gaps higher deer browse pressure changed plant community and soil properties. These changes then affect soil-dwelling fauna like earthworms. They believed the higher worm densities in closed-canopy sites might be the result of greater volumes of nutrient-rich tree leaf litter which provides both shelter and food. The closed canopy sites also lacked recent soil disturbances. (Other authors cited in that blog describe varying impacts of deer browsing on plant communities and succession.)

A study I have not previously included in my blogs focused on invasions in the forest understory of the Katharine Ordway Natural History Study Area, which is in eastern Minnesota on the bluffs of the Mississippi River. The now dominant oaks are being replaced by a more mesic forest with a growing proportion of Ulmus americana, U. rubra, Acer negundo, Prunus serotina, Tilia americana, and Fraxinus pennsylvanica. (I note that three of these species are being suppressed by two introduced organisms, “Dutch” elm disease and emerald ash borer).  

Davis et al. (2015) found that all common herb layer species – native and non-native – established in microsites favorable to plants in general. Under the forest’s mostly closed tree canopy, light levels played almost no role in determining where herbaceous understory plants grew. However, abundant earthworms and deer were deemed to be larger factors explaining most of the changes in native herbs’ abundance and distribution. The earthworms’ effect arose from changes to the soil and litter environment.

I have not found a more recent analysis of the Ordway forest understory, so I don’t know whether these trends continued. I also wonder whether the conclusions about herb species’ interactions would have differed if the non-native species studied were those that completely dominate the ground level, such as Ficaria instead of Alliaria petiolata; or a dense shrub layer, e.g., Rosa multiflora.

A new analysis provides a large-scale description of worm invasions. McCay et al. (2026) report that about 300 species of earthworms inhabit North America, of which about 70 are non-native. They sought to determine the relative importance of Pleistocene glaciation in explaining earthworms’ present assemblages. Their study sampled 94 sites across 13 states of the eastern and central U.S. over a twelve year period (2013 – 2025). Seventy-four of the sites were located in previously-glaciated locations, 20 sites in non-glaciated places.

The study confirmed the presence of 16 species; only three were considered to be native to North America (Aporrectodea rubidus, Eisenoides carolinensis and E. lonnbergi). Minimum species richness at individual sites ranged from zero to eight species. Species richness was markedly greater in the glaciated regions of the Midwest and Northeast. By both dry biomass and numbers, European lumbricids dominated throughout. Lumbricus species constituted 45% by number and 69% by biomass across all sites. Their dominance was highest in the Midwest Glaciated region.

Native earthworms were rare, constituting only 2 or 3% at those sites where present. Invasion by Asian pheretimoid megascolecid (“jumping worm”) species has just begun; they were present at only 10% of study sites.

Earthworms – apparently both native and non-native – were most abundant and diverse in the Midwest Glaciated region (Ohio, Michigan, Minnesota, and Wisconsin), where non-indigenous earthworm invasion is more recent than in the Northeastern Glaciated Region (Massachusetts and New York). Earthworms were least common and diverse in areas south of the terminus of the Pleistocene glaciation. McCay et al. (2026) speculated that development of forests in northern North America over thousands of years with few or no earthworms might have led to accumulations of organic matter in forms useful to earthworms (“banking” of soil organic matter), which supported a pulse of earthworm proliferation following colonization. 

Some other factors play a role.  Earthworm presence – measured by biomass – and diversity increased with higher soil pH. Many earthworm species are known to be sensitive to soil acidity. Epigeic earthworms (those that feed on leaf litter) are often more tolerant of acidic conditions than endogeic earthworms (which live in and consume soil).

The study did not measure co-occurring variables such as calcium abundance, buffering capacity, or exchangeable aluminum. All might more directly affect worms’ physiology than pH per se.

Soil structure also matters. Soil-feeding species might be disadvantaged by sandy and gravelly soils, which do not support persistent burrow formation and are often nutrient deficient. On the other hand, they thrive better in clay soils.

While each study participant established at least one site in a relatively undisturbed habitat, e.g., a mature forest, the majority of sites tended to be within a disturbed landscape, less than .8 km from a road.

Earthworm abundance and activity vary seasonally but only 4 sites were observed over more than one season. Across all sites, there was greater species richness in autumn and spring than summer. McCay et al. (2026) think that this might have been because many earthworms aestivate during dry weather, so they are less detectable during summer although they are still present.

Distribution of native North American earthworms suggests there was some natural colonization of previously glaciated landscapes before European people arrived.

McCay et al. (2026) also did not document land use history at the sampling sites, although that can profoundly affect worms and vertical distribution of carbon in the soil. Nor did their habitat classification system [deciduous and coniferous forests, mowed and unmowed grasslands] describe the vegetation in sufficient detail to determine whether food quality might have been a factor. It is recognized that litter varies in C:N ratios, lignin content, and palatability.

McCay et al. (2026) note an interesting pattern at the global scale: Australia, New Zealand, South Africa and North America (U.S. and Canada) have been invaded by the same suite of invasive European earthworm species. One common factor, not addressed by the scientists, is that all were settled by British colonists. Instead, they focus on ecological factors. They suggests that the species’ niche requirements are broad and well-matched to temperate forest soils worldwide, and that climate and soil conditions, rather than biotic resistance from native communities, are primary factors limiting their distribution and abundance.

Another factor supporting this hyptothesis, in their view, is that the composition of earthworm communities was relatively similar above and below the southern glacial limit in North America.  Here, European earthworms colonized not just the relatively “open” soils of previously glaciated north but also non-glaciated areas farther south – assisted by human introductions and creation of disturbed habitats. They suggest that the novel species might have benefitted from reduced competition because the European species had functional differences from resident native species.

The current rapid expansion of “jumping” earthworms in North America is a fundamentally different invasion wave than the centuries-old invasion by European lumbricid species. The Asian pheretimoid species reproduce parthenogenetically and have shorter generation times. They achieve high population densities at the soil surface, process organic matter rapidly, and create a loose casting layer, potentially creating different soil conditions in ways not true after invasion by European earthworms. Although it is too early to know the outcome, McCay et al. (2026) note emerging evidence that the Asian pheretimoids might outcompete European earthworms through more flexible resource exploitation, preemptive foraging during the late summer and early fall, and tolerance of environmental stress.

Effects on atmospheric carbon levels

McCay et al. (2026) point out that the introduced earthworms are disrupting the significant pool of accumulated organic matter in previously glaciated soils. As earthworms move in, they facilitate more rapidly cycling but also translocate carbon into deeper soil strata. They conclude that while earthworms initially accelerate carbon loss through increased decomposition and respiration, their long-term effects might protect soil carbon storage. Earthworm casts and burrows can create microsites with different oxygen and moisture conditions that might promote carbon stabilization through different mechanisms than the original forest floor.

SOURCE

Davis, M.A., M.D. Anderson, L. Bock-Brownstein, A. Staudenmaier, M. Suliteanu, A. Wareham and J.J. Dosch. 2015. Little evidence of native and NIS species influencing one another’s abundance and distribution in the herb layer of an oak woodland. Journal of Vegetation Science · June 2015

DOI: 10.1111/jvs.12302

McCay, T.S., Anderson, L.J., C.P. Bloch, A.E. Cahill, S.L. Cooke, B.J. Dolan, K.M. Flinn, D. Garneau,  N.J. Hains, K. Hopfensperger, M.Beth Kolozsvary, C. Mankiewicz, S.E. Scanga, J.L. Schafer, E. Schwartzberg, D.A. Scott, K.L. Shea, J. Simmon, J.N. Styrsky. 2026. Earthworm assemblages in the Eastern and Midwestern United States and the legacy of glaciation. Biol Invasions (2026) 28:91 https://doi.org/10.1007/s10530-026-03798-3

Reed, S.P., D.R. Bronson, J.A. Forrester, L.M. Prudent, A.M. Yang, A.M. Yantes, P.B. Reich, and L.E. Frelich. 2023. Linked disturbance in the temperate forest: Earthworms, deer, and canopy gaps

Ecology. 2023;104:e4040. https://onlinelibrary.wiley.com/r/ecy  

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

Help Minnesota track invasive jumping worms

Amynthas agrestis; photo by John Abrams via Wikimedia

The University of Minnesota is seeking to learn the extent and impact of invasive Asian jumping worms (Amynthas spp.). Scientists fear that jumping worms will remove the naturally deep litter layer and create  extremely loose soils that cannot be held by plant roots. These changes will expose soil on the state’s hillsides to erosion by human footsteps, rainfall, and water runoff. They worry about the future sustainability of forested hills in Minnesota. 

The research project began in January 2024; it is funded at $430,000. The research seeks to answer the following questions:

  • What is the magnitude and rate at which jumping worms accelerate soil erosion in forested hillslopes in Minnesota?
  • What are the mechanisms of soil erosion by jumping worms in hardwood forests?
  • What is the spatial extent of jumping worms in forested hillslopes?
  • What species of native plants are capable of holding soils against jumping worms and could act as erosion-prevention?
  • What management practices could help to reduce soil erosion induced by jumping worms in forested hillslopes?

The scientists are asking volunteers to actively look for jumping worms in the forests of southeastern Minnesota and report them to EDDMapS.

Boundary Water Canoe Area; photo by Chad Fennell via Wikimedia

The scientists remind us that invasive European earthworms have already infested nearly all of the state’s  forests, even in the remote Boundary Waters Wilderness. Forest soils and understory vegetation transformed, and invasive earthworm impacts are cascading through ecological and socio-economic processes. They expect the state to become divided into two distinct areas, each dominated by a different invasive earthworm group.

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

EEICAT: improved method for assessing bioinvasion impacts

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

SOURCE

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

Posted by Faith Campbell

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

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

Or https://fadingforests.org/

Tree-killing pests can undermine conservation programs on tropical islands

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

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

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

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

diademed lemur, courtesy of Animalia

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

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

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

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

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

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

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

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

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

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

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

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

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

SOURCES

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

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

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

Horizon Scanning – 2 experiences

sorting coffee beans; photo by Niels Van Iperen via Wikimedia

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

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

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


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

Aedes aegypti; photo by James Gathany via Flickr


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

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

brown marmorated stinkbug; courtesy of Oregon Department of Agriculture


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

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

A New Year …Will there be a new priority on countering invasive species?

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.

  1. Increasing Profitability of Farmers & Ranchers — especially reducing volatility in profitability. Goals include reducing inputs or increasing mechanization and automation.
  2. 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.
  3. 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.
  4. 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.
  5. 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

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

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

Or

https://fadingforests.org

Welcome high-level attention to bioinvasions – although key issues remain unresolved

Japanese knotweed (Reynoutria japonica) – one of the worst invaders around globe. Photo by Will Parson, Chesapeake Bay Program via Flickr

On 23 October, Science published a five-page, data-packed analysis of bioinvasion impacts on terrestrial ecosystems!!! 

Thakur, Gu, van Kleunen, and Zhou (full citation at end of this blog) analyzed 775 studies with the goal of improving understanding of factors contributing to invasions’ impacts – as distinct from “invasibility” (ability to establish). This knowledge is essential to assessing the risk posed by introduced species and setting priorities for management. They analyzed five ecological contexts—diversity of native species and introduced species in the recipient systems, latitude, invader residence time, and invader traits.

They concluded that ecological factors commonly used to explain invasion success do not consistently translate into strong predictors of invasion impacts. Impacts vary in response to the context of the invasion.

[In January 2026, the authors announced changes in details of the article due to some errors in the database and their understanding of it. (Science 8 Jan 2026 Vol. 391 Issue 6781) They conclude that the corrected analysis did not alter the trends described or the overall conclusions.]

limber pine (Pinus flexilis) – one of the species killed by Cronartium ribicoli; photo by F.T. Campbell

Among the studies available for analysis, reports on plants dominated: 605 focused on plant invasions, 114 on animal invasions, and only 56 on microbial invasions. Among the animals were one study of Adelges tsugae (hemlock woolly adelgid), two studies of Agrilus planipennis (emerald ash borer) and one study each of Lymantria dispar (spongy moth), and Ips pini (North American pine engraver). Studies also addressed earthworms, ants, rats, and feral hogs. Microorganisms included Cronartium ribicoli (white pine blister rust) and several Phytophthora species, including P. agathidicida (kauri dieback), P. alni (affects alders), and P. ramorum (sudden oak death).

Thakur et al. note the skewed taxonomic coverage and say that the low number and narrow taxonomic/ecological variety in the animals and microorganisms probably limit their ability to reach robust conclusions about the impacts of such invasions.

The most consistent negative impact they found is reductions in native plant diversity. While this is not surprising given the studies analyzed, I think it is still important since it counters the widespread sense that plant invasions are somehow less deserving of a robust response.

The authors also detected some broader ecosystem impacts of plant invasions. Plant invasions increased soil organic carbon; soil nitrogen (ammonium and nitrate), and available phosphorus; soil moisture, litter biomass; and emissions of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). The changes in biogeochemical properties might reinforce impacts on native plant communities. The reported increase in greenhouse gas emissions might reflect a bias in the studies so Thakur et al. call for more research to solidify this finding.

High native plant species richness had only a weak overall effect on ecosystem-level impacts. While plant invasions often resulted in higher overall plant species richness, when considering only native community responses, the gain in species numbers did not necessarily indicate conservation benefits. Native plants’ biomass increased after invasion. This might reflect short-term increases in productivity in response to altered resource conditions or structural facilitation, rather than a long-term reversal of competitive exclusion. Finally, the longer the invasive [plant] species had been present, the greater the negative effects on native diversity. However, soil abiotic property impacts weakened over time. In fact, the initial increase in soil organic carbon and total nitrogen disappeared after 6 to 10 years. This development might reflect fertilization of ecosystems by long-established nitrogen-fixing invaders such as non-native legumes.

Traits of non-native plant species related to growth and resource acquisition were overall weak predictors of ecosystem impacts. Thakur et al. consider that this finding reflects the relatively narrow range of specific leaf area exhibited by the plant species studied most commonly.

Consequently, Thakur et al. urge managers to focus on containment and impact mitigation, and to prioritize persistent losses of native plant diversity. When considering abiotic responses that might lessen over time, managers should apply “adaptive monitoring” (which is not defined).

Thakur et al. had greater difficulty determining the impacts of animal and microorganism invasions because of the smaller number of studies. They could not determine the effect of native species richness. The observed decline in soil organic carbon they thought was attributable to the large proportion of studies (9 out of 114) that focused on introduced earthworms. Earthworms reduce organic matter by consuming litter. Mammals were also found to reduce soil organic carbon. Introduced insects had no significant ecosystem effects on soil organic carbon. Non-native animals also increased soil emissions of carbon dioxide and nitrous oxide. The microorganisms included in reviewed studies decreased soil ammonium and increased nitrate, consistent with elevated nitrification. While data on body size of invasive animals were sparse, the authors could determine that larger-bodied species tended to increase soil nitrate while reducing effects on total soil N.

Applying the Results

Thakur et al. report that residence time outperformed other factors as a predictor of invasion impacts. The authors regret the scarcity of long-term studies, especially in the Global South, that could increase our understanding of whether these impacts persist or shift under sustained invasion pressure.

How can scientists apply this information in risk assessments evaluating not-yet introduced species or in deciding what is the appropriate intensity of immediate response to newly detected incursions. Should they give greater weight to others’ studies that focus on long-established invasions by the species in question? Otherwise, this finding seems to largely duplicate the long-established “invasion curve”.

I hope scientists will note that observational studies generally showed stronger impacts than experimental ones, particularly in the case of plant invasions. Perhaps this is true because observational studies better incorporate environmental heterogeneity and longer time spans.

Agrostis stolonifera – one of the plants invading on Prince Edward Island, an Antarctic region island under South African jurisdiction. Photo by Stefan Iefnaer via Wikimedia

Thakur et al. note that one factor they analyzed, “latitude”, incorporates several ecological and anthropogenic components relevant to invasion impacts. One element is the greater native bioidiversity in warmer, lower-latitude, regions. According to the “biotic resistance” hypothesis, greater diversity might make these systems more resistant to bioinvasion. However, the situation is complicated by the fact that temperate regions have also often experienced longstanding and intensive land-use modifications — which are believed to facilitate invasive species establishment and spread. I regret that the authors make no attempt to separate the effects of factors that are anthropogenic from those arising from immutable conditions, e.g., latitude, topography, weather patterns, etc.

Thakur et al. call for more studies that cover a wider geographic range. In addition, the studies should include more experimental designs and explore the relationship between invaders’ traits and impacts — especially regarding animals and microbes.

SOURCE

Thakur, M.P., Z. Gu, M. van Kleunen, X. Zhou. 2025.  Invasion impacts in terrestrial ecosystems: Global patterns and predictors. Science 23 October 2025

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

Status of Hawaiian species threatened by bioinvasion

stand of Miconia under albizia overstory on Big Island, Hawai`i; photo by F.T. Campbell

As I will describe in another blog, participants in the annual meeting of the National Plant Board link in Honolulu learned the basics about the uniqueness of agriculture and native species on remote Pacific islands. I want to complement this information by reminding you about other Hawaiian and Guamaian species at risk – although did not learn anything new.

As Martin and Andreozzi pointed out, the Pacific islands import nearly all their food and other consumables. Considerable interest in some quarters in Hawai`i to increase agricultural production. However, large swaths of land in the low-elevation area surrounding Pahoa on the Big Island is completely dominated by the albizia (Falcataria Molucca) [see photo above]. J.B. Friday says it is cost-prohibitive to remove these trees in order to restore agriculture in the area. Local people are concerned because in storms the trees fall onto houses and roads, causing considerable damage.

I saw numerous clumps of the notorious invasive plant Miconia calvescens. Dr. Friday told me that conservationists now focus on keeping this plant out of key areas, not trying to eradicate it completely.

area being restored by volunteers; photo by F.T. Campbell

Local people trying to restore disease-damaged forests by planting other native plants and hand-clearing invasive plants. Some of the ohia seedlings infected by Austropuccinia psidii.

ohia seedling with symptoms of ohia rust (Austropuccinia psdii); detected by J.B. Friday; photo by F.T. Campbell

Dr. Friday showed me many areas where ʻōhiʻa trees have been killed by rapid ʻōhiʻa death. Since this mortality occurred a decade or more ago, other plants have grown up. Pic  In many if not most cases, this jungle includes dense growths of guava Latin the most widespread invasive tree on the islands (Potter). ‘Ōhi‘a trees continue to thrive in Hawai`i Volcanoes National Park – also on the Big Island – because the NPS makes considerable efforts to protect them from wounding by feral pigs. Demonstrates importance of fencing and mammal eradication in efforts to protect this tree species.

healthy ʻōhiʻa tree on cinder cone created by eruption of Kilauea Iki in 1959; photo by F.T. Campbell

I also saw healthy koa (Acacia koa) in the park, especially at sites along the road to the trail climbing Mauna Loa.

Regarding the wiliwili tree, I was told that it remains extremely scarce on Oahu.

wiliwili tree in flower; photo by Forrest Starr

I heard nothing about the status of naio – another shrub native to the Big Island – but on the dry western side of the island.

I rejoice that scientists are making progress in protecting and restoring Hawaii’s endemic bird species. Specifically, they are at the early stages of controlling mosquitoes that transmit fatal diseases. All 17 species of endemic honeycreepers that have persisted through the 250 years since Europeans first landed on the Islands are now listed as endangered or threatened under the federal Endangered Spp Act. The “Birds, not Mosquitoes” project has developed lab-reared male mosquitoes that, when they mate with wild female, the resulting eggs are sterile. (Male mosquitoes don’t bite, so increasing their number does not affect either animals or people.) Over time, the invasive mosquito population will be reduced, giving vulnerable native bird populations the chance to recover. Scientists began releasing these modified mosquitoes in remote forests on Maui and Kaua‘i in November 2023. In spring 2025, they began testing releases using drones. Use of drones instead of helicopters reduces the danger associated with flying close to complicated mountain rides in regions with variable weather.   This project should be able to continue; the Senate Appropriations Committee report for FY26 allocates $5,250,000 for this project.

American Bird Conservancy is sponsoring a webinar about this program. It will be Wednesday, August 27, 2025 4:00 PM – 5:00 PM ET. Sign up for the webinar here

thicket of guava on the Big Island, Hawai`i; photo by F.T. Campbell

Finally, scientists are releasing a biocontrol agent targetting strawberry guava, Psidium cattleyanum, the most widespread invasive tree on the Islands (Potter et al. 2023). Distribution involves an interesting process. A stand of guava is cut down to stimulate rapid growth. The leaf-galling insect Tectococcus ovatus reproduces prolifically on the new foliage. Twigs bearing the eggs of these insects are collected and tied into small bundles. The bundles are then dropped from helicopters into the canopies of dense guava stands, where they establish and feed – damaging the unwanted host.  

brown tree snake; photo via Wikimedia

Guam

Guam’s endemic birds have famously been extinguished by the non-native brown tree snake. Dr. Aaron Collins, State Director, Guam and Western Pacific, USDA APHIS Wildlife Services, informed participants at the National Plant Board meeting about the extensive efforts to suppress snake populations in military housing on the island, reduce damage to the electric grid, and prevent snakes from hitchhiking to other environments, especially Hawai`i and the U.S. mainland.

The program began more than 30 years ago, in 1993. The program now employs 80 FTEs and has a budget of $4 million per year. It was initiated because live and dead snakes had been found in shipments and planes that landed in Hawai`i and the U.S. mainland. Avoiding the snake’s establishment on Hawai`i is estimated to save $500 million per year. The program is a coordinated effort by USDA, U.S. Fish and Wildlife Service, and the Department of Defense. Probably this estimate helped advocates reverse a decision by the “Department of Government Efficiency” to defund the program.

The program enjoys some advantages over vertebrate eradication programs on the mainland. For example, since Guam has no native snakes, it can use poison, e.g., in mouse-baited traps that can be dropped from planes. A recent innovation is auto-resetting traps baited with mammals; they can electrocute numerous snakes per night.

SOURCE

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. Lands. Ecol. https://doi.org/10.1007/s10980-023-01662-6

Posted by Faith Campbell

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

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

Or

https://fadingforests.org