Category: invasive species policy

Act Now!!! Administration Proposes to “0 out” key USFS Programs

The Trump Administration’s budget for Fiscal Year 2026 [which begins at the end of September 2025] proposes to eliminate funding for nearly all  USFS research & Forest Health Protection.

Proposed Cuts to USFS Research: Timber the Sole Aim

 In a letter from Office of Management and Budget (OMB) to Senate Appropriations Committee Chair Susan Collins (R-Maine, Director Russell Vought says the Administration wants to manage National forests “for their intended purpose of producing timber” and that the research and development program “is out of step with the practical needs of forest management for timber production.” The Administration proposes to eliminate funding for USFS research projects other than the small portion covering Forest Inventory and Analysis.

I understand that the USFS Chief told various NGOs that his job is to run the National Forest System, increase timber production by 40%, and do nothing else.

This single aim conflicts with the 1897 legislation founding and authorizing the USFS. It also violates provisions of subsequent legislation such as the Multiple-Use Sustained-Yield Act of 1960 and the National Forest Management Act of 1976. It also departs from long-standing US Forest Service policy – which is the intention. 

The “intended purpose” of establishing “forest reserves” [which were later renamed National forests] has never been solely for timber production. The “Organic Act” of 1897 provided that any new forest reserves would have to meet the criteria of forest protection, watershed protection, and timber production.

Specifically, the ORGANIC ACT OF 1897 [PUBLIC–No.2.] says:

“[All public lands heretofore designated and reserved by the President of the US under the provisions of the Act [of] March 3rd 1891, the orders for which shall be and remains in full force and effect, unsuspended and unrevoked, and all public lands that may hereafter be set aside as public forest reserves under said act, [these were the “forest reserves,”predecessors of “National Forests]” shall be as far as practicable controlled and administered in accordance with the following provisions:

“No public forest reservation shall be established, except to improve and protect the forest within the reservation, or for the purpose of securing favorable conditions of water flows, and to furnish a continuous supply of timber for the use and necessities of [US] citizens; but it is not the purpose or intent of these provisions, or of the Act providing for such reservations, to authorize the inclusion therein of lands more valuable for the mineral therein, or for agricultural purposes, than for forest purposes.”

The Department of the Interior, which then managed these forest reserves, promptly issued implementing regulations. The regulations stated that the “object” of forest reservations was:

“2. Public forest reservations are established to protect and improve the forests for the purpose of securing a permanent supply of timber for the people and insuring conditions favorable to continuous water flow.”

Therefore, I think the Administration has exaggerated the emphasis on timber production by calling it “the” intended purpose of the original establishment of National forests. The Administration has also chosen to ignore subsequent legislation, such as the Multiple-Use Sustained-Yield Act of 1960 and the National Forest Management Act of 1976.

Sec. 13 of the NFMA limits the sale of timber from each national forest to a quantity equal to or less than a quantity which can be removed from such forest annually in perpetuity on a sustained-yield basis. This limit might be exceeded under certain circumstances, but such excess must still be consistent with the multiple-use management objectives of the land management plan. Further, Sec. 14 requires public input into any decision to raise timber allowances.

During his period as Chief (1905 – 1910), Gifford Pinchot invented and applied the concept of “conservation” of natural resources. As a result “wise use” became accepted as the national goal.

Culminating more than a century of legislation and informed policy, the mission of the USDA Forest Service is to “sustain the health, diversity, and productivity of the nation’s forests and grasslands to meet the needs of present and future generations.”

Proposed Cuts to State, Private, and Tribal Forests

The budget also cuts $303 million from the State, Private, and Tribal Forests program. (I understand this zeroes out the entire program). The OMB Director alleges that the program has been “plagued by oversight issues, including allegation of impropriety by both the Agency and State governments.” I understand that this would eliminate the cooperative projects managed by the Forest Health Protection program, too.

Implications for Non-native Insects and Pathogens

Remember that USFS’s research and development program is intended to improve forest managers’ understanding of ecosystems, including human interactions and influences, thereby enabling improvements to the health and use of our Nation’s forests and grasslands. Most importantly to me, this program provides foundational knowledge needed to develop effective programs to prevent, suppress, mitigate, and eradicate the approximately 500 non-native insects and pathogens that are killing America’s trees.

The Forest Health Program provides technical and financial assistance to the states and other forest-management partners to carry out projects (designed based on the above research) intended to prevent, suppress, mitigate, and eradicate those non-native insects and pathogens. The program’s work on non-federal lands is crucial because introduced pests usually start their incursions near cities that receive imports (often transported in crates, pallets, or imported plants).

Eliminating either or both programs will allow these pests to cause even more damage to forest resources – including timber.

Both supporting research and on-the-ground management must address pest threats across all U.S. forests, including the more than 69% that are located on lands managed by others than the USFS. Already, the 15 most damaging of these pests threaten destruction of 41% of forest biomass in the “lower 48” states. This is a rate similar in magnitude to that attributed to fire (Fei et al. 2019). It is ironic that the Administration considers the fire threat to be so severe that it has proposed restructuring the government’s fire management structure.

I remind you that the existing USFS R&D budget allocates less than 1% of the total appropriation to studying a few of the dozens of highly damaging non-native pests. I have argued that this program should be expanded, not eliminated. Adequate funding might allow the USFS to design successful pest-management programs for additional pests (as suggested by Coleman et al.).

As a new international report (FAO 2025) notes, genetic resources underpin forests’ resilience, adaptability, and productivity. Funding shortfalls already undercut efforts to breed trees able to thrive despite introduced pests and climate change (the latter threat is still real, although the Administration disregards it). I have frequently urged the Congress to increase funding for USFS programs – which are sponsored primarily by the National Forest System and State, Private, and Tribal, although some are under the R&D program.

Please ask your Member of Congress and Senators to oppose these proposed cuts. Ask them to support continued funding for both USFS R&D and its State, Private, and Tribal Programs targetting non-native insects and pathogens. America’s forests provide resources to all Americans – well beyond only timber production and they deserve protection.

Contacting your Representative and Senators is particularly important if they serve on the Appropriations committees.

House Appropriations Committee members:

Republicans: AL: Robert Aderholt, Dale Strong; AR: Steve Womack; AZ: Juan Ciscomani; CA: Ken Calvert, David Valadao, Norma Torres; FL: Mario Diaz-Balart, John Rutherford, Scott Franklin; GA: Andrew Clyde; ID: Michael Simpson; IA: Ashley Hinson; KY: Harold Rogers; LA: Julia Letlow; MD: Andy Harris; MI: John Moolenaar; MO: Mark Alford; MS: Michael Guest;  MT: Ryan Zinke; NC: Chuck Edwards; NV: Mark Amodei; NY: Nick LaLota; OH: David Joyce; OK: Tom Cole, Stephanie Bice; PA: Guy Reschenthaler TX: John Carter, Chuck Fleishmann, Tony Gonzales, Michael Cloud, Jake Ellzey; UT: Celeste Maloy; VA: Ben Cline; WA: Dan Newhouse; WV: Riley Moore

Democrats: CA: Pete Aguilar, Josh Harder, Mike Levin; CT: Rosa DeLauro; FL: Debbie Wasserman Schultz, Lois Frankel; GA: Sanford Bishop; HI: Ed Case IL: Mike Quigley, Lauren Underwood; IN: Frank Mrvan; MD: Steny Hoyer, Glenn Ivey; ME: Chellie Pingree; MN: Betty McCollum; NJ: Bonnie Watson Coleman NY: Grace Meng, Adriano Espaillat, Joseph Morelle; NV: Susie Lee;  OH: Marcy Kaptur;  PA: Madeleine Dean; SC: James Clyburn;  TX: Henry Cuellar, Veronica Escobar; WA: Marie Gluesenkamp Perez; WI: Mark Pocan

Senate Appropriations Committee members:

Republicans: AK: Lisa Murkowski; AL: Katie Britt; AR: John Boozman (AR); KS: Jerry Moran; KY: Mitch McConnell; LA: John Kennedy; ME: Susan Collins; MS: Cindy Hyde-Smith; ND: John Hoeven; NE: Deb Fischer; OK: Markwayne Mullin; SC: Lindsey Graham; SD: Mike Rounds TN: Bill Hagerty; WV: Shelley Moore Capito;

Democrats: CT: Chris Murphy; DE: Chris Coons; GA: Jon Ossof; HI: Brian Schatz; IL: Richard Durbin; MD: Chris van Hollen; MI: Gary Peters; NH: Jeanne Shaheen; NM: Martin Heinrich; NY: Kirsten Gillibrand; OR: Jeff Merkley; RI: Jack Reed; WA: Patty Murray; WI: Tammy Baldwin

SOURCES

Coleman, T.W, A.D. Graves, B.W. Oblinger, R.W. Flowers, J.J. Jacobs, B.D. Moltzan, S.S. Stephens, R.J. Rabaglia. 2023. Evaluating a decade (2011–2020) of integrated forest pest management in the United States. Journal of Integrated Pest Management, (2023) 14(1): 23; 1–17

FAO. 2025. The Second Report on the State of the World’s Forest Genetic Resources. FAO Commission on Genetic Resources for Food and Agriculture Assessments, 2025. Rome.

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. 2019. Biomass losses resulting from insect and disease invasions in United States forests. PNAS August 27, 2019. Vol. 116 No. 35  17371–17376

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/

or

www.fadingforests.org

Does a long-established non-native insect threaten America’s cedars?

Guest blog by Kristy M. McAndrew, Department of Forestry, Mississippi State University

Virginia juniper (Juniperus virginiana) preforming its ecological role: succession in a field (in Ohio); photo by Greg Hume via Wikimedia

Spread of non-native species is a facet of global change that is an unintended consequence of the modern global trade network. Despite efforts put in place to limit such transport, such as International Standards for Phytosanitary Measures (ISPMs), unintentional spread of species continues, and thus, an important part of forest health research and management includes non-native monitoring and control efforts. As other aspects of global change, such as climate and weather patterns, shift, the dynamics between native landscapes and introduced pests may unexpectedly shift as well. For example, increased climate stress of tree hosts may weaken tree defenses, allowing species that historically have not been pests of concern to reach pest status.

Japanese cedar longhorned beetle (Callidiellum rufipenne; JCLB) is a wood boring beetle in the longhorned beetle family, Cerambycidae. The adults are reddish brown in color, and relatively small for longhorned beetles, at only around 1 cm in length. Japanese cedar longhorned beetle has a long history of establishing outside of its native range but has largely been considered a non-issue. It has long been disregarded as a pest because it feeds primarily on dead or dying trees in both the native and invaded ranges. However, there are more examples of these beetles feeding on stressed, but alive, trees in North America. Therefore, I think it is an important insect to take a closer look at.

Life cycle

These beetles have a one-year life cycle, most of which is spent inside a host tree. Adults emerge from host trees in the early spring and seek out other adults to mate with and trees to lay eggs on. Eggs are laid on thin parts of bark or in bark crevices, and when the eggs hatch larvae chew beneath the bark where they feed on the phloem until they have completed larval development. Once larvae are fully developed, they burrow further into the tree, into the xylem tissue, where they pupate, overwinter as fully formed adults, and continue the cycle the following spring.

Native range

The native range of JCLB is eastern Asia. It is common throughout the Korean peninsula and across the islands of Japan. It is also considered native to Eastern China and Russia. Within the native range JCLB is found primarily on dead and/or dying trees and is thus considered a secondary pest. On dead trees they can be found on any diameter of dead woody material, but on declining trees they will likely be in the small diameter branches and stems.

Arborvitae (Thuja occidentalis); photo by James St. John via Flickr

Invasion history

Japanese cedar longhorned beetle was first documented as an invasive pest in the early 1900s in France, and since then has established in at least fifteen countries (Clément 2023). Most of these countries are in Europe, but the United States and Argentina also have established populations. As with most woodboring insects, the invasion pathway is believed to have been wood packaging material being transported via global trade routes. Between 1914 and 2022 it was intercepted over 700 times (reviewed by KM). Since the implementation of ISPM No. 15, only six interceptions have been reported up to 2022 (USDA APHIS data reviewed by K.M.). [For Faith’s view on the regulation of wood packaging, see Fading Forests II and III (links provided at the end of this blog) and earlier blogs posted here under the category “wood packaging”. esp. 1 from 2015].

A USDA risk assessment completed in 2000 suggested other possible pathways of introduction, including balled nursery stock, green logs, and pruned branches (USDA APHIS and Forest Service, 2000). 

In terms of establishments in North America, JCLB was first detected in natural forests in North Carolina in 1997. It was soon discovered in Connecticut in 1998; in neighboring New York in 1999; and in Massachusetts, New Jersey, and Rhode Island in 2000. It was quickly discovered feeding on live arborvitae (also called northern white cedar; Thuja occidentalis) in these invaded regions. JCLB has since been found in Pennsylvania (in 2010) and Maryland (in 2011). It is important to note that it is not clear when this species truly established, because of its previously discussed long history of being intercepted in ports of entry.

Most introduced populations of JCLB are found in either dead hosts or in the damaged/dead limbs of live hosts. In Buenos Aires, for example, storm-damaged trees with broken limbs are often where beetles are collected (Turienzo 2007). In the United States, eastern red cedar (Juniperus virginiana) and common juniper (Juniperus communis ) are the two native species most commonly affected, but so far there is no evidence of live trees of these species being infested (Maier 2007). However, a growing concern in the United States is that JCLB has been documented on live trees – particularly in urban environments. These trees are typically arborvitae, and they are typically stressed urban trees that have been overwatered and often show signs and symptoms of other health issues.

Host breadth

The host breadth of JCLB encompasses much of the family Cupressaceae. Maier (2007) identified 19 potential hosts from the literature and research, with the vast majority (14) of the hosts being Cupressaceae species, which is indicative of JCLB being a relative generalist, especially when considering species in the cypress family. This is important, because there are over 130 species within Cupressaceae worldwide that could be suitable hosts for JCLB, meaning host will not be a limiting factor in many invasion scenarios for this insect. Most often trees infested by JCLB need to be either stressed or dead, which limits suitability to an extent. However, many landscape trees are inherently stressed, whether it be from a history of roots being balled and wrapped in burlap, being planted in less than ideal scenarios, or being overwatered.

A few reports from research in Japan record JCLB feeding on plants in Pinaceae, primarily Pinus and Abies species. One article reports use of Larix kaempferi; another documented JCLB on the Taxaceae species, Taxus cuspidata. North American pine (Pinus spp.) and fir (Abies spp.) species have not been tested, but if they are revealed as suitable that would increase the availability of hosts in North America significantly.

In southern New England at least nine species have been confirmed as suitable, all of which are in the family Cupressaceae. Native and abundant junipers, such as Juniperus virginiana, appear to be highly suitable hosts. Additional host testing would be beneficial – especially Cupressaceae species that are either threatened or have a limited range. Within the United States there are a total of 28 native Cupressaceae species. Thus the suitable range (in terms of hosts) covers the entire Eastern half of North America through central Texas, most of the Pacific Coast, and widespread but spotty/disjunct areas throughout the Intermountain West and High Plains regions.

Atlantic white cedar swamp (Chamaecyparis thyoides) in Brendan Byrne State Forest, New Jersey; photo by Famartin via Wikimedia

Suitability

Tools such as environmental niche models can give helpful estimates of suitability. For species that are typically secondary pests, such as JCLB, it can be difficult to obtain non-biased data with good coverage to make reliable predictions. Preliminary research (unpublished) has been completed to estimate suitable habitat with limited occurrence records from the native range. Despite limited occurrences, models performed well and estimated moderate to high suitability in most temperate regions globally. These preliminary models are still being optimized by working with collaborators within the native range of JCLB to increase the number of occurrences. It is also important to note that these models are only accounting for climate data. Host data was not included, but Cupressaceae species are abundant globally, and therefore host availability is not likely a limiting factor for JCLB in establishing in regions.

Importance of monitoring species

While JCLB is still mostly limited to dead, dying trees, many of the species it may affect in the Eastern United States are already of heightened conservation concern. Wetland Cupressaceae, such as bald cypress (Taxodium distichum) and Atlantic White Cedar (Chamaecyparis thyoides), are valuable in terms of ecosystem services they provide in coastal, and inland, wetlands. These wetlands are encountering heightened stress in the form of increasing saltwater intrusion, increased storm strength, and changing landscapes, all of which may predispose trees to insect attack. Japanese cedar longhorned beetle has been successfully reared out of logs of Atlantic White Cedar, but thankfully has not been documented on live trees of this species (Maier 2009)[Ma1] . Bald cypress has not yet been tested for suitability. It is unknown if the stressors these trees are facing and will continue to face will impact JCLB’s ability to infest these landscapes, or if they will remain restricted to dead trees in these coastal forests. Regardless, given JCLB already has an established foothold in the Eastern United States, it is important to better understand the potential impacts of this insect.

First steps to understanding those impacts include 1) better documenting the host range in the regions and 2) determining the climate that may support the species. Hopefully we can continue research in these areas to best manage this non-native pest.

Much of the research conducted on JCLB in North America took place almost 20 years ago (Maier 2007, 2009), so updated sampling has potential to provide a wealth of information regarding spread rate, suitable climate, and establishment patterns.

bald cypress(Taxodium distichum); photo by Kej605 via Wikimedia; it is unknown whether this species is vulnerable to the Japanese cedar longhorned beetle

Sources

Clément F. 2023. Le point sur la distribution en France et en Europe de Callidiellum rufipenne (Motschulsky, 1861)(Coleoptera, Cerambycidae, Cerambycinae, Callidiini). Le Coléoptériste. 26(3):188–203.

Maier CT. 2007. Distribution and Hosts of Callidiellum rufipenne (Coleoptera: Cerambycidae), an Asian Cedar Borer Established in the Eastern United States. JOURNAL OF ECONOMIC ENTOMOLOGY. 100(4).

Maier CT. 2009. Distributional and host records of Cerambycidae (Coleoptera) associated with Cupressaceae in New England, New York, and New Jersey. Proceedings of the Entomological Society of Washington. 111(2):438–453. https://doi.org/10.4289/0013-8797-111.2.438

Turienzo P. 2007. New records and emergence period of Callidiellum rufipenne (Motschulsky, 1860) [Coleoptera:Cerambycidae: Cerambycinae: Callidiini] in Argentina. Boletín de Sanidad Vegetal, Plagas. 33:341–349.

United States Department of Agriculture Animal and Plant Health Inspection Service and Forest Service 2000. (Pasek, J.E., H.H. Burdsall, J.F. Cavey, A. Eglitis, R.A. Haack, D.A. Haugen, M.I. Haverty, C.S. Hodges, D.R. Kucera, J.D. Lattin, W.J. Mattson, D.J. Nowak, J.G. O’Brien, R.L. Orr, R.A. Sequeira, E.B. Smalley, B.M. Tkacz, W.W. Wallner) Pest Risk Assessment for Importation of Solid Wood Packing Materials into the United States. USDA APHIS and Forest Service. August 2000.

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/

or

www.fadingforests.org

 [Ma1]another old source

Great progress in predicting impact of introduced forest insects

results of invasion by emerald ash borer (photo courtesy of Nathan Siegert, USFS ); one of the woodboring beetles found to be so damaging to hardwood trees

Over the last nine years scientists have made significant progress in identifying aspects of insect-plant host relationships that play important roles in determining how much damage an introduced, non-native pest is likely to cause within forest ecosystems in the United States. Predicting which introductions will probably cause the greatest damage is vitally important because scientists, phytosanitary officials, and resource managers cannot address all the hundreds of established insects, much less the thousands which might be introduced. This shortfall increases with each surge in import volumes (see my previous blogs about wood packaging by scrolling down the website below the “Archives” to “Categories”, then find “SWPM”), proliferation of goods types and source areas, and cutbacks in funding.

I hope USDA APHIS and Forest Service are adjusting their procedures to apply the scientists’ path-breaking findings.

Their progress will help protect our forests. I apologize if I seem ungrateful — but we need similar progress in managing plant pathogens. Consider the damage caused by chestnut blight, white pine blister rust, Dutch elm disease, sudden oak death, beech leaf disease … (All these and other pathogens are described briefly here.) Understanding the universe of introduced fungi, water molds, nematodes, viruses, etc., is per se much more challenging. Ashley Schulz points out that among the complications are pathogens’ complex life cycles, and possible new relationships with vectors.

Undertaking this analysis will be set back decades if agencies’ resources – funds and staffs – are decimated during the current “downsizing” of government. We must speak up!!

At least regarding non-native insects that attack North American tree species, scientists’ analyses promise a new ability to set priorities. This should improve the efficacy of phytosanitary programs – if government downsizing is not allowed to destroy USDA’s scientific, regulatory, and resource management programs.

We must speak up!!

What science tells us now

Schulz et al. (2025) summarize current findings. (Full citation to all references appear at the end of the blog.)

Earlier, scientists sought to find commonalities associated with introduced insects that caused high impacts on North American conifer trees [Mech et al. (2019)] and hardwoods (angiosperms) [Schulz et al. (2021)] (Full citations at the end of the blog; earlier blogs posted here and here.) Both studies found that the time elapsed since tree species in North America diverged from the host plants of the insects in their native range (i.e., host evolutionary history) is a diagnostic factor. This factor best predicted non-native insect impact compared to the other factors that were significant for conifer and hardwood specialists. For conifers, the other significant factors included the shade and drought tolerance of the North American host plants and whether there was a related insect native to North America on the same hosts that the non-native insect impacted. For hardwoods, another important factor explaining a specialist insect’s impact is if the insect is a wood borer, especially a scolytine beetle. The wood density of the North American host plant was also considered a significant factor when predicting impact of the non-native insect.

In 2022, Uden et al. applied the divergence time method to insect species not yet introduced to North America that might attack conifer species. They hoped to identify both insects posing the greatest hazard and tree species most vulnerable to introduced pests.

Now, a new team again led by Ashley Schulz and Angela Mech (see Schulz et al. 2025) has applied a similar approach to a more comprehensive range of pest-host relationships, including the pests that specialize on host plants and pests that feed on a broader array of hosts. Some feed on both conifers and hardwoods. They found that:

  • It is possible to quantify insect host breadth and identify the cutoff where “specialists” and “generalists” diverge. Specifically, the split occurs around 2,250 cumulative million years, where insects that feed on hosts that add up to less than that have narrow host breadth (i.e., “specialists”) and insects that feed on hosts that add up to more than that have broad host breadth (i.e., “generalists”). This technique also helps categorize insects that fall within the middle range of host breadth and are traditionally difficult to classify as either specialists or generalists based on differing qualitative definitions of the terms.
  • Insects that use more hosts in their native range also tend to use more hosts in the introduced range (North America). However, many of these insects utilized fewer hosts in the introduced range compared to the native range. This shrinkage was not universal, however; about 30% of insects increased their host breadth in the introduced range. Most of these fed on a single species in their native range but attacked additional species in the same family in North America. The corresponding i-Tree Pest Predictor tool uses the list of hosts in the insect’s native range and these models to determine the insect’s likelihood that it would cause high impact, as well as each North American tree species’ susceptibility to the insect entered into the tool.
  • Certain feeding guilds had – on average — a significantly narrower host breadth in North America than in their native ranges. These were gall makers (13 species analyzed); sap feeders (120 species); and wood borers (35 species). In contrast, host ranges did not differ for folivores (68 species), reproductive feeders (7 species), and root feeders (5 species). Still, we know that wood borers, as a group, have caused enormous damage to a range of North American tree taxa (see emerald ash borer, redbay ambrosia beetle, invasive shot hole borers (all described briefly here). Again, the i-Tree Pest Predictor tool can help identify the threat to particular tree species.

Of course, APHIS should not disregard pests with narrow host ranges; several have caused enormous damage.

red spruce (Pikea rubens) in Great Smoky Mountains National Park; photo by famartin via Wikipedia. Red spruce is the species found to be most vulnerable by the Uden et al. study

Schulz et al. (2025) developed models for three groups of introduced herbivorous insects that feed on trees:

1) conifer specialists (based on analysis of 69 species);

2) hardwood specialists (based on analysis of 141 species);

3) hardwood generalists (based on analysis of 30 species).

Because of their quantification of host breadth, they defined the “specialist” group more broadly than is commonly done, e.g., an insect that feeds on the three families Betulaceae, Fagaceae, and Juglandaceae would be considered “specialists” because all three host families are in the Fagales clade.

Tree relatedness was the only significant explanatory factor for all three host breadth categories. As determined in the previous studies, North American host tree species that were too closely or distantly related to the insect’s hosts in its native range were less impacted than hosts that diverged somewhere in the middle – the “Goldilocks” range. The divergence period differs among the three pest-risk categories: 3–4 million years ago for conifer specialists, 5–9 million years ago for hardwood specialists, ~1–2 million years ago for hardwood generalists. Schulz et al. suggest that the reason why the peak probability of high impact differs among these groups is that different feeding guilds cause the most damage to the specific host category, and each feeding guild is challenged by different tree host defenses. Bark and wood boring beetles (the hardwood specialists with the greatest impact) must overcome lethal constitutive and induced tree defenses in order to survive for long periods in the cambial layer. These insects have adapted the ability to locate and select poorly defended individuals in the host population. Folivores (i.e., the generalists with the highest impact) adapt to plant chemistry and trichomes (hair-like or scale-like outgrowths), or can avoid host defenses by moving off the foliage. Sap feeders (which include many high impact conifer specialists) are usually tolerated by trees, unless they stimulate hypersensitive reactions or vector pathogens.

Of course, scientists’ estimates of how long ago tree taxa diverged from common ancestors differ. Fortunately, Uden et al. (2022) found that these differences only rarely affect the predicted impact of a non-native insect – at least in the case of the 62 European insects and 47 North American conifer species they analyzed. In only 1.37% of the 2,914 pairs analyzed did the predicted risk differ depending on which source phylogeny was used. These cases were associated with 27 conifer-specialist insects and 9 conifer hosts. The article does not tell us which pest/host pairs these are but, overall, this paper demonstrates that the estimate differences in the phylogenetic trees does not differ enough to be problematic when forecasting insect impact.

Changes Needed in the Way Agencies Set Priorities

Schulz et al. (2025) urged agencies to stop relying only on insect traits as the basis for developing models & phytosanitary regulations. The only insect trait that predicted impact is the insect’s feeding guild. Considering hardwoods, they found that wood borers pose the greatest risk among specialists to hardwoods; folivores among generalists. While sap feeders do not cause statistically higher damage on hardwood tree species, four of the seven high-impact conifer specialists are sap feeders (hemlock woolly adelgid, balsam woolly adelgid, red pine scale, and spruce aphid). Therefore, the i-Tree Pest Predictor tool incorporates consideration of whether a pest of conifers is a sap feeder.

Schulz et al. (2025) also caution agencies against relying on just the number of hosts an insect might exploit. Assessors must consider the range of underlying plant chemistry / host defenses that the insect encounters. They found that hosts that are shade tolerant are more susceptible to high impact from conifer specialists and hosts that have intermediate to no shade tolerance are more susceptible to high impact from generalists.

Uden et al. (2022) identified a possible weakness in USDA efforts to prioritize pest prevention targets. They found that APHIS’ Prioritized Offshore Pest List included only 12 conifer specialists from Europe among the 150 species listed. They go on to note that while sap feeders constitute 53% of tree pest species established in the U.S., APHIS listed none. The models applied by Uden, Schulz, and Mech do not consider whether the insect is likely to become established. Improving our understanding of the many factors influencing an insect’s likelihood of being transported to North America or becoming established requires additional research. This might eventually lead to a usable tool for predicting this aspect of bioinvasion by forest pests.

There is an urgent need for such a tool. As Uden et al. noted, they found that 66% of the insect species they analyzed fell into the “high impact” category. This is a much higher proportion than estimates based on earlier studies, so identifying which of these insects are likely to establish versus not establish in North America can provide more resolution and help identify which insects are going to be most problematic.

Mature Fraser fir killed by balsam woolly adelgid; Clingman’s Dome; photo by Ben Ramsey via Flickr

Tree species at risk

The analysis undertaken by Uden et al. determined that three conifer species face a high level of hazard from European insects if they are introduced. They identified particularly high threats to two species, Fraser fir (Abies fraseri) and Carolina hemlock (Tsuga caroliniana). The fir is determined to be vulnerable to 17 insect species which are predicted to have high likelihood of a high impact. The hemlock is highly vulnerable to one of the insect species they sampled. They note that both of these conifers have a limited geographic range and ecological habitat, so they likely have a relatively narrow genetic pool. A third species said to be at elevated risk is red spruce (Picea rubens) – which, although more widespread, is also under attack by a non-native insect. All three species fit earlier finding by Mech et al. that conifer trees with high shade tolerance but low drought tolerance more vulnerable to non-native pests. In none of these cases do Uden et al. mention that the tree species have already been severely diminished by established non-native insects – i.e., balsam woolly adelgid on the fir (above), hemlock woolly adelgid on the Carolina hemlock. The Schulz/Mech team is working to refine methods for identifying tree species and regions at greatest risk.

Meanwhile, Uden et al. have suggested that phytosanitary authorities and forest managers apply their findings to identify the European herbivorous insects that pose the greatest threat to North American conifer species. They should identify Palearctic tree species that fall within the high-impact “Goldilocks” zone of divergence times in relation to specific North American tree species, then identify the insects that feed on those Palearctic trees. These insects would presumably pose the highest predicted hazard to those North American tree species. They suggest that species so identified should be added to the USFS’ list of species targetted by its wood borer early detection program. To address likelihood of introduction, they suggest incorporating data on insect species commonly intercepted at ports – an indication of high propagule pressure. There will always be exceptions though. For example, Ips typographus feeds on spruce and has been frequently detected at the ports, but it has not established in North America.

For those focused on identifying species or ecoregions at greatest risk, Uden et al. suggest scientists use several sources to identify vulnerable vegetation communities. Sources suggested include USFS Forest Inventory and Analysis (FIA) and NatureServe Explorer plant community descriptions) that have relatively high-value tree species predicted to be at risk from introduced species.

SOURCES

Aukema, J.E., D.G. McCullough, B. Von Holle, A.M. Liebhold, K. Britton, and S.J. Frankel. 2010. Historical Accumulation of Nonindigenous Forest Pests in the Continental United States. BioScience 60(11): 886-897. https://doi.org/10.1525/bio.2010.60.11.5

Mech,  A.M., K.A. Thomas, T.D. Marsico, D.A. Herms, C.R. Allen, M.P. Ayres, K.J. K. Gandhi, J. Gurevitch, N.P. Havill, R.A. Hufbauer, A.M. Liebhold, K.F. Raffa, A.N. Schulz, D.R. Uden, & P.C. Tobin. 2019. Evolutionary history predicts high-impact invasions by herbivorous insects. Ecology and Evolution 9(21): 12216–12230. https://doi.org/10.1002/ece3.5709

Schulz, A.N.,  A.M. Mech, M.P. Ayres, K. J. K. Gandhi, N.P. Havill, D.A. Herms, A.M. Hoover, R.A. Hufbauer, A.M. Liebhold, T.D. Marsico, K.F. Raffa, P.C. Tobin, D.R. Uden, K.A. Thomas. 2021. Predicting non-native insect impact: focusing on the trees to see the forest. Biological Invasions 23: 3921-3936. https://doi.org/10.1007/s10530-021-02621-5

Schulz, A.N., N.P. Havill, T.D. Marsico, M.P. Ayres, K.J.K. Gandhi, D.A. Herms, A.M. Hoover, R.A. Hufbauer, A.M. Liebhold, K.F. Raffa, K.A. Thomas, P.C. Tobin, D.R. Uden, A.M. Mech. 2025. What Is a Specialist? Quantifying Host Breadth Enables Impact Prediction for Invasive Herbivores

Ecology Letters 28: e70083. https://doi.org/10.1111/ele.70083

Uden, D.R., A.M. Mech, N.P. Havill, A.N. Schulz, M.P. Ayres, D.A. Herms, A.M. Hoover, K.J.K. Gandhi, R.A. Hufbauer, A.M. Liebhold, T.D. Marsico, K.F. Raffa, K.A. Thomas, P.C. Tobin, C.R. Allen. 2022. Phylogenetic risk assessment is robust for forecasting the impact of European insects on North American conifers. Ecological Applications 33(2): e2761. https://doi.org/10.1002/eap.2761

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/

or

www.fadingforests.org

“Ecological memory” determines a forest’s resilience — implications of bioinvasion to New Zealand’s unique flora

kauri dieback

Scientists in New Zealand are saying explicitly that a forest’s unique mixture of species matters when considering the future. This mixture is the result of the forest’s evolutionary history. Losing members of the biological community reduces the forest’s ability to respond to current and future stresses – its resilience.

New Zealand’s forests are part of the broader legacy of the ancient supercontinent of Gondwanaland – the island nation’s plants have close relatives in South America, the Pacific Ocean islands, and Australia. Still, these forests are unique: 80% of New Zealand’s plant species are endemic. The forests are also species-rich. The warm temperate evergreen rain forests of the North Island are home to at least 66 woody plant species that can reach that reach heights above six meters (Simpkins et al. 2024).

These forests have been severely changed by human activity. In just ~ 750 years people have cut down approximately 80% of the original forest cover! (Simpkins et al. 2024) Of the eight million hectares of surviving native forest, a little over five million hectares is managed for the conservation of biodiversity, heritage, and recreation.  Another 2 million hectares are plantations of non-native species.

sites in New Zealand where pine plantations are “wilding”

All these forests are challenged by introduced mammals – from European deer to Australian possums. Climate change is expected to cause further disturbance, both directly (through e.g., drought, extreme weather) and indirectly (e.g., by facilitating weed invasion and shifting fire regimes) (Simpkins et al. 2024).

Pathogen threats are also common threats to the native trees of the Pacific’s biologically unique island systems. For example, Ceratocystis lukuohia and C. huliohia (rapid ‘ōhi‘a death, or ROD). The latter is killing ‘ōhi‘a (Metrosideros polymorpha) on the Hawaiian Islands. More than 40% of native plant species in Western Australia are susceptible to Phytophthora cinnamomi. Here I focus on two pathogens, kauri dieback and myrtle rust, now ravaging New Zealand’s native flora. No landscape-level treatment is available for either pathogen.

When considering this suite of challenges, Simpkins et al. focus on these two pathogens’ probable impact on forest carbon sequestration. They worry in particular about erosion of the forests’ resilience due to loss of “ecological memory” – the life-history traits of the species (e.g., soil seed banks) and the structures left behind after individual disturbances.

one of the largest remaining kauri trees, “Tane Mahuta”, in Waipoua Kauri Forest; photo by F.T. Campbell

Kauri Dieback

The causal agent of Kauri dieback, Phytophthora agathidicida, is a soil-borne pathogen that spreads slowly in the absence of animal or human vectors. The disease affects a single species, Agathis australis (kauri, Araucariaceae). However, kauri is a long-lived, large tree that is a significant carbon sink. It probably modifies local soil conditions, nutrient and water cycles, and associated vegetation. Also, kauri has immense cultural significance.

Simpkins et al. note that kauri dieback threatens stand-level loss of A. australis – that is, local extinctions. In the absence of disturbance Kauri trees can grow to awe-inspiring size. In the 19th Century, before widespread logging, some were measured at 20 meters or more in circumference. Consequently, kauri dieback might cause a decline in aboveground live carbon storage of up to 55%. This loss would occur over a period of hundreds of years, not immediately.

Huge kauri are not likely to be replaced by other long-lived emergent conifers (based on an analysis of one species, Dacrydium cupressinum). Instead, kauri are probably going to be replaced by late-successional angiosperms. The authors discuss the ecological implications for levels of carbon storage and proportions of trees composed of Myrtaceae – exacerbating damage caused by myrtle rust (see below).

The expectation of Simpkins et al. that kauri will suffer at least local extinctions is based on an assumption that no kauri trees are resistant to the pathogen. Fortunately, this might not be true: different Agathis populations show various levels of tolerance to Agathis dieback. Identification and promotion of some levels of resistance could enable A. australis to retain a diminished presence in the landscape.

However, Lantham, et al. make clear that containing kauri dieback remains “challenging,” despite its discovery nearly 20 years ago (in 2006). Scientists and land managers have little information on the distribution of symptomatic trees, much less of the pathogen itself. This means they don’t know where infection foci are or how fast the disease is spreading.

As is often true, the pathogen is probably present in a stand for years, possibly a decade or more, before symptoms are noticed. This means that the current reliance on public reports of diseased trees, or targetting surveillance on easy-to-access sites (e.g., park entrances and along existing track networks), or at highly impacted areas readily identified through aerial methods, fails to detect early stages of infection. Indeed, it seems probable that P. agathidicida had been present in New Zealand’s ecosystems for decades before its formal identification.

The Waipoua forest is one of the largest areas of forest with old kauri stands in the country. A new analysis of aerial surveys done between 1950 and 2019, shows how the forest is changing. The number of dead trees increased more than four-fold and the number of unhealthy-looking trees increased 16-fold over these 70 years. Kauri dieback is now widespread in this forest, especially in areas near human activities like clearing for pasture or planting commercial pine plantations).

Lantham et al. have developed a model which they believe will help identify areas of higher risk so as to prioritize surveillance and inform responses. These could delimit the disease front and help implement quarantines or other measures aimed at limiting the spread of P. agathidicida to uninfected neighboring sites.

I hope New Zealand devotes sufficient resources to expand surveillance and management to levels commensurate with the threat to this ecologically and culturally important tree species.

Leptospermum scoparia; photo by Brian Gatwicke via Flickr

Myrtle Rust

Myrtle rust is a wind-borne disease that affecting numerous species in the Myrtaceae, including some of the dominant early successional species (e.g., Leptospermum spp.). Simpkins et al. expect that myrtle rust might hasten the decline of two such tree species (L. scoparium and Kunzea ericoides). However, these trees’ small size and rapid replacement by other species during succession minimizes the effect of their demise on carbon storage.

Because I am concerned about the irreplaceable loss to biodiversity, I note that Simpkins et al. also feared immediate threats to some trees in the host Myrtaceae family, specifically highly susceptible species such as Leptospermum bullata.

As I reported in a recent blog, a second group of scientists (McCarthy et al.) explored the threat from myrtle rust more broadly. Austropuccinia psidii has spread through Myrtaceae-dominated forests of the Pacific islands for about 20 years.

Trees in the vulnerable plant family, Myrtaceae, are second in importance (based on density and cover) in New Zealand’s forests. Successional shrub communities dominated by the two species named above, Kunzea ericoides and Leptospermum scoparium, are widespread in the northern and central regions of the North Island and in northeastern and interior parts of the South Island. These regions’ vulnerability is exacerbated by the area’s climate, which is highly suitable for A. psidii infection (Simpkins et al. 2024).

McCarthy et al. concluded that if Leptospermum scoparium and Kunzea ericoides prove to be vulnerable to myrtle rust, their loss would cause considerable change in stand-level functional composition across these large areas. They probably would be replaced by non-native shrubs, which are already common on the islands. Any resulting forest will differ from that formed via Leptospermeae succession.

These authors also worry that the risk to native ecosystems would increase if more virulent strains of the myrtle rust pathogen were introduced or evolved. They note that A. psidii is known to have many strains and that these strains attack different host species.

SOURCES

Latham, M.C., A. Lustig, N.M. Williams, A. McDonald, T. Patuawa, J. Chetham, S. Johnson, A. Carrington, W. Wood, and D.P. Anderson. 2025.  Design of risk-based surveillance to demonstrate absence of Phytophthora agathidicida in New Zealand kauri forests. Biol. Invasions (2025) 27, no. 26

McCarthy, J.K., S.J. Richardson, I. Jo, S.K. Wiser, T.A. Easdale, J.D. Shepherd, P.J. Bellingham. 2024. A Functional Assessment of Community Vulnerability to the Loss of Myrtaceae from Myrtle Rust. Diversity and Distributions, https://doi.org/10.1111/ddi.13928

Simpkins, C.E., P.J. Bellingham, K. Reihana, J.M.R. Brock, G.L.W. Perry. 2024. Evaluating the effects of two newly emerging plant pathogens on North Aotearoa-New Zealand forests using an individual-based model.  Ecological Modelling, www.elsevier.com/locate/ecolmodel

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/

or

www.fadingforests.org

EAB biocontrol – evidence of impact

riparian ash killed by EAB; in this case, Mattawoman Creek in Maryland. Photo by Leslie A. Brice

Good news at the recent 33rd USDA Research Forum on Invasive Species. Scientists presented the first study that demonstrates significantly lower ash tree mortality in sites with high parasitism rates of two larval parasitoids, Tetrastichus planipennisi and Spathius galinae.

Their study area is the ash-dominated riparian area along the Connecticut River that flows north to south across the middle of Massachusetts. Knowing in advance that the emerald ash borer (Agrilus planipennis; EAB) would invade the area, scientists established monitoring plot that consisted of marked individual ash trees. EAB was first detected in the southern reach of the riparian area in 2015. It gradually moved north. By 2020 isolated mortality was observed at all sites. Meantime, they released three biocontrol agents – T. planipennis, S. galinae, and Oobius agrilii – early in the invasion at three of the six monitoring sites. These released occurred in 2018 – 2020 and again in 2022. 

In 2021 and 2025, the scientists counted the numbers of biocontrol agents in the marked trees or sentinel logs. Thus the first evaluation occurred six years after EAB arrived, three years after the first releases of biocontrol agents.

They found that at southern Massachusetts sites, where EAB density was higher at the time of the biocontrol agents’ initial release, remaining ash grew more slowly than in the North. They believe the trees’ growth rate was suppressed by the trees having fewer resources.  They also observed dieback. Smaller trees grew faster, perhaps responding to opening of the canopy as mature ash succumbed to EAB invasion.

The most important finding was that ash mortality at all sites was ~50% or less … not the 90% expected based on experience in the upper Midwest where the EAB invasion occurred before biocontrol agents were developed.

SOURCE

Ash survival and growth response to emerald ash borer invasion in Massachusetts riparian forests: impacts of biological control. Mitchell A. Reed, Jian Duan, Ryan S. Crandall, Roy G. van Driesche, Jeremy C. Anderson, Joseph S. Elkington. Presentation to the 33rd USDA Interagency Research Forum on Invasive Species, Annapolis, Maryland February 25-28, 2025  (The proceedings should be posted online before the end of the year.)

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/

or

www.fadingforests.org

Wood packaging: serious data gaps … but clear opportunities to act

discarded pallets next to developed area in Glacier National Park (!); photo by F.T. Campbell

Since July 2015 I have posted nearly 50 blogs about non-native insects introduced via movement of solid wood packaging material (SWPM). Why? Because SWPM is one of two most important pathways by numbers introduced & by impact of the species introduced. (The other pathway is P4P.) To read those earlier blogs, scroll below “archives” to “categories”, choose “wood packaging”.

Examples of insects introduced via the wood packaging pathway include Asian longhorned beetle, emerald ash borer, redbay ambrosia beetle, Mediterranean oak borer, and possibly, three species of invasive shot hole borers.

dead redbay trees in Everglades National Park; killed by laurel wilt vectored by redbay ambrosia beetle

As I have reported in the earlier blogs and in my “Fading Forests” reports (links at the end of this blog), in 2002, the parties to the International Plant Protection Convention (IPPC) adopted an international “standard” to guide countries’ programs intended to reduce the presence of damaging insects in the wood packaging: International Standard for Phytosanitary Measures (ISPM) #15). The U.S. and Canada adopted the standard through a phase-in process culminating in 2006. [For a discussion of the phase-in periods and process, read either of the studies by Haack et al. cited at the end of this blog.] In other words, the U.S. and Canada have implemented ISPM#15 for almost 20 years. China specifically has been subject to requirements that it treat its SWPM even longer – since December, 1998, i.e., more than 25 years.

Unfortunately, ISPM#15 is not intended to prevent pest introductions.  As stated in Greenwood et al 2023, “Prior to 2009, the goal of compliance with ISPM 15 was to render the risk of wood-borne pests “practically eliminated,” in 2009 the standard was amended to “significantly reduced”.  

Despite almost universal adoption of the standard by countries engaged in international trade, insects have continued to be present in wood packaging. A very high proportion of these infested shipments — 87% – 95% — of the SWPM found by U.S. officials bears the ISPM#15 stamp – that is, is apparently compliant. (See my blogs by clicking on the “Category” “wood packaging” listed below the “Archives”.) The same proportion was found in a narrower study in Europe (Eyre et al. 2018). All the post-2006 examples of infested wood analyzed by Haack et al. (2022) (see below) carry the stamp. I conclude that the ISPM#15 mark has failed in its purpose: to reliably indicate that SWPM accompanying imports has been treated so as to minimize the likelihood that an insect pest will be present.  

Dr. Robert Haack, retired USFS entomologist, has twice tried to estimate the “approach rate” of insects in SWPM entering the United States (both studies are cited at the end of this blog). A study published in 2014 that relied on data from 2009 found that U.S. implementation of ISPM#15 was associated with a reduction in the SWPM infestation rate reported of 36–52%. The authors estimated the infestation rate to be 0.1% (1/10th of 1%, or 1 consignment out of a thousand). (See Haack et al. 2014; citation at the end of this blog.)

In their second study, published in 2022, Haack and colleagues found a 61% decrease in rates of borer detection in wood packaging when comparing numbers of wood borer detections in 2003 – before the U.S. implemented ISPM#15 – to those in 2020. Specifically, detections dropped from 0.34% in 2003 to 0.21% in 2020. This decrease occurred despite the volume of U.S. imports rising 68% between 2003 and 2020. (My blogs document a further increase in import volumes over the years since 2020.) In addition, the number of countries from which the SWPM originated more than doubled from 2003–2004 to 2010–2020. This expansion exposes North America to a wider range of insect species that might be introduced, as well as a wider range of individual countries’ effectiveness in enforcing the standard’s requirements (Haack et al. 2022).

These decreases are encouraging. However, Haack et al. (2022) note some caveats:

  • The reduction in pest presence was greatest during the initial implementation of the program the first phase, 2005-2006 (61%); in subsequent periods pest approach rate inched back up. In the 2010-2020 period, the pest detection rate was only 36% below the pre-ISPM#15 level. Detection rates have been relatively constant since 2005. Does this stasis mean that exporters learned that they could ignore or circumvent the requirements without suffering significant penalties? Or is some of this rise related to increased trade volumes, increasing variety of country of origin for trade, or other global trade patterns unrecognized in the data? (However, see the next bullet point.)
  • Certain types of commercial goods and exporting countries have consistently fallen short. Specifically, the rate of wood packaging from China that is infested remained relatively steady over the 17 years since 2003. The proportion of consignments with infested wood packaging coming from China was more than five times the proportion of all inspected shipments for this period. In other words, China has had a consistent record of poor compliance with phytosanitary regulations since they were imposed in December 1998. Why is USDA not taking action to correct this problem? (As I note below, DHS CBP has ramped up enforcement efforts.) Some other countries, e.g., Italy and Mexico, have reduced the rate at which wood packaging accompanying their consignments is infested. In fact, Mexico’s improved performance largely explains the overall infestation rate estimate of 0.22% during the period 2010-2010. Mexico’s successes affect the overall statistics in a way that makes other countries’ failure to reduce the presence of pests in wood packaging they ship to the United States far less obvious.

Haack et al. (2022) discuss ten possible explanations for their finding that pest approach rates – as determined by their study — have not decreased more. See the article or my blog about the study.

Although USDA APHIS has not taken steps to strengthen its enforcement, U.S. Customs and Border Protection [an agency in the Department of Homeland Security] has done so twice — see here and here.  CBP staff have expressed disappointment that these actions reduced the numbers of shipments in violation of ISPM#15 by only 33% between Fiscal Year 2017 and FY2022. True, more than 60% of these violations consisted of a missing or fraudulent ISPM#15 stamp. However, 194 consignments still harbored live pests prohibited under the standard.

APHIS did agree in 2021 to enable the study by Robert Haack and colleagues, via an interoffice data sharing agreement between USDA APHIS and the Forest Service- this resulted in Haack et al. 2022.

APHIS and CBP also collaborated with an industry initiative to train inspectors that insure other aspects of foreign purchases. The ideas was that CBP or APHIS and their Canadian counterparts would inform importers about which foreign treatment facilities have a record of poor compliance or suspected fraud. The importers could then avoid purchasing SWPM from them. I have heard nothing about this initiative for three years, so I fear it has collapsed.

We lack data on which to base a rigorous analysis

While the two studies by Robert Haack and colleagues are the best available, and they relied on the best data available, the fact is that those available data do not provide a full picture of the risk of pest introduction associated with wood packaging. As pointed out by Leigh Greenwood of The Nature Conservancy in her presentation to 2025 USDA Invasive Species Research Forum, available data have been collected for different purposes than to answer this question. Leigh’s powerpoint is posted here.

Leigh has identified the following data gaps:

  1. In their studies, Haack and colleagues rely on data from the Agriculture Quarantine Inspection Monitoring (AQIM) system. This dataset is based on random sampling of very distinct segments of incoming trade. It is therefore a better measure of insect approach rates than reports of interceptions by either APHIS or CBP.

However, AQIM includes data from only those very distinct segments of trade: perishable goods, SWPM associated with maritime containerized imports, Italian tiles, and “other” goods, AQIM does not contain a segment of trade that includes wood packaging associated with maritime breakbulk or roll-on, roll-off (RORO) cargo. These exclusions have prevented scientists and enforcement officials from determining, inter alia, how great a risk of pest introduction is associated with various types of wood packaging, especially dunnage, as the randomized sample does not include entire pathways for the entrance of dunnage.

Greenwood states that she has not found another country that operates a similar analysis of randomly collected data at ports of entry.

2) USDA does not collect data on consignment size, piece-specific infestation density, nor consignment-wide infestation density. As Haack et al. (2022) point out, reporting detections by consignment doesn’t reveal the number of insects present. If implementation of ISPM#15 resulted in fewer live insects being present in an “infested” consignment, this would reduce the establishment risk because there is lower propagule pressure. However, we cannot know whether this is true.

3) Neither USDA nor CBP reports the inspection effort. Nor do they conduct a “leakage survey” to see how often target pests are missed. This means, inter alia, that we cannot estimate inspectors’ efficiency in detecting infested wood packaging. If their proficiency has improved as a result of improvements in training, inspection techniques, or technology, the apparent impact of ISPM#15 would be under-reported in recent years.

4) USDA does not require port inspectors to report the type of SWPM in which the pest was detected. Leigh participated in an effort that included industry representatives, DHS CBP and USDA APHIS to define the types of wood packaging in legal terminology so that they could be incorporated in the drop-down menu on inspectors’ reporting system. This was first successfully included in the legal glossary within USDA APHIS system of record, ACIR Glossary. Last fall the team was working to integrate the requirement for using these definitions into the inspection data collection system used by DHS CBP, which would then make this data available in Agricultural Risk Management, ARM (see Abstract here for adequate primer on ARM). However, it is unclear now whether the new administration will do so. One potential barrier is that asking the port of entry inspection staff to record these data will add to the time and training required for reporting inspection results.

In summary, Leigh reports that current data systems do not support

  • estimating probabilities of pest infestation of via volume or type of SWPM (e.g. pallet vs dunnage)
  • measuring the risk of arrival associated with a specific hazard (in this case, a hazard being a live pest or pathogen associated with SWPM)
  • extrapolating or supporting findings for some types of wood packaging to other types of wood packaging

Scientists from Canada, Mexico, and the United States have formed a working group under the auspices of the North American Plant Protection Organization (NAPPO). The group is trying to determine whether various types of wood packaging are more likely to harbor pests. This study is currently hampered by the many data gaps, including those Leigh outlined above. The best data available, cited by Haack et al. (2022), found that in maritime containerized shipping, crates were more likely to harbor pests than pallets- however, other forms of SWPM (dunnage, bracing, etc.) had such low sample size that no analysis of those is possible. One of the main objectives of the NAPPO study is to evaluate if dunnage poses the same or higher risk, so this is a major impediment.

Two issues need to be resolved.

One is scientific: why are insects continuing to be detected in wood packaging marked as having been treated? What is the relative importance of insects surviving the treatment versus treatment facilities applying the treatments incorrectly or inadequately?

The second issue is legal and political: what proportion of the detections is due to treatment facilities committing outright fraud – claiming to treat the wood, stamping it with an IPPC stamp, while not actually performing any treatments at all?

Knowing which measures will most effectively solve these quandaries / reduce pest presence in wood packaging depends on knowing what the relative importance of these factors are in causing the problem.  The lack of basic data on which to base any analysis certainly hampers efforts to improve protection.

Leigh calls for researchers to recognize these data needs and work to fill them.

•Understand, account for, and communicate data realities

•Work collectively to increase useable data quality

•Use additional research to validate, or to demonstrate disparities

Why Wait for the Science?

In the meantime, however, I assert that more vigorous enforcement efforts by responsible agencies should help reduce the occurrence of fraud. I have suggested the following actions:

  • U.S. and Canada refuse to accept wood packaging from foreign suppliers that have a record of repeated violations – whatever the apparent cause of the non-compliance. Institute severe penalties to deter foreign suppliers from taking devious steps to escape being associated with their violation record.
  • APHIS and CBP and their Canadian counterparts follow through on the industry-initiated program described above and here aimed at helping importers avoid using wood packaging from unreliable suppliers in the exporting country.
  • Encourage a rapid switch to materials that won’t transport wood-borers. Plastic is one such material. While no one wants to encourage production of more plastic, the Earth is drowning under discarded plastic. Some firms are recycling plastic waste into pallets.

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/

or

www.fadingforests.org

Pest Alerts – is USDA (able to) pay attention?

redbay (Persea borbonia killed by laurel wilt

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
  1. 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.
  2. 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), Quercus spp. (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.

  1. It noted the presence in Thailand of the fungus Pseudoplagiostoma perseae (Sordariomycetes: Diaporthales) on Persea americana.
  2. 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.

  1. 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.
  2. 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.

Coming to an Ecosystem Near You??

Xylotrechus chinensis; EPPO photograph

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-x  www.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/

or

www.fadingforests.org

New Shothole Borer in California — Alert! & Opportunity to Advise Whether the State or County Should Lead the Response

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 (Euwallacea kuroshio [(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.

SOURCES

California Department of Food and Agriculture, California Pest Rating Proposal Euwallaceae interjectus (Blanford): Boxelder ambrosia beetle https://blogs.cdfa.ca.gov/Section3162/wp-content/uploads/2025/01/Euwallacea-interjectus.pdf  

Comments due by February 17, 2025.

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/

or

www.fadingforests.org

Urban forests – resource under many threats

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.

SOURCES

Threats to Urban Forests in the United States Roots in Research Issue 45 | December 2024 https://research.fs.usda.gov/nrs/  products/rooted-research/threats-urban-forests-united-states?utm_source=MarketingCloud&utm_medium=email  accessed 24-12/31

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/

or

www.fadingforests.org