Category: resistance breeding

Resistance Breeding – Let’s Do It! (Instead of thinking about it)

TACF back-crossed American-Chinese chestnut; photo by F.T. Campbell

I have advocated for considerably expanding efforts to breed trees resistant to non-native pests (including pathogens) for a decade. Again and again, I and others have pointed out the dire consequences for our forests if we Americans do not rise to the challenge.

In 2014, Scott Schlarbaum – coauthor of Fading Forests III – American Forests: What Choice Will We Make? warned that without restoration becoming an integral part of a strategy addressing non-native plant pests, American ecosystems are doomed to continuing transformation. Once established, a non-native pest is never eliminated, but its impact can be reduced through a combination of measures – as long as support is made available. Scott advised initiating a germplasm conservation strategy when invasion is imminent or once the pest is likely to become a resident pest. (See Chapter 6).

I have posted seven blogs since August 2021 describing the current status of various efforts and urging the U.S. Government and conservation organizations to step up.  [To view these blogs, go to www.nivemnic.us, scroll below Archives to “Categories” and click on “resistance breeding.” 

More, and Recent, Voices: Implications of Not Acting

More recently, several USDA Forest Service (USFS) experts, including Richard Sniezko, C. Dana Nelson, and Jennifer Koch, have published articles making the same point. These scientists note that many of the decimated species were formerly among the most common trees in our forests. Therefore, the cumulative effect of their disappearance on forest species composition and function is multiplied.

One blog, posted in 2022, is particularly pertinent. It summarizes a special issue of the journal Plants, People, Planet devoted to resistance breeding. The opening essay, by R.J.A. Buggs, concisely reviews six major reasons why so many believe that resistance breeding is a failed strategy.

Port-Orford cedar – one of the trees for which resistance breeding has been successful; photo courtesy of Richard Sniezko, USFS

Others say there have been successes – all through application of classic tree improvement measures, not “genetic engineering.” Pike, Koch and Nelson (2021) list as successes Port-Orford-cedar (Chamaecyparis lawsoniana), the western five-needle pine species,  koa (Acacia koa), and resistance to fusiform rust (Cronartium quercuum f. sp. fusiforme) in the commercially-important loblolly (Pinus taeda) and slash (P. elliottii) pines. They also cite encouraging progress by The American Chestnut Foundation (TACF) through backcross breeding of America and Asian chestnuts and a USFS/private foundation effort to expand the genetic base of American elms (Ulmus americana). I regret to say this, but some of these efforts seem to me to be still in experimental stages or — at best — early in widespread – ‘though still experimental — plantings.

Participants in a 2021 Purdue University workshop have again called for greatly expanding breeding. See the special issue of New Forests, Vol. 54 Issue 4. Once again, experts reiterate the urgency of acting, then outline the opportunities and challenges.

In one of the articles (Jacobs et al.) several people – including me! – note that several keystone tree species or genera in North America and Europe have been driven to functional extinction by non-native pests. By this we mean they are no longer sufficiently abundant and/or of adequate size to reproduce sexually or perform their ecological function. Examples include – on both continents – ashes (Fraxinus) and elms; and on North America – American chestnut (Castanea dentata), butternut (Juglans cinerea), and whitebark pine (Pinus albicaulis).If these threats are left unchecked, these at-risk tree species might develop truncated ranges, lose genetic diversity, and face becoming threatened, endangered, or extinct.

In another article, Nelson says the question that should be asked about applying genetic engineering (GE) techniques to tree breeding is whether we should let a species be reduced to a marginal role — or disappear — when GE provides a solution to saving and restoring the species. His case study is a detailed history of TACF’s development of a transgenic American chestnut (called “Darling 58”). He points out that decades of breeding efforts were based on the hope of developing blight resistance within the native gene pool or to obtain resistance from related species through hybridization. However, those efforts have not yet provided trees suitable for restoring the “king of the Appalachian forest” to native landscapes. Nelson wrote his description before TACF discovered flaws in the GE trees they had been working with and decided to pursue different GE “lines” (see below).

Barriers

The overall strategy is clear. Schlarbaum, Sniezko, and Dana Nelson all describe essentially the same steps, built on the same kinds of expertise and facilities.

Of course, each species will require years of input by a range of experts. These challenges are not trivial. However, the experts named above agree that the principal barrier is the absence of sustained, long-term commitment of resources and facilities. With sufficient resources, many of the scientific challenge can be overcome for at least some of the species at risk.

So, what are the scientific challenges? First, scientists must assess whether the tree species contains sufficient genetic variation in resistance. This involves locating candidate resistant trees; developing and applying short-term assay(s) to screen hundreds or thousands of candidate trees; and determining the levels of resistance present. Second, scientists must develop resistant planting stock for use in restoration. This stage includes scaling up the screening protocol; selecting the resistant candidates or progeny to be used; breeding to increase resistance; establishing seed orchards or other methods to deliver large numbers of resistant stock for planting; and additional field trials to further validate and delineate resistance. Sniezko and Koch (2017) and Sniezko and Nelson (2022) discuss the challenges and describe successes.

facilities at Dorena Genetic Resource Center; photos courtesy of Richard Sniezko, USFS

Complicating the restoration phase is the fact that the resistant tree must be able to thrive and compete in an ecosystem that has changed greatly from that in which it formerly resided. Causes of these changes include repercussions from the absence of the tree species – and possibly associated species; the possible presence of other biotic stresses (pests); and climate change. This is discussed by Nelson (2022). See also my blog.

Successfully completing these steps requires a long-term commitment, which includes significant funding and strong supportive infrastructure. Schlarbaum pointed out that the public and politicians don’t understand the complexity of the restoration challenge and the resources required. He documented the shrinking tree improvement infrastructure as of 2014. At that time, funding for all USFS regional breeding programs was just $6 million. State and land grant university breeding programs were fragmented and seriously underfunded. Only 28 states still had some type of tree improvement activity – and some of these programs were only seed orchards, not active breeding and testing programs. Members of university-industrial cooperatives focus on a small number of commercial species – which are not the species threatened by non-native pests. I believe these resources have shrunk even farther in the decade since 2014.

A separate source of funds for resistance breeding is the Forest Health Protection program, which is under the Deputy Chief for State, Private, and Tribal Forestry rather than the Deputy Chief for Research and Development. While nation-wide data on seed or scion collection or screening to identify and evaluate genetic resistance are poorly reported, Coleman et al. indicate that the USFS Dorena Genetic Resource Center screens unspecified “hundreds” of seed lots for resistance to pathogens annually. The Center also participates in seed, cone, and scion collections, especially of white pines vulnerable to white pine blister rust (WPBR). Supplemental Table S3 lists projects funded over the two decades analyzed by Coleman et al. (2011 – 2020). These included efforts to identify and evaluate possible genetic bases for resistance to, e.g., hemlock woolly adelgid, balsam woolly adelgid, laurel wilt, emerald ash borer, butternut canker, rapid ʻōhiʻa death; and gene conservation for eastern hemlock, ashes, chestnut, in addition to the five-needle pines. Currently, FHP allocates $1.2 million annually to support the group of activities called Genetic Conservation, Resistance and Restoration (R. Cooksey, pers. comm.). 

American beech grafts to be tested for resistance to beech bark disease; at USFS center in Delaware, Ohio; photo courtesy of Jennifer Koch, USFS

USFS scientists involved in these projects describe challenges arising from efforts to cobble together funding from these many sources to support coherent programs. Overall funding levels still fall short of the need, and failure to obtain funding for one component of a program stymies the entire endeavor.

However, some developments are encouraging. The number of private foundations devoted to tree breeding has increased in the last decade. The American Chestnut Foundation (TACF) and American Chestnut Cooperators Foundation (ACCF) have been joined by the White Pine Ecosystem Foundation,  the Great Lakes Basin Forest Health Collaborative, Forest Restoration Alliance, ‘Ohi‘a Disease Resistance Program … These organizations raise awareness, coordinate efforts by multiple parties, and provide opportunities for individuals to contribute funds and volunteer work.

In Hawai`i, disease resistance programs with both koa (Dudley et al.) and ʻōhiʻa ((Metrosideros polymorpha) (Luiz et al.) are active. Work with ash species to find and develop resistance to emerald ash borer is under way but limited due to lack of funds.

Finally, we can persuade Congress to incorporate the provisions of two bills, H.R. 3174 and S. 1238, into the next Farm Bill. The bills would, inter alia, create two grant program. One would fund research addressing specific questions impeding the recovery of native tree species that have suffered severe levels of mortality caused by non-native plant pests. The second would fund implementation of projects to restore these pest-decimated tree species to the forest.

Funded projects would be required to be part of a forest restoration strategy that incorporates a majority of the following components:

(1) Collection and conservation of native tree genetic material;

(2) Production of propagules of the target tree species in numbers sufficient for landscape-scale restoration;

(3) Preparation of planting sites in the target tree species’ former habitats;

(4) Planting of native tree seedlings; and

(5) Post-planting maintenance of native trees.

For a detailed description, see this blog.

Details:

Facilities needed to support successful breeding programs

Sniezko and Nelson identified these needs as follows:

(a) growing space (e.g., greenhouses);

(b) seed handling and cold storage capacity;

(c) inoculation infrastructure;             

(d) field sites for testing;

(e) database capability for collecting, maintaining, and analyzing data;

(f) areas for seed orchard development;

(g) skilled personnel (tree breeders, data managers, technicians, administrative support personnel, and access to expertise in pathology and entomology).

There are very few facilities dedicated primarily to development of populations of trees with resistance to non-native pests; the most notable is the Dorena Genetic Resource Center. Even the existing programs require significant funding increases to accelerate current programs or expand to address additional species. Sniezko and Nelson stress further that a resistance breeding program has different objectives, magnitude and focus than most research projects. It is applied science, that is, an action-oriented effort that is solution-minded—countering the impact of a major disturbance caused by a pest (in our case, a non-native pest).

Schlarbaum provides a shorter but similar list of facilities needed:

  1. production of propagules (seed or clones);
  2. mass propagation in growing facilities, e.g., bare-root seedling nursery or greenhouses;
  3. site preparation of former habitat and planting; and
  4. post-planting maintenance.

Schlarbaum emphasized that each of these activities requires different skill sets, equipment, facilities, and infrastructure.

Genetic Engineering as a Specific Tool

There is considerable interest in the potential role of genetic engineering in pest resistance breeding. None of the successful programs world-wide has yet used genetic engineering (Sniezko and Koch 2017). While incorporating it into holistic breeding programs might result in greater efficiency for certain processes, it raises legal and social acceptability issues. Jacobs et al. discuss the type of education and outreach program needed to generate widespread public support this approach to tree species “rescues.” They call for USDA Forest Service to lead this education effort.

The focus of the 2021 workshop hosted by Purdue University was to explore the pros and cons of using biotechnology in restoring pest-threatened forest tree species. The special issue of New Forests contains several participants’ analyses.  

The overall conclusions are that:

  • “Genetic engineering” – defined as “any technique that uses recombinant, synthesized, or amplified nucleic acids to modify a genome” – is only one type of biotechnology applicable to tree breeding. Other biotechnologies include tissue culture-based propagation, molecular-based genetic markers, gene cloning and sequencing, and genome mapping and sequencing.
  • These new technologies can increase the efficiency of more traditional breeding techniques, However, biotechnologies cannot substitute for holistic programs that incorporate all helpful methods. Careful consideration goes into selecting which techniques are appropriate for a particular host-pest system.
  • Each tree species has unique needs regarding seed or scion collection; seedling propagation in nurseries; site preparation and planting techniques; and management of regeneration after its re-introduction into forests. Scientists don’t yet understand these various needs of many threatened species.
  • In the eastern U.S., the tree-breeding infrastructure is based in the Southeast and focused on a few pine species grown commercially. The facilities do not match the greatest need. That is, many of the at-risk species are hardwoods native to the Northeast.
  • Current resources are inadequate to support the sustained, long-term commitment of resources and facilities necessary to be successful.

Dana Nelson addressed the role of genetic engineering (GE) in detail. He emphasized repeatedly that GE is not a short-cut to tree improvement. Incorporating a GE component does not avoid the other steps. It can, though, provide new possibilities to address problems. Nelson says the crucial, initial question is – can GE solve the specific forest conservation or management problem more effectively and efficiently than existing methods? There are some important subtleties to consider. First, success does not require achieving immunity (100% resistance); the level of resistance needs to be only sufficient to allow the tree species to survive, reproduce and co-evolve with the pest. Second, “efficiency” is an important consideration. We cannot afford delay because during those years or decades the wild tree loses genetic variability as more trees die. Also, changes in the environment continues to change, and the decimated tree species is not adapting.

If genetic engineering promises to contribute meaningfully, then the breeders must answer several follow-up questions before proceeding to develop a specific plan. Nelson also stresses that the planned activities must be integrated with an ongoing tree breeding program to ensure project success.

Nelson provides a lengthy description of the process of integrating genetic engineering into tree breeding programs.

GE in Chestnut Breeding – Setback

The most prominent breeding effort incorporating genetic engineering in the U.S. has been The American Chestnut Foundation’s (TACF) program to restore American chestnut (Castanea dentata). For decades, TACF has pursued development of trees resistant to the fungus which causes chestnut blight (Cryphonectria parasitica). Over the past decade, hopes have centered on a genetically engineered line into which was inserted a gene from wheat (oxalate oxidase; OxO). The OxO gene detoxifies the oxalic acid produced by the chestnut blight fungus and thus prevents the cankers from killing the tree.

Years of tests have shown the gene to be effective and to cause no environmental harm. In 2023, when trees in outside test plots grew larger, scientists observed disappointing results. Trees’ blight tolerance varied greatly. Worse, resistant trees grew more slowly and exhibited lower overall fitness. [For a full discussion of the issues, visit TACF’s website] Prompted by these disappointments, scientists carried out further molecular analyses. They found that the OxO gene was on a different chromosome than expected.

TACF researchers now suspect that the trees’ variable performance stems primarily from the placement of the OxO gene and the fact that the gene is always “switched on”. That constant expression appears to result in high metabolic costs for the trees. Since all the genetic lines developed to date have this defect, TACF is no longer pursuing research efforts with any of the GE trees developed to date. The Foundation believes it would be irresponsible to continue efforts – by itself and by partners – focused on a genetic line that looks unable to compete successfully when introduced to the forest.

Instead, TACF has begun investigating other transgenic lines that use a “wound inducible” promoter that switches on the OxO gene only in cells where the plant is wounded. Researchers at both the State University of New York College of Environmental Science and Forestry (SUNY-ESF) and the University of Georgia are working with a variety of inducible promoters. TACF is also testing whether inducible OxO expression can be “stacked”onto genes for blight resistance present in the backcross hybrids. Finally, TACF and Virginia Tech are also exploring whether resistance can be enhanced by insertion of genes from Chinese chestnut directly into American chestnut using methods similar to OxO insertion.

 It will be years before we know if these approaches provide sufficient levels of resistance. TACF will undertake more extensive testing for efficacy through the tree’s full life cycle – in the lab, greenhouse, and field – before submitting a new GE organism to regulators for review. Meanwhile, it will continue rigorous testing for plant health and environmental risks and will strengthen the cooperative structure to facilitate sharing of intellectual property and provide full transparency.

The Darling GE line was the most important transgenic hybrid chestnut line TACF had invested in. So this is a major setback – and comes when regulatory approval seemed near.

Let’s keep this in perspective, however. As a colleague has said, based on his years of teaching science to middle school students, “There are no failures in science, just reductions in the unknown; Edison failed a thousand times before getting the light bulb right, etc….”  The technology is ready when it is ready. In addition, he praised TACF for choosing to explain its decision frankly: “nothing builds credibility like early failures openly admitted.”   

Meanwhile, TACF continues to make gains in blight resistance with its traditional American chestnut backcross hybrid breeding program. They have established a genetically diverse, reproducing population of thousands of trees representing hundreds of breeding lines. These trees are planted in TACF’s expansive network of germplasm conservation orchards and regional breeding and backcross orchards. They have substantially increased resistance to both the blight and Phytophthora cinnanomi in these populations. The future inclusion of transgenic and/or gene-edited trees will further increase those gains.

Another Approach

Meantime, the American Chestnut Cooperators Foundation (ACCF), which breeds from persistent pure American chestnut, now has some trees that are nearly 50 years old. The program has bred five generations of pure American chestnuts that show durable blight resistance. Many trees are 60 feet tall or higher; they produce nuts. Vice President Jenny Abla (pers. comm.) reports that they show excellent canker response (swollen and superficial). The picture shows one of their most notable stands, which is in the Jefferson National Forest. Dr. Sniezko is exploring whether this program shows sufficient promise to justify increased support from the USFS.

ACCF chestnut trees; photo courtesy of Jenna Abla

Improving Coordination – will funds follow?

In July 2023, representatives from essentially all the forest tree resistance breeding programs in the U.S. met at Dorena Genetic Resource Center in Oregon to discuss their current successes and how to fast-track all programs. This is the first such meeting since 1982 (Richard Sniezko, pers. comm.). I encourage us all to study the report when it emerges and encourage USFS leadership to support the more unified enterprise.

Status of Efforts to Conserve Other Tree Species

The special issue of New Forests (Vol. 54 Issue 4) included several articles exploring the specifics of breeding elms, ashes, and ʻōhiʻa. These describe difficult challenges … and scientists determined to make progress on overcoming them.

“survival” American elm at Longwood Gardens; photo by F.T. Campbell

Elms (Ulmus spp.) (see article by Martin et al.)

Let’s not forget that elms were keystone species in Europe and North America until attacked by two epidemics of “Dutch” elm disease during the 20th Century. While hybrid elms are available for urban plantings, many consider them not appropriate for planting in natural forests because these genotypes are not native.

Martin et al. describe a bewildering conglomeration of complexities and possibilities arising from biotic and abiotic factors. Initiation and especially intensity of the disease in a particular tree depend on

  • the species or strain of the tree, vectoring beetle, and pathogen;
  • timing of the attack; and
  • adequacy of water supplies at that time.

Possible targets for manipulation include the pathogen, its beetle vector, and the tree’s response — either in its bark or xylem. Martin et al. suggest that a combination of resistance to the pathogen within the xylem, resistance to beetles’ feeding wounds, and lowering tree clues that attract the beetles could considerably enhance longer-term overall resistance in the field.

However, verifying which approaches produce the best result will be complicated by the trees’ sensitivity to environmental factors such as season and water supply. Apparent resistance might actually be tied to, for example, low water supplies during the spring when the attack occurred.

Restoration strategies, including resistance to pests, must accommodate the diverse ecological conditions in the species’ large range, the rapid evolution of the Ophiostoma pathogens; and other pests and pathogens that attack elms. Nor do scientists know appropriate planting strategies.

Martin et al. believe Dutch elm disease is unlikely to be spread by movement of living elm plants, although other pests could be (and have been).

ash trees to be tested for resistance to emerald ash borer; photo courtesy of Jennifer Koch, USFS

Ashes (Fraxinus spp.)

While a USFS team led by Jennifer Koch link are conducting much of the on-the-ground efforts to breed ash trees resistant to the emerald ash borer (EAB; Agrilus plannipennis), Stanley et al. note that scientists cannot simply cross most North American ash species with the Asian ash, F. mandshurica, because the two groups are sexually incompatible. Scientists have instead focused on trying to enhance the resistance to EAB that is apparently present in a small proportion of ash trees, called “lingering ash.” Scientists funded by USDA Forest Service have already devoted over 14 years to finding such lingering ash to be tested for resistance.

Testing these trees is not simple (see Stanley et al.). But scientists are overcoming some of the obstacles.  They have shown that the capability of a few green ash (Fraxinus pennsylvanica) (less than 1%) to defend themselves from EAB attack is genetic. Genes determine the relative abundance of specific metabolites manufactured by the tree; high levels kill more beetle larvae. These trees’ tolerance is not immunity but it might be sufficient to allow the tree to survive and grow. The level of metabolites synthesized by succeeding generations of the tree can probably also be enhanced by breeding.

To restore ash it is necessary to propagate large numbers of clones and to root the resulting embryos. This has been challenging. Merkle et al. describe five years of efforts to develop techniques that allow in vitro propagation to speed up selection and breeding. These techniques will facilitate establishment of numerous groups of propagules with the genetic differences needed to accommodate the large geographic range of several ash trees. For example, the green ash range covers more than half the continental U.S. plus multiple Canadian provinces.

ʻōhiʻa on lava field, Hawaii Volcanoes National Park

‘Ōhi‘a (Metrosideros polymorpha)

‘Ohi‘a is the most widespread tree species on the Hawaiian Islands. It provides vitally important habitat for conservation of countless taxa of endemic birds, insects, and plants. It is also of great cultural importance for Native Hawaiians.

Luiz et al. review the tree species’ importance, the many threats to native Hawaiian forests, and a coalition’s efforts to counter the most recent – and alarming – threat, rapid ʻōhiʻa death (ROD).

Rapid ʻōhiʻa death is caused by two introduced species of in the genus Ceratocystis. C. lukuohia colonizes the tree’s sapwood and kills the tree quickly. This disease is present on two islands, Hawai`i and Kaua‘i. It has the potential to devastate ‘ohi‘a forests across the state. The other pathogen, C. huliohia, invades the phloem, cambium, and outer xylem, resulting in a well-defined area of necrotic tissue and slower mortality. This disease is on Hawai`i and Kaua‘i, plus Maui and O‘ahu. The two pathogens have different origins. C. lukuohia belongs to a genetic line that is based in Latin America, C. huliohia to a genetic line based in Asia and Australia.

Conservationists formed a coalition and developed a strategy to guide the process of identifying and developing disease resistance in M. polymorpha and, if possible, other Metrosideros species on the Islands. Luiz et al. describe the coalition’s many activities. The challenges are familiar ones:

  • obtaining sufficient facilities to screen large numbers of seedlings;
  • developing techniques for inoculation, propagation, and speeding up growth of seedlings;
  • improving techniques for detecting individual infected and healthy trees across difficult terrain;
  • testing trees native to all parts of the tree’s range, which is not large in area, but covers a great variety of elevations and climates); and
  • needing to develop trees resistant to both C. lukuohia and C. huliohia.

Luiz et al. reiterate the necessity to manage all threats to healthy ʻōhiʻa stands, for example, by  

  • curtailing human spead of infected wood, using both quarantines and supportive public education;
  • testing repellants to reduce beetle attack.
  • reducing injuries to trees by fencing forests and removing feral ungulates. link to website?

SOURCES

Buggs, R.J.A. 2020. Changing perceptions of tree resistance research. Plants, People, Planet. 2020;2:2–4. https://doi.org/10.1002/ppp3.10089

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

Dudley, N.; Jones, T.; Gerber, K.; Ross-Davis, A.L.; Sniezko, R.A.; Cannon, P.; Dobbs, J. 2020. Establishment of a Genetically Diverse, Disease-Resistant Acacia koa A. Gray Seed Orchard in Kokee, Kauai: Early Growth, Form, and Survival. Forests 2020, 11, 1276 https://doi.org/10.3390/f11121276

Jacobs, D.F., R. Kasten Dumroese, A.N. Brennan, F.T. Campbell, A.O. Conrad, J.A. Delborne, et al. 2023. Reintroduction of at-risk forest tree species using biotech depends on regulatory policy, informed

by science and with public support. New Forests (2023) 54:587–604

https://doi.org/10.1007/s11056-023-09980-y

Luiz, B.C., C.P. Giardina, L.M. Keith, D.F. Jacobs, R.A. Sniezko, M.A. Hughes, J.B. Friday, P. Cannon, R. Hauff, K. Francisco, M.M. Chau, N. Dudley, A. Yeh, G. Asner, R.E. Martin, R. Perroy, B.J. Tucker, A. Evangelista, V. Fernandez, C. Martins-Keli.iho.omalu, K. Santos, R. Ohara. 2023. A framework for establishing a rapid ‘Ohi‘a death resistance program. New Forests https://doi.org/10.1007/s11056-021-09896-5

Martín, J.A., J. Domínguez, A. Solla, C.M. Brasier, J.F. Webber, A. Santini, C. Martínez-Arias, L. Bernier, L. Gil1. 2023. Complexities underlying the breeding and deployment of Dutch elm disease resistant elms. New Forests https://doi.org/10.1007/s11056-021-09865-y  

Merkle, S.A., J.L. Koch, A.R. Tull, J.E. Dassow, D.W. Carey, B.F. Barnes, M.W.M. Richins, P.M. Montello, K.R. Eidle, L.T. House, D.A. Herms and K.J.K. Gandhi. 2023. Application of somatic embryogenesis for development of emerald ash borer-resistant white ash and green ash varietals. New Forests  https://doi.org/10.1007/s11056-022-09903-2

Nelson, C.D. 2023. Tree breeding, a necessary complement to genetic engineering. New Forests

https://doi.org/10.1007/s11056-022-09931-z

Pike, C.C., J. Koch, C.D. Nelson. 2021. Breeding for Resistance to Tree Pests: Successes, Challenges, and a Guide to the Future. Journal of Forestry, Volume 119, Issue 1, January 2021, Pages 96–105, https://doi.org/10.1093/jofore/fvaa049

Sniezko, R.A., J. Koch, J-J. Liu and J. Romero-Severson. 2023. Will Genomic Info Facilitate Forest Tree Breeding for Disease and Pest Resistance? Forests 2023, 14, 2382.

https://doi.org/10.3390/f14122382

Sniezko, R.A. and C.D. Nelson. 2022. Chapter 10, Resistance breeding against tree pathogens. In Asiegbu and Kovalchuk, editors. Forest Microbiology Volume 2: Forest Tree Health; 1st Edition. Elsevier

Stanley, R.K., Carey, D.W., Mason, M.E., Doran, A., Wolf, J., Otoo, K.O., Poland, T.M., Koch, J.L., Jones, A.D. and Romero-Severson, J. 2023. Emerald ash borer (Agrilus planipennis) infestation bioassays and metabolic profiles of green ash (Fraxinus pennsylvanica) provide evidence for an induced host defensive response to larval infestation. Front. For. Glob. Change 6:1166421. doi: 10.3389/ffgc.2023.1166421

Posted by Faith Campbell

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

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

or

www.fadingforests.org

SOD – 3 strains spreading in the West …

locations of P. ramorum in forests of Oregon in 2023

In a recent blog I offered several critiques of APHIS’ new Phytophthora ramorum risk assessment regarding possible establishment of the causal agent of sudden oak death, in the eastern U.S. states. One of my objections was the brevity of its discussion of the likelihood of sexual combination of the recently introduced EU1 strain with the strain established in North America, NA1 and – more recently – NA2.

This blog provides updates on the status of the Phytophthora ramorum invasion in California and Oregon. My information comes primarily from the newsletter posted by the California Oak Mortality Task Force (COMTF),  supplemented by presentations at the recent on-line meeting.  

Research by several scientists, including Tyler Bourret, now with USDA Agricultural Research Service, [summarized in the November 2023 COMTF annual meeting] reported that 216 species are now recognized in the genus Phytophthora.

Establishment of Additional Strains of the Pathogen

Scientists now recognize 12 strains of P. ramorum (Sondreli et al., summarized in COMTF newsletter for August 2023). Three of these strains are established in western North American forests. All three – NA1, NA2, & EU1 – are established in southern Curry County, Oregon. Two of the three – EU1 & NA1– are established in neighboring Del Norte County, California. The genetic lineage of the EU1 population in Del Norte points to a link to the Oregon outbreak.  [Robinson/Valachovic presentation to COMTF annual meeting November 2023] Given the poor record of efforts to prevent additional introductions of P. ramorum to the United States (the APHIS risk assessment notes that the pathogen has been introduced eight to14 times – or more! — in California), continued introductions of strains not yet established in the U.S. appear likely. Once a strain is established in a North American nursery, it is very likely to spread to nurseries – and possibly forests – in other parts of the country. Remember, the risk assessment reported that P. ramorum has probably been moved over a thousand times on nursery stock from West Coast nurseries across the U.S.

P. ramorum-infected Rhododendron; photo by Jennifer Parke, Oregon State University

Why this matters

Phytophthora ramorum can reproduce sexually only when gametes of the two different mating types (A1 & A2) combine. Most of the North American populations are A2 mating type and most European populations are A1. Establishment of the European EU1 in Oregon and California increases the likelihood that sexual reproduction will occur, which in turn increases the probability that the pathogen will evolve. Sexual combination between NA2 (mating type A2) & EU1 (mating type A1) has occurred at least once – in a nursery in British Columbia. Authorities believe this hybrid has been eradicated. However, the possibility of such matings remains.

The most widespread strain in North America is NA1. It was first detected in the forests north of San Francisco in the middle 1990s; and in Oregon in 2001. Infestations of NA1 are now found from central Curry County, Oregon to Monterey County, California.

The EU1 lineage was first detected in Oregon in 2015. How did it get there since it was previously known only in Europe? The outbreak in Del Norte County, California – detected in 2020 – apparently is associated with the Oregon infection. [Robinson/Valachovic presentation to COMTF annual meeting November 2023] Both states attempted eradication, but the strain is well established. By 2023, the Oregon infestation was detected spreading at sites where intensive surveys in previous years detected no symptomatic trees. In California, new centers of infection have been detected along additional tributary creeks in the area. Scientists expect these infections to spread downhill. Control efforts and even surveys have been hampered by a large fire in the area, which diverted needed personnel and funding. [COMTF newsletter for October 2023 & Robinson/Valachovic]

The NA2 lineage has been found in some nurseries in the Pacific Northwest since 2005. The first detection in forests occurred near Port Orford, Oregon in 2021. Port Orford is 30 miles north of Gold Beach – the hitherto northern extent of the SOD infestation. Oregon authorities believed this signaled a new introduction to the state. By 2023, three sites in the state are now infested with this strain. [Ritokova presentation to COMTF annual meeting November 2023] Oregon now focuses its control efforts on NA2 outbreaks near Port Orford.

In California’s Del Norte County, there are now infestations of two strains of opposite mating types ~ 6 miles apart.The forests between them are conducive to infection, so interactions are likely. Robinson & Valahovic [COMTF annual meeting November 2023] ask how land managers should deal with any interactions. I ask – given the likelihood of hybrids forming – shouldn’t the APHIS risk assessment have tried harder to analyze this risk to the East?

Meanwhile, the NA1 strain continues to spread

In Oregon, the NA1 strain has spread 18 miles to the north and eight miles to the east since 2001 [Ritakova COMTF newsletter October 2023]. In California, spread after the wet winter of 2022-2023 has so far been less than expected. The SOD Blitz [Garbelotto at COMTF annual meeting November 2023] found that the statewide rate of positive trees rose from 7.1% in 2022 to 8.8% in 2023. In the Big Sur region some canyons now test negative that once were positive. Scientists think the negative tests reflect the multi-year drought. Scientists expect the spread will be more visible next year – especially if there is a second wet winter.

As noted above, the exception is in Del Norte County – an area described by CAL FIRE forester Chris Lee as a very wet “pathology” site. SOD (NA1 strain) was first detected in the area north of Crescent City in 2019 [Robinson and Valachovic]. This outbreak could not be re-confirmed for three years, despite intensive surveys. But, in 2022, scientists detected a new concentration of dying tanoak. The infected area is near both rare plants associated with serpentine soils and Jedediah Smith State Park, a unit of Redwood National Park. [Robinson] Meanwhile, the infestation of EU1 strain was first detected in 2020; it has expanded in 2022 and 2023.

In addition to spread facilitated by weather, we also see a continuing role in pathogen transfer via movement of shrubs intended for planting. In fall 2022 Oregon authorities were alerted by a homeowner to an outbreak in Lincoln City, Oregon. This was alarming for four reasons:

  • it was 201 miles north of the generally infested area in southern in Curry County.
  • it was well established and had apparently been present for many years.
  • P. ramorum was not detected in any associated waterways, raising questions about the efficacy of this standard detection method for use in community detections.
  • one of the infected plants was a new host: western sword fern (Polystichum munitum).

Fortunately, the infection has not (yet) been detected in nearby natural forests. Perhaps this is because there are no tanoaks this far north.

Detection Difficulties

Forest pathologists report several examples of outbreaks involving dozens of trees or plants suddenly being detected in areas which had been surveyed intensively in preceding years with no detections. See Robinson/Valachovic presentation [COMTF annual meeting November 2023, re: both EU1 & NA1 strains in Del Norte County]. I noted above that streams near the Lincoln City, Oregon neighborhood outbreak did not test positive. Nor did water associated with a positive nursery in Oregon[description of Oregon Department of Agriculture nursery regulatory program in COMTF newsletter for August 2023]. Stream baiting is an important component of detection surveys, so I worry about the possible implications of these negative results.

Identification of Additional Hosts  [all from COMTF newsletter for August 2023.]

  • silverleaf cotoneaster Cotoneaster pannosus (an invasive non-native plant species) 
  • “Mountain Moon” dogwood Cornus capitata [host previously identified in the United Kingdom]
  • western swordfern (Polystichum munitum) (discussed above)
Oregon P. ramorum eradication attempt; photo by Oregon Department of Forestry

Management

Oregon has tried to manage SOD in the forest since its first detection, but the pathogen’s spread and the recent appearance of two additional strains have overwhelmed the program. One hope was to find a less expensive eradication or containment method. For 20 years, attempts to suppress the disease has focused on eradicating local populations of tanoaks (Notholithocarpus densiflorus) because they are the principal host supporting sporulation in Oregon. When an outbreak has been detected and delimited, they first kill the tanoaks with herbicides to prevent resprouting from the roots. The trees are then felled, piled, and burned. This treatment costs $3,000 – $5,000 / acre. Scientists tested whether they could greatly reduce the cost of the suppression programs by leaving tree boles standing after they have been killed by herbicide. Unfortunately, leaving dead, herbicide-killed trees standing increased sporulation, so this approach would probably exacerbate pathogen spread. [See Jared LeBoldus presentation to COMTF annual meeting November 2023]

Worrying Developments in Europe

In Ireland, sudden larch death – caused by the EU1 strain on Japanese larch (Larix kaempferi) – has spread to several counties. This strain is also causing disease on European beech (Fagus sylvatica) & Noble fir(Abies procera) in locations where these tree grow in association with nearby heavily infected Japanese larch. The EU2 lineage was found in late 2021, infecting L. kaempferi at one site.

Several other Phytophthora species are causing disease on trees, including P. lateralis on Lawson’s cypress, Port-Orford cedar (Chamaecyparis lawsoniana); P. pseudosyringae on Japanese larch; and P. austrocedri on trees in the Juniperus and Cupressus genera.

[information about Ireland from R. O’Hanlon, summarized in COMTF newsletter for August 2023]

Regulation

The European Union has relaxed phytosanitary regulation of Phytophthora ramorum. Previously the species – all strains – was considered a quarantine pest. Now its regulatory status depends on the origin of the infected material. “Non-EU isolates” of Phytopththora ramorum are still quarantine pests (presumably the two North American strains [NA1 & NA2] and the eight other strains identified in Asian forests). These pests are treated as the most serious pests in the Union; when they are detected, extensive control actions must be taken. “EU isolates” (presumably EU1 & EU2) are now treated as regulated non-quarantine pests. The focus is to limit the spread of these on plants for planting only.

The European Union and USDA APHIS regulatory emphases differ to some extent (APHIS does not regulate P. ramorum in natural settings, only interstate movement via, inter alia, the nursery trade). However, I am worried that both seem intent on minimizing their regulatory programs.

Arbutus canariensis; photo by Moreno José Antonio via Plantnet

Another region at risk

Macaronesia is a group of several North Atlantic islands,e.g., Madeira and the Azores, Canary, and Cape Verde islands. The islands have climates similar to areas affected by P. ramorum. The Macaronesian laurel forest is a remnant subtropical evergreen forest which shares some plant taxa with those that host the pathogen elsewhere. Moralejo et al. found that, overall, plant species showed considerable tolerance of the pathogen. However, P. ramorum was “rather aggressive” on Viburnum tinus, Arbutus canariensis and Ilex canariensis. Furthermore, mean sporangia production on five Macaronesian laurel forest species was similar to levels on Umbellularia californica, a key host driving the SOD epidemics in California.Moralejo et al. concluded that there is a moderate to high risk of establishment if Phytophthora ramorum were introduced in the Macaronesian laurel forest. [Study summarized in October 2023 COMTF newsletter.]

Important Research

The COMTF August newsletter reports exciting work developing improved detection tools for Phytophthora species, especially P. ramorum. Sondreli, Tabima, & LeBoldus have developed a method to quickly distinguish among the four most common clonal lineages (NA1, NA2, EU1 and EU2). These assays are sensitive to weak concentrations and effective in testing a variety of sample types including plant tissue and cultures. Oregon State University is already using in its diagnostic laboratory.

YuFang, Xia, Dai, Liu, Shamoun, and Wu have developed a simple, rapid, sensitive detection system for the molecular identification of P. ramorum that does not require technical expertise or expensive ancillary equipment. It can be used in laboratory or using samples collected from the field.

Quiroga et al. found that thinning – with or without burning of the slash – significantly reduced stand density and increased average tree size without significantly decreasing total basal area. This effect persisted for five years after treatments – especially when supported by follow-up basal sprout removal. Preventative treatments also significantly increased dominance of tree species not susceptible to Phytophthora ramorum.

In a study summarized in the October 2023 COMTF newsletter, Bourret et al. reported results of nearly 20 years of leaf baiting in watersheds covering an 800-mile section of the Pacific Coast in northern and central California. They found 22 Phytophthora & Nothophytophthora species. Several – including P. ramorum — were abundant and widespread. Some isolates in northern California differ from those found elsewhere. Mitochondrial sequences revealed multiple hybridization events between P. lacustris and P. riparia.

Bourret et al. also found that P. pluvialis is probably native to Western North America. The strain invasive on conifers in New Zealand probably originated in California rather than Oregon or Washington.

Jared LeBoldus and colleagues are studying the ecological impact of tanoak mortality in Oregon forests. [Summarized in November 2023 COMTF newsletter.] They expect impacts at various trophic levels and functions. Preliminary findings regarding the plant community show increases in understory and herbacious species diversity; a shift away from tanoak to Douglas-fir; and increased coarse woody debris. These findings are similar to results from studies in central California by Dave Rizzo and colleagues at UC Davis. LeBoldus is now studying the microbiome of plant leaves; soil mycorrhizal diversity; invertebrates and pollinators (loss of the large annual flower crop of tanoaks presumably affects pollinators). They hope in the future to study small mammal communities (which they expect to be affected by the loss of acorns).

Jared LeBoldus and colleagues also reported early results of genomic studies exploring disease resistance in tanoaks. Various scientists started such studies in the past, but so far all efforts have petered out due to absence of sustained funding, support from agency management, and links to facilities with the necessary tree improvement/breeding resources. (See Richard Sneizko’s description of requirements for resistance breeding, here.) I hope this project proves more sustainable.

Posted by Faith Campbell

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

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

or

www.fadingforests.org

USFS Forest Health Protection program: what it funds

affects of mountan pine beetle on lodgepole pine in Rocky Mountain National Park, Colorado photo from Wikimedia; one of pests addressed by USFS FHP

Several USFS scientists have published an assessment of the agency’s program to enhance forest health across the country: the Forest Health (FHP) program. [see Coleman et al., full citation at end of this blog.] The program assists cooperators (including other federal agencies) to prevent, suppress, and eradicate insect and pathogen outbreaks affecting trees, regardless of land ownership.

Each year, I advocate for adequate funding for the FHP program — which comes from annual Congressional appropriations. Funding has remained static at about $100 million per year. I interpret the article as providing support for my call for increased appropriations. First, it reports that the number of projects and extent of area treated have declined from 2011 to 2020. This is because static funding levels are stretched increasingly thin as costs to implement the same activities rise. Second, the program does not address many damaging forest pests already in the country. The result is growth of established threats to forest health. Finally, new insects and pathogens continue to be introduced. Protecting forest health necessitates tackling these new pests – and that requires money and staff.   

Coleman et al. analyzed data from the decade 2011- 2020 to determine the most frequently used project types, integrated pest management (IPM) strategies and tactics, dominant forest pests and associated hosts managed, and most comprehensive forest IPM programs in practice. While there is a wide range of possible projects, most of those funded consist of some form of treatment (more below). The databases relied on do not include funding through the National Forest System aimed at improving forest health through such  management activities as stand thinning treatments and prescribed fire. Nor are all pest management activities recorded in the centralized databases. I regret especially the fact that “genetic control” (= resistance breeding) are left out.

Port-Orford cedar seedlings in trial for resistance to Phytophthora lateralis at Dorena center; photo courtesy of Richard Sniezko, USFS

Summary of Findings

The data are sorted in various categories, depending on whether one wishes to focus on the type of organism being managed or the management approach. All presentations make evident a dramatic imbalance in the projects funded. Again and again, spongy moth (Lymantria dispar dispar), southern pine beetle (SPB, Dendroctonus frontalis), and several bark beetles attacking conifers in the West (in particular mountain pine beetle, [MPB] Dendroctonus ponderosae) dominate, as measured by both funding and area treated.

oak trees in Shenandoah National Park killed by spongy moth; photo by F.T. Campbell
  • The bulk of the funding went to the above species, plus hemlock woolly adelgid (HWA; Adelges tsugae); emerald ash borer (EAB, Agrilus planipennis), oak wilt (caused by Bretziella fagacearum), and white pine blister rust (WPBR, Cronartium ribicola).
  • 95% of the projects focused on only four taxa: oaks, Quercus spp. [spongy moth suppression and eradication]; loblolly and ponderosa pines [bark beetle prevention and suppression]; and eastern hemlock [HWA suppression].
  • Projects seeking to suppress an existing pest outbreak covered 87% of the total treatment area. However, 98% of the treated area was linked to only 20 taxa; again, spongy moth dominated.
  • Projects seeking to prevent introduction or spread of a pest constituted only 30% of all projects and covered only 11% of the total treatment area.
  • Eradication and restoration projects each equaled less than 5% of total projects and treatment areas.
  • Native forest pests were targetted by 79% of projects; non-native pests by 21%. However, non-native pests accounted for 84% of the total treatment area (again, the spongy moth).
  • While 67% of projects took place on USFS lands (focused on MPB and SPB), 89% of the total treatment area was on lands managed by others (state or other federal agencies, or private landowners). Again, the size of the non-USFS  area treated was driven primarily by the spongy moth Slow the Spread program.
  • Insect pests received nearly all of the funding: 70% of funding targetted phloem-feeding insects, especially SPB and MPB; 10% targetted foliage feeders, especially spongy moth; 6% targetted sap feeders. 4% tackled rusts (e.g., WPBR); just 2% addressed wood borers (e.g., Asian longhorned beetle, emerald ash borer).
  • The ranking by size of area treated differs. In this case, 82% of areas treated face damage by foliage feeders (e.g., spongy moth); 15% of the treated areas are threatened by phloem feeders (e.g., MPB); only 1.4% of the area is damaged by sap feeders (e.g., HWA); 0.6% is threatened by rust; and 0.2% by wood borers.
  • Re: control strategies, 32% of projects relied on silvicultural strategies; 22% used semiochemical strategies; 21% exploited other chemical controls; and 18% used physical/mechanical control methods.

Coleman et al. regretted that few programs incorporated microbial/biopesticide control strategies; these were applied on only 10% of total treated area. Again, the vast majority of such projects were aerial applications of spongy moth controls, Bacillus thuringiensis var. kurstaki (Btk) and nucleopolyhedrosis viruses (NPV) (Gypchek). Coleman et al. called for more research to support this approach efforts to overcome other obstacles (see below).

Coleman et al. also called for better record-keeping to enable analysis of genetic control/ resistance breeding projects, treatment efficacy, and survey and technical assistance activities.

History

The article provides a brief summary of the history of the Forest Service’ pest management efforts. Before the 1960s, the USFS relied on labor-intensive physical control tactics, classical biocontrol, and widespread chemical applications. Examples include application of pesticides to suppress or eradicate spongy moth; decades of Ribes removal to curtail spread of white pine blister rust; salvage logging and chemical controls to counter phloem feeders / bark beetles in the South and West. These strategies were increasingly replaced by pest-specific management tactics during the 1970s.

Over the decade studied (2011-2020), tree defoliation attributed to various pests (including pathogens) affected an estimated 0.7% of the 333 million ha of U.S. forest land annually. Mortality attributed to pests impacted an estimated 0.8% of that forest annually. See Table 1. Two-thirds of the area affected by tree mortality is attributed to phloem feeders; a distant second agent is wood borers. These data are incomplete because many insects, diseases, and parasitic higher plants are not tracked by aerial surveys.

As I noted above, these data do not include projects that screen tree species to identify and evaluate genetic resistance to a pest; or efforts to collect cones, seed, and scion. I consider these gene conservation and resistance programs to be some of the most important pest-response efforts. I have blogged about the USFS’ Dorena Genetic Resource Center’ efforts to breed five-needle pines, Port-Orford cedar, and ash. link

41% of silvicultural control treatments targetted phloem feeders; 48% addressed cankers and rusts together. Restoration planting was done in response to invasions by ALB, EAB, and WPBR, as well as native bark beetles and mistletoes.

effort to eradicate SOD in southern Oregon; partially funded by USFS FHP. Photo courtesy of Oregon Department of Forestry

Physical/mechanical control projects were most widely applied in the Rocky Mountains in response particularly to diseases: vascular wilts, rusts, and cankers, including WPBR. This type of project was also used to deal with non-native diseases in other parts of the country, e.g., oak wilt, sudden oak death (SOD), Port-Orford cedar root rot, and rapid ʻōhiʻa death. Sanitation treatments (i.e., removal of infected/infested trees) was used for native mistletoes and root rots, and some non-native insects, e.g., EAB and coconut rhinoceros beetle (Oryctes rhinoceros). Pruning is a control strategy for WPBR. Trenching is applied solely to suppress oak wilt.

Chemical controls were limited to small areas. These projects targetted seed/cone/flower fruit feeders, foliage and shoot diseases, sap feeders [e.g., balsam woolly adelgid (BWA), HWA], wood borers (e.g., EAB) and phloem feeders (e.g., Dutch elm disease; DMF oak wilt vectors). Cover sprays have been used against goldspotted oak borer (GSOB); and many native insects. Fungicides are rarely used; some is applied against the oak wilt pathogen in areas inaccessible by heavy equipment.

treating hemlock trees in Conestee Falls, NC; photo courtesy of North Carolina Hemlock Restoration Initiative

Classical biocontrol projects funded by the program targetted almost exclusively HWA. Some 4.3 million predators have been released since the early 1990s; 820,057 in just the past 10 years.

Gene conservation and breeding projects were directed primary at commercially important hosts, e.g., loblolly Pinus taeda and slash pine P. elliottii; and several non-native pests, including chestnut blight, EAB, HWA, and WPBR.

Survey and technical assistance (i.e., indirectly funded activities) conducted by federal, state, and tribal personnel contributed to education/outreach, evaluating effectiveness, identification, monitoring, and record keeping strategies.

As should be evident from the data presented here, suppression treatments dominated by number of projects and treatment area. The poster child project is the national spongy moth Slow the Spread program. The authors say this program is the most advanced forest IPM program in the world. It has successfully slowed spongy moth’s rate of spread by more than 80% for more than 20 years.

A second widely-used subset of suppression programs consists of physical / mechanical control. This is often the principal suppression strategy in high-visitation sites (e.g., administration sites, campgrounds, picnic areas, and recreation areas). Sanitation harvests are one of the few viable management techniques for suppressing or slowing the spread of recently introduced non-native pests. Nevertheless, the largest number of suppression projects and use of sanitation treatments focused on a native pest, mountain pine beetle, at the height of its outbreak in early 2010s.

Silvicultural control, specifically tree thinning, represents the predominant forest pest prevention tactic, especially on lands managed by the USFS. Two programs dominate: the Southern Pine Beetle Prevention Program and the Western Bark Beetle Initiative. Again, Coleman et al. assess these treatments as very successful. Forest thinning treatments also address other management concerns, i.e., reduce threat of catastrophic wildfires and reduce adverse effects of climate change.

Chemical control tactics are applied to suppress most forest insect feeding guilds in high-value sites and seed orchards. Soil or tree injections of systemic pesticides are used to protect ash and hemlock trees. Topical sprays have been applied to protect whitebark pine (Pinus albicaulis) from mountain pine beetle. Whitebark pine was listed as threatened under the Endangered Species Act in December 2022.

dead whitebark pine at Crater Lake NP; photo by F.T. Campbell

Soil or tree injections target two non-native insects, EAB and HWA.

Genetic control via resistance breeding represents the primary strategy to combat several non-native diseases. (More options are typically available for insects than diseases.) Coleman et al. focus on the extensive effort to protect many of the five-needle pines from WPBR. As I have described in earlier blogs, the Dorena Genetic Resource Center in Oregon has engaged on numerous other species, too.

Coleman et al. describe pest-management associated monitoring efforts as consisting largely of coordinated annual aerial detection surveys, detection trapping, stream-baiting of Phytophthora ramorum, and ground surveys to address site-specific issues.

Coleman et al. call for improvement of record-keeping / databases to encompass all pests, management actions, and ownerships. They also advocate for additional decision-making tools, development of microbial/biopesticides, genetic research and breeding, and biocontrol strategies for several pest groups.

They consider the southern pine beetle and spongy moth programs to be models of comprehensive IPM programs that could be adapted to additional forest health threats. They note, however, that development and implementation of these programs require significant time, financial commitments, and collaborations from various supporting agencies. Not all programs enjoy such resources.

SOURCE

Coleman, T.W, A.D. Graves, B.W. Oblinger, R.W. Flowers, J.J. Jacobs, B.D. Moltzan, S.S. Stephens, R.J. Rabaglia. 2023. Evaluating a decade (2011–2020) of integrated forest pest management in the United States

Journal of Integrated Pest Management, (2023) 14(1): 23; 1–17

Posted by Faith Campbell

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

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

or

www.fadingforests.org

USFS Lays Out Incomplete Picture of the Future

tanoak trees in southern Oregon killed by sudden oak death; photo by Oregon Department of Forestry; this pathogen is not mentioned by USFS RPA report

In August the USDA Forest Service published the agency’s 2020 assessment of the future of America’s forests under the auspices of the Resources Planning Act. [See United States Department of Agriculture Forest Service Future of America’s Forests and Rangelands, full citation at the end of the blog.] To my amazement, this report is the first in the series (which are published every ten years) to address disturbance agents, specifically invasive species. In 2023! Worse, I think its coverage of the threat does not reflect the true state of affairs – as documented by Forest Service scientists among others.

This is most unfortunate because policy-makers presumably rely on this report when considering which threats to focus on.

Here I discuss some of the USFS RPA report and what other authors say about the same topics.

The RPA Report’s Principle Foci: Extent of the Forest and Carbon Sequestration

The USFS RPA report informs us that America’s forested area will probably decrease 1- 2% over the next 50 years (from 635.3 million acres to between 619 and 627 million acres), due largely to conversion to other uses. This decline in extent, plus trees’ aging and increases in disturbance will result in a slow-down in carbon sequestration by forests. In fact, if demand for wood products is high, or land conversion to other uses proceeds apace, U.S. forest ecosystems are projected to become a net source of atmospheric CO2 by 2070.

Eastern forests sequester the majority of U.S. forest carbon stocks. These forests are expected to continue aging – thereby increasing their carbon storage. Yet we know that these forests have suffered the greatest impact from non-native pests.

I don’t understand why the USFS RPA report does not explicitly address the implications of non-native pests. In 2019, Songlin Fei and three USFS research scientists did address this topic. Fei et al. estimated that tree mortality due to the 15 most damaging introduced pest species have resulted in releases of an additional 5.53 terragrams of carbon per year. Fei and colleagues conceded this is probably an underestimate. They say that annual levels of biomass loss are virtually certain to increase because current pests are still spreading to new host ranges (as demonstrated by detection of the emerald ash borer in Oregon). Also, infestations in already-invaded ranges will intensify, and additional pests will be introduced (for example, beech leaf disease).

I see this importance of eastern forests in sequestering carbon as one more reason to expand efforts to protect them from new pest introductions, and the spread of those already in the country, etc.

A second issue is the role of non-native tree species in supporting the structure and ecological functions of forests. Ariel Lugo and colleagues report that 18.8 million acres (7.6 million ha, or 2.8% of the forest area in the continental U.S.) is occupied by non-native tree species. (I know of no overall estimate for all invasive plants.) They found that non-native tree species constitute 12–23% (!) of the basal area of those forest stands in which they occur.

Norway maple (Acer platanoides); one of the most widespread invasive species in the East. Photo by Hermann Falkner via Flickr

Lugo and colleagues confine their analysis of ecosystem impacts to carbon sequestration. They found that the contribution of non-native trees to carbon storage is not significant at the national level. In the forests of the continental states (lower 48 states), these trees provide 10% of the total carbon storage in the forest plots where they occur. (While Lugo and colleagues state that the proportion of live tree biomass made up of non-native tree species varies greatly among ecological subregions, they do not provide examples of areas on the continent where their biomass – and contribution to carbon storage — is greater than this average.) In contrast, on Hawai`i, non-native tree species provide an estimated 29% of live tree carbon storage. On Puerto Rico, they provide an even higher proportion: 36%.

Brazilian pepper (Schinus terebinthifolius) – widespread invasive in Hawai`i and Florida; early stage invasive in Puerto Rico. Photo by Javier Alexandro via Flickr

In the future, non-native trees will play an even bigger role. Since tree invasions on the continent are expanding at ~500,000 acres (202,343 ha) per year, it is not surprising that non-native species’ saplings provide 19% of the total carbon storage for that size of trees in the lower 48 states (Lugo et al.).

Forming a More Complete Picture: Biodiversity, Disturbance, and Combining Data.

The USFS RPA report has a chapter on biodiversity. However, the chapter does not discuss historic or future diversity of tree species within biomes, nor the genetic diversity within tree species.

Treatment of Invasive Species

The USFS 2020 RPA report is the first to include a chapter on disturbance, including invasive species. I applaud its inclusion while wondering why they have included it only now? Why is the coverage so minimal? I think these lapses undercut the report’s purpose. The RPA is supposed to inform decision-makers and stakeholders about the status, trends, and projected future of renewable natural resources and related economic sectors for which USFS has management responsibilities. These include: forests, forest products, rangelands, water, biological diversity, and outdoor recreation. The report also has not met its claim to “capitalize on” areas where the USFS has research capacity. One excuse might be that several important publications have appeared after the cut-off date for the assessment (2020). Still, the report’s authors cite some of the evaluations that were in preparation as of 2020, e.g., Poland et al.

I suggest also that it would be helpful to integrate data from other agencies, especially the invasive species database compiled by the U.S. Geological Survey, into the RPA. For example, the USGS lists just over 4,000 non-native plant species in the continental U.S. (defined as the lower 48 plus Alaska). On Hawai`i, the USGS lists 530 non-native plant species as widespread. Caveat: many of the species included in these lists probably coexist with the native plants and make up minor components of the plant community.

Specifically: Invading Plants

The USFS RPA report gives much more attention to invasive plants than non-native insects and pathogens. The report relies on the findings of Oswalt et al., who based their data on forested plots sampled by the Forest Inventory and Analysis (FIA) program. (The RPA also reports on invasive plants detected on rangelands, primarily grasslands.) Oswalt et al. found that 39% of FIA plots nationwide contained at least one plant species that the FIA protocol considers to be invasive and monitors. The highest intensity of plant invasions is in Hawai`i – 70% of the plots are invaded. The second-greatest intensity is in the eastern forests: 46%. However, the map showing which plots were inventoried for invasive plants makes clear how incomplete these data are – a situation I had not realized previously.

I appreciate that the USFS RPA report mentions that propagule pressure is an important factor in plant invasions. This aspect has often been left out in past analyses. I also appreciate the statement that international trade in plants for ornamental horticulture will probably lead to additional introductions in the future. Third, I concur with the report’s conclusions that once forest land is invaded, it is unlikely to become un-invaded. Invasive plant management in forests often results in one non-native species being replaced by another. In sum, the report envisions a future in which plant invasion rates are likely to increase on forest land.

If you wish to learn more about invasive plant presence and impacts, see the discussion of invasive plants in Poland et al., my blogs based on the work by Doug Tallamy, and several other of my blogs compiled under the category “invasive plants” on this website.

I believe all sources expect that the area invaded by non-native plant species, and the intensity of existing invasions, will increase in the future.

The USFS RPA links these invasions to expansion of the “wildland-urban interface” (“WUI”). These areas increased rapidly before 2010. At that time, they occupied 14% of forest land. The report published in 2023 did not assess their future expansion over the period 2020 to 2070. However, it did project increased fragmentation in many regions, especially in the RPA Western and Southeastern regions. Since “fragmentation” is very similar to wildland-urban interfaces, the report seems implicitly to project more widespread plant invasions in the future.

plant invasions facilitated by fragmentation; northern Virginia; photo by F.T. Campbell

Specifically: Insects and Pathogens

The USFS RPA report on insects and pathogens is brief and contains puzzling errors and gaps. It says that the tree canopy area affected by both native and non-native mortality-causing agents has been consistently large over the three most recent five-year FIA assessment periods. It notes that individual insects or diseases have extirpated entire tree species or genera and fundamentally altered forests across broad regions. Examples cited are chestnut blight and emerald ash borer.

The USFS RPA report warns that pest-related mortality might be underreported in the South, masked by more intense management cycles and higher rates of tree growth and decay. On the other hand, the report asserts that pest-related mortality is probably overrepresented in the Northern Region in the 2002 – 2006 period because surveyors drew polygons to encompass large areas affected by EAB and balsam woolly adelgid (Adelges piceae) infestations. The latter puzzles me; I think it is probably an error, and should have referred to hemlock woolly adegid, A. tsugae. Documented mortality has generally been much more widespread from insects than diseases, e.g., bark beetles, including several native ones, across all regions and over time, especially in the West – where the most significant morality agents are several native beetles. The USFS RPA report mentions that the Northern Region has been particularly affected by non-native pests, including EAB, HWA, BWA, beech bark disease, and oak wilt. It mentions that Hawai`i has also suffered substantial impacts from rapid ʻōhiʻa death.  

Defoliating insects have affected relatively consistent area over time. This area usually equaled or exceeded the area affected by the mortality agents. Principal non-native defoliators in the Northern Region have been the spongy moth (Lymantria dispar); larch casebearer (Coleophora laricella); and winter moth (Operophtera brumata). In the South they list the spongy moth.

More disturbing to me is the USFS RPA report’s conclusion that the future impact of forest insects is highly uncertain. The authorsblame the complexity of interactions among changing climate, those changes’ effects on insect and tree species’ distributions, and overall forest health. Also, they name uncertainty about which new non-native species will be introduced to the United States. I appreciate the report’s avoidance of blanket statements regarding the effects of climate change. However, other studies – e.g., Poland et al. – have incorporated these complexities while still offering conclusions about a number of currently established non-native pests. Finally, I am particularly dismayed that the USFS RPA does not provide analysis of any forest pathogens beyond the single mention of a few.

I am confused as to why the USFS RPA report makes no mention of Project CAPTURE (Conservation Assessment and Prioritization of Forest Trees Under Risk of Extirpation). This is a multi-partner effort to prioritize U.S. tree species for conservation actions based on invasive pests’ threats and the trees’ ability to adapt to them. Several USFS units participated, including the Southern Research Station, the Eastern Forest Environmental Threat Assessment Center, and the Forest Health Protection program. The findings were published in 2019. See here. Lead scientist Kevin Potter was one of the authors of the RPA’s chapter on disturbance.

redbay (Persea borbonia) trees in Georgia killed by laurel wilt; photo by Scott Cameron. Redbay is ranked by Project CAPTURE as 5th most severely at risk due to a non-native pest

“Project CAPTURE” provided useful summaries of non-native pests’ impacts, including the facts that

  •  54% of the tree species on the continent are infested by one or more non-native insect or pathogen;
  • nearly 70% of the host/agent combinations involve angiosperm (broadleaf) species, 30% gymnosperms (e.g., conifers). When considering only non-native pests, pests attacking angiosperms had greater average severity.
  • Disease impacts are more severe, on average, than insect pests. Wood-borers are more damaging than other types of insect pests.
  • Non-native agents have, on average, considerably more severe impacts than native pests.

Project CAPTURE also ranked priority tree species based on the threat from non-native pests  (Potter et al., 2019). Tree families at the highest risk to non-native pests are: a) Fagaceae (oaks, tanoaks, chestnuts, beech), b) Sapindaceae (soapberry family; includes maples, Aesculus (buckeye, horsechestnut); c) in some cases, Pinaceae (pines); d) Salicaceae (willows, poplars, aspens); e) Ulmaceae (elms) and f) Oleaceae (includes Fraxinus). I believe this information should have been included in the Resources Planning Act report in order to insure that decision-makers consider these threats in guiding USFS programs.

I also wish the USFS RPA had at least prominently referred readers to Poland et al. Among that study’s key points are:

  • Invasive (non-native) insects and diseases can reduce productivity of desired species, interactions at other trophic levels, and watershed hydrology. They also impose enormously high management costs.
  • Some non-native pests potentially threaten the survival of entire tree genera, not just individual species, e.g., emerald ash borer and Dutch elm disease.  I add white pine blister rust and laurel wilt.
  • Emerald ash borer and hemlock woolly adelgid are listed as among the most significant threats to forests in the Eastern US.
  • White pine blister rust and hemlock woolly adelgid are described as so profoundly affecting ecosystem structure and function as to cause an irreversible change of ecological state.
  • Restoration of severely impacted forests requires first, controlling the non-native pest, then identifying and enriching – through selection and breeding – levels of genetic resistance in native populations of the impacted host tree. Programs of varying length and success target five-needle pines killed by Cronartium ribicola; Port-Orford cedar killed by the oomycete Phytophthora lateralis; chestnut blight; Dutch elm disease; butternut canker (causal agent Ophiognomonia clavigignenti juglandacearum), emerald ash borer; and hemlock woolly adelgid.
  • Climate change will almost certainly lead to changes in the distribution of invasive species, as their populations respond to increased variability and longer-term changes in temperature, moisture, and biotic interactions. Predicting how particular species will respond is difficult but essential to developing effective prevention, control, and restoration strategies.

Poland et al. summarizes major bioinvaders in several regions. Each region except Hawai`i (!!) includes tree-killing insects or pathogens.

It is easier to understand the RPA report’s not mentioning priority-setting efforts by two other entities, the Morton Arboretum and International Union for the Conservation of Nature (IUCN). These studies were published in 2021 and their lead entities were not the Forest Service – although the USFS helped to fund the U.S. portion of the studies.

The Morton Arboretum led in the analysis of U.S. tree species. It published studies evaluating the status of tree species belonging to nine genera, considering all threats. The Morton study ranked as of conservation concern one third of native pine species; 31% of native oak species; significant proportion of species in the Lauraceae. The report on American beech — the only North American species in the genus Fagus – made no mention of beech leaf disease – despite it being a major concern in Ohio – only two states away from the location of the Morton Arboretum near Chicago.

valley oak (Quercus lobata) in Alameda Co, California; photo by Belinda Lo via Flickr

Most of the species listed by the Morton Arboretum are of conservation concern because of their small populations and restricted ranges. The report’s coverage of native pests is inconsistent, spotty, and sometimes focuses on odd examples.

Tree Species’ Regeneration

Too late for consideration by the authors of the USFS RPA report come new studies by Potter and Riitters that evaluate species at risk due to poor regeneration. This effort evaluated 280 forest tree species native to the continental United States – two-thirds of the species evaluated in the Kevin Potter’s earlier analysis of pest impacts.

The results of Potter and Riitters 2023 only partially matched those of the IUCN/Morton studies. The Morton study did not mention three genera with the highest proportions of poorly reproducing species according to Potter and Riitters: Platanus, Nyssa, and Juniperus. Potter, Morton, and the IUCN largely agree on the proportion of Pinus species at risk. Potter et al. 2023 found about 11% of oak species to be reproducing poorly, while Morton designated a third of 91 oak species to be of conservation concern.

I believe Potter and Riitters and the Morton study agree that the Southeast and California are geographic hot spots of tree species at risk.

Potter and Riiters found that several species with wide distributions might be at risk because they are reproducing at inadequate rates. Three of these exhibit poor reproduction across their full range: Populus deltoids (eastern cottonwood), Platanus occidentalis (American sycamore), and ponderosa pine(Pinus ponderosa). Four more species are reported to exhibit poor reproduction rates in all seed zones in which they grow (the difference from the former group is not explained). These are two Juniperus, Pinus pungens, and Quercus lobata. As I point out in my earlier blog, valley oak is also under attack by the Mediterranean oak borer.

SOURCES

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. 2019. Biomass losses resulting from insect and disease invasions in United States forests. Proceedings of the National Academy of Sciences. Vol. 116, No. 35. August 27, 2019.

Lugo, A.E., J.E. Smith, K.M. Potter, H. Marcano Vega, and C.M. Kurtz. 2022. The Contribution of Nonnative Tree Species to the Structure and Composition of Forests in the Conterminous United States in Comparison with Tropical Islands in the Pacific and Caribbean. USDA USFS General Technical Report IITF-54

Poland, T.M., T. Patel-Weynand, D.M. Finch, C.F. Miniat, D.C. Hayes, V.M. Lopez, eds. 2021. Invasive Species in Forests and Rangelands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector. Springer Verlag. Available gratis at https://link.springer.com/book/10.1007/978-3-030-45367-1

Potter, K.M., M.E. Escanferla, R.M. Jetton, G. Man, and B.S. Crane. 2019. Prioritizing the conservation needs of United States tree species: Evaluating vulnerability to forest insect and disease threats. Global Ecology and Conservation.

Potter, K.M. and Riitters, K. 2023. A National Multi-Scale Assessment of Regeneration Deficit as an Indicator of Potential Risk of Forest Genetic Variation Loss. Forests 2022, 13, 19. https://doi.org/10.3390/f13010019

United States Department of Agriculture Forest Service. 2023. Future of America’s Forests and Rangelands: The Forest Service 2020 Resource Planning Act Assessment. GTR-WO-102 July 2023

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Support House & Senate bills to Enhance Response to Forest Pests

white ash: a species that might be restored under the programs envisioned in the proposed bills

Bills have been introduced into both the House and Senate to enhance USDA APHIS and Forest Service programs intended to curtail introduction and spread of non-native forest pests and disease and – especially – programs aimed at restoring pest-decimated trees to the forest.

The House bill is H.R. 3174; it was introduced by Reps. Becca Balint (VT).

The Senate bill is S. 1238; it was introduced by Senators Peter Welch (VT), Mike Braun (IN), and Maggie Hassen (NH). [Both senators Welch and Braun are on the Agriculture Committee – which will write the bill.]

CISP hopes that the contents of these two bills will be incorporated in the Farm Bill that Congress is expected to adopt this year or next. The proposals have the support of the Forests in the Farm Bill coalition. [Unfortunately, neither the “Consolidated Recommendations” nor “Summarized Recommendations appears to be posted on the internet at present.]

In the last Congress, a nearly identical bill introduced by then-Representative Peter Welch was endorsed by the organizations listed below. We hope they will endorse the new bills now! If you are a member of one of these organizations, please ask them to do so.

Organizations that endorsed the previous bill: Vermont Woodlands Association, American Forest Foundation, Center for Invasive Species Prevention, Reduce Risk from Invasive Species Coalition, National Woodland Owners Association (NWOA), National Association of State Foresters (NASF), The Society of American Foresters (SAF), the North American Invasive Species Management Association (NAISMA), the Ecological Society of America, Entomological Society of America, a broad group of university professors and scientists, The Nature Conservancy (TNC) Vermont, Audubon Vermont, the Massachusetts Forest Alliance, the New Hampshire Timberland Owners Association, the Maine Woodland Owners Association, and the Pennsylvania Forestry Association.

I seek your help in generating support for incorporating these proposals into the 2023 Farm Bill. Please urge your representative and senators to co-sponsor the bills or otherwise support that action.

beech in a breeding experiment at The Holden Arboretum; photo by Jennifer Koch

Key points of the two bills:

  • They strengthen APHIS’ access to emergency funds. APHIS has had the authority to access emergency funds from the Commodity Credit Corporation since 2000. However, the Office of Management and Budget has often blocked its requests. See § 2, of the bills, EMERGENCY AUTHORITY WITH RESPECT TO INVASIVE SPECIES.
  • It creates two separate but related grant programs.
    • The first grant program – in § 3. FOREST RECLAMATION GRANTS – funds research addressing specific questions impeding the recovery of tree species that are native to the US and have suffered severe levels of mortality caused by non-native plant pests or noxious weeds.
    • The second grant program – in § 4. FOREST RESTORATION IMPLEMENTATION GRANTS – funds implementation of projects to restore these pest-decimated tree species to the forest. These projects must be part of a forest restoration strategy that incorporates a majority of the following components:

(1) Collection and conservation of native tree genetic material.

(2) Production of propagules of the target tree species in numbers sufficient for landscape-scale restoration.

(3) Preparation of planting sites in the target tree species’ former habitats.

(4) Planting of native tree seedlings.

(5) Post-planting maintenance of native trees.

  • § 5 states that the absence of a national policy on addressing nonnative forest pests has resulted in their receiving a low priority within all Federal agencies. It then mandates a study to analyze agencies’ available resources, raise the issue’s priority, and improve coordination among agencies. This study is to be carried out by an independent institution, for example the National Academy of Sciences. The authors are to consult with specialists in entomology, genetics, forest pathology, tree breeding, forest and urban ecology, and invasive species management.
  • Funding for all three action components – the emergency response and both grant programs – would come from the Commodity Credit Corporation, so it would not be subject to the vagaries of annual appropriations bills.
Forest Restoration Alliance volunteers potting hemlock seedlings; photo provided by Fred Hains

Entities which could apply for the research grants (§ 3 of the bills) include Federal agencies; State cooperative institutions; academic institutions offering degrees in the study of food, forestry, and agricultural sciences; and non-profit organizations exempt from taxes under §501(c)(3) of the tax code. Types of research funded could include:

      ‘‘(A) biocontrol of nonnative pests & diseases or noxious weeds severely damaging native tree species [the bill does not specify, but Project CAPTURE identifies many qualifying species; see also my earlier blog];  

‘‘(B) exploration of genetic manipulation of the plant pests or noxious weeds;

‘‘(C) enhancement of pest-resistance mechanisms of hosts; and

‘‘(D) development of other strategies for restoring individual tree species.

The maximum amount of such grants is $400,000 per year.

Entities which could apply for the implementation grants (§ 4 of the bills) include a cooperating forestry school; a land-grant college or university; a State agricultural experimental station; a 501(c)(3) organization. Funding would begin at $3 million for FY 2023 and rise to $10 million for FY 2026.

The Secretary of Agriculture would be guided in implementing these programs by two committees. One – the committee of experts – would constitute representatives of the USFS, APHIS, ARS & State forestry agencies. The second – the advisory committee – would be composed of representatives of land-grant colleges and universities and affiliated State agriculture experiment stations, forest products industry, recreationists, and professional forester, conservation, and conservation scientist organizations.

Port-Orford cedar seedlings at USFS Dorena Center – a model for success! Photo provided by Richard Sniezko

Please contact your Member of Congress (Representative) and senators to urge them to support inclusion of these provisions in the Farm Bill.  [Remember: they work for us!] Telling them of your support for these bills is especially important if your Representative or Senator is on the Agriculture Committee.  I list those legislators here:

StateHOUSE AGRIC COMMSENATE AGRIC COMM
ALBarry MooreTommy Tuberville
ARRick CrawfordJohn Boozman
CADoug Lamalfa
John Duarte
Jim Costa
Salud Carbajal		 
COYadira CaraveoMichael Bennet
CTJahana Hayes 
FLKat Cammack
Darren Soto		 
GAAustin Scott
David Scott
Sanford Bishop		Raphael Warnock
HIJill Tokuda 
IARandy Feenstra
Zach Nunn		Joni Ernst
Charles Grassley
ILMike Bost
Mary Miller
Nikki Budzinski
Eric Sorensen
Jonathan Jackson		Richard Durbin
INJim BairdMike Braun
KSTracey Mann
Sharice Davids		Roger Marshall
KY Mitch McConnell
MAJim McGovern 
MEChellie Pingree 
MIElissa SlotkinDebbie Stabenow
MNAngie CraigAmy Klobuchar
Tina Smith
MOMark Alford 
MSTrent KellyCindy Hyde-Smith
NCDavid Rouzer
Alma Adams		 
ND John Hoeven
NEDon BaconDeb Fischer
NJ Cory Booker
NMGabe VasquezBen Ray Lujan
NYMarc Molinaro
Nick Langworthy		Kirsten Gillibrand
OHMax Miller
Shontel Brown		Sherrod Brown
OKFrank Lucas 
ORLori Chavez-Deremer
Andrea Salinas		 
PAGlenn ThompsonJohn Fetterman
  
SDDusty JohnsonJohn Thune
TNScott Desjarlais
Brad Finstad		 
TXRonny Jackson
Monica de la Cruz
Jasmine Crockett		 
VAAbigail Spanberger 
VTPeter Welch 
WAMarie Gluesenkamp Perez 
WIDerrick van Orden 

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Protecting ash & hemlock – latest information

nearly dead ash in Shenandoah National Park; photo by F.T. Campbell

I participated in the annual USDA Interagency Invasive Species Research Forum in Annapolis in January 2023; as usual, I learned interesting developments. I focus here on updates re: efforts to protect ash and hemlock

Hopeful Developments re: countering EAB to protect ash

There are hopeful results in both the biocontrol and resistance breeding programs. The overall goal is to maintain ash as a viable part of the North American landscape.

Biocontrol

Juli Gould (APHIS) reminded us that the agency began a classical biocontrol program targetting emerald ash borer (EAB) in 2003 – only a year after EAB had been detected and much earlier than is the usual practice. [Thank you, former APHIS PPQ Deputy Administrator Ric Dunkle!] By 2007 scientists had identified, tested, and approved three agents; a fourth was approved in 2015.

Nicole Quinn (University of Florida) stressed that the egg prarasitoid, Oobius — if it is effective — could prevent EAB from damaging trees. However, it is so small that it is very difficult to sample. One small study demonstrated that Oobius will parasitize EAB eggs laid in white fringe trees (Chionanthus virginicus) as well as in ash. This is important because it means this secondary host is not likely to be a reservoir of EAB.

The numbers

According to Ben Slager (APHIS), more than 8 million parasitoids have been released at 950 sites since the program began in 2007. These releases have been in 418 counties in 31 states, DC, and four Canadian provinces. Still, these represent just 28% of infested counties. Parasitoids have been recovered in 21 states and two provinces.

Rafael de Andrade (University of Maryland) specified that these releases included more than 5 million Tetrastichus in 787 sites; ~2.5 million Oobius in 828 sites in 30 states; ~500,000 Spathius agrili – lately only north of the 40th parallel. Releases of Spathius galinae began in 2015; so far ~ 470,000 in 395 sites.

 Impact

Several presenters addressed questions of whether the agents are establishing, dispersing, and – most important – improving ash survival. Also, can classical biocontrol be integrated with other management techniques, especially use of the pesticide emamectin benzoate.

Dispersal

Several studies have shown that the four biocontrol agents disperse well (with the caveat that Oobius is very difficult to detect so its status is much less certain).

Implementation considerations

De Andrade found that the longer the delay between the date when EAB was detected and release of Oobius, the less likely Oobius will be recovered. Tetrastichus surprised because the higher the numbers released, the fewer were recovered. He could determine no association between recovery of S. agrili and variations in release regime [numbers released; delay in releasing biocontrol agents; or frequency of releases]. He said it is too early to assess Sp. galinae since releases began only in 2015, but he did see expected relationship to propagule pressure – the more wasps released, the higher the number that were recovered. Sp. galinae did surprise in one way: it seemed to perform better at lower latitudes. De Andrade noted he was working data from less than half of release sites. He asked collaborators to submit data!!!!

Initial signs of ash persistence and recovery 

Claire Rutledge (Connecticut Agriculture Experiment Station) determined that

  • More large trees were surviving in plots where the biocontrol agents were released
  • EAB density was lower at long-invaded sites
  • Parasitism rates were similar across release age treatments and release/control plots

Gould focused on protecting saplings so they can grow into mature trees which could be sources of seeds to establish future generations. She noted that there are many “aftermath” forests across the northern United States – those dominated by ash saplings.

In Michigan, at a site of green ash, as of 2015 – 2021, EAB populations are still low, parasitism rate by Tetrastichus and S. galinae high. The percentage of saplings that remained healthy was greater than 80%. There were similar findings in white ash in New York: very low EAB larval density; and more than 70% of ash saplings had no fresh galleries. Gould reported that Tetrastrichus impcts could be detected within three years of release.

So, EAB are being killed by the biocontrol agents combined with woodpecker predation; but in their fourth instar, after considerable damage to the trees.

downy woodpecker in Central Park, NYC. photo by Steven Bellovin, Columbia University

Jian Duan reported on two long-term studies in green & white ash in Michigan and New England. His team used the most labor-intensive but best approach to determine EAB larval mortality and the cause – debarking trees – to determine whether the EAB larva were parasitized, were preyed on by woodpeckers, or were killed by undetermined cause, such as tree resistance, disease, or competition. In Michigan, he linked a crash of EAB population in 2010 was caused by Tetrastichus; EAB tried to recover, but crashed again, due to S. galinae. EAB larval densities had been reduced to 10 / m2. Predation by abundant woodpeckers and the native parasitoid Atanycolus was also important.

In New England, EAB has also declined from 20-30 larvae /m2 to ~ 10 m2.

In Michigan, healthy ash with dbh of larger than 5 inches were much more plentiful in sites where parasitoids had been released. Their survival/healthy rate also was much higher in release sites but the difference declined as years passed. In New England there were growing numbers of healthy trees in 2021-22; (almost none in 2017). Duan conceded that he could not prove a direct link but the data points to recovery.

Tim Morris (SUNY-Syracuse) found that white ash saplings continued to die in large numbers, but the mortality rate was significantly below the rate in 2017. Canopy conditions varied; some trees that were declining in 2013 were recovering in 2017. Forty percent of “healthy” ash in 2013 continued recovering in 2021. Few living trees were declining; trees were either healthy or dead. He thinks probably a combination of genetics and presence of parasitoids explains which trees recover. Morris also reported some signs of regeneration.

beaver feeding on ash saplings, Fairfax County, Va;
photo by F.T. Campbell

At this point, I noted that in parts of northern Virginia, beavers have killed ash saplings. Morris reported finding the same in some sites in New York. Perhaps others have, also; my comment was greeted by laughter.

Theresa Murphy (APHIS) looked at integration of biocontrol and insecticide treatment in urban and natural sites. A study of black and green ash in Syracuse, NY Naperville, IL, and Boulder, CO found continued high parasitism by Tetrasticus and S. galinae and woodpecker attacks in trees treated with emamectin benzoate. Researchers could not detect Oobius. By 2020, most of the untreated trees had died but treated trees remained healthy.

Murphy has begun studying integration of biocontrol and pesticides in green and black ash forests. The goal is to protect large trees to ensure reproduction; the biocontrol agents do not yet protect the large trees. This is especially important for black ash because it declines very quickly after EAB invades. Sites have been established in New York, through collaboration with New York parks, Department of Environmental Conservation, and the Mohawk tribe. She is still looking for sites in Wisconsin – where EAB is spreading more slowly than expected.

1 of the infested ash in Oregon; photo by Wyatt Williams, ODF

Max Ragozzino of the Oregon Department of Agriculture reported on imminent release of biocontrol agents targetting the recently detected outbreak there. I am encouraged by the rapid response by both the state and APHIS.

EAB resistance in ash

Jennifer Koch (USFS) said the goal is not to produce populations where every seedling is fully EAB-resistant, but to develop populations of ash trees with enough resistance to allow continued improvement through natural selection while retaining sufficient genetic diversity to adapt to future stressors (changing climate, pests, diseases). The program has developed methods to quantify resistance in individuals.. Initial field selections of “lingering ash” were shown to be able to kill as many as 45 % of EAB larvae. Already green ash seedling families have been produced by breeding lingering ash parents.  This first generation of progeny had higher levels of resistance, on average, than the parent trees.  Each generation of breeding can increase the proportion of resistance. Although the bioassays to test for EAB-resistance are destructive (e.g., cutting and peeling to count numbers of surviving larvae), the potted ash seedling stumps can resprout. Once the new sprouts are big enough they are planted in field trials to correlate bioassay results with field performers.  Poor performers are culled; those with higher levels of resistance remain and become sources of improved seed.

To ensure preservation of local adaptive traits, this process must be repeated with new genotypes to develop many seed orchards from across the species’ wide range. To support this work, concerned scientists are building multi-partner collaborative breeding networks. These organizations provide ways for citizens and a variety of partners to engage through monitoring and reporting lingering ash, making land available for test planting, and helping with the work of propagation.

See Great Lakes Basin Forest Health Collaborative » Holden Forests & Gardens (holdenfg.org), Monitoring and Managing Ash (MaMA) – A citizen-science-driven program for conservation and mitigation (monitoringash.org), and TreeSnap – Help Our Nation’s Trees! for more information.

Resistance levels in some of the first generation progeny were high enough for use in horticulture, where it is important that trees can remain healthy in challenging environments (street trees, city parks, landscaping, etc.). Koch hopes to develop about a dozen cultivars comprising the best-performing trees, appropriate for planting in parts of Ohio, Michigan, Indiana, and Pennsylvania.   Local NGO partners are planting some of these promising genotypes in Detroit to see how they withstand EAB attack.

a black ash swamp; photo via Flickr

The threat to black ash is especially severe, and this species presents unique difficulties. While scientists found several seedlings from unselected seedlots had killed high levels of larvae, those deaths did not always result in better tree survival. Koch thinks the tree’s defense response becomes detrimental to tree by blocking transport of water and nutrients. She is working with experts in genomics and others, such as Kew Royal Botanic Gardens, to try to identify candidate trees for breeding programs.  The genomics work has been supported by APHIS and the UK forest research agency, DEFRA. Michigan and Pennsylvania have supported the breeding work. USFS Forest Health Protection has supported work with black and Oregon ash (see below) (J. Koch, USFS, pers. comm.).

Koch has also begun working with Oregon ash, in collaboration with the USFS Dorena Genetic Resource Center (located in Cottage Grove, Oregon) and other partners.

dead hemlock in Massachusetts; photo by Ian Kinahan,
University of Rhode Island

Hemlock woolly adelgid

Scientists are still trying to find the right combination of biocontrol, chemical treatments, and silvicultural manipulation.

For several years, hope has focused on two has been on two predatory beetles, Laricobius nigrinus and L. osakiensis. Scott Salom (Virginia Tech) reports that release of these beetles over the past 20 years has had a significant impact on HWA density and tree photosynthetic rate and growth. However, Laricobius aredifficult to rear and they attack only the sistens generation of the adelgid. Ryan Crandall (University of Massachusetts) reports it has been difficult to establish these beetles in the Northeast. He links this difficulty is caused by temporary drops in HWA populations after cold snaps.

Scientists now agree that need to find predators that attack HWA during other parts of its lifecycle. Hope now focuses on silverflies — Leucotaraxis argenticollis and Le. piniperda.  While both species are established in eastern North America, the clades in the east feed almost exclusively on pine bark adelgid, and have not begun attacking HWA. Biocontrol practitioners therefore collect flies in the Pacific Northwest for release in the east. Salom is increasing his lab’s capacity to rear silverflies and exploring release strategies.

Preliminary evidence indicates that the western clades of Leucotaraxis are establishing, although data are not yet definitive (Havill, USFS).

Detecting the presence of biocontrol agents presents several challenges. Tonya Bittner (Cornell) described efforts to use eDNA analysis for this. Some puzzles have persisted; e.g., at some sites, she detected eDNA but caught no silverflies. This raised the question of long eDNA associated with the original release might persist. Another problem is that the assay cannot separate the introduced western L. nigrinus from the native congener, L. rubus (which also does not feed on HWA). She continues efforts to improve this technique.

Others explored interactions of the biocontrol agents with insecticides. Salom is studying the impact of soil-applied insecticides on Laricobius populations, which aestivate in the soil. Preliminary results showed significant reduction in the beetle’s population under soil drench application but not under soil injection. He has not yet analyzed all the data.

Michigan is trying to prevent spread of HWA from five counties along the eastern shore of Lake Michigan (where HWA was introduced on nursery stock) to widespread hemlock forests in northern part of the state. Phil Lewis (APHIS) is studying persistence of systemic insecticides in hemlock tissues, particularly twigs and needles. The pesticides involved are imidacloprid, dinotefuran, and Olefin. He has found that pesticide levels are highest 18 – 22 months after treatment, then decline. They are significantly higher after trunk injection compared to bark spray or soil treatments. Imidacloprid had higher residues in twigs; dinotefuran in needles. This difference affects the likelihood of adelgids actually ingesting the toxin.

healthy hemlock in experimental gap; Jefferson National Forest, VA; photo by Bud Mayfield, USFS

Bud Mayfield (USFS) reported on his study of silvicultural strategies to support healthier hemlocks. While hemlocks normally thrive in shade, it has been determined that sunlight assists small trees  reducing HWA sufficiently to counter the tree’s leaf-level stress. Small sapling hemlocks grown in sunlight fix more carbon and convert it to growth in shoots and trunk diameter.

Mayfield found promising immediate suppression of HWA in large gaps in Georgia and Tennessee. By the third year the saplings were still growing, although their faster growth had attracted more HWA. These findings were less clear farther north in central Virginia and western Maryland – Mayfield thinks because HWA pressure there is lower. However, managers must maintain the gaps by cutting rapidly-growing competing woody species. He plans to test this strategy farther north in Pennsylvania. He is still trying to determine the optimal size of the gap.

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Restoring American chestnut: importance of Phytophthora root rot

TACF back-crossed chestnut growing in southern Fairfax County, Virginia

same chestnut, dying in 2021; probably from Phytopthora root rot

In the first half of the 20th Century, American chestnut (Castanea dentata) was functionally extirpated from US forests east of the Mississippi River by chestnut blight, caused by a fungus from Asia, Cryphonectria parasitica. Today, only 10% of the pre-blight chestnut population remains, most as root sprouts less than 2.5 cm dbh (Dalgleish et al. 2015; full citation at the end of the blog).

Volunteer organizations — with recent help from federal and state agencies – have worked for more than a century to develop chestnut trees resistant to the blight. Their aim is to restore the species to the forest.  Their decades of hybridization efforts now appear unlikely to produce a highly blight-resistant chestnut with a genome that is predominantly American, so TACF now plans to incorporate the use of transgenic techniques to enhance resistance to the blight fungus.

However, restoration of chestnut requires addressing a second Asian pathogen: Phytophthora cinnamomi, which causes a fatal root disease. Several studies indicate that up to 80% of seedlings are killed. The pathogen is widespread in soils south of 40o North Latitude, which falls just north of the Maryland-Pennsylvania line. Thus, P. cinnamomi occupies the southern half of American chestnut’s former range. Scientists expect this pathogen to move north in response to the warming climate; indeed, some project that the root disease could reach throughout the entire current chestnut range by 2080.

historic range of American chestnut

Gustafson et al. 2022 modelled chestnut’s vulnerability to P. cinnamomi to current and expected environmental conditions in two state forests in the Appalachians of western Maryland to evaluate the probable impact of the root disease on efforts to restore the tree species.

They found that root rot greatly reduced chestnut biomass on the landscape, even when resistance to root rot was at the target level for selection of root rot-resistant chestnut families using traditional breeding methods.

Gustafson et al. 2022 recommend that chestnut restoration apply the following strategies:

  • Locate restoration plantings at latitudes, elevations, and sites where root rot is not expected to be present well into the future. This probably means sites in the Northeastern US and Canada (Burgess et al. 2017)
  • Enhance the planting stock’s resistance to P. cinnamomi through breeding.
  • Identify soil conditions, including soil microbes, that suppress the pathogen or protect tree roots.
  • Since planting stock – both bareroot and containerized – can transmit P. cinnamomi, either raise seedlings in nurseries located outside the pathogen’s current range or rely on direct seeding. These strategies have their own downsides. Restricting locations of nurseries might complicate efforts to ensure seedlings are adapted to local conditions in the restoration area and seeds would need to be protected from seed predators.

The authors specify these additional important conditions:

  • Planting locations: while Canada is currently outside the range of American chestnut, the same climatic warming that will facilitate northward spread of P. cinnamomi will probably allow the tree to thrive farther north (Barnes and Delborne 2019). Perhaps the tree’s range will shift farther north than the pathogen’s.
  • Breeding: some resistance to Phytophthora root rot has been found in families providing blight resistance used in The American Chestnut Foundation (TACF) breeding program. TACF now plans to cross individuals from those families with transgenic blight-resistant chestnut to combine both resistances.
  • Soils: P. cinnamomi is favored by compacted soils with poor aeration or that tend to remain saturated. These include heavy clay soils and those highly disturbed by agriculture or mining. Restoration sites should be non-disturbed, well-drained sites. (This recommendation contradicts others’ proposals that chestnuts be planted on reclaimed mining sites.) Silvicultural management should also minimize environmental stresses.
that dying chestnut trying to reproduce!

Restoring chestnut will be challenging in any case: successful restoration requires chestnut trees that can compete successfully in the forest and adapt to conditions which are now quite different from those a century ago when the species was dominant. These include abiotic factors, e.g., climate and atmospheric CO2 levels; and biotic factors, e.g., different forest pests and invasive plant species.

In an earlier publication, Gustafson and colleagues (Gustafson et al. 2018) modelled the effects of warmer temperature and elevated atmospheric CO2 levels on chestnut’s growth and competition and the tree’s adaptation to natural and anthropogenic disturbances. They concluded that aggressive restoration programs – involving clearcutting, then planting chestnuts – could restore chestnut as an important component of forested ecosystems in the Appalachian Mountains.  

However, this earlier study did not consider the effects of Phytophthora root rot. The 2022 study demonstrates that these recommendations are probably applicable only to the northernmost portion of former chestnut range, outside the areas infested by Phytophthora root rot, unless breeding is successful in substantially increasing resistance to root rot.

Several studies indicate American chestnut is highly susceptible to P. cinnamomi; rates of root rot induce mortality of 80% or higher have been documented. TACF has found that hybrid chestnut families selected for root rot resistance have a mortality rate of about 45%. Even with this level of tolerance, the model shows that chestnut could not regain anything approaching its former abundance on the landscape. Since the threat of P. cinnamomi to chestnut restoration has become evident, TACF is assessing how to integrate increased tolerance to root rot into their larger blight resistance breeding program (Westbrook et al. 2019).

Soil properties – texture, land use, drainage, waterlogging, drought, temperature, and water-holding capacity – influence infection. So does weather: a single heavy rain event might saturate soil sufficiently to facilitate a P. cinnamomi infection. For these reasons, climate change is expected to exacerbate its geographic spread and pathogenicity.

The sites used in both studies are at the center of chestnut’s former range, which is also at the northern edge of the root rot pathogen’s range. However, the two sites differ in important ways, especially in rainfall and soils. The researchers considered one a mesic site and the other, xeric.

Their 2022 model showed that root rot caused a dramatic reduction in chestnut biomass on both the mesic and xeric sites. Apparently temperature and wetness levels offset each other. That is, higher soil temperatures intensified P. cinnamomi virulence at the xeric site sufficiently to overcome its relative soil dryness. At the mesic site, soil temperature sometimes dropped to levels that are lethal to Phytophthora. On the whole, then, climate change is expected to intensify P. cinnamomi infection rates on both sites and reduce the number of sites where the pathogen is absent.

Gustafson et al. (2022) discuss several assumptions and data gaps that require further study.

SOURCES

Barnes, J.C. and Delborne, J.A., 2019. Rethinking restoration targets for American chestnut using species distribution modeling. Biodiversity and Conservation, 28(12), pp.3199-3220.

Burgess, T.I., Scott, J.K., Mcdougall, K.L., Stukely, M.J., Crane, C., Dunstan, W.A., Brigg, F., Andjic, V., White, D., Rudman, T. and Arentz, F., 2017. Current and projected global distribution of Phytophthora cinnamomi, one of the world’s worst plant pathogens. Global Change Biology, 23(4), pp.1661-1674.

Dalgleish, H.J., Nelson, C.D., Scrivani, J.A. and Jacobs, D.F., 2015. Consequences of shifts in abundance and distribution of American chestnut for restoration of a foundation forest tree. Forests, 7(1), p.4.

Gustafson, E.J., B.R. Miranda, T.J. Dreaden, C.C. Pinchot, D.F. Jacobs. 2022. Beyond blight: Phytophthora root rot under climate change limits populations of reintro Am chestnut Ecosphere. 2022;13:e3917.

Gustafson, E.J., A.M.G. De Bruijn, N. Lichti, D.F. Jacobs, B.R. Sturtevant, D.M. Kashian, B.R. Miranda, and P.A. Townsend. 2018. “Forecasting Effects of Tree Species Reintroduction Strategies on Carbon Stocks in a Future without Historical Analog.” Global Change Biology 24: 5500–17. https://doi.org/10.1111/gcb.14397

Westbrook, Jared W., et al. “Resistance to Phytophthora cinnamomi in American chestnut (Castanea dentata) backcross populations that descended from two Chinese chestnut (Castanea mollissima) sources of resistance.” Plant disease 103.7 (2019): 1631-1641.

Posted by Faith Campbell

[An earlier version of this blog has now been corrected, with additional sources added. I think Cornelia Pinchot, USFS, for the corrections.]

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

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

or

www.fadingforests.org

West Coast Steps Up Efforts to Protect Ash

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

A video explaining the campaign to save Oregon ash is at https://youtu.be/uZmfLrxEA7g

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Hemlock biocontrol – need summer parasitoids

healthy hemlocks in Cook Forest, Pennsylvania; photo by F.T. Campbell

I blogged recently about North Carolina’s multi-pronged hemlock conservation program. As noted there, scientists are putting considerable hope in biological control as the most promising strategy to protect eastern (Tsuga canadensis) and Carolina hemlocks (T. caroliniana) from the hemlock woolly adelgid (HWA; Adelges tsugae). For a more detailed discussion of the adelgid’s life cycle, go here.    

A new study by Crandall, Lombardo and Elkinton (full citation at end of blog) cheers us by supporting the probable efficacy of this approach – as long as a complete suite of biocontrol agents is deployed. The study points to the need to introduce additional biocontrol agents, specifically those that feed in the summer.

The study analyzed the relative importance of two different mechanisms to protect plants from herbaceous insects: do some hemlock species have an enhanced ability to fend off the adelgid (bottom-up protection); or do predators apply sufficient pressure (top-down protection) to reduce adelgid populations to levels that the tree can withstand?  The study simultaneously analyzed

(1) the relative importance of summer-active and winter-active native predators;

(2) whether HWA colonization and abundances differed on western and eastern hemlock species;

(3) the relative importance of top-down and bottom-up forces on HWA feeding on western and eastern hemlocks in the adelgid’s native range;

4) tested whether the adelgid is ubiquitous at low densities across the Pacific Northwest (PNW) and compared HWA abundance in PNW to invaded range in New England.

The study was carried out in Washington State, where both western hemlock (Tsuga heterophylla) and HWA are native. They were able to compare adelgid impacts on eastern hemlock because the tree is planted in parks and gardens in the PNW.

Eastern hemlock infested by HWA; USDAFS via Bugwood

In an earlier study, (Crandall et al. 2020) found that L. nigrinus was not able to reduce HWA densities in the east. Laricobius spp have their greatest impact on HWA by larval feeding on the progrediens eggs produced by the sistens. However, 90% of hatching progrediens die naturally because there are a finite number of needles for them to settle on. To have an impact on HWA populations, Laricobius spp would have to prey on more than 90% of progrediens eggs. The solution appears to be summer-active predators – e.g., silver flies — which feed on the progrediens eggs and the sistens eggs which the progrediens generation lays.

western hemlock in British Columbia; photo by F.T. Campbell

KEY FINDINGS

  • Western hemlock is a native host of the adelgid. Crandall, Lombardo, and Elkinton found no evidence that western hemlock’s structure, chemistry, or other attributes help it fend off adelgid attack. The proportion of branches colonized by HWA was significantly higher on western than on eastern hemlock. Indeed, HWA populations were able to reach levels similar to those in eastern North America and were able to persist on western hemlock for multiple generations. Thus there is no evidence for bottom-up control of HWA on western hemlock.
  • HWA survival was significantly lower on branches of western hemlock when predators were allowed access. Crandall assumes that the smaller, non-significant, decrease in HWA densities on eastern hemlocks in the Pacific Northwest is also attributable to predation, although the data are too few to support a definitive conclusion. These predators included a species that has been released as a biocontrol agent in the east, Laricobius nigrinus. More important, apparently, was the presence of summer-active predators, including Leucotaraxis spp. and generalists. These summer-active predators are active from the progrediens nymph stage in April through the aestivating sistens nymph stage until about October. Laricobius nigrinus doesn’t become active until September. These results support the hypothesis that predator-caused mortality is responsible for suppressing HWA during rare and localized outbreaks on western hemlock in the PNW. In the east there are no native natural enemies that attack HWA – which is introduced to the region.
  • Effective control of HWA on the eastern naïve hosts will require establishment of a suite of predators which – together — attack the adelgid during both summer and winter.While several possible biocontrol agents have been introduced in the region, and at least some – e.g., Laricobius nigrinus – have established self-sustaining populations, are spreading, and have high predation rates, they have had very limited success in reducing HWA populations. Crandall, Lombardo and Elkinton say these data support the recent decision by the USDA Forest Service to augment the HWA biocontrol effort by introducing two species of silver flies, Leucotaraxis argenticollis and Le. piniperda, that feed on both the sistens and progrediens generations in PNW.
  • Tree-adelgid interactions are probably significantly affected by the lineage of both – whether the tree species has co-evolved with the specific lineage of the adelgid with which it is interacting. Crandall, Lombardo and Elkinton think evaluation of any Tsuga species’ resistance to HWA or any potential biocontrol agent needs to be studied in relation to the appropriate lineage of the adelgid.

When they compared HWA abundance (in 2021) on hemlock forests in western Washington with HWA abundance at introduced HWA range in New England, Crandall, Lombardo and Elkinton found that HWA abundance was higher in New England. They note that these comparisons are between two different linages of HWA – the lineage native to PNW and the introduced Japanese lineage in the East.

The authors note that HWA densities in the PNW are higher at the urban site (Seattle) than rural sites. Perhaps the reason is lower densities of HWA predators in non-forest settings because some, e.g., La. nigrinus, require a duff layer for pupation. Duff layers are rarely permitted to accumulate in urban areas. The authors call for studies to assess the relative abundance and identify factors affecting the abundance of HWA predators in rural and urban settings.

SOURCES

Crandall R.S., Jubb C.S., Mayfield A.E., Thompson B., McAvoy T.J., Salom S.M. and J.S. Elkinton. 2020. Rebound of Adelges tsugae spring generation following predation on overwintering generation ovisacs by the introduced predator Laricobius nigrinus in the eastern United States. Biological Control 145, 104-264. https://doi.org/10.1016/j.biocontrol.2020.104264

Crandall, R.S., J.A. Lombardo, and J.S. Elkinton. 2022. Top-down regulation of hemlock woolly adelgid (Adelges tsugae) in its native range in the Pacific Northwest of North America. Oecologia 199, 599-609. https://doi.org/10.1007/s00442-022-05214-8

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Funding APHIS & USFS in FY23 – Senate Recommendations

The Senate Appropriations Committee has adopted its recommendations for funding APHIS and the US Forest Service in Fiscal Year 2023, which begins on October 1. The full Senate has not yet acted; most people expect that it will not act before October, so the agencies will have to operate under a “continuing resolution” for at least the first several months. Under a “CR”, funding is maintained at the current level.

SOD-infected rhododendron plants detected by state officials in Indiana in 2019

Funding for APHIS in FY23

The Senate Appropriations Committee issued a report [available here] that recognizes APHIS’ objective of protecting the animal and plant resources of the Nation from diseases and pests. These objectives are carried out through, inter alia, Safeguarding and Emergency Preparedness/Response and Safe Trade and International Technical Assistance.

The Committee recommends the following funding for specific APHIS programs (in $millions)

PROGRAMFY22 FUNDINGFY23 ADMIN REQHOUSE $SENATE COMM RECOMMCISP ASK
Border inspections (AQI appropriated)33.84936.725 36.650X
Pest Detection28.21829.13729.82529.07530
Methods Development21.21721.85431.80723.55723
Specialty Crops209.533219.533219.698222.072219
Tree & Wood pests61.21762.85462.56262.71970
Subtotal, Plant health379.144385.560 397.603X
Emerg. Prepare & Response42.02144.242 44.317X

Specific programs mentioned:

  1. Northern (Asian) giant hornet eradication: $1.75 million to continue cooperation with Washington State to eradicate this pest; also to improve monitoring methods and lures, and build a rapid response platforms
  2. sudden oak death (SOD): recognize that the EU1 and NA1 strains of this pathogen threaten Douglas-fir / tanoak forests and lead foreign governments to impose quarantines on U.S. timber exports. So APHIS should spend no less that FY22 funding to better understand threat and treatment methods in wildlands. This earmark disappoints because it focuses on APHIS’ role as certifying timber exports as pest-free rather than the spread of the pathogen within the U.S. via the nursery trade. The same language appears in the report’s discussion of the Agriculture Research Service (see below).

Pertinent action re: Agriculture Research Service

The Senate Committee report sets several priorities, including the following:

  1. Invasive Pests: The Committee is concerned about the threats invasive pests pose to agriculture, the economy, environment, human health, and national security of the Pacific region. The Committee directs ARS to continue working with stakeholders in the region to assess options for combatting invasive species, including biocontrol research facilities, containment facilities, additional laboratory space.
  2. Sudden oak death: the same language as for APHIS. Again, I wish the language referred to the pathogen’s spread via the nursery trade.

These numbers are disappointing; the increase for “specialty crops” demonstrates the lobbying clout of the nursery and berry industries! I appreciate the attention to sudden oak death – with the caveat I mentioned.

SOD-infected tanoaks in southern Oregon; photo by Oregon Department of Forstry

Forest Service

The Senate Appropriations Committee issued a report [available here] . The Senate Appropriations Committee recommends the following funding levels for USFS programs that address non-native forest pests and other invasive species (in $millions):

PROGRAMFY22 FUNDINGFY ADMIN REQUESTHOUSE $S COMM RECOMMCISP ASK
Research296.616317.733$360.4$302.773317.733
State & Private Forest Health Protection TOTAL4859.232$52.2325083
S&P FHP Federal lands16,00022,485?17,00051
S&P FHP non-federal lands32,00036,747?33,00032

R&D

The Senate wants to retain the current structure of five regional stations, International Institute of Tropical Forestry, and Forest Products Laboratory.

The Senate listed several research priorities. Two pertain to forest health: 1) needle pathogens, and 2) Northeastern States Research Cooperative working to sustain the health of northern forest ecosystems and biological diversity management. I am disappointed that no mention is made of the need to respond to 400 introduced tree-killing insects and pathogens.

planting to test ash trees’ resistance to emerald ash borer; photo courtesy of Jennifer Koch, USFS

S&P

The Senate Committee recommends a significant increase in S&P overall ($8 million above FY22 level), but not for Forest Health Management. This is disappointing.

The Committee is concerned about high tree mortality on National Forests due to bark beetle infestations and instructs USFS to work with states and tribes to prioritize insect prevention, suppression & mitigation projects.

The Committee expects the Forest Service and Bureau of Land Management (BLM) to continue efforts to treat sudden oak death in California and Oregon. It provides $3 million for this purpose, including for partnerships with private landowners.

Posted by Faith Campbell

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

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

or

www.fadingforests.org