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 quarantinescontinue 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. 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
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 mothsLymantria 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
ovenbird (Seiurus aurocapilla); photo by Rhododentrities via Wikimedia
Studies of forest ecosystems in eastern North America that claim to be comprehensive still too often make no reference to invasive species – pests, earthworms, or plants. I try here to bridge these gaps.
Akresh et al. (2023) conducted a meta-analysis of bird species’ use of forests as nesting habitat. They applied the Partners-in-Flight to evaluate the community-wide bird conservation values of unmanaged forests compared to various levels of tree removal by harvest. Because of the decline of many bird species that prefer shrubland or early-successional stands, their process gave highest ranks to management approaches that retained 40%–70% of the canopy trees.
Their study notes that habitats for shrubland birds comprise only about 6% of forests in the eastern U.S. They don’t provide data for southeastern Canada. But hasn’t this scarcity of open upland, non-wetland, habitats in this region been true for thousands of years?
The type of forest that undoubtedly has shrunk significantly in recent centuries is “virgin” (or old-growth or late-seral) forests. As Akresh et al. (2023) report, contemporary closed-canopy forests in eastern North America are predominantly structurally homogeneous, mid-seral, even-aged, stands that have regenerated on land previously cleared for either agriculture or timber. These forests are much younger from a forest developmental perspective than precolonial forests; they lack the latter’s range of tree fall gap sizes and multiple age-classes. The tiny fraction of eastern forests that are in the late-seral stage might have higher species richness and conservation value for birds, but since they are usually not under management, Akresh et al. (2023) did not include that question in their analysis.
Akresh et al. (2023) list the bird species whose density appears to be closely linked to various tree canopy densities. For example, ovenbirds and brown creepers promptly decline in abundance in response to any amount of tree harvesting. Two other species — wood thrush and cerulean warbler — have declined steeply range-wide in recent decades. Nesting densities of three of these four species (excluding the warbler) are significantly higher in areas harvested in ways that retain a greater percentage of trees. Densities of another five bird species (Acadian flycatcher, hermit thrush, black-throated green warbler, and red-breasted nuthatch) are also higher in areas with a greater proportion of trees retained.
Another nine species had a more complex relationship with tree densities but still had lower densities in stands with low tree retention. These were blue-gray gnatcatcher, blue-headed vireo, blackburnian warbler, black-throated blue warbler, eastern wood-pewee, least flycatcher, red-eyed vireo, scarlet tanager, and yellow-bellied sapsucker. They found little relationship between bird density and tree retention for five putative mature-forest species (American redstart, great-crested flycatcher, hooded warbler, veery, and yellow-rumped warbler).
scarlet tanager (Piranga olivacea); photographed in scrub at Edwin B. Forsythe (Brigantine) NWR by F.T. Campbell
Akresh et al. (2023) claim that silviculture approaches can be used to restore aspects of the structural and compositional conditions found in old-growth forests to second-growth systems, providing a potential pathway for rapidly increasing the conservation value of these areas for bird species. They advocate reducing canopies moderately via variable retention harvests, shelterwood establishment harvests, and irregular shelterwood systems. This strategy can increase understory vegetation density, which they assert can then increase foraging and nesting opportunities for both many mature-forest bird species and many shrubland birds.
I am skeptical; it is much easier to create openings in the canopy than to “create” large trees supporting cavities and associated fauna and flora utilized by some bird species. The authors do advise managers that late-seral, unharvested stands can provide important habitat for old-growth-dependent taxa and any intensive forestry should also take into account other factors.
old-growth hemlock stand in Cook Forest State Forest, Pennsylvania; photo by F.T. Campbell
In addition, often the understory vegetation that responds to the more open environment will be invasive non-native plants. Already about half of eastern U.S. forests have been invaded by non-native plants (Oswalt et al. 2016; Kurtz 2023). Many of these are shrubs: honeysuckles, privets, roses, buckthorn. Management of these plants is difficult – especially when opening the canopy to allow light to reach the forest floor. (at www.nivemnic.us, scroll down to “categories”, click on “invasive plants”.) So the question arises, do the non-native plant species adequately substitute for native shrubs in providing resources needed by those birds?
Maybe. Gleditsch and Carlo (2014) found that a shrub layer dominated by non-native honeysuckle shrubs (Lonicera species) does support nesting populations of several common species, especially catbird (Dumetella carolinensis), American robin (Turdus migratorius ), and northern cardinal (Cardinalis cardinalis). However, they did not consider the species of concern to Akresh et al. (2023) – the rare species that prefer open-canopy, early-successional communities. So they do not inform us whether these high-priority species can utilize shrublands dominated by non-native species. Gleditsch and Carlo (2014) apparently did not find nests of several species considered to be associated with mature forests. So, again, these forests’ value for conservation remains unclear. Gleditsch and Carlo (2014) do counter earlier fears that these non-native shrubs are “traps” for nesting passerine birds. (The concern was that the plants’ structure facilitated nest raiding by predators.) They say, instead, that these plants’ effects are species-specific, context-dependent, and often a mix of both positive and negative outcomes.
invasive shrub honeysuckle; photo by Kevin Casper via public.domain.pictures.net
Akresh et al. (2023) also do not address the impact of browsing by super-abundant deer. Others (at www.nivemnic.us, scroll down to “categories”, click on “deer”.) have demonstrated that interactions of deer predation with invasive plants is especially damaging to native flora. Considering forests from Virginia to Maine, Miller et al. (2023) advise opening the canopy or subcanopy of forests to promote tree regeneration where deer and invasive shrubs overlap only where deer are controlled.
I have seen no recent analyses of the impact of widespread pest-caused tree mortality beyond some early efforts focused on eastern hemlocks and on high-altitude whitebark pines.
SOURCES
Akresh, M.E., D.I. King, S.L. McInvale, J.L. Larkin, and A.W. D’Amato. 2023. “Effects of Forest Management on the Conservation of Bird Communities in E North America: A Meta-Analysis.” Ecosphere 14(1):e4315. https://doi.org/10.1002/ecs2.4315
Gleditsch, J.M. and T.A. Carlo. 2014. Living with Aliens: Effects of Invasive Honeysuckles on Avian Nesting. PLOS One. September 2014. Volume Nine Issue Nine. E107120
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
Oswalt, C.M., S. Fei, Q. Guo, B.V. Iannone III, S.N. Oswalt, B.C. Pijanowski, K.M. Potter. 2016. A subcontinental view of forest plant invasions. NeoBiota. 24:49-54 http://www.srs.fs.usda.gov/pubs/48489
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
Alaska yellow cedar (Chamaecyparis nootkatensis); one of the species vulnerable to Phytophthora austrocedri; APHIS has determined it is too late to try to slow its spread. Photo by Nucatum amygdalarum via Wikimedia
On 30 December 2025, US Department of Agriculture Secretary Brooke L. Rollins issued a Secretary’s Memorandum setting five new priorities for research and development. One is to protect agriculture from invasive species. Another is to resolve longstanding trade barriers due to sanitary and phytosanitary concerns.
The Secretary’s intention is to strengthen US agriculture to benefit both farmers and consumers. He justifies the action by claiming that President Lincoln’s original purpose in establishing USDA was to acquire and diffuse useful information on subjects connected with agriculture. According to this interpretation, Lincoln recognized that working to improve agriculture and secure the nation’s food supply would benefit everyone. The emphasis on research and development was reiterated by the almost simultaneous adoption of the Morrill Act of 1862, which created the system of land-grant universities and development of the Cooperative Extension System via the Smith-Lever Act of 1914.
The memorandum specifies five priority areas of research to be pursued by all USDA agencies and offices – to the maximum extent permitted by law and in accordance with any applicable regulations and procedural requirements.
Increasing Profitability of Farmers & Ranchers — especially reducing volatility in profitability. Goals include reducing inputs or increasing mechanization and automation.
Expanding Markets for US agricultural products. Two approaches are mentioned: generating science and data to resolve longstanding sanitary and phytosanitary trade barriers; and expanding use of agricultural commodities in novel biobased products and bioenergy.
Protecting the Integrity of American agriculture from Invasive Species. The memorandum lists four examples of current invasive pest and pathogen threats: new world screwworm in Mexico; continued westward expansion of spotted lanternfly; persistence of highly pathogenic avian influenza in poultry flocks; and citrus greening. It notes that invasive species threaten both agriculture and natural resources. The research is to focus on new and effective methods for preventing, detecting, controlling,and eradicating these threats.
Promoting Soil Health to Regenerate Long-Term Productivity of Land. The research is to promote soil health practices, increase water-use efficiency, & reduce the need for inputs.
Improving Human Health through Precision Nutrition and Food Quality. Research on “precision nutrition” is said to improve understanding of how healthy dietary patterns impact individuals. Research will also focus on increasing foods’ nutritional content and quality.
Vaccinium myrtillus (photo by Anneli Salo via WikiMedia); one of several species in genera shared with North America that are infected by Phytophthora spp in the Italian alps
The memorandum also instructs USDA’s Office of the Chief Scientist (that is, the Under Secretary for Research, Education, & Economics) to coordinate these priorities within USDA and among key partners in other federal agencies.
Does This Policy Mean Substantially Stronger USDA Efforts to Counter Bioinvasions?
Can we expect new energy in USDA’s programs aimed at managing non-native forest pests and invasive plants that damage forests, wetlands, grasslands, and other natural systems? The first paragraph of the memorandum states that it is USDA policy to reaffirm a focus on the Department’s original objectives of maximizing and promoting American agriculture; ensuring a safe, nutritious, and secure food supply; enhancing rural prosperity; and protecting our National Forests & Grasslands. That is promising.
The explicit recognition that invasive species pose severe threats to both agriculture and natural resources is also promising. I welcome the inclusion of two plant pests among the examples. Livestock diseases usually receive far more attention in USDA pronouncements.
I note three caveats:
The prominence of enhancing markets for US agricultural exports (# 2). In the past, this longstanding emphasis has led to undercutting phytosanitary agencies’ ability to counter suspected — but incompletely understood — pest risks. I discussed the impracticality of determining a newly detected species’ probable impacts in Chapter 3 of my report, Fading Forests II.
The memorandum makes no reference to implementing stronger sanitary or phytosanitary policies. In my view, the Animal and Plant Health Inspection Service has sufficient knowledge to support adoption of a more assertive regulatory stance with regard to both new introductions and spread within the country? Does the memorandum signal support for such a stance by high-ranking USDA officials?
These officials have often reminded APHIS that it is not a research agency. However, its staff do “methods development” and it funds considerable research through the Plant Pest and Disease Management and Disaster Prevention Programs – Section 7721 of the Plant Protection Act and a matching program for animal diseases.
The US Forest Service does have a research division – although the Trump Administration proposed its virtual elimination in early 2025. The Congressional appropriators have provided funding for USFS R&D – but those bills have not yet been enacted into law. I have complained for years that USFS R&D allocates too few resources (about 1% of the total budget) to research on introduced pests and disease pathogens. Might this new directive help fix this problem?
I hope the emphasis on protecting National Forests & Grasslands does not result in narrowing the types of invasive pests addressed.
Posted by Faith Campbell
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
It used to be thought that closed-canopy forests are resistant to bioinvasion because of the low light availability and relatively infrequent disturbance. Yet many are badly invaded! (On this site, scroll down past the Archives, choose “invasive plants” category.)
Nor is it just temperate forests in North America. Subtropical and tropical forests have also been invaded, as have the temperate forests of South America and, to a lesser extent, Europe. Temperate forests in Asia are less invaded; boreal forests very little (Fridley et al. 2025; see full citation at the end of this blog).
Fridley et al. (2025) have proposed a conceptual model to explain how this happens: “superinvaders” – a special class of woody plants – that achieve competitive dominance across a wide range of forest conditions. The “superinvaders” pose especially grave threats to native biodiversity because they use life-history strategies unlike those of early successional native species.
The result is that existing invasion and succession theories poorly predict which forests are most invasible and by which species. This failure undermines pest risk analyses and early detection.
Fridley et al. have raised lots of interesting ideas – some of which cannot yet be demonstrated by observations.
Temperate forests of North and South America are increasingly dominated by non-native deciduous and semi-evergreen shrubs and trees that combine fast growth rate in high light and high survivorship in forest interiors. These traits enable them to outcompete the native species. Many invaders also produce many more seeds than co-occurring native species. Similar traits are found in the successful non-native plants in subtropical and tropical forests.
Amur honeysuckle via Flickr
Fridley et al. stress that shade tolerance alone does not endow the invasive plants with sufficiently large advantages in their competition with native species. The forest “superinvader” phenotype must combine this ability to persist in shade with high maximum growth rate and high fecundity when conditions become favorable for reproduction.
They explain the invader’s competitive advantage as the result of their experiencing relatively fewer carbon costs because of enemy release in the novel environment, recent environmental changes that alleviate some stress formerly present in the novel environment, or phylogenetic constraints on the local flora that limit natives’ resource-use efficiency. The non-native plant species enjoy this advantage regardless of whether they also possess other competitive mechanisms, e.g., production of allelopathic compounds, denser growth or shading, greater apparent quantum yield. However, Fridley et al. concede that they lack sufficient evidence to incorporate these other competitive mechanisms into their model.
Since any reduction in carbon costs will enhance both shade tolerance and growth rate when light levels are high, these “superinvaders” can outcompete native species in either situation.
To support these concepts, Fridley et al. note that increased abundance of invaders following disturbance is more pronounced in forests than other habitats. They suggest this is because of the much greater magnitude of change in light levels in forests than in open habitats such as grasslands.
They propose that an analogous situation applies to the presence or absence of mutualist microbial associations, although existing studies are insufficient to reach conclusions about the role of carbon allocation to mycorrhizae in the “superinvader” phenotype. The extent to which these forest invasions alter ecosystem-level carbon dynamics, especially soil processes and litter decomposition is also largely unknown.
Fridley et al. emphasize the role of carbon costs in driving both growth rate and whole-plant light compensation point. This point is defined as the light level at which carbon gain through photosynthesis balances carbon losses from tissue respiration (maintenance and growth) and turnover (shedding and loss from disturbance and herbivory).
To survive in low-light conditions, plants must minimize tissue respiration and turnover. The traits that enable those behaviors have been thought to prevent rapid growth and competitive dominance in high-light conditions. However, the “superinvaders” defy this trade-off by growing faster than most co-occurring native species when light is abundant. Fridley et al. say this is because the plants’ reduced carbon costs enhance competitive advantage in both shade and adequate light conditions.
Fridley et al. name several reasons why a native plant’s carbon costs might exceed those of an introduced species. First on the list is either herbivory or investment in defensive traits. Native plants might be challenged by rising abundance or consumption rates of native or introduced herbivores, such as deer or seed predators, that avoid the introduced species.
A second factor is that the non-native species expends fewer resources to sustain adaptations that confer resistance to other stresses, such as drought or freezing. If a long-standing stress is weakened by global change processes (e.g., atmospheric CO2 levels, growing season duration, precipitation levels and seasonality, suppression of fire, atmospheric nitrogen deposition), a non-native plant that lacks defenses against that now-weakened stress will have a lower carbon cost and therefore an advantage. In some cases, the non-native species might benefit directly from these changes, e.g., droughts.
In some regions phylogenetic constraints have limited evolution of adaptive solutions to various biotic and abiotic stresses. This is most obvious on tropical oceanic islands. Fridley et al. report that native trees in Hawaiian montane rain forests are less energy-efficient conducting photosynthesis than are the invaders. However, this phenomenon also occurs on continents. Two continents’ floras might experience different climatic histories even when at they are at similar latitudes. For example, Eurasian woody species leaf out earlier and senesce later than North American trees and shrubs – possibly as a result of more predictable spring and autumnal climate across Eurasia. They name as one example Norwegian maple (Acer platanoides) in North America.
The future is uncertain
Fridley et al. consider enemy release to be a key factor in these shrub invasions of closed-canopy forests. Therefore, if enemy release decays over time because the introduced plant species accumulate pests, or the forest environment shifts to favor more stress-tolerant phenotypes of some native species, then the dominance of superinvaders will decline. If, on the other hand, resource enrichment continues, e.g., nitrogen deposition and elevated CO2, the impacts of woody invaders – present or newly introduced – might continue to rise. The likelihood that additional introductions of more resource-efficient species will continue to damage floras of oceanic islands.
Implications for risk assessments and management
Fridley et al. warn that habitat-matching criteria might be unreliable predictors of forest invasiveness. Among several examples of species that are invasive in interior forest systems in a novel region that do not exhibit this trait in their native range is red oak (Quercus rubra). It is locally dominant in both natural and managed forests in central Europe while in North America, red oak struggles to regenerate in closed-canopy forests. They suggest that Q. rubra in Europe has escaped seedling pathogens present in its native range in North America.
red oak sapling in swampy forest in Virginia; photo by F.T. Campbell
Fridley et al. call for research on traits they have identified as important but that are rarely measured in invasion studies. These include rates of tissue loss and respiratory processes above- and below- ground, plant carbon allocation to tissues and processes, and the whole-plant light compensation points of native and invasive plant species.
The Fridley et al. hypothesis has been supported explicitly by Kinlock et al. (2025). This article says that consistent findings have been reported by earlier small-scale studies in U.S. forests.
I ask for your input on how well the Fridley et al. hypothesis explains shrub and tree invasions in American forests – including those on tropical islands! Is it helpful? Is APHIS incorporating these ideas into plant risk assessments? –
Fridley et al. take pains to reiterate the long-accepted importance of ornamental horticulture in explaining invasive plants’ entry and establishment. They do so in the context of concurring that ruderal traits are not universally advantageous; traits’ benefits depend on the landscape into which the species was being introduced.
SOURCES
Fridley, J.D., P.J. Bellingham, D. Closset-Kopp, C.C. Daehler, M.S. Dechoum, P.H. Martin, H.T. Murphy, J. Rojas- Sandoval, D. Tng. 2025. A general hypothesis of forest invasions by woody plants based on whole-plant carbon economics.
Kinlock, N.L., D.W. Adams, W. Dawson, F. Essl, J. Kartesz, H. Kreft, M. Nishino, Jan Pergl, P. Pyšek, P. Weigelt and M. van Kleunen. 2025. Naturalization of ornamental plants in the United States depends on cultivation and historical land cover context. Ecography 2025: e07748 doi: 10.1002/ecog.07748
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
Kevin Saville reports for the Journal of Commerce that containerized imports in 2025 are expected to be only 25.2 million TEUs, a decrease of 1.4% from 2024.
Declines are particularly large in the final months of 2025 since importers frontloaded their purchases to try to get ahead of the Trump Administration’s new tariffs. Imports for the first half of the year were up 3.6% compared with 2024 at 12.53 million TEUs. Thus, Saville’s sources expect November import levels to be 11.6% lower than in November 2024; December’s to be almost 13% lower.
Analysts expect the steeper decline to continue into the new year. Ben Hackett, of Hackett Associates, expects import volumes in the first four months of 2026 to be 10.3%, 8.5%, 16.8% , and 11% lower than the corresponding months a year earlier. The data source covers the ports of Los Angeles/Long Beach, Oakland, & Seattle & Tacoma on the West Coast; New York/New Jersey, the Port of Virginia, Charleston, Savannah, Port Everglades, Miami & Jacksonville on the East Coast; & Houston on the Gulf Coast. These are not all the maritime ports, but they are the major ones.
Another JOC reporter, Michael Angell, quoted several sources as saying they expect import volumes for all of 2026 to be flat or down 2% from 2025. Illustrating the reversal from past trends, The Port Authority of New York and New Jersey expects total container volumes in 2026 to be 8.5 million TEUs, a decline of about 2% from 2024. Since 2016, NY-NJ port container volumes have grown at an annual average of 4.2%.
As I have blogged before — see here and here — these swings in import volumes threaten to undermine programs intended to prevent introductions of wood-boring insects hitching rides in wood packaging material. While the higher volumes arriving from Asia in the first half of 2025 pose the most obvious risk, falling volumes reduce fee-based funding that support port inspectors. Another factor is the shift to suppliers other than China – primarily countries in Southeast Asia. Two beneficiaries of this shift are Vietnam and – at least initially – India. They have much better records of compliance with ISPM#15-mandated treatments for wood packaging link than does China.
A third JOC source reports that while US and European imports are down, trade volumes in Asia, Africa, the Middle East and Latin America are rising. I expect this growing trade to facilitate new pest introductions, although we will have to wait several years to see any data.
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
Erythronium americanum dominating herb layer in woods owned by the Institute for Advanced Studies, Princeton, in the 1970s; photo by F.T. Campbell
I fell in love with spring ephemerals in the woods of the Institute for Advanced Studies in Princeton. While the degree I was pursuing had no relationship to birding in the swamp, I spent a lot of time enjoying the woods. At that time, more than 50 years ago, the herbaceous layer was dominated by spring beauties (Claytoniavirginica), trout lilies (Erythronium americanum), and violets (Viola species).
Beyond the beauty that delights us (or at least, me!), spring ephemerals are important ecologically. They support specialist pollinators and reduce nutrient losses at a time of year when vegetation cover is low and leaching and runoff rates high.
In the decades since I left Princeton, scientists and nature lovers have observed declines in native understory plant communities. These are predicted to continue due to invasion by plants and worms, worm blogs herbivore pressure by deer, E NPS blog, Blossey blog land use changes, and climate change.
Where I live, in the suburbs of the District of Columbia, these forces are clear. The formerly glorious riparian forests where I walk are overrun by invasive plants. The herb layer is dominated by Japanese stiltgrass (Microstegium vimineum) and – increasingly — lesser celandine (Ficaria verna = Ranunculus ficaria). (I found it interesting that Ficaria began taking over floodplain forests only in the last decades of the 20th century, although it was introduced more than 100 years earlier.) Many invasive shrubs (Rosa multiflora, various Lonicera species. …) and vines (Ampelopsis sp, Orbiculatus, Lonicera japonica, Hedera helix …) compound the problem. While I am not sure whether most earthworms here are native or not, high deer populations certainly are a factor.
Ficaria invasion in Fairfax County, Virginia in 2023; photo by F.T. Campbell
So I rejoice that scientists are studying how one taxon of spring ephemerals, trout lilies – Erythronium species – are coping with individual and combined threats. Gutiérrez and Hovick (full citation at the end of this blog) investigated how two species of Erythronium performed in the absence of a leaf litter layer – with and without competition by Ficaria. They chose to manipulate leaf litter as a proxy for impacts from invasive earthworms and non-native shrubs, especially those with rapidly decomposing leaves. They refer to others’ studies focused on different spring ephemerals.
Gutiérrez and Hovick found that the absence of leaf litter reduced asexual reproduction (corm biomass) in both Erythronium albidum and E. americanum species by 30%. That is, the absence of leaf litter alone reduced the native plants’ performance. This is alarming because persistent leaf litter has been reduced across much of the deciduous forests of eastern North America as a result of action by invasive earthworms and the rapid decomposition of the leaves of most invasive shrubs.
Trout lilies’ performance declined even more when litter absence was coupled with direct competition from Ficaria. Under those conditions, corm biomass declined by 50%. Impacts by lesser celandine occurred despite these plants’ being smaller than counterparts in nearby woodlands. The reduced size of Erythronium corms was sufficient, in their view, to reduce the likelihood that Erythronium would flower to nearly zero. This has clear implications for the long-term population viability of Erythronium andtheir specialist pollinators.
Gutiérrez and Hovick conclude restoration of these floodplain forests’ herb layer must incorporate management strategies that not only reduce Ficaria’s presence but also restore leaf litter.
Erythronium albidum along Accotink Creek in Fairfax County, Virginia; photo by F.T. Campbell
Underlying Factors
Native spring ephemerals in eastern North America evolved to emerge through litter layers in early spring. The litter layers impose both costs and benefits. In response to shading by leaf litter, Erythronium produces larger petioles compared to same-sized leaves, thus reducing the proportion of resources allocated to building photosynthetic tissue. In these cases, the corms that both perpetuate the individual and carry out asexual reproduction are smaller.
On the other hand, leaf litter increases moisture retention and reduces frost damage by buffering soil temperatures. While these results were seen in their experiment, Gutiérrez and Hovick believe the benefits are greater in nature than demonstrated in the study using potted plants. Leaf litter also increases nutrient availability, directly by increasing supply and indirectly by facilitating fine root growth. In this context, they note that their experiment used litter composed of just two tree species — red oak (Quercus rubra) and red maple (Acer rubrum). This narrow sample probably failed to capture the varied properties of other tree species’ litter and associated microbial activity.
Erythronium americanum along Pohick Creek; photo by F.T. Campbelle
Plants in the Erythronium genus reproduce primarily asexually through producing runners that form corms. The parent corm and runners disintegrate before summer dormancy; the offspring corms persist. Some individuals do not reproduce asexually; they simply replenish their own corm.
The few previous studies give mixed results regarding lesser celandine’s impacts on co-occurring native herbaceous plants (see the summaries in Gutiérrez and Hovick). The authors do not explicitly say whether lesser celandine is usually associated with low litter levels, but that appears to be the implication. They do say that it is not clear whether lesser celandine drives leaf litter loss by altering soil physiochemistry and microbial activity. Or, rather, that it simply performs well when leaf litter is absent.
Where lesser celandine and Erythronium co-occur at high densities, the former’s biomass per square meter can be more than an order of magnitude higher than Erythronium. Gutiérrez and Hovick suggest that competition between the species is primarily belowground. They cite their finding that by the time Erythronium shoots matured, lesser celandine roots occupied most of the belowground pot volume. They expect belowground competition in forests to be even more pronounced because of accumulated lesser celandine root biomass.
Aboveground, the principal factor appears to be the necessity for trout lilies to grow longer petioles to raise their leaves above lesser celandine rosettes, perhaps starving leaf formation. Since leaves are the plant’s photosynthetic organ, this tradeoff could ultimately result in fewer resources returned to the corm for future growth and reproduction. Although Gutiérrez and Hovick also mention that lesser celandine competition might delay Erythronium emergence and flowering, they do not discuss that.
A factor not mentioned by Gutiérrez and Hovick is the probability that Ficaria verna is allelopathic. See the article by Kendra Cipollini listed as a source at the end if this blog.
one of the few floodplains in Fairfax County still dominated by native herbs – Pohick Creek in the Burke area of Fairfax County, Virginia. Note the prevalence of beech in the canopy and subcanopy! photo by F.T. Campbell
Details of Impaired Performance of Erythronium
At the time of senescence, Erythronium plants grown in pots with leaf litter were nearly twice as large as those grown in bare soil conditions. One-third of their offspring corms grew to be larger than the putative biomass threshold for flowering. Only 9% of corms of plants grown in bare soil and 2% (one individual) of those grown with lesser celandine did. As noted above, corms developed by Erythronium grown in the presence of Ficaria actually lost biomass. This is the basis for their conclusion that there would be almost no sexual reproduction the following year where litter was absent and lesser celandine present.
Gutiérrez and Hovick think the principle mechanisms by which leaf litter affects performance of Erythronium plants is by buffering temperature ranges and increasing moisture retention. Indeed, they found that daily temperature ranges and maxima of soil in pots with bare soil or lesser celandine plants were both higher than temperatures under leaf litter. Reducing temperature maxima could be especially important with the increasing frequency and intensity of late-spring heatwaves associated with climate change. Absence of leaf litter advanced trout lily’s shoot emergence, flower emergence, and petal opening by 14 or more days.
This change might expose the plants to increased risk of frost damage. These dynamics will be system-specific, especially with complications added by climate change. However, Therefore, Gutiérrez and Hovick encourage future research to explore species-specific litter effects on spring ephemerals.
Broader Implications
Their findings regarding these two species of spring ephemerals prompt Gutiérrez and Hovick to assert that negative impacts from invasive plant species might be especially underestimated in spring ephemeral communities due to the combination of their short period of annual aboveground activity and tendency towards long lives. Changes might be very subtle over short timeframes.
They add that it is important to learn the role different conditions might play in the futures of related species. The two species’ ranges largely overlap, but E. americanum extends into the extreme southeast and northeast, E. albidum into the prairie states. Although these species’ respond to loss of leaf litter and lesser celandine invasions in similar ways, the fact that E. albidum occurs in areas of higher soil moisture makes it more vulnerable to negative population-level impacts from lesser celandine invasions.
Note about additional threats
Most of the photos of Erythronium americanum in this blog were taken along a particular creek in Fairfax County, Virginia. Ficaria has just begun to invade this area (see photo above); deer are plentiful. These plants face another bioinvasion: beech leaf disease has arrived. Widespread mortality of the predominantly beech understory will presumably open areas to more light, probably spread of the extant invasive plants.
beech in Fairfax County, Virginia with symptoms of beech leaf disease; photo by F.T. Campbell
SOURCES
Cipollini, K. and K.D. Schradin. 2011. Guilty in the Court of Public Opinion: Testing Presumptive Impacts and Allelopathic Potential of Ranunculus ficaria”
Gutiérrez, R.G. and S.M. Hovick. 2025. Compounding negative effects of leaf litter absence and belowground competition from an invasive spring ephemeral on native spring ephemeral growth and reproduction. Biol Invasions (2025) 27:213 https://doi.org/10.1007/s10530-025-03668-4
ohia trees killed by ROD near Pahoa, Hawai`i; with JB Friday; photo by F.T Campbell … APHIS has not applied NAPPRA to this pathogen
As I have documented numerous times in these blogs, [see here, here, here, here, here, here, here and here] forests throughout the world are being reshaped by rising numbers of introduced, non-native pathogens. Once established, these diseases are nearly impossible to contain, much less eradicate.
While the worst effect of such bioinvasions is widespread mortality of host species, even “lesser” results produce significant changes in the impacted ecosystems.
I believe that the international phytosanitary “system” adopted by the World Trade Organization (WTO) and amended by the International Plant Protection Convention (IPPC) in the mid-1990s impedes efforts to prevent introductions of pathogens. These rules require unattainable levels of certainty about an organism’s impacts before it can be restricted. Scientists such as Haoran Wu and Kenneth Raffa have called for phytosanitary approaches that will be more effective because they are realistic, reflect the true level of threat, and the limits of current science. I agree and have repeated their calls.
How Well Is This “System” Keeping Pathogens At Bay?
If the world’s phytosanitary system worked well, we should be seeing fewer high-risk forest pathogens being introduced to new countries. Instead, examples abound of pests invading new ecosystems in the post-WTO/IPPC era: Austropuccinia psdii — detected in Hawai`i in 2005, Japan in 2009, Australia in 2010, China in 2011, New Caledonia and South Africa in 2013, Indonesia and Singapore in 2016, and New Zealand in 2017.
Phytophthora ramorum – 8 to 14 additional introductions to California after its initial detection.
Fusarium disease vectored by beetles in the Euwallaceae genus:
Euwallacea fornicatus s.s.— detected in southern California in 2003, Hawai`i in 2007, Israel in 2009, in South Africa in 2012, in Australia in 2021, and in Argentina and Uruguay in 2023 and 2024 . The haplotype detected in South America and several European greenhouses differs from that established elsewhere.
E. kuroshio detected in southern California in 2013; has spread to nearby Mexico
E. interjectus detected in central California in 2024.
Boxwood blight fungus Calonectria pseudonaviculata — first detected in the Caucuses in 2010 and the US in 2011. Now established in at least 24 countries in three geographic areas: Europe and western Asia; New Zealand; and North America. Boxwood blight has caused rapid and intensive defoliation of native stands of Buxus sempervirens. Although disease was detected in United Kingdom in the mid-1990s, the causal agent was not determined until 2002.
Beech leaf disease caused by the nematode Litylenchus crenatae subsp. mccannii — detected near Cleveland, Ohio, in 2012. Has since spread east to the Atlantic Ocean, south to Virginia, north into Ottawa.
Phytophthora austrocedrii — detected in nurseries in Ohio and Oregon in 2024. Previously known from Argentina and in England and Scotland. At the latter location it is causing mortality of native Juniperus and introduced Cupressaceae. See here and here.
Most of these pathogens were unknown at the time they were discovered – because they were causing disease in the invaded ecosystems.
beech leaf disease symptoms in northern Virginia; photo by F.T. Campbell
In the Face of International Failures, How Can USDA’s APHIS Succeed?
When countries choose to prioritize preventing bioinvasions, they can impose more restrictive controls than those implemented by the WTO/IPPC system.
I urge USDA to more proactively use its authority to protect America’s plant resources. In particular, I urge USDA leaders to use the NAPPRA authority more effectively and quickly. This allows the agency to temporarily prohibit importation of plants that host potentially damaging pathogens. ). https://www.aphis.usda.gov/plant-imports/nappra
We Americans can’t protect our forests from pathogens without APHIS responding more promptly to recent detections of pathogens in North America and on Pacific islands. Recent events are not encouraging.
The agency did undertake an analysis of Phytophthora austrocedrii after it was detected in nurseries in two states. Unfortunately, in my view, APHIS and the states decided the pathogen was too widespread so they dropped any idea of regulating it. This was despite the apparent threat to junipers across the country. See here and here. P. austrocedri also attacks cypress trees, including Port-Orford cedar, Chamaecyparis lawsoniana. USFS scientists recently announced success in breeding POC trees resistant to a different pathogen.
There are no indications that APHIS will respond to detection of a new pathogen causing wilt disease in elms (Plenodomus tracheiphilus) recently discovered in Alberta, Canada. The pathogen is spread primarily through movement of infected plant material, including on asymptomatic material. Current U.S. regulations do not prohibit importation of plants or cut greenery in the Ulmus genus from Canada. Beyond the risk associated with elm material, I think it is probable that this pathogen also survives on plants in additional taxa, since it was formerly known for causing disease on citrus trees.
Although APHIS has classified Leptosillia pistaciae as a federal quarantine pest, I have learned of no response to detection of the pathogen on the native California shrub, lemonade berry (Rhus integrifolia), in 2019.
Rhus integrifolia – host of Leptosillia pistaciae
Has APHIS Changed its Practices in Response to Recent Detections?
We’ve known about gaps and weaknesses in APHIS’ approach for a long time. Here are specifics.
Has APHIS upgraded its attention to nematodes – as should have been prompted by detection of the beech leaf disease nematode (above) and as recommended by Kantor et al.?
Has APHIS changed any of its practices or policies in response to detection of plant and human pathogens associated with wooden handicrafts from countries other than China? Or wood pieces used for unanticipated purposes, e.g., to decorate aquaria? All 31 fungal taxa detected by one of these studies were viable despite having been subjected to various phytosanitary requirements.
USDA has no authority to regulate organisms that pose a risk to non-plant hosts, like us humans! Has APHIS contacted officials at the relevant agency?
Does APHIS respond to detections abroad when pests attack congeners of North American trees? I have blogged about several — see here, here, here and here — detected in Europe or Asia that attack cypress, magnolia, dogwood, Persea, and oaks. PestLens — an alert system created by APHIS — reported these.
How has APHIS incorporated the findings at various “sentinel garden” projects? And the wider implications of findings by Eliana Torres Bedoya and Enrico Bonello regarding findings on asymptomatic plants?
How is APHIS applying the impact assessment tools developed (for insects) by Ashley Schulz and Angela Mech? Has APHIS incorporated Kenneth Raffa’s advice about the strengths and weaknesses of various prediction tools?
I wonder whether APHIS has responded in any way to the rash of woodborer introductions on the west coast, including three species in the invasive shot hole borer complex and the Mediterranean oak borer. Has the agency explored the threat that the spotted poplar borer (Agrilus fleischeri) – another wood-boring beetle native to northern Asia – might pose to North American Populus species? Canada has twice intercepted the species on solid wood packaging material .
USDA APHIS is explicitly not a research agency. However, it claims that its decisions are science-based. In my view, this means APHIS has a responsibility to respond to scientific findings (such as those above) and to bring about research aimed at answering pertinent questions,e.g., those related to risks of pest introduction and establishment, effective detection and management technologies, etc.
APHIS has occasionally done this:
It established the NORS-DUC research facility to study what aspects of nursery management facilitate establishment of Phytophthora ramorum.
It enabled and participated in several studies of wood-borer introduction via wood packaging, including those by Robert Haack and colleagues (see blogs on this website under the category “wood packaging”).
It enabled and participated in a study of introduction pathways that included plants-for-planting – relying on 2009 data. (Liebhold et al. 2012)
Did APHIS support the study by Li et al. to evaluate the vulnerability of two oak and two pine species to 111 fungi associated with Old World bark and ambrosia beetles?
APHIS could do much more to determine whether North American trees are vulnerable to pathogens and arthropods detected on the congeners in trade partner countries. Opportunities include:
studying which North American species might be vulnerable to the growing number of the 38 new Phytophthora species detected overseas. This would be a monumental task: 216 species have been recognized in the genus. I have focused specifically on the 38 species detected by Jung, Brasier, and others in Vietnam and now the 18 Phytophthora species detected in the Alps. (I have already noted that APHIS and the states dropped any idea of regulating one of those species, P. austrocedrii).
Regarding P. ramorum specifically, scientists now recognize 12 genetic strains; 8 are in Southeast Asia, a ninth (EU2) in Europe. How likely is it that some of these will be introduced to the U.S.? Three strains are known to be established in western North American forests – NA1, NA2, and EU1.
In addition, new hosts continue to be identified. APHIS has pledged to update the host list annually. In the past I have criticized APHIS for not accepting hosts identified in the United Kingdom.
While APHIS is not well-funded, it has largely escaped budget slashing by “DOGE,” other Trump Administration cuts, and congressional decreases. Scientific expertise at the USDA Forest Service has been shrinking for decades (see Chapter 6). Now, loss of expertise has reached crisis levels. The result will be less capacity to assist APHIS in evaluating pest risks and research needs.
Earlier, I noted the importance of APHIS using its full NAPPRA authority. Unfortunately, the record is not encouraging here, either.
Since the agency gained this authority in 2011, it has adopted lists of species temporarily prohibited for importation only three times – in 2013, 2017, and 2021. I complained that the last action was tardy and provided insufficient protection to Hawai’i’s unique flora arising from multiple strains of the ‘ōhi‘a rust pathogen Austropuccinia psidii and here. Even worse, four years after promising to close the loophole that allowed continued imports of cut flowers and foliage – the most likely pathway by which the rust was introduced to Hawai`i, APHIS has not proposed the necessary rule.
Pathogens are more difficult to detect and manage than invasive insects. The “disease triangle” is complex! Numerous pathways are involved! But they also get less attention – and this reflects unwise decisions by agency leaders. I suggest that they should respond to this complexity by adding resources. Voglmayr et al. (full reference at the end of this blog) also called for more attention to pathogens. Kantor et al. noted that nematodes are also neglected.
Of course, I have repeatedly urged APHIS leadership to enhance enforcement of regulations governing imports of wood packaging. One suggestion is that it prohibit importation of Chinese wood packaging because of its 25-year record of not complying with – first – U.S. and Canadian regulations and – later – the international regulation known as ISPM#15.
Information Gaps Impede APHIS’ Domestic Program
I have criticized APHIS’ failure to find answers to several questions important to managing the sudden oak death pathogen, Phytophthora ramorum. Like the many questions listed earlier, these also need priority attention.
APHIS has regulated interstate movement of nursery stock to contain P. ramorum for over 20 years. I appreciate its creation of NORS-DUC. But it is also responsible for protecting natural systems in regions not yet invaded, e.g, in the East. APHIS should have studied these issues years ago, given the frequency with which pests spread nationwide via the nursery trade.
Other pathogen systems also have genetic variation that might be important in determining pest-host relationships. As of 2022, scientists had identified 43 haplotypes (genetic variants) of E. fornicatus s.s. worldwide, with the greatest diversity in several Asian countries (P. Rugman-Jones, pers. comm). Other species of plant pathogens also have several haplotypes.
Forests At Risk Outside of North America
North American forests are not alone in being besieged by non-native pathogens. Their numbers have been rising also in Europe and Oceania. The record is less clear in Africa, South America, and Asia.
Reports of tree pathogens in Europe began rising suddenly after the 1980s – admittedly 15 years before the WTO took effect. By 2012, more than half of infectious plant diseases in Europe were caused by introduction of previously unknown pathogens https://www.nivemnic.us/?p=5164
Antonelli et al. (full citation at the end of this blog) report that three previously undetected species of Phytophthora have been detected in European nurseries since 2016. Voglmayr et al. reported that the number of alien fungi in Austria increased 4.6-fold over 20 years. Eighty percent were plant pathogens. The introductory pathway was unclear for the vast majority. They note that differences in research efforts probably explain some discrepancies.
The ash decline pathogen, Hymenoscyphus fraxineus, has apparently been present in eastern Europe since the 1980s, so its spread has probably not been facilitated by the downsides of the WTO/IPPC system.
Other sources report recent introductions of insects to Europe. Musolin et al. reported that 192 species of phytophagous non-native insects had been documented in European Russia as of 2011. They included the emerald ash borer detected in Moscow in 2003. Some of these insects were probably introduced to Europe (outside Russia) before the WTO/IPPC system came into effect. Examples are two insects from North America that were detected in 1999 and 2000, respectively – the western coniferous seed bug, Leptoglossus occidentalis, which vectors a pathogenic fungus Sphaeropsis sapinea (=Diplodia pinea); and the oak lace bug, Corythucha arcuata.
Australia was slow to respond to detection of myrtle rust, Austropuccina psidii. Few federal resources were made available to study its impacts – although the Australian flora includes at least 1,500 species in the vulnerable plant family. Carnegie and Pegg said this experience demonstrated the need to integrate the work of agencies responsible for conservation of natural ecosystems with those determining and implementing phytosanitary policy. New Zealand initially responded more assertively, but also found little funding to support resistance breeding or even to track the rust’s spread.
The record is less clear regarding Africa, South America, and Asia.
Africa
Sitzia et al. expressed concern that bark and ambrosia beetles threaten to cause significant damage to tropical forests. Several factors contribute to these threats: the long history of plant movement between tropical regions; conversion of tropical forests that disturbs canopies, understory plant communities, and soils; and, generally, regions with fewer resources to prevent or respond to invasions.
In Africa, Graziosi et al. reported on the cumulative economic impact of invasive species and the continent’s limited capacity to prevent or respond to introductions. They don’t discuss whether pests attacking plantations of non-native trees followed those trees from their point of origin. They found that some introduced insects pose significant threats to native tree species. They mentioned the Cypress aphid, Cinara cupressi, which was attacking both native African cedar, Juniperus procera, and exotic cypress plantations. All the examples appear to have been introduced before the WTO/IPPC system took effect. All the examples appear to have been introduced before the WTO/IPPC system took effect.
Cinara cupressi; photo by Blackman & Eastop via Wikimedia
Graziosi et al. point out that South Africa plays a central role because it imports significant volumes of goods that can transport pests. At most immediate risk is South Africa’s highly diverse and endemic flora. For example Phytophthora cinnamomi is attacking native Proteaceae, which are important components of the unique Cape Floral Kingdom. Other pathogens are attacking native conifers in the Podocarpus genus, Ekebergia capensis (Meliaceae), and Syzygium trees. However, pests first introduced to South Africa often spread. Graziosi et al. name several insects and pathogens of Eucalyptus and the wood-boring pest of pine Sirex noctilio.
Pests in Asia
Available information about China is not definitive. The FAO reports that half of the most damaging forest pests are non-indigenous. They were estimated to occur over an area of 1.3 million ha and to kill over 10 million trees per year. However, the three tree-killing pests which receive the most attention are the pinewood nematode (Bursaphelenchus xylophilus), red turpentine beetle (Dendroctonus valens), and fall webworm (Hyphantria cunea). These were all introduced before the World Trade Organization was founded.
The FAO notes several non-native insects that attack native trees in India, but all were introduced decades before the World Trade Organization began. There is no discussion of tree pathogens.
Thu et al. report a growing number of pest outbreaks damaging plantations of non-indigenous trees in Vietnam. In most cases the pests are indigenous to the country. They report that almost nothing is known about pests that attack species in the highly diverse native forests.
The September 2025 meeting of the International Forest Quarantine Research Group (IFQRG) had a session devoted to the topic “Risk of international trade in plants for planting”. The specific presentations are titled
“Using molecular tools to elucidate the pathways of cryptic pests on plants for planting”
“Risk-based approach to the movement of germplasm into Australia: the luxury afforded to an affluent continent” (note my earlier blog criticizing Australian efforts re forest pests)
“Challenges in the validation of methods for detection of quarantine pathogen – P. ramorum”
“Challenges in surveillance and detection of quarantine fungal tree pathogens in European Union”
“Pathogens in trade and the risk of establishment – update”
I hope that some of these discussions begin to tackle the crucial questions I raised in this blog and earlier. Also, I hope IFQRG continues to explore these important questions.
As Wu and Raffa et al. have said, Earth’s forests cannot afford delay in finding solutions to the challenges posed by introductions of novel pathogens to naïve systems.
SOURCES
Antonelli, C.; Biscontri, M.; Tabet, D.; Vettraino, A.M. 2023. The Never-Ending Presence of
Phytoph Spp in Italian Nurseries. Pathogens 2023, 12, 15. https://doi.org/10.3390/pathogens12010015
Voglmayr, H., A. Schertler, F. Essl, I. Krisai-Greilhuber. 2023. Alien and cryptogenic fungi and oomycetes in Austria: an annotated checklist (2nd edition). Biol Invasions (2023) 25:27–38 https://doi.org/10.1007/s10530-022-02896-2
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
I, and many others, have given much attention to the emerald ash borer (EAB), a species in the Agrilus genus. This attention is deserved. In 30 years EAB has spread from then-localized infestations in Michigan and Ontario to natural and urban ash ecosystems across North America. The EAB is spreading in Europe, too.
coast live oak killed by GSOB at Heisey State Park, San Diego County, California; photo by F.T. Campbell
We have paid far less attention to a second Agrilus, the goldspotted oak borer (GSOB), Agrilus auroguttatus. In roughly 30 years, the GSOB infestation has become the primary agent of oak mortality across much of southern California, an area of roughly 37 million square miles. This is bigger than the combined land areas of West Virginia, Maryland, and Delaware.
While the number of trees killed has generally expanded slowly, there have been periods of explosive growth. For example, annual mortality was estimated to have reached 40,000 trees in 2017. The officially documented cumulative total is over 142,000. At least one scientist, Joelene Tamm, considers this number to be a significant underestimate; she estimates the true number of trees killed as probably close to 200,000. As she explains (see here), the USFS’ Aerial Detection Surveys is not very effective at capturing mortality within fragmented urban landscapes, narrow riparian corridors, or when the target species have sprawling canopies (as oaks do).
Ravaged oak forests grow on five mountain ranges. People losing valuable resources and paying to manage the invasion include
U.S. taxpayers — three National forests have lost oaks; a fourth Forest is on the brink;
Residents of California – trees killed in at least four State parks, 10 County parks, and two major private reserves;
Native Americans on at least five reservations
City dwellers and property owners: up to 300,000 coast live oak trees live in built-up sections of just one heavily infested city, Los Angeles.
areas vulnerable to GSOB
This damage is almost guaranteed to spread in the future. Three oak species host GSOB: coast live oak (Quercus agrifolia), California black oak (Q. kelloggii), and canyon live oak (Q. chrysolepis). The ranges of black and canyon live oak stretch north along the Coastal Mountain Range and the foothills of the Sierra Nevada Mountain Range into southwest Oregon. The range of coast live oak reaches Mendocino County. A risk assessment concluded that GSOB could invade all these regions. Among urban areas, Santa Barbara faces the highest risk because of the large number of oaks in its urban forest. While this county has not yet been invaded by GSOB, the beetle is now in adjacent Ventura County – although at the other end of the county.
GSOB is transported to new locations primarily by the movement of firewood. This means of human-assisted spread almost certainly explains its initial introduction to from southeastern Arizona to California – in eastern San Diego County – in the 1990s. (See here for the explanation why it is unlikely that the beetle would have spread to California through natural dispersal.) It is blamed for the establishment of numerous disjunct populations that propelled its spread. These outbreaks led to recognition of invasions in additional counties in new counties in 2012, 2014, 2015, 2018, and 2024.
Death of these trees causes numerous ecological impacts. Oaks provide food, habitat, and climate control for hundreds of species. Oak mortality also increases the probability and severity of wildfire. The few natural enemies, including woodpeckers and some parasitoids, are not keeping GSOB populations in check. Urban trees provide important ecological services, including shade which reduces energy use and expense associated with air conditioning; they also reduce storm water runoff. Larger trees – those preferred by GSOB – provide more of these services. Dead oaks not only deny people of these services; they also demand prompt removal to prevent them falling on people or structures; this is done at considerable expense.
GSOB invasions are now known to be present in six counties: San Diego, Orange, Los Angeles, Riverside, San Bernardino, and Ventura. Since the state has opted out of leading management of the beetle (see below), coordination of these many players presents significant challenges on top of the usual difficulties that hinder most U.S. efforts to reduce threats from non-native forest insects and pathogens:
Detection of outbreaks occurs years after the pest’s actual introduction. Locations of disjunct outbreaks are difficult to predict. They fuel more rapid dispersal.
The host species are not important commercial timber sources, so key forest stakeholders do not act – despite the tree species’ great ecological importance.
USDA APHIS does not engage because GSOB has become a non-native tree-killing organism in a single state (although it was introduced from a separate state – Arizona).
Problems more specific to GSOB are:
Some authorities dismiss this invasion because the beetle is native in one U.S. state.
California State agencies and the National Park Service have not taken effective action to control movement of the principal vector – in this case, firewood.
Fortunately, a broadening alliance of locals is trying to fill the gaps. These efforts are truly encouraging. Concerned individuals and organizations in Southern California have put together a broad coalition that works to ensure an outbreak-wide response. Participants include staffers in the USDA’s Forest Service and Natural Resources Conservation Service; the U.S. Bureau of Indian Affairs; CalFire; California Department of Conservation; State parks; agencies of four counties; community Fire Safe councils; regional conservation agencies; several Resource Conservation districts; various Tribes and Tribal Nations; and University of California extension. In some counties, there are also geographically-focused coordinating bodies.
Money is scarce, but somehow they manage to carry out detection and monitoring, vigorous outreach and education projects, and — at some sites — treatment of vulnerable trees and removal of “amplifier” trees. Teams working under the umbrella of this coalition have developed GSOB-killing treatments for logs (firewood); search for tools to increase survey efficacy; investigate the area-wide impact of the beetle, and its interaction with drought. Scientists have also explored possible biocontrol agents in the species’ native habitat in Arizona. However, the two parasitic wasps found there are already present in California, where their parasitism rates are much lower.
Some of the participants have been willing to “go political” in search of resources and official actions.
Might this coalition be a model for addressing other pests?
As if GSOB were not a sufficient threat to California’s oaks, several other non-native pests are already established in the state. These include at least seven pests and pathogens:
three shot hole borers — polyphagous, Kuroshio, and Euwallaceae interjectus; they attack at least Coast live oak (Quercus agrifolia), Engelmann oak (Quercus engelmannii), Valley oak (Quercus lobata), Canyon live oak (Quercus chrysolepis)
Mediterranean oak borer; attacks valley oak (Quercus lobata); blue oak (Q. douglasii); and Oregon oak (Q. garryana).
acute oak decline (bacterium Rahnellav victoriana);
At least GSOB, SOD, and two of the shot hole borers have received official “zone of infestation” (ZOI) designation by the California Board of Forestry. This designation enables
the Board to specify required pest mitigation measures for any timber harvest;
the Board & the CalFire authority to enter private properties to abate pest problems if necessary.
calls attention to the presence of the pest within the Zone and provides the Department with a talking point to motivate landowners & land managers to address problems caused by the pest in question.
The southern California coalition includes these other bioinvaders in its efforts.
Lobbying by members of the coalition – especially John Kabashima – resulted in the state legislature providing funds to address the invasive shot hole borers (see here and here.)
Although oak decline was observed in eastern San Diego County as early as 2002, and a GSOB was caught in a survey trap in 2004, the beetle’s role in killing these oaks was identified only in 2008. This detection was followed by the discovery of disjunct infestations were detected in towns surrounded by National forests first in Riverside County (2012), then in Orange County (2014) and Los Angeles County (2015). Outbreaks in San Bernardino County were detected in 2018 – although the beetle had probably been present since 2013. The LA County populations continued to spread, despite management efforts. The obvious danger prompted neighboring Ventura County to initiate surveillance trapping in 2023. Sure enough, this sixth county found its first outbreaks in 2024. Most of the initial outbreaks have been on private land bordering or surrounded by National forests.
black oak in Cleveland National Forest killed by GSOB; photo by F.T. Campbell
Responses: State, County, and Federal
The California Department of Food and Agriculture (CDFA) classifies GSOB as a level “B” pest. Pests in this category are known to cause economic or environmental harm; however, their distribution is considered to be “limited”. Efforts to eradicate, contain, suppress, or control the species are at the discretion of individual county agricultural commissioners.
There is some outside support – usually because of the link to increased fire danger. Grants from the National Forest Foundation have enabled local Fire Safe councils, CalFire, and the Inland Empire Resource Conservation District (IERCD) to conduct surveys and in some cases removal of amplifier trees in Riverside and San Bernardino counties. However, the funds no longer support the earlier practice of spraying at-risk trees.
County-by-County
In Orange County, a coalition of academics from the University of California and scientists with CalFire and USFS are testing various pesticide applications and efficacy of removing heavily infested trees. The county has adopted an Early Detection Rapid Response Plan.
Since the first detection of GSOB in Los Angeles County in 2015, authorities have removed nearly 10,000 “amplifier” trees. Because the Santa Monica Mountains are home to 151,000 oaks, LA County Agricultural Commissioner of Weights and Measures, the Santa Monica Mountain Resource Conservation District (RCD), Los Angeles National Forest and UC Cooperative Extension established a joint “Bad Beetle Watch” program with Ventura County. The program is training agency personnel, tree professionals, and recreationists to detect GSOB. A state agency – Mountains Recreation and Conservation Authority – is managing two outbreaks in the Santa Monica Mountains. The Los Angeles County Fire / Forestry Division is surveying the oak-dense San Fernando Valley and Santa Susana Mountains after GSOB was found nearby. The Los Angeles County Regional Planning agency will target oak-dense communities with advocacy for oak woodland health and warnings not to move firewood.
Most encouraging, the Los Angeles County Board of Supervisors is considering declaring a local or state emergency related to the risk of the spread of GSOB in the County and to the Santa Monica Mountains.
Ventura County began trapping at green waste facilities and campgrounds in 2023. Now that GSOB has been detected, several agencies — CalFire, Ventura County Fire, Ventura County Resource Conservation District, California Coastal Conservancy, Rivers and Mountains Conservancy, Santa Monica Mountains Conservancy, Mountains Recreation and Conservation Authority, Ojai Valley Land Conservancy, Ventura Fire Safe Council, Ojai Valley Fire Safe Council as well as the state lands commission and Los Padres National Forest – are gearing up educational programs focused on the risk of GSOB spread to additional areas. The non-governmental organization Tree People helped to spark this effort. Efforts are under way to fund and formalize a regional coalition, with collaboration from California Department of Conservation, CAL FIRE, and UC Agriculture and Natural Resources.
Despite the damage to state parks and the clear nexus with firewood, the California State Park agency encourages – but does not require – campers and picnickers to purchase certified clean firewood on site from camp hosts.
Affected Tribal Lands
Among affected Native American reservations, the La Jolla Band of Luiseño Indians has already removed almost one thousand large coast live oak trees in the Tribe’s campground; another thousand trees must be removed in coming years. Since 2019, the Tribe has been applying contact insecticides annually on 200 to 300 trees. In addition, the Tribe is planting seedlings and conducting research in partnership with UC Riverside, San Diego State University, and UC Irvine. Obtaining funds to develop management capacity is a constant challenge.
A second tribe, the Pala Band of Mission Indians, began a systematic survey of its lands in 2022. At that time, they found a light infestation in coast live oaks and some dispersal. Hundreds of dead trees are visible from highways bordering the Mesa Grande, Santa Ysabel, and Los Coyotes reservations. Even reservations that have no oaks on their land are affected because tribal members harvest acorns as a culturally important food.
Private Reserves
Two private reserves in Orange County responded aggressively to arrival of GSOB. The Irvine Ranch Conservancy started active management immediately after detection of GSOB in 2014. Their efforts – annual surveys, treating lightly infested trees, and removing heavily infested or “amplifier” trees – have paid off: by 2023, only 21 of 187 coast live oaks surveyed had new exit holes – and in most cases only one or two. Weir Canyon is considered a successful control program.
Managers of the California Audubon Starr Ranch Sanctuary began monitoring for GSOB by 2016. No GSOB were detected until 2023. Difficult terrain impedes survey and response. Orange County Fire Authority hired contractors to remove amplifier trees and treat others. Monitoring continues.
Responses by Federal Agencies
The Angeles, Cleveland, and San Bernardino National forests all have extensive and evolving management plans for GSOB. Actions include annual surveys, tree removal and/or treatment, regulating concessionaires’ sources of firewood, and restricting wood harvest permits. Each forest has also partnered with appropriate counties, NGOs, FireSafe councils, and Resource Conservation districts to expand outreach, monitoring, and management. Many of the efforts are centered around communities within and adjacent to National Forest boundaries and recreation sites, since they are the main source of GSOB ingress. Success is not guaranteed. Six years of applying contact insecticides to high-visit recreation sites did not prevent establishment of at least two new infestations on private inholdings in Trabuco Canyon (Cleveland National Forest).
The fourth National Forest in southern California, Los Padres NF – which lies partially in Ventura and Los Angeles counties – has not yet found any GSOB but it is preparing. The Forest conducted a forest health training with heavy emphasis on GSOB in spring 2024 and is in the process of creating its own monitoring and management plan to include preemptive evaluation of environmental concerns under the National Environmental Protection Act (NEPA) and planning.
GSOB management is an important facet of the National Forest Wildfire Crisis Strategy implemented by all four National Forests in southern California. Challenges include steep and inaccessible terrain; wilderness designations; designation of sensitive habitat for wildlife, ecological, or heritage sites; and the sheer amount of land managed. Despite this, the forests have expanded their efforts each year. At the National Plant Board meeting in July, Sky Stevens reported that GSOB is one of the priority pests being addressed by the Forest Health Protection program. However, this program has been severely downsized by the Trump Administration, so its ability to assist is unclear. Budgets for individual National forests are also in limbo.
The Issue of Firewood
Several National parks located in California contain important oak forests and woodlands that are also at risk, especially given the importance of firewood in spreading the pest. Yosemite and Kings Canyon-Sequoia National parks and other campgrounds in the Sierra Nevada receive large numbers of campers from the Los Angeles area.
A 2014 National Park Service resource guide for firewood management summarized federal plant pest regulations at the time. These have since changed because emerald ash borer is no longer federally regulated. The guidance advised Park staff to define their park’s forest resources, keep abreast of present and potential forest pest species, and act to manage risks from potentially infested firewood. Park concessioners are required to purchase and sell only locally grown and harvested firewood in accordance with state quarantines. However, California does not have relevant quarantines for either firewood as a commodity or for oak pests specifically. The websites of Yosemite and Kings Canyon-Sequoia National parks ask people not to bring firewood obtained from a source more than 50 miles from the parks.
California does participate in the Firewood Scout program, Firewoodscout.org which advises campers on local sources from which to purchase their wood. Statewide, a consortium of several agencies, academia, and non-government agencies operates a “Buy It Where You Burn It” campaign that promotes this message with the public and firewood vendors.
Funding is a perpetual problem. No agency, not even CalFire, is funded to remove amplifier trees. The agency does use its crews to remove GSOB infested trees when they can. Most funding for treating infested trees comes from competitive grants awarded by CalFire or National Forest Foundation.
In 2012 the California Board of Forestry and Fire Protection (which is appointed by the Governor) officially designated a Zone of Infestation (ZOI) for GSOB. The Zone has been expanded as the infestation spread. The Zone of Infestation formally recognizes GSOB as a threat to California’s woodland resources and seeks to raise awareness among the governor, legislature, and public. The action was also intended to foster collaborative efforts to manage the beetle.
Joelene Tamm, Vice Chair of the California Forest Pest Council Southern California Committee (CFPC), is leading an initiative to address wildfire risks from invasive pests, including GSOB, South American Palm Weevil, and the invasive shothole borers. She presented a pest update with potential solutions to the California Board of Forestry (BOF) and followed up with a presentation to the BOF Resource Protection Committee, which is now identifying responsive actions. The Governor’s Wildfire Task Force is considering incorporating the topic into future meetings. The initiative’s core message is that the state must address the root cause of pest proliferation, as treating the symptom of wildfire alone is an unsustainable strategy (Tamm, pers. comm. August 2025).
For more details and sources, visit the GSOB brief here.
[I could find no recent updates about a third Agrilus, the soapberry borer (Agrilus prionurus), which is established in Texas from Mexico and was earlier said to kill the western soapberry (Sapindus saponaria var drummondii). It is established in at least 42 counties, reaching from the Dallas-Ft. Worth area to the Rio Grande valley.
soapberry borer; photo by Texas A&M Forest Service
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
healthy eastern hemlock in Shenandoah National Park; photo by F.T. Campbell
PestLens reports newly detected insects and pathogens that seem to pose a threat to North American forests.
Insects on hemlock – Tsuga spp
a) Adelgeslepsimon (Hemiptera: Adelgidae) – found infesting Tsuga dumosa (Himalayan hemlock) trees in Bhutan.
b) bark beetle Pityokteines spinidens (Coleoptera: Curculionidae) – infesting Tsuga canadensis trees in an arboretum in the Czech Republic. Affected trees showed branch dieback, entry holes, and internal galleries.
2. Several fungi infesting loblolly pine – Pinus taeda
needle chlorosis and drying, canopy dieback, and root necrosis on loblolly pines in Brazil is caused by the fungi Ilyonectria leucospermi, I. protearum, I. robusta, and I. vredehoekensis (Sordariomycetes: Hypocreales).
PestLens is supposed to alert APHIS to threats; I hope the agency is paying attention!
The USFS Southern Research Station reports that it is investigating brown spot needle blight, caused by the fungal pathogen called Lecanosticta acicola. The report says the pathogen has been present in the U.S. for more than 100 years, but does not indicate an origin. Other sources show it as widespread in both North America and Europe. The USFS notes two recent significant outbreaks, one affecting more than a million acres of loblolly pine in the Southeast, the second on eastern white pine in the Northeast. The pathogen also infects other species. .
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