The pest alert system “PestLens” has again alerted us to plant pests in Europe or Asia that feed on species closely related to tree species native to North American forests. Two of the insects named in the alert apparently pose a hazard to icons of the forests of America’s Pacific coast forests, giant sequoia and redwood.
I hope APHIS is using this information to alert port and on-the-ground staff and perhaps initiating more in-depth risk assessments.
The posting on February 27, 2025 reported that cotton jassid, Jacobiasca lybica (Hemiptera: Cicadellidae), affects not just cotton and citrus but also Cupressus sempervirens (Mediterranean cypress) [Cupressaceae]. More than a dozen North American trees species are in this family, including
Sequoiadendron giganteum or giant sequoia. Giant sequoia is listed as an endangered species by the IUCN with fewer than 80,000 remaining in its native California.
Chamaecyparis thyoides and C. lawsoniana (Port-Orford cedar). Port-Orford cedar has been decimated in its native range by an introduced pathogen, Phytopthora lateralis. A major breeding effort has developed trees that are resistant to the pathogen; they are now available for people to plant.
Thuja occidentalis, also known as northern white-cedar, eastern white-cedar, or arborvitae,
Taxodium ascendens, also known as pond cypress
several Juniperus
Hesperocyparis macrocarpa also known as Cupressus macrocarpa, or the Monterey cypress. NatureServe ranks the cypress as GI – critically imperiled.
Cotton jassid been reported from several countries in Europe, Africa, and the Middle East.
China has reported the existence of a previously unknown bark beetle species, Phloeosinus metasequoiae (Coleoptera: Curculionidae). It was found infesting Metasequoia glyptostroboides (dawn redwood) trees in China. Affected trees exhibited reddened leaves and holes and tunnels in branches.
China has also discovered a several new hosts utilized by the fungus Pestalotiopsis lushanensis (Sordariomycetes: Amphisphaeriales). Formerly known to infect tea (Camellia sinensis) and several other plant species, P. lushanensis has now been found shoot causing blight and leaf drop on a conifer, deodar cedar (Cedrus deodara) and leaf spots on an angiospermwith congeners in North America — the rare Chinese species, Magnolia decidua. There are eight species of Magnolia native to North America.
Magnolia grandiflora; photo by DavetheMage via Wikimedia
APHIS’ ability to respond to alerts remains uncertain.
The agency’s probationary employees have been fired – just as at other agencies. APHIS staff were prohibited from participating in last week’s annual USDA Invasive Species Research Forum – the 33rd such meeting. The bird flu emergency is demanding all the attention and funds.
So – how can the rest of us fill in?
At the USDA Research Forum I again presented a poster urging greater attention to tree-killing pathogens. Scientists have made considerable progress in identifying factors that indicate whether a non-native insect might pose a significant threat (see blogs on conifer and deciduous species; more to come!). However, USDA had not funded a similar effort to improve understanding of pathogens. The most promising strategy so far are sentinel plantings. However, these systems have weaknesses; I will blog in the near future about another analysis.
I propose that APHIS start by working with independent scientists to determine the actual, current level of pathogens associated with various types of incoming goods. Contact me directly if you wish to read the text of my poster.
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 https://treeimprovement.tennessee.edu/
The pest alert system “PestLens” provides information about new reports of plant pests around the world. Notices are published weekly. These provide North American stakeholders advance notice of pests to be on the lookout for. While I have followed these postings for several years, I have been alarmed by recent notices report documenting the presence of insects or pathogens that feed on species in the same genera as tree species native to North American forests. The alerts cover pests of all types of crops, not just trees.
I note that several of these not-yet-introduced pests attack the genus Persea, which contains several native tree and shrub species that are already severely affected by laurel wilt disease.
The report for 19 December, 2024, provided information about two pathogens.
flowering dogwood Cornus florida; photo by F.T. Campbell
The bacterium Pectobacterium aroidearum (Gammaproteobacteria: Enterobacteriales) was detected in China. The bacterium infests several crops and Persea americana(avocado). Although the detection in China is new, the bacterium is apparently already widespread, since it has been earlier been reported from parts of Africa, the Middle East, Asia, Brazil, and Jamaica.
The dagger nematodes Xiphinema simile and X. zagrosense (Longidoridae) were reported in Syria. X. simile is associated with economically important plants, including Cornus spp. (dogwood; North American species already decimated by the introduced pathogen dogwood anthracnose), Malus spp.(apple), Prunus spp. (stone fruit),Quercusspp. (oaks – already under attack by many non-native organisms), and Vitis vinifera (grape). X.zagrosense is also associated with Poaceae. X. simile has earlier been reported from parts of Europe, Kenya, Iran, and Russia. X.zagrosense has also been reported from Iran.
The report for 9 January, 2025, conveyed information about 1 pathogen and 1 insect.
It noted the presence in Thailand of the fungus Pseudoplagiostoma perseae (Sordariomycetes: Diaporthales) on Persea americana.
The South American palm borer, Paysandisia archon (Lepidoptera: Castniidae), is infesting several palms at multiple locations in Switzerland. It attacks several economically important palm species and the native genus Washingtonia spp. (fan palm).
native California fan palm, Washingtonia filifera; photo by F.T. Campbell
The report for 13 February, 2025, gave information about 1 pathogen and 1 insect.
An anthracnose fungus Colletotrichum aenigma (Sordariomycetes: Glomerellales) infecting Carya illinoinensis (pecan) and Ilex cornuta (Chinese holly) in China. Colletotrichum aenigma infects other economically important plants. These include the following genera with native species in North America: Vaccinium (blueberry),Malus(apple), Persea americana (avocado), and Vitis vinifera (grape). Colletotrichum aenigma is also widespread; it has been reported from parts of Europe, the Middle East, Asia, New Zealand, and South America.
South African citrus thrips, Scirtothrips aurantii (Thysanoptera: Thripidae) in a greenhouse in the Netherlands. The thrips infests several woody plants, including Ilex crenata (Japanese holly), Rosa spp., Malus (apple), Persea americana (avocado), Prunus spp. (stone fruit), and Vitis vinifera (grape). S. aurantii it is under eradication in Portugal and Spain. It has also been reported from parts of Africa, Yemen, and Australia.
Scirtothrips aurantii; photo by Pablo Alvarado Aldea, Spain
A few weeks ago I wanted to conclude this blog by stating my hope that APHIS is using this information to alert port and on-the-ground staff and perhaps initiating more in-depth risk assessments. Now – as we learn about mindless firings of USDA staff, I fear I must limit my hopes to a future for APHIS’ programs and skilled staff in more general terms.
Do we face shut-down of pest prevention/response efforts across the board?
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 here or here.
Europe has been invaded by two insect species that North Americans should be watching out for. First, a Cerambycid, the wasp-mimicking tiger longicorn beetle, Xylotrechus chinensis. And second,the Buprestid cypress jewel beetle, Lamprodila festiva. We should also ensure that none of the other 500+ beetles introduced to Europe poses a threat to our trees. These are summarized in a 2024 paper by Bunescu et al.
Tiger Longicorn Beetle
This beetle is native to eastern Asia. It feeds on and kills mulberry trees (Moraceae: Morus spp.). It might also attack apple and pear trees and grapevines – Asian sources report these as hosts. The status of grapevines has been questioned by a Spanish experiment, in which artificial inoculations failed. I have seen no further information about the vulnerability of apple (Malus spp.) and pear (Pyrus spp.) (Saarto i Monteyu, Costa Ribeu, and Savin 2021)
In Europe, the pest threatens mulberry trees which are commonly planted for shade and ornamentation, especially in southern France, Spain and Greece (Saarto i Monteyu, Costa Ribeu, and Savin 2021). For example, there are more than 20,000 mulberry trees in Athens (EFSA 2021). The trees’ abundance contributes to spread of any associated pests, the level of damage caused by falling branches, and the expense of tree removal. Economic damages are those typically associated with wood-borer invasions of urban areas. That is, the cost of tree removals, loss of shade and amenity values, and increased risk of injury from falling branches.
We Americans should be concerned, too. Wild red mulberry (Morus rubra) occupies much of the eastern United States, from southern New England west to southeastern Minnesota, then south along the eastern edge of the Great Plains to central Texas, and east to southern Florida. It is also found in Bermuda. It grows primarily in flood plains and low moist hillsides. . Presumably it would also be attacked by Xylotrechus chinensis, although I don’t know whether anyone has tested this. As a native tree, red mulberry plays a role in natural ecosystems, including wildlife food supplies. Thus, America would see even more significant losses if Xylotrechus chinensis were to establish.
Morus rubra in Fairfax County, Virginia; photo by Fmartin via Wikipedia
Red mulberry is already declining in parts of its central range, possibly due to a bacterial disease. The effects and extent of this disease have not been investigated thoroughly.
Apples and pears are important crops across North America; the farm-gate value is estimated at $3.2 billon.
Introductions of the beetle to Spain, France, and Greece might have resulted from inadequately-treated wood packaging or other wood products. Detections of the species in wood imports were reported in Germany in 2007 and 2017 (Saarto i Monteyu, Costa Ribeu, and Savin 2021). The U.S. has also intercepted X. chinensis at least once, at the port of Philadelphia, in 2011 (EFSA 2021).
These detections have raised questions to which no-one yet has answers. First, can X. chinensis develop in cut logs? The European Food Safety Agency concluded that it can (EFSA 2021). Second, one detection involved a shipment of wooden items made from birch (Betula spp.) and willow (Salix spp). It is not yet clear whether these taxa are also hosts (EFSA 2021). (The wood species were not specified in the case of the other interceptions.) I have blogged often about how “leaky” the wood packaging pathway has been; to see these blogs, scroll below the “archives” section of the webpage, then click on the category “wood packaging”.
European scientists believe X. chinensis might also be transported in shipments of plants for planting. However, the beetle prefers to oviposit on large trees. This pathway is less viable for the United States since USDA APHIS allows imports of mulberries (Morus) and pears (Pyrus) only from Canada. Apple trees (Malus spp.), however, may be imported from France – which hosts an introduced population of X. chinensis – and other European countries.
Detection of any invasion by X. chinensis will pose the usual difficulties associated with woodborers. In some European cities, hundreds or even a thousand trees were infested before the outbreak was detected (EFSA 2021).
I am concerned that the Europeans appear to have been slow to respond to the threat from Xylotrechus chinensis. After several outbreaks were discovered in Greece, France, and Spain in 2017 and 2018, the European and Mediterranean Plant Protection Organization (EPPO) added X. chinensis to its Alert List. This action requires member states (which are not limited to European Union members) to report new outbreaks and inform about efforts to either stop or eradicate them (Saarto i Monteyu, Costa Ribeu, and Savin 2021).
Shortly afterwards the European Union Commission requested the European Food Safety Agency (EFSA) to conduct a risk assessment. This analysis was completed in 2021. (It contains lots of photos of the insect and its damage.) The analysis concluded that Xylotrechus chinensis could probably infest most areas in the Union and cause significant damage. The species meets the criteria for designation as a quarantine pest in the Union. However, as of December 2024, this action had not been taken. As a result, control measures for this species are not mandatory.
Introductions continue; an outbreak in Lombardy, Italy, was found in June 2023 (Sarto i Monteys, Savin, Torras i Tutusaus & Bedós i Balsach 2024). European regulations – following IPPC standards – also are linked to named pests and known outbreak locations. Such restrictions almost guarantee that the pest will continue to spread from not-yet-detected outbreaks. (Decades ago, after the emerald ash borer invasion, Michigan’s State Plant Regulatory Official, Ken Rasher, noted that, to be effective, “slow the spread” efforts must apply to areas beyond the known limits of the pest’s range.) The EFSA risk assessment did suggest delimitation of buffer zones around known European outbreaks. I don’t know whether such zones have been set up.
The risk assessment also recommended [true?] improving detection of this insect by developing male pheromones as lures. These have not been acted on. Guidance on best timing for treatment [trunk injections of systemic insecticides] also appears to have been taken up by Greece but not by Spain (Sarto i Monteys, Savin, Torras i Tutusaus & Bedós i Balsach 2024).
These authors include more information about the Xylotrechus chinensis life cycle and trajectory of the invasion,. They note that climate change appears to be altering the insect’s phenology. Especially, the adult flight period is beginning earlier in the spring.
Lamprodila festiva; Udo Schmidt via flickr
Cypress jewel beetle
This second pest of concern is a buprestid that attacks trees in the Cupressaceae. Infested trees generally die within a few years.
In its native Mediterranean range, the beetle feeds on native Juniperus, Cupressus and Tetraclinis. In invaded urban landscapes of Europe it attacks primarily introduced Cupressaceae , particularly Thuja, Chamaecyparis, Platycladus, Callitris, and some hybrids (Cupressocyparis). It has also been recorded as damaging Sequoia sempervirens (Brunescu, et al., 2024). (Genera in bold are native to North America.)
Thuja occidentalis; photo by H. Zell via Wikimedia
White cedar, Thuja occidentalis is the focus of Brunescu, et al.’s article. It is native to eastern Canada and much of the north-central and northeastern United States. The European and Mediterranean Plant Protection Organization (EPPO) has identified eight species in the Lamprodila genus as important pests, (Brunescu et al. 2024) so the danger might be more widespread. The invasion of Europe is probably the result of adult flight or other short-range transport. The article does not suggest pathways that the species might exploit to cross oceans.
SOURCES
Bunescu, H., T. Florian, D. Dragan, A. Mara, I-B. Hulujan, X-D. Rau. 2024 The Cypress Jewel Beetle Lamprodila Festiva Linné, 1767 (Coleoptera: Buprestidae), an Invasive Major Pest of Thuja Occidentalis Linné in Romania Hop and Medicinal Plants, 2024 XXXII, No. 1-2, 2024.
Saarto i Monteyu V., A. Costa Ribeu. I. Savin. 2021a. The invasive longhorn beetle Xylotrechus chinensis, pest of mulberries, in Euro: Study on its local spread & efficacy of abamectin control Plos One January 29, 2021. https://doi.org/10.1371/journal.pone.0245527
Sarto i Monteys, V., I. Savin, G. Torras i Tutusaus & M. Bedós i Balsach. 2024b. New evidence on the spread in Catalonia of the invasive longhorn beetle, Xylotrechus chinensis, & the efficacy of abamectin control. Scientific Reports | (2024) 14:26754 | https://doi.org/10.1038/s41598-024-78265-xwww.nature.com/scientificreports/
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 https://treeimprovement.tennessee.edu/
several Euwallaceae species; E. interjectus is 2nd from the top. Photo from Gomez et al. 2018; ZooKeys 768 19-68
In December 2024, California officials announced detection of a third species of invasive shothole borer beetle in the state. This invasion was found in Santa Cruz County in October 2024. The beetle has been identified as Euwallacea interjectus; the associated fungus is Fusarium floridanum. Like other non-native shothole borers in the same genus already known to be in California, Euwallacea interjectus is native to Southeast Asia.
So far, the infestation extends across at least 75 acres (CDFA proposal). It is affecting primarily box elders (Acer negundo). Other tree species have also been attacked: California sycamore (Platanus racemose), coast live oak (Quercus agrifolia), arroyo willow (Salix lasiolepis), red willow (Salix laevigata), and black cottonwood (Populus balsamifera ssp. trichocarpa). [See the CDFA risk assessment referred to below]. While it is too early to know precisely, E. interjectus is expected to pose a risk of tree dieback in urban, wildland and agricultural landscapes similar to that already caused by its relatives — the Polyphagous shot hole borer (Euwallacea fornicatus s.s. [PSHB]) and Kuroshio shot hole borer (Euwallaceakuroshio [(KSHB)].
The Santa Cruz County Department of Agriculture and University of California Cooperative Extension Service are coordinating with the California Department of Food and Agriculture (CDFA) to monitor and respond to the infestation. Research is being conducted by the University of California to evaluate the full range of potential tree species that may be affected by the beetle.
CDFA is seeking input on whether to designate Euwallacea interjectus as a category “B” pest. Under this category, response to the pest would be carried out by the counties at their own discretion, not by the state. You can advise CDFA’s on this decision until 17 February. Go here.
In its proposal, CDFA notes that several tree hosts of the beetle grow throughout California. The analysis gave a risk ranking of “High (3)” in four categories: climate/host interaction, host range, dispersal and reproduction, and ecosystem-level impacts. The economic risk rank is “Medium (2)” because it might attack only stressed trees – although CDFA concedes that drought stress is common in California. The overall determination is that the consequences of Euwallacea interjectus’ introduction to California is “High (14)”. Still, CDFA proposes to leave response to this introduction up to affected counties.
Santa Cruz County is outside the areas identified by a model developed by Lynch et al. (full citation below) as being at high risk of establishment of the Euwallacea-Fusarium complex, based on analysis of sites where Euwallacea fornicatus and E. kuroshio are already established. Nearby areas are ranked at high risk; these include drier areas in the San Francisco Bay region.
There are at least three four beetles in the Euwallacea fornicatus species complex. Several look almost identical to one another; the only reliable way to tell them apart is by looking at their DNA. However, E. interjectus is substantially larger than E. fornicatus and E. kuroshio, the two already-established shothole borers causing damage in southern California.
Various members of the Euwallacea fornicatus species complex have invaded countries around the world and other parts of the United States. While many of these introductions occurred decades ago – e.g., Hawai`i, Florida, possibly Israel, there appears to have been a spurt of introductions around or after 2000. The PSHB was first detected in California in 2003; the KSHB in 2013. As of 2022, disease caused by these two complexes had spread throughout Orange, San Diego, Los Angeles, Riverside, San Bernardino and Ventura counties. Outbreaks have been detected as far north as Santa Barbara /Santa Clarita. The KSHB had “jumped” to more distant locations in San Luis Obispo and Santa Clara counties. So far, the two later detections apparently do not represent established populations. In November 2023, the PSHB beetle–pathogen complex was confirmed killing hundreds of trees in riparian forests in San Jose, in the San Francisco Bay region. Two host trees – California sycamore and valley oaks – are important in the urban forest canopy of the region
NOTE: the invasive shot hole borers and their associated fungi attacking trees in California are completely unrelated to the laurel wilt complex killing trees in the Lauraceae family in eastern States. This complex involves an ambrosia beetle Xyleborus glabratus and associated fungus Harringtonia (formerly Raffaelea) lauricola.
Lynch, S.C., E. Reyes-Gonzalez, E.L. Bossard, K.S. Alarcon, N.L.R. Love, A.D. Hollander, B.E. Nobua-Behrmann & G.S. Gilbert. 2024. A phylogenetic epidemiology approach to predicting the establishment of multi-host plant pests Communications Biology
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 https://treeimprovement.tennessee.edu/
ash tree in Michigan killed by emerald ash borer; photo courtesy of (then) Mayor John Hieftje
The Forest Service is promoting its efforts to protect urban forests [see the Northeast Region’s “Roots in Research” in mid-December 2024]. The rationale is that urban forests provide substantial environmental and economic benefits that deserve more attention. These include air purification, temperature regulation and energy savings, water absorption, and improved public health. At the same time, urban forests face multiple and overlapping threats – including the one of greatest concern to us, introduction of tree-killing non-native insects and pathogens.
The article on which the Roots in Research “Science Brief” is based was actually published in 2022 in the Journal of Forestry. In it, David Nowak, Eric Greenfield, and Alexis Ellis evaluated historical and current threats to urban forests across the contiguous states and projected them 50 years into the future. Threats included urban expansion, climate change, insect infestation, and extreme weather events. Their goal was to help urban forest managers and policymakers prioritize resources and planning efforts.
I believe stakeholders should view these projects as underestimates because the sources Nowak et al. relied on for both future climatic conditions and non-native pest impacts are incomplete or outdated. I am not criticizing the choice of sources – they are the standard ones. But events have raised questions about their accuracy.
Nowak, Greenfield, and Ellis expected that urban tree cover will decline significantly by 2060. The principle cause is urban expansion — development of previously wooded areas. Development has traditionally been the leading cause of urban forest loss.
Newer threats have become obvious in recent decades – i.e., pest and disease attacks and extreme weather events.
coast live oak infected by GSOB; Heisey County Park, San Diego County photo by F.T. Campbell
The most troubling example of the sources’ weaknesses is the Alien Forest Pest Explorer (AFPE), on which the authors rely for their list of non-native insects and pathogens present in the United States. However, the compilers of this database decided not to include pests that are native to some parts of North America but are behaving as bioinvaders in other regions. The premier example is the goldspotted oak borer (GSOB), Agrilus auroguttatus. This insect kills three species of oaks native to southern California – coast live oak (Quercus agrifolia), California black oak (Q. kelloggii), and canyon live oak (Q. chrysolepis). Twelve years ago scientists estimated that GSOB had killed at least 100,000 trees in San Diego County; it has since been detected in widespread infestations in four other counties in southern California.
Not including GSOB (or Mediterranean oak borer; see below) skews the findings because of the importance of the oaks in California’s urban forests. Their genus is the second most-abundant native genus in the state’s urban forest, making up 6.5% of the trees. Because many of these trees are large, they contribute significantly to the ecosystem benefits provided by urban forests. Out of the 152,594 coast live oaks in 287 cities statewide, at least 30,000 of them meet GSOB’s preferred size limit (DBH greater than 18 – 20 inches [~45 cm]) (Love et al. 2022). The highest presence of oaks in urban forests in the South is in Santa Barbara – which has not yet been invaded by GSOB. However, built-up sections of Los Angeles – which are heavily invaded already — have between 250,000 and 300,000 coast live oak trees.
The Alien Forest Pest Explorer also does not include pests of palms. Palms are the first and second most the abundant species in urban areas of both the Southern California Coast and Southwest Desert regions (Love et al. 2022). Of course, palms contribute little to the ecosystem benefit associated with urban forests, but they are iconic symbols of the region. California’s palms are under attack by the South American palm weevil. https://cisr.ucr.edu/invasive-species/south-american-palm-weevil
More difficult to understand is the AFPC’s failure to include the Mediterranean oak borer, (MOB) (Xyleborus monographus). MOB has been introduced from Europe, so it fits the AFPE’s criteria for inclusion. MOB is killing valley (Quercus lobata) and blue oaks (Q. douglasii) in Lake, Napa, Sacramento, and Sonoma counties in California and Oregon oak (Q. garryana) in Troutdale, Salem, and other towns in Oregon.
Quercus lobata, killed by Mediterranean oak beetle
As to the data sources relied on for projections of future climatic factors, several measurements of the changing climate already exceed projections in the models. They expect intensified threats from changes in air temperature, precipitation, aridity, wildfire risk, flooding, and sea level rise. By 2060, temperatures in urban areas are expected to increase by 1.2 – 3.5° C. Nowak and colleagues expected this warming to exacerbate threats from heat stress, flooding, increased salinity, drought, and wildfire. Less certain but possible are more intense storms and pest outbreaks. As I noted above, perhaps even these projections understate the threats.
For example, in discussing flooding the authors relied on measurements of the historic 100-year flood plain. I understand that experts now say this standard is inadequate, given existing records and projected further increases in precipitation (especially high-intensity storms). Urban areas in 98% of the 2,424 counties Nowak et al. analyzed contain flood-prone areas.
Nowak et al. do mention two additional elements exacerbating the flood risk: the spread of impervious surfaces and location of many cities next to bays or wide rivers. In these latter cases, risks might include salt intrusion linked to higher water levels, even in the absence of flooding. The National Oceanographic and Atmospheric Administration’s “intermediate high” scenario projects sea level will rise 61 cm by 2060.
Nowak, Greenfield, and Ellis said the greatest overall threat is in the eastern states, especially New England other than Vermont and Maine; the mid-Atlantic; South Carolina; and Ohio. They say this arises from the combination of high levels of urbanization and accumulation of several threats. The specific threats include projected precipitation changes, storms (hurricanes in the southeast; ice storms in the Appalachians); sea level rise; and the abundance of non-native pests. I think that reliance on data from the past results in understating the hurricane risk in the Northeast (especially the Hudson and Connecticut river basins) and in North Carolina.
Nowak, Greenfield, and Ellis reminded us that a healthy urban forest canopy can help mitigate some of the threats associated with climate change. This applies particularly to local air temperatures. Reducing urban heat islands not only addresses a direct threat; it can also moderate such other threats as pest infestations, wildfire, aridity, and storm damage, especially runoff. They advocate science-based tree management programs including preserving existing trees and planting species that can thrive in the expected new local and regional environment, e.g., withstand droughts, flooding, saltwater exposure, or extreme temperatures.
I think their recommendation on pest threats is lame: they suggested “monitoring and managing local pest threats.” Non-native pests demand additional actions at all levels of authority — local, state, and federal. (See the “Fading Forests” reports linked to at the end of this blog, and earlier blogs under the category “invasive species policy”.) I have already noted troubling exclusion of some pests already present in urban areas of the continental United States. I understand that it is impossible to predict which additional pests might be introduced in the next 50 years. But I would have appreciated a sentence stating the near certainty that more pests will be introduced and cause damage to urban forests in the next 50 years.
Given the recent fires in the Los Angeles region, I believe we need new analyses of the risk of wildfire in cities and the positive and negative interactions with the urban forest.
Nowak, D.J., E.J. Greenfield, and A. Ellis. 2022. Assessing Urban Forest Threats across the conterminous United States. Journal of Forestry, 2022, Vol. 120, No. 6
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/
emerald ash borer; some of PPA grants are funding evaluation of biocontrol efficacy
USDA APHIS has released information about its most recent annual allocation of funds under the Plant Pest and Disease Management & Disaster Prevention Program under §7721 of the Plant Protection Act. (Also see Fading Forests II and III; links provided at the end of this blog.) These funds support both critical needs and opportunities to strengthen the nation’s infrastructure for pest detection, surveillance, identification, and threat mitigation. Since 2009, this USDA program has provided nearly $940 million to more than 5,890 projects.
For FY25 APHIS allocated $62.725 million to fund 339 projects, about 58% of the proposals submitted. About $10 million has reserved for responding to pest and plant health emergencies throughout the year.
According to APHIS’ press release, the highest amount of funds (almost $16 million) is allocated to the category “Enhanced Plant Pest/Disease Survey.” Projects on “Enhanced Mitigation Capabilities” received $13.6 million. “Targetting Domestic Inspection Efforts to Vulnerable Points” received nearly $6 million. “Improving Pest Identification and Detection Technology” was funded at $5 million. Outreach & education received $4 million. I am not sure why these do not total $63 million.
Funding for States and Specific Pests
Wood-boring insects received about $2.3 million. These included more than $869,800 to assess the efficacy of biocontrol for controlling emerald ash borer (EAB) Agrilus planipennis, $687,410 was provided for various detection projects, and $450,000 for outreach efforts related to various pests. Ohio State received $93,000 to optimize traps for the detection of non-native scolytines (bark beetles).
Biocontrol efficacy will also be assessed for hemlock woolly adelgid, invasive shot hole borers, cactus moth, and several invasive plants (including Brazilian pepper). (Contact me to obtain a copy of CISP’s comments on this biocontrol program.)
Opuntia basilaris in Anza Boreggo; one of flat-padded Opuntia vulnerable to the cactus moth; photo by F.T. Campbell
Funding for other pests exceeded $1 million for spotted lanternfly (nearly $1.4 million), Asian defoliators ($1.2 million) and box tree moth (just over $1 million).
$630,000 was provided for detection surveys and studies of the sudden oak death pathogen Phytophthora ramorum, especially how it infects nursery stock. Nursery surveys are funded in Alabama, Louisiana, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee, Virginia, and West Virginia. Most of these states are in regions considered most at risk to SOD infection of wildland plants.
sudden oak mortality of tanoak trees in southern Oregon; photo by Oregon Department of Forestry
Oregon received much-deserved $41,000 to evaluate the threat of the NA2 and EU2 lineages of P. ramorum to nurseries and forests Oregon also received $104,000 to respond to the detection of Phytophthora austrocedri in nurseries in the state. The Oregon outbreak has been traced to Ohio, but I see no record of funds to assist that state in determining how it was introduced.
Asian defoliator (e.g., Lymantrid moths) surveys have been funded for several years. This year’s projects are in Alaska, Arkansas, California, Kentucky, Maryland, Massachusetts, Mississippi, Montana, Nevada, North Carolina, Oregon, Tennessee, Texas, Washington, and West Virginia. While I agree that the introduction risk is not limited to coastal states with maritime ports, I don’t what criteria were applied in choosing the non-coastal states which are funded to search for these insects
Spotted lanternfly surveys (including technological improvements) or related outreach are funded in Alabama, Connecticut, Delaware, Kentucky, New Hampshire, New Jersey, North Carolina, Oregon, Pennsylvania, and Tennessee. California’s project is focused on postharvest treatments.
The Don’t Move Firewood project continues to be funded by APHIS. Several states also direct attention specifically to the firewood pathway: Kentucky, Maine, and Michigan.
I applaud the precautionary funding of the Agriculture Research Service to generate of high-quality genomic resources for managing the causal agent of Japanese oak wilt Dryadomyces quercivorous
Florida Department of Agriculture, North Carolina State University, and West Virginia University each received more than $100,000 to improve detection and management of invasive hornets.
Tennessee State University got $100,000 to continue efforts to detect and understand Vascular Streak Dieback in redbud Cercis canadensis.
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 https://treeimprovement.tennessee.edu/
The U.S. Fish and Wildlife Service (USFWS) has taken new action to protect North America’s salamanders from the pathogenic Salamander Chytrid Fungus Batrachochytriumsalamandrivorans; Bsal). The Center for Invasive Species Prevention (CISP) welcomes this action and urges you to help the Service to finalize it.
To read and comment on the interim rule, go here. The comment period closes on March 11.
oriental fire-bellied newt (Cynops orientalis); one of the non-native species imported in largest numbers before the 2016 Lacey Act interim rule; photo by Sebastian Voitel
USFWS acted under its authority to contained in the “injurious wildlife” provisions of the Lacey Act [18 U.S.C. 42(a)]. This statute, first adopted in 1900, empowers the Secretary of Interior to regulate human-mediated transport of any species of wild mammal, wild bird, fish, mollusk, crustacean, amphibian, or reptile found to be injurious to human beings; to the interests of agriculture, horticulture, or forestry; or to America’s wildlife or wildlife resources. Regulated articles include offspring or eggs of the listed species, dead specimens, and animal parts.
Any importation of a listed taxon into the U.S. is regulated. However, regulation of transport within the United States is complicated because of clumsy wording of the statute. In 2017, the D.C. Circuit Court of Appeals [U.S. Association of Reptile Keepers, Inc. v. Zinke [852 F.3d 1131 (D.C. Cir. 2017)] ruled that the law regulates transport of listed species (and their progeny, parts, etc.) between the contiguous 48 States and several other jurisdictions: Hawai`i, Puerto Rico, other U.S. territories, and the District of Columbia. However, transport among the “lower 48” states (e.g., from Virginia to Kentucky) or from the “lower 48” states to Alaska, is not regulated (unless the route to or from Alaska passes through Canada). In past years conservationists asked Congress to amend the law to close this obvious gap in protection, but without success.
It is still illegal to transport listed species across any state borders if the wildlife specimen was either imported to the U.S. or transported between the above-enumerated jurisdictions in violation of any U.S. law. [Lacey Act Amendments of 1981, 16 U.S.C. 3372(a)(1)]
Those wishing to transport a listed species for zoological, educational, medical, or scientific purposes may apply for a permit from USFWS to do so.
The threat to salamanders
The United States is a center of diversity for salamanders. Our nation is home to 221 species of salamanders, more than any other country. These species are in 23 genera in nine families. In fact, nine of the 10 families of salamanders worldwide are found in the U.S. Highest diversity is found along the Pacific Coast and in the southern Appalachian Mountains. As the most abundant vertebrates in their forest habitats, salamanders make significant contributions to nutrient cycling and even carbon sequestration.
Because they depend on both aquatic and terrestrial habitats, salamanders face many threats to their existence. Twenty species of American salamanders from 6 genera (Ambystoma, Batrachoseps, Eurycea, Necturus, Phaeognathus, Plethodon) are listed under the Endangered Species Act link as endangered or threatened. A subspecies of hellbender salamander (Cryptobranchus alleganiensis alleghaniensis) has been proposed for listing.
Amylosterium xxx – marbled salamander; photo by John B. Clare via Flickr
Over the last 12 years, they have faced an alarming new threat.
In 2013, European scientists detected rapid, widespread death of salamander populations in the Netherlands. They determined that the cause was a fungal disease caused by Batrachochytrium salamandrivoran (Bsal). Their alarm was heightened because this fungus is closely related to another, Batrachochytrium dendrobatidis (Bd), which had recently caused serious decline of more than 100 frog and toad species, including driving several to extinction, and had been transported to all continents except Antartica.
Responding to this new threat, amphibian conservation specialists and wildlife groups generally banded together to put pressure on the USFWS to take regulatory action. In response, in 2016, the USFWS adopted an interim rule link prohibiting importation of 20 genera of salamanders. These genera had been shown by scientists to contain at least one species which either suffered mortality when it was exposed to Bsal or could transmit the disease to other salamanders. At the time, Bsal had been shown by scientific studies to be lethal to two American species; USFWS had evidence that U.S. species in other genera could “carry” the pathogen and infect other animals. Three of the species included in the 2016 action had already been listed as endangered or threatened. USFWS’ action cut down the number of salamanders being imported annually by ~95% (based on official import data compiled by the USFWS’ Office of Law Enforcement).
The prohibitions do not apply to articles that cannot transmit the fungus. These include eggs or gametes; parts or tissues that have been chemically preserved, chemically treated, or heat treated so that the pathogen, if present, is rendered non-viable; and molecular specimens consisting of only the nucleic acids from organisms.
Now, 8 years later, the USFWS is acting to finalize the 2016 “interim” rule and to regulate importation and transportation of an additional 16 genera of salamanders. This step had been urged by the National Environmental Coalition on Invasive Species (NECIS), and many others, in their public comments on that Interim Rule. Extending protection to these 16 genera is based on research conducted since the 2016 Rule. Species in 13 of the newly protected genera are considered likely carriers of the disease. Nine species have been demonstrated to be killed by Bsal. No studies have yet determined the vulnerability of more than 50 species in 10 genera of North American salamanders, including four species listed under the Endangered Species Act.
The 36 genera covered by the combined actions of 2016 and 2025 actions are currently considered to comprise ~ 426 species. However, changes in taxonomy are frequent. So USFWS is no longer enumerating the species protected, but is instead relying on listing genera. The regulations apply to all species in a listed genus (whether so classified now or in the future) as well as hybrids of species in any listed genus, including offspring from a pair in which only one of the parents is in a genus listed as injurious.
Appalachian hellbender Cryptobranchus alleganiensis alleghaniensis; historic book illustration via Flickr
USFWS chose to issue “interim” rules in both 2016 and 2025 because that action takes effect almost immediately. (The 2025 interim rule take effect on January 25th.) The usual rulemaking process governed by the Administrative Procedure Act (5 U.S.C. 551 et seq.) often takes years to complete. During that time, the species proposed for listing may still be imported and transported – that is, they could place additional salamander populations at risk of infection by Bsal. The USFWS states that it is unlikely to be able to protect or restore species and ecosystems if the pathogen does become established in the U.S.
In the interval between 2016 and now, Canada banned importation of all living or dead salamanders, eggs, sperm, tissue cultures, and embryos in response to the Bsal threat.
During these years scientists also completed several studies aimed at clarifying which salamander species are either at risk of infection by Bsal or are able to harbor and transmit the pathogen to other salamanders. The USFWS cites studies by, inter alia, Yuan et al. 2018, Carter et al. 2020, Barnhart et al. 2020, Grear et al. 2021, and Gray et al. 2023. USFWS says it cannot act in the absence of such studies, since it must justify its protective actions on scientifically defensible information.
Another relevant question is whether Bsal is already established in North America? Waddle et al. 2020 carried out an intensive search in 35 states that found no evidence that it is. The USFWS concludes that prohibiting importation of additional salamander taxa is still an effective measure to protect North American biodiversity. This is because the international commercial trade in salamanders is the most likely pathway by which Bsal would be introduced to the United States. We note in support of this assertion that former USFWS employee Su Jewell found years ago that none of the 288 non-indigenous species listed as injurious while they are not established in the U.S. has become established since the listing.
The Federal Register document includes a lengthy discussions of why the USFWS has chosen to act under the Lacey Act rather than try some other approach, e.g., setting up quarantine areas or a disease-free certification program for traded salamanders. Among the factors they considered were the current absence of certainty in testing procedures and the possibility of falsified documentation.
WEAKNESSES THE LACEY ACT
The Lacey Act is the principal statute under which the U.S. Government tries to manage invasive species of wildlife – at least those that are not considered “plant pests”. It is not surprising that a law written 125 years ago is no longer the best fit for current conservation needs. See our earlier blog and discussions by, inter alia, Fowler, Lodge, and Hsia and Anderson.
Here, the USFWS lacks authority to regulate pathogens [viruses, bacteria, and fungi that cause disease] or fomites (materials, such as water, that can act as passive carriers and transfer pathogens). Instead, USFWS regulates the hosts. The USFWS previously listed dead salmonids as “injurious” because their carcasses can transmit several viruses.
Another issue is that USFWS cannot designate a taxon “injurious” and regulate trade in it until the Service has conclusive scientific evidence that the species or genus meets the definition. The USFWS has chosen to rely on genus-level data rather than require that each species be tested. Still, as we noted above, American salamanders in 10 genera remain outside the Lacey Act’s protections because studies have not yet been conducted. The USFWS concedes that many of these genera might contain species that are vulnerable to this potentially deadly fungus.
As to relying on laboratory tests of a taxon’s response to the pathogen, the USFWS believes that environmental stresses inherent living in the wild might exacerbate a salamander species’ vulnerability to the disease.
The USFWS is requesting public comment specifically on:
(1) the extent to which species in the 16 genera listed by this interim rule are currently in domestic production for sale – and in which States this occurs? How many businesses sell salamanders from the listed genera between enumerated jurisdictions (e.g., between “lower 48” states and Hawai`i or the District of Columbia)?
(2) What state-listed endangered or threatened species would be affected by introduction of Bsal?
(3) How could this interim rule be modified to reduce costs or burdens for some or all entities, including small entities, while still meeting USFWS’s goals? What are the costs and benefits of the modifications?
(4) Is there any evidence suggesting that Bsal has been established in the U.S.? Or that any of these genera are not carriers of Bsal? Or that additional genera are carriers of Bsal? Is there evidence that eggs or other reproductive material pose a greater risk than USFWS determined, so should be regulated?
(5) Could a reliable health certificate system be developed that would allow imports of Bsal-free salamanders? Are there treatments that would ensure imported salamanders are reliably free of Bsal? How could compliance be monitored? As to salamander specimens, parts, or products, are there other treatments proven adequate to render Bsal non-viable?
(6) Do any Federal, State, or local rules duplicate, overlap, or conflict w/ this interim rule?
CISP encourages those with knowledge of amphibian conservation and disease to comment. Slow progress has been made toward blocking Bsal from the U.S., but the story is not yet closed.
See also the articles by Su Jewell,
Jewell, S.D. 2020 A century of injurious wildlife listing under the Lacey Act: a history. Management of Biological Invasions 11(3): 356–371, https://doi.org/10. 3391/mbi.2020.11.3.01
Jewell, S.D. and P.L. Fuller 2021 The unsung success of injurious wildlife listing under the Lacey Act. Management of Biological Invasions 2021 Volume 12 Issue 3
Posted by Faith Campbell and Peter Jenkins (former member of CISP’s board and consultant to NECIS and other groups on amphibian disease regulation)
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.
obvious risk of pest introduction! photo by F.T. Campbell
Because of the many damaging insects introduced in wood packaging, I often blog about numbers of shipping containers entering the country. [On the “nivemnic.us” website, scroll down below “archives” to “categories”, then click on “wood packaging” to see my previous blogs discussing this issue.]
The Department of Homeland Security’s Bureau of Customs and Border Protection (CBP) reports processing 36.6 million shipping containers holding imports in Fiscal Year 2023 – which ended in September 2023. These presumably included about 13 – 16 million containers arriving via ship from Asia, Europe, and other overseas trading partners. The remaining millions probably entering from Mexico and Canada via land transport. Together, Mexico and Canada provided 30% of U.S. imports in 2022.
It is difficult to pin down the actual number of containers entering the country. In contrast to the figure provided by CBP, Laura Robb of the Journal of Commerce reports that 25.6 million TEUs carrying imports entered the country in 2024. This figure apparently includes containers carried by all forms of transport. CBP counts containers by actual numbers, and about 90% of waterborne containers are actually 40 feet long, not the 20 feet measured by “TEU” (U.S. DoT). Halving the JOC number results in a total of about 13 million – well below that reported by CBP.
Overall volumes of imports carried by ship continue to rise. The monetary value of goods imported by the U.S. in maritime trade grew 15% from 2021 to 2022 (U.S. DoT). Robb reported that trade experts believe imports rose another 15% between 2023 and 2024. This rise is driven by retailers trying to protect themselves from a possible longshoremen’s strike (which might occur beginning 15 January), Trump’s threatened tariffs (he might act as early as 20 January); and the annual slowdown of production in Asia during Tet (which begins on 29 January). If import volumes meet expectations and continue through April, the series will outdo the previous (pandemic-era) record of 19 straight months when imports exceeded 2 million TEUs. What happens later in 2025 depends in part on whether the anticipated strike happens and/or actual levels of any new tariffs.
One concern about imports from Mexico and Canada is that some proportion of these goods actually originated in Asia or Europe, but were shipped through Mexican or Canadian ports. I have not found a source to clarify how many shipments fit this pattern. USDA APHIS used to blame forest pests introduced to the Great Lakes region on goods transported from the principal Canadian Atlantic port, St. John, Nova Scotia.
A useful publication for identifying where the pest-introduction risk is highest are the annual reports issued by U.S. Department of Transportation’s Bureau of Transportation Statistics. In calendar year 2022, U.S. maritime ports handled just under 43% of U.S. international trade (measured by value). There are two caveats: the data include both imports and exports; and the most recent data are from 2021.
Two-thirds of America’s maritime cargo (imports and exports) is shipped in traditional containers. This includes most consumer goods. The top 25 container ports handled a total of 45.6 million TEU (U.S. DoT). Map 4-3 in the report shows these ports and the proportions that are imports and exports.
The highest-ranking Container Ports in 2021 are those we expect. The ports of Los Angeles and Long Beach were numbers one and two. Together they received 10.7 million TEU. The third highest number of containers entered through the Port of New York & New Jersey. Nearly 5 million TEU entered there. The Port of Savannah ranked fourth. Savannah and nearby Charleston (ranked seventh) handled 4.2 million incoming TEUs in 2021.
Ranked above Charleston were the Port of Virginia and Houston. Each processed approximately 1.8 million containers filled with imports. Three West coast ports follow: Oakland, California and Tacoma and Seattle. Just over 1 million TEUs entered Oakland. The two Washington ports received a little over 1.5 million. Florida has four ports ranked in the “top 25”. In total, they processed 1.2 million TEU; most entered through PortMiami and Port Everglades. Baltimore, Philadelphia, Mobile, New Orleans, Wilmington, North Carolina and Wilmington, Delaware, South Jersey Port Corporation, and Boston all handled less than 500 imported containers in 2021. Domestic shipments from other U.S. states dominated containers processed through the ports of San Juan, Honolulu, and Alaska.
gantry crane in operation at the Port of Savannah; photo by F.T. Campbell
The top ports must have appropriate facilities needed to load / unload container vessels efficiently– that is, adequate numbers of gantry cranes, especially super post-Panamax cranes, which have the greatest capacity. The top 25 container ports of 2021 operated a total of 539 ship-to-shore gantry cranes in 2023, of which 322 (60%) are post-Panamax cranes. Ports are adding cranes – there were 29 more in 2023 than in 2021. The Port of Virginia appears to be striving for significant increases in tonnage; it has 28 Panamax cranes, more than Charleston and almost as many as Savannah (U.S. DoT).
Another important port component is efficient facilities to load containers onto rail cars or trucks for transfer to land-based warehouses and retailers. Ports have more than one terminal; for example, the Port of Long Beach has six, New York/New Jersey has five. Nationwide, 70% of container terminals have on-dock facilities to transfer containers directly onto rail cars. All but three of the 33 terminals located at Long Beach. Los Angeles, New York, Savannah, Charleston, Houston 2/2, Seattle, and Tacoma have on-dock transfer equipment.
The U.S. DoT reports also inform us about the top 25 ports that handle other categories of cargo: overall tonnage, dry and liquid bulk cargo, break bulk cargo, and roll-on-roll-off cargo. Visit the report to view these data.
SOURCES
Robb, L. 2024. U.S. import “surge” to persist into spring amid continued frontloading: retailers. Journal of Commerce Daily Newswire December 10, 2024
U.S. Department of Transportation, Bureau of Transportation Statistics, Annual Report 2024 Port Performance Freight Statistics January 2024 https://www.bts.gov/explore-topics-and-geography/modes/maritime-and-inland-waterways/2024-port-performance-freight
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 https://treeimprovement.tennessee.edu/
BLD symptoms; photo by Matt Borden, Bartlett Tree Experts
As beech leaf disease (BLD) is detected in an ever-expanding number of counties from Michigan to Maine south to Virginia, scientists are trying to clarify how the causal nematode — Litylenchus crenatae ssp. mccannii (Lcm) – spreads. One focus is on local spread from tree to tree. Mankanwal Goraya and colleagues set up an experiment in Stone Valley Forest, a recreation and research site managed by Penn State in Huntington County, Pennsylvania. BLD is present – although I have not been able to determine for how many years. [The full citation to Goraya et al. is provided at the end of this blog.]
Goraya et al. (2024) set up four stands, each bearing three funnels, at varying distances from naturally BLD-infected American beech (Fagus grandifolia) trees. Two stands were at 3.51 m from symptomatic trees of starkly different sizes: one of the trees had a dbh of 50 cm, the other of only 5.6 cm. A third close-up stand was set up at 2.20 m from another large tree, having a dbh of 46 cm. The fourth stand was set up at a significantly longer distance, 11.74 m from a symptomatic beech tree; this tree was also small, with a dbh of 5 cm. This arrangement allowed the scientists to detect influences of both distance from the source of infection and relative canopy size of the source tree. They consider dbh to be an adequate substitute for canopy size. There was apparently no other effort to determine or vary the height of “source” trees, although I think that might influence speed of the wind flowing through the canopy.
Goraya et al. also tested whether it is possible to detect the presence of Lcm in association with other invertebrates that live in beech forests. To do this, they counted numbers of nematodes in frass from six species of caterpillars that had been feeding on leaves of infected trees, and in two spider webs spun in the branches of symptomatic trees. They also determined whether these nematodes were alive (active) or inactive – presumably dead.
The study makes clear that Lcm’s life cycle and impact are not as surprising as initially thought. Several species in the family Anguinidae – to which Lcm belongs – are considered significant pests. These nematodes can parasitize aerial parts of the plants (leaves, stems, inflorescences and seeds), causing swellings and galls. Furthermore, they are migratory; they can move across the surface of host tissues using water films. Once they have penetrated the host tissues, they can induce host cell hyperplasia and hypertrophy, resulting in leaf or bulb deformities, shorter internodes, and neoplastic tissues. Furthermore, heavy rainfall and wind are known to play significant roles in the dissemination of plant-infecting nematodes. In their desiccated state on infected seeds, some species of this family can survive passage through animals’ gastrointestinal digestive tract (e.g., domestic livestock, insects, & birds).
A crucial factor is that Lcm can reach densities of thousands of nematodes per leaf by late summer or early fall, increasing the likelihood of their exposure to facilitating environmental conditions at the time they migrate from leaves to buds. And once established within the bud tissues, the nematodes feed on bud scales and newly forming leaves to develop & increase their pop #s. They also use the bud as protection from adverse environmental conditions.
Goraya and colleagues collected samples every other day from September 9 to November 23, 2023 – the period when Lcm migrate from highly infected leaves to newly forming buds. [I note that it in the mid-Atlantic – where Lcm is spreading – we had an extensive drought in autumn 2024 – more than 30 days without any rain from early October into November. I hope scientists are monitoring BLD spread sufficient closely to see whether this drought affected dispersal.]
Nematodes dispersal linked to weather
Goraya and colleagues collected 324 samples from the funnels. Eighty-two percent (n =266) of the samples had nematodes; up to 92% were identified as Lcm. Non-Lcm nematodes were distributed across different genera, mostly classified as free-living nematodes. While several hundred nematodes were found in the funnels on most days, numbers peaked noticeably on some days in September and October. A startling 2,452 nematodes were recovered from a single funnel in October. Depending on the sample, up to 67% of Lcm recovered from the funnels were active.
Analysis of the environmental (weather) variables found that increases in wind speed, humidity, and precipitation (rainfall) coincided with higher numbers of Lcm being recovered from the funnels. However, the effect of wind speed becomes less positive as precipitation increases or vice versa. Goraya et al. suggest a pronounced negative interaction between wind and rain. At low precipitation levels, increased wind speed might facilitate Lcm dispersal. As rainfall increases, higher wind speeds might carry the Lcm nematodes farther away. Support is seen in the fact that fewer nematodes were found in the funnels closer to the BLD-infected trees during these periods. Really heavy rain might push a significant preponderance of nematodes to the ground. The scientists point to a very complex interplay between weather patterns and Lcm population dynamics and dispersal.
BLD symptoms on beech tree in Fairfax County, Virginia – a dozen miles from known infestation; photo by F.T. Campbell
The model did not show any significant influence of maximum temperature on nematode numbers in autumn. Goraya et al. do not speculate on whether temperatures might play a role during summer, as distinct from cooler autumn periods.
Goraya et al.’s findings differ from those of previous studies. Earlier documentation of wind dispersal of nematodes concerned primarily free-living species. It was unexpected to find consistently much higher numbers of Lcm – especially because Lcm is a plant-parasitic nematode. Another surprise is the high proportion of nematodes that are active.
Goraya et al. conclude that because Lcm is actively migrating in large numbers during autumn months, it is primed to take advantage of favorable weather. This nematode will likely survive and thrive in the environmental conditions of beech forests in northeastern North America.
Considering the effect of distance, some findings fit expectations: significantly more Lcm were recovered from funnels placed near symptomatic “source” trees than from those farther away. However, this was not a simple relationship. For example, in two cases the scenarios seemed nearly alike: both “source” trees were large (dbh 46 or 50 cm) and symptoms were “medium-high” (more than half of leaves presenting dark-green interveinal bands). Distance of funnels from the “source” tree differed minimally: 2.2 m versus 3.51 m. Still, the number of nematodes retrieved from the two sets of funnels differed significantly: one set of funnels recovered the highest number of Lcm nematodes obtained during the entire experiment – 2,452; the second contained only up to 600 nematodes. The authors do not offer an explanation.
I am not surprised by the apparently strong correlation between numbers and proximity to the disease source (a symptomatic tree). Nor am I surprised that Lcm nematodes were also found in funnels 11 meters away. I do wonder, however, why they are certain that no source was closer. Detecting early stage infections is notoriously difficult.
beech with large canopy; photo by F.T. Campbell
Goraya et al. also evaluated the effect of size of the source tree. They used dbh a substitute for larger canopies. Trees with larger canopies can host more nematodes, so are likely to contribute more to dispersal events. Two sets of funnels were equidistant from separate “source” trees – 3.51 m. One tree was small – 5.6 cm dbh, 11% as large as the other tree (50 cm). They collected many fewer Lcm nematodes from the smaller tree – the maximum was only 132 compared to 600 (a decrease of 78%).
Still, small trees can apparently support spread of the nematode to a reasonable distance. The fourth set of funnels was set up more than three times farther away (11.74 m) from an infected tree of a similar size (dbh = 5 cm) but recovered almost the same number of Lcm nematodes (0 – 119).
I find it alarming that both small trees in this part of the experiment had low BLD symptoms – only a few leaves were banded. Yet they apparently are the source of Lcm spread. The alternative, as I noted above, is that other “source” trees were in the vicinity but were not detected, possibly because they did not yet display symptoms?
Goraya et al. conclude that “source” tree size directly impacts the number of recovered nematodes. In addition, wind plays a pivotal role in their local distribution. This suggests a complex dispersal pattern in which proximity to the source leads to higher numbers of nematodes but longer-distance spread is possible.
Tussock moth; photo by Jon Yuschock via Bugwood
Nematodes’ association with other organisms
Goraya et al. (2024) collected one each of six caterpillar species from BLD-symptomatic trees. The frass of one – the tussock moth caterpillar (Halysidota tessellaris) — contained 12 nematode specimens — 10 of them Lcm. Two of the Lcm were alive and active. Their presence indicates that Lcm can survive passage through the caterpillar’s gastrointestinal tract. The authors conclude that caterpillars feeding on symptomatic leaves might contribute to local dispersal of Lcm.
Hundreds of Lcm were recovered from the two spider webs collected from the branches of a BLD-infected beech tree. From one web, 255 nematodes were captured; 58 were active. In the second web there were only 34 Lcm, but one-third — 10 – were active.
Goraya et al. (2024) hypothesized that any biotic form having the ability to move from a BLD-infected tree would be able to transport Lcm to other non-infected trees. Beyond caterpillars, they speculate that birds consuming these caterpillars might also disperse Lcm. Doug Tallamy has documented that many birds feed on caterpillars, link although he is focused on those that consume caterpillars in the spring, not the autumn. They note that others are studying that the bird species that feed on beech buds (e.g., finches) might transport nematodes. They note the need for additional research to clarify whether the nematode can survive birds’ digestive system.
Re: detection of live Lcm in spider webs, Goraya et al. suggest two possible interpretations: 1) this finding demonstrates that nematodes might fall from leaves, potentially spreading the infection to other trees beneath the canopy. (Supporting this idea is the fact that sub-canopy trees are often heavily infected with BLD and are frequently the first to exhibit BLD symptoms.) 2) Nematodes in spider webs are very likely to be transported by other “incidental organisms” (e.g., insects, birds, mammals) that feed on invertebrates trapped in webs — thereby potentially increasing the number and impact of nonspecific nematode vectors.
In conclusion, Goraya et al. found that many factors, e.g., distance & size of infected beech trees, wind speed, & humidity, contribute significantly to Lcm dispersal. The multitude of organisms interacting beneath the canopy also play a role.
They suggest that several major questions still need to be explored. These include how Lcm navigate environmental factors in their spread; and whether Lcm can survive – perhaps in a anhydrobioses state –transport over long distances, whether by abiotic or biotic vectors.
I remind my readers of the importance of beech in the hardwood forests in northeastern North America. Many wild animals, including squirrels, wild turkeys, white-tailed deer, and bears depend on beechnuts for fats and proteins. Moreover, some insects birds rely on beech tree canopies for shelter & nesting.
Other Hosts
Beech leaf disease attacks not just American beech (Fagus grandifolia). In North America, it has also attacked planted European beech(F. sylvatica), Chinese beech (F. engleriana), and Oriental beech (F. orientalis). Thus if it spreads it could have severe impacts across forests of much of the Northern Hemisphere.
range of European beech; from Royal Botanic Gardens, Kew
I appreciate that this project was funded by the USDA Forest Service International Program. I will pursue information concerning efforts by USFS Research and Development and the Forest Health Protection program.
SOURCE
Goraya, M., C. Kantor, P. Vieira, D. Martin, M. Kantor. 2024 Deciphering the vectors: Unveiling the local dispersal of Litylenchus crenatae ssp mccanni in the American beech (Fagus grandifolia) forest ecosystem PLOS ONE |https://doi.org/10.1371/journal.pone.0311830 November 8, 2024 1 / 16
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 https://treeimprovement.tennessee.edu/
Yet again, studies focusing on issues of regeneration and mortality failing to consider all aspects.
Two studies focused on persistence of oak forests – a topic of great concern because of economic and ecological importance of oak-dominated forests. Since they dominate forests covering 78.5 million ha (51% of all forestland in the eastern United States) (Dey 2013), oaks shape stand structure and composition; their extensive crowns support many bird and arboreal mammal species; their acorns and leaf litter are the foundation of complex food webs; they live in symbiotic relationships with mycorrhizal fungi that enhance nutrient cycling and uptake within forest ecosystems. Deep roots prevent soil erosion. Oaks play a pivotal role in carbon sequestration (Khadka, Hong, and Bardhan 2024).
Until recently concern has focused on mortality of species in the red oak group (Section Lobatae). Now there is increasing concern about white oak (Quercus alba) mortality. Forest managers reported elevated mortality not just in resource-limited sites,e.g., those characterized by drought conditions, poor drainage, and soil nutrient deficiencies. Deaths are also occurring in higher-quality mesic sites, especially in forests with high stand density and advanced maturity stages. While white oaks go through a self-thinning phase – when dense stands of younger trees compete intensely for limited resources –it appears that some of the concern is focused on this stage (Khadka, Hong, and Bardhan 2024).
I think much of the concern is driven by economic rather than ecological considerations. None of oak species mentioned by Duana et al. (2024) is considered at risk by the authors of the recent conservation gap analysis (Beckman et al. 2019). (This is not surprising since presumably these species are sufficiently numerous to support commercial harvests). Furthermore, complaints about forest regeneration in the East are broader than oaks. A multi-author examination of the future of the northern forest projected decreases for four forest types = aspen-birch, elm-ash-cottonwood, oak-hickory, and spruce-fir. One type –maple-beech-birch – was expected to expand (Shifley and Moser 2016).
Regarding oaks specifically, Khadka, Hong, and Bardhan (2024) found that 30% of FIA plots in ten states composed primarily of white oak met their criteria for considering white oaks to be “declining”. However, higher mortality was limited to scattered areas (see map in Fig. 2B in the article). They suggested that contributing factors included higher elevation and distance from water in the north, intense competition in central regions, and drought stress in oak-hickory forests in the south. They also mentioned mature stands which are not replacing themselves in the southern region. Khadka, Hong, and Bardhan (2024) noted that oak decline complex is a factor in the southern region, and localized non-native insect pests (apparently spongy moth) in the northern region. (I will discuss both regeneration failures and the impacts of non-native pests below.) Still, these authors focus most attention to environmental stresses, e.g., droughts or water logging, poor soils, extreme weather events; and to human management, e.g., fire suppression, logging intensity, edge effects. They suggest strategies for mitigating these factors.
A second study, published by Duana et al. (2024), considered stocking levels of several species of oaks (Q. alba, Q. coccinea, Q. prinus, Q. rubra, and Q. velutina) but limited themselves to a large, temperate hardwood forest landscape in southeastern Ohio. Their purpose was to evaluate the efficacy of two levels of silvicultural intervention in sustaining oaks and restraining maples over the long-term, defined as 150-years (to 2060).
red oak (Quercus rubra); photo by F.T. Campbell
Their model suggested that continuing “business as usual” management would result in oaks shrinking from 22.8% dominance in 2010 to 12% dominance in 2160. Many of the remaining oaks would be large — in the 70 cm DBH class. The undesired maples would rise from 23% of total relative dominance in 2010 to 58% in 2160. The maples grew to almost the same size as the oaks: 50–65 cm DBH. As a result of these developments, the maple basal area increase by more than five times. The basal area of early successional species, e.g., poplars and aspens, decreased from 25% dominance to 11% dominance by 2160. Shade-tolerant species like elms, hickories, beech, and hemlock were suppressed by more competitive maples, occupying 17% of the total dominance.
Under the more manipulative alternative management strategy, oaks’ relative dominance on private land would stay above 20% of total relative dominance; all ages and sizes would be present. Maples would hold steadier at 23% to 33%. Shade-tolerant species would also rise, reaching a quarter of relative dominance on private some site (private public lands).
Duana et al. (2024) explained the outcome of “business as usual” management on maples’ ability to thrive in shaded conditions while oak regeneration requires sunlight to reach the forest floor. Another factor is the prevalence of high-grading harvesting practices. These factors result in a significant absence of oak trees in the sapling and midstory sizes, reflecting challenges to both oak seedlings and saplings. In other words, despite the continued growth of mature overstory oaks, the trees cannot reproduce. As Duana et al. (2024) point out, these results are supported by other field-based studies — including ones I have blogged about. Duana et al. (2024) discuss barriers and incentives to private landowners adopting more active management.
However, as I pointed out above, many tree species are regenerating poorly, not just oaks. Indeed, none of the eastern species fulfilling Potter and Riitters’ (2022) criteria for species threatened by poor regeneration was an oak. See Table 2 in Potter and Riitters (2022).
American sycamore (Platanus occidentalis) – one of the tree species not regenerating adequately; photo by F.T. Campbell
Hanberry et al. (2020) found that actual changes in forest species composition and density do not conform to expectations arising from three factors proposed as drivers: increased precipitation, increased white-tailed deer densities, and functional extinction of American chestnut. They found disappearance of frequent low-intensity fires to be determinative. However, Hanberry et al. (2020) also do not mention invasive plants or non-native pests other than chestnut blight.
Here I review others’ discussion of browsing by overabundant deer and competition from non-native plants as factors widely recognized as impeding regeneration of canopy trees, including oaks.
Deer
There is widespread agreement that browsing by overabundant deer is a major cause of poor regeneration of deciduous forests, especially but not limited to oaks (Quercus species.). Sources cited in my previous blogs include most studies discussed at the 2023 Northern Hardwood research forum (USDA, FS 2023b Proceedings), Spicer et al. (2023), Miller et al., and two studies based in either Ohio (the location of the study by Duana et al. [2024]) or neighboring Pennsylvania: Yaccuci et al. (2023) and Reed et al. 2023. Yacucci et al. reported that stem density of red (Q. rubra) and pin oaks (Q. palustris) was 13 times higher in canopy gaps located in areas with low densities of deer than in gaps in high-deer-density locations. In these gaps, oak saplings were growing into the subcanopy. Reed et al. said deer herbivory might be one of the most important drivers of forest composition and canopy structure over long time-scales.
Deer might be less important in New England. Stern et al. (2023), working in Vermont, focused on the importance of changing precipitation patterns in shifting numbers of red maple (Acer rubrum), sugar maple (Acer saccharum), American beech (Fagus grandifolia), and yellow birch (Betula alleghaniensis). Northern red oak was described as a common co-occurring dominant species in their plots, but was not discussed. In New Hampshire, Ducey et al. reported changing species composition as the forest ages but did not mention deer.
Some of these authors advocated wide-scale efforts to reduce deer populations in order to restore forest ecosystems. Yacucci et al. proposed enlisting those military posts that regularly cull deer into efforts to conserve and regenerate native plants. Otherwise, they say, the prognosis for regeneration is poor. Blossey et al. urged creation of a nation-wide lethal removal program.
Some of these studies indicated that additional biological entities were also important. Miller et al. stressed the role of invasive plants in suppressing forest regeneration in National parks from Virginia to Maine. Reed et al. focused on invading earthworms. One study – again, conducted in Ohio – Hovena et al. (2022), found that interactions between non-native shrubs and soil wetness overshadowed even the impact of deer herbivory on the species richness and abundance of seedlings.
Invasive Plants
FIA data indicate that 46% of forests in the eastern United States are invaded by alien plant species (Oswalt et al. 2016). Across the region, hundreds of non-native plant species are established in forests and woodlands. (See lists compiled by the Southeast Exotic Pest Plant Council, Mid-Atlantic Invasive Plant Council, Midwest Invasive Plants Network). Forests of the northern Midwest are among the most heavily invaded; in Ohio specifically, two studies found that more than 90% of FIA plots harbor at least one invasive plant species (Oswalt et al. [2016] and Kurtz (USDA NRS 311).
Many of these invaders are herbs, shrubs, or trees which can invade shaded environments. I remind you that a high proportion of these invasive plant species have been deliberately planted either directly in “natural” areas or in yards and gardens throughout the region.
Invasive plants can reduce native diversity, alter forest structure, suppress tree regeneration, alter nutrient cycling, and modify disturbance regimes (Miller et al. 2023).
Japanese stiltgrass (Microstegium vimineum) is widespread in forests of both Northeast (Oswalt et al. (2016) and Southeast. Stiltgrass invasions can suppress oak regeneration – at least as part of interactions with herbivore browsing and harvest history (Johnson et al. 2015).
Amur honeysuckle; via Flickr
Several non-native shrub and vine species are also widespread. For example, multiflora rose (Rosa multiflora) is the most frequently recorded invasive plant, present on 16.6% of surveyed plots in 39 states and five Canadian provinces. Again, the state with the highest proportion of plots invaded is Ohio – 85% (USDA Forest Service NRS-109). A study in central Ohio found that the presence of Amur honeysuckle (Lonicera mackii) had a stronger influence on tree species diversity than on the size or number of trees. Removing honeysuckle from heavily invaded areas promoted native tree growth (e.g., the height of tallest trees) and increased the tree canopy’s structural complexity for up to 10 years. Forest recovery began within two years of honeysuckle removal Fotis et al. (2022). (To access earlier blogs, visit www.nivemnic.us; scroll below “archives” to “categories”, click on “invasive plants.)
This impediment to forest regeneration is expected to get worse: non-native plant species are already more widely distributed than native species although the average invasive plant inhabits only about 50% of its expected range (Bradley, Early and Sorte 2015). From Virginia and West Virginia north to Maine, 80% of National Park units have experienced a significant increase in at least one trend measuring abundance of invasive plants in recent decades. In 10 parks (a quarter of all parks studied), total invasives increased significantly in two of three metrics (Miller et al. 2023).
Non-native Pests
Another set of biological factors affecting forest persistence and possibly regeneration is non-native pests that kill North American trees. I have complained that too few of the studies of regeneration discuss implications of these bioinvasions. So Khadka, Hong, and Bardhan (2024), Duana et al. (2024), and Hanberry et al. (2020) continue a tradition that I think is most unfortunate.
American elm in full glory; photo by F.T. Campbell
In Ohio specifically, Hovena et al. and Yacucci et al. did not mention loss of canopy elms, or ash, or the impending threat from beech leaf disease. All these trees are – or used to be – quite common in Ohio. More understandable, perhaps, is lack of attention to laurel wilt disease, which is just now at the state’s southern border. It might decimate an important native shrub, Lindera benzoin. American chestnut was also present in Ohio before its near disappearance following introduction of the chestnut blight fungus early in the 20th Century.
Another possibly damaging pest that has recently turned up in Ohio is the elm zigzag sawflyAproceros leucopoda. This Asian insect was first detected in North America in 2020 in Ontario. It quickly became apparent that it was more widespread. The Ohio detection came in 2023 – too recent to be discussed by Hovena et al. or Yacucci et al. Its impact several elm species is currently unknown.
There are exceptions. Both Stern et al. (2023) and Ducey at al. (2023) reported robust growth rates of American beech (Fagus grandifolia) despite decades-long establishment of beech bark disease. DMF Neither mentioned beech leaf disease – to be fair, this bioinvader is just starting to appear in New England. Stern et al. (2023) did not discuss hemlock woolly adelgid although Eastern hemlock (Tsuga canadensis) is also a common co-occurring dominant species in their plots. Ducey et al. did anticipate pest-driven reversals of increased numbers of eastern hemlock (Tsuga canadensis) and of white ash (Fraxinus americana). Stern et al. (2023) also did not mention oak wilt, despite a vulnerable host — northern red oak — being a common co-dominant species in his study site in Vermont. To be fair, oak wilt is not yet established in New England, although it is in New York and in western Ontario.
The most complete discussion of non-native pests is by Payne and Peet, working in the Piedmont of North Carolina. They state that several “specialist” pathogens have caused loss of important tree species, resulting in drastic and long-lasting shifts in community dynamics. They mention elms and dogwoods plus impending insect-caused widespread mortality of ash.
flowering dogwood (Cornus florida); photo by F.T. Campbell
Miller et al. describe the impact of EAB on ash resources in the National parks and express concern that BLD will cause considerable damage to some units of the system.
I think the failure of scientists to integrate invasive species’ impacts into assessments of changes in forest tree composition will mean that recommendations for management will be – at best – incomplete; at worst – wrong.
SOURCES
Beckman, E., Meyer, A., Denvir, A., Gill, D., Man, G., Pivorunas, D., Shaw, K., and Westwood, M. (2019). Conservation Gap Analysis of Native U.S. Oaks. Lisle, IL: The Morton Arboretum.
Blossey. B., D. Hare, and D.M. Waller, 2024. Where have all the flowers gone? A call for federal leadership in deer management in the US. Front. Conserv. Sci. 5:1382132. doi: 10.3389/fcosc.2024.1382132
Bradley, B.A., R. Early and C. J. B. Sorte. 2015. Space to invade? Comparative range infilling and potential range of invasive and native plants. Global Ecology and Biogeography
Dey, D.C. 2013. Sustaining Oak Forests in Eastern North America: Regeneration and Recruitment, the Pillars of Sustainability. For. Sci. 60(5):926–942 October 2013. http://dx.doi.org/10.5849/forsci.13-114
Duana, S., H.S. He, L.S. Pile Knapp, T.W. Bonnot, J.S. Fraser. 2024. Private land management is more important than public land in sustaining oaks in temperate forests in the eastern U.S. Journal of Environmental Management 352 (2024) 120013
Ducey, M.J, O.L. Fraser, M. Yamasaki, E.P. Belair, W.B. Leak. 2023. Eight decades of compositional change in a managed northern hardwood landscape. Forest Ecosystems 10 (2023) 100121
Fotis, A., Flower, C.E.; Atkins, J.W. Pinchot, C.C., Rodewald, A.D., Matthews, S. 2022. The short-term and long-term effects of honeysuckle removal on canopy structure and implications for urban forest management. Forest Ecology and Management. 517(6): 120251. 10 p. https://doi.org/10.1016/j.foreco.2022.120251
Hanberry, B.B., M.D. Abrams, M.A. Arthur & J.M. Varner. 2020. Reviewing Fire, Climate, Deer, & Foundation Spp as Drivers of Historically Open Oak & Pine Forests & Transition to Closed Forests. Front. For. Glob. Change 3:56. doi: 10.3389/ffgc.2020.00056
Hovena, B.M., K.S. Knight, V.E. Peters, and D.L Gorchov. 2022. Woody seedling community responses to deer herbivory, intro shrubs, and ash mortality depend on canopy competition and site wetness. Forest Ecology and Management. 523 (2022) 120488
Johnson, D.J., S.L. Flory, A. Shelton, C. Huebner and Keith Clay. 2015 Interactive effects of a non-native invasive grass Microstegium vimineum and herbivore exclusion on experimental tree regeneration under differing forest management. Journal of Applied Ecology 2015, 52, 210–219 doi: 10.1111/1365-2664.12356
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Miller, K.M., S.J. Perles, J.P. Schmit, E.R. Matthews, and 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 Open Access
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Deer browse susceptibility limits c’nut restoration success in northern hardwood forests PUBLIC
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USDA Forest Service Northern Research Station Rooted in Research ISSUE 18 | SEPTEMBER 2023
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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 https://treeimprovement.tennessee.edu/
