white flowered trillium (Trillium grandiflorum); via PICRYL One of the “charismatic wildflowers” mentioned by Blossey and colleagues
Bernd Blossey, Darragh Hare, and Don Waller have published a plea that America’s federal government take the lead in formulating a new national program on managing deer. Otherwise, they fear that deer populations will not be reduced to ecologically sustainable levels. I find their argument convincing and well-sourced. I agree that Americans need to figure out how to address this threat. (The full citation is at the end of this blog).
First, Blossey and colleagues describe the damage caused by overabundant deer:
severe declines in populations of many native forest herbs and shrubs, probably including disappearing wildflowers;
their replacement by non-native species that are less palatable;
poor regeneration of many canopy hardwood species;
decreased forest resilience, lowering forests’ ability to adapt to stressors, especially climate change;
decreased ability of forests to deliver benefits that are of increasing value to many people;
increased prevalence of wildlife and human diseases associated with the spread and size of growing tick populations; and
people – and deer — killed vehicle accidents on roads.
The widespread impacts of white-tailed deer (Odocoileus virginianus) in forests of the East are well-documented (see my previous blogs for a few examples; scroll below the “Archives” to find “Categories”). Blossey and colleagues note examples of similar impacts in the West, attributed to elk (Cervus elaphus) and black-tailed and mule deer (Odocoileus hemionus).
The authors review the decimation of deer populations in earlier centuries and the efforts of state wildlife agencies to rebuild their populations during the 20th Century. The problem, in their view, is that federal and — especially — state wildlife agencies have retained their traditional focus on managing wildlife for recreational hunters. However, recreational hunters make up a small and shrinking proportion of all Americans. Many more people now engage in “non-consumptive” enjoyment of wildlife.
lack of regeneration in Rock Creek Park, Washington D.C.; photo by Sam Sheline, NatureServe, via Flickr
State agencies’ narrow focus might partly arise from fragmented authorities. Agencies other than wildlife departments are responsible for addressing some repercussions of overabundant deer. These include threats to human health, loss of agricultural crops.
For several reasons, Blossey and colleagues call for federal leadership. They think that only a national strategy can address, in a holistic way, the interrelated deer, human health, forest, and biodiversity crises. The strategy’s goal should be to protect species that are in decline because of over-browsing by deer and to avoid further declines in environmental and human health.
The authors reason that states are tied to traditional constituencies. Also, they have difficulty acting across jurisdictional boundaries. Second, few state wildlife agencies have authority to protect plant and invertebrate species. Yet these are the taxa most directly affected by overabundant deer. Blossey and colleagues point out that, of the ~1,300 species listed under the federal Endangered Species Act, 942 are plants and 287 are invertebrates.
They point out that deer also suffer the effects of overpopulation. Chronic wasting disease is spreading. It causes a slow, agonizing death of affected animals. Another 2.1 million deer are killed each year in vehicle crashes. [According to the World Animal Foundation, the current number of deer killed in traffic crashes is 1.8 million — 300,000 fewer.) Again, these deaths are often gruesome. Finally, the principal population “control” now is death by starvation in winter. This, too, is cruel.
Blossey and colleagues say that return of large predators, even where feasible, will not result in sufficient reduction in deer populations. Nor will encouragement of greater hunting pressure on does.
They note that the federal government owns nearly 30% of the United States’ terrestrial surface area. Management is divided among many agencies – National Park Service, Fish and Wildlife Service, Bureau of Land Management, USDA Forest Service, Department of Defense, and many smaller agencies. Management approaches vary. However, it would be possible to bring them into agreement – although, in some cases, this would require new legislation.
Another issue requires resolution: federal agencies’ authority to manage wildlife on federal land.. The states have repeatedly claimed constitutional and legal authority to manage (vertebrate) wildlife on the federal lands within their borders. This assertion was countered years ago by Nie et al. (2017):
‘Federal land management agencies have an obligation, not just the discretion, to manage and conserve fish and wildlife on federal lands. … [M]ost states have not addressed the conservation obligations inherent in trust management; rather, states wish to use the notion of sovereign ownership as … a source of unilateral power but not of public responsibility. Furthermore, the states’ trust responsibilities for wildlife are subordinate to the federal government’s statutory and trust obligations over federal lands and their integral resources.’
Blossey and colleagues assert that managing wildlife (typically defined as mammals, birds, and fish) is much broader than establishing hunting seasons or methods. Furthermore, the concept of “public trust resources” means resources should be managed for all citizens, not just the fewer than 10% of US residents who hunt. A growing proportion of society expects this management to support healthy and diverse environments.
The authors stress that reducing deer overpopulations is necessary to meet numerous policy goals. These include fulfilling obligations under international treaties related to climate change, invasive species, and threatened species; restoring and conserving the nation’s forests to provide habitat; and adopting “nature-based” climate adaptations, such as carbon sequestration. They express the hope that recent presidential mandates to better quantify and value natural assets will increase awareness of the harm caused by deer overpopulation. Their proposed national strategy would develop goals and metrics to match specific environmental and human health outcomes.
Of course, management of deer must extend beyond federal property lines. This will require cooperation among states, Tribes, and private landowners.
The paper proposes the North American Waterfowl Management Plan as a model. Under this scheme the US Fish and Wildlife Service works with states, tribal governments, Mexico, and Canada to ensure accurate information on waterfowl populations a to calculate harvest levels. States implement their assigned quotas through their own regulations. Waterfowl hunters purchase Duck Stamps to fund the monitoring efforts. This program has worked well for most species covered by the program. Waterfowl are one of the few bird groups that have not declined dramatically.
Reducing deer populations will probably require lethal control. Studies indicate that at least 60% of does must be removed from a population to reduce herd sizes over time. Other means have been attempted at regional or larger landscape levels, such as sterilization, fertility control. These methods have failed even when paired with recreational hunting. Lethal approaches will probably distress many people. However, Blossey, Hare, and Waller believe the program would be supported if it is understood to be undertaken with the goal of improving the health of both humans and also the environment.
In the end, Blossey, Hare, and Waller say they are not willing to leave the killing to cars, disease, and starvation. They emphasize our moral responsibility to protect humans and the many other species that rely on diverse ecosystems. Our policies and choices created the problem, so we must try to correct it.
SOURCES
Blossey. B., D. Hare, and D.M. Waller, 2024. Where have all the flowers gone? A call for federal leadership in deer management in the US. Front. Conserv. Sci. 5:1382132. doi: 10.3389/fcosc.2024.1382132
Nie, M., C. Barns, J. Haber, J. Joly, K. Pitt and S. Zellmer. 2017. Fish and Wildlife Management on Federal Lands: Debunking State Supremacy. Environmental Law, Vol. 47, no. 4 (2017).
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
African Tulip Tree (Spathodea campanulata) on Puerto Rico; photo by Joe Schlabotnik via Flickr
While it is widely accepted that tropical island ecosystems are especially vulnerable to invasions, there has been little attention to terrestrial bioinvaders in the Caribbean; there has been more attention to marine bioinvaders such as lionfish. I am glad that is starting to change. Here I review a new study by Potter et al. (full citation at end of this blog), supplemented by information from other recent studies, especially Poland et al.
Potter et al. used USFS Forest Inventory and Analysis (FIA) survey data to examine regeneration rates by non-native tree species introduced to the continental United States, Hawai`i, and Puerto Rico. I rejoice that they have included these tropical islands, often left out of studies. They are part of the United States and are centers of plant endemism!
Potter et al. sought to learn which individual non-indigenous tree species are regenerating sufficiently to raise concern that they will cause significant ecological and economic damage in the future. That is, those they consider highly invasive. They defined such species as those for which at least 75% of stems of that species detected by FIA surveys are in their small tree categories – saplings or seedlings. They concluded that these species are successfully reproducing after reaching the canopy so they might be more likely to alter forest ecosystem functions and services. They labelled species exhibiting 60 – 75% of stems in the “small” categories as moderately invasive.
The authors recognize that many factors might affect tree species’ regeneration success, especially at the stand level. They assert that successful reproduction reflects a suite of factors such as propagule pressure, time since invasion, and ability of a species to adapt to different environments.
As I reported in an earlier blog, link 17% of the total flora of the islands of the Caribbean archipelago – including but not limited to Puerto Rico – are not native (Potter et al.). In Puerto Rico, two-thirds of forests comprise novel tree assemblages. The FIA records the presence of 57 non-native tree species on Puerto Rico. Potter et al. identified 17 non-native tree species as highly invasive, 16 as potentially highly invasive, and two as moderately invasive. That is, 33 of 57 nonnative tree species, or 58% of those species tallied by FIA surveyors, are actual or potential high-impact bioinvaders. While on the continent only seven non-native tree species occurred on at least 2% of FIA plots across the ecoregions in which they were inventoried, on Puerto Rico 21 species occurred on at least 2% of the FIA plots (38%). They could not assess the invasiveness of the eight species that occurred only as small stems on a couple of survey plots. These species might be in the early stages of widespread invasion, or they might never be able to reproduce & spread.
The high invasion density probably reflects Puerto Rico’s small size (5,325 mi² / 1,379,000 ha); 500 years of exposure to colonial settlement and global trade; and wide-scale abandonment of agricultural land since the middle of the 20th Century
Naming the invaders
The most widespread and common of the highly invasive non-native tree species are river tamarind (Leucaena leucocephala), on 12.6% of 294 forested plots; algarroba (Prosopis pallida) on 10.9%; and African tuliptree (Spathodea campanulata)on 6.1%. Potter et al. attribute the prevalence of some species largely to land-use history, i.e., reforestation of formerly agricultural lands. In addition, some of the moderately to highly invasive species currently provide timber and non-timber forest products, including S.campanulata, L. leucocephala, Syzgium jambos (rose apple) and Mangifera indica (mango).
Potter et al. contrast the threat posed by Spathodea campanulata with that posed by Syzgium jambo. The latteris shade tolerant and can form dense, monotypic stands under closed canopies. Because it can reproduce under its own canopy, it might be able to remain indefinitely in forests unless it is managed. In contrast S. campanulata commonly colonizes abandoned pastures. Since it is shade intolerant, it might decline in the future as other species overtop it. Meanwhile, they suggest, S. campanulata might provide habitat appropriate for the colonization of native tree species.
Second-growth forest in Caribbean National Forest “El Yunque”
Poland et al. say the threat from Syzgium jambos might be reduced by the accidentally introduced rust fungus Puccinia psidii (= Austropuccinia psidii), which has been killing rose apple in Puerto Rico. In Hawai`i, the same fungus has devastated rose apple in wetter areas.
Potter et al. note that stands dominated by L. leucocephala and Prosopis pallida in the island’s dry forests are sometimes arrested by chronic disturbance – presumably fire. However, they do not report whether other species – native or introduced – tend to replace these two after disturbance. The authors also say that areas with highly eroded soils might persist in a degraded state without trees. The prospect of longlasting bare soil or trashy scrub is certainly is alarming.
Potter et al. warn that the FIA’s sampling protocol is not designed to detect species that are early in the invasion process. However, they do advise targetting eradication or control efforts on the eight species that occurred only as small stems on a couple of survey plots. While their invasiveness cannot yet be determined, these species might be more easily managed because presumably few trees have yet reached reproductive age. They single out Schinus terebinthifolius (Brazilian pepper), since it is already recognized as moderately invasive in Hawai`i. I add that this species is seriously invasive in nearby peninsular Florida and here! APHIS recently approved release of a biocontrol insect in Florida targetting Brazilian pepper. It might easily reach nearby Puerto Rico or other islands in the Caribbean. I am not aware of native plant species in the Caribbean region that might be damaged by the biocontrol agent. However, two native Hawaiian shrubs might be harmed if/when this thrips reaches the Hawaiian Islands. Contact me for specifics, or read the accompanying blog about Potter et al. findings in Hawai`i.
Poland et al. looked at the full taxonomic range of possible bioinvaders in forest and grassland ecosystems. The Caribbean islands receive very brief coverage in the chapter on the Southeast (see Regional Summary Appendices). This chapter contains a statement that I consider unfortunate: “Introduction of species has enriched the flora and fauna of Puerto Rico and the Virgin Islands.” The chapter’s authors assert that many of the naturalized species are restoring forest conditions on formerly agricultural lands. They say that these islands’ experience demonstrates that introduced and native species can cohabitate and complement one another. I ask – but in what kind of forest? These forests, are novel communities that bear little relationship to pre-colonial biodiversity of the islands. Was not this chapter the right place to note that loss? Forests are more than CO2 sinks.
I also regret that the chapter does not mention that the Continental United States can be the source of potentially invasive species (see several examples below).
Mealybug-infested cactus at Cabo Rojo National Wildlife Refuge, Puerto Rico. Photo by Yorelyz Rodríguez-Reyes
The chapter does concede that some introduced species are causing ecological damage now. See Table A8.1. Some of these troublesome introduced species are insects:
the South American Harrisia cactus mealybug (Hypogeococcus pungens) is killing columnar cacti in the islands’ dry forests. The chapter discusses impacts on several cactus species and control efforts, especially the search for biocontrol agents.
the agave snout weevil (Scyphophorus acupunctatus), native to the U.S. Southwest and Mexico , is threatening the endemic and endangered century plant (Agave eggersiana) in St. Croix & Puerto Rico.
Tabebuia thrips (Holopothrips tabebuia) is of unknown origin. It is widespread around mainland Puerto Rico. Its impacts so far are primarily esthetic, but it does apparently feed on both native and introduced tree species in the Tabebuia and Crescentia genera.
The Caribbean discussion also devotes welcome attention to belowground invaders, i.e., earthworms. At least one species has been found in relatively undisturbed cloud forests, so it is apparently widespread. Little is known about its impact; more generally, introduced earthworms can increase soil carbon dioxide (CO2) emissions as through speeded-up litter decomposition and soil respiration.
A factsheet issued by the British forestry research arm DEFRA reports that the pine tortoise scale Toumeyella parvicornis has caused the death of 95% of the native Caicos pine (Pinus caribaea var. bahamensis) forests in the Turks and Caicos Islands (a UK Overseas Territory). The scale is native to North America. It has recently been introduced to Italy as well as to Puerto Rico, and the Turks and Caicos Islands.
SOURCES
Lugo, A.E., J.E. Smith, K.M. Potter, H. Marcano Vega, C.M. Kurtz. 2022. The Contribution of Non-native Tree Species to the Structure & Composition of Forests in the Conterminous United States in Comparison with Tropical Islands in the Pacific & Caribbean. USFS International Institute of Tropical Forestry General Technical Report IITF-54.
Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector. Especially the Appendix on the Southeast and Caribbean. Springer Verlag. Available gratis at https://link.springer.com/book/10.1007/978-3-030-45367-1
Potter K.M., Riitters, K.H. & Guo. Q. 2022. Non-nativetree regeneration indicates regional & national risks from current invasions. Frontiers in Forests & Global Change Front. For. Glob. Change 5:966407. doi: 10.3389/ffgc.2022.966407
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
Oregon-ash dominated swamp in the Ankeny National Wildlife Refuge, Willamette Valley, Oregon; photo by Wyatt Williams, Oregon Department of Forestry
In April 2022 I blogged about efforts on the West Coast to prepare for arrival of the emerald ash borer (EAB).
That blog focused on Oregon ash (Fraxinus latifolia), which is an important component of riparian forests. I alerted you to the availability of ODA/ODF EAB 2018 Response Plan.
I also mentioned Oregon’s active participation in “don’t move firewood” campaigns.
California has long inspected incoming firewood. In 2021 it establishment of a state quarantine in response to APHIS ending the federal quarantine. Washington State operates a statewide trapping program for invasive insects but does not regulate firewood.
Contributions from the Tualatin Soil and Water Conservation District enabled the USDA Forest Service Dorena Genetic Resource Center to begin testing Oregon ash for resistance to EAB and related genetics work. Other funding came from the USFS Forest Health Protection program.
EAB has now been detected in Oregon — in the Willamette Valley! (See photo above, by Wyatt Williams) Concerned stakeholders have established a new newsletter to keep people informed and promote cooperative efforts.
The newsletter is “Ash across the West”.
The first issue of the newsletter provides the following information:
there are eight ash species in the West; all are vulnerable to the emerald ash borer (EAB)
Single-leaf ash (Fraxinus anomala) CA, NV, AZ, UT, NM, CO, WY
Fragrant ash (Fraxinus cuspidata) NV, AZ, NM, UT
Calif ash (Fraxinus dipetala) CA, NV, AZ, UT
Fresnillo (Fraxinus gooddingii) AZ
Gregg’s ash (Fraxinus greggii) AZ
OR ash (Fraxinus latifolia) WA, OR, CA
Chihuahuan ash (Fraxinus papillosa) AZ, NM, TX
Velvet ash (Fraxinus velutina) CA, NV, AZ, UT, NM, TX
EAB Risk Map for OR: based upon known occurrences of ash & corresponding human activities associated with known pathways of EAB introduction and establishment.
2022 status of the two field trials
the Dorena Genetic Resource Center (DGRC): planted 600 seedlings from 27 families; 85% survival in 2022; controlling competing vegetation
Washington State University Puyallup Research Center: planted seedlings from 26 of these families; 95% survival rate. Possible complication from a foliar disease.
Seedlings from 17 Oregon ash families (including 14 of those in the DGRC field trial) sent to Dr. Jennifer Koch (USFS) in Ohio) for EAB resistance/susceptibility testing.
Seed collections began in 2019; interrupted by COVID-19 in 2020 but resumed in 2021 and continue in 2022. Several consortia are involved in Oregon and Washington. In California and the other states, The Huntington Botanical Gardens will lead the collecting effort. Funding is from USFS Forest Health Protection. Seeds are stored for gene conservation; some are used for the field trials in Oregon and Washington and the initial EAB-resistance studies going on in Ohio.
Penn State Ash Genomic Project: Dr. Jill Hamilton is trying to create a ‘genomic passport’ for Oregon ash populations for use in establishing genotype-environment associations to inform seed transfer guidelines. If you would like to help Dr. Hamilton collect leaves for sampling, contact: Dr. Jill Hamilton at jvh6349@psu.edu
To help with seed collection, ash monitoring, documenting the importance of ash to various communities, and other activities; or to get on the mailing list for the newsletter, contact Richard Sniezko at Richard.sniezko@usda.gov
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
symptoms of beech leaf disease; photo by Dr. Chagas de Freitas
Three webinars during April and May provided updates on efforts to address three non-native, tree-killing pests: hemlock woolly adelgid (HWA), link invasive shot hole borers (ISHB), link and beech leaf disease (BLD) link. I attended each and summarize here.
Hemlock conservation in North Carolina – the NC Hemlock Restoration Initiative (HRI) see SaveHemlocksNC.org
I was pleased to learn about the major effort under way in North Carolina, where eastern and Carolina hemlocks are extremely important components of multiple ecosystems. In 2013, the Commissioner of Agriculture decided to make protecting hemlocks a signature project. He wanted to ensure that three state agencies – the Forest Service, Wildlife Department, and State Parks – worked together to improve the efficacy of treating trees. (Treatments available at the time were expensive and time-consuming.)
HRI treatment at Conestee Falls; HRI photo
Thom Green described the result: North Carolina’s Hemlock Restoration Initiative (HRI). The initiative is administered by the Western North Carolina Communities – a non-governmental organization with strong connections to rural communities and a history of successful collaborative projects that support agriculture and forestry. It engages state agencies, local and county governments, local NGOs, and federal agencies and works on both public and private lands with the goal of ensuring that hemlocks can survive to maturity.
HRI staff work with local partners to identify priority hemlock conservation areas (HCAs). It then sends a “strike team” to guide the partners in treating as many trees as possible. (North Carolina allows non-licensed volunteers to apply pesticides under supervision; also, landowners can treat trees on their own property.) These collaborative projects can treat up to 1,000 trees per day.
The chemicals used are imidacloprid and, where poor tree health justifies emergency treatment, dinotefuran. These are usually applied as a soil drench because it is easier for people to transport the equipment into the woods. Bark spray is used in sensitive areas. They have found that imidacloprid provides five to seven years of protection. A new product, CoreTech, is even easier to transport and works much faster than imidacloprid, however, it costs more.
The HRI believes it is minimizing non-target impacts of the neonictenoid imidacloprid because:
hemlocks are pollinated by wind, not insects
hemlocks don’t exude resins that attract insects
pesticide applications are tightly targetted at the base of trunk, with 10-foot setbacks from water
long intervals between treatments (5 – 7 years) allow soil invertebrates to recover
The program has treated 100,000 trees between 2016 and 2021 on state and private lands. Now they are starting the second round of treatments for trees treated at the beginning of the program.
Treatment priorities are based primarily on the extent to which the trees are able to take up the chemical, evaluated by the percentage of the crown that is alive and the density of foliage. Since imidacloprid can take a year to reach the canopy of a mature tree, it is used only on trees with greater than half the crown rated as healthy. When trees have a lower status, dinotefuran is added (because it can reach the canopy within weeks). Trees with less than 30% live crown are not treated.
The Initiative also supports biocontrol programs. It has assisted releases of Laricobiusnigrinis (a beetle in the family Derodontidae) and helps volunteers monitor releases and survival. Dr. Green reports that L. nigrinis has spread almost throughout western North Carolina but that questions remain regarding its impact on tree health. He thinks biocontrol is not yet reliable as stand-alone tool; success will require a suite of predatory insects.
The HRI measures the success of various treatments (Hurray!). “Impact plots” are established at the start of treatment. Staff or volunteers return every three years to monitor all aspects of the health of a few designated trees – including untreated ones. So far, they have seen encouraging responses in crown density and new growth.
Invasive Shot Hole Borers (ISHB) in California
See www.ishb.org and video recordings of the meeting at:
A host of scientists from California spent two full days describing research and management projects funded by specific state legislation – Assembly Bill (AB)-2470 on two invasive shot hole borers.
Adoption of this legislation resulted largely from lobbying by John Kabashima. Additional funding was provided by CalFire (the state’s forestry agency). The agency responsible for managing invasive species – California Department of Food and Agriculture (CDFA) had designated these organisms as not a threat to agriculture. So it did not fund many necessary activities.
The Problem and Where It Is
“Fusarium dieback” is the disease caused by this insect-pathogen complex. The insects involved are two ambrosia beetles in the Euwallacea genus – the polyphagous (E. whitfordiodendrus) and Kuroshio (E. Kuroshio) shot hole borers. link to DMFAccording to Dr. Bea Nabua-Behermann, Urban Forestry and Natural Resources Advisor with University of California Cooperative Extension (UCCE), other fungi are present on both beetle species but its matching Fusarium sp. is the principal associated fungus and is required for the beetle’s reproduction. These are Fusarium euwallaceae and F. kuroshium.
As of spring 2022, the beetle/fungus complex has spread as far north as Santa Barbara /Santa Clarita; and inland to San Bernardino and Riverside (see the map here). They are very widespread in Orange and San Diego counties. At least 65 tree species in southern California are reproductive hosts (globally, it is 77 species; see full list here). The preferred and most succeptible hosts are several species in the Acer, Parkinsonia, Platanus, Quercus, and Salix genera. Box elder (A. negundo) is so susceptible that it is considered a sentinel tree.
Because the beetles spend most of their life inside trees, their life cycle leaves few opportunities to combat them. Females (only) fly but tend to bore galleries on their natal tree. Several speakers on the webinar said management should focus on heavily infested “amplifier trees”. Much spread is human assisted since the beetles can survive in dead wood for months if it is damp enough for the fungus. Possible vectors are green waste, firewood, and even large wood chips or mulch.
Management – from Trapping to Rapid Response to Restoration
Akiv Eskalen of University of California Davis discussed trapping and monitoring techniques to confirm presence of the insect and pathogen. Also, he talked about setting priorities for treating trees based on the presence of reproductive hosts, host value, infestation level, and whether the trees pose a safety hazard. The disease causes too little damage to some hosts to warrant management. He emphasized the importance of preventing spread. This requires close monitoring of infested trees to see whether beetles move to neighbors. Dr. Eskalen described a major and intensive monitoring and treatment program at Disneyland. The 600 acres of parks, hotels, and parking lots have ~16,000 trees belonging to 681 species.
Several speakers described on-going efforts in Orange County. Danny Hirchag (IPM manager for Orange County Parks) described how his agency is managing 60,000 acres of variable woodlands containing 42,000 trees, of which 55% are hosts of ISHB and their associated fungi. Of greatest concern are California sycamore and coast live oak in areas of heavy public use. The highest priority is protecting public safety; next is protecting historic trees (which can’t be replaced); third is minimizing impacts to ecosystem services. Orange County Parks is currently removing fewer than 50 trees each year. Hirchag noted the importance of collaborating in the research trials conducted by the University of California Cooperative Extension.
infested California sycamore; photo by Bea Nabua-Behermann
Maximiliano Regis and Rachel Burnap, of County of Los Angeles Department of Agricultural Commissioner/Weights and Measures, described Los Angeles County’s efforts more broadly. The challenge is clear: LA County has more than 160 parks. In 2021, they placed nearly 2,500 traps, mapped infected trees, carried out on-ground surveys to find amplifier trees, removed both amplifier and hazard trees (using funds provided by CalFire), and educated the public. Their efforts were guided by an early detection-rapid response (ED/RR) Plan (2019) developed by Rosi Dagit (see below). While London plane trees (Platanus x hispanica) and California sycamores (Platanus racemose) were initially most affected, now black locusts (Robinia pseudoacacia) and box elders (Acer negundo) are succumbing. [Note: both are widespread across North America.] The researchers are trying to determine why some areas are largely untouched, despite the presence of the same tree species. Regis and Burnap noted the increasing difficulty getting confirmation of the pathogen’s presence because laboratories are overwhelmed. They continue looking for funding sources.
Rosi Dagit, Senior Conservation Biologist, Resource Conservation District of the Santa Monica Mountains, described the creation of that ED/RR system for Los Angeles County as a whole, without regard for property lines. Participants established random study plots across the entire Santa Monica Mountains Natural Recreation Area (NRA), based on proximity to areas of particularly sensitive ecological concerns. The fact that the NRA’s forests are aging and that the risk of infestations is especially high in riparian forests helped persuade policy-makers to fund the effort. The accompanying rapid response plan informs everyone about what to do, who should do it, and who pays. This information incorporates agencies’ rules about what and where to plant. It also provides measures to evaluate whether the action was effective. It did take more than two years for the county to set staffing needs etc.
John Kabashima link discussed his criteria for replanting and ecosystem restoration following tree removal in the southern California region. He recommends prompt removal of amplifier trees – especially box elder and California sycamore. He relies on replanting guidance developed by UC-Irvine (which is on the website) – especially avoiding monocultures. Kabashima reiterated the importance of close monitoring to track beetle populations and responding quickly if they build up.
Economics of Urban Forests and Cities Most at Risk
Karen Jetter (an economist at the UC Agriculture Issues Center) has developed a model to compare the costs of an early detection program to the environmental and monetary costs of infestation by Fusarium disease. She noted that early detection and monitoring programs are often hard to justify because — when they are successful — nothing changes! She found that averted or delayed costs (including tree removals, lost ecosystem services, lost landscape asset value [replanting value] and the cost to replant) always far exceeded the cost of monitoring programs. Unfortunately, a written report about this effort (Jetter, K., A. Hollander, B.E. Nobua-Behrmann, N. Love, S. Lynch, E. Teach, N. Van Dorne, J. Kabashima, and J. Thorne. 2022. Bioeconomic Modeling of Invasive Species Management in Urban Forests; Final Report) appears to be available only through the University of California “collaborative tools” website dedicated to practitioners and stakeholders engaged on ISHB issues. If you are not a member of the list, contact me using the comment button and ask that I send it to you. Include your email address (the comment process makes determining emails difficult if not impossible.)
Shannon Lynch (UC Davis) developed a model to estimate vulnerability of urban areas based on phylogenetic structure (relationship between tree species), host abundance, and number of beetle generations/year (linked to temperature). She found that areas with less favorable host communities can become vulnerable if the climate becomes favorable. Where the host community is already favorable, climate not important.
She evaluated 170 California cities based on their tree inventories. The cities at highest risk were San Diego, Los Angeles, the San Francisco Bay area, and the Central Valley – e.g., Sacramento. For areas lacking tree inventories, she based her risk determination on the estimated number of generations of beetles per year – based on climate. This analysis posited a very high risk in the eastern half of southern California and the Central Valley. Participants all recognized the need to apply this model to cities in Arizona and Nevada.
Possible Management Strategies
Shannon Lynch (UC Davis) studied whether endophytes might be used to kill the Fusarium fungi. She reported finding 771 fungal strains and 657 bacterial strains in tree microbiomes. Some of the fungal isolates impeded growth of the Fusarium fungi in a petri dish. She began testing whether these fungi can be used to inoculate cuttings that are to be used for restoration. She also planned to test more endophytes, and more native plant species to explore creation of a multi-fungus cocktail.
Richard Stouthamer of UC Riverside is exploring possible biocontrol agents. Of three he has evaluated, the most promising is Phasmastichus sp., which is new to science. He is still trying to establish laboratory cultures so he can test its host specificity.
symptoms of beech leaf disease; photo by Dr. Chagas de Freitas
At this meeting, scientists described research aimed at improving basic understanding of beech leaf disease’s causal agents, its mechanisms of spread, etc. Their findings are mostly preliminary.
These findings are of greatest importance now:
presence of the nematodes varies considerably across leaf surface – if one collects samples from the wrong site on leaf, one won’t detect nematode (Paulo Vieria, Agriculture Research Service)
developing predictive risk maps that combines temperature, humidity, elevation, soils (Ersan Selvi, Ohio State). So far, he has found that BLD is greater in humid areas – including under closed forest canopies. The USFS is funding studies aimed at incorporating disease severity in detection apps.
determining extent of nematode presence. Sharon Reed of Ontario has found nematode DNA in trap fluids throughout the Province. It is much more common at known disease sites. Reed is also studying the presence of arthropods on beech leaves and buds.
Longer term findings and questions
possible vectors:
nematode DNA has been detected from birds – although it is not clear whether the DNA came from bird feces, feathers, or dust (DK Martin)
a few live nematodes have been extracted from the excrement of caterpillars that fed on infected leaves (Mihail Kantor, ARS)
nematode damage to leaves:
presence of the nematode in leaf buds before they open (Vieria and Joe Mowery, both ARS). The nematode can create considerable damage in leaf buds before they open. Nematodes are present as early as October of the preceding year.
damage to leaves by nematode (Mowery, ARS) Leaf epidermal cells are distorted, stomata blocked, chlorobasts are larger than normal, irregular shape
possible management tools
are there parasites that might attack the nematode? (Paulo Vieria, ARS)
experimental treatment of infested trees using phosphite (Kandor, ARS)
ecology: how do root microbiomes compare on infested and healthy trees? (Caleb Kime, Ohio State; and David Burke, Vice President for Science at Holden Arboretum)
infested European beech in Rhode Island; photo by Dr. Nathanial A. Mitkowski
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
sassafras – vulnerable to the rapidly spreading laurel wilt disease; photo by F.T. Campbell
In summer 2019 I posted several blogs summarizing my analysis of forest pest issues after 30 years’ engagement. I reported the continuing introductions of tree-killing insects and pathogens; their relentless spread and exacerbated impacts. I noted the continued low priority given these issues in agencies tasked with preventing and solving these problems. Also, Congress provides not only insufficiently protective policies but also way too little funding. I decried the impediments created by several Administrations; anti-regulatory ideology and USDA’s emphasis on “collaborating” with “clients” rather than imposing requirements.
In my blogs, I called for renewed effort to find more effective strategies – as I had earlier advocated in my “Fading Forests” reports (link provided at the end of this blog), previous blogs, and Lovett et al. 2016
Areas of Progress
Now two years have passed. I see five areas of progress – which give me some hope.
1) Important Activities Are Better Funded than I had realized
a) The US Forest Service is putting significant effort into breeding trees resistant to the relevant pests, more than I had realized. Examples include elms and several conifer species in the West – here and here.
b) USDA has provided at least $110 million since FY2009 to fund forest pest research, control, and outreach under the auspices of the Plant Pest and Disease Disaster Prevention Program (§10201 of the Farm Bill). This total does not include additional funding for the spotted lanternfly. Funded projects, inter alia: explored biocontrol agents for Asian longhorned beetle and emerald ash borer; supported research at NORS-DUC on sudden oak death; monitored and managed red palm weevil and coconut rhinoceros beetle; and detected Asian defoliators. Clearly, many of these projects have increased scientific understanding and promoted public compliance and assistance in pest detection and management.
This section of the Farm Bill also provided $3.9 million to counter cactus pests – $2.7 million over 10 years targetting the Cactoblastismoth & here and $1.2 million over four years targetting the Harissia cactus mealybug and here.
flat-padded Opuntia cactus – vulnerable to the Cactoblastis moth; National Park Service photo
2) Additional publications have documented pests’ impacts – although I remain doubtful that they have increased decision-makers’ willingness to prioritize forest pests. Among these publications are the huge overview of invasive species published last spring (Polandet al.) and the regional overview of pests and invasive plants in the West (Barrettet al.).
3) There have been new efforts to improve prediction of various pests’ probable virulence (see recent blogs and here.
4) Attention is growing to the importance of protecting forest health as a vital tool in combatting climate change — see Feiet al., Quirionet al., and IUCN. We will have to wait to see whether this approach will succeed in raising the priority given to non-native pests by decision-makers and influential stakeholders.
Rep. Peter Welch
5) Some politicians are responding to forest pest crises – In the US House, Peter Welch (D-VT) is the lead sponsor of H.R. 1389. He has been joined – so far – by eight cosponsors — Rep. Kuster (D-NH), Pappas (D-NH), Stefanik (R-NY), Fitzpatrick (R-PA), Thompson (D-CA), Ross (D-NC), Pingree (D-ME), and Delgado (D-NY). This bill would fund research into, and application of, host resistance! Also, it would make APHIS’ access to emergency funds easier. Furthermore, it calls for a study of ways to raise forest pests’ priority – thus partially responding to the proposal by me and others (Bonello et al. 2020; full reference at end of blog) to create federal Centers for Forest Pest Control and Prevention.
This year the Congress will begin work on the next Farm Bill – might these ideas be incorporated into that legislation?
What Else Must Be Done
My work is guided by three premises:
1) Robust federal leadership is crucial:
The Constitution gives primacy to federal agencies in managing imports and interstate trade.
Only a consistent approach can protect trees (and other plants) from non-native pests that spread across state lines.
Federal agencies have more resources than state agencies individually or in likely collective efforts – even after decades of budget and staffing cuts.
2) Success depends on a continuing, long-term effort founded on institutional and financial commitments commensurate with the scale of the threat. This requires stable funding; guidance by research and expert staff; and engagement by non-governmental players and stakeholders. Unfortunately, as I discuss below, funding has been neither adequate nor stable.
3) Programs’ effectiveness needs to be measured. Measurement must focus on outcomes, not just effort (see National Environmental Coalition on Invasive Species’ vision document).
Preventing New Introductions – Challenges and Solutions
We cannot prevent damaging new introductions without addressing two specific challenges.
1) Wood packaging continues to pose a threat despite past international and national efforts. As documented in my recent blogs, the numbers of shipping containers – presumably with wood packaging – are rising. Since 2010, CBP has detected nearly 33,000 shipments in violation of ISPM#15. The numbers of violations are down in the most recent years. However, a high proportion of pest-infested wood continues to bear the ISPM#15 mark. So, ISPM#15 is not as effective as it needs to be.
We at CISP hope that by mid-2022, a new analysis of the current proportion of wood packaging harboring pests will be available. Plus there are at least two collaborative efforts aimed at increasing industry efforts to find solutions – The Nature Conservancy with the National Wooden Pallet and Container Association; and the Cary Institute with an informal consortium of importers using wooden dunnage.
2) Imports of living plants (“plants for planting”) are less well studied so the situation is difficult to assess. However, we know this is a pathway that has often spread pests into and within the US. There have been significant declines in overall numbers of incoming shipments, but available information doesn’t tell us which types of plants – woody vs. herbaceous, plant vs. tissue culture, etc. – have decreased.
APHIS said, in a report to Congress (reference at end of blog), that introductions have been curbed – but neither that report nor other data shows me that is true.
Scientists are making efforts to improve risk assessments by reducing the number of organisms for which no information is available on their probable impacts (the “unknown unknowns”).
Solving Issues of Prevention
While I have repeatedly proposed radical revisions to the international phytosanitary agreements (WTO SPS & IPPC) that preclude prevention of unknown unknowns (see Fading Forests II and blog), I have also endorsed measures aimed at achieving incremental improvements in preventing introductions, curtailing spread, and promoting recovery of the affected host species.
The more radical suggestions focus on: 1) revising the US Plant Protection Act to give higher priority to preventing pests introductions than to facilitating free trade (FF II Chapter 3); 2) APHIS explicitly stating that its goal is to achieve a specific, high level of protection (FF II Chapter 3); 3) APHIS using its authority under the NAPPRA program to prohibit imports of all plants belonging to the 150 genera of “woody” plants that North America shares with Europe or Asia; 4) APHIS prohibiting use of packaging made from solid wood by countries and exporters that have a record of frequent violations of ISPM#15 in the 16 years since its implementation.
Another action leading to stronger programs would be for APHIS to facilitate outside analysis of its programs and policies to ensure the agency is applying the most effective strategies (Lovett et al. 2016). The pending Haack report is an encouraging example.
I have also suggested that APHIS broaden its risk assessments so that they cover wider categories of risk, such as all pests that might be associated with bare-root woody plants from a particular region. Such an approach could speed up analyses of the many pathways of introduction and prompt their regulation.
Also, APHIS could use certain existing programs more aggressively. I have in mind pre-clearance partnerships and Critical Control Point integrated pest management programs. APHIS should also clarify the extent to which these programs are being applied to the shipments most likely to transport pests that threaten our mainland forests, i.e. imports of woody plants belonging to genera from temperate climates. APHIS should promote more sentinel plant programs. Regarding wood packaging, APHIS could follow the lead of CBP by penalizing importers for each shipment containing noncompliant SWPM.
Getting APHIS to prioritize pest prevention over free trade in general, or in current trade agreements, is a heavy lift. At the very least, the agency should ensure that the U.S. prioritize invasive species prevention in negotiations with trading partners and in developing international trade-related agreements. I borrow here from the recent report on Canadian invasive species efforts. (I complained about APHIS’ failure to even raise invasive species issues during negotiation of a recent agricultural trade agreement with China.)
Solving Issues of Spreading Pests
The absence of an effective system to prevent a pest’s spread within the U.S. is the most glaring gap in the so-called federal “safeguarding system”. Yet this gap is rarely discussed by anyone – officials or stakeholders. APHIS quarantines are the best answer – although they are not always as efficacious as needed – witness the spread of EAB and persistence of nursery outbreaks of the SOD pathogen.
areas at risk to goldspotted oak borer
APHIS and the states continue to avoid establishing official programs targetting bioinvaders expected to be difficult to control or that don’t affect agricultural interests. Example include laurel wilt, and two boring beetles in southern California – goldspotted oak borer, Kuroshio shot hole borer and polyphagous shot hole borer and their associated fungi.
One step toward limiting pests’ spread would come from strengthening APHIS’ mandate in legislation, as suggested above. A second, complementary action would be for states to adopt quarantines and regulations more aggressively. For this to happen, APHIS would need to revise its policies on the “special needs exemption” [7 U.S.C. 7756]. Then states could adopt more stringent regulations to prevent introduction of APHIS-designated quarantine pests (Fading Forests III Chapt 3).
Finally, APHIS should not drop regulating difficult-to-control species – e.g., EAB. There are repercussions.
APHIS’ dropping EAB has not only reduced efforts to prevent the beetle’s spread to vulnerable parts of the West. It has also left states to come up with a coherent approach to regulating firewood; they are struggling to do so.
Considering interstate movement of pests via the nursery trade, the Systems Approach to Nursery Certification (SANC) program) is voluntary and was never intended to include all nurseries. Twenty-five nurseries were listed on the program’s website as of March 2020. It is not clear how many nurseries are participating now. The program ended its “pilot” phase and “went live” in January 2021. Furthermore, the program has been more than 20 years in development, so it cannot be considered a rapid response to a pressing problem.
Solving Issues of Recovery and Restoration via Resistance Breeding
I endorse the findings of two USFS scientists, Sniezko and Koch citations. They have documented the success of breeding programs when they are supported by expert staff and reliable funding, and have access to appropriate facilities. The principle example of such a facility is the Dorena Genetic Resource Center in Oregon. Regional consortia, e.g., Great Lakes Basin Forest Health Collaborative and Whitebark Pine Ecosystem Foundation are trying to overcome gaps in the system. I applaud the growing engagement of stakeholders, academic experts, and consortia. Questions remain, though, about how to ensure that these programs’ approaches and results are integrated into government programs.
resistant and vulnerable ash seedlings; photo courtesy of Jennifer Koch, USFS
In Bonello et al., I and others call for initiating resistance breeding programs early in an invasion. Often other management approaches, e.g., targetting the damaging pest or manipulating the environment, will not succeed. Therefore the most promising point of intervention is often with by breeding new or better resistance in the host. This proposal differs slightly from my suggestion in the “30 years – solutions” blog, when I suggested that USFS convene a workshop to develop consensus on breeding program’s priorities and structure early after a pest’s introduction.
Funding Shortfalls
I have complained regularly in my publications (Fading Forests reports) and blogs about inadequate funding for APHIS Plant Protection program and USFS Forest Health Protection and Research programs. Clearly the USDA Plant Pest and Disease Management and Disaster Program has supported much useful work. However, its short-term grants cannot substitute for stable, long-term funding. In recent years, APHIS has held back $14 – $15 million each year from this program to respond to plant health emergencies. (See APHIS program reports for FYs 20 and 21.) This decision might be the best solution we are likely to get to resolve APHIS’ need for emergency funds. If we think it is, we might drop §2 of H.R. 1389.
Expanding Engagement of Stakeholders
Americans expect a broad set of actors to protect our forests. However, these groups have not pressed decision-makers to fix the widely acknowledged problems: inadequate resources – especially for long-term solutions — and weak and tardy phytosanitary measures. Employees of federal and state agencies understand these issues but are restricted from outright advocacy. Where are the professional and scientific associations, representatives of the wood products industry, forest landowners, environmental NGOs and their funders, plus urban tree advocates – who could each play an important role? The Entomological Society’s new “Challenge” is a welcome development and one that others could copy.
SOURCES
Bonello, P., Campbell, F.T., Cipollini, D., Conrad, A.O., Farinas, C., Gandhi, K.J.K., Hain, F.P., Parry, D., Showalter, D.N, Villari, C. and Wallin, K.F. (2020) Invasive Tree Pests Devastate Ecosystems—A Proposed New Response Framework. Front. For. Glob. Change 3:2. doi: 10.3389/ffgc.2020.00002
Green, S., D.E.L. Cooke, M. Dunn, L. Barwell, B. Purse, D.S. Chapman, G. Valatin, A. Schlenzig, J. Barbrook, T. Pettitt, C. Price, A. Pérez-Sierra, D. Frederickson-Matika, L. Pritchard, P. Thorpe, P.J.A. Cock, E. Randall, B. Keillor and M. Marzano. 2021. PHYTO-THREATS: Addressing Threats to UK Forests and Woodlands from Phytophthora; Identifying Risks of Spread in Trade and Methods for Mitigation. Forests 2021, 12, 1617 https://doi.org/10.3390/f12121617ý
Krishnankutty, S., H. Nadel, A.M. Taylor, M.C. Wiemann, Y. Wu, S.W. Lingafelter, S.W. Myers, and A.M. Ray. 2020. Identification of Tree Genera Used in the Construction of Solid Wood-Packaging Materials That Arrived at U.S. Ports Infested With Live Wood-Boring Insects. Journal of Economic Entomology 2020, 1 – 12
Liebhold, A.M., E.G. Brockerhoff, L.J. Garrett, J.L. Parke, and K.O. Britton. 2012. Live plant imports: the major pathway for forest insect and pathogen invasions of the US. Front. Ecol. Environ. 2012; 10(3):135-143
Lovett, G.M., M. Weiss, A.M. Liebhold, T.P. Holmes, B. Leung, K.F. Lambert, D.A. Orwig, F.T. Campbell, J. Rosenthal, D.G. McCullough, R. Wildova, M.P. Ayres, C.D. Canham, D.R. Foster, SL. Ladeau, and T. Weldy. 2016. NIS forest insects and pathogens in the US: Impacts and policy options. Ecological Applications, 26(5), 2016, pp. 1437–1455
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. Ecol Evol. 2019 Nov; 9(21): 12216–12230.
Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Spp in Forests and Grasslands of the US: A Comprehensive Science Synthesis for the US Forest Sector. Springer Verlag. (in press).
Roy, B.A., H.M Alexander, J. Davidson, F.T Campbell, J.J Burdon, R. Sniezko, and C. Brasier. 2014. Increasing forest loss worldwide from invasive pests requires new trade regulations. Front Ecol Environ 2014; 12(8): 457–465
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.
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
Willow forest in the Tijuana River Valley killed by Kuroshio shot hole borer the “boom” part of the cycle photo by John Boland
I have blogged earlier about the damage caused by the Kuroshio shot hole borer (KSHB, Euwallacea kuroshio), which is one of two invasive shot hole borers established in southern California. The beetle and its symbiotic fungi had caused amazing levels of damage in the Tijuana River Valley in San Diego County, California. The wood borer is described here and here.
Most of the earlier blogs focused on the absence of a response by California’s phytosanitary agency and here – until John Kabashima created sufficient political demand for a response.
A scientist who has devoted considerable effort to understanding the KSHB is John Boland of Boland Ecological Services. He has posted annual reports analyzing five years of the outbreak in the Tijuana River Valley (see full citations at the end of the blog). His principal findings (Boland and Uyeda 2020): the invasion went through a boom and bust cycle, with willows in the wettest parts of the estuary having largely recovered. So far, Kuroshio shot hole borers have not re-infested the growing trees, despite the presence of all conditions seeming to favor invasion. His principal worry is enhanced invasion by the non-native grass or reed Arundo donax.
The study site is a coastal floodplain crossed by an intermittent stream. The Tijuana River valley provides several ecosystem services, including filtering pollutants before the water reaches the ocean, open space, and important wildlife habitat, including Critical Habitat for the federally endangered least Bell’s vireo (Vireo bellii pusillus).
There is a mosaic of forests of different ages and at different distances from the current flows. They range from wet forests growing in the current river beds; dry forests growing in older river beds that get some current flows; and scrub forests growing far from current river flows. All these forests are dominated by two willows: the black willow (Salix gooddingii) and the arroyo willow (Salix lasiolepis). Both are preferred hosts of KSHB; both are pioneer species that establish in disturbed wet areas; both resprout vigorously. The riparian scrub woodlands surrounding the forests are dominated by the perennial shrub, mule fat (Baccharis salicifolia), with scattered willows of both species (Boland and Uyeda 2020).
The river carries high levels of raw sewage and industrial waste from Tijuana, Mexico. Raw sewage contains important plant nutrients – nitrogen, phosphorus and potassium. The willows in or near the nutrient-enriched channel water were growing quickly and vigorously, and had wood characteristics that differed significantly from those of trees in the dry or scrub forests. Dr. Boland notes that these trees’ phloem sap is loaded with sugars from the fast-growing leaves, and xylem sap is loaded with nutrients from the enriched soil. His Enriched Tree Hypothesis (discussed further below) suggests that these nutrients promote fast growth of the symbiotic fungi and ideal conditions for KSHB (Boland and Woodward 2019).
Boland and his colleagues have carried out detailed annual field surveys of the infestation since 2015. Using the same study plots in each year, they analyzed infestation and mortality rates, canopy damage, and survivorship of tagged willows.
Funding originally came from the U.S. Navy and U.S. Fish and Wildlife Service – agencies probably worried about the potential destruction of the vireos’ habitat. As of 2019 KSHB had infested 91% of all the willows in the valley – estimated to be more than 350,000 willows. KSHB had killed 30% of the trees, or nearly 123,000 (Boland 2019). Dr. Boland considers this estimate to be an underestimate because he could not accurately carry out surveys of individual trees in the extensively-damaged Wet Forest units in 2018. There was considerable variation in pest impacts depending on host trees’ proximity to the intermittent river. Of all of the willow deaths in the valley, 93.8% occurred in the Wet Forests, 6.1% in the Dry Forests and 0.1% in the Scrub Forests. This variation occurred even though the sites contain the same willow species (Boland and Uyeda 2020).
Infestation rates over the four-year period averaged 99% of willows in the Wet Forest units, 82% in the Dry Forests and 3% in the Scrub Woodlands. Considering 2019 alone, the overall infestation rate was only 9%. Looking at differences among forest types, 1% of the willows in Wet Forests were infested (down from 95% in 2015), 29% of the willows in dry forests (down from 73% in 2016), and 0% of the willows in the scrub forests (down from 2% in 2018). (2019 infestation rates from Boland and Uyeda 2020; earlier years from Boland 2019.)
Infestation rates had to be very high before trees died, but then mortality was very high. Only after sites reached infestation rates of more than 95% did sites have significant mortality rates – and then, very high — up to 97%. In agreement with other findings, most of the high-mortality sites were in Wet Forest units. These had a mean maximum mortality rate of 49%. The mean maximum mortality rate was only 9% in Dry Forest and 2% in Scrub Forest units (Boland and Uyeda 2020).
The size of the tree is also important. In the Wet Forests, in 2019, infestation rates were 0% for seedlings and young trees; 3% for the relatively undamaged trees that are more than 5 years old; and 1% of the resprouting adult trees that had been broken during the first wave of invasion. KSHB prefers young trees with a trunk dbh of at least 4.5 cm. Smaller trees were generally avoided. Trees with very large dbh (> 30 cm) appear to be able to survive a KSHB attack (Boland and Uyeda 2020).
At the end of the five year period, Dr. Boland had documented interesting/puzzling findings.
Recovery of the willow forest in Tijuana River Valley – 2019 photo by John Boland
Wet Forests
KSHB in the valley went through a rapid boom-and-bust cycle. In the Wet Forests, KSHB infestation progressed over the course of a few months from barely noticeable to heavy infestation and dramatic canopy collapse. Infestation rates of 80 – 95% in the West Forests in 2015 and 2016 led to virtual elimination of the canopy between 2016 and 2017 as tunnel-ridden trees were broken by wind storms. These severe damage levels occurred over 94 acres (Boland and Uyeda 2020).
After apparently depleting their preferred hosts in the wettest parts of the forest, beetle numbers fell and host trees began a rapid recovery. Mean canopy cover rose from 5% in 2017 to 56% in 2019. This recovery has taken three forms: survival of a few, scattered mature infested trees (‘Big Trees’) which grew new wood over KSHB galleries (Boland 2019); resprouting of mature KSHB-damaged trees (‘resprouts’); and seeding of new trees (‘seedlings’). Some of the forests have recovered so much in just 4 years that they are now similar to their pre-KSHB stature (Boland and Uyeda 2020).
Dr. Boland suggests that KSHB is promoted by high nutrient (pollution) levels in the water, which result in rapid growth by trees near the most steady of the intermittent streams. He has developed an Enriched Tree Hypothesis (explained briefly below; for a full discussion, see Boland and Woodland 2019).
As of autumn 2019, beetles have not attacked the recovering hosts – despite apparently favorable conditions and the absence of management interventions. 2019 infestation rates were 3% of the remaining Big Trees, 2% of the resprouting trees, 1% of the young trees, and 0% of the seedlings. Dr. Boland suggests three possible reasons (Boland and Uyeda 2020), which I will discuss below.
The resprouting trees are now old & vigorous enough to flower
It is likely that these recovering willow forests will provide good breeding habitat for least Bell’s vireo (all Boland publications).
Dry Forests
Infestation in the Dry Forests spread more slowly – infestation rates averaged 82% in the Dry Forests over four years. The infestation progressed more slowly and the canopy remained mostly intact. But in 2019 the infestation rate in the Dry Forest was substantially higher than in the Wet Forest — 29% versus 1% (Boland and Uyeda 2020).
Still, only 16% of more than 200 willows tagged in February 2016 had been killed by KSHB by autumn 2019. Among the living trees were three quarters of trees already infested in 2016, and half of trees that became infested after 2016 (Boland and Uyeda 2020).
Lack of Reinfestation (Boland and Uyeda 2020).
The absence of reinfestation is surprising, especially because the conditions thought favorable to KSHB are all present:
1. The regenerating trees belong to host species known to be preferred – black and arroyo willows.
2. The regenerating trees have reached the preferred size with trunk dbh exceeding 4.5 cm. In fall 2019 the trees in the recovering Wet Forests included many resprouting trees with mean diameters of 6.5 cm, and many new seedlings with mean diameters of 11.7 cm.
3. Recovering forests are located in the preferred nutrient-rich sites. Sewage levels remain high.
4. The trees in the recovering forests are in the condition preferred by KSHB, i.e., the trees are fast-growing and vigorous.
5. The KSHB is present – in low numbers in the Wet Forests, more numerous in Dry Forests which are < 1 km away.
It is not known whether KSHB will eventually re-infest.
The KSHB infestation reversed the presence of large trees. Originally 53% of the large trees were in the Wet Forests, 38% in the Dry Forests. The KSHB invasion damaged so many of the trees in the Wet Forests that now they represent only 24% of all the ‘Big Trees’ in the Valley; 58% of the ‘Big Trees’ are now in the Dry Forests. In many Dry Forests the remaining tall trees form a continuous canopy layer, whereas in the polluted Wet Forests they are usually only single ‘Big Trees’ (Boland and Uyeda 2020).
Other plant species
Dr. Boland expresses great concern about the spread of the invasive plant, Arundo donax, in response to canopy openings caused by the initial invasion and canopy collapse (willow trees are Arundo’s only competitors in the valley).
Surveys during fall 2019 found that most plant species growing in the Tijuana River Valley are native, dominated by the willows (mean cover of 60%). The most abundant non-native species is castor bean (10% cover). Arundo had a mean cover of only 6% in the belt transects, but it was more abundant outside the transects. Arundo is spreading as rhizomes cut loose by bulldozing, disking, and mowing on property managed by International Boundary and Water Commission (Boland and Uyeda 2020). Both willows and Arundo had increased their percent cover between 2018 and 2019 (Boland 2019).
Dr. Boland’s Recommendations (Boland and Uyeda 2020)
1) The different invasion trajectories in the three habitat types contradict some researchers’ expectation that all trajectories are similar from regardless of site characteristics or that a light infestation must be recent while a heavy infestation must be old.
2) Unique characteristics of the Tijuana River valley – especially the high sewage levels – mean that the severe infestation and damage seen there should not be expected to occur at other natural, unpolluted riparian sites.
3) Dr. Boland disputes recommendations that “heavily infested” trees be removed because they are doomed and support beetle reproduction. Although Dr. Boland studied primarily willows, he did evaluate 24 California sycamores (Platanus spp.) that had been planted in various parts of the valley.
He found that none had died and only two (8%) were infested. The two infested trees were lightly infested and growing near the sewage-enriched stream. Dr. Boland concluded that sycamores were also unlikely to be heavily infested and killed in habitats less favorable to shot hole borers (Boland 2019).
4) The ease with which native willows became densely established in wet forest sites after the first infestation wave leads Dr. Boland to advocate reliance on natural restoration projects … as long as Arundo invasion can be controlled.
5) Avoid over-fertilization or over-watering of trees in planted landscapes.
6) Focus detection searches for KSHB in nutrient-enriched areas. … e.g., near storm drain outfalls.
Research recommendations:
A) Determine why KSHB has not substantially reinvaded the recovering willow forests despite the presence of preferred species in “correct” condition and size. Dr. Boland suggests testing of three hypotheses:
Induced response of hosts. Have the infested willows changed their chemistry as a result of the borer attack, thus increasing their resistance ….
Overall forest structure. Have the less dense and more mixed forest stands reduced attractiveness to the beetle?
A disease or predator. Has a biocontrol agent been introduced accidentally? None has yet been identified …
B) Understand the possible mechanisms for the high initial infestations rates in the Wet Forests.
To evaluate the Enriched Tree Hypothesis measure the sugars and nutrients (both concentrations and loading rates) in trees subject to differing amounts of sewage or fertilizers. Then conduct controlled trials in the lab on the growth response of ISHB’s fungal symbionts to various sugar and nutrient concentrations and loading rates.
Evaluate whether willows growing in the nutrient-enriched sites produced fewer tannins that might inhibit beetle and fungal growth.
C) Can ISHB disperse by wind? Dr. Boland recommends searching for ISHB in the air high above infested trees; this could involve the use of nets or traps attached to aircraft, hot-air balloons, helium balloons or drones.
D) Determine whether surviving mature trees have superior characteristics re: morphology, vigor, and pest or disease resistance that make them less vulnerable to KSHB attack.
E) Incorporate site and ecology data and varying levels of host vulnerability into models predicting KSHB impacts. Include the ecological costs of removing the trees.
My questions
Are other scientists applying these findings in their research on KSHB or polyphagous shot hole borer outbreaks in other parts of California? I am particularly interested in the issues of possible resistance in some willows – innate or induced; and the potential role of excess nutrients in promoting fungal and beetle growth. Are they finding the ecological components of the Enriched Tree Hypothesis to be helpful in defining the impact of PSHB outbreaks in other parts of the state, and of older ages?
SOURCES
Boland, J.M. 2109. The Ecology and Management of the Kuroshio Shot Hole Borer in the Tijuana River Valley. Final Report for Naval Base Coronado under Cooperative Agreement N62473-18-2-0008
Boland, J.M. and D.L. Woodward. 2019. Impacts of the invasive shot hole borer (Euwallacea kuroshio) are linked to sewage pollution in southern Calif: the Enriched Tree Hypothesis. PeerJ 7:6812
Boland, J.M. and K.A Uyeda. 2020. The Ecology and Management of the Kuroshio Shot Hole Borer in the Tijuana River Valley 2019-20 (Year 5) Final Report. For Naval Base Coronado, Department of Navy and Southwest Wetlands Interpretive Association. Under Cooperative Agreement N62473-18-2-0008
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
The California Department of Food and Agriculture (CDFA) is seeking comments on the appropriate pest rating for Leptosillia pistaciae, a recently discovered fungus that causes pistachio canker.
The
Department’s draft pest ranking assigns the highest Economic Impact score –
three. It assigns a medium Environmental Impact – two. This is because the
pathogen can kill an important native shrub, with possible follow-on
consequences of reduced biodiversity, disrupted natural communities, or changed
ecosystem processes.
CDFA
states that there is no uncertainty in its evaluation, but I see, and describe
here, numerous questions about the possible true extent of the invasion and
possible host range.
Comments are due
on April 4, 2020.
The
pathogen was detected in June 2019, when a habitat manager from an ecological
reserve in San Diego County noticed multiple dead lemonade berry shrubs (Rhus integrifolia) in one of the parks.
This is the first known detection of Leptosillia
pistaciae in the United States and on this host. USDA APHIS has classified Leptosillia pistaciae as a federal quarantine
pest. Rhus and Pistacia are in the same family, Anacardiaceae (cashews and sumacs).
According
to the CDFA, Leptosillia pistaciae is
the only member of this fungal genus known to be associated with disease
symptoms on plants. Other species are endophytes or found in dead plant
tissues. [It is not at all unusual for fungal species to be endophytes on some
plant hosts but pathogenic on others. A California example is Gibberella
circinata (anamorph Fusarium circinatum), which causes
pitch canker on Monterey pine (Pinus
radiata) but is an endophyte on various grass species (Holcus lanatus and Festuca
arundinacea).]
(Reminder: this is the second new pest of native species detected in California state in 2019; I blogged about an ambrosia beetle in Napa County here. )
Rhus integrifolia (lemonade berry
or lemonade sumac) is native to California. It grows primarily in the south, along
the coast – from San Diego to San Luis Obispo. However, some populations are
also found in the San Francisco Bay area. This and other sumacs are also sold
in the nursery trade.
On
pistachio trees in Italy, symptoms are observed in the winter and late spring. During
the winter dormant season, trees had gum exudation and cracking and peeling of
bark on trunks and branches. On trunks and large branches, cankers appeared
first as light, dead circular areas in the bark; subsequently they became
darker and sunken. Under the bark, cankers were discolored with necrotic
tissues; in some cases, these extended to the vascular tissues and pith. During
the active growing season, the symptomatic plants also showed canopy decline.
Inflorescences and shoots, originating from infected branches or twigs, wilted
and died. When the trunk was girdled by a canker, a collapse of the entire tree
occurred.
range map for Rhus integrifolia
On
lemonade berry, large clumps of dead
adult shrubs were observed on the edge of hiking trails. Some shrubs that had completely
dead foliage were re-sprouting from their bases. Trunks of shrubs that were not
completely dead were copiously weeping sap and fluids and showed foliage
browning and die back with symptoms of stress.
It
is thought that spores could be spread by wind, rain splashing, and the
movement of dead or dying trees, greenwaste, and infected nursery stock. Contaminated
pruning tools might also transport the spores. The possibility of a latent
phase – or perhaps asymptomatic hosts – adds to the probability of
anthropomorphically assisted spread.
I question how much effort has been put into detection surveys, especially in natural systems with native Rhus species. California has three other native sumacs: R. ovata, R. aromatica, and Malosma laurina (CNPS; full citation at the end of the blog). In addition, there are numerous other species in the family, including poison oaks (Toxicodendron spp.) and the widespread invasive plant genus Schinus.
Furthermore, some plants in the family (other than pistachios) are grown for fruit or in ornamental horticulture, including two of the native sumacs and two non-native species, Rhus glabra and R. lanceolata, cashew, mango, and smoke trees (Cotinus spp.).
Yet
CDFA confidently states that there are only two hosts and that it has been
detected in only one population – that in San Diego. This is because CDFA
considers only official records identified by a taxonomic expert and supported
by voucher specimens.
CDFA
states that the pathogen is likely to survive in all parts of the state where
pistachios are grown – primarily in the Central Valley. California supplies 98%
of the pistachios grown in the United States; the remainder is raised in
Arizona and New Mexico. California production occurred on 178,000 acres in
2012. A map is included in a flyer on production available at the url listed at
the end of this blog.
In
discussing spread potential, no mention is made of possible human-assisted
spread.
The CDFA document includes instructions for submitting comments; the deadline is April 4.
Sources:
Rhus and related
species native to California: California Native Plant Society
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.
last year’s leaves showing symptomatic striping (F.T. Campbell)
Back in December I blogged about beech leaf disease, a disease affecting American beech in northeastern Ohio and neighboring parts of Pennsylvania and New York, as well as across Lake Erie in Ontario.
[For more information and photos of symptoms, visit
Scientists do not know what is causing the disease. So far it’s only clear that it appears to have been introduced to a single site and is spreading. At the beginning of May I participated in a workshop providing the most recent information on beech leaf disease.
workshop participants (budbreak was later than usual, so we could not observe deformed leaves) (F.T. Campbell)
Over the past three or four years, scientists have tried hard to understand the disease, its causes, and its likely prognosis. For example, scientists from the U.S. Department of Agriculture and the State of Ohio have looked for insects, fungal pathogens, bacteria, viruses, nematodes, phytoplasmas – all without finding a causative agent. Attention is currently focused on a previously undescribed nematode in the Litylenchus genus. The only other species in this genus is a foliar feeder found in New Zealand. Studies continue, with most scientists tackling the problem without special funding.
Beech is a very important component of the forests of northeastern Ohio. Beech ranks third in number of stems per acre; second for “shrubs”. Consequently, scientists working for Lake Metroparks and Cleveland Metroparks continue to monitor spread of the disease and its impacts. Symptoms – deformed leaves – were first detected in 2012. In 2017, the results of a long-term vegetation monitoring project revealed that of 307 plots with beech present, 154 had symptomatic trees. Of the symptomatic plots, 49% of beech stems were affected. While initially only small trees had been killed, more recently some larger ones have died and others bear only very few leaves. Leaves with light, medium, or heavy symptoms of infection – as well as asymptomatic leaves – can occur on the same branch of an individual tree.
The disease seems to spread faster between stems along the interlocking roots of beech clone clusters.
Weather does not appear to be a factor, as the disease has spread every year despite great variations in heat and cold as well as levels of moisture.
Preliminary versions of a mathematical model of the disease’ spread indicates that approximately 90% of monitoring plots deployed across the full 24,000 acres of Cleveland Metropark system will be infected within 10 years.
Cleveland Metroparks has initiated intensive monitoring of a subset of 13 plots in order to clarify the disease’s impact. Monitoring revealed a 4% mortality rate from 2015 to 2017. More than half of these plots now have dead beech that had previously been symptomatic. Most are small trees less than 4.9 cm dbh. Efforts to obtain funding from the USFS Forest Health program have so far failed.
The disease – whatever its cause! – appears to be moved by trade in nursery plants. An Ontario retailer received – and rejected – a shipment of diseased beech from an Ohio nursery. Lake County, Ohio, has many nurseries that grow and ship European beech (which can also be infected by beech leaf disease). These nurseries are reported to be cooperating with Ohio authorities. No official entity has imposed regulatory restrictions – not any of the states or provinces with the disease present or threatened by it; nor USDA APHIS or the Canadian Food Inspection Agency (CFIA).
Another threat to beech also not under regulation
CFIA has also not imposed a federal quarantine on another non-native pest killing beech, the European leaf-mining weevil, Orchestes fagi. First discovered in Halifax in 2012 – probably 5 years after its introduction – it has since spread throughout Nova Scotia. The weevil kills beech over 3 – 5 years.
New information added in June: according to Meurisse et al. (2018), the weevil overwinters under the bark of beech and trees that are not hosts, so it can be transported by movement of firewood and other forms of unprocessed logs and branches. [Meurisse, N. D. Rassaati, B.P. Hurley, E.G. Brockerhoff, R.A. Haack. 2018. Common Pathways by which NIS forest insects move internationally and domestically. Journal of Pest Science. https://doi.org/10.1007/s10340-018-0990-0]
The Importance of American Beech – and Protecting It
Beech is an extremely important tree in northern parts of the United States and Canada east of the Great Plains. It is co-dominant (with sugar maple) in the Northern Hardwood Forest [see two maps]. A summary of the species’ ecological importance can be found in Lovett et al. 2006. Forest Ecosystem Responses to Exotic Pests and Pathogens in Eastern North America. BioScience Vol. 56 No. 5.
native range of American beech; USFS map
Consequently, I am most distressed by the lack of attention to these new threats to the species. It is true that regulating an unknown disease agent (as would be the case with beech leaf disease) stretches traditional policy practice and possibly legal authorities. Furthermore, it has not yet been demonstrated that the disease can kill mature beech. However, neither of these caveats applies to the weevil, which is an identified species that has been documented to kill mature trees.
U.S. phytosanitary officials (the National Plant Board) will meet in Cleveland (!!) in August. Will the several state officials and their APHIS colleagues discuss how to address this new threat? Will any funds be made available to expand efforts to understand the disease, its spread, and possible measures to curtail it?
healthy beech, northern Virgina (F.T. Campbell)
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.
I have written numerous times about the risk posed to urban and rural forests posed by the polyphagous and Kuroshio shot hole borers and their associated fungi. (Blog exploring risk to urban forests; discussion of need for regulation.)
Yet neither California authorities nor USDA APHIS has put significant effort into containing these insects – which continue to spread north in the state. Perhaps this will change in response to the U.S. Senate’s Agriculture appropriations report, which on p. 39 instructs the Secretary of Agriculture to report on steps being taken to “to minimize the spread of other pests such as the polyphagous and Kuroshio shot hole borers.”
Another possible spur to action is that scientists have now proved that the Fusarium euwallaceae fungus – the primary fungus transported by these beetles – can infect almond trees — a major economic crop in the San Joaquin Valley of California. The polyphagous shot hole borer is known to be in Santa Barbara and San Luis Obispo counties – ever closer to the agricultural areas. California produces 82% of total global production of almonds. In 2015, the state’s almond production was valued at $5.33 billion. $5.14 billion (96%) of this production was exported (California Agricultural Production Statistics).
Already, the polyphagous shot hole borer threatens a wide range of native and horticultural trees in the region. (Damage to avocado trees is less than originally believed.) Together, the polyphagous and Kuroshio shot hole borers and their associated fungi threaten more than a third of trees in the urban forests in southern California, with a cost for the trees’ removal and replacement estimated at $36 billion.
Moreno, K., J.D. Carrillo, F. Trouillas, A. Eskalen. 9/24/2017 Almond (Prunus dulcis) is susceptible to Fusarium euwallaceae, a fungal pathogen vectored by the Polyphagous Shot Hole Borer in Calif | Plant Disease. http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-07-17-1110-PDN 1/2
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.
Photo by John Boland – willows killed by Kuroshio shot hole borer, Tijuana River, California
The polyphagous (PSHB) and Kuroshio (KSHB) shot hole borers are causing havoc in riparian and planted landscapes in four counties in southern California and are spreading north. (For current information go here or here .
As I described in a blog last July, the two insects are known to attack hundreds of tree species; at least 40 are reproductive hosts. Trees known to support PSHB include box elder, big leaf maple, Californiasycamore, willows, cottonwoods, and several California oaks. The insect-fungi combinations threaten more than a third of trees in the urban forests in southern California, with a cost for the trees’ removal and replacement estimated at $36 billion. Costs and hosts are discussed more fully in the July blog linked to above.
The High Cost of Management
Already, UC Irvine has spent close to $2 million to manage trees on campus that have been attacked.
Orange County has both polyphygous and Kuroshio shot hole borers. One agency – Orange County parks – has spent $1.7 million on shot hole borer surveys, tree inventory, public outreach materials, staff training, and some research. The parks agency is trying to engage other county agencies, such as Public Works and Waste & Recycling to get their help. For example, Public Works is putting together a tree ordinance with enforceable provisions.
While scientists have not yet published their analysis of the vulnerability of forest areas in other parts of the country, we do know that some reproductive hosts are widespread across the country — box elder, sweet gum, Japanese wisteria, and tree of heaven. Less is known about the hosts for Kuroshio shot hole borer. For a full list of known hosts, visit the two sources linked to in the first paragraph.
How Agencies Should Respond to this Threat
The shot hole borers and associated fungi clearly represent serious threats to urban, rural, and wildland forests across California and probably much of the rest of the country. Clearly it is important that we:
Increase our understanding of these insects and their associated fungi – including their possible geographic and host ranges;
Use this evolving understanding to develop detection tools; and
Use this evolving understanding to develop methods to slow their spread or to protect trees.
So what is being done? Individuals – academics; staff of local, state, and federal agencies; and concerned conservationists – are working hard. But they get little support from state or federal phytosanitary agencies.
The Need for New State and Federal Regulations
I have written earlier about the refusal of California Department of Food and Agriculture to either designate the polyphagous and Kuroshio shot hole borers as quarantine pests [] or to regulate movement of firewood – one of the major pathways for spread of the insects.
Nor has USDA APHIS designated the insects and their fungi as quarantine pests. The apparent explanation for the agency’s inaction is the considerable taxonomic confusion about the beetles and the possibility that the insects are already established elsewhere in the U.S. In addition, since the two shot hole borers are currently known only from California, APHIS is unlikely to take action unless California does. However, there is no legal requirement that APHIS defer to the state on this matter.
The Results of Funding and Regulatory Shortfalls
Both CDFA and APHIS are providing some funds to support research and development. Research on detection, spread, and possible biocontrols — for the insects or fungi — have received a total of $385,000 in FY16 and $419,549 in FY17 from a grant program operated under the USDA Plant Pest and Disease Management and Disaster Prevention Program (Farm Bill Sec. 10007). Still, the principal investigators and affected county, state, and federal agencies are scrambling to fill funding gaps – projects that will improve our understanding and put forward practical advice.
The San Diego Association of Governments (SANDAG) and Natural Communities Coalition (NCC) of Orange County are supporting research by Akif Eskalen and Shannon Lynch of UC Riverside on both (a) biocontrol using endophytes naturally occurring in various host tree species and (b) models to predict the disease’ behavior in native vegetation. Dr. Eskalen and Dr. John Kabashima of Orange County Cooperative Extension are seeking funds to support additional work on outreach and extension for advisors, land managers, master gardeners and homeowners.
Santa Barbara County officials – where at least one of the shot hole borer species was recently detected – are struggling to fund an expanded trap program to detect the insects. The CDFA does have traps deployed but UC Santa Barbara is considering launching a trapping program in riparian areas (where many of the host trees play especially important ecological roles). Officials are still not certain which species of insect is present (they think it is KSHB) and whether the beetles are carrying the typical fungal complex or something novel.
In the past, some of the work on the shot hole borers has been funded by associations of avocado growers. However, it is now clear that the beetle attacks only avocado tree branches, so it does not kill the tree. No longer facing a dire threat to their industry, the avocado commission is no longer funding research work on this pest-disease complex.
The experts – Dr. Eskalen for the fungi and his colleague Dr. Richard Stouthamer for the insects – have no funds to process samples sent to their laboratories for the confirmation of the beetles and fungi. They might soon have to charge fees for each sample – thereby discouraging collections that track each species’ spread and find new introductions.
In the absence of CDFA designation of the shot hole borers as regulated pests, neither state nor county agencies have a firm foundation on which to base regulations to curtail movement of firewood, green waste, or other pathways by which these pests can be spread to new areas.
Conservation Agencies are Cobbling Together Responses As Best They Can
Southern California staff of the California Department of Fish and Wildlife agency, responding to the damage caused by the Kuroshio shot hole borer in the Tijuana River estuary (described here and here), have formed a coalition to develop strategies for natural resource and urban forestry settings and ensure coordination. Natural resource agencies have access to some funding sources, such as Natural Communities Coalition (NCC) grants and funding for management of invasive species in protected habitats.
Southern California staff of the U.S. Fish and Wildlife Service are seeking grants from internal agency sources – citing the threat to riparian-dependent wildlife, especially the endangered Least Bell’s vireo.
Santa Monica National Recreation Area and the three National forests in the vicinity – the Angeles, Cleveland, and San Bernardino National forests – have taken actions that should help prevent the shot hole borers’ introduction via firewood. Santa Monica Recreation Area does not allow wood fires, only charcoal (this action probably is in response to the high fire danger in the area rather than the pests specifically). The National forests’ webpages on camping include a graphic with the statements “Buy It Where You Burn It” and “Be aware that firewood can harbor insects and diseases; transporting it can move these pests to new locations.” (See my earlier blog about firewood alerts on National forests, parks, etc. here).
What You Can Do
Many Californians are pushing for action … they need our help! If you live in California, contact your state legislators. If you live elsewhere, your forests are also at risk from California’s failure to act. So, if you know someone who lives there, ask that person to contact his/her legislators. Ask the legislators to (a) demand state designation of PSHB, KSHB, and GSOB as quarantine pests and adoption of state firewood regulations and (b) support funding for these programs.
The U.S. Congress has a role in convincing APHIS to play a bigger role. Contact your federal Senators and Member of Congress and urge them to ask USDA APHIS to regulate movement of firewood, green waste, and nursery stock from areas infested by the polyphagous or Kuroshio shot hole borers and goldspotted oak borer.
President Trump will soon propose funding levels for government programs, including APHIS’ “tree and wood pest” program. Please keep informed about these proposals – and contact your Congressional representative to express support for adequate funding. Contact me using the “Contact us” button on our website if you wish to receive informative alerts about the upcoming appropriations process.
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.
