Category: forest pathogens

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

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

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

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

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

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

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

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

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

Other facts that challenge traditional phytosanitary practices

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

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

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

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

Phytophthora dieback in Western Australia

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

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

USDA Secretary Brooke Rollins

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

I suggested prioritizing research on the following issues:

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

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

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

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

Challenges:

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

SOURCES

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

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

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

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

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

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

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

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

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

Posted by Faith Campbell

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

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

Or https://fadingforests.org/

A “fix” for some invaded Hawaiian ecosystems?

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

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

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

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

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

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

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

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

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

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

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

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

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

Conclusions

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

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

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

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

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

SOURCES

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

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

Dr. Friday provided the following more local references:

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

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

Posted by Faith Campbell

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

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

Or     https://fadingforests.org/

Tree-killing pests can undermine conservation programs on tropical islands

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

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

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

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

diademed lemur, courtesy of Animalia

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

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

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

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

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

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

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

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

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

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

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

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

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

SOURCES

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

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

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

Horizon Scanning – 2 experiences

sorting coffee beans; photo by Niels Van Iperen via Wikimedia

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

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

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


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

Aedes aegypti; photo by James Gathany via Flickr


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

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

brown marmorated stinkbug; courtesy of Oregon Department of Agriculture


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

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

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

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

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

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

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

Hawaiian birds threatened by avian malaria; picture via Flickr

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

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

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

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

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

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

A Subset of Threats: Invasive Species and Forest Pests

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

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

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

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

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

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

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

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

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

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

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

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

SOURCES

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

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

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

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

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

Pest Threats to Plantations: Will At-Risk Countries Demand Improvements to IPPC?

pines in a plantation in Argentina killed by Sirex noctilio; photo by J. Villacide

 A decade ago, Payn et al. (2015) compiled studies from around the globe to evaluate threats to widespread tree plantations. At that time, they said climate change posed the greatest threat to plantation forestry globally, in the forms of storm and flood damage and simultaneous warming and drying trends with extreme temperatures.

Still, the authors warned that forest health would be an increasingly important constraint to plantation productivity. They were optimistic, however, that modern breeding and other technologies could offset losses.

What is the current situation? The countries that depend on these plantations for fiber production are not demanding that leaders of the international phytosanitary structure build a more effective system to protect their investments. Instead, individual scientists struggle to better understand threats. Mostly, they propose expanded research.

Economic Importance of these Species

Eucalypts

“Eucalypts” comprises three genera in the family Myrtaceae: Angophora, Corymbia and Eucalyptus. These include more than 700 tree species native primarily to Australia. A few species are native to Indonesia, New Guinea and the Philippines (Paine et al. 2011; Crous et al. 2019). Some of these species have been extensively planted outside their native ranges for more than 100 years. These plantations have expanded rapidly in recent decades, especially in Southeast Asia and the Southern Hemisphere (Crous et al. 2019). Eucalypts are now the most widely planted hardwood timber in the world (Paine et al. 2011).

Eucalypt plantation in Brazil; photo by Jonathan Wilken via Wikimedia

Eucalypts’ popularity has been driven chiefly by their rapid growth; short rotation times including through coppicing; and adaptability to a very wide variety of sites and climatic conditions (Paine et al. 2011; Crous et al. 2019). Also, these trees are an important source of the short-fiber pulp required for production of high-quality paper used in modern office copiers and printers (Paine et al. 2011). Plantations are increasing even in Australia, where harvesting of native forests is increasingly being restricted (Paine et al. 2011).

Pines

Pines – a genus restricted naturally to the Northern Hemisphere – is second in global popularity. South America hosts 4.6 million hectares of pine plantations (Lantschner and Villacide 2025). South America is more dependent on forestry plantations for wood production than any other region. In 2012, 88% of its industrial roundwood was produced by non-native plantations. This far exceeded the global proportion of approximately 19%.

These intensively managed plantations have enabled Brazil and Chile to become “planted forest powerhouses.” Uruguay and, more slowly, Argentina are following the same path (Payn et al. 2015). 

Documentation of the Damage

Euclaypts

The highly diverse eucalypts host an even greater diversity of fungi. As of 30 years ago, scientists were aware of more than 500 species of just one type, the leaf-infecting fungi. Additional fungi are associated with seeds, capsules, twigs, branches, and stems. Little is known about the vast majority of these fungi. Even species considered causal agents of important diseases have not yet been confirmed using Koch’s Postulates. Areas of origin for most is also unknown (Crous et al. 2019).

Crous et al. (2019) compiled information on 110 genera of fungi found on eucalypt foliage. Some genera include well-recognized primary pathogens. They name Austropuccinia and Calonectria, Coniella, Elsinoe, Pseudocercospora, Quambalaria and Teratosphaeria. Other genera are thought to include species that are opportunists that develop on stressed or dying tissues. Many other leaf fungi are putative pathogens, but unstudied. Additional fungi cause vascular wilts (e.g. Ceratocystidaceae), stem canker diseases (Cryphonectriaceae, Botryosphaeriaceae) and root diseases (e.g. Armillaria, Ganoderma) of eucalypts.

Crous et al. (2019) state that the rust Austropuccinia psidii is one of the most damaging of the foliage fungal pathogens. They consider it to be a greater threat to eucalypt plantations outside the trees’ native ranges. (The Myrtaceous species in Australia most damaged by A. psidii are in other genera.)

Two families of leaf fungi – Mycosphaerellaceae and Teratosphaeriaceae – include species that cause serious diseases. Pérez, et al. report a study in plantation in Uruguay that detected six new species. They also discovered new hosts for some known species. (Such initial detections of new fungal species in out-of-native-range plantations is a usual occurrence.)

Over the 100-year history of planting eucalyptus outside Australasia, dozens of leaf pathogens have been transported to novel regions. Crous et al. 2019 report the wide geographic breadth of many of these introductions. For example, Mycosphaerella heimii is crippling plantation forestry in five global regions – South America (Brazil and Venezuela); Asia (Indonesia and Thailand); Africa (Madagascar), Europe (Portugal); and in its presumably native Australia. A second species, M. marksii, has a similarly wide introduced range: Portugal, China and Indonesia, South Africa, Ethiopia, and Uruguay. Pérez et al. calls Mycosphaerella leaf diseases one of the most important impediments to Eucalyptus plantation forestry in Uruguay.

Although Crous et al. do not provide dates of detection, it appears that many of these leaf pathogens were introduced outside Australasia before the mid-990s, when the World Trade Organization (WTO) and International Plant Protection Convention (IPPC) came into force. Together, these agreements govern what actions phytosanitary officials may take to curtail international movement of plant pests. (To see my critique of the WTO/IPPC system, visit here.) The possible exception might be Kirramyces gauchensis, a well-known pathogen of Eucalyptus grandis in South America (Argentina and Uruguay), Hawai`i, and Africa (Uganda and Ethiopia) (Pérez, et al. 2009). Crous et al. (2019) expect another genus, Quambalaria species, to become a threat to eucalypt plantation forestry globally in the future.

Phoracantha semipunctata; photo by Umo Schmidt via Flickr

Arthropod pests have also been spread to many Eucalyptus-growing regions in North and South America, Europe and Africa since the 1980s. Some species have colonized virtually all eucalypt-growing regions, e.g., Phoracantha semipunctata. Some have – so far – appeared on only one continent.

In an effort to determine how many of these introductions have occurred after adoption of the WTO/ IPPC system, I Googled the species named by Paine et al. (2011). I used the year 2000 as the cutoff date, to allow for detection lag. Among the insect species that fit this criterion are a lerp psyllid, a leaf beetle, and two gall wasps detected in North America; a true bug, two galling insects, and a leaf beetle in South Africa; and three psyllids in Europe.

Asia stands out as having very few introduced Australian insects plaguing eucalyptus plantations. Only one insect of Australian origin is causing significant damage in this region, Leptocybe invasa. It was detected after 2000, so it might have been introduced under the WTO/IPPC regime. Many widespread species, e.g., Phoracantha semipunctata, are notably absent. Instead, large numbers of endemic insects use these trees. This contrasts with the situation in the Southern Hemisphere, where few of the numerous native insects have shifted onto eucalypts.

New Zealand has detected only two new species of Australian origin since 1999 — two psyllids. This is despite the two nations’ proximity, the large volume of trade that passes between them, and the likelihood that at least some small sap-suckers might be introduced via aerial dispersal. New Zealand is famous for its strict phytosanitary (and sanitary) policies and programs.

Eucalyptus plantation in Kwa-Zulu, South Africa

Plantations’ vulnerability has been increased by expanding reliance on clonal, artificially-induced hybridization. Developers’ goals – and initial results – are enhanced adaptation to specific environments, desired fiber characteristics, and hybrid vigor. However, these vast areas planted in genetically identical trees are sitting ducks. An insect or pathogen that overcomes the host’s defenses can spread rapidly across the entire planting.

These hybrids also can act as “bridges,” facilitating spread of fungi to formerly resistant host species. Crous et al. (2019) fear that this process will undermine resistance in Eucalyptus pellita to the pathogen Teratosphaeria destructans. Plantations in Southeast Asia and South Africa now comprise hybrids between this resistant species and the highly susceptible Eucalyptus brassiana.

Pines

As with the eucalypts, the intensively managed pine plantations are comprised of fast-growing exotic species, all at the same developmental stage, and with minimal genetic diversity, planted to maximize wood production. These practices again lead to biological homogenization and reduced resilience to pests (Villacide and Fuetealba, 2025)

In the Southern Hemisphere, Sirex noctilio has become the most significant economic pest of Pinus species. These attacks can cause up to 80% mortality. Several other Sirex species have also been introduced, all apparently in the 1980s or earlier (Wilcken et al., 2025) – before adoption of the current international phytosanitary regime. However, in 2023, a new species, Sirex obesus, was discovered causing tree mortality in pine plantations in southeastern Brazil. This species is indigenous to the United States and Mexico.

Stazione et al. (2026) discuss two other non-native pine pests that established recently in South America.

Analysis of mitochondrial DNA of Orthotomicus erosus points to a western Eurasian lineage. The low genetic diversity of the introduced population in Argentina and Uruguay suggests a single or limited introduction event followed by regional spread.

The source region of Cyrtogenius luteus is more difficult to determine but is probably somewhere in China. The higher haplotype diversity might reflect multiple introductions. Again, shared haplotypes between Argentina and Uruguay countries indicates a contiguous regional spread, possibly driven by extensive pine plantations & intra-regional trade (Stazione et al. 2026)

Policy Aspects

Some scientists express concern about the failure of international phytosanitary measures. But are their countries speaking up in regulatory bodies, especially the International Plant Protection Convention?

Studies by Crous et al. (2019) and Pérez et al. (2009) clearly show that pathogens from Australia continue to be transported to regions where eucalypt plantations are grown. This happens despite most of the movement of genetic material being in the form of seeds – which should be less likely to transport pathogens than trade in plants. Pérez et al. (2009) explicitly raise concerns about the effectiveness of current quarantine procedures. Crous et al. (2019) state that quarantines continue to fail in many parts of the world.

Burgess and Wingfield (2017) list pathogens that have spread widely since the beginning of the 21st Century: Austropuccinia psidii, Calonectria (= Cylindrocladium) eudonaviculata (=Cylindrocladium buxicola), Ceratocystis lukuohia and C. huliohia introduced to Hawai`i. I add that insect-vectored diseases such as Euwallacea species carryingFusarium fungi have also experienced a burst of introductions around the globe since 2000.

Crous et al. (2019) attribute this failure partially to the enormous difficulty of applying effective quarantine to the huge volumes of planting material traded globally. Another factor is undoubtedly the poor understanding of microbial species, their pathogenicity, hosts, pathways of spread, even taxonomies. Some genera cannot be grown in culture.

Furthermore, pathogens’ impacts vary, possibly due to environmental conditions of the location or differing virulence on different hosts. Finally, with so many fungi and so little knowledge, it is difficult to separate true disease agents from multiple secondary infections.

Crous et al. (2019) express the hope that increased recognition of the importance of pathogens, along with improved detection and identification tools, will clarify patterns of spread. But is that enough? Are there no policy changes needed?

Crous et al. (2019) also warn us about additional pathways for spreading pathogens. Some potential pathogens of eucalypts have been moved on plants of other, related genera. Furthermore, Botryosphaeriaceae have been detected in the skins of mangoes (Mangifera indica) and avocados (Persea americana). Both of these fruits move globally in large volumes.

mangoes; photo by Obsidian Soul via Wikimedia

Regarding insects, Paine et al. (2011) focus on a concern that species native to the plantation countries and generalist herbivores from other parts of world will invade Australia and threaten eualypts in their native ranges. See other blog They also call for research to understand international pathways, develop detection methods, improve understanding of patterns of host suitability, susceptibility, and selection.

Villacide and Fuetealba (2025) note that while the introductory pathway for that new species, Sirex obesus, has not been determined, they suspect it might have been wood packaging materials. Villacide and another colleague (Lantschner and Villacide 2025) suggest an initial step would be for Argentina and other countries in the region to negotiate with Brazil to adopt more protective protocols governing trade in wood products, including wood packaging.

I have repeatedly advocated strengthening regulation of wood packaging. Such measures could improve protection of Earth’s forests from pests that use a well-documented high-risk introductory pathway. To see my arguments and underlying data, scoll down below the “archives” to “Categories” and click on “wood packaging”.

SOURCES

Burgess, T.I. and M.J. Wingfield. 2017. Pathogens on the Move: A 100-Year Global Experiment with Planted Eucalypts. Bioscience. Volume 67, Issue 1, January 2017. https://doi.org/10.1093/biosci/biw146

Crous, P.W., M.J. Wingfield, R. Cheewangkoon, A.J. Carnegie, T.I. Burgess, B.A. Summerell, J. Edwards, P.W.J. Taylor, and J.Z. Groenewald. 2019. Folia pathogens o eucalypts. Studies in Mycology 94:125-298 (2019).

Lantschner, V. and J. Villacide. 2025. Invasion Potential of the Recently Established Woodwasp Sirex obesus. Neotropical Entomology. (2025) 54:117  https://doi.org/10.1007/s13744-025-01347-6

Paine, T.D., M.J. Steinbauer, and S.A. Lawson. 2011. Native and Exotic Pests of Eucalyptus: A Worldwide Perspective. Annu. Rev. Entomol. 2011. 56:181-201

Payn, T., J-M. Carnus, P. Freer-Smith, M. Kimberley, W. Kollert, S. Liu, C. Orazio, L. Rodriguez, L. Neves Silva, M.J. Wingfield. 2015. Changes in planted forests and future global implications. Forest Ecology and Management 352 (2015)

Pérez,, C.A., M.J. Wingfield, N.A. Altier, and R.A. Blanchette. 2009. Mycosphaerellaceae and Teratosphaeriaceae associated with Eucalyptus leaf diseases and stem cankers in Uruguay For. Path. 39 (2009) 349–360   doi: 10.1111/j.1439-0329.2009.00598.x www3.interscience.wiley.com

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

Villacide, J. and A. Fuetealba. 2025. Pests in plantations: Challenging traditional productive paradigms in the Southern Cone of America. Forest Ecology and Management 597 (2025) 123127

Wilcken, C.F., T.A. da Mota, C.H. de Oliveir, V.R. de Carvalho, L.A. Benso, J.A. Gabia, S.R.S. Wilcken, E.L. Furtado, N.M. Schiff, M.B. de Camargo, M.F. Ribeiro. 2025. Sirex obesus (Hymenoptera: Siricidae) as invasive pest in pine plantations in Brazil. Scientific Reports. 2025. 15:22522  https://doi.org/10.1038/541598-025-06418-7

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

Threat to Native Myrtaceae in South America

Blepharocalyx salicifolius – a tree in the Myrtaceae native to South America on which found symptoms similar to those caused by Mycosphaerellaceae or Teratosphaeriaceae; photo by Pablo di Flores via Wikimedia

Pests that have followed their hosts to plantations outside the trees’ native ranges might threaten native plants in their new, introduced ranges. That is, the countries where the plantations are located.

Eucalypts

Eucalypts are now the most widely planted hardwood timber taxon in the world (Paine et al 2011). The 700 – 800 species in the three genera considered “eucalypts” (Angophora, Corymbia, and Eucalyptus) host a highly diverse fungal community — more than 500 species have been identified of just one type, leaf-infecting fungi (Crous et al. 2019).

As I described in a related blog, link dozens of leaf pathogens have been transported to countries hosting eucalypt plantations. Among them, two families – Mycosphaerellaceae and Teratosphaeriaceae – are prominent in both numbers of introductions and potential to cause serious diseases.

Nunez Chapa

Pérez et al. (2009) reported that a relatively large number of Mycosphaerellaceae and Teratosphaeriaceae are found on Eucalyptusin Uruguay. The authors cite one troubling case of host shifting: Mycosphaerella lateralis is causing leaf disease on a Musa cultivar (banana!) which is not in the Myrtaceae.

A follow-up study by the same authors (Pérez et al. 2013) surveyed several native forests, paying special attention to those located close to Eucalyptus plantations. They found five species belonging to the Mycosphaerellaceae and Teratosphaeriaceae clades on native Myrtaceous trees; three of these had previously been reported on Eucalyptus in Uruguay. Those occurring on both Eucalyptus and native Myrtaceae included Pallidocercospora heimii, Pseudocercospora norchiensis, and Teratosphaeria aurantia. A fourth species, Mycosphaerella yunnanensis, not previously recorded in Uruguay, was found on the leaves of two native Myrtaceous hosts. Pérez et al. (2013) believe circumstances indicate that all these fungi have been introduced. They warn that these apparent jumps to new hosts have the potential to result in serious disease problems and they should be carefully monitored. This finding is more than a decade old; I have not found a more recent report.

On the global level, Pérez et al. (2013) report, at least 23 species of Mycosphaerellaceae and Teratosphaeriaceae have been found on non-Eucalyptus species in the Myrtaceae. These hosts are in several plant orders, including Myrtales, Proteales, Fabaes and Apiales. The authors express “considerable concern” about the apparent ease of movement in these fungi between hosts. I have been unable to learn more details about these introductions.

Arthropod pests have also been spread to many Eucalyptus-growing regions in North and South America, Europe, and Africa since the 1980s – but not to Asia or New Zealand (Paine et al. 2011). blog

Myrrhinium atropurpureum – another South American plant in the Myrtaceae on which symptoms found; photo by Prof. Atilio L, Botanical Garden of Uruguay

Pines

Pines – a genus restricted naturally to the Northern Hemisphere – is second in popularity for intensively managed plantations. South America has 4.6 million hectares of pine plantations (Lantschner and Villacide 2025). Most are in Brazil, Chile, Uruguay, and Argentina (Payn et al. 2015). 

Cinara cupressi; photo by LBM via Wikimedia

As I reported in an earlier blog, some of the insect pests that followed pines to South America have entered native forests. The most alarming of which I am aware is the aphid Cinara cupressi. It attacks the native conifer Austrocedrus chilensis, which forms pure and mixed stands with southern hemisphere beech (Nothofagus spp.) across approximately 160,000 hectares (Villacide and Fuetealba 2025). Cordilleran cypress is also under attack by the oomycete Phytophthora austrocedri, an oomycete of unknown origin.

Some scientists express concern about phytosanitary measures … but are their countries speaking up in meetings of the International Plant Protection Convention?

Studies by Crous et al. and Pérez et al. clearly show that pathogens from Australia continue to be transported to regions where eucalypt plantations are grown – despite the fact that most of the movement of tree genetic material is in the form of seeds – which should be less likely to transport pathogens than trade in plants. Pérez et al. (2009) explicitly raise concerns about the effectiveness of current quarantine procedures. Crous et al. (2019) state that the quarantines continue to fail in many parts of the world.

See my critique of the international phytosanitary system under the IPPC by visiting the Fading Forest II report (see link below) and reading other blogs under the categories “invasive species policy” and “plants as vectors of pests”.

SOURCES

Crous, P.W., M.J. Wingfield, R. Cheewangkoon, A.J. Carnegie, T.I. Burgess, B.A. Summerell, J. Edwards, P.W.J. Taylor, and J.Z. Groenewald. 2019. Foliar pathogens of eucalypts. Studies in Mycology 94:125-298 (2019)

Lantschner, V. and J. Villacide. 2025. Invasion Potential of the Recently Established Woodwasp Sirex obesus. Neotropical Entomology. (2025) 54:117  https://doi.org/10.1007/s13744-025-01347-6

Paine, T.D., M.J. Steinbauer, and S.A. Lawson. 2011. Native & Exotic Pests of Eucalyptus: A Worldwide Perspective. Annu. Rev. Entomol. 2011. 56:181-201

Payn, T., J-M. Carnus, P. Freer-Smith, M. Kimberley, W. Kollert, S. Liu, C. Orazio, L. Rodriguez, L. Neves Silva, M.J. Wingfield. 2015. Changes in planted forests & future global implications. Forest Ecology and Management 352 (2015)

Pérez, C.A., M.J. Wingfield, N.A. Altier, and R.A. Blanchette. 2009. Mycosphaerellaceae & Teratosphaeriaceae associated with Eucalyptus leaf diseases & stem cankers in Uruguay For. Path. 39 (2009) 349–360   doi: 10.1111/j.1439-0329.2009.00598.x www3.interscience.wiley.com

Pérez, C.A., M.J. Wingfield, N. Altier, and R.A. Blanchette. 2013. Species of Mycosphaerellaceae and Teratosphaeriaceae on native Myrtaceae in Uruguay: evidence of fungal host jumps. Fungal Biology Volume 117, Issue 2, February 2013.

Villacide, J. and A. Fuetealba. 2025. Pests in plantations: Challenging traditional productive paradigms in the Southern Cone of America. Forest Ecology and Management 597 (2025) 123127

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

Pest Threats to Eucalypts and Australia

Chilecomadia valdiviana – one of the South American moths that attack Eucalyptus; photo by Natural History Museum of London via Wikimedia

Fifteen years ago, Paine, Steinbauer, and Lawson (2011) worried that insects in South America, Africa, Asia, and Europe that adapt to attacking Eucayptus trees planted there might be introduced to Australasia and threaten the genus in its native range. Their analysis applies to species in all three genera considered to be “eucalypts” — Angophora, Corymbia and Eucalyptus.

Some insects native to those continents have made this host shift already. Paine, Steinbauer, and Lawson reported that such host switching was especially prevalent among lepidopterans. They name several from Brazil, the Chilean cossid moth, Chilecomadia valdiviana, and southern African Coryphodema tristis. In their view, Brazilian eucalypt plantations’ proximity to native vegetation facilitates host-switching. Still, at that time they thought that there were no established pathways for introduction of the South American moths to Australia.

Host-switching is exceptionally common in Asia. Paine, Steinbauer, and Lawson (2011) thought the risk was greatest from insects on native eucalypts in near-neighbors Papua New Guinea, Timor, and The Philippines. An earlier risk assessment evaluating 10 insect species from the region concluded that most are polyphagous and probably switched to eucalypts. Two woodborers – Agrilus opulentus and A. sexsignatus –seem to have coevolved with Eucalyptus deglupta in New Guinea and The Philippines.

According to the same authors, most of the insects that have switched hosts are either polyphagous or normally feed on other myrtaceous species native to these regions. Thus, the Brazilian moth Thyrinteina arnobia feeds on Psidium guajava and several other Myrtaceae. Sarsina violascens is also a pest of Psidium species, as well as species in the Asteraceae, and Oleaceae. And the foliar rust Austropuccinia psidii was first described from Psidium guajava in Brazil and boasts a wide host range in the Myrtaceae in South America. It has been introduced to many regions with plants in the Myrtaceae, notably Hawai`i, Australia, South Africa, New Caledonia, and New Zealand. At least 15 Myrtaceae species in Australia are threatened with extinction.

Still, few non-native insects were damaging eucalypts in Australia’s native forests or plantations as of 2011. Those few are highly polyphagous. Several, if not most, were introduced in the first half of the 20th Century.

Why so few? Paine, Steinbauer, and Lawson (2011) suggest three possibilities: (a) Australia’s diverse endemic insects already occupy most niches, so they exclude new, foreign competitors; (b) most introduced insects were not previously exposed to Myrtaceae in their native range; and (c) Australia has strong quarantine procedures aiming to limit introductions of non-native herbivores.

The fact that none of the introduced insects has adapted to feed significantly on mature eucalypts’ above-ground tissues seems to me to point to protection provided by the adult trees’ phytochemicals and leaf structure. Paine, Steinbauer, and Lawson (2011) discuss some aspects of leaf structure and wax coatings.

As to Australia’s quarantine procedures, as I reported before, the country has been much less proactive regarding plant pests and diseases that threaten tree species rather than agricultural crops. Significant new programs were established only after 2000, when Plant Health Australia (PHA) was incorporated. The PHA is supposed to facilitate preparedness and response arrangements between governments and industry for plant pests (once an alien pest has become established, management becomes responsibility of the land manager). In 2005, federal, state, and territorial governments and plant industry bodies signed a legally-binding agreement — the Emergency Plant Pest Response Deed (EPPRD).  As of 2022, 38 were engaged. It sets up a process to implement management and funding of agreed responses to the detection of exotic plant pests – including cost-sharing and owner reimbursement.

Still, studies documented significant gaps in post-border forest biosecurity systems and the country’s response to the anticipated introduction of the foliar rust Austropuccinia psidii was disappointing. This prompted yet another initiative: development of the National Forest Biosecurity Surveillance Strategy (NFBSS) in 2018. The strategy was; accompanied by an Implementation Plan and appointment of a National Forest Biosecurity Coordinator. The forest sector fund a significant proportion of the proposed activities for the first five years. Still, Drs. Carnegie and Nahrung thought that in-country forest pest surveillance was still too fragmented.

Paine, Steinbauer, and Lawson (2011) consider the Asian spongy moths Lymantria dispar and Orgyia thyellina to pose serious threats. Five eucalypt species were assessed to be at risk of attack as are two preferred host oaks in Europe, Quercus pubescens and Q. robur. They note high volumes of imports from East Asia of containers, vehicles, and machinery, which are known to transport spongy moth egg-masses. It is not known whether the numerous natural enemies of Australia’s diverse lymantriid fauna [which includes four in the genus Lymantria] might provide some protection. These experts also worried that the highly polyphagous Asian longhorned beetle (Anoplophora glabripennis) might arrive in Australia. Eucalypts are not recognized as hosts.

Australia has adopted an enhanced surveillance program for ships arriving from Asian and European Lymantria ranges during female flight periods. Described here. Nahrung and Carnegie (2021) though that the high priority assigned to Lepidoptera exceeded the actual risk; only two non-native species had established in Australia over 130 years.

Paine, Steinbauer, and Lawson (2011) suggest several research topics aimed at reducing the risk to eucalypts in Australia. These include interactions between these insects and mechanisms by which insects adapt to new hosts; host chemistry and resistance mechanisms), chemical ecology (including host selection), population and community dynamics, including possible biocontrol agents, and pathway and risk analysis.

On the other hand, Carnegie and Nahrung (2019) called for developing more effective methods of detection, especially of Hemiptera and pathogens. They also promoted national standardization of data collection. Finally, they advocated inclusion of technical experts from state governments, research organizations and industry in developing and implementing responses to pest incursions. They noted that surveillance and management programs must expect and be prepared to respond to  introductions of unanticipated species. They had found that 85% of the pests detected over the last 20 years—and 75% of subsequently mid-to high-impact species established—were not on high-priority pest list.

SOURCES

Carnegie A.J. and H.F. Nahrung. 2019. Post-Border Forest Biosecurity in AU: Response to Recent Exotic Detections, Current Surveillance and Ongoing Needs. Forests 2019, 10, 336; doi:10.3390/f10040336 www.mdpi.com/journal/forests

Nahrung, H.F. and A.J. Carnegie. 2021. Border interceptions of forest insects established in Australia: intercepted invaders travel early and often. NeoBiota 64: 69–86. https://doi.org/10.3897/neobiota.64.60424

Paine, T.D., M.J. Steinbauer, and S.A. Lawson. 2011. Native & Exotic Pests of Eucalyptus: A Worldwide Perspective. Annu. Rev. Entomol. 2011. 56:181-201

Native & Exotic Pests of Eucalyptus: A Worldwide Perspective

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

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

Alaska yellow cedar (Chamaecyparis nootkatensis); one of the species vulnerable to Phytophthora austrocedri; APHIS has determined it is too late to try to slow its spread. Photo by Nucatum amygdalarum via Wikimedia

On 30 December 2025, US Department of Agriculture Secretary Brooke L. Rollins issued a Secretary’s Memorandum setting five new priorities for research and development. One is to protect agriculture from invasive species. Another is to resolve longstanding trade barriers due to sanitary and phytosanitary concerns.

The Secretary’s intention is to strengthen US agriculture to benefit both farmers and consumers. He justifies the action by claiming that President Lincoln’s original purpose in establishing USDA was to acquire and diffuse useful information on subjects connected with agriculture. According to this interpretation, Lincoln recognized that working to improve agriculture and secure the nation’s food supply would benefit everyone. The emphasis on research and development was reiterated by the almost simultaneous adoption of the Morrill Act of 1862, which created the system of land-grant universities and development of the Cooperative Extension System via the Smith-Lever Act of 1914.

The memorandum specifies five priority areas of research to be pursued by all USDA agencies and offices – to the maximum extent permitted by law and in accordance with any applicable regulations and procedural requirements.

  1. Increasing Profitability of Farmers & Ranchers — especially reducing volatility in profitability. Goals include reducing inputs or increasing mechanization and automation.
  2. Expanding Markets for US agricultural products. Two approaches are mentioned: generating science and data to resolve longstanding sanitary and phytosanitary trade barriers; and expanding use of agricultural commodities in novel biobased products and bioenergy.
  3. Protecting the Integrity of American agriculture from Invasive Species. The memorandum lists four examples of current invasive pest and pathogen threats: new world screwworm in Mexico; continued westward expansion of spotted lanternfly; persistence of highly pathogenic avian influenza in poultry flocks; and citrus greening. It notes that invasive species threaten both agriculture and natural resources. The research is to focus on new and effective methods for preventing, detecting, controlling,and eradicating these threats.
  4. Promoting Soil Health to Regenerate Long-Term Productivity of Land. The research is to promote soil health practices, increase water-use efficiency, & reduce the need for inputs.
  5. Improving Human Health through Precision Nutrition and Food Quality. Research on “precision nutrition” is said to improve understanding of how healthy dietary patterns impact individuals. Research will also focus on increasing foods’ nutritional content and quality.
Vaccinium myrtillus (photo by Anneli Salo via WikiMedia); one of several species in genera shared with North America that are infected by Phytophthora spp in the Italian alps

The memorandum also instructs USDA’s Office of the Chief Scientist (that is, the Under Secretary for Research, Education, & Economics) to coordinate these priorities within USDA and among key partners in other federal agencies.

Does This Policy Mean Substantially Stronger USDA Efforts to Counter Bioinvasions?

Can we expect new energy in USDA’s programs aimed at managing non-native forest pests and invasive plants that damage forests, wetlands, grasslands, and other natural systems? The first paragraph of the memorandum states that it is USDA policy to reaffirm a focus on the Department’s original objectives of maximizing and promoting American agriculture; ensuring a safe, nutritious, and secure food supply; enhancing rural prosperity; and protecting our National Forests & Grasslands. That is promising.

The explicit recognition that invasive species pose severe threats to both agriculture and natural resources is also promising. I welcome the inclusion of two plant pests among the examples. Livestock diseases usually receive far more attention in USDA pronouncements.

I note three caveats:

  • The prominence of enhancing markets for US agricultural exports (# 2). In the past, this longstanding emphasis has led to undercutting phytosanitary agencies’ ability to counter suspected — but incompletely understood — pest risks. I discussed the impracticality of determining a newly detected species’ probable impacts in Chapter 3 of my report, Fading Forests II.
  • The memorandum makes no reference to implementing stronger sanitary or phytosanitary policies. In my view, the Animal and Plant Health Inspection Service has sufficient knowledge to support adoption of a more assertive regulatory stance with regard to both new introductions and spread within the country? Does the memorandum signal support for such a stance by high-ranking USDA officials?

These officials have often reminded APHIS that it is not a research agency.  However, its staff do “methods development” and it funds considerable research through the Plant Pest and Disease Management and Disaster Prevention Programs – Section 7721 of the Plant Protection Act and a matching program for animal diseases.

  • The US Forest Service does have a research division – although the Trump Administration proposed its virtual elimination in early 2025. The Congressional appropriators have provided funding for USFS R&D – but those bills have not yet been enacted into law. I have complained for years that USFS R&D allocates too few resources (about 1% of the total budget) to research on introduced pests and disease pathogens. Might this new directive help fix this problem?

I hope the emphasis on protecting National Forests & Grasslands does not result in narrowing the types of invasive pests addressed.

Posted by Faith Campbell

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

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

Or

https://fadingforests.org

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Applying the Results

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

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

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

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

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

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

SOURCE

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

Posted by Faith Campbell

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

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

Or

https://fadingforests.org