Southern Hemisphere forests: unique biomes face high invasion risk

native *Olia woodiana* in forest of Kwa-Zulu-Natal, South Africa. Photo by MJK via Wikimedia

The forests of the Southern Hemisphere faces an elevated risk from introductions of tree-killing arthropods and pathogens. I have already blogged about individual threats to the trees of South Africa, Australia, South America, and Madagascar. This blog will add information about those invasions and provide an overview and call for action.

Burgess and Winfield (2026) [full citation at the end of this blog] – eminent pathologists from South Africa – warn their colleagues that the economic and biological barriers that have long protected the biomes of the Southern Hemisphere from bioinvasion have now collapsed. While these countries remain geographically distant from each other and the Northern Hemisphere, and their floras are certainly still unique, they are now participating in global trade. In addition, they increasingly rely on industrial plantation forestry dominated by non-native tree species – some of them from the North. Finally, climate change is putting additional stress on all these systems.

Burgess and Winfield (2026) advise their colleagues to learn lessons from the alarming history of bioinvasion in the Northern Hemisphere. Over the past century, these forests have been battered by a series of invasions by tree-killing pathogens. They mention the examples we know too well: chestnut blight (Cryphonectria parasitica), white pine blister rust (Cronartium ribicola), “Dutch” elm disease (Ophiostoma ulmi/Ophiostoma novo-ulmi), pine wilt nematode (Bursaphelenchus xylophilus), sudden oak death (Phytophthora ramorum), ash decline (Hymenoscyphus fraxineus), laurel wilt (Harringtonia lauricolia), ʻōhiʻa or myrtle rust (Austropuccinia psidii), https://www.dontmovefirewood.org/pest_pathogen/ohia-rust-html/ and rapid ʻōhiʻa death (Ceratocycstis lukobia and huliohula). They do not address the similarly depressing history of arthropod interchanges among these realms.

Burgess and Winfield (2026) warn that these invasions are not anomalies but rather predictable outcomes of global commerce – especially in “plants for planting” – interacting with the ecological vulnerability arising from the biogeographic similarity of these temperate and boreal forests. The Northern Hemisphere is dominated by a single flora (the Holarctic).

The Southern Hemisphere has an astounding seven floral kingdoms, distributed as follows: Chile-Patagonian, Neotropical, African, Indo-Malesian, Australian, Novozealandic, and Cape. These regions were formerly part of Gondwanaland. Each has an exceptionally high level of endemism (Burgess and Wingfield 2026), but with phylogenic relationships to the flora of other regions. Changing trade patterns are opening introductory pathways for exchange of tree pests hosted by related but geographically distant species. The regional floras’ uniqueness multiplies the conservation importance of protecting them. I summarize Southern Hemisphere countries’ levels of endemism at the end of this blog.

The lessons Burgess and Wingfield (2026) draw from the bioinvasion history of the Northern Hemsphere include:

1) Trade in living plants – and even seeds – creates a high risk that accompanying microbes will be introduced. As noted by others – e.g., Tanney et al. (2025) – members of each plant species’ “phytobiome” are ubiquitous, diverse, difficult to detect, and sometimes capable of causing serious diseases, especially in naïve hosts.

2) After introduction, these microbes can evolve rapidly to adapt to new environments or hosts. They often become more aggressive and difficult to manage in the process. Plant health officials need to anticipate this evolution.

3) Impacts can be catastrophic when a dominant tree species is killed. When chestnut blight killed the vast majority of chestnut trees in North America it destabilized ecosystems and reshaped successional trajectories.

4) The threat is magnified when the receiving ecosystem is a forestry plantation because of the extensive monocultures.

Building on Burgess and Wingfield (2026) and other sources (where noted), I provide the following summary of threats to native and planted forests in these regions. Some, e.g., Phytophthora cinnamomi and Sirex noctilio, were introduced many decades ago. But too many are recent arrivals.

I. Threats to tree species native to the region.

1) Australia

trees killed by *Phytophthora cinnamomi*; photo by Western Australia Parks & Wildlife

Carnegie et al. (2026) report that more 300 non-native insect pests, pathogens and nematodes are established on tree or shrub hosts in Australia. Twenty percent have caused moderate to high impacts to commercial plantations, urban forests, or trees in natural ecosystems.

Phytophthora cinnamomi: As noted, this pathogen was introduced decades ago. It has devastated jarrah (Eucalyptus marginata) forests and diverse plant communities. It causes severe mortality in Proteaceae, Epacridaceae, and Fabaceae. Of ~5700 described plant species in the state of Western Australia, 40% ( >2,300) can be killed (Carnegie et al. 2026).

Austropuccinia psidii (myrtle rust): threatens trees in the Myrtaceae worldwide. The rust has spread widely recently, causing severe ecological impacts in invaded regions. The “epidemic strain” introduced to Australia (and other regions) does not infect the commercially important genus Eucalyptus, which probably explains Australian authorities’ lackluster response. However, other lineages of the pathogen found in South America do infect Eucalyptus; introduction of one of these to Australia could be disastrous. Cautionary example of how rapidly a plant pathogen can conquer new ecosystems (Burgess and Wingfield 2026). Already, plant 76 species have been determined to be at risk to myrtle rust. The early focus has been on understory species in the eastern rainforests. Now that myrtle rust has been detected in Western Australia, a biodiversity hotspot with more than a thousand Myrtaceae taxa, most of which are expected to be susceptible. [Summary of Proceedings: Australian Myrtle Rust Conference Sydney, June 2023]

Polyphagous shot hole borer Euwallacea fornicatus s.s. (PSHB) and associated pathogen F. euwallacea were detected in 2021, probably three years after it established in Western Australia. Nearly 9% of hosts are regionally indigenous species, 21.3% native to other parts of the continent. There will probably be a considerable impact on the health of conservation reserves & national parks in the future. After trying for four years to eradicate the population, in November 2025, the National Management Group began a transition to a Management Response Plan. This new approach will impose significant additional expenses on local governments and communities for tree removal and replacement (Dell, Xu, & Chi 2026). Meanwhile, the state of New South Wales (2,000 miles away on the other side of the continent) initiated surveillance for PSHB. An assessment determined that 47% of urban trees in Sydney are susceptible to PSHB (Carnegie et al. 2026).

Erythina gall wasp Quadrastichus erythrinae (Carnegie and Nahrung 2019). Although Australia is home to at least one native species in the Erythrina genus, E. vespertilio, this pest has not been included on the environmental pest watch list.

2) New Zealand

native forest on North Island, New Zealand, with kauri tree; photo by F.T. Campbell

Kauri dieback / Phytophthora agathidicida is killing Agathis australis, a keystone species that shapes forest structure and has enormous cultural importance for the Maori.

3) South Africa

Phytophthora cinnamomi — in the country since 1931 — threatens ecosystem collapse in Cape Floral Kingdom (Burgess and Wingfield 2026).

Polyphagous shot hole borer Euwallacea fornicatus s.s. and associated pathogen F. euwallacea The largest outbreak of Fusasrium disease in the world: it is present in every province except Limpopo. The Disease is recorded on 162 tree species. Seventy-eight of these species are indigenous to the country. Eighty-four are “competent” hosts and 78 are “Fusarium colonised” hosts (Townsend, Hill, Hurley and Roets 2025).

Fungus Seiridium neocupressi detected on the native tree, Widdringtonia nodiflora year The two other species in the genus, W. wallichii and W. schwartzii, occur in small endemic and threatened populations (Wingfield et al. 2022).

4) Madagascar

Leptographium calophylli killing an endemic tree species in mid-level elevation humid and subhumid forests, Calophyllum paniculatum.

5) South America

Polyphagous shot hole borer Euwallacea fornicatus s.s. and associated pathogen F. euwallacea has been detected in Brazil, Argentina, and Uruguay. Dell, Xu, & Chi (2026) report that in Uruguay a significant number of native species are reproductive hosts for the beetle. Models developed by Coates and Philips (2026) indicate PSHB could thrive in more suitable habitats.

One of the continent’s native conifers, Austrocedrus chilensis is under attack by both an introduced aphid, Cinara cupressi and the pathogen Phytophthora austrocedri

Chilean cypress; photo by LBM via Wikipedia

Lantschner et al. (2026) identified seven independent introduction events of E. fornicatus: to the continental U.S., Hawai`i, South America, Central Europe, Spain, Türkiye, & South Africa.

II. Threats to plantations:

1) Co-evolved insects and pathogens have followed their Pinus hosts to plantations in the Southern Hemisphere due to biosecurity failures

Insects: Sirex noctilio (decades ago); recently Sirex obesus in Brazil (2023); Orthotomicus erosus and Cyrtogenius luteus (Stazione, Soliani, and Cognato 2026).
Pathogens: Fusarium circinatum, Dothistroma septosporum, Diplodia sapinea, Phytophthora pinifolia, Lecanosticta acicula.

2) Because the Myrtaceae family is distributed around the Southern Hemisphere, plantations of Eucalyptus trees are now being damaged by both pathogens from their native Australian range (Teratosphaeria spp.) and local pathogens that have switched hosts (Chrysoporthe cubensis and Chrysoporthe deuterocubensis).

Burgess and Wingfield (2026) express fear that another set of pathogens, rapid ohia death (Ceratocystis lukuohia and Ceratocystis huliohia) might spread from Hawai`i farther across Oceania to New Zealand and other locations with important species in the Metrosideros genus. I note that the more virulent (on ʻōhiʻa) C. lukuohia belongs to an Asian-Australian clade (Luiz et al. 2023).

Australia

I blogged in November 2022 about how surprising tardy Australia was in implementing phytosanitary programs to protect the nation’s forests. Scientists had spent 30 years trying to get such a program implemented. Burgess and Wingfield (2026) point out that 16 of 17 pathogens detected in Australia over the period 1996 – 2017 had established; several had had major impacts. None has been eradicated. They also note that the introduction of Austropuccinia psidii exposed significant weaknesses in post-border surveillance and response.

The Australian federal govt has implemented a detection trapping program targeting the Asian spongy moth (= flighted spongy moth complex) at the 4 major ports (i.e., Melbourne, Hastings, Geelong and Portland) since 1996.

Carnegie et al. (2026) describe some helpful steps. They focus on establishment in 2022 of a National Forest Pest Surveillance Program (now called Forest Watch Australia). The program is funded by a levy on forest plantation growers and State governments, based on the relative risk to each region. Surveillance efforts are concentrated in areas deemed high risk areas for entry and establishment of forest pests. Program is coordinated through the federal agency, Plant Health Australia. It provides professional training for surveillance and diagnostic staff on an annual basis. Staff also conduct risk modelling and analysis to identify high-risk areas for surveillance in all major capital cities — Sydney, Melbourne, Brisbane, Hobart, Adelaide, Perth and Darwin.

The Australian program encounters the universal challenges regarding sustained resources, the diagnostic burden placed on scientists, and ownership of data. Carnegie et al. (2026) and Burgess and Wingfield (2026) discuss the growing availability of new tools for detection, e.g., molecular diagnostic tools.

Response options are guided by the national Emergency Plant Pest Response Deed and PlantPlan, which outlines agreed government and industry responsibilities and cost-sharing protocols.

Carnegie et al. (2026) praise especially the sentinel tree component of the surveillance program. Participants include governments at the federal, state, and municipal levels; botanical gardens; and industry. In 2024/25, trained staff inspected 5,136 trees of more than 50 species across 45 genera nationwide. Thanks to this expanded effort, the detection rate of new species has doubled since 2018, from ~ 1.5 to ~ 3 / year. Still, in three of four cases discussed by Carnegie et al. (2026), the introduced organisms were determined to be too widespread for eradication to be successful. They cite the PSHB outbreak in Perth as an example. Carnegie et al. (2026) advocate strengthening sentinel tree surveillance in urban landscapes so detection will occur sufficiently early to allow consideration of initiating an eradication or containment response. One worrisome aspect: there is no requirement to conduct more thorough surveillance or diagnostics on a species detected in the country once it has been ruled not “of concern”.

Burgess and Wingfield (2026) advocate embracing broader preventative approaches that address the underlying mechanisms of pathogen emergence and spread. I forthcoming blog will discuss proposed new approaches.

Background: Southern Hemisphere Flora

South Africa

As I blogged recently, South Africa’s flora is diverse (more than 20,000 indigenous species) and has high levels of endemism. That blog did not discuss the Myrtaceae family – my focus now because of the spread of the pathogen Austropuccinia psidii. According to Braam van Wyk and Hugh Glen (pers. comm.), the country has 24 native Myrtaceous species. These include 14 species in the Eugenia genus, six in the Syzygium genus. The one Metrosideros grows in the Cape Floristic Region. All the others occur in forest or grassland along the Indian Ocean Coastline well into Mozambique and further inland – some into Botswana and Zimbabwe.

Australia

Australia ranks second on Earth in the proportion of its flora that is endemic: 88% of plants. Australia comprises the native range of 38% of all Myrtaceae species on Earth, and of 66% of genera in the family (Brett Summerell, 2023 workshop). These 87 or 88 genera contain ~ 2,250 species and subspecies (Makinson 2018). This plant family constitutes ~10% of the continent’s native flora. They occur in 11 of 13 major vegetation formations (Carnegie et al.2026). The southwestern corner of Western Australia alone has ~5700 described plant species (Carnegie et al 2026).

The island of Madagascar is home to 12,000 plant species, of which 83% are endemic.

SOURCES

Burgess T.K., and M.J. Wingfield. 2026. Unveiling a Hidden Menace: Invasive Tree Pathogens, Less Known but Increasingly Threatening Southern Hemisphere Forests Annual Review of Phytopathology #s

Carnegie AJ, Summerell BA, Trollip C, Tovar F, Smith DI and McDonald J (2026) Sentinel trees for early detection of non-native forest pests and pathogens in AU. Front. For. Glob. Change 9:1801183. doi: 10.3389/ffgc.2026.1801183

Ceriani-Nakamurakare, E., Johnson, A.J. and Gomez, D.F. (2023) Uncharted Territories: First report of Euwallacea fornicatus (Eichhoff) in South America with new reproductive hosts records. Zootaxa, 5325 (2), 289–297. https://doi.org/10.11646/zootaxa.5325.2.10

Lantschner, M.V., Ceriani-Nakamurakare, E., Johnson, A.J. et al. Invasion history reconstruction and potential distribution of the ambrosia beetles Euwallacea fornicatus and E. perbrevis, two global emerging pests. J Pest Sci 99, 100 (2026). https://doi.org/10.1007/s10340-026-02070-w

Luiz, B.C., C.P. Giardina, L.M. Keith, D.F. Jacobs, R.A. Sniezko, M.A. Hughes, J.B. Friday, P. Cannon, R. Hauff, K. Francisco, M.M. Chau, N. Dudley, A. Yeh, G. Asner, R.E. Martin, R. Perroy, B.J. Tucker, A. Evangelista, V. Fernandez, C. Martins-Keli’iho.omalu, K. Santos, R. Ohara. 2023. A framework for establishlishing a rapid ‘Ohi‘a death resistance program New Forests 54, 637–660. https://doi.org/10.1007/s11056-021-09896-5

Stazione, L., Soliani, C., Cognato, A. et al. Reconstructing the invasion history of the bark beetles Orthotomicus erosus and Cyrtogenius luteus (Coleoptera, Curculionidae, Scolytinae) in South America. Biol Invasions 28, 49 (2026). https://doi.org/10.1007/s10530-026-03779-6

Tanney, J.B., M. Kemler, M. Vivas, M.J. Wingfield, and B. Slippers. 2025. Silent invaders: the hidden threat of asymptomatic phytobiomes to forest security. New Phytologist (2025) 247: 533–545 doi: 10.1111/nph.70209

Wingfield, M.J. S. Marincowitz, N.Q. Pham, F. Roets, T. Paap, B.D. Wingfield, J. Aylward. 2022. Cypress canker: An important disease discovered for the first time on a native South African tree. Plant Pathology 2022;71:1735-1742

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

https://fadingforests.org

Tree regeneration update

sycamores overcome by invasive vines, primarily porecelain berry; photo by F.T. Campbell

18 months ago I blogged about the impacts of invasive plant species and deer on regeneration of tree species. I provide more information on some National Park units’ efforts to counter these threats – contemporaneous with release of the report.

Emma Brentjens has posted a report with pictures. She focuses on National parks in the National Capital Region (NCR). These are the National parks in Maryland, Virginia, and a small part of West Virginia, including Catoctin Mountain Park; Antietam, Manassas, and Monocacy National battlefields; Harpers Ferry and Chesapeake & Ohio National Historical parks; Rock Creek Park; some parkways; and some urban parks, e.g. Anacostia and East Potomac. Forests constitute three-quarters of the landcover in National parks of this region. Regional NPS staff noted poor regeneration as early as 2006. In the years since, most have ramped up IAS plant management, & begun deer population management. As result, the previously steady regeneration declines have begun to reverse.

They analyze forest vegetation data using the Stocking Index, which calculates seedling density per hectare. “Acceptable” forest regeneration is defined as 67% of plots being adequately stocked. Unfortunately – from my perspective – the program accepts non-native tree species as successful regeneration.

Comparing the parks’ Stocking Index in 2006-2009 to 2020-2024 showed that most of these parks have seen an increase in the Stocking Index, including most sites managing deer populations. Still, no parks have yet achieved adequate stocking for more than 30% of the plot.

Most parks that are managing their deer populations show growth in seedling density, e.g., Catoctin Mountain Park (illustrated in the report); Harpers Ferry National Historical Park; and Monocacy National Battlefield. In Rock Creek Park, which also manages deer, many seedlings have grown into saplings.

deer in Shenandoah National Park; photo by F.T. Campbell

Most of the sites with declines in seedling density have not implemented deer management. These include several segments of Chesapeake & Ohio Canal National Historical Park and the parkways. Unfortunately, it also includes Prince William Forest Park, which at 15,000 acres is the largest protected area near Washington, D.C.

Brentjens notes that while these early results are promising, seedling levels are highly variable and do not guarantee forest regeneration. Continued management is necessary to sustain improvements.

As part of deer management, the NP units are also monitoring spread of chronic wasting disease (CWD) among white-tailed deer. Current CWD rates are very low (< 1%). The disease has been confirmed at four parks in the region: Antietam, Manassas, and Monocacy National battlefields and Harpers Ferry National Historical Park.

(Chronic wasting disease is not an effect too to reduce deer populations. First, is relying on such suffering an ethical approach? Second, significant declines in deer populations are not observed until infection rates reach about 29% of the population. Parks in the National Capital Region are not expected to reach that level for at least 20 years.

Posted by Faith Campbell

https://fadingforests.org

Protecting forests’ ecosystem values: minimize disturbance & curtail nearby planting of non-native species

old-growth forest in Tioresta Research Natural Area, Allegheny National Forest (Pennsylvania); photo by Nicholas T via Flickr

The implied or explicit recommendations are not new. But they are supported by new data!

Several measures of forest health drawn from survey plots of the Forest Inventory and Analysis (FIA) show that federally-owned forested lands – in both National forests and National parks – are healthier than neighboring forests under different ownership. Forest inventory plots in federal forests have significantly greater tree species and structural diversity and evenness; basal area and biomass per hectare; and seedling density. They are also less invaded by non-native plants. These findings hold across the continental United States, four regions (North, South, Rocky Mountains, and Pacific Coast) analyzed separately, and 22 common forest types.

The consistent finding of more “mature forest” features in eastern National parks and National forests – regardless of longer-term land-use histories (Potter et al. 2026b) – seems to me to indicate that recent and current management practices might overcome influences of centuries of pre-protection land use histories of exploitation and degradation.

1. Forest Health Inside vs. Outside Federal Forested Lands

Legally designated USFS National forests comprise ~19% of the Nation’s total forest area (~59 million out of 310 million hectares). Since adoption of the Forest and Rangeland Renewable Resources Act of 1974, the National Forest System (NFS) within USDA has been managed to maintain “appropriate forest cover . . . to secure the maximum benefits of multiple use sustained yield management in accordance with land management plans”. The Department of Interior’s National Park Service units are managed to conserve unimpaired the natural and cultural resources and values in the system for the enjoyment, education, and inspiration of this and future generations (National Park Service “Organic Act” of 1916).

Potter et al. 2026b assessed the ability of National forests to provide ecosystem services and forest products in the face of dramatically increasing threats: (1) more intense and frequent wildfires; (2) uncharacteristically long and hot drought conditions; (3) mortality and compositional changes caused by invasive forest pests; (4) competition from invasive plant species; and (5) forest fragmentation and conversion to other land uses. To do this, they asked whether National forests (1) have greater biodiversity – as measured by species and structural diversity; (2) are denser and encompass more biomass; (3) experience more regeneration; and (4) are less invaded by non-native plants. The FIA surveys were carried out from ~2010 to ~2022. As noted, they analyzed each comparison across the conterminous states, the four regions, and the 22 forest types.

Potter et al. (2026b) and an earlier study by Miller et al. (2016) agree that ownership determines forest management, specifically the level of anthropogenic disturbance allowed. Miller et al. demonstrated that, in the eastern United States, forests in National parks have greater live tree basal area, a larger volume of coarse woody debris, and greater proportions of late-successional tree species than nearby forests. They also have lower rates of tree growth and mortality.

Potter et al. (2026b) found that all biodiversity indicators except number of saplings per hectare were higher for plots inside the NFS than neighboring forests under other ownerships. This was true across the continent and in all four regions.

In some of the 22 forest types the indicators were particularly strong. Thus, basal area was notably higher on NFS forests populated by loblolly/shortleaf pine, Western larch, hemlock/Sitka spruce, maple/beech/birch, and oak/hickory forest types. Tree species richness was significantly higher on NFS plots for Western larch, elm/ash/cottonwood, longleaf/slash pine, pinyon/juniper, and loblolly/shortleaf pine. Differences in regeneration were seen most prominently in loblolly/shortleaf pine, oak/hickory, oak/pine, and white/red/jack pine. The authors do not speculate on the reasons.

a large loblolly pine in Congaree National Park; via Picaryl

The FIA data showed that invasive plant richness and cover were both greater on plots outside National forests across the Continent and in all four regions. However, invasive plant richness did not differ by ownership for some specific forest types: elm/ash/cottonwood, pinyon/juniper, Western larch, and hardwood woodlands. (National parks are even less invaded by non-native plants than National forests; see below.)

2. Regions Differ – Why?

Geographic regions differed noticeably. Tree species richness and evenness; diversity and evenness of tree height classes; biomass/ha; seedlings and saplings per hectare; and invasive plant diversity and cover were higher in the East – in both USFS Northern and Southern regions. Tree species richness was by far highest in the South – especially in the southern Appalachians and on the Cumberland Plateau. Seedling density was highest in the North, moderately high in the South. In the North, tree species and tree height evenness were both higher on non-federal lands.

Invasive plant richness was highest in some parts of the South. [See a more detailed discussion of invasive plants below.] Tree diameter class diversity and evenness were significantly higher in the West. Basal area was by far the highest in the northern part of the Pacific coast region (Washington, Oregon, and California.). Seedling density was moderately high in some National forests in the Rocky Mountains. Tree diameter evenness was higher outside National forests in the Rocky Mountains.

These differences had been expected given the marked regional dissimilarities in floristic, climatic, and edaphic factors, as well as ownership patterns.

Potter et al. (2026b) report that tree recruitment was stronger in the East than the Rocky Mountain and Pacific coast regions. I wish they had discussed how this finding relates to earlier findings (Potter and Riitters 2022) that numbers of species experiencing poor regeneration were highest in the Southeast, followed by the Northeast and Midwest. Miller et al. (2023) also found that tree regeneration was poor in National parks from Virginia to Maine. The latter study attributed this failure to a combination of browsing by overabundant deer and competition by invasive plants. The latter is presumably even more important in national forests, which are invaded by non-native plants at twice the rate of national parks. Nonfederal forests are invaded at even higher rates – up to 3 times greater. [See here for a study of improve regeneration in National parks which control their deer populations.]

Potter et al. (2026b) note that the higher forest health indicator values for NFS forests prevailed across the Continent despite notable differences in land-use and management histories and landscape contexts. Most NFS land in the West was put under federal management before arrival of European pioneers, so more of their groves are classified as old-growth or mature. In the East, nearly all lands incorporated into the National Forest System were privately owned until they were purchased in the 20^th Century. At that time these forests were often highly degraded. Not only did the eastern National forests have to recover from overexploitation; they are still typically embedded in a matrix of other land ownerships, often largely cleared of trees.

In their analysis, Potter et al. (2026b) controlled for differences in site productivity and some environmental conditions e.g., elevation and slope, but not soil or hydrological conditions. So they believe that the suite of environmental factors do not explain the “older” attributes of eastern forests managed by the USDA Forest Service and USDI National Park Service,. These attributes generally include a more complex forest structure; higher tree species richness; and greater basal area and density of live trees (Miller et al. 2016).

What differs is management. Miller et al. (2016) say explicitly that protection from forest harvesting for many decades probably is an important explanation of why forests in the eastern National parks have greater tree species diversity than forests owned by other parties. Potter et al. (2026b) instead emphasize the impacts of different land-use histories outside of National forest boundaries. Much of this land (especially in the East) has experienced continuous, centuries-long agriculture and residential development and more acute disturbance pressures associated with higher human population density. They also note that managers of non-federal forests goals often call for harvests or other active management – which can reduce forest structure, species richness, size of live trees, presence of downed woody debris, etc.

I note that the consistent finding of more “mature forest” features in eastern National parks and National forests – regardless of longer-term land-use histories (Potter et al. 2026b) – indicates that recent and current management practices might overcome older influences. Many of these forests have enjoyed protective management for less than a century; the Forest and Rangeland Renewable Resources Act of 1974 was adopted just 50 years ago. I assert that the decisive factor might be the much lower presence – although not absence! – of deliberately planted non-native plant species on federal properties. [Again, see a more detailed discussion of invasive plant issues below.]

Potter et al. (2026b) also comment that regeneration on NFS land is almost exclusively natural. As discussed above, they consider this regeneration to be successful, in that seedlings generally are being produced in greater numbers than on surrounding forests in other ownerships. Again, I would like to learn how this finding relates to the earlier study by Potter and Riitters (2022).

Potter et al. (2026b) state that National forests benefit from their greater size and stability of management goals. These are necessary for large-scale approach to conserve or imitate the processes that create diversity

As Potter et al. (2026b) note, in the East, reserved areas like National forests (or to a greater extent, National parks) represent a small proportion of the landscape. Their distinctness from neighboring forestlands emphasizes their ecological value. They call for managers to be alert to potential invasions of non-native plants or tree-killing pests from the surrounding agricultural and developed land. In the West, private forests abut federal forested lands less often and thus have less influence on the status of forest health indicators on National forests.

3. Plant Invasions in Forests

Several studies by Kevin Potter, Kurt H. Riitters and colleagues have documented the extent of plant invasions in America’s forests. Data supporting these studies come from the same forest plot surveys conducted under the Forest Inventory and Analysis (FIA) program.

The region most invaded is Hawai`i: 83% of FIA plots have one or more invasive plant species. The region that ranks second is the East, specifically the 37 states comprising the USDA Forest Service’s former Northern and Southern regions. Nearly 53% of FIA plots in this region have one or more invasive plant species (Potter et al. 2024). FIA plots in the Rocky Mountain West had only 11% (Potter et al. 2026a).

student volunteers in Camp S.E.E.D. (Students Encouraging Environmental Recovery) program pulling invasive plants in Shenandoah National Park; via Picaryl

As noted above, invasive plants are particularly problematic in the South. There, invasive plants have been documented on 55.3 million hectares. In the Northern Region, an incomplete survey found invasive plants on 36.9 million ha. In some counties of the 37 states, 80% of inventoried forest plots contain invasive plants. Spread of these invaders is largely unchecked. The invasions’ extent and intensity are so great that their complete removal – or elimination of their impacts – is “practically impossible” (Potter et al., 2024; Potter et al. 2026a).

Plant invasions in eastern forests are undoubtedly worse than these data indicate because the records include only some of the non-native plant species present — those considered to be the worst invaders at the time regional lists were compiled (Potter et al. 2026a). Not included on the survey list are wavy-leaf basketgrass (Oplismenus undulatifolius), fig buttercup (Ficaria verna), shrub and creeping Euonymus, callery pear (Pyrus calleryana). Only one privet (Ligustrum vulgare) is included.

Furthermore, Bradley, Early and Sorte (2015) report that while non-native plant species are already more widely distributed than native species, the average invasive plant species inhabits only about 50% of its expected range.

Sites Most Heavily Invaded

Analyses of the FIA data reveal several overlapping definitions of which locations and situations have been invaded most severely. These factors are separate from the issue of ownership discussed above. Invasive plants are more numerous, widespread, and diverse in more disturbed or fragmented sites. One study found that 65% of plots that experienced greater fragmentation were invaded compared to 46% of plots that experienced low fragmentation. Invasion rates are highest in the “wildland-urban interface” (WUI). Unfortunately, the WUI is growing faster than any other land use type in the country – especially in the East (Potter et al. 2024). Because the East is so heavily developed, a plot’s distance from a road was nearly irrelevant. Furthermore, development in the WUI also promotes planting of non-native species that might then invade the nearby forest. See my more detailed discussion of these issues here.

Highly productive sites [defined as a site’s ability to grow industrial timber; Potter et al. 2026b] are also prone to invasion: 76% of highly productive plots were invaded compared to 40% of low-productivity plots. It is not known whether highly productive sites are inherently more invasible, or, instead, that such plots were converted to agriculture earlier, so exposed to human disturbance longer (Riitters et al. 2017).

A third analysis found that the best predictor of the odds that a site would be invaded was the site’s ecological province as defined by Robert G. Bailey in 1995 (Riitters et al. 2017)

Propagule Pressure: the Role of Deliberate Planting

Over 25 years (Reichard and White 2001) numerous scientists have documented the role of deliberate planting – especially ornamental horticulture – in facilitating introduction and spread of invasive plants. Kinlock et al. (2025) found that more than 1,600 plant species sold by nursery and seed catalogs over 200 years had “naturalized” somewhere in the continental 48 states. Fertakos and Bradley (2024) found that species were likely to establish if they were introduced to as few as eight locations. Beaury et al. (2023) found that half of 89 plant species recognized as invasive are sold in the same locations where they are invasive. Another 25 species are sold in an area that is currently unsuitable for those species, but that will become more suitable for invasion as temperatures warm.

Japanese barberry – invasive that is widely sold; photo by Matthew Beziat via Flickr

Both Potter et al (2024) and Potter et al. (2026a) note that the flora of suburban and rural residential landscapes is dominated by non-native plant species. I add that the people who live there promote plant invasions in various ways, including planting shrubs or flowers in the woods and dumping yard waste there. The older the human settlement, the more years for these plants to spread – assisted by birds, wind, or water. Go here for a more detailed discussion of these issues.

What Should We Do to Curtail Introduction and Spread of Invasive Plants?

a. Regulations The ornamental plant market – whether brick and mortar stores or internet sales — is interstate in scope. Regulations need to match (Beaury et al. 2023). This requires Congress to adopt a new federal law. Under the Constitution, the appropriate entity for regulating interstate commerce is the federal government. But the current statute (the Federal Noxious Weed Act) does not address long-established, widespread species.

States currently have the lead in regulating sales of horticultural plants. Beaury et al. (2023) and Evans et al. (2024) criticize state restrictions as outdated, limited to a few weeds that plague agriculture, and irregularly enforced. The result is a checkerboard of places where a species is offered for legal sale next to places where that sale is prohibited. Finally, the regulations are reactive; they rarely include plants in anticipation of their spread to new areas. Evans et al. (2024) urge state regulators to prioritize those species in the ornamental trade that are projected to remain or become abundant under evolving climate conditions.

b. Voluntary Actions

Potter et al. (2024) call for efforts to encourage homeowners to plant more native and environmentally friendly private landscapes. They concede the complication that some non-native – even invasive – species provide valued ecosystem and cultural services. They also suggest that local governments adopt land-use planning rules that protect forests of high conservation value. They do not discuss the extreme improbability of the latter action given the magnitude of predicted land-use changes in the country, powerful demographic factors driving them, and lobbying clout of affected economic interests, including the nursery industry.

Many citizen associations – native plant societies, regional or state invasive plant councils, etc. – are pursuing the education approach. (See the websites for state native plant societies, Southeast Exotic Pest Plant Council, Mid-Atlantic Invasive Plant Council, Midwest Invasive Plant Network, and Virginia Invasive Plant Coalition.) These voluntary efforts have yielded some success. But they have not resulted in adequate protection for our ecosystems.

c. Land-Managing Agencies

Many land-managing agencies work with local and regional groups to monitor and remove invasive plants, e.g., Blue Ridge PRISM. Databases that verify and post their findings, e.g., iNaturalist and EDDmapS can provide early warning of new invaders. See here for a discussion of these matters.

Blue Ridge PRISM removing English ivy; photo courtesy of Rowena Zimmerman, Director of Virginia Invasive Plant Coalition & Blue Ridge PRISM

Potter et al. (2026a) also suggest that the USDA Forest Service update the lists of invasive plants to be included in future FIA surveys. I agree. See above for examples of highly invasive species not now included.

Of course, the influence of plants on ecosystems is broader than invasive species. Dr. Douglas Tallamy has demonstrated that even non-invasive, non-native plants can disrupt food webs.

SOURCES

Beaury, E.M., J.M. Allen, A.E. Evans, M.E. Fertakos, W.G. Pfadenhauer, B.A. Bradley. 2023. Horticulture could facilitate invasive plant range infilling and range expansion with climate change. BioScience 2023 0 1-8 https://doi.org/10.1093/biosci/biad069

Bradley, B.A., R. Early and C. J. B. Sorte. 2015. Space to invade? Comparative range infilling and potential range of invasive and native plants. Global Ecology and Biogeography

Evans, A.E., C.S. Jarnevich, E.M. Beaury, P.S. Engelstad, N.B. Teich, J.M. LaRoe, B.A. Bradley. 2024. Shifting hotspots: Climate change projected to drive contractions and expansions of invasive plant abundance habitats. Diversity and Distributions 2024;30:4154

Fertakos, M.E. and B.A. Bradley. 2024. Propagule pressure from historic U.S. plant sales explains establishment but not invasion. Ecology Letters 2024;27:e14494 doi: 10.1111/ele.14494

Kinlock, N.L., D.W. Adams, W. Dawson, F. Essl, J. Kartesz, H. Kreft, M. Nishino, Jan Pergl, P. Pyšek, P. Weigelt and M. van Kleunen. 2025. Naturalization of ornamental plants in the United States depends on cultivation and historical land cover context. Ecography 2025: e07748 doi:10.1002/ecog.07748

Miller, K. M., F. W. Dieffenbach, J. P. Campbell, W. B. Cass, J. A. Comiskey, E. R. Matthews, B. J. McGill, B. R. Mitchell, S. J. Perles, S. Sanders, J. P. Schmit, S. Smith, and A. S. Weed. 2016. National parks in the eastern United States harbor important older forest structure compared with matrix forests. Ecosphere 7(7):e01404. 10.1002/ecs2.1404

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

Potter, K.M and Riitters, K. 2022. A National Multi-Scale Assessment of Regeneration Deficit as an Indicator of Potential Risk of Forest Genetic Variation Loss. Forests 2022, 13, 19. https://doi.org/10.3390/f13010019.

Potter, K.M., K.H. Riitters, B.V. Iannone III, Q. Guo and S. Fei. 2024. Forest plant invasions in the eastern United States: evidence of invasion debt in the wildland‑urban interface. Landsc Ecol (2024) 39:207 https://doi.org/10.1007/s10980-024-01985-y

Potter, K.M., B.V. Iannone III, K.H. Riitters, Q. Guo, K. Pandit, C.M. Oswalt. 2026a. US Forests are Increasingly Invaded by Problematic Non-Native Plants. Forest Ecology and Management 599 (2026) 123281

Potter, K.M., Q. Guo, F.H. Koch, S. Lim-Hing, E.R. Matthews, and K. Pandit. 2026b. U.S. National Forests Are More Diverse, Denser and Less Invaded than Neighboring Forests. Forests 2026 17

Reichard, S.H. and P. White. 2001. Horticulture as a Pathway of Invasive Plant Introductions in the United States. BioScience 103. Vol. 51 No. 2. February 2021.

Riitters, K., K. Potter, B.V. Iannone III, C. Oswalt, S. Fei, Q. Guo. 2017. Landscape correlates of forest plant invasions: A high-resolution analysis across the eastern United States. Diversity and Distributions. DOI: 10.1111/ddi.12680

Tallamy, D.W. and K.J. Shropshire. 2009. Ranking Lepidopteran Use of Native Versus Introduced Plants

Conservation Biology, Volume 23, No. 4, 941–947 2009 Society for Conservation Biology

DOI: 10.1111/j.1523-1739.2009.01202.x

Posted by Faith Campbell

https://fadingforests.org

Invasive species on the African Continent

We are beginning to get more information about invasive species on the African continent.

a flyer naming principal invasive ornamental plants in Kruger National Park

In several countries, the focus has been on threats to agriculture. Previous blog about horizon-scanning in Ghana. In Zimbabwe, N. Mudada and colleagues (2026; full citation and the end of this blog) found alarming, if not surprising, levels of risk to food production from introduced invasive plants. They investigated 1,668 human-aided transboundary plant introductions at 14 ports of entry and non-official crossing points over the course of four years.

They estimate that the 20,000 trucks that transported maize into the country over the four years carried over 20,700 metric tons of weed seeds and rubbish! They recorded detections of 11 species in eight orders. The pathways are familiar. As noted, several weeds were contaminants of grain shipments; Convolvulus arvensis in wheat for human consumption, Helianthus annus and Datura stramonium in maize for animal feed. Adenium obesum and Vitex agnus-castus were being smuggled for planting as flowers and ornamentals. (Vitex agnus-castus was also smuggled in passenger baggage for its medicinal properties). Several Lemna species (an aquatic plant) were also smuggled for planting as animal feeds.

In some cases, the focus is the threat to native ecosystems. I posted a blog the about threat of an introduced pathogen to trees in the remnant rain forests of Madagascar.

South Africa still has the lead in addressing invasive species. Regarding invasive plants specifically, the country has the benefit of more than 150 years of botanizing. The richness of the region’s flora is globally recognized. South Africa also has a long history of studying and managing invasive species, especially plants.

South African scientists and colleagues in Botswana, Eswatini, Lesotho, and Namibia have published four editions of the Flora of the Southern Africa region since 1984. In 2006, the PRECIS database of the South African National Biological Diversity Institute (SANBI) was combined with the Tropical African Plant Checklist published by the Conservatory and Botanical Garden of Geneva to create the African Plant Checklist and Database Project. It is continually updated. This is the first continental flora checklist for Africa; it fulfils countries’ obligations under the Convention on Biological Diversity’s Global Strategy for Plant Conservation.

For South Africa specifically, scientists have produced a national plant checklist that is updated annually.

The 2025 Checklist reports that 21,539 plant species are extant outside cultivation in the country; these comprise 20,204 indigenous species and 1,329 naturalized species. Thus, 6% of the total flora is non-indigenous. Of these, 649 (48.8% of the non-indigenous species, 3% of all plants) of them are invasive.

[Naturalized species are defined as species whose documented natural range does not include South Africa, but have overcome a biogeographic barrier and now sustain self-replacing populations for two or more life cycles or over a given period of time in the country. These populations are maintained without direct intervention by people, or despite human intervention. Invasive species meet the above definition plus produce reproductive offspring, often in large #s at considerable distances from the parent and/or site of introduction, and have the potential to spread over long distances.]

Since the previous checklist was published in 2006, botanists have identified 1,048 additional species – a 4.9% increase. Eighty-two percent of the newly identified species (865 species) are “naturalized”. Specifically, 414 new species are categorized as naturalized (a 31.1% increase), and 451 new species are classified as invasive (a whopping 69.5% increase). Le Roux and Klopper attribute these steep increases to active botanizing by SANBI’s Invasive Species Programme (begun in 2008), and the Southern African Plant Invaders Atlas Project (begun in 2010).

Of the 384 plant families present in South Africa, 350 contain at least some indigenous species. Thirty-four families contain only naturalized species. Among the 2,189 plant genera present, 459 (21%) contain only species that are non-indigenous.

Three families stand out because of the particularly high numbers of naturalized species: Fabaceae (143 species; 11% of all naturalized species), Asteraceae (140 species; 10%), Poaceae (123 species; 9%). Two of these families — Asteraceae and Fabaceae — are also the largest families among native South African plants. The third, grasses (Poaceae), ranks seventh in the list of most specious families indigenous to South Africa. The next group of families with high numbers of naturalized species has less than half as many invasive species: Myrtacae (55), Amaranthacea (52), Solanaceae (48). None of these families ranked within the top 20 families of indigenous plant species.

The genera with the most naturalized species were Solanum, Euphorbia and Acacia (all 24 or 23 species).

*Acacia cyclops*; photo by David M. Richardson

South African scientists are also exploring how to balance conflicting goals and perspectives when an invasive plant species has economic or social value. The example chosen by Mbobo et al. (2025) is guava (Psidium guajava) – a nutritious and popular tropical fruit grown commercially in South Africa, but also invasive along roadsides, watercourses and forest margins. Invasions are especially common in eastern parts of country; large monocultures are found in KwaZulu-Natal. Outbreaks have also been detected at five sites in Western Cape in riparian zones and at a hot spring. Mbobo et al. (2025) note that the microclimatic conditions at this last location differ from the broader conditions in the region – which are what most models would measure.

The scientists used models to predict where guava might invade – especially in large monocultures – and compared those areas to where the tree can be grown in cultivation with human inputs, e.g., irrigation. They then assessed whether six regulatory approaches would avoid restricting guava farming in areas at minimal or low risk while still protecting vulnerable locations. They also considered the amount of information required to implement the approach and costs of acquiring the information; and level of likely public acceptance. Mbobo et al. (2025) laid out the trade-offs between continuing to regulate planting of the species at the provincial level vs. at the municipal level. Prohibiting planting of guava in provinces where it is recorded as invasive allows some plantings near natural forests and riparian areas that are highly susceptible to guava invasions. On the other hand, nearly half of the prohibited area is outside the known or likely at-risk area. The provinces do allow exceptions through a permit process. Adopting more geographically limited rules by regulating at the municipal level would enable a tighter link to geographic areas at highest risk. However, this approach does not address long-distance seed dispersal by animals. Furthermore, the very detailed regulations might confuse stakeholders and complicate enforcement. Also, the models lack sufficiently fine spatial resolutions to predict invasible areas so accurately. Finally, the reduction in regulated area is minimal (~ 14%), so the economic benefits are unlikely to outweigh the significantly higher administrative costs and risk of allowing guava invasions in new sites.

Guava fruit on tree; Roenashy via Wikimedia

Gildenhuys et al. (2026) analyzed the factors that drive which non-native plants establish where. They assessed the roles of temperature, precipitation, urbanization intensity, urban area, travel time, year of city’s establishment, and human population density in determining which plant species are present in 54 urban centers in Western Cape Province. The cities have significant differences in climate: Mediterranean in the far southwest, warm temperate in the southeast, and semi-arid towards the interior. The expectation was that these drivers and assembly processes are influential at more advanced invasion stages when the species have already overcome some barriers to dispersal, so are now found in reasonably suitable habitats.

Gildenhuys et al. (2026) found temperature and precipitation were most important in determining plant species’ presence. This was especially true at the boundary between arid and mesic climates. These strong environmental gradients are the same ones which have driven high differences in native species presence across the province. [See pamphlet describing invasive plants in Cape Town.] This finding supports the “Goldilocks hypothesis”: that non-native plant species assemblages are driven by the same abiotic variables as native species assemblages. While did not directly study the “Biome decides hypothesis” (the composition of non-native flora is mediated by the biotic effects of native flora and fauna), Gildenhuys et al. (2026) doubt its applicability here because native species’ presence has probably been greatly reduced by the effects of urbanization.

Urbanisation intensity itself ranked third as a factor. Its effect was strongest at low to medium urbanization intensities. Because urbanization creates novel habitats, such as, “hardscapes” of paved surfaces that resemble deserts, their non-native plant assemblages are dominated by similar, urban specialist, species. At lower urbanization intensities a greater variety of habitats is available. Gildenhuys et al. (2026) conclude that urbanization acts primarily as a driver of opportunistic habitats for species at later invasion stages rather than as a filter of species introduction.

An earlier study found a similar effect from road density (often associated w/ urbanization) as an explanation for where specific woody non-native species establish. They do concede that larger urban areas might experience greater propagule pressure.

Gildenhuys et al. (2026) note that recent globalization of the plant trade has probably changed the specis planted in urban centers. For example, cities in the Western Cape are increasingly replacing English oak (Quercus robur) with more disease-resistant oaks. The change might reflect greater environmental awareness and regulations issued under the National Environmental Management: Biodiversity Act 10 of 2004. In newly established urban centers, fewer invasive species are being planted — at least among trees.

SOURCES

Gildenhuys, C.P., L.J. Potgieter, C. Hui, D.M. Richardson. 2026. Drivers of compositional turnover of the NIS urban flora in the W Cape, South Africa. Urban Ecosystems (2026) 29:51 https://doi.org/10.1007/s11252-026-01919-3

Le Roux, M.M., R.R. Klopper. 2025. Taking stock of South Africa’s flora. South African Journal of Botany 184 (2025) 571-579

Mbobo, T., D.M. Richardson, A. Datta, K.T. Faulkner, J.R.U. 2025. Wilson. Spatially-Differentiated Reg of NIS Can Be Improved Using Spp Distribution Models: Psidium guajava in South Africa as a Case Study. Diversity and Distributions. 2025 31:e70102 https://doi.org/10.1111/ddi.70102

Mudada, N., J. Chitamba, E. Nyangani, C. Chapano, N. Mapope,and W. Ngezimana. 2026. Weeds associated with cross border traffic, their approach and infestation rates in Zimbabwe. ISABB Journal of Food and Agricultural Sciences. Vol. 12(1) January-June 2026. DOI: 10.5897/ISABB-JFAS2025.0192

Posted by Faith Campbell

https://fadingforests.org

EAB infestation at 20 years: focus on green & white ash & white fringetree

dying ash in Shenandoah National Park; photo by F.T. Campbell

The emerald ash borer (Agrilus plannipennis; EAB) was detected in North America in 2002. So both U.S. and Canadians have been motivated to evaluate the probable trajectory of the primary hosts – the ash genus Fraxinus – in the face of the ongoing invasion. See Deschênes et al. 2026 and Wilson et al. 2025 – full citations at the end of this blog. Both studies focused on white (Fraxinus americana) and green ash (F. pennsylvanica); they say next to nothing about black ash (F. nigra). I regret this silence because of the unique ecology of black ash swamps. Neither addresses the threat to Oregon ash (F. latifolia) in the West.

The two assessments have similar findings: high mortality of larger trees (canopy and “recruit” size trees); abundant regeneration (seedling and saplings sizes) after an initial period; and uncertainty as to whether persisting EAB populations will kill the saplings before sufficient numbers grow into reproductive size.

There are two conspicuous differences. First, the American study does not consider the possible impact of biological control – although USDA APHIS has placed all its effort on this approach since January 2021. The Canadians report that self-sustaining populations of the wasps are now found across the northern U.S. and eastern Canada. In their study, conducted in Ontario, they detected only Tetrasticus planipennisi; it was parasitizing 16% of the EAB larvae in dissected stems. This wasp’s affinity for colder climates and short ovipositor – which limits it to parasitizing larvae inhabiting small stems – are portrayed as positive traits under these circumstances.

Second, the Canadians did not find “lingering” adult ash trees as have the Americans. These trees indicate the probability of finding workable levels of genetic resistance to the EAB. USDA Forest Service scientists are pursuing a breeding program. While in south-central Michigan, where overstory ash mortality typically exceeded 80%, 46% of overstory ash and 82% of ash recruits were relatively healthy (Wilson et al. 2025), in Ontario none of 1,129 overstory ash trees survived beyond seven years after EAB detected. No trees exceeded 15 cm dbh (Deschênes et al. 2026).

ash resistance breeding trial at Holden Arboretum; photo courtesy of Jennifer Koch, USFS

Regeneration

As Deschênes et al. (2026) state, the future of ash stands depends on the complex of interactions among environmental conditions, management interventions, efficacy of natural enemies (natural or introduced), and life-history traits of the insect and its host. Coexistence might be possible if EAB larval densities remain sufficiently low to support survival of residual trees and successful seedling recruitment.

Larval densities in Ontario were said to be generally low, suggesting reduced carrying capacity in post-invasion forests, lower EAB fecundity, and higher EAB mortality in regenerating stems. Deschênes et al. (2026) note that in more northern areas colder temperatures are thought to slow larvae development. Perhaps these larvae might also be less vigorous, so they night disperse only over short distances. Still, there were sufficient EAB present after all the overstory trees had died to create 97% of the 298 galleries in regenerating ash stems (Deschênes et al. 2026). Furthermore, Wilson et al. (2025) say that EAB densities in infested trees in Michigan were similar to densities recorded during the initial invasion. This seems ominous to me – a solid foundation from which beetle populations could build up again as regenerating ash grow and provide more phloem for the insect to exploit.

Ash reproduce by both flowering/seeding and sprouting from the base. EAB predation is not the only complication. First, ash are dioecious so mature trees of both sexes must grow within a few hundred meters. Second, predation by the ash seed weevil (Lignyoodes helvolus) reduces seed supplies. Dense sedge mats can prevent germination (Wilson et al. 2025). Scientists generally believe that the soil seed bank is quickly exhausted, although Wilson et al. (2025) cite others’ conflicting findings. Neither article discusses predation by mammals, e.g., deer or rabbits. Wilson et al. (2025) mention attacks by beavers.

ash saplings felled by beavers; photo by F.T. Campbell

Wilson et al. (2025) did not study whether stump-sprouted ash were able to successfully recruit into the overstory. They do report that in one study in southeastern Michigan stump sprouts were the dominant form of green ash regeneration and about a quarter of these sprouts produced seeds at least once. Deschênes et al. (2026) found that on average 47% of regenerating stems at their Ontario research sites originated from stump sprouts.

EAB has been documented to attack and kill trees when the main stem is as small as 2.5 cm. While EAB probably prefer larger stems, Deschênes et al. (2026) suggest that stems become acceptable at the lower range of size required for seed production – 8–10 cm dbh. Reliable and abundant seed production doesn’t occur until white or green ash achieve > 20 cm dbh. At their Ontario sites, Deschênes et al. (2026) found that 42% of regenerating stems has been infested by EAB at least once; 14% had been attacked five or more times. They removed 74 EAB larvae from 28 stems; 49 (66%) were alive. Fifteen EAB (16% of current year galleries) had been parasitized — all by Tetrastichus planipennisi. They also observed numerous signs of defensive responses.

In Michigan, no ash recruits — living or dead – were found in plots in 28% of the cells. In the remaining 128 cells, an average of ~33% of ash recruits were infested by EAB, and ~21.4% of ash recruits dead. As is typical, white ash fared better than green ash. Recruit sized ash trees were twice as likely to die than to survive and mature into overstory size (Wilson et al. (2025).

In Ontario, as noted, all canopy ash had died. There were 119 live trees 5 – 10 cm dbh – a tenth as many “mature” ash as when EAB arrived, and all were smaller. There was abundant regeneration in most sites initially, but at the longest-infested sites in Essex County, regenerating ash stems were half as numerous as early after the transition (Deschênes et al. 2026).

The Canadians found it encouraging that some of the regenerating stems were vigorous despite containing EAB gallery densities greater than 20 larvae·m?2 of phloem. They did not know the mechanisms underlying survival of these stems. Possible explanations ranged from the low EAB carrying capacity of smaller trees to stronger host defenses in regenerating stems to EAB mortality due to parasitism.

Wilson et al. (2025) note that despite more than 20 years of EAB presence, densities of ash recruits, saplings, and seedlings were high relative to other species. However, they remind us, ~ one-third of the live ash recruits were infested so their survival into reproductive size was uncertain. The high mortality of overstory ash results in loss of seed resources, greater sun exposure, and cascading consequences for forest composition and function. In upland sites, cells with low ash basal area favored Quercus rubra and Tilia americana. They conclude that changes to forest composition is probably site specific — largely depend on what tree species are already present.

Despite the challenges described above, the Canadian scientists also believe that these findings demonstrate that ash has a capacity for long-term regeneration (Deschênes et al. 2026).

Changing Species Composition in the U.S. (Wilson et al. 2025)

Canopy gaps caused by ash mortality have largely been filled by lateral ingrowth of species already there — American elm (Ulmus americana), black cherry (Prunus serotina), and northern red oak (Quercus rubra). The regeneration strata (saplings and seedlings) is dominated by Fraxinus (white outnumbering green when differentiated), maples (Acer rubrum, A. saccharum), black cherry, Crataegus species and Carya ovata. Elms are consistently among most common non-ash taxa among overstory, recruit, sapling and seedling strata. At some Ohio sites there was also increased abundance of non-native tree and shrub seedlings. This is not surprising since invasive plants are widespread in the forests of Ohio and other eastern states. A decade ago 93% of Forest Inventory and Analysis (FIA) plots in Ohio had at least one of 50 invasive plant species.

In another paragraph they mention Tilia americana as one of the important species in these forests.

Situation in Canada (Deschênes et al. 2026)

Deschênes et al. (2026) express concern that the death of nearly all canopy-level trees will substantially reduce ash’ ability to fulfill its ecological roles in these ecosystems. Still, ash regeneration is persisting for decades following overstory mortality. The taxon’s continued presence is driven largely by strong sprouting, which has been observed in several locations in Ontario. In some areas, low EAB infestation rates and evidence that regenerating stems can withstand multiple infestations raises hope that some might reach maturity and produce seeds. This scenario would be similar to that of elms, in which surviving trees contribute to ongoing regeneration and might eventually facilitate development of some level of resistance to the invasive fungus. A second possibility is that ash’ high sprouting capacity might point to a scenario similar to that of American chestnut. This species has persisted for a century primarily as sprouting shrubs — although they rarely reach reproductive maturity.

White Fringetree

Scientists also reviewed the status of a secondary host of EAB in North America, white fringetree (Chionanthus virginicus). Earlier studies of this host-pest relationship had been conducted on ornamental plantings where the trees tend to be scattered across open lawns and actively managed – including protection from pests. The Cipollinis (see full citation at the end of this blog) believe they might be better able to ward of EAB attack than are wild, unmanaged trees in forests that must compete for resources. They wanted to assess the current status and likely trajectory of the tree species in the wild.

To do so they revisited a wild population of the tree in southern Ohio previously assessed 10 years earlier. White fringetree is a small multi-stemmed tree native to the southeastern U.S. It is widely planted as an ornamental in across the east. In Ohio, white fringetree grows wild in only a few southern counties, in small populations or as widely scattered individuals. The species is classified as “Potentially Threatened” at the state level.

In 2015, 30% of the white fringetrees at the site were infested. These trees had signs of stress but none had died. EAB larvae grow more slowly on fringetree than on North American ash species. Meanwhile, all mature white ash trees at the site had been killed by EAB. Smaller white ash trees more comparable in size to the white fringetrees had attack rates and impacts comparable to those on the fringetrees.

In their new study, the Cipollinis found that nine of 31 trees tagged in 2015 (29%) had died; 22 (71%) were alive. Of those 22 living trees, 12 (55%) stayed the same or improved slightly over the five-year period; 10 (45%) declined. Five of these 22 living trees (23%) had evidence of current infestation. Trees that had died had a higher incidence of old EAB galleries, adult exit holes, and woodpecker activity. This is interpreted as demonstrating that EAB must cause extensive damage to kill fringetrees.

In summary, fringetrees in a wild unmanaged population continued to be attacked by EAB over 10 years and suffered higher attack rates and more significant impacts than those previously observed in managed pops. The Cipollinis conclude that trees large enough to attract EAB oviposition will continue to decline in health and be killed as long as beetles are present. They expect that wild white fringetrees might meet the same fate as ash trees, but over longer time scales.

At the same time, this delay in complete mortality might create a refugium for remnant populations of EAB after most ash have been killed. This status would be exacerbated if it turns out that the biocontrol agents cannot find their target — EAB — in the alternative host. The Cipollinis found lower parasitism rates by Tetrastichus planipennisi in fringetrees, although this was not true for the egg parasite Oobius agrili and two Spathius larval parasites.

Whitebark fringetree populations can produce few adult EAB because the trees are small and contain low amounts of phloem. Still, as young trees grow into vulnerable sizes they might help sustain the EAB population – as young ash trees in the area appear to do.

While caution is appropriate in interpreting findings from a study of a single population, the Cipollinis argue that this population has been studied intensively: assessed six times over 10 years, beginning at the start of the EAB infestation. Therefore they think their analysis provides useful informative regarding the long-term impacts of EAB on fringetree.

They concede that larger populations in areas deep within the tree’s native range might experience different dynamics and impacts. So far, however, observations in Chattahoochee National Forest in Georgia and at Great Falls Park on the Maryland-Virginia border generally support their finding that wild fringetrees in natural landscapes will suffer higher attack rates and be more severely impacted by EAB than trees in managed landscapes.

Finally, the Cipollinis fear that a close relative, pygmy fringetree, Chionanthus pygmaeus, is at particularly high risk because it is endemic to only a few counties in the sandhills of central Florida. The species is already classified as endangered by both the state and the federal governments. The pygmy fringetree is smaller than white fringetree, so its size might help it escape attack. However, adults achieve sizes comparable to that of fringetree in some cases. So when EAB reaches Florida, the specie appears to be highly vulnerable.

SOURCES

Cipollini, D. and K. Cipollini. 2026 The Fate of a Wild White Fringetree (Chionanthus virginicus) Population in Ohio 10 Years After Invasion by Emerald Ash Borer (Agrilus planipennis) Forests 2026, 17, 712

Deschênes, É., C.J.K. MacQuarrie, L. Scott, C. Zimmerman, and I. Aubin. 2026. Ash population dynamics after two decades of emerald ash borer infestations in Canada. Canadian Journal of Forest Research. Can. J. For.Res. 56: 1–13 (2026) | dx.doi.org/10.1139/cjfr-2026-0075

Wilson, C.J, L. Labbate, T.R. Petrice, T.M. Poland, D.G. McCullough. 2025. Ongoing regeneration of ash and co-occurring species 20 years following invasion by emerald ash borer. Forest Ecology and Management 580 (2025) 122546

Posted by Faith Campbell

https://fadingforests.org

Bioinvader Threat to Caribbean cacti – Who is Protecting Them?

Photo of infested cactus at Cabo Rojo National Wildlife Refuge, Puerto Rico. Taken August 20, 2018 by Yorelyz Rodríguez-Reyes

For 15 years I have maintained a profile of the Harrisia cactus mealybug Hypogeococcus pungens because it threatens columnar cacti in the subfamily Cactoideae from the Caribbean basin and possibly in the American Southwest and Mexico. My recent attempts to clarify the current situation have been frustrated by the apparent collapse of funding support for scientists trying to conserve these cactus species.

The dry regions of the Caribbean Islands are home to about 100 native cacti, 75% of which are endemic. According to the Center for Plant Conservation, 20 species are listed as threatened by the IUCN. Puerto Rico specifically is home to 14 cactus species, at least three of which are endemic.

How and when the mealybug first invaded the Caribbean and North America is unknown. The presence of the insect now known as H. pungens Hyp-C on Puerto Rico was detected in the Guánica Commonwealth Forest and Biosphere Reserve on the island’s southern coast in 2005 (Zimmerman et al. 2010). However, the actual introduction probably occurred about ten years earlier, in about 1996 (Poveda-Martinez et al. 2022). See map of locations below.

In the 20 years since then, the mealybug has spread across the island’s dry districts. By 2010, it was estimated to be present on about 1,400 km². By 2014 – nine years after detection — the mealybug had reached the small island of Caja de Muertos. The most recent survey of which I am aware (date unclear) detected the mealybug on 268 out of 445 cactus plants examined (60%) in 12 out of 39 sites examined (Poveda-Martinez et al. 2022). The mealybug is also killing native cacti on the nearby U.S. Virgin Islands (Poland et al. 2019), although I have found no data on this invasion or its impact.

Below – columnar cacti on St. John, US Virgin Islands; photos by F.T. Campbell

H. pungens Hyp‑C threatens seven of 14 native cactus species in Puerto Rico. Three of the cacti are endemic; two are federally listed as endangered species: Harrisia portoricensis and Leptocereus grantianus (USDA ARS). Since the mealybug’s detection in Puerto Rico, it has caused extensive damage to Pilosocereus royenii (Royen’s tree cactus), Leptocereus qaudricostatus (pitaya), Melocactus intortus (turk’s cap), and an introduced cultivar, Cereus hexagonus. It has caused minor damage to Stenocereus fimbriatus (Zimmerman et al. 2010). These cacti provide food or shelter for endemic bats, birds, moths and other pollinators (Segarra and Ramirez; USDA ARS).

The insect’s attack promotes abnormal gall-like growth on the stem and deformed flowers. These deformations severely affect infested plants’ reproduction and eventually survival (Poveda-Martinez et al. 2022).

Biological Control

When the mealybug was first detected Commonwealth and federal agencies tried to counter it. A search for possible biocontrol agents in the insect’s native range in Argentina began the 2010. While no funds have ever been appropriated for this activity, for several years the U.S. Department of Agriculture supported the work by allocating funds to the Agriculture Research Service Insect Behavior and Biocontrol laboratory in Gainesville, Florida, from broader programs. Dr. Stephen Hight took the lead, working with colleagues in South America. According to Dr. Hilda Diaz-Soltero, then a USDA official, these funds came primarily from the USDA Invasive Species Coordination Program and APHIS Eastern Region. In fiscal years 2017 and 2019, an additional ~$550,000 came in the form of grants under APHIS’ Plant Pest and Disease Management and Disaster Prevention Program. Link Scientists at the Center for Excellence in Quarantine and Invasive Species at the University of Puerto Rico devoted at least a decade to the search.

Scientists focused on two parasitoid wasps, Anagyrus cachamai and A. lapachosus (Hymenoptera: Encyrtidae). A third candidate, the predator Hyperaspis conclusa, was also assessed (Aguire et al.).

Research on the mealybug-wasps interaction uncovered troubling patterns. First, it has long been known that some mealybugs believed to be belong to the species Hypogeococcus pungens feed on columnar cacti while others feed on plants in two unrelated families, Amaranthaceae and Portulacaceae (USDA ARS; Zimmerman et al. 2010). Would the introduced wasps attack the cactus-feeding mealybug in sufficient numbers?

The confusion over how many mealybug species have been introduced – and where – severely hampered development of a program. (The mealybug has been introduced to control invasive cactus in Australia and South Africa. Most sources say it has been highly effective – prompting the initial concern when it appeared on Puerto Rico.) I have been unable to find any information about the status of the candidate biocontrol agents more recent than 2022.

Genetic Conservation

The USDA also partnered with the Naples (Florida) Botanical Garden to collect fruits and vegetative material for ex situ conservation. Rigorous phytosanitary procedures were followed to ensure the absence of the mealybug. Collections of fruits and vegetative material provided 1,298 cacti samples from 13 species, representing 1,173 maternal lines from 91 sites throughout Puerto Rico. A total of 90,720 seeds representing 8 species are banked at the NBG for long-term storage. Propagation of the vegetative material has 56% success, and plants are incorporated into the NBG’s living collections. (These figures include Opuntia cacti that are hosts of a second invasive insect, Cactoblastis cactorum.)

Genetic Concerns

Scientists now consider Hypogeococcus pungens (Hemiptera: Pseudococcidae) to be a species complex composed of at least five putative species. The species are separated in part by the plants they use as hosts. Two of the complex have apparently been introduced to Puerto Rico: H. pungens Hyp‑C feeds on cacti; H. pungens Hyp‑AP feeds on hosts in the Portulacaceae & Amaranthaceae. Both evolved from putative source populations in Brazil (Poveda-Martinez et al. 2022).

The two species H. pungens Hyp-C and Hyp-AP are currently separated on Puerto Rico by host preferences and climatic niches. They also occupy different geographic areas. Scientists fear that ongoing climate change could allow H. pungens Hyp-C to establish farther into the island’s interior and in a large area in the north. Such range expansion would end the geographic separation. Overlapping of the two species is likely to exacerbate the threat to Puerto Rico’s cacti. Most directly, it would complicate implementation of management strategies, especially biological control. Intermixing of the two species could also facilitate hybridization which might result in more vigorous attacks or a broadened host range. Hybridization is frequent in closely related species (Poveda-Martinez et al. 2022).

The Mealybug is Frequently Introduced

Mealybugs that feed on cacti and believed to be in the species Hypogeococcus pungens made multiple appearances in southern California between 2000 and 2018 – in gardens and in nurseries. Confusingly, CDFA reports interception of the mealybug on alternanthera and ludwigia plants shipped from Florida (CDFA 2018). I have no more recent data. The population in Florida was reported to be present in 16 counties in 2009); it might be the species that feeds on plants other than cacti (Poveda-Martinez et al. 2022). Other populations has been reported in the Dominican Republic (no date) (CDFA 2018); and in Hawai`i in 2005 (Hawaii Department of Agriculture new pest report). A mealybug that feeds on Amaranthaceae and Portulacaceae was detected in 2000 in San Juan, Puerto Rico (Poveda-Martinez et al. 2022).

In the absence of control measures, scientists expect H. pungens Hyp-C to continue decimating Puerto Rican cactus diversity and threaten other cactus rich ecosystems across the Caribbean islands, Central America and, potentially, North America (Poveda-Martinez et al. 2022).

saguaro and organ pipe cacti in Organ Pipe Cactus National Monument; photo by F.T. Campbell

North America has more than 500 columnar cactus species in the Cactoideae (Zimmerman et al. 2010). Some of these cacti are already endangered, e.g., several Pediocactus. Others are totems of the desert, e.g., the saguaro (Carnegiea gigantea) and organ pipe (Stenocereus thurberi) cacti. Picture The larger ones, particularly, play important ecological roles. It is not known how vulnerable individual species are to the mealybug (Golubov pers. comm. January 2011). In Mexico several mealybugs in the same genus are already present. The natural enemies of these mealybugs might be able to attack H. pungens Hyp-C if it invades the country (Zimmerman et al. 2010). Despite the well-founded concern, apparently no funds have been allocated by governments or conservation organizations to studying the vulnerability of these cacti to one or more mealybugs in the Hypogeococcus genus.

The most likely pathway by which the mealybug is spread is the trade in plants for planting (the horticultural trade) (Zimmerman et al. 2010). A decade ago APHIS reported intercepting mealybugs on cactus (primarily on roots) imported from Germany, Peru, and Puerto Rico. APHIS has also intercepted several other mealybugs in the same genus – on plants (including orchids and bromeliads as well as cacti) from Belize, Costa Rica, Ecuador, Guatemala, Honduras, Mexico, Panama, Peru, and Venezuela (USDA APHIS alert).

A decade ago NatureServe and IUCN found that 31% of Earth’s cactus species were threatened with extinction. They named overharvesting (often for the illegal horticultural trade) and destruction of habitat by smallholder livestock ranching and farming. Did not mention predation by introduced insects – although that is now manifest not only in the cactus mealybug but also the cactus moth.

Sources

Aguirre, M. G. Logarzo, S. Triapitsyn, H. Diaz-Soltero, S. Hight, O. Bruzzone. 2023? Effect of egg production dynamics on the functional response of parasitoids

California Plant Pest and Disease Report. 2005. Vol. 22 No. 1. Covering Period from July 2002 through July 2005.California Department of Food and Agriculture. 2018.California Pest Rating for Hypogeococcus pungens Granara de Willink | Harrisia cactus mealybug Hemiptera: Pseudococcidae Pest Rating: A California Pest Rating for Hypogeococcus pungens Granara de Willink | Harrisia cactus mealybug Hemiptera: Pseudococcidae Pest Rating: A

Hawaii Department of Agriculture. 2006. https://hawaii.gov/hdoa/pi/ppc/2006-annual-report/new-pest-detections (accessed 11/1/10)

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

Poveda-Martinez, D. N.A. Salinas, M. Belen Aguirre, A.F. Sanchez-Restrepo, S. Hight, H. Diaz-Soltero, G. Logarzo, and E. Hasson. 2022 Geonomic & ecol evidence shed light on the recent demographic history of two related invasive insects. Scientific Reports.

Segarra-Carmona, A.E., A. Ramirez-Lluch. No date. Hypogeococcus pungens (Hemiptera: Pseudococcidae): A new threat to biodiversity in fragile dry tropical forests.

Segarra-Carmona, A.E., A. Ramírez-Lluch, I. Cabrera-Asencio and A.N. Jiménez-López. 2010. First Report of a New Invasive Mealybug, the Harrisia Cactus mealybug Hypogeococcus pungens (Hemiptera: Pseudococcidae). J. Agrie. Univ. RR. 94(1-2):183-187 (2010)

Srivastava, M., P. Srivastava, R. Karan, A. Jeyaprakash, L. Whilby, E. Rohrig, A.C. Howe, S.D. Hight, and L. Varone. 2019. Molecular detection method developed to track the koinobiont larval parasitoid Apanteles opuntiarum (Hymenoptera: Braconidae) imported from Argentina to control Cactoblastis cactorum (Lepidoptera: Pyralidae). Florida Entomologist 102(2): 329-335.

Triapitsyn, Aguirre, Logarzo, Hight, Ciomperlik, Rugman-Jones, Rodriguez. 2018. Complex of primary and secondary parasitoids (Hymenoptera: Encyrtidae and Signiphoridae) of Hypogeococcus species. mealybugs (Hemiptera: Pseudococcidae) in the New World. Florida Entomologist Volume 101, No. 3 411

USDA Agriculture Research Service, Research Project: Biological Control of the Harrisia Cactus Mealybug, Hypogeococcus pungens (Hemiptera:pseudococcidae) in Puerto Rico Project Number: 0211-22000-006-10 Project Type: Reimbursable

Zimmermann, H.G., M.P.S. Cuen, M.C. Mandujano, and J. Golubov. 2010. The South American mealybug that threatens North American cacti. Cactus and Succulent Journal. 2010 Volume 82 Number 3

Countries Fall Short on Plant Conservation Efforts

*Prostanthera cuneata* – member of a genus endemic to Australia. Photo by Leonora (Ellie) Enking via Flickr

In 2023 a global meeting of plant conservation experts convened by The Royal Botanic Gardens, Kew (U.K.) released the 5^th edition of a report on the State of the World’s Plants and Fungi.

Associate Professor of Plant Ecology and Conservation Science Rachael Gallagher from Western Sydney University had led the global evaluation of conservation assessments for unique flora species. She is also the lead author of an article (2023; full citation at the end of this blog) evaluating how well countries around the world met their treaty obligation to assess the conservation status of endemic plant species native to their territories. The analysis identified 221,399 endemic plant species in a total of 173 countries. The treasure is not distributed evenly. Five countries harbor a third of the endemic plant species: in descending order, Brazil, Australia, China, Mexico, and South Africa. (The United States, including its islands, ranks 8^th.)

On average, countries completed assessments of just 34% of their endemic species. New Zealand and here and South Africa shone: they assessed 87% of their unique species. China assessed 71%. One of the world’s poorest countries, Madagascar, evaluated 42% of its ~10,000 endemic plant species. Reminder: tiny Madagascar ranks 6^th in the number of endemic plants. Australia – one of the richest countries– carried out the process for 39% — slightly more than the global average. Other countries that are stewards of numerous endemic plants were below the average: Brazil reviewed 29%, Mexico assessed only 24%.

Rachael Gallagher and her colleagues in the Australian Biodiversity Council were quite critical of Australia’s low level of performance. They called on their countrymen to do much more to prevent the decline and extinction of the country’s unique plant species. Australia, as party to the Convention on the Conservation of Biological Diversity, has a treaty obligation to prevent extinction of species which occur nowhere else. Remember, Australia’s flora and fauna rank extremely high on a scale of phylogenetic distinctness as an heir of the isolated continent of Gondwanaland.

Gallagher and colleagues concede that many endemic plant taxa in Australia have huge ranges — averaging 235,829 km². But these vast expanses do not prevent sudden population crashes caused by calamities. They mention the megafires of 2019–2020 and – over the longer term – climate change. I think of the invasion by the rust fungus Austropuccinia psidii.

When we think about Australia, we wonder at the kangaroos and koalas. I assume Australians consider their unusual fauna to be iconic symbols of their country. Why are they not equally committed to their flora – 88% of their plant species are endemic. Do they suffer from the same “plant blindness” I have encountered in the United States? South Africa undertook an assessment of her endemic flora that concluded that a quarter of these species are threatened. Sixty percent of the country’s 20,000 plant species are endemic.

a protea in South Africa’s fynbos; photo by Michael Wingfield

[I have found no parallel analysis of America’s endemic plant species. Our nation’s rank of 8^th in number of endemic species is explained by the highly unique floras of the islands, especially the Hawaiian archipelago. More than 95% of native species on the Islands are endemic. This includes 67% of the large trees still present in the forests (Potter et al. 2023).]

This study reflects the findings of the International Union for the Conservation of nature (IUCN)’s 2024 Red List of Threatened Species. A decade-long global project had found that at least 16,425 of the 47,282 tree species (38%) assessed are at risk of extinction. Trees accounted for over one quarter of species on the IUCN Red List. Tree species are at risk of extinction in 192 countries around the world.

Sources

Gallagher, R.V., S. P. Allen, R. Govaerts, M.C. Rivers, A.P. Allen, D.A. Keith, C. Merow, B. Maitner, N. Butt, T.D. Auld, B.J. Enquist, W.L. Eiserhardt, I.J. Wright, J.C.O. Mifsud, S. Espinosa-Ruiz, H. Possingham, V.M. Adams. 2023. Global shortfalls in threat assessments for endemic flora by country. Plants, People, Planet. DOI: 10.1002/ppp3.1036

Potter, K.M., C. Giardina, R.F. Hughes, S. Cordell, O. Kuegler, A. Koch, E. Yuen. 2023. How invaded are Hawaiian forests? Non-native understory tree dominance signals potential canopy replacement. Landsc Ecol 2023 https://doi.org/10.1007/s10980-023-01662-6

Posted by Faith Campbell

https://fadingforests.org

USFS Reorganization — implications unclear

Salt Lake City; by invictus323 via Wikimedia

In a press release on 31 March, 2026, the USDA announced major changes to the USFS structure. Agency headquarters will be moved to Salt Lake City. They point out that nearly 90% of USFS land is west of the Mississippi … but promise to sustain engagement in the Southeast (America’s “wood basket) by creating a regional office there. Furthermore, they will change the current regional organization to a state-based one; they plan to create 15 state directorships. State directors will serve as national leaders with primary oversight of forest supervisors, operational priorities, & relationships with states, tribes, & other partners. Each state office will include a small leadership support team responsible for functions such as legislative affairs, communications, & intergovernmental coordination.

There will still be some “operational service centers” in other cities; that for research will be in Fort Collins. The goal is to unify research priorities, accelerate the application of science to management decisions, & reduce administrative duplication. Information on which facilities will be retained or closed is available at this webpage. (I could not open this site.)

No specific information is provided re: forest health management program.

Posted by Faith Campbell

https://fadingforests.org

USDA invasive species research forum 2026: tree pests

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

The most important information from the meeting:

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

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

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

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

an ash resistance breeding plot at the Holden Arboretum, Ohio

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

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

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

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

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

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

Progress on each taxon:

beech grafts in a breeding experiment at the Holden Arboretum

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

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

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

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

The program has had to overcome several difficulties, including:

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

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

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

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

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

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

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

Dutch elm disease (DED)

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

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

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

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

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

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

Managing established non-native pest species

Asian longhorned beetle (ALB)

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

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

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

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

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

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

Beech leaf disease

The disease has now been detected in Nova Scotia.

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

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

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

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

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

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

Butternut canker

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

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

Hemlock woolly adelgid

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

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

Biocontrol of Emerald ash borer

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

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

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

Biocontrol of Spotted lanternfly

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

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

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

Asian spongy moths

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

Early Detection of Wood-Associated Beetles

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

*Xyleborus monographus*; photo by U. Schmidt

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

Other Pests and Pathogens

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

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

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

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

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

Brown spot needle blight

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

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

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

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

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

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

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

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

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

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

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

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

SOURCES

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

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

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

Posted by Faith Campbell

https://fadingforests.org

USDA invasive species research forum 2026: invasive plants

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

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

The most important information from the meeting:

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

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

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

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

Two presentations focused on Callery / Bradford pear

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

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

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

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

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

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

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

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

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

Fulcher is looking for collaborators to help collect plant samples

Other invading plants

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

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

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

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

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

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

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

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

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

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

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

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

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

Posted by Faith Campbell

https://fadingforests.org