Category: Uncategorized

I and others have recently emphasized risks linked to plant-pathogenic fungi and fungal-like organisms such as oomycetes – e.g. Phytophtoras and more broadly. I welcome a new focus on another group of plant-killing organisms: nematodes. We have good reason to want attention to improving strategies to prevent their introduction and spread, and to manage their impact: beech leaf disease (BLD) and my blog.

Kantor et al. 2025 have published a review of nematodes – what is now known, what needs to be learned. They propose the “emergence triangle” as a tool for understanding how abiotic stresses affect nematode adaptation and how nematologists use innovative techs to enhance surveillance.

The authors point out that plant parasitic nematodes already cause billions of dollars in losses to agricultural crops annually. They expect climate change to trigger significant shifts in nematode populations, behaviors, and host ranges. These changes – combined with a rising risk of new introductions – could cause even more severe damage to agricultural and forest ecosystems

Kantor et al. call for continuing surveillance to detect nematode-related disease. They describe current methods and recent advances, particularly using machine learning. However, greater progress is needed to maximize for detection and quantification of nematode populations. Detection must also be linked to improved diagnostics.

Biology

Nematodes are the most abundant multicellular organisms; about 27,000 species have been described. (Kantor et al. do not hazard a guess as to how many species might remain undescribed.) Nematodes occupy every trophic level of food webs. The article describes – briefly – the role free-living nematodes play in contributing to healthy soils helping to control plant–pathogenic bacteria, fungi and nematodes

About 15% of described nematodes are plant pathogens. Kantor et al. provide brief profiles of five species newly recognized as problems in the United States. They use these profiles to illustrate interactions among climate change, nematode adaptation, and advances in detection and diagnostic tools – what they call examples of the “emergence triangle”. Four of the nematodes discussed damage agricultural crops, ranging from grains to tomatoes to cotton. The fifth example is the beech leaf disease nematode, Litylenchus crenatae mccannii (LCM); although Kantor et al. don’t use the subspecies; is this important?). They callits threat to forest ecosystems “distinct”.  But does the apparent uniqueness reflect our ignorance rather than biology?

Kantor et al. note that LCM has spread more rapidly than any other nematode species reported to date, probably due to dispersal by wind and rain. They call for regulatory agencies to monitor the BLD nematode because of potential impact on landscapes

Kantor et al. raise concern that many of newly introduced nematodes – or those invigorated by changed environmental conditions – will go undetected until the damage they cause is sufficiently visible. By that time, the disease is much more difficult if not impossible to manage.

Introductions are hard to detect because, first, nematodes are microscopic. Second, scientific attention has focused on nematodes causing the greatest economic damage now. These species are widespread, so they are not regulated under international phytosanitary programs. Furthermore their presence complicates scientists’ ability to surveil and assess newly detected species. Nematodes often do not cause obvious, distinguishable symptoms at low levels of infection. Finally, there are too few experts and a lack of appropriate equipment to enable timely detection of nematodes in supply chains and ports of entry. All these challenges mean that methods for regulating nematodes in trade pathways fall afoul of requirements of the World Trade Organization Agreement on Sanitary and Phytosanitary Measures (SPS Agreement) and implementing protocols issued by the International Plant Protection Convention (IPPC). [To read additional criticisms of failures of the SPS/IPPC system, read Fading Forests II and my blogs.]

Improving management of nematode invasions will require overcoming significant scientific challenges. Each element of Kantor et al.’s “emergence triangle” – climate stress, adaptations, surveillance and diagnostics – mutually influences the others. The elements act collectively to influence a nematode’s  emergence and spread. As an illustration of the complications they note that climate change will probably shift nematode populations, dynamics, and host ranges. To understand and forestall the new diseases, it is imperative to understand the mechanisms nematodes use to adapt and succeed in changing environments. For example, warmer soil temperatures – in response to climate change – can sometimes favor nematode development and thus raise their impact. However, those warmer temperatures sometimes disfavor nematode life cycle. Temperature changes might also affect crop plants’ natural resistance mechanisms and levels.

Assuming some aspects of adaptation depend on genetic mechanisms. Nematodes have very complex genomes. Unravelling these factors can now be facilitated by whole-genome sequencing. Kantor et al.  discuss possible mechanisms and study methods.

They discuss strengths and weaknesses of current and emerging surveillance technologies, including visual inspection of roots for symptoms [described as direct but invasive]; and various remote sensing methods. The latter are described as still being “works in progress” or in early stages. Kantor et al. specify certain technologies that need to be improved before they can rely on.

They also report on innovations in diagnostics. Various molecular technologies are reported as providing useful specificity, sensitivity, and speed. However, the DNA-based diagnostics require primers designed for specific nematode sequences – which might not be available for emerging species. Metabarcoding can compare DNA from all nematodes to learn which species are present at that time. But, again, completeness depends on reference databases. Further, extracting nematodes from soil samples demands care.

In sum, recent advances in artificial intelligence and remote sensing have significantly improved early detection and management by enabling precise, non-invasive data collection and assessment of plant health.

Focusing on biosecurity for the United States, Kantor et al. call for nematologists to discuss changes needed with the regulatory agencies, i.e. the Animal and Plant Health Inspection Service (APHIS). These discussions should seek agreement that nematodes play a significant role in plant diseases that could devastate major agricultural economies. Furthermore, the declining number of nematologists raises the likelihood that threats will be missed. 

I support the call for discussions with APHIS. I would add talking with representatives from the  U.S., Canada, and Mexico to the North American Plant Protection Organization (NAPPO).

I suggest another topic as well: the imperative that national and international phyrtosanitary policies and programs reflect the true level of threat from introduced plant pathogens (of all Phyla) and the limits of current science.  See calls by Wu and by Raffa et al. for policies that reflect the true threat level & the limits of current science.

SOURCES

Kantor, C., Teixeira, M., Kantor, M., and Gleason, C. 2025. Tiny Invaders, Big Trouble: Emerging Nematode Threats in the United States. Phytopathology 2025   115:587-595  https://doi.org/10.1094/PHYTO-09.-24-0290-IA

Raffa, K.F., E.G. Brockerhoff, J-C. Gregoirem R.C. Hamelin, A.M. Liebhold, A. Santini, R.C. Venette, and M.J. Wingfield. 2023. Approaches to Forecasting Damage by Invasive Forest Insects and Pathogens: A Cross-Assessment. Bioscience Vol. 73, No. 2. February 2023.

Wu, H. 2023/24. Modelling Tree Mortality Caused by Ash Dieback in a Changing World: A Complexity-based Approach MSc/MPhil Dissertation Submitted August 12, 2024. School of Geography and the Environment, Oxford University.

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 https://fadingforests.org/

A complex of closely related ambrosia beetles continues to be introduced to new places and cause increasing damage. The most widespread is the polyphagous shot hole borer (PSHB) Euwallacea fornicatus ss. Other members of the complex include the Kuroshio shot hole borer (KSHB) E. kuroshio and a third species, E. interjectus. Each beetle harbors its own plant-pathogenic fungus – all in the Fusarium genus.

Places invaded and impacts

The PSHB is established in the U.S. (southern and central California), Israel, South Africa, & Australia. The outbreak in South Africa covers the largest geographic area; the PSHB-Fusarium disease has been found in eight of the country’s nine provinces (every province except Limpopo) (Bierman et al. 2022). The South Africa outbreak is the most extensive geographically of all of them (Mudede et al. 2025).

The KSHB is established in southern California, from where it has spread to neighboring Mexico. E. interjectus is established in Santa Cruz County in California. 

A fourth member of the species complex, E. perbrevis, has been established for decades on several Hawaiian islands and for at least 20 years in Florida. E. perbrevis has also been detected in nurseries in the Netherlands, but authorities reported it has been eradicated. E. perbrevis has long been known to be present in northern Queensland; this region might be part of its native range.

South America

In 2023 PSHB had been detected in Argentina – reported as E. fornicatus. A few weeks ago it was reported in neighboring Uruguay (PestLens for June 26, 2025). The beetle in South America is a different haplotype (genetic strain) than that introduced in South Africa, Israel, and California. It is more similar to specimens found in European greenhouses (Ceriani-Nakamurakare & others) As of 2022, scientists had identified 43 haplotypes (genetic variants) of E. fornicatus s.s. identified around the world; the greatest diversity is in several Asian countries  (P. Rugman-Jones, pers. comm). The other species also comprise several haplotypes.

In South America the beetle has been observed attacking several new hosts. The most frequently attacked hosts are are Acer japonicum (Japanese maple) and a Ficus sp. Other hosts that support the full life cycle of the beetle and its associated fungus are Bauhinia forficata (cow’s foot), Ceiba speciosa (floss silk tree), Diospyros inconstans (jacuiba), Ficus aspera (mosaic fig), Fraxinus excelsior (European ash), Gardenia thunbergia (white gardenia), Geoffroea decorticans (chañar), Myrsine laetevirens, and Neltuma (Prosopis) caldenia (caldén) plants (PestLens June 26, 2025).

South Africa

The beetle and disease have been present since 2012 or earlier although it was not detected until 2017 (Winzer et al.). (This delay in detection is typical; in California PSHB was present for probably nine years before it was detected.) Winzer et al. decry the communication failure that resulted in the delayed official detection in South Africa and propose a system to correct the breakdown.

The haplotype (genetic strain) is the same as that found in Vietnam and introduced in California and other sites (Mudede et al.).

The South Africa outbreak is the most extensive geographically of all the outbreaks globally; within five years of its official detection, the PSHB-Fusarium disease was confirmed to be present in eight of the country’s nine provinces (every province except Limpopo) (Bierman et al. 2022).

More than 100 tree species – native and exotic – have been confirmed as hosts. Sources differ on the specific number: Mudede et al. report 130 species; Townsend et al. 2025 report 162. Both figures include both hosts that support reproduction of the insect and those that do not.

Mudebe et al. cite other studies that project the Fusarium disease will cause a decline in tree populations over a 10-year period of between 3.5% and 15.5%. They estimate the cost of removing urban trees killed by the disease will be $USD18.45 billion.

The impact in South Africa might differ from other invaded areas. Mudebe et al. report that over the five years of the study none of the Platanus species or A. buergerianum was dying despite being heavily infested. They say this suggests that trees can survive for more than 5 years.

Townsend et al. present a more disturbing picture. Their study examined PSHB impacts in plots in native forests in two provinces — KNZ (where PSHB first detected) and Western Cape. Over five years, PSHB invaded seven forest types; the only forest type not invaded was mangroves. PSHB colonization was detected on 43 native tree species. Eighteen species were recorded as competent hosts (able to support PSHB reproduction), eight as kill-competent hosts (can be killed by PSHB).

Over the five years 11 individual trees belonging to seven species died as a result of PSHB infestations.  Some died very rapidly (within 2–5 years of first infestation); some died after apparently minor levels of infestation.

Each year of the study trees had a 7.5% increased chance of PSHB infestations; the number of entrance holes rose by over 10%. This means – no surprise – that the longer PSHB is active in the enviro the more trees it will infest, the higher its impact will be on hosts, & the higher the # of dispersing individuals produced. This will substantially increase the chances & rates of additional areas becoming infested, especially in areas close to infestation borders. Townsend et al. state that PSHB populations might be increasing exponentially – as occurred in California and Israel.

Townsend et al. discuss factors that might explain differing levels of infestation. Currently, a higher proportion of trees in the study plots in KwaZulu-Natal were infested than in the plots in Western Cape. The most likely explanation is that PSHB established there first – before 2012 compared to possibly five years later in the Western Cape. Other factors might be that source populations in the Western Cape were often found in alien tree species in urban areas distant from the study plots, while in KwaZulu-Natal, the beetles were frequently found in indigenous trees within monitoring plots. Forests in KZN are also fragmented, unlike the nearly contiguous woodlands in the Western Cape, and closer to urban areas with high PSHB infestation levels.

Although the PSHB’s spread into natural forests seems to be slow, Townsend et al. warn that they expect an increase in the rate of infestations as progressively more competent host individuals are infested. They fear severe ecological effects from rapid mortality of some key tree species, especially those sensitive to comparatively few attacks. They mention the native Erythrina caffra (coral tree), which is an important component of coastal forest ecosystems, especially in KwaZulu-Natal.

Other native trees at particular risk of PSHB infestations are Diospyros glabra, Ficus, Sparmannia africana, Trichelia emetic, and Vepris lanceolata. Townsend et al. remind us that each native tree species has a specific role in normal ecosystem functioning and supports a unique suite of species. Even if attacked trees do not die, Fusarium infection might weaken them, thereby increasing their susceptibility to other pathogens and pests, decreasing their longevity, or reducing their ability to produce fruits and flowers which can have long-term direct & indirect effects on normal ecosystem functioning & resilience.

Remember, South Africa is a biodiversity hotspot, home to its own Floral Kingdom!

The South Africans are trying to find more efficient methods for tracking spread of PSHB. Mudede et al. 2025 tested whether Google street view (GSV) images can be used to monitor its spread in urban forests. The test took place in Johannesburg. The test demonstrated that GSV images can be useful for mapping and monitoring PSHB-FD infestation on Platanus trees – but not on trees with rougher bark, e.g., Acer.  While there were no false positives for any host species, most of the maple trees were misclassified as non-infested (false negatives).

Vietnam

Even in its native range, PSHB is a threat – in this case, to plantations utilizing non-native or exotic tree species. Thu et al. describe a growing number of pests threatening reforestation efforts in Vietnam. Surveys over the period 2011 to 2020 revealed outbreaks by 14 new insect species and 2 pathogens. Only two of the trouble-causing species are themselves non-native to Vietnam. One of these is PSHB. Thu et al. report the species’ range has spread rapidly in the country.

Thu et al. inform us that Vietnam has a high diversity of forest trees – and that almost nothing is known about pests that attack these trees.

I welcome their call for higher investment in selection and breeding of hosts resistant to the various pests.  The limited effort so far has identified provences of Neolamarckia cadamba and Nauclea orientalis that display some resistance to PSHB. Thu et al. advocate breeding programs to address the main biotic threats. They also recommend several actions to improve biosecurity, including enhanced hygiene in tree nurseries; improved silvicultural practices to minimize damage to trees; diversification of tree species being grown; and strengthening biosecurity and quarantine programs. They note that early detection of pest outbreaks is critical, so the country should develop forest health monitoring protocols for extensive forest reserves – sentinel plantings and remote sensing to detect trees under stress.

On a personal level, I found it interesting that Mudede et al. report that Google street view imagery determined that the invasive tree Ailanthus altissima dominates the street tree population in Istanbul – despite not having been intentionally planted. I visited Istanbul in April – and saw evidence of invasive vines and possibly the North American tree Cercis canadensis.

SOURCES

Ceriani-Nakamurakare, E., A.J. Johnson, D.F. Gomez. 2023. Uncharted Territories: First report of Euwallacea fornicates (Eichhoff) in South America with new reproductive host records. Zootaxa, 5325 (2), 289-297. https://doi.org/10.11646/zootaxa.5325.10

Mudede, M.F., S.W. Newete, K. Abutaleb, M.J. Byrn. 2025 Monitoring a polyphagous shot hole borer infestation in an urban forest using Google street view in the City of Johannasburg, South Africa Biol Invasions (2025) 27:144         https://doi.org/10.1007/s10530-025-03595-4

Thu, P.Q., D.N. Quang, N.M. Chi, T.X. Hung, L.V. Binh, B. Dell. 2021. New and Emerging Insect Pest and Disease Threats to Forest Plantations in Vietnam. Forests 2021, 12, 1301. https://doi.org/10.3390/f12101301

Townsend, G., M. Hill, B.P. Hurley, and F. Roets. 2025 Escalating threat: increasing impact of the polyphagous shot hole borer beetle, Euwallacea fornicatus, in nearly all major South African forest types. Biol Invasions (2025) 27:88 https://doi.org/10.1007/s10530-025-03551-2

Winzer, L.F, K.T. Faulkner, T. Paap, and J.R.U. Wilson. Preprint. From detection to action—a proposed workflow to ensure first reports of alien spp from molecular analyses are acted upon DOI: https://doi.org/10.3897/arphapreprints.e162421

Pest-lens link:  https://pestlens.info/

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

https://fadingforests.org

One of the pathways is wooden handicrafts – identified as a pathway more than a decade ago but only partially regulated. The other is new: wood used to decorate aquaria. Two new papers demonstrate that both carry multiple and diverse taxa of fungi. At least 30 have never been detected before in the US. They include both plant and human pathogens.  

Both sets of authors call on the U.S. Department of Agriculture to remedy ineffective regulations. However, it appears unlikely that APHIS will be able to do so now, when its budget and staff are being cut. (Lawsuits might restore some of these resources.) Extending APHIS’ authority to regulate organisms that are not plant pests would require Congress to adopt new legislation.

Live Pathogens Imported in Wooden Handicrafts

In 2022, Jason Smith and others (full citation at the end of this blog) published an analysis of the viability and diversity of fungi brought to the U.S. in imported wooden handicrafts. They isolated 47 fungal taxa originating from at least seven countries on three continents. All remained viable despite being subjected to various phytosanitary requirements. Fourteen were plant pathogens; 17 were human pathogens; several were producers of mycotoxins. Three taxa have not been reported before in North America: Bipolaris austrostipae, Paecilomyces formosus, and Xylaria badia. All three are plant pathogens. P. formosus is a human pathogen as well.

Three quarters of the taxa have tolerances that would increase their likelihood of surviving standard heat or fumigation treatments.

Smith et al. point out that wood from sources other than China are subject only to general permit requirements outlined here. Only if pests are detected during port inspections are quarantine actions taken.

APHIS has certified more than a thousand Chinese exporters of handicrafts that incorporate wood, straw, or other biological components. APHIS encourages importers to buy products from these businesses. However, importers may choose other sources. In that case, the product must be treated before entry.

However, as Smith et al. point out, regulation and treatments are focused on arthropods. They do not address the risk from disease pathogens. Smith et al. conclude that these regulations are insufficient to protect plants from damage.

A second issue is that USDA has no authority to regulate organisms that pose a risk to non-plant hosts, including humans. This is especially worrying in this case because many of the handicrafts being intended for food preparation and distribution. Others are handled by purchasers during crafting activities, or used in bath and beauty products.

Live Fungi Imported in Decorative Wood for Aquaria

A second study has expanded the types of material raising concern. The Minnesota Invasive Terrestrial Plant and Pests Center sponsored research that confirms that pieces of wood imported to decorate aquatic and terrestrial aquaria support live fungal-like organisms. The scientists worry that the wood – and the organisms it harbors – might be discarded in a way that facilitates escape and establishment of these organisms. Another possible route of escape is if the water from these mini-habitats is dumped into surface waters.

Blanchette, Rajtar, Lochridge and Held (2025; full citation at end of this blog) obtained 44 samples of such wood from on-line sellers. Some samples had evidence of fungal infestation. Many of the wood pieces were extensively degraded, with large holes, some of which held mud or sand.

The scientists isolated 202 cultures representing 123 fungal taxa in the Ascomycota, Basidiomycota, and Mucoromycota. They detected no Oomycota. The organisms included 30 or 31 species that have not previously been reported in the United States. Twenty-one species are potential plant pathogens, 37 species are wood decay fungi. Twenty-four taxa appear to be previously unknown.

The origins of the wood pieces have not been revealed by the sellers. The scientists believe wood might have come from China, Vietnam, Thailand, and possibly other Asian countries.

Blanchette et al. note that many fungal-like pathogens that have caused devastating diseases in North American forests came from Asia, although not all were introduced directly from there. They name as examples chestnut blight, white pine blister rust, Dutch elm disease, Port-Orford cedar root disease, sudden oak death, and laurel wilt. [Brief descriptions of all these diseases can be found here.] These past introductions occurred via transport of soil, timber, wood products, living trees, or other plant material.

Blanchette et al. cite Smith et al. regarding detection of novel fungal pathogens of both plants and people on imported wooden handicrafts. They cite Brasier, Jung, and others for the likely Asian origins of many Phytophthora species (see citations at the end of this blog). They note the risk associated with the many undescribed species found in that region. In agreement with many others, Blanchette et al. suggest that fungal pathogens pose a very high risk for the U.S. due to rapid emergence of new diseases, low resistance in host populations, and limited surveillance infrastructure for detection.

The Blanchette et al. study was prompted by detection of Xylaria apoda growing on wood submerged in aquariums located in two states which are quite far from each other – Minnesota and Colorado. Despite the pieces of wood having been dried, shipped and stored for a long period during the import process, the fungus remained viable and was producing fruiting bodies. In total, they isolated eight species as known pathogens of agricultural crops and trees. They also report other fungi that might have potential to be plant or human pathogens. Blanchette et al. express specific concerns about possible impacts of the saprophytic taxa on ecosystem functions. That is, wood decay communities could be adversely affected by changes to biomass degradation and native wood-inhabiting insects.

Blanchette et al. point out that their detections came from 44 samples, which represent a very small fraction of the wood being imported for these purposes. Nevertheless the researchers detected impressive quantities and diversity of viable fungi.

Although they did not isolate any Oomycota species, Blanchette et al. say the presence of mud and soil indicates this type of wood could be a pathway for introduction of various exotic Phytophthora – which reside in aquatic and wet soil environments. They call for additional sampling and investigation using more selective methods of isolating Phytophthora species to determine if this could be a successful avenue for importing species of plant pathogenic Oomycota.

Blanchette et al. recommend that people who purchase wood for aquaria repeatedly soak and rinse the wood in water before putting it into an aquarium. This helps eliminate some of the heartwood extractives from the tropical woods and reduces water discoloration in aquariums, as well as possible toxicity to fish and plants. They warn that disposal of the water in contact with this wood into waterways or outdoors could easily release fungal species or Phytophthora spp. that might be in the wood.

Blanchette et al. say their results support earlier indications that current regulations to prevent the importation of non-native fungi on decorative woods used in aquariums are ineffective. In this investigation alone, they cultured more than 100 different live taxa that survived any fumigation or sterilization treatment. They note that scientists have repeatedly called for stronger phytosanitary regulations on imported wood.

One important step they suggest is increasing biosurveillance at the global level. They also suggest prohibiting importation of fungi and fungal-like organisms via this pathway before they become serious problems in their new environment. I concur with these suggestions – with the caveat that while the importation ban is in effect, APHIS and other agencies with authority over invasive species threats to non-plant resources should assess the risks and identify what steps each should take to address them.

[For the history of earlier critiques of weak regulation of imported wood, see blogs on this site under the category “wood packaging” and Fading Forest reports Two and Three (links at the end of this blog). For my critique of regulation of pathogens, see here or contact me.

SOURCES

Blanchette, R.A., Rajtar, N.N., Lochridge, A.G. et al. 2025. Intercontinental movement of exotic fungi on decorative wood used in aquatic and terrestrial aquariums. Scientific Reports 15, 9142. https://doi.org/10.1038/s41598-025-94540-x

Smith, J.A., T. Quesada, G. Alake, N. Anger. 2022. Transcontinental Dispersal of Nonendemic Fungal Pathogens through Wooden Handicraft Imports. mBio July/August 2022 Volume 13 Issue 4 10.1128/mbio.01075-22

Background sources

Brasier, C. M. 2008. The biosecurity threat to the UK & global environment from international trade in plants. Plant Pathol. 57, 792–808.

Brasier, C. M., Vettraino, A. M., Chang, T. T. & Vannini, A. 2010. Phytophthora lateralis discovered in an old growth Chamaecyparis forest in Taiwan. Plant. Pathol. 59, 595–603.

Jung, T., B. Scanu, C.M. Brasier, J. Webber, et al. 2020. A survey in natural forest ecosystems of Vietnam reveals high diversity of both new & described Phytophthora taxa including P. ramorum. Forests 11, 93.

Jung, T., Horta Jung, M.; Webber, J.F. et al. 2021. The destructive tree pathogen Phytophthora ramorum originates from the Laurosilva forests of East Asia. J. Fungi 7, 226.

Jung, T., Milenković I, Balci Y,  et al. 2024 Worldwide forest surveys reveal forty-three new spp in Phytophthora major clade 2 with fundamental implications for the evolution & biogeography of the genus & global plant biosecurity. Stud. Mycol. 107, 251-388.

Roy, B. A. et al. 2014. Increasing forest loss worldwide from IAS pests requires new trade regulations. Front. Ecol. Environ. 12, 457–465.

Wingfield, M. J., Brockerhoff, E. G., Wingfield, B. D. & Slippers, B. 2015. Planted forest health: The need for a global strategy. Science 349, 832–836.

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Those of us striving to increase action! to curb bioinvasion have had a hard time demonstrating socio-economic costs sufficiently compelling to prompt adoption of more effective policies. However, see

• Donovan, et al. 2013. The Relationship Between Trees and Human Health. American Journal of Preventive Medicine. Volume 44 Issue 2.
• Fantle-Lepczyk, et al. 2022. Economic costs of biological invasions in the United States. Science of the Total Environment 806 (2022) 151318    

Now, two new papers show how high the costs can be under some circumstances.

Eyal G. Frank compared the rate of infant mortality in counties across the U.S. where insectivorous bats had been severely reduced by whitenose syndrome to that in counties where bat populations were not affected. He found that “internal” infant mortality – defined as deaths not caused by accidents or homicides — rose, on average, 7.9%. An estimated additional 1,334 infants died. [A related finding not directly pertinent to this blog’s purpose: Frank notes that real-world use levels of insecticides have a detrimental impact on health, even when used within regulatory limits.]

Whitenose syndrome (WNS) is caused by Pseudogymnoascus destructans, a fungus native to Europe. It was introduced to North America around the beginning of the 21^st Century. It has spread quickly since its initial detection in 2006. By 2024, populations of 12 of ~ 50 insectivorous bat species in the US have been negatively affected. The fungus has caused an estimated decline of more than 90% in bat populations monitored in hibernating caves (Larson, Engst, and Noack 2024).

This population crash is devastating, especially where pest control is supplied by bats. Individual bats are voracious predators. But, for pest control to succeed, the total population must be high. .  

Frank compiled information at the county level on:

• the spread of white nose syndrome to new counties;
• rates of pesticide application, presuming that higher rates reflected increased insect presence on crops; and
• infant mortality rates.

Larson, Engst, and Noack (2024) call Frank’s findings on infant mortality “shockingly large”. The increase in insecticide application rates was just 2.7 kg/km². These findings show that technological substitutes for suppressed biological services can markedly and adversely affect human well-being.

Both Frank and Larson, Engst, and Noack emphasize the value in demonstrating that declines in biological diversity do have repercussions for human well-being. They call for more expansive and intensive monitoring of biodiversity trends, especially among non-charismatic taxa such as insects. Furthermore, there should be more multidisciplinary studies that integrate social, natural, and health datasets and research methods to distill information of policy relevance.  The Science authors’ expectation is that quantifying these relationships will guide better decisions about conservation policies.

All the authors devote considerable attention to the difficulty in establishing these links because scientists cannot manipulate large-scale ecosystems to conduct experiments. They recommend taking advantage of natural experiments – such as tracking the spread of a newly introduced disease that kills large proportions of a taxon that provides demonstrated ecosystem services. Frank studied the loss of insectivorous bats. Larson, Engst, and Noack (2024) mention an earlier study of the collapse of amphibian populations in Central America caused by the fungal pathogen Batrachochytrium dendrobatidis. One result in this case was an increase in the incidence of malaria.

Frank and Larson, Engst, and Noack clearly hope that this approach will promote stronger and more targetted biodiversity conservation policies and programs. I hope they are right!  But did enough Americans hear about these results? I heard a report on “BBC America” radio. I searched and found a print report published by Vox – which connected me to Science. How do we expand media coverage of this type of information?

SOURCES

Frank, E.G. 2024. The economic impacts of ecosystem disruptions: Costs from substituting biological pest control. Science. 6 Sep 2024 Vol 385, Issue 6713 DOI: 10.1126/science.adg0344

The economic impacts of ecosystem disruptions: Costs from substituting biological pest control | ScienceThe econ impacts of ecosystem disruptions: Costs from substituting biological pest control | Science

Larson, A.E., Engist, D., Noack, F. 2024. The long shadow of Biodiversity loss: Technological substitutes are poor proxies for functioning ecosystems. Science 5 Sep 2024 Vol 385, Issue 6713 pp. 1042-1044 DOI: 10.1126/science.adq2373 The long shadow of BD loss | Science 

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Recently, plant pathologists have paid more attention to pathogens — native to eastern North America — now killing trees on the West Coast. Years ago, the likelihood of such “domestic invaders” was hotly debated. However, these new detections provide examples of native micro-organisms that are apparently benign in the ecosystems in which they evolved, but that cause disease when moved to relatively nearby — but naïve — environments. I would argue that it is the absence of co-evolution of pathogen and host, not distance, that matters. In both cases, environmental stress on the trees appears to play a significant role. Such stress is expected to increase as the climate changes.

[In the past, these issues arose re: goldspotted oak borer – introduced to California from Arizona; and thousand cankers disease – introduced from Arizona to Western states and now to the East.]

Little is known about these diseases. So far, scientists have examined the pathogens’ impacts more thoroughly on plantings that are introduced to the location, so already outside of the forest biomes in which they evolved. Less attention has been paid to hosts native to the regions newly affected. I find this disturbing because I am most concerned about the possible impact to native ecosystems.

I will describe two such diseases. Both attack native tree species, not just the exotic trees described in research. Both were first detected in the Pacific Coast states in the late 1960s – i.e., more than 50 years ago. Why are they becoming prominent now – is it changes in the climate? Evolution? Just slow adaptation?

Example One – Sooty Bark Disease

Sooty-bark disease (Cryptostroma corticale) of maples (Acer spp.) is native to the Great Lakes region, where it causes no problems. However, it has been introduced to the West Coast, where all sources agree that the disease kills trees stressed by heat and drought. These stresses are expected to increase as the climate changes.  The disease is also a serious threat to human health. The fungus’ spores can cause serious pulmonary disease in humans. 

Sooty bark disease was detected in Pullman, Washington, near the Idaho border, in 1968. Now it is more widespread: it was detected in the Seattle area as of 2020 and the Sacramento area of California in 2019 [Curtis Ewing pers. comm.]. Sooty-bark disease has also spread to at least ten countries in Europe, ranging from the United Kingdom to Italy and Bulgaria.

Sources in Washington say hosts include several non-native species widely planted in the area – sycamore maples (Acer pseudoplatanus) [Chastagner], Norway maples (Acer platanoides), Japanese maple (A. palmatum), and horsechestnut (Aesculus hippocastanum) [Chastagner and Washington State University]. More troubling is the fact that several native tree species are also hosts. Big leaf maple (A. macrophyllum), and Pacific dogwood (Cornus nuttallii) are among the most significant. [Big leaf maple is a large hardwood tree in a region dominated by conifers. Pacific dogwood has already been decimated by the introduced disease dogwood anthracnose.] Sources in California add two other maples, these native to eastern North America, red (A. rubrum) and silver (A. saccharinum) maples.

The fungus initiates infection in a tree’s small branches, then spreads into the heartwood and both up and down the tree. It might also invade pruning wounds. The fungus grows more rapidly at higher temperatures. It is also facilitated by drought stress. When the fungus grows out to the bark, it causes the bark to blister; it then forms spore-forming structures. The spores are dispersed by wind. (Chastagner)

Washington State University’s Ornamental Plant Pathology division has called for more research on all aspects of the disease in trees:  

• Distribution and spread of the disease;
• Plant species susceptibility and host range;
• Diagnostic methods and molecular approaches to improve diagnostic efficiency and capacity;
• Pathogen life history and genetic diversity;
• Factors that affect disease development and vulnerability (site, stress, age of host, etc.);
• Potential of human mediated dispersal and vectors such as pruning tools;
• Best management practices and worker protection.

So far, little has been done. Scientists in the Pacific Northwest have received a small amount of funding from the USDA Forest Service Forest Health Protection Emerging Pests program link + blog on appropriations to increase diagnostic services and to surveys trees elsewhere in the Puget Sound region.

Example Two – Bacterial Pathogen on Oaks

There is always concern about threats to oaks (Genus Quercus) because of their ecological, economic, and social importance. As Kozhar et al. point out, this genus is one of the most important groups of trees in many regions of the Northern Hemisphere. In North America specifically, oak forests compose a significant part of many forest ecosystems, especially in the East. California has 20 native species, Colorado has one. In addition, oaks are also often planted as shade trees in urban environments, which has resulted in movement of oak species to new geographic areas. There where they experience different environmental conditions, they might find new pests or alert us to the effects of climate change.

The bacterial oak pathogen Lonsdalea quercina is indigenous to the native range of northern red oak (Quercus rubra) in eastern North America. There, it does not cause disease in its co-evolved host. However, it has recently caused two outbreaks in the West – in California and Colorado. In the latter, trees themselves can die; in the former, acorns are damaged, threatening forest regeneration. Other Lonsdalea species have caused similar tree diseases in Europe.

California

In California, the bacterium has been present since at least 1967. It infects acorns of native oaks, including coast live oak (Q. agrifolia), Q. parvula (presumably the mainland subspecies, also named Q. p. var. shrevei),and interior live oak (Q. wislizeni).  The Morton Arboretum link says Q. parvula (presumably – again – the mainland subspecies) is currently threatened by sudden oak death (SOD). Coast live oak has also been highly affected by sudden oak death (SOD), DMF but it is not considered to be threatened. I expect – but sources don’t say – that the bacterium is affecting these species’ reproduction.

Various genotypes of L. quercina are randomly distributed across trees in both native and human-altered habitats and among all host species. Kohzar et al. say this is not surprising since all the host oak species are native to the region. Coast live oak is a major component of native forests and is also widely planted as a shade tree in residential areas. Furthermore, there has been no attempt to restrict the pathogen’s movement by adopting quarantines or other measures by phytosanitary agencies.

As a result, the inoculum can be moved across large distances by insects, birds, small mammals, and humans.

Bacterial pathogens can be associated with insects, relying on their feeding sites and other wounds to facilitate entry to the host’s tissues or for dissemination among hosts. In California, L. quercina might enter host tissue via wounds made by acorn weevils, filbertworms, and some cynipid wasps Kohzar et al.).

Colorado

The situation in Colorado is different. Significant dieback of exotic oaks planted in the state came to attention in the early 2000s. The hosts include non-native northern red oak, pin oak (Q. palustris), and Shumard oak (Q. shumardii). In Colorado, the bacterium causes “drippy blight disease” on the trees, not the acorns. The disease causes abundant ooze on symptomatic tissue. There has been a significant increase in tree mortality – with associated removal costs. The bacterium also has been found attacking Colorado’s one native oak, Q. gambelii; in this case, the pathogen attacks the acorns rather than the tree.

Due to small sample sizes, Kohzar et al. were unable to answer three key questions:

• whether the Colorado L. quercina population comprises a new taxonomic species;
• whether genetic variation in the bacterial populations are explained by the habitat (native or human-altered) or host; and 
• whether the L. quercina infections on native Q. gambelii serves as an inoculum reservoir for planted Q. rubra hosts or vice versa.

Surprisingly, despite its more recent emergence, the Colorado population of L. quercina has higher genetic diversity. Kohzar et al. suggest this might be due to repeated introductions of the bacterium on nursery stock brought in from the northern red oak’s native range in the East. [see below]

As in California, L. quercina infections are associated with insects, especially kermes scale (Allokermes galliformis). This insect does not travel long distances, which might help explain why the Colorado genotypes are limited to nearby trees, not dispersed randomly as in California.

However, kermes scale has been present in the state for far longer than the disease. The scale’s population spiked at the same time as the drippy blight outbreak was detected. Kohzar et al. could not determine whether the rise in scale populations and associated increase in number of entry points through feeding sites led to the increase of bacterial populations, or vice versa.

Kohzar et al. did determine that the Colorado populations of L. quercina were not introduced from California. They cannot explain the original introduction but think there might be continuing introductions from the native range of both northern red oak and L. quercina – the northeastern United States. They call for further studies to understand evolutionary relationships among L. quercina populations from different areas, including the native habitat of red oak in the East to clarify possible causes and sources of the recent outbreak of drippy blight in Colorado.

Role of Environmental Conditions

Kohzar et al. stress the importance of factors other than species’ introductions to new environments as the cause of emerging forest diseases. They say such other factors as changes in environmental conditions, new host-vector associations, cryptic disease agents (e.g., pathogens with a very long latency period or endophytes changing their behavior to pathogenic), hypervirulent strains of known pathogenic species, and/or newly emerging species of unknown origin as key factors leading to disease emergence in forest ecosystems around the globe.

In the case of L. quercina in California and especially Colorado, Kohzar et al. point to stress on the trees caused by new environmental factors, e.g., rapid climate change. [Of course, oaks from humid regions of eastern North America are already outside their natural habitat in much-dryer Colorado.] They support this conclusion by noting the simultaneous appearance of four new diseases caused by Lonsdalea species in different parts of the world during the 1990s and early 2000s. These were Lonsdalea quercina in Colorado; L. britannica on oaks in Great Britain; L. iberica in Spain; and L. populi bark canker on poplar species in Hungary, China, and Spain. All cause similar symptoms of drippy blight disease.

SOURCES

Chastagner, Gary. Professor, Plant Pathology, Washington State University. https://pnwhandbooks.org/plantdisease/host-disease/maple-acer-spp-sooty-bark-disease

Ewing, Curtis. Entomologist, CalFire. Pers. comm. March 2023.

Kozhar, O., R.A. Sitz, R. Woyda, L. Legg, J.R. Ibarra Caballero, I.S. Pearse, Z. Abdo, J.E. Stewart. 2023. Population genomic analysis of an emerging pathogen Lonsdalea quercina affecting various species of oaks in western North America. BioRxiv  https://www.biorxiv.org/content/10.1101/2023.01.20.524998v1

Washington State University Ornamental Plant Pathology https://ppo.puyallup.wsu.edu/sbd/

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

Environmental Entomology, in partnership with other journals from the Entomological Society of America, has published a special collection of papers on the spotted lanternfly, Lycorma delicatula. All papers in the collection are freely available to read and download through February 16, 2022. I will summarize key points, with brief references to the specific article.

The papers are available at https://academic.oup.com/ee/pages/research-on-spotted-lanternfly 

Areas at Risk

 As this map shows, the spotted lanternfly (SLF) is thought able to establish in more than 26 states. 

Source: T.T Wakie et al., 2020. The Establishment Risk of Lycorma delicatula (Hemiptera: Fulgoridae) in the United States and Globally. Journal of Economic Entomology, Volume 113, Issue 1, February 2020, Pages 306-314,  https://doi.org/10.1093/jee/toz259

Host Trees

SLF prefers the invasive tree species, Tree of Heaven (Ailanthus altissima), especially for oviposition. Ailanthus is widespread, so this is not very limiting. However, the SLF can complete its life cycle in the absence of this host. [O. Uyi et al. 2020. Spotted Lanternfly (Hemiptera: Fulgoridae) Can Complete Development and Reproduce Without Access to the Preferred Host, Ailanthus altissima. Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 1185–1190, https://doi.org/10.1093/ee/nvaa083]

Spotted lanternflies have been recorded as feeding on at least 56 plant species in North America and 103 plant species worldwide; most are shrubs, trees, or stout vines. [L. Barringer and C.M. Ciafré. 2020. Worldwide Feeding Host Plants of Spotted Lanternfly, With Significant Additions From North America. Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 999–1011, https://doi.org/10.1093/ee/nvaa093]

SLF aggregates on tree-of-heaven by its adult stage. However, egg masses are found on 24 types of substrates with tree-of-heaven, black cherry, black birch, and sweet cherry. [H. Liu. 2019. Oviposition Substrate Selection, Egg Mass Characteristics, Host Preference, and Life History of the Spotted Lanternfly (Hemiptera: Fulgoridae) in North America. Environmental Entomology, Volume 48, Issue 6, December 2019, Pages 1452–1468, https://doi.org/10.1093/ee/nvz123]

An evaluation of spotted lanternfly survivorship on 26 host plant species in 17 families found that eight species supported development from first instar to adult: black walnut, chinaberry, oriental bittersweet, tree-of-heaven, hops, sawtooth oak, butternut, and tulip tree. When offered a choice between black walnut and tree-of-heaven, nymphs showed no preference; adults showed a significant preference for tree-of-heaven. [K. Murman et al. 2020. Distribution, Survival, and Development of Spotted Lanternfly on Host Plants Found in North America. Environmental Entomology, Volume 49, Issue 6, December 2020, Pages 1270–1281, https://doi.org/10.1093/ee/nvaa126]

Dispersal

Spotted lanternfly nymphs (all instars) usually moved only short distances over a 7-day period, but a few were discovered 50-65 meters away. [J.A. Keller et al. 2020. Dispersal of Lycorma delicatula (Hemiptera: Fulgoridae) Nymphs Through Contiguous, Deciduous Forest. Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 1012–1018, https://doi.org/10.1093/ee/nvaa089]

Detection – Traps & Lures

A test of 43 host plant volatiles found 11 to be significantly attractive. [N.T. Derstine et al. 2020. Plant Volatiles Help Mediate Host Plant Selection and Attraction of the Spotted Lanternfly (Hemiptera: Fulgoridae): a Generalist With a Preferred Host. Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 1049–1062, https://doi.org/10.1093/ee/nvaa080]

A comparison of several trap types found that circle traps caught more SLF than sticky bands, and fewer non-target organisms. Traps placed on the trunks of trees caught more SLF than traps placed in the tree canopy.  [J.A. Francese, et al. 2020. Developing Traps for the Spotted Lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae). Environmental Entomology, Volume 49, Issue 2, April 2020, Pages 269–276, https://doi.org/10.1093/ee/nvz166] In one study, addition of a lure containing methyl salicylate did not increase captures. [L.J. Nixon, et al. 2020. Development of Behaviorally Based Monitoring and Biosurveillance Tools for the Invasive Spotted Lanternfly (Hemiptera: Fulgoridae). Environmental Entomology, Volume 49, Issue 5, October 2020, Pages 1117–1126, https://doi.org/10.1093/ee/nvaa084] his contradicted an earlier study that suggested that traps with high release methyl salicylate lures did capture more SLF. [M.F. Cooperband, et al. 2019. Discovery of Three Kairomones in Relation to Trap and Lure Development for Spotted Lanternfly (Hemiptera: Fulgoridae). Journal of Economic Entomology, Volume 112, Issue 2, April 2019, Pages 671–682, https://doi.org/10.1093/jee/toy412]

Potential Controls: Parasites, Parasitoids, and a Pathogen

Significant efforts are afoot to find possible biocontrol agents. Scientists have surveyed SLF and associated parasites/parasitoids across 27 provinces and administrative regions of China from 2015 to 2019. They recovered an egg parasitoid, Anastatus orientalis, and a nymphal parasitoid, Dryinus sinicus, and are studying these further as potential biological control agents of spotted lanternfly. [B. Xin et al. 2020. Exploratory Survey of Spotted Lanternfly (Hemiptera: Fulgoridae) and Its Natural Enemies in China  Environmental Entomology, nvaa137, https://doi.org/10.1093/ee/nvaa137]

The egg parasitoid Anastatus orientalis has the advantages of being easy to rear and long lived. Research is under way to tests its host specificity. [H.J. Broadley et al. 2020. Life History and Rearing of Anastatus orientalis (Hymenoptera: Eupelmidae), an Egg Parasitoid of the Spotted Lanternfly (Hemiptera: Fulgoridae). Environmental Entomology, nvaa124, https://doi.org/10.1093/ee/nvaa124]

The spotted lanternfly leaves behind a chemical trail when walking – a trail which the parasitoid wasp Anastatus orientalis uses to locate the host’s eggs. [R. Malek et al. 2019. Footprints and Ootheca of Lycorma delicatula Influence Host-Searching and -Acceptance of the Egg-Parasitoid Anastatus orientalis [Environmental Entomology, Volume 48, Issue 6, December 2019, Pages 1270–1276, https://doi.org/10.1093/ee/nvz110]

The established gypsy moth egg parasitoid Ooencyrtus kuvanae has been observed attacking SLF egg masses in the field. [H. Liu and J. Mottern. 2017. An Old Remedy for a New Problem? Identification of Ooencyrtus kuvanae (Hymenoptera: Encyrtidae), an Egg Parasitoid of Lycorma delicatula (Hemiptera: Fulgoridae) in North America. Journal of Insect Science, Volume 17, Issue 1, January 2017, 18, https://doi.org/10.1093/jisesa/iew114]

Single applications of the insect pathogenic fungus Beauveria bassiana strain GHA killed 43-48% of spotted lanternflies on preferred host plants in a park. Adult spotted lanternflies feeding on potted grapevines were sprayed with the same fungus, resulting in 100% mortality after 9 days. [E.H. Clifton, et al. 2020. Applications of Beauveria bassiana (Hypocreales: Cordycipitaceae) to Control Populations of Spotted Lanternfly (Hemiptera: Fulgoridae), in Semi-Natural Landscapes and on Grapevines Environmental Entomology, Volume 49, Issue 4, August 2020, Pages 854 – 864, https://doi.org/10.1093/ee/nvaa064]

control of multiflora rose

Nancy Dagli, USDI National Park Service, Bugwood.org

 

Nearly two years ago I posted a blog based on a study by Christopher Oswalt and colleagues (2016; source/link provided at end of blog) using data from the national Forest Inventory and Analysis (FIA) program of the United States Forest Service to determine what proportion of American forests are invaded by non-native plants. Nationwide, 39% of forested plots sampled contained at least one invasive species. Eastern forests are second in the density of invasive plants to Hawai`i, with 46% of plots invaded by at least one plant species.

FIA sampling plots are randomly located across the country. Plots are inventoried once every 5–7 years in the eastern U.S. and once every 10 years in the western U.S. The program inventories only plots that are at least 10% stocked by trees. Phase 2 (P2) plots represent approximately 6,000 acres; Phase 3 (P3) plots represent about 96,000 acres, except in some states and National Forests where there is a regional intensification of plots. Invasive plant species are measured on a subset of the field plots – on the P2 invasive plots, invasive plants of interest are recorded; on the P3 plots, all plant species (invasive, exotic, and native) are recorded.

The US Forest Service Northern Region (Region 9) has issued a report providing details for 50 invasive plant species on plots in the 24 states of the Region. (These states reach from Maine to the Dakotas, south to Kansas, then across to Delaware.) For this report, in states where both P2 invasive and P3 data were collected, the invasives data from the P3 plots were folded into the P2 invasive plots. When there were no P2 invasive plots for a particular inventory or species, the IPS data were calculated solely from P3 plots. In addition, the taxa reported varied over time and in some cases from state to state. Finally, the inventories took place over a period of years; the most recent inventories included in the report date from 2010. Presumably, the extent and intensity of plant invasions have increased in the intervening seven years. [The report is posted here.

Given the variety of plots inventoried, changes in taxa recorded, and time lag, the report cannot provide an up-to-date and detailed picture of any one site.  However, it does allow us to get an overall picture that is more detailed than the nation-wide summary provided by Oswalt et al. 2016 and reported in Faith’s blog from spring 2016.

The report contains a wealth of data on the 50 individual species – a page for each, providing background, characteristics, distribution, monitoring data, and regulatory status in the various states. Also, there are 10 pages of summary tables. Since FIA inventories are conducted on the schedule of five to seven years, future reports based on these “[r]epeated measurements will help determine factors … associated with the presence of these species” and that the data can help “educate individuals of potential risk species”.

 

Our Interpretation

It is unfortunate that the USFS Southern Region has not prepared a similar report so that we could understand the extent of invasion by the individual taxa across the entire eastern deciduous forest. This is especially unfortunate because the Northern Region report found that the number of invasive plant species on a plot is higher in the southeastern portion of the Region (i.e., the states of West Virginia, Maryland, and Delaware). The arbitrary boundary between the Northern and Southern regions prevent our getting a true regional picture for the Mid-Atlantic states. The Oswalt et al. 2016 summary does allow some comparisons.

Still … we found it striking that seven of the 15 invasive plant species ranked highest in terms of proportion of plots invaded are shrub or vine species that were deliberately planted for improving wildlife habitat, horticulture, or other purposes.

 

Detailed Findings

The report does not state the proportion of all survey plots invaded by at least one invasive plant species for the region as a whole. Table 3 does report the proportion of plots in specific states. This varies from a high of 93% of plots in Ohio to a low of about 11% in Minnesota and New Hampshire. Several other Midwestern states also experience high levels of invasion: Iowa 81%, Indiana 79%, Illinois 72%, and Missouri 46%. Plots in Mid-Atlantic states and southern New England also are heavily invaded: West Virginia 79%, Maryland 65%, Pennsylvania 61%, Connecticut 54%, Rhode Island 51%, New York 49%, New Jersey 48%, Delaware 47%, Massachusetts 44%. In general, states in the far north have lower rates of invasion, like Minnesota and New Hampshire (above): Vermont 18%, South Dakota 15%, Michigan 14%, Maine 12%. However, North Dakota, at 29%, and Wisconsin, at 28%, differ from this generalization.

The most frequently recorded invasive plant is multiflora rose. According to the report, it is present in 39 states and five Canadian provinces. Across the region, multiflora rose is present on 16.6% of surveyed plots. It is the most common invasive plant in 10 of the 24 states of the region. It is almost ubiquitous in some states; in Ohio 85% of the plots were invaded. Oswalt reports that “roses” were the third most common invasive plants in the USFS Southern Region.

The third most frequently recorded invasive plant species is garlic mustard. It is reported to be present in 36 states and five Canadian provinces. Across the region, garlic mustard is present on 4.5% of the surveyed plots. Several states report high levels of infestation. In Ohio, garlic mustard is present on 30% of the plots; in Maryland, on 27% of the plots; in Pennsylvania, on 22% of the plots; in New Jersey, on 20%.

The fourth most frequently recorded invasive is common or European buckthorn. It is reported to be present in 34 states and eight Canadian provinces. Buckthorn is present on 4.4% of survey plots across the northeastern region – about a quarter of the plots on which multiflora rose is found. The highest proportion is in New York, where the invasive shrub is found on 16.8% of the plots.

Several bush honeysuckles rank high in the survey. Because of their close relationship and similar ecological impacts, we will discuss them together. Morrow’s honeysuckle is the fifth most commonly detected invasive plant species. This species is found on 3.8% of plots across the region. Amur honeysuckle ranks tenth; it is found on 3.1% of plots. Tatarian honeysuckle ranks sixteenth; it occurs on 1.5% of plots across the region. The hybrid showy fly, or Bell’s, honeysuckle ranks eighteenth; it occurs on 1.1% of plots. The data do not indicate whether there is much overlap in the plots invaded by the various species, so we cannot determine an overall invasion extent for bush honeysuckles – although clearly they occupy a significant proportion of the forest of the region. If there is almost no overlap, bush honeysuckles occupy 9.5% of all surveyed plots – second only to multiflora ros. During the first year of the survey, bush honeysuckles were recorded by genus – but only in four Midwestern states. In that survey, the genus was found on 6.5% of the plots surveyed.

The sixth most frequently recorded plant species is also an Asian honeysuckle – the vine Japanese honeysuckle, which is found on 3.6% of survey plots across the region. Oswalt et al. 2016 report that Japanese honeysuckle is the most common invasive plants in forests in the Southern region.

The second and seventh most frequently recorded plant species are native to parts of the region surveyed – although they have spread. These are black locust and reed canarygrass. We are confused as to how many of the reported plots actually represent invasions by these species since several states with high proportions of plots bearing black locust, for example, are in or next to the Appalachian mountains and the Ozarks, where the species is native.

The eighth and eleventh most frequently recorded invasive plant species are thistles — Canada thistle is eighth, bull thistle is eleventh. Both are found in more than 40 states and all 10 of the Canadian provinces. Each is present on approximately three percent of the plots, with concentrations in the upper Midwest.

The ninth and twelfth highest ranking invasive plant species in the region are additional shrubs which were deliberately planted for various purposes. Autumn olive ranks ninth; it occurs on approximately three percent of plots across the region. It is particularly dense in West Virginia, where it occurs on one fifth of all plots surveyed. Japanese barberry ranks 12^th. It occurs on 2.4% of the plots across the region. In Connecticut, barberry is found on one-third of the plots.

The thirteenth most common species is common burdock – found on 2.2% of the plots. Again, the highest densities are found on forest plots in the upper Midwest along the edge of the prairie.

The fourteenth most commonly reported species is Nepalese browntop or Japanese stiltgrass. Stiltgrass has spread without much artificial assistance. Although stiltgrass is more common in the Southeast (outside the study region), it still occupies 2.1% of surveyed plots in the Northern region. Owald et al. 2016 report that stiltgrass is the fifth most common invasive plant in the Southern region.

Additional Studies Needed

• The USFS Northern and Southern regions should coordinate their reports so that at least some use compatible methods and combine their findings so can see the picture for the entire Eastern forest.
• USFS scientists should collaborate with other programs that map invasive plants – e.g., EDDMapS, the National Park Service, and Invasive Plant Councils – in both selection of species to target and developing an overall picture. As noted in Faith’s earlier blog, the Mid-Atlantic Invasive Plant Council has a list of 285 invasive plants in the region. Does the subset of 50 species selected for the FIA inventories provide an accurate picture of plant invasions in this sub-region?
• Scientists should cooperate to evaluate the relative importance of propagule pressure v. forest fragmentation as factors in facilitating invasions. Their relative roles probably vary by species, receiving forest, etc.
• We welcome the attention to invasions of interior forests – a topic previously neglected. Nevertheless, forest “edges” are also important ecologically – and – based on what we see in the Mid-Atlantic region – are even more heavily invaded. What impact does a wall of vines have on wildlife and plant species that evolved to live in area of greater light and temperature variation of trees, shrubs, herbaceous species that made up the edge before invasion?

Actions to Counter Plant Invasions

• Those who sell plants for any use – ornamental horticulture, ground cover, livestock forage, soil amelioration, wildlife habitat management, biofuels – should commit to avoiding species that are known or suspected to be invasive in the region.
• Voluntary efforts to limit sales of invasive plants have fallen by the wayside. The various Invasive Plant Councils should work with industry groups and others to renew this effort. Also, the Councils should propose a joint list of additional plants for APHIS regulation under NAPPRA (see below).
• Those who buy plants for these various uses should make a similar commitment – especially large, institutional buyers like state highway departments.
• Concerned citizens should lobby their state governments and the Congress to fund “noxious weed” programs and to ensure that these programs include plant species that threaten natural areas, not just weeds of agriculture.
• Concerned citizens should lobby the Congress to increase funding for federal agencies’ invasive plant control programs, especially those addressing natural areas, and especially in Hawai’i and the eastern United States. Also, the U.S. Department of Agriculture needs to adopt procedures that enable APHIS to act more quickly to curtail introduction and human-assisted spread of invasive plants.

In June 2017, APHIS finalized its May 2013 proposal to restrict importation of 22 potentially invasive plant species – as provide by its NAPPRA program. (For a description of this program and the recent action, visit Faith’s blog here. APHIS should be empowered to use this program more aggressively to list additional plant taxa that appear likely to be invasive.

Source

Christopher M. Oswalt, Songlin Fei, Qinfeng Guo, Basil V. Iannone III, Sonja N. Oswalt, Bryan C. Pijanowski, Kevin M. Potter 2016. A subcontinental view of forest plant invasions. NeoBiota. 24: 49-54 http://www.srs.fs.usda.gov/pubs/48489

posted by Faith Campbell & guest Jil Swearingen

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.