forest pest insects – Page 9 – Center for Invasive Species Prevention

Canada Again: Report on Forest Pest Efforts

Asian longhorned beetle

I recently posted a blog based on a new report evaluating Canada’s invasive species efforts across all taxa (see Reid et al. reference at the end of this blog). That report focused on federal measures aimed at preventing introductions, including cross-border introductions from the U.S. After posting that blog I learned about a second report by Allison, Marcotte, Noseworthy and Ramsfield (2021) that focuses on non-native insects and diseases that threaten Canada’s trees and forests.

The first report’s authors lamented that invasive species responsibilities are divided among several agencies, depending on the associated commodity or resource. It noted claims by the Canadian government in its 2018 report to the Convention on Biological Diversity to have identified priority pathways. These included several relevant to forest pests: shipping, horticulture, transport containers, and recreation. The Government claimed that the wood packaging, forestry products, and plant products pathways were at least partially regulated and also that national plans had been developed for several priority species, including the Asian subspecies of Lymantria dispar and the emerald ash borer. Reid et al. (2021) included four case studies, two of which dealt with non-native forest pests: successful eradication (the second time around) of the Asian longhorned beetle (ALB); and the high threat to Canada posed by the spotted lanternfly (SLF).

I was pleased to learn of the second 2021 report (Allison, et al.) because of its focus on pests in trees and forests. This is important because U.S. and Canada share four types of forests; evergreen needle leaf forests, sparse trees/parkland, mixed broadleaf / needle leaf forests, and deciduous broadleaf forests (See Fading Forests III, Chap. 1, Fig. 1, Box 2 [link at end of this blog]). Together, North American forests are comprised of 1,165 different native tree species. They offer many potential hosts to any introduced insect or pathogen. Thus the two countries need to coordinate pest-prevention and responses when prevention fails.

It is more likely that a pest from overseas will be introduced first to the U.S. because the U.S. imports a much higher volume of goods and has greater variety of climates and forests. Data show this: as of 2010, more than 181 exotic insects that feed on woody plants were established in Canada (USDA 2009) compared to at least 475 in the U.S. (Aukema et al. 2010). However, sometimes a pest is first introduced in Canada, then spreads south. One examples is beech bark disease.

Forests occupy 40% of Canada’s land cover. Because the country is so large, there are a wide variety of ecozones and forest regions. Almost all (95%) regenerate naturally; 90% are publicly owned (federal and provincial). These forests, which equate to 9% of the Earth’s total forest area, are important not just to Canadians but also to the world for water regulation, carbon sequestration, habitat for biological diversity and the economy. (See Fig.1 in Allison et al.)

Both Canadian reports emphasize Canada’s international obligations, especially under the Convention on Conservation of Biodiversity (CBD). (This is far more than in similar U.S. reports; of course, the U.S. is not a party to this convention.) Allison et al. also mention the Montréal Process Working Group on Criteria and Indicators for the Conservation and Sustainable Management of Temperate and Boreal Forests; international carbon emission mandates and agreements; and the International Plant Protection Convention (IPPC). Allison et al. also stress the importance of international collaborative research, mentioning the International Forestry Quarantine and Regulations Group (IFQRG), expert groups convened by the IPPC and North American Plant Protection Organization (NAPPO), Plant Health Quadrilateral Working Group and participation in the annual USDA interagency research forum on invasive species.

Both new Canadian reports focus on federal efforts, especially those of the Canadian Food Inspection Agency (CFIA), Canada Border Services Agency (CBSA), and Canadian Forest Service of Natural Resources Canada (CFS).

CFIA (Canada’s national plant protection organization, or NPPO in IPPC parlance) is responsible for analyzing risks, setting policy, and managing responses to forest biosecurity incursions. Its authority comes from Canada’s Plant Protection Act and Regulations (S.C. 1990, c. 22). The CBSA enforces regulations at most, but not all, international ports of entry. The CFS conducts research and analysis to support development and implementation of phytosanitary regulations. CFS is also charged with maintaining market competitiveness for forest products and meeting the country’s global commitments to sustainably develop its natural resources. The 10 provinces and three northern territories have jurisdiction over most of the country’s forests, including promoting forest health. Thus, protection and management of Canada’s forests is a shared responsibility among federal, provincial, territorial, municipal and indigenous governments and other stakeholders including the forest industry and non-governmental organizations.

Allison et al. (2021) discuss the effects of invasions on forest ecosystems, including altering forest ecology and the ability of forest ecosystems to provide services. For instance, invasions can change: competitive interactions among tree species; forest food webs; microenvironments; nutrient cycles; successional trajectories; understory plant communities; transpiration rates; water dynamics; and nitrogen and carbon flows, including carbon sequestration and storage. They cite the emerald ash borer and Dutch elm disease as examples.

Much of these authors’ discussion of invasion processes, bioinvaders’ impacts and biosecurity procedures is familiar from a U.S. point of view. However, I appreciate that they explicitly concede knowledge gaps in three particular situations.

First, when discussing the absence of recognized ecological impacts associated with most introduced forest insects and pathogens, they state that this lack of known impacts is often likely due to an incomplete understanding of complex phenomena and delays in perception of effects. They cite — again — the case of the emerald ash borer, when impacts were reported only 10 years or more after its establishment.

Second is their discussion of the drivers of invasion. After saying that the interactions of species’ traits, introductory pathways, and receiving habitats are incompletely understood, they note that it is difficult to determine the relative contribution of reproductive traits and propagule pressure in explaining the invasion success of Hemiptera – which reproduce asexually but are also extremely common in invasion pathways. As I have said in a previous blog, the report due by Haack and colleagues later this year can help clarify the current contribution of the wood packaging pathway to propagule pressure.

Third, they note the limited predictive power of border interception records – and possibly other data resources such as risk assessments, surveillance programs – as a basis for understanding pathways. They note that Ips typographus has been intercepted hundreds of times by North American authorities but has never established.

There are some puzzling gaps in Allison, et al. For example, in discussing the costs associated with forest pest introductions, they do not mention the risk to “leaf-peeper” tourism – as U.S. evaluations of the Asian longhorned beetle do. In discussing the role of propagule pressure they mention pathway volume (i.e., the amount and frequency of trade) and the invasive species’ population levels in the point of origin, but not the invader’s ability to exploit the pathway. (Perhaps that is assumed within the pathway volume measurement?) The example cited is heightened arrivals of Lymantria dispar asiatica during periods of outbreak in its native Asian range.

The report provides helpful clarity on Canadian biosecurity practices. For example, wood packaging entering the country at thefour main Canadian commercial marine ports (Halifax, Montreal, Vancouver, and Prince Rupert) is inspected by CBSA. However, CFIA enforces compliance at the other marine ports and along the 8,891 km (5,500 mile) land-border with the U.S. Apparently CBSA joins in “border blitzes” at selected strategic land-border crossings.

In discussing the provinces’ efforts to slow the spread of established pests, the report mentions the western efforts to prevent introduction of Dutch elm disease. Also, it covers British Columbia’s attempt to prevent spread of balsam woolly adelgid (BWA) into its interior. (I mourn that this effort was not successful.)

elm zigzag sawfly; photo by Georgy Csoka

The report cites the first record of the elm zigzag sawfly, Aproceros leucopoda in North America as an example of citizen detections.

I note that a periodic reassessment of the Canadian regulations governing emerald ash borer in 2014 resulted in a decision to expand the regulated area to reduce regulatory burden, increase awareness of the regulated areas, and maximize compliance. I regret that USDA APHIS decided to fully de-regulate the pest instead. Canada similarly expanded the regulatory zone for a second pest, the brown spruce longhorned beetle (in 2015).

Canada has deregulated pests judged to have spread to the limits of their potential invaded range, e.g., the Pine shoot beetle, Tomicus piniperda.

The report includes three case studies.

whitebark pine infected by WPBR; photo by FT Campbell

White Pine Blister Rust Case Study

This pathogen was introduced more than 100 years ago and has caused extensive damage to Canadian populations of the commercial species western white pine (Pinus monticola) and eastern white pine (P. strobus). It has also contributed to the decline of whitebark pine (P. albicaulis) and limber pine (P. flexilis). An early warning by Gussow (in 1916) about the pathogen’s probable impact apparently led Canada to prohibit further imports of five-needle pines.

Multiple consequences followed the pathogen’s spread. These included reduced volumes of eastern and western white pine due to the combined effects of disease-caused mortality and foresters shifting to alternative species to avoid future losses. Furthermore, both whitebark and limber pines have been ranked as “Endangered” by the Committee on the Status of Endangered Wildlife in Canada. Whitebark pine is also listed on Schedule 1 of the federal Species at Risk Act; limber pine is currently under consideration for such listing.

The report concludes by stating that resistance breeding is an important strategy and that extensive work has been carried out by both the U.S. and Canada.

Asian Longhorned Beetle Case Study

After noting that this pest of maples is of high concern in Canada, the report lays out the history of the first and second detections in Toronto. Because a risk assessment had been completed beforehand, actions could be taken rapidly. CFIA was encouraged to pursue eradication by the success of several previous eradication efforts, as well as the significant negative impact anticipated to the economy. The Ontario Ministry of Natural Resources, NRCan-CFS, the cities of Toronto and Vaughan, and regional authorities and USDA – which shared information – all contributed. The program removed 5,000 trees in the first six months. In 2018, after five consecutive years of no detections, the ALB was declared eradicated. However, four months later, another ALB was reported – two km from the boundary of the first regulated area. The program was renewed, over a larger area. In total, considering both detections, more than 36,000 trees have been removed. Eradication of the pest following the second detection was declared in June 2020.

The report attributes success to 1) surveillance following IPPC guidelines; 2) reliance on science for evidence-based decision-making, including input on several issued by a science committee chaired by CFS; 3) Early engagement of partners and proactive communication that increased public awareness and reporting.

Oak Wilt Case Study

Oak wilt is established in U.S. states that border Ontario. Also, models suggest that the disease (Bretziella fagacearum) would not be limited by Canada’s climate and that it would cause serious economic harm. Therefore, Canada considers it to pose a high risk. Consequently, CFIA led development of a response framework to guide an incursion response. As usual, this was done in collaboration with representatives from federal, provincial and municipal governments, plus New York and Michigan.

Oak wilt is regulated under the federal Plant Protection Act. In addition to adopting various CFIA directives related to imports, the framework includes a communication strategy; provisions for detection and monitoring; and management activities aimed at its eradication if it is discovered in Canada. The framework also identified research needs and provided funding to address them. map from photos

In their conclusion, Allison, et al. (2021) state that the close relationship between CFIA and CFS is unusual but do not explain how or why.

They also suggest several ways Canada’s biosecurity efforts targetting non-native forest pests could be improved. The first is to increase information-sharing between agencies and with partners, plus better integration of information into policy development. Also, they suggest adoption of new post-border technologies (e.g., “smart” technologies; in-field chemical analyses, and optimization of surveillance programs) and additional research to build a stronger scientific understanding of pest biology, epidemiology, and trade economics. Generally, their recommendations do not overlap with those of Reid et al. (2021) – which was probably being written at the same time. They do both seem to suggest: 1) strengthening partnerships with the public and Indigenous communities and 2) to be prepared to adapt to future conditions.

SOURCES

Allison JD, Marcotte M, Noseworthy M and Ramsfield T (2021) Forest Biosecurity in Canada – An Integrated Multi-Agency Approach. Front. For. Glob. Change 4:700825. doi: 10.3389/ffgc.2021.700825 Frontiers in Forests and Global Change July 2021 | Volume 4 | Article 700825

Aukema, J.E., D.G. McCullough, B. Von Holle, A.M. Liebhold, . Britton, and S.J. Frankel. 2010. Historical Accumulation of Nonindigenous Forest Pests in the Continental United States. BioScience • December 2010 / Vol. 60 No. 11 www.biosciencemag.org

Reid CH, Hudgins EJ, Guay JD, Patterson S, Medd AM, Cooke SJ, and Bennett JR. 2021. The state of Canada’s biosecurity efforts to protect BD from species invasions. FACETS 6: 1922– 1954. doi:10.1139/facets-2021-0012 Published by: Canadian Science Publishing connorreid@cmail.carleton.ca

United States Department of Agriculture, Animal and Plant Health Inspection Service. 2009. Risk analysis for the movement of solid wood packaging material (WPM) from Canada into the US.

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

Interactions of 2 (of 3) Threats to Beech

American beech (Fagus grandifolia) is a widespread and beautiful tree of the eastern deciduous forest. Its range reaches from Nova Scotia to eastern Wisconsin, then south to Mississippi and Louisiana and east to mid-Georgia. It is an important food source for 40 wildlife species, particularly in the northern parts of its range where few other species produce hard mast. (See Lovett et al. 2006.)

Threats

Unfortunately American beech is under threat from three non-native organisms or complexes: 1) beech bark disease, 2) beech leaf disease, and 3) beech leaf mining weevil. A fourth pest, a previously unknown – and still unnamed bark beetle in the genus Agrilus – has been detected in New York City on European beech trees. It is not yet known whether it will attack American beech and, if so, whether it will also cause serious damage (Michael Bohne, USFS, pers. comm.)

symptoms of beech bark disease; photo by Linda Haugen, USFS; via Bugwood

Beech bark disease (BBD) results from the interaction of the introduced European beech scale insect (Cryptococcus fagisuga) and several fungi in the Neonectria genus – some of which are also introduced. The resulting disease has been killing American beech trees since the beginning of the 20^th Century. It has spread from Nova Scotia to much of the tree’s range. It has dramatically altered the composition and structure of stands containing beech.

symptoms of beech leaf disease; photo provided by Jennifer Koch, USFS

Beech leaf disease (BLD) was initially detected in 2012, near Cleveland. As of December, 2021, it has spread due east across New York, Pennsylvania, and New Jersey to the Atlantic, then up the coast through Connecticut and eastern Massachusetts, with a separate outbreak in central Maine. The disease is apparently associated with a nematode, Litylenchus crenatae ssp. mccanni, although additional pathogens, like bacteria, might also play a role. The origin of the North American population of the nematode is unknown; it is a related but separate subspecies from a Japanese nematode (Reed et al. 2022).

American beech defoliated by leaf mining weevil; photo courtesy of Jon Sweeney, CFS

Beech leaf mining weevil (Orchestes fagi) is, so far, limited to Nova Scotia. However, it is expected that the weevil will continue spreading throughout the range of American beech through both natural dispersal and human-assisted movement. Repeated defoliation by the weevil might increases mortality rates in forests that are surviving in the “aftermath” stage of BBD (Sweeney et al. 2020).

A new study (Reed et al. 2022) concludes that, despite being detected only 10 years ago, BLD has already become pervasive in forests surrounding Lake Erie in the U.S. and Ontario. While somewhat more prevalent in U.S. states on the eastern side of the Great Lakes (on 54% of trees) than in Ontario (on 46% of trees), BLD is spreading rapidly and affecting every canopy layer. Mortality is highest in seedlings and saplings; understory saplings die within 2 – 5 years. The occasional mortality of overstory trees occurs within seven years of [observed] infection. Defoliation and mortality of saplings allow more light to pass through to the understory; this is expected to alter plant communities on the forest floor.

Beech scale is more widespread in Ontario (found on 60% of trees) than in the U.S. (38% of trees). This is not surprising since the scale was detected in Ontario in 1960, 24 years before it was detected in portions of Ohio, New York and Pennsylvania included in the study (in 1984). Throughout this region, beech scale is disproportionately affecting overstory trees.

Only 4% of trees throughout the study area are infected with Neonectria cankers. In other words, full-scale beech bark disease is not yet widespread and is spreading surprisingly slowly. Scientists do not understand this phenomenon.

These findings are based on a network of monitoring plots a network of monitoring plots set up in 2019 set up in areas surrounding the Great Lakes. They comprise 34 plots at 17 locations in southwest Ontario and 30 plots at 25 locations in Ohio, Pennsylvania, and New York. In total the plots hold 646 live American beech trees — 412 saplings; 85 in the intermediate/suppressed (subcanopy) category; and 149 in the dominant/codominant (canopy) class.

Forest composition is similar throughout the study area. The most common species in association with American beech are sugar and red maples (Acer spp.), and white and green ash (Fraxinus spp.). Other tree species present include eastern hemlock (Tsuga canadensis), white pine (Pinus strobus), oaks (Quercus spp.), and birches (Betula spp.). Study plots had few invasive plants – although the invasive species present are well-documented to invade forests.

Ontario disease assessment

In Ontario, BLD was identified in 25 of the 34 plots. It was present on 171 saplings, 53 intermediate trees, and 70 dominant trees. Both prevalence and severity were greatest on intermediate trees. Beech scale was present at all 34 plots. While scales were found on trees of all sizes, they were almost two times more prevalent and were more severe on mature trees than saplings. Neonectria cankers were detected at 34 plots. Neonectria was rare but most severe on dominant trees. Fewer than one third of saplings and one-sixth of mature trees were pest free.

U.S. disease assessment

BLD was present in 17 of the 30 plots. It was found on 75 saplings, 30 intermediate trees, and 38 dominant trees. Saplings and dominant trees had similar levels of disease; intermediate trees had significantly less. However, BLD severity was twice as high on saplings compared to mature trees. BLD was present on more than half of the seedlings assessed – 46 out of 82. Beech scale was present in 20 of the 30 plots. It was significantly less common and severe on saplings than on mature trees. Neonectria cankers were present in only 4 of 30 plots. Canker prevalence and severity did not differ significantly among size classes.

Distribution and Effects of Beech Scale and BBD

While beech scale attack facilitates invasion by the Neonectria fungi, the disease – BBD complex – had the most limited distribution of the three pests in this study. It was found on only ~4% of beech trees throughout the study area. The disease was first reported there in the early 2000s. Although no one knows why, it has spread more slowly there than in areas to the east (Reed et al. 2022).

As is the case with beech scale, BBD disproportionately affects large diameter trees. Typically, BBD kills more than half of mature beech within 10 years of its arrival. Dying trees produce prolific root sprouts resulting in dense beech sapling understories that impede regeneration of less shade-tolerant tree species. The persistence of thickets of disease-vulnerable small beech perpetuates the disease. BBD is the only forest disease in North America that can inadvertently intensify itself by increasing densities of its host while suppressing other species.

Beech Forest Community Change in Response to Combined Impacts of BBD and BLD

It is unclear how forests will change as beech die. Some expect saplings of species already present — red maple, white ash, and, especially sugar maple — to exploit the canopy gaps. Of course, white and green ash are under attack by the emerald ash borer; DMF their ability to reach the canopy will depend on the success of biocontrol agents.

However, if BBD or BLD resistant beech survive or if BLD fails to persist, future forests might instead consist of beech thickets that would prevent all but the most shade tolerant species from establishing. Heavy deer predation on maple seedlings and saplings might also play a role. A third possibility is that morbidity from BBD and BLD might lead to uneven-aged conditions that allow younger trees — perhaps even shade intolerant species e.g., oaks — to establish.

Invasive plants also have the potential to fill gaps left by declining beech. While maple-beech forests often have sparse understories due to low understory light levels, pest-caused canopy gaps are expected to increase the abundance of invaders, especially in small woodlots and forests near urban areas. Several shade-tolerant invasive shrubs are already present in low numbers: Japanese barberry (Berberis thunbergii), tatarian honeysuckle (Lonicera tatarica), multiflora rose (Rosa multiflora), and buckthorn (Frangula sp.). Reed et al. (2022) note that these species, plus privet and autumn olive, can take advantage of small canopy gaps, especially when soils are disturbed, e.g., by active intervention to counteract the loss of beech.

Precautionary Research and Management

Reed et al. (2022) call for enhanced monitoring of beech forests focused on

the timing of BLD presence relative to tree age and size – which might affect competitiveness of sprouting beech in the understory; and
compositional and structural change in forests with BLD or to which it is likely to spread

They also recommend abandoning the management approach for BBD currently recommended by foresters. It calls for removing scale-susceptible beech so that resistant genotypes increase in prevalence. In forests with both BBD and BLD, they conclude, management of natural regeneration is unlikely to succeed because BLD will kill sprouts and saplings that might be resistant to scale. They recommend instead active management of the forest to promote mast-producing, shade intolerant species, such as oaks and hickories.

They also recommend increased support for resistance-breeding programs. Such programs already target BBD, based on the estimated 1% of American beech that show some resistance. Now those programs need to incorporate BLD resistance. (Reed et al. note that small numbers of beech show few or no BLD symptoms so might possess resistance or tolerance.)

grafted beech for resistance breeding; photo by Rachel Kappler, then USFS (now Great Lakes Basin Initiative & Holden Arboretum)

Unfortunately, the Canadian beech breeding program’s future funding is highly uncertain. To counter this threat, in part, Reed et al. (2022) suggest cryopreserving beech embryos from Canada to develop a beech conservation collection that would be available for a more robust, future Canadian breeding program. The USFS is trying to develop methods to screen trees for resistance to BLD, specifically to the nematode (J. Koch, USFS, pers. comm.)

Another approach would actively manage beech stands in which potentially BLD-resistant beech grow to help these trees reach the canopy and reproduce. In the absence of management, any BLD-resistant beech seedlings might be overtopped by faster growing, shade-intolerant species – especially if the gaps promote soil drying or sun scald.

Finally, breeding programs need to factor in the beech leaf mining weevil, DMF which — as I noted in the beginning — is spreading across Nova Scotia and could spread to the rest of the native range of beech (Sweeney et al., 2020).

The Department of Agriculture has created a website on the Department’s plant-breeding efforts. It includes a subwebsite on USFS efforts. However, I did not find much useful information there.

SOURCES

Lovett, G.M., C.D. Canham, M.A. Arthur, K.C. Weathers, and R.D. Fitzhugh. 2006. Forest Ecosystem Responses to Exotic Pests and Pathogens in Eastern North America. BioScience Vol. 56 No. 5 May 2006)

Reed, S.F., D. Volk, D.K.H. Martin, C.E. Hausman, T. Macy, T. Tomon, S. Cousins. 2022. The distribution of beech leaf disease and the causal agents of beech bark disease (Cryptoccocus fagisuga, Neonectria faginata, N. ditissima) in forests surrounding Lake Erie and future implications Forest Ecology and Management 503 (2022) 119753

Sweeney J.D., Hughes, C., Zhang, H., Hillier, N.K., Morrison, A. and Johns R. (2020) Impact of the Invasive Beech Leaf-Mining Weevil, Orchestes fagi, on American Beech in Nova Scotia, Canada. Frontiers in Forests and Global Change | www.frontiersin.org 1 April 2020 | Volume 3 | Article 46

Posted by Faith Campbell

British & Irish Efforts to Prevent or Combat Pathogens

I often blog about the forest pest situation in the UK because its scientists provide lots of easily accessible information. This blog has new information on Britain and – I am pleased to add – on Ireland!

European ash trees alongside the Malham Cove path in Yorkshire; KA via geograph

UK Overview

British woodlands cover just 13% of total land area (just over one-third of the European average of 37%). Their value is increasingly recognized—especially their role in combating climate change through carbon sequestration, flood mitigation and urban cooling. Realization of these benefits is driving new policy to increase woodland cover. In 2019–2020, 13,700 ha of new woodland was created in the United Kingdom (Green et al. 2021). The U.K. government has pledged to plant 30,000 ha of broadleaf and coniferous woodland every year as part of its climate change mitigation strategy (Donald et al. 2021). One example, the ‘northern forest’ scheme, involves planting 50 million native trees over 25 years (Green et al. 2021).

Risks Associated with Conservation Plantings or Translocations

On-going conservation planting efforts plus these ambitious new plans prompted Donald et al. (2021) to assess risk that pathogens might be introduced into the environment as a result of putting native plants in natural habitats. The focus of their study is the planting of common juniper (Juniperus communis)in habitats throughout England, Scotland, and Wales.

Juniper killed by *Phytophthora austrocedri*; photo from British Forest Research

Juniper is one of three native conifers in the UK. It has been in decline for decades, which conservationists hope to reverse. Now, though, juniper populations are experiencing significant mortality from disease. In 2012, the causal agent was determined to be the non-native pathogen Phytophthora austrocedri. The presence of a single genotype in ~60 geographically separate locations across Scotland and England lends support to idea that the pathogen is being introduced to these sites through some human mechanism. Phytophthora austrocedri has not [yet] been detected in Northern Ireland.

British and European nurseries have contained many Phytophthora pathogens. Hence Donald et al. (2021) sought to determine whether the pathogen is being introduced through use of nursery stock in these well-intentioned plantings. (I have blogged about a similar problem in California restoration plantings.)

The authors found that 19% of P. austrocedri detections are within 2 km of a known planting. The more frequently junipers were planted at a site, and the more cuttings planted during each planting effort, the higher the likelihood that nearby junipers would be infested by P. austrocedri. They conclude that transplanting material is a significant risk pathway for the introduction of disease. The key factor appeared to be the origin of the material. A higher percentage of stock at sites with P. austrocedri outbreaks for which data were available had been raised in a central location by the organization doing the planting or obtained from commercial nurseries. No P. austrocedri was detected in Wales. There, unlike in Scotland or England, the majority of plants were sourced from a commercial nursery that only grew juniper collected from Welsh populations and did not trade with other retailers.

Planting juniper has risen rapidly since the mid-1990s. The highest percentage of planting events co-occurring with disease outbreaks were conducted in 2000–2009. It is likely that there is a time lag between planting and disease detectability. If so, the even larger planting effort since 2010 probably will produce many more P. austrocedri outbreaks that will become visible in the future. And that might not be the end. Planting guidelines have been revised based on pathogen detection. However, the entities doing the planting have not changed their approach, especially regarding site selection.

Donald et al. (2021) also found serious data gaps in these programs beyond the health of propagules. They found:

1) very incomplete knowledge of which organizations are doing the planting;

2) poor attention to traceability of source material; and

3) very little follow-up to check the success of planting projects.

The authors concluded that planting projects have had mixed success in restoring juniper populations. They called for changes in planting strategy to reduce the risks of pathogen introduction.

They also note that efforts to slow the spread of P. austrocedri – for which there is no treatment – are more expensive and less likely to succeed than measures aimed at ensuring that nurseries are free of Phytophthoras. California native plant nurseries have shown that nurseries can maintain Phytophthora-free stock.

Risk of Nursery-spread Pathogens & Willingness of UK Nurseries to Adopt BMPs

Great Britain has experienced an accelerating series of Phytophthora outbreaks and disease epidemics affecting British trees. Introductions detected just since early 2000s include P. ramorum, P. kernoviae, P. lateralis, P. austrocedri and P. pseudosyringae. In all the above cases, imported planting material either is confirmed or strongly implicated as the likely route of intro (Green et al. 2021).

To address this threat – and with massive planting projects proposed – in 2016 the British forest research entity initiated the multidisciplinary ”Phyto-threats” project. Its goal was to understand the drivers of rising Phytophthora infestations and opportunities for mitigating them. The project:

(i) examined Phytophthora distribution and diversity in different nursery management systems;

(ii) assessed the social and economic feasibility of a nursery accreditation programs to curb the risk; and

(iii) identified Phytophthora risks by modelling introduction, establishment and spread of species in relation to biological characteristics, environmental factors and trade flows.

The assessment of Phytophthora presence in nurseries involved collecting 3,624 water and root samples from 163 host genera growing in plant nurseries across the U.K. over a three-year period. Sampling was not random but targetted to facilities thought to harbor Phytophthora. About half of the samples tested positive. They identified 63 species of Phytophthora. Among the most commonly detected species are several that are considered pathogenic — P. cinnamomi, P. cryptogea/pseudocryptogea, P. syringae, P. cactorum, P. cambivora, P. plurivora and P. nicotianae. P. ramorum was found in 12 samples; P. lateralis and P. austrocedri were each found in 10 samples. Several Phytophthora species are potential new records for the U.K. (i.e., P. castanetorum, P. palmivora, P. pseudotsugae,P. tentaculata,P. terminalis, P. uliginosa).

They also saw evidence for Phytophthora root infections in newly arrived plants imported from the European Union.

Their finding raised question about whether Phytophthora can be transported in peat-free potting media, that is, coconut fiber or coir.

The widespread presence and the diversity of Phytophthora found in nurseries was linked to high-risk management practices. These included: careless disposal of culled plants, the near presence of trees along nursery boundaries, and, especially, open water sources. [These factors are essentially identical to infection-facilitating factors found by researchers in California, Oregon, and Washington State. See advisory issued by Oregon State University Extension.]

The project also assessed the feasibility of nursery accreditation programs. The authors consulted widely with nursery owners and customers and conducted a cost-benefit analysis. Regarding nursery practices, owners claimed they were already addressing issues related to water storage in enclosed tanks, clean/covered storage of growing media, installation of drains or free-draining gravel beds, raised benches, and tool disinfestation stations. Therefore the new analysis focused on seven other topics: water testing for pathogens; water treatment s; quarantine holding areas for imported plants; composting or incineration of culled plants; boot and vehicle washing stations; and purchase from only trusted or accredited UK suppliers.

The study found that nurseries would support an accreditation program. However, their support required that costs not be “prohibitive”, actions required not be “unreasonable”, the scheme provide a safety net; and that measures exist to deter non-compliance. Nursery staff wanted to see evidence of consumer demand – a willingness to drive farther to buy “clean” plants, or to pay higher prices for them. The cost-benefit analysis reached a worrying conclusion: nurseries would benefit financially from introducing best practices only when the program would prevent introduction of a wider range of pests and pathogens, not only Phytophthoras. Green et al. (2021) note that the overall net benefit to society from nurseries adopting best practices would be much more substantial. That is, healthy trees are important in meeting carbon sequestration goals. They did not explore whether society should subsidize nurseries’ participation in BMP accreditation programs.

Ireland and Northern Ireland

The island of Ireland (Ireland and Northern Ireland) is thought to have fewer plant pests than other European countries due to its island status and because of its national and international phytosanitary regulations. O’Hanlon et al. (2022) do not mention another possible factor: the likelihood that import volumes to Ireland were probably much lower until the recent vitalization of the Republic’s economy.

O’Hanlon et al. (2022) sought to establish baseline information so scientists can track changes as trade increases and the climate changes. Their search of the literature and unpublished sources identified 396 forest pests on the island, including 11 bacteria, 20 oomycetes, 150 fungi and 215 arthropods. They believe these figures are all probably underestimates. At least 44 of the pests or pathogens are probably non-native to Ireland. (Determining original ranges is difficult, especially for pathogens.)

The Republic of Ireland is one of the least forested countries in Europe. Forests cover ~ 11% of the land area. In Northern Ireland, it is even less: ~ 8%. These forests are predominantly plantations of exotic species. In the Republic, Picea sitchensis makes up 51% of the forest area, Pinus contorta another 10%. Other exotic species planted are Picea abies (4%) and Larix kaempferi. In Northern Ireland, ~ 62% of the forest area is composed of conifer mixtures. Planting of P. sitchensis has accelerated recently, probably as a result of removal of ash and larch because of their vulnerability to pests already established on the island.

Sitka spruce plantation in U.K. Adam Ward, Geograph.org.uk

O’Hanlon et al. (2022) note the great vulnerability of these monocultures to pests. They found 51 pests native to Ireland that are associated with non-indigenous tree genera. They are also concerned about pests introduced from other parts of Europe. For example, green spruce aphid (Elatobium abietinum, native to Central and Eastern Europe) is already attacking Sitka spruce. A second pest of spruce, Ips typographus, which is native to much of Europe but not the British/Irish isles, is not yet established on the island. Northern Ireland imports bark and wood from Europe for processing. Ips typographus has been associated with at least one such shipment.

Non-native forest pests and pathogens also threaten tree species native to Ireland. These include:

Dutch elm disease caused by fungi from the genus Ophiostoma vectored by bark beetles of the genus Scolytus. The second outbreak, caused by the more aggressive pathogen 0. novo-ulmi, was detected in Britain in 1965 and in Ireland in 1977. It caused considerable mortality of elms in Northern Ireland throughout 1970s.

Phytophthora ramorum was recognized as a threat to forests in Europe only in 2010, when extensive mortality of Japanese larch was detected in Britain. The Republic of Ireland has only the EU1 lineage of the species. Northern Ireland has both the EU1 and EU2 lineages – the former only in nurseries.

Phytophthora disease of alder (caused by several Phytophthora species) was confirmed in Ireland in 2001. However, symptoms of the disease were noted as far back as 1995. It is likely that there are many other Phytophthora species present but not yet recorded.

Ash dieback disease (causal agent Hymenoscyphus fraxineus) on European ash (Fraxinus excelsior) has spread across Europe from Poland beginning in the 1990s. It was confirmed on the Irish island in 2012. Authorities made significant attempts to eradicate the disease, but were not successful. It is now recorded in every county in both Northern Ireland and Ireland. Damage to the economy, environment, and society are expected to be large. The Irish government had helped plant more than 13,000 ha of ash between 1992 and 2012. An estimated 2.9 million ash trees are in Northern Irish hedgerows. British scientists say more than 1,000 fauna species are associated with ash trees.

A second pest on ash — ash sawfly (Tomostethus nigritus) — was detected in Northern Ireland in 2016; it has defoliated hundreds of trees in Belfast.

In recent years, forest pest incursions have increased at a relatively steady rate, comparable to other countries, including Britain. In the 1970s, 26 species were reported; in the 1980s, 27; in the 1990s, 16; in the 2000s, 37; between 2010 and 2017, 28. See the graph in Fig. 2

There is a strong link between pest and pathogen findings in Britain and Ireland. O’Hanlon et al. (2021) list 16 insects and pathogens detected in Britain after 1960 which were later detected in Ireland. The list includes H. fraxineus, 0. novo-ulmi, Phytophthora ramorum, and Phytophthora lateralis. The average delay was 10 years. The authors note that the two islands share similar ecological conditions and hosts, are nearby, plus there is substantial travel and exchange of goods between them. For example, in 2018 an estimated 30,000 metric tonnes of conifer roundwood was sent from Scotland to Northern Ireland for processing.

There are very limited physical checks on plants or plant products moving between Ireland and Northern Ireland. The exception is conifer wood that is not bark-free. European Union regulations require that such shipments be accompanied by a plant passport that certifies that the wood has been inspected by a professional operator authorized by the NPPO of the exporting country. What rules will apply now, after BREXIT, remains unclear. Because of concerns about re-igniting sectarian conflict, most political figures want the border on the island to be almost invisible.

The Europhyt database for the period February 2006 – November 2016 documented interception of numerous high-risk pests at the British and Irish borders, including Anoplophora chinensis and A. glabripennis; I. typographus; Monochamus alternatus; H. fraxineus; and P. ramorum O’Hanlon et al. (2021). believe many more go undetected. O’Hanlon et al. (2021) report specifically on detections on commodities from China, especially on wood packaging. One detection on imported plants of interest to me is that of Discula destructiva (dogwood anthracnose). The article does not mention the origin of the shipment. The native British dogwood, Cornus sanguinea, would presumably be vulnerable to this Asian fungus, which has already caused widespread mortality of woodland dogwoods in North America.

*Cornus sanguinea*; photo by Hans Hillewaert

In addition to reviewing the current situation, O’Hanlon et al. (2021) note pertinent facts about current policy and future science. First, while the two political units on the island have a history of plant pathology expertise, there has recently been a reduction in the number of practicing forest pathologists, mycologists and entomologists. (I and others have complained about the same deterioration in expertise in the United States.)

Second, they describe the years of delay before official recognition that the pathogen Gremmeniella abietina was present in Northern Ireland. This delay resulted from officials refused to accept data from molecular detection tools.

O’Hanlon et al. (2021) add their voice to others criticizing the international phytosanitary system (they cite six major publications: Brasier 2008; Liebhold el. al. 2012; Santini et al. 2012; Eschen et al. 2015; Jung et al. 2016; Meurisse et al. 2019). The failures are (i) visual inspections can miss asymptomatic infections, (ii) limited resources mean only a small proportion of commodities can be inspected, (iii) allowing the use of fungicides masks disease symptoms on plants, (iv) list-based regulations don’t address undescribed organisms and (v) countries vary in how aggressively they carry out the required phytosanitary procedures. O’Hanlon et al. (2021) conclude that “Until these issues are addressed it is likely further increases in the numbers of non-native pests and pathogens of trees will increase.”

The authors note that Eschen et al. (2018) suggested that risk analysis should focus on the commodity (commodity risk assessment) rather than on an individual pest. I have made a similar suggestion, although less clearly worded.

Finally, O’Hanlon et al. (2021) note that climate change is expected to increase the island’s vulnerability to tree-killing pests and pathogens due to fewer frost days, more rain in winter, increased chance of drought in summer, increased average annual temperatures, and more frequent weather extremes. These changes are likely to affect the amount of damage caused by both native and introduced pests organisms. Range shifts in both pests and pathogens and their natural enemies; physiological or behavioral responses in the pests; phenological changes in the hosts; and increased stress on the trees will combine to affect damage.

SOURCES

Donald, F.; Purse, B.V.; Green, S. 2021. Investigating the Role of Restoration Plantings in Introducing Disease—A Case Study Using Phytophthora [UK] Forests 2021, 12, 764

Green, S., D.E.L. Cooke, M. Dunn, L. Barwell, B. Purse, D.S. Chapman, G. Valatin, A. Schlenzig, J. Barbrook, T. Pettitt, C. Price, A. Pérez-Sierra, D. Frederickson-Matika, L. Pritchard, P. Thorpe, P.J.A. Cock, E. Randall, B. Keillor and M. Marzano. 2021. PHYTO-THREATS: Addressing Threats to UK Forests and Woodlands from Phytophthora; Identifying Risks of Spread in Trade and Methods for Mitigation. Forests 2021, 12, 1617 https://doi.org/10.3390/f12121617ý

O’Hanlon, R., Ryan, C., Choiseul, J., Murchie, A.K. and Williams, C. D. 2021 Catalogue of P&P of trees on the island of Ireland. Biology and Enviro

Proceedings of the Royal Irish Academy 2021. Vol. 121, No. 1.12-45 DOI: 10.3318/ BIOE.2021.02

Posted by Faith Campbell

Breeding Pest Resistance in Trees – Thoughtful Perspectives

Scott Schlarbaum collecting butternuts; photo by F.T. Campbell

I have blogged several times about the need to enhance efforts to breed trees resistant to the most damaging of the hundreds of introduced insects and pathogens. Others concur – see reports by the National Academy of Sciences in 2018; several publications by USFS scientists Richard Sniezko and Jennifer Koch; a workshop hosted by Purdue w/ USFS support, the creation and efforts of several consortia – Whitebark Pine Ecosystem Foundation, Great Lakes Basin Forest Health Collaborative, Forest Restoration Alliance …

Also, Richard J. A. Buggs, of the Royal Botanic Gardens, Kew, recently summarized barriers to tree breeding. It was published as an especially thoughtful editorial in Plants People Planet in anticipation of the International Year of Plant Health in 2020 (see reference at the end of this blog). That issue included several related articles, also noted below.

R.J.A. Buggs’ Perspective on Tree Breeding

Buggs says the need for tree resistance research is greater than ever before. First, damage caused by introduced insects and pathogen is rising. Plus, we now recognize trees’ importance in capturing atmospheric carbon. He sees encouraging signs of growing public awareness of both factors. Also, he thinks citizen science might reduce the cost of some activities … although he doesn’t name which they are.

Dr. Buggs lists six major hindrances to breeding programs, including some aspects that I, at least, have not considered:

1) Trees’ size and long generation times mean research is necessarily slow. One result is it is hard to formulate research proposals that match funding cycles. This in turn means a dependence on long-term institutional commitment from well-funded organizations, and such institutions are rare.

I point out that the U.S. government – especially the USFS – is one such institution. Unfortunately, it has so far been reluctant to take commit major resources to breeding pest-resistant trees. Every year I urge you to lobby Congress on appropriations for the agency. In this context, do you understand that while the USFS Research budget receives approximately $300 million each year, less than $5 million of that total is allocated to researching invasive species (of all taxa)? Some gaps are filled by projects funded by the Forest Health Program. You will have a new opportunity to lobby Congress for Fiscal Year 2023 in the spring!

2) On the other hand, reliance on long-term institutional funding shelters projects from multidisciplinary peer-review that could introduce improved technology or methods. This lack of peer review also contributes to a perception among other scientists that tree resistance research is a scientific backwater.

3) Similarly, studies requiring a long time horizon don’t fit publication schedules. Again, the result is that the findings often appear only in institutional reports or conference proceedings. This means they are hard to find and often lack external peer review at not only the proposal stage but also before publication.

4) The long decades without clear success in dealing with Dutch elm disease (but see recent encouraging developments here) and chestnut blight (see The American Chestnut Foundation here) gave the impression that resistance breeding of forest trees is impossible. Buggs says pest resistance problems are easier to tackle for other trees.

TACF American chestnut; photo by F.T. Campbell

5) Those considering what efforts to fund might demand complete resistance to the pest. This goal is not only unrealistic – it is often unnecessary. Often lower levels of resistance or tolerance can result in trees that can be self-sustaining. Dr. Sneizko concurs; see his article appearing in this issue.

6) Forest stakeholders differ over the goal of developing resistant trees. Some think any human intervention is unwarranted in wilderness areas. Some want a tree as similar as possible to pre-epidemic trees. Others want a tree that produces more timber.

Other Significant Articles

A second article in the same issue of Plants People Planet (Federman and Zankowski) discusses the USDA’s commitment to new approaches in tree resistance research.

I found a third article that discusses British approaches to mitigating tree pests to be more informative than Federman and Zankowski – although somewhat worrying. Spence, Hill and Morris praise the U.K.’s Plant Health Risk Register, which they say has enhanced vigilance on possible new pest introductions. However, the authors describe resistance breeding as a strategy to be considered “when a pest has established such that a tree population is unable to recover, and where a genetic basis for resistance is demonstrable in a proportion of the tree population.” Dr. Sneizko, and others – and I! – call for initiating exploration of the potential for resistance breeding much earlier in an invasion.

A fourth article – by Richard Sniezko and colleagues — describes encouraging levels of partial resistance to white pine blister rust in two western white pines and evidence for both qualitative and quantitative resistance to Phytophtohora lateralis in Port-Orford Cedar.

Port-Orford test seedlings; photo courtesy of Richard Sniezko

A fifth – by Showalter et al. — reports encouraging levels of resistance to both emerald ash borer DMF and ash dieback in European ash. The authors conclude that a breeding program might be a viable solution to both pests.

SOURCE

Special issue of Plants People Planet for 2020 — the International Year of Plant Health. https://nph.onlinelibrary.wiley.com/toc/25722611/2020/2/1

Posted by Faith Campbell

An Evaluation of Canadian Invasive Species Efforts

A group of scientists has published a report on Canada’s invasive species programs (see reference at the end of this blog). It compares the structures and procedures of Canada’s federal government to those in the U.S., Australia, and New Zealand.

The report focuses on proactive measures aimed at preventing introductions, including cross-border introductions from the U.S. It does not describe efforts to prevent spread between provinces. Nor does it address efforts by provincial or territorial governments, Tribes, or non-governmental organizations (NGOs).

The authors seek to understand how federal infrastructure, strategies, and decisions have contributed to outcomes. Their principal recommendation is that Canada should accord protecting biodiversity as much importance as preventing direct economic impacts from invasive species – unlike now and in the past. Those economic impacts are substantial, estimated at $34.5 billion (Canadian) each year.

The authors think that such a focus is appropriate because Canadians depend on the stability and function of a wide range of ecosystems and express strong interest in protecting their environment. Canada has also accepted obligations to protect biological diversity by joining the Convention on Biological Diversity (CBD). One of those obligations was that, by 2020, the country would have put in place plans targetting high risk species and pathways of introduction..

The report notes that Canada faces some unique challenges: three coastlines, the intimate relationship with the U.S. (i.e., a long border and diverse shared water bodies), vast area, and very low human population density. The last might result in fewer incidents of human-mediated dispersal. However, it is likely to present logistical challenges in detecting and managing any invaders. In addition, common, popular Canadian recreational activities — camping, boating, and fishing — can contribute to invasive species’ introduction and spread.

hemlock mortality due to hemlock wooly adelgid in Nova Scotia; HWA had spread from the U.S. Photo courtesy of Celia Boone, NS Department of Land and Resources

Canada’s Biosecurity Efforts

Canada adopted its Invasive Alien Species Strategy in 2002. The plan addresses four stages of invasion: 1) prevention of new introductions; 2) early detection of newly introduced species; 3) rapid response to new invaders; and 4) management of species that are established and spreading.

The report laments that Canada lacks centralized oversight of it biosecurity efforts in preventing new introductions across all pathways. That is, responsibilities are divided among several agencies, depending on the associated commodity or resource. One result is that similar pathways are regulated differently. One example is ship-mediated vectors. Ballast water is strictly regulated by both Canadian regulations and the 2004 Convention for Control and Management of Ship’s Ballast Water and Sediments (which took effect in 2017). However, commercial fishing and recreational boats are not federally regulated.

In accordance with the CBD, the Canadian government submitted a report in 2018, claiming to be on track to achieve its 2020 targets. The government had identified priority pathways: shipping, horticulture, aquarium/pet trade, transport containers, road construction, and recreation (e.g., boating). Several had been regulated at least partially, including wood packaging, forestry products, and plant products. Legislative and regulatory tools had been strengthened, including risk assessments and management plans for ballast water, recreational boating, and wood packaging. (I cannot explain the conflicting assessments of the regulation of recreational boating.) Also, national plans had been developed for several priority species, including the Asian subspecies of Lymantria dispar and emerald ash borer. The country acknowledged gaps with regard to emerging animal diseases, the pet trade, and dispersal across the U.S. border.

Comparing Canada to Other Countries (see Table 2)

The United States: I am disappointed by the report’s comparison of Canadian and U.S. invasive species programs because it considers formal structures rather than how the programs work in reality. The Canadian report allots much greater authority to the U.S.’ interagency National Invasive Species Council (NISC) than I think it actually enjoys.

The report notes the abundance of U.S. data on invasive species’ distribution and hosts. It cites specifically the USDA Forest Service Forest Inventory Analysis. It also notes the importance of several transborder non-governmental organizations, including North American Invasive Species Management Association (NAISMA) and EDDmaps and binational entities such as the Great Lakes Fishery Commission.

Australia: The Canadian report praises the existence of an Inspector-General of Biosecurity who conducts independent reviews of biosecurity issues. It also applauds the coordinating role of the Intergovernmental Agreement on Biosecurity, which sets roles, responsibilities and governance agreements for biosecurity responses at all levels of government. Finally, it notes that the Department of Agriculture, Water and Environment (DAWE) created a National Priority List of Environmental Pests, Weeds and Diseases.

I have no independent understanding of how successful Australia has been in addressing invasive species. However, several forest health experts appear to have been dissatisfied with the country’s response to the introduction of Eucalyptus rust; see my blog.

New Zealand: Again, the report praises centralization of policy and government efforts in the Ministry for Primary Industries (MPI) under the provisions of the Biosecurity Act of 1993. The MPI advises the Minster for Biosecurity – which has no counterpart in the government of Canada. The report also notes that while New Zealand expects landowners and individuals to manage their own biosecurity risks, they can claim compensation if they suffer loss due to a biosecurity action, e.g., destruction of nursery stock. The Canadians think this provision might encourage people to report invasive species. New Zealanders are trying to create an all-citizen “team” to address invasive species. One way they promote this idea is to issue awards recognizing individuals’ efforts.

I wish the Canadian report had also looked at South Africa, which has done such a good job in its invasive species reports.

Four Case Studies

The report includes four case studies: a “historical failure”, a “historical success”, and two substantial current threats.

Preventing introductions of zebra and quagga mussels is described as a “historical failure”. There was no relevant preventive measure in place at the time they were introduced. Since preventive measures were made compulsory, no invasive species have been documented as becoming established in the Great Lakes via the ballast water pathway. Such introductions have occurred in less well-regulated marine systems.

Eradication of the Asian longhorned beetle (ALB) is described as a “historical success”. The initial Toronto outbreak was not completely eradicated; a small residual population was detected about a decade later and eradicated then. The report notes that the Toronto outbreaks were noticed by citizens rather than the relevant government agency. So “success” is attributable to chance and astute citizens rather than rigorous enforcement. I note that most U.S. detections of wood borer infestations are also detected by citizens. It is probably unrealistic to expect all detections to result from official programs.

The threat to Canada from the spotted lanternfly (SLF) is high since it could cross the land border from the U.S. Its principal host, Ailanthus, is widespread in southern Canada – not just in the East but also in Saskatchewan and Alberta. The insect’s egg masses are easily transported on a wide variety of vehicles. The report does not enumerate how many trucks or trains cross the border each year. The report laments that Canada has not adopted a clear monitoring plan aimed at detecting early SLF introduction.

Finally, four species of carp native to Asia threaten to invade the Great Lakes, for example through the Chicago canal or Sandusky River. Canada has asked citizens to be on the alert, and is exploring use of eDNA monitoring systems.

Lessons and Recommendations

The report highlights lessons learned in its four-country review and makes a series of recommendations:

1) Value biodiversity as well as economic and industrial interests.

The Canadian Species at Risk Act (its endangered species legislation) does not mention invasive species as a cause of endangerment. The Natural Sciences and Engineering Research Council now provides a centralized repository of biodiversity monitoring data which will help overcome data limitations associated with invasive species surveillance and risk modelling.

2) Consolidate regulatory frameworks

Canada should follow Australia and New Zealand in assigning a single body to be responsible for biosecurity. It should set biosecurity priorities, coordinate research and management at various government levels, and lay the groundwork for consistent actions.

3) Strengthen partnerships with the public and Indigenous communities

The report’s authors praise New Zealand’s efforts to engage all citizens in biosecurity. Canada would benefit from enhanced educational efforts – which are stronger now thanks to the growing availability of phone apps. Canada should ensure that Indigenous communities’ perspectives and knowledge are integrated into the program.

4) Strengthen partnerships with other countries

Canada should prioritize discussion of biosecurity with its trading partners, particularly in developing multinational trade agreements. This is a key improvement that the U.S. could make, too.) It is particularly important to strengthen collaboration with the U.S.

4) Adapt to future conditions

Canada will need to anticipate changes due to population increase and climate change. Research needs to recognize and overcome current taxonomic and geographic biases. Also, research should focus on developing new technologies and treatment techniques proactively, before they are needed. One area of concern will be migration corridors (or “assisted migration”) undertaken to protect biodiversity as the climate changes.

5) Anticipate conflict

The government must expect different perspectives among stakeholders. Greater transparency in education campaigns might help prevent disagreements from becoming serious barriers to action.

SOURCE

Posted by Faith Campbell

Forest Pests: What’s Improved, What’s Still to Do

sassafras – vulnerable to the rapidly spreading laurel wilt disease; photo by F.T. Campbell

In summer 2019 I posted several blogs summarizing my analysis of forest pest issues after 30 years’ engagement. I reported the continuing introductions of tree-killing insects and pathogens; their relentless spread and exacerbated impacts. I noted the continued low priority given these issues in agencies tasked with preventing and solving these problems. Also, Congress provides not only insufficiently protective policies but also way too little funding. I decried the impediments created by several Administrations; anti-regulatory ideology and USDA’s emphasis on “collaborating” with “clients” rather than imposing requirements.

In my blogs, I called for renewed effort to find more effective strategies – as I had earlier advocated in my “Fading Forests” reports (link provided at the end of this blog), previous blogs, and Lovett et al. 2016

Areas of Progress

Now two years have passed. I see five areas of progress – which give me some hope.

1) Important Activities Are Better Funded than I had realized

a) The US Forest Service is putting significant effort into breeding trees resistant to the relevant pests, more than I had realized. Examples include elms and several conifer species in the West – here and here.

b) USDA has provided at least $110 million since FY2009 to fund forest pest research, control, and outreach under the auspices of the Plant Pest and Disease Disaster Prevention Program (§10201 of the Farm Bill). This total does not include additional funding for the spotted lanternfly. Funded projects, inter alia: explored biocontrol agents for Asian longhorned beetle and emerald ash borer; supported research at NORS-DUC on sudden oak death; monitored and managed red palm weevil and coconut rhinoceros beetle; and detected Asian defoliators. Clearly, many of these projects have increased scientific understanding and promoted public compliance and assistance in pest detection and management.

This section of the Farm Bill also provided $3.9 million to counter cactus pests – $2.7 million over 10 years targetting the Cactoblastis moth & here and $1.2 million over four years targetting the Harissia cactus mealybug and here.

flat-padded *Opuntia* cactus – vulnerable to the *Cactoblastis* moth; National Park Service photo

2) Additional publications have documented pests’ impacts – although I remain doubtful that they have increased decision-makers’ willingness to prioritize forest pests. Among these publications are the huge overview of invasive species published last spring (Poland et al.) and the regional overview of pests and invasive plants in the West (Barrett et al.).

3) There have been new efforts to improve prediction of various pests’ probable virulence (see recent blogs and here.

4) Attention is growing to the importance of protecting forest health as a vital tool in combatting climate change — see Fei et al., Quirion et al., and IUCN. We will have to wait to see whether this approach will succeed in raising the priority given to non-native pests by decision-makers and influential stakeholders.

5) Some politicians are responding to forest pest crises – In the US House, Peter Welch (D-VT) is the lead sponsor of H.R. 1389. He has been joined – so far – by eight cosponsors — Rep. Kuster (D-NH), Pappas (D-NH), Stefanik (R-NY), Fitzpatrick (R-PA), Thompson (D-CA), Ross (D-NC), Pingree (D-ME), and Delgado (D-NY). This bill would fund research into, and application of, host resistance! Also, it would make APHIS’ access to emergency funds easier. Furthermore, it calls for a study of ways to raise forest pests’ priority – thus partially responding to the proposal by me and others (Bonello et al. 2020; full reference at end of blog) to create federal Centers for Forest Pest Control and Prevention.

This year the Congress will begin work on the next Farm Bill – might these ideas be incorporated into that legislation?

What Else Must Be Done

My work is guided by three premises:

1) Robust federal leadership is crucial:

The Constitution gives primacy to federal agencies in managing imports and interstate trade.
Only a consistent approach can protect trees (and other plants) from non-native pests that spread across state lines.
Federal agencies have more resources than state agencies individually or in likely collective efforts – even after decades of budget and staffing cuts.

2) Success depends on a continuing, long-term effort founded on institutional and financial commitments commensurate with the scale of the threat. This requires stable funding; guidance by research and expert staff; and engagement by non-governmental players and stakeholders. Unfortunately, as I discuss below, funding has been neither adequate nor stable.

3) Programs’ effectiveness needs to be measured. Measurement must focus on outcomes, not just effort (see National Environmental Coalition on Invasive Species’ vision document).

Preventing New Introductions – Challenges and Solutions

We cannot prevent damaging new introductions without addressing two specific challenges.

1) Wood packaging continues to pose a threat despite past international and national efforts. As documented in my recent blogs, the numbers of shipping containers – presumably with wood packaging – are rising. Since 2010, CBP has detected nearly 33,000 shipments in violation of ISPM#15. The numbers of violations are down in the most recent years. However, a high proportion of pest-infested wood continues to bear the ISPM#15 mark. So, ISPM#15 is not as effective as it needs to be.

We at CISP hope that by mid-2022, a new analysis of the current proportion of wood packaging harboring pests will be available. Plus there are at least two collaborative efforts aimed at increasing industry efforts to find solutions – The Nature Conservancy with the National Wooden Pallet and Container Association; and the Cary Institute with an informal consortium of importers using wooden dunnage.

2) Imports of living plants (“plants for planting”) are less well studied so the situation is difficult to assess. However, we know this is a pathway that has often spread pests into and within the US. There have been significant declines in overall numbers of incoming shipments, but available information doesn’t tell us which types of plants – woody vs. herbaceous, plant vs. tissue culture, etc. – have decreased.

APHIS said, in a report to Congress (reference at end of blog), that introductions have been curbed – but neither that report nor other data shows me that is true.

Scientists are making efforts to improve risk assessments by reducing the number of organisms for which no information is available on their probable impacts (the “unknown unknowns”).

Solving Issues of Prevention

While I have repeatedly proposed radical revisions to the international phytosanitary agreements (WTO SPS & IPPC) that preclude prevention of unknown unknowns (see Fading Forests II and blog), I have also endorsed measures aimed at achieving incremental improvements in preventing introductions, curtailing spread, and promoting recovery of the affected host species.

citrus longhorned beetle exit hole in bonsai tree; USDA APHIS photo

The more radical suggestions focus on: 1) revising the US Plant Protection Act to give higher priority to preventing pests introductions than to facilitating free trade (FF II Chapter 3); 2) APHIS explicitly stating that its goal is to achieve a specific, high level of protection (FF II Chapter 3); 3) APHIS using its authority under the NAPPRA program to prohibit imports of all plants belonging to the 150 genera of “woody” plants that North America shares with Europe or Asia; 4) APHIS prohibiting use of packaging made from solid wood by countries and exporters that have a record of frequent violations of ISPM#15 in the 16 years since its implementation.

Another action leading to stronger programs would be for APHIS to facilitate outside analysis of its programs and policies to ensure the agency is applying the most effective strategies (Lovett et al. 2016). The pending Haack report is an encouraging example.

I have also suggested that APHIS broaden its risk assessments so that they cover wider categories of risk, such as all pests that might be associated with bare-root woody plants from a particular region. Such an approach could speed up analyses of the many pathways of introduction and prompt their regulation.

Also, APHIS could use certain existing programs more aggressively. I have in mind pre-clearance partnerships and Critical Control Point integrated pest management programs. APHIS should also clarify the extent to which these programs are being applied to the shipments most likely to transport pests that threaten our mainland forests, i.e. imports of woody plants belonging to genera from temperate climates. APHIS should promote more sentinel plant programs. Regarding wood packaging, APHIS could follow the lead of CBP by penalizing importers for each shipment containing noncompliant SWPM.

Getting APHIS to prioritize pest prevention over free trade in general, or in current trade agreements, is a heavy lift. At the very least, the agency should ensure that the U.S. prioritize invasive species prevention in negotiations with trading partners and in developing international trade-related agreements. I borrow here from the recent report on Canadian invasive species efforts. (I complained about APHIS’ failure to even raise invasive species issues during negotiation of a recent agricultural trade agreement with China.)

Solving Issues of Spreading Pests

The absence of an effective system to prevent a pest’s spread within the U.S. is the most glaring gap in the so-called federal “safeguarding system”. Yet this gap is rarely discussed by anyone – officials or stakeholders. APHIS quarantines are the best answer – although they are not always as efficacious as needed – witness the spread of EAB and persistence of nursery outbreaks of the SOD pathogen.

APHIS and the states continue to avoid establishing official programs targetting bioinvaders expected to be difficult to control or that don’t affect agricultural interests. Example include laurel wilt, and two boring beetles in southern California – goldspotted oak borer, Kuroshio shot hole borer and polyphagous shot hole borer and their associated fungi.

One step toward limiting pests’ spread would come from strengthening APHIS’ mandate in legislation, as suggested above. A second, complementary action would be for states to adopt quarantines and regulations more aggressively. For this to happen, APHIS would need to revise its policies on the “special needs exemption” [7 U.S.C. 7756]. Then states could adopt more stringent regulations to prevent introduction of APHIS-designated quarantine pests (Fading Forests III Chapt 3).

Finally, APHIS should not drop regulating difficult-to-control species – e.g., EAB. There are repercussions.

APHIS’ dropping EAB has not only reduced efforts to prevent the beetle’s spread to vulnerable parts of the West. It has also left states to come up with a coherent approach to regulating firewood; they are struggling to do so.

Considering interstate movement of pests via the nursery trade, the Systems Approach to Nursery Certification (SANC) program) is voluntary and was never intended to include all nurseries. Twenty-five nurseries were listed on the program’s website as of March 2020. It is not clear how many nurseries are participating now. The program ended its “pilot” phase and “went live” in January 2021. Furthermore, the program has been more than 20 years in development, so it cannot be considered a rapid response to a pressing problem.

Solving Issues of Recovery and Restoration via Resistance Breeding

I endorse the findings of two USFS scientists, Sniezko and Koch citations. They have documented the success of breeding programs when they are supported by expert staff and reliable funding, and have access to appropriate facilities. The principle example of such a facility is the Dorena Genetic Resource Center in Oregon. Regional consortia, e.g., Great Lakes Basin Forest Health Collaborative and Whitebark Pine Ecosystem Foundation are trying to overcome gaps in the system. I applaud the growing engagement of stakeholders, academic experts, and consortia. Questions remain, though, about how to ensure that these programs’ approaches and results are integrated into government programs.

resistant and vulnerable ash seedlings; photo courtesy of Jennifer Koch, USFS

In Bonello et al., I and others call for initiating resistance breeding programs early in an invasion. Often other management approaches, e.g., targetting the damaging pest or manipulating the environment, will not succeed. Therefore the most promising point of intervention is often with by breeding new or better resistance in the host. This proposal differs slightly from my suggestion in the “30 years – solutions” blog, when I suggested that USFS convene a workshop to develop consensus on breeding program’s priorities and structure early after a pest’s introduction.

Funding Shortfalls

I have complained regularly in my publications (Fading Forests reports) and blogs about inadequate funding for APHIS Plant Protection program and USFS Forest Health Protection and Research programs. Clearly the USDA Plant Pest and Disease Management and Disaster Program has supported much useful work. However, its short-term grants cannot substitute for stable, long-term funding. In recent years, APHIS has held back $14 – $15 million each year from this program to respond to plant health emergencies. (See APHIS program reports for FYs 20 and 21.) This decision might be the best solution we are likely to get to resolve APHIS’ need for emergency funds. If we think it is, we might drop §2 of H.R. 1389.

Expanding Engagement of Stakeholders

Americans expect a broad set of actors to protect our forests. However, these groups have not pressed decision-makers to fix the widely acknowledged problems: inadequate resources – especially for long-term solutions — and weak and tardy phytosanitary measures. Employees of federal and state agencies understand these issues but are restricted from outright advocacy. Where are the professional and scientific associations, representatives of the wood products industry, forest landowners, environmental NGOs and their funders, plus urban tree advocates – who could each play an important role? The Entomological Society’s new “Challenge” is a welcome development and one that others could copy.

SOURCES

Bonello, P., Campbell, F.T., Cipollini, D., Conrad, A.O., Farinas, C., Gandhi, K.J.K., Hain, F.P., Parry, D., Showalter, D.N, Villari, C. and Wallin, K.F. (2020) Invasive Tree Pests Devastate Ecosystems—A Proposed New Response Framework. Front. For. Glob. Change 3:2. doi: 10.3389/ffgc.2020.00002

Krishnankutty, S., H. Nadel, A.M. Taylor, M.C. Wiemann, Y. Wu, S.W. Lingafelter, S.W. Myers, and A.M. Ray. 2020. Identification of Tree Genera Used in the Construction of Solid Wood-Packaging Materials That Arrived at U.S. Ports Infested With Live Wood-Boring Insects. Journal of Economic Entomology 2020, 1 – 12

Liebhold, A.M., E.G. Brockerhoff, L.J. Garrett, J.L. Parke, and K.O. Britton. 2012. Live plant imports: the major pathway for forest insect and pathogen invasions of the US. Front. Ecol. Environ. 2012; 10(3):135-143

Lovett, G.M., M. Weiss, A.M. Liebhold, T.P. Holmes, B. Leung, K.F. Lambert, D.A. Orwig, F.T. Campbell, J. Rosenthal, D.G. McCullough, R. Wildova, M.P. Ayres, C.D. Canham, D.R. Foster, SL. Ladeau, and T. Weldy. 2016. NIS forest insects and pathogens in the US: Impacts and policy options. Ecological Applications, 26(5), 2016, pp. 1437–1455

Mech, A.M., K.A. Thomas, T.D. Marsico, D.A. Herms, C.R. Allen, M.P. Ayres, K.J. K. Gandhi, J. Gurevitch, N.P. Havill, R.A. Hufbauer, A.M. Liebhold, K.F. Raffa, A.N. Schulz, D.R. Uden, & P.C. Tobin. 2019. Evolutionary history predicts high-impact invasions by herbivorous insects. Ecol Evol. 2019 Nov; 9(21): 12216–12230.

Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Spp in Forests and Grasslands of the US: A Comprehensive Science Synthesis for the US Forest Sector. Springer Verlag. (in press).

Roy, B.A., H.M Alexander, J. Davidson, F.T Campbell, J.J Burdon, R. Sniezko, and C. Brasier. 2014. Increasing forest loss worldwide from invasive pests requires new trade regulations. Front Ecol Environ 2014; 12(8): 457–465

Schulz, A.N., A.M. Mech, M.P. Ayres, K. J. K. Gandhi, N.P. Havill, D.A. Herms, A.M. Hoover, R.A. Hufbauer, A.M. Liebhold, T.D. Marsico, K.F. Raffa, P.C. Tobin, D.R. Uden, K.A. Thomas. 2021. Predicting non-native insect impact: focusing on the trees to see the forest. Biological Invasions.

United States Department of Agriculture Animal and Plant Health Inspection Service. Report on the Arrival in the US of Forest Pests Through Restrictions on the Importation of Certain Plants for Planting. https://www.caryinstitute.org/sites/default/files/public/downloads/usda_forest_pest_report_2021.pdf

Posted by Faith Campbell

Wood packaging – Progress? or Paralysis by Analysis?

This February marks 16 years since APHIS began full implementation of ISPM#15. I have blogged often about the failure of ISPM#15 to curtail the risk associated with wood packaging; scroll below the chronological list of blogs to the “categories”, click on “wood packaging”. The best summary of the issues is found in a blog posted in September 2017.

As I have reported in many previous blogs, U.S. imports – especially those from Asia – have been rising since August 2020. Thus, January through October 2021, U.S. imports from Asia are 10.5% higher than the same period in 2020 (Mongelluzzo Dec. 9, 2021). Port officials expect import volumes from Asia to remain high in the first half of 2022, with perhaps a pause in February linked to Asian New Year celebrations (Mongelluzzo Dec. 15 2021). Shipping tonnage devoted to carrying goods from Asia to North America rose by 17% when one compares 2020 to 2021 (Lynch and Wadekar 2021).

These increases are important because of the history of pest introductions in wood packaging from Asia.

This increase is seen most acutely at the ports of Los Angeles and Long Beach, which handle about 50% of all U.S. imports from Asia. Such imports during January – November 2021 were 19.4% higher than the same period in 2020; 21.2% higher than during the same period in 2019 (Mongelluzzo Dec. 15 2021).

The rise in imports – and associated pest risk — is not limited to southern California. At the largest port on the East coast – New York/New Jersey – import volumes through October were 20% higher than the same period a year ago. The port is also receiving a higher number of large ships – those carrying 9,000 or more containers (Angell Dec. 22, 2021).

We do not know how many of these containers hold the heaviest commodities most often associated with wood packaging infested by insects — machinery (including electronics); metals; tile and decorative stone (such as marble or granite counter tops). I see many potential links to the COVID-prompted “home improvement” boom. I wonder whether furniture should be included here …

wood packaging associated with stone; photo courtesy of Canadian Food Inspection Agency

1. 2021 Data on Violations

A recent webinar sponsored by The Nature Conservancy’s Continental Dialogue on Non-Native Forest Insects and Diseases and the Entomological Society of America revealed important new information on the pest risk associated with these imports. (Presentations have been posted on the Dialogue’s website). Several of the presentation have particularly significant implications for protecting the US from pests.

Jared Franklin, acting director for agriculture enforcement for DHS’s Customs and Border Protection (CBP), reported that pest detections and shipper violations in Fiscal Year (FY) 2021 follow patterns set earlier. There is, however, an interesting decline in numbers of violations despite enhanced inspection intensity. When the number of incoming air passengers crashed because of COVID-19, CBP assigned inspectors to cargo instead.

Type of violation	FY2018	FY2019	FY2020	FY2021
Lack ISPM#15 mark	1,662	1,825	1,662	1,459
Live quarantine pest found	756	747	509	548
TOTAL VIOLATIONS	2,418	2,572	2,171	2,007

Unfortunately, in FY2016 CBP stopped recording whether pests were detected on marked or unmarked SWPM.

As usual, most of the pests were detected in wood packaging accompanying miscellaneous cargo. Also, as usual, the most commonly detected pests are Cerambycid beetles. During a discussion of why Cerambycids outnumber Scolytids, Bob Haack pointed out that most bark beetles are eliminated by the debarking required by ISPM#15.

2. Updating a Key Study of the Wood Packaging Pathway

Bob Haack revealed that he has received permission to update his earlier landmark study aimed at determining the arrival rate of pests in wood packaging (see Haack et al., 2014). I have long advocated for an update. All my comment about the wood packaging risk have – perforce – relied on this now outdated report. Bob hopes to have results in a few months.

This time, he will work with Toby Petrice (USFS) and Jesse Hardin and Barney Caton (APHIS). While the 2014 study focused on changes in approach rates resulting from U.S.’ implementation of ISPM#15, the new study will presumably uncover current levels of compliance. The authors will use more than 73,000 new port inspection records to detect trends from 2010 through 2020, as well as the original database of about 35,000 inspections made during 2004-2009.

Bob notes that there have been significant changes in ISPM#15 since 2009. These include: a) a requirement that wood be debarked before treatment; b) approval of new treatments (dielectric heat in 2013 and sulphuryl fluoride in 2018); and c) new official definitions of “reuse,” “repair,” and “remanufacturer”.

Besides discovering overall levels of compliance, Bob and colleagues will probably select some aspects of the wood packaging pathway for specific analysis. For example, Dialogue participants want to know whether dunnage has a higher interception rate than pallets. Also, the earlier study included only wood packaging that bore the ISPM mark. This new research might compare live pest interception rates on marked versus unmarked wood.

3) A Study to Improve ISPM#15

Erin Cadwalader reported on the Entomological Society’s Grand Challenge, particularly the request from APHIS that the Society provide guidance on improving ISPM#15. This request was made in 2019; subsequent efforts to conduct a broad scoping process have been complicated and delayed by COVID-19. The goal is to determine what area of effort would lead to either 1) the highest reduction in pest incidence; or 2) the best ISPM#15 compliance.

ESA’s preliminary proposal aims to evaluate the risk associated with various types of wood packaging by analyzing data from five ports over a period of five years. Webinar participants discussed the proposal, especially trying to determine why data already collected by APHIS and CBP – specifically via Agriculture Quarantine Inspection Monitoring (AQIM) – are not adequate to support the study. Another question is whether it is useful for ESA investigators to attempt to rear insects from wood packaging rather than rely on APHIS’ identifications using molecular techniques. Erin noted that some insects – probably particularly small wood borers – might escape detection by inspectors but show up when the wood is placed in rearing chambers.

There will be further discussion of the study’s scope and methodology at the Society’s annual meeting in Autumn 2023 near Washington, D.C. (The 2022 meeting will be in Vancouver; USDA officials rarely get permission to travel to meetings outside the U.S.) ESA estimates that the study will take five years and be completed in 2028.

I am concerned that APHIS might not act on the basis of Bob Haack’s findings as soon as they are available. If they wait for completion of the ESA study, it could be at least six years from now before action is even proposed. I hope that if Haack and colleagues uncover persistent inadequacies in ISPM#15 implementation, APHIS will act unilaterally to address the problem – at least as regards the threat to the U.S. The ESA study might then become the foundation for revising the overall standard per se, that is, the entire world trading system.

Also, APHIS has already carried out a focused study of pests in wood packaging. How can their findings be incorporated into APHIS’ decisions so as to expedite action?

Wu et al. (2017) proved the efficacy of DNA identification tools and that serious pest species continued (at that time) to be present in wood packaging. Krishnankutty et al. (2020) found that 84% of interceptions occurred in wood belonging to only three families: pine, spruce, and poplar. Shipments with coniferous wood came about equally from Europe, Asia, and Mexico. Wood packaging made from poplars came primarily from China. Most of the pests in hardwood were polyphagous, and were considered to pose a higher risk. Pests in softwood samples were mostly oligophagous (feed on two or more genera in the same family). I presume that these findings prompted the studies by Mech et al. and Schulz et al.

As has been true in most studies, pest detections were often associated with shipments of heavy items, such as stone, ceramics, and terracotta; vehicles and vehicle parts; machinery, tools, and hardware; and metal. A high proportion (87%) of the wood packaging bore the ISPM15 mark, also as usual. (Data provided by CBP in past Dialogue meetings showed an even higher proportion of pest-infested wood to be marked.)

Conclusion

Clearly, programs aimed at curtaining the pest risk associated with wood packaging have not been sufficiently effective. I hope APHIS’ approval of Bob Haack’s study and agreement with the Entomological Society indicates a new willingness to understand why and take actions to fix the problems.

SOURCES

Haack, R.A., K.O. Britton, E.G. Brockerhoff, J.F. Cavey, L.J. Garrett. 2014. Effectiveness of the International Phytosanitary Standard ISPM No. 15 on Reducing Wood Borer Infestation Rates in Wood Packaging Material Entering the United States. PLoS ONE 9(5): e96611. doi:10.1371/journal.pone.0096611

Lynch, D.J. and N. Wadekar. 2021. “Africa left with fallout of US supply chain crisis”. The Washington Post. December 17, 2021.

Mongelluzzo, B. Dec 09, 2021. New long-dwell container fee bearing fruit in Oakland https://www.joc.com/port-news/terminal-operators/new-long-dwell-container-fee-bearing-fruit-oakland_20211209.html?utm_campaign=CL_JOC%20Ports%2012%2F15%2F21%20%20_PC00000_e-production_E-121985_TF_1215_0900&utm_medium=email&utm_source=Eloqua

Mongelluzzo, B. Dec. 15 2021. LA port expects imports to surge further in Q2https://www.joc.com/port-news/us-ports/la-port-expects-imports-surge-further-q2_20211215.html?utm_source=Eloqua&utm_medium=email&utm_campaign=CL_JOC%20Daily%2012/16/21_PC00000_e-production_E-122356_KB_1216_0617

Wu,Y., N.F. Trepanowski, J.J. Molongoski, P.F. Reagel, S.W. Lingafelter, H. Nadel1, S.W. Myers & A.M. Ray. 2017. Identification of wood-boring beetles (Cerambycidae and Buprestidae) intercepted in trade-associated solid wood packaging material using DNA barcoding and morphology. Scientific Reports 7:40316

Posted by Faith Campbell

Living Plant Imports: Scientists Try to Counter Longstanding Problems

American chestnut – nearly eradicated by a disease introduced on imported plants

Shipments of living plants (called by phytosanitary agencies “plants for planting”) have long been recognized as the most “effective” pathway for transporting pests. To those of us concerned about forest ecosystems, the focus is on woody plants. I have no reason to think herbaceous plant imports are any less risky.

International Rules Impede Prevention Efforts

Efforts to prevent pest introductions via shipments of plants for planting suffered a severe setback when the World Trade Organization Agreement on the Application of Sanitary and Phytosanitary Standards (SPS Agreement) came into force in 1995. Two years later the International Plant Protection Convention (IPPC) was amended to conform to those new trade rules.

David McNamara, then Assistant Director of the European and Mediterranean Plant Protection Organization, identified the ramifications of the new regime: phytosanitary agency officials “have come to realize that our work has changed from ‘preventing introduction of pests while not interfering unduly with trade’ to ‘facilitating trade while doing our utmost to prevent pest introduction.’” [See Chapter 3 of Fading Forests II (2003), available here where I detail how the SPS Agreement and IPPC rules changed phytosanitary policy.]

I was not alone in raising the alarm about the ramifications of the new regime: that phytosanitary regulations target only pests known to cause damage; that commodities from all sources be treated as if they posed equal pest risks, which is not true; that phytosanitary rules impose the lowest level of restriction on trade required to achieve the chosen level of protection.

Scientists Try to Reverse the Damaging Requirements

For example, world-renowned UK pathologist Clive Brasier (2008; full reference at end of the blog) criticized the requirement that pests be identified before they can be regulated. Dr. Brasier estimated that 90% of plant pathogens might be unknown to science, and thus not eligible for regulation under the WTO/IPPC regime. This means that damaging pests are frequently regulated only after they have been introduced and initiated the essentially permanent alteration of the receiving (naïve) environment. He called for an approach based on Darwinian evolutionary theory: maintenance of the geographic barriers that separate species.

A growing number of scientists have reiterated the criticisms in hopes of persuading regulators to reverse the flaws identified in the international trade rules. More than 70 scientists affiliated with the International Union of Forest Research Organizations signed the Montesclaros Declaration in 2011. Circa 2015 – 20 years after the SPS Agreement came into force – several publications reiterated these criticisms and provided scientific support for changing the rules: Roy et al. 2014; Eschen, Roques and Santini 2015; Jung et al. 2015; Klapwijk et al. 2016; and now Barwell et al. 2021. Summaries follow.

Roy et al. (2014) said the WTO SPS rules have been largely ineffective at protecting forests and other ecosystems (natural or managed) for two main reasons: (1) their primary aim is to promote international trade rather than protect the environment and (2) they require that a species be identified as a pest before it can be regulated, even though invading organisms are often either “new” (i.e. scientifically unknown) species or not troublesome within their native ranges.

Eschen, Roques and Santini (2015) found that regulators’ focus on known pests meant that 90% of the exotic insect pests detected in Europe 1995–2004 had not been designated for regulation before they became established on the continent.

Klapwijk et al. (2016) concluded that the European Union phytosanitary rules have provided insufficient protection because often harmful organisms that enter the EU were unknown, and therefore unregulated, before establishment. A pending amendment would still not provide for precautionary assessments of high-risk commodities or provide for restrictions on the highest-risk commodities, such as imports of large plants or plants in soil. Green et al. (2021) call the international system “fallible” in the face of huge volumes of imports, including large, semi-mature trees. As Jung et al. 2018 point out, the scientific community has repeatedly urged regulators to require the use of preventative system approaches for producing Phytophthora-free nursery stock.

Scott Schlarbaum, University of Tennessee, and I reiterated these issues and cited additional examples in Chapter 7 of Fading Forests III. Since 2015 I have blogged numerous times about the risks associated with imported plants for planting and detection of numerous previously unknown Phytophthora species in Vietnam. [On the website, scroll to the bottom of the monthly listing of blogs, find the “categories” section, click on “plants as pest vectors”.]

Billions of Plant on the Move

Shipment of plants among America, Europe and Asia put all three continents at risk. First, North America, Europe and Asia share more than 100 genera of tree species (USDA 2000), so introduced insects and microbes are likely to find suitable hosts in their new home.

Second, North America and Europe import high volumes of plants. The U.S. imported an estimated 3.2 billion plant “units” (cuttings, rooted plants, tissue culture, etc.) in 2007 (Liebhold et al. 2012). By 2020, imports had declined to 1.8 B plant units plus nearly 723,000 kilograms of woody plant seeds (USDA 2021). Epanchin-Niell (pers. comm.) found that in the period FY2010-FY2012, the U.S. imported an average of about 300 million woody plant units per year (in 16,700 shipments). The plants included representatives of 175 woody plant genera. Europe imports even more plants; just 10 continental countries imported 4.3 billion living plants from overseas in 2010; 20.8% were woody plants (Jung 2015). The United Kingdom, home to famously enthusiastic gardeners, imported £1.3 billion worth of plants in 2018 (Green et al. 2021). Eschen, Roques and Santini (2015) document the rising number of invertebrate pests and pathogens associated with these imports. Green et al. (2021) note the risk to social values, especially tree plantings to sequester carbon, posed by rising introductions of tree-killing pathogens.

In response to the obvious failings of the international phytosanitary system, non-governmental experts have sought strict limits on imports of plant taxa and types posing the highest risk. Campbell and Schlarbaum (2003 and 2014) and Roy et al. (2014) advocate allowing entry of woody plants only in the form of seed and tissue cultures. Lovett et al. (2016) calls for applying APHIS’ NAPPRA authority to prohibit imports of woody plants in the 150 genera that North America shares with Europe and Asia. (I have criticized how NAPPRA is applied in earlier blogs – here and here.) Eschen, Roques and Santini (2015) suggest requiring that most imported plants be subjected to post-entry quarantine.

illustration of poor management practices that facilitate infection by *Phytopthora ramorum*; from nursery education material circulated by Washington State University

Yet, I see no evidence that either American or European governments are willing to consider substantial alteration of the international system – even in order to curb the highest risk. The current WTO/IPPC system at least contemplates another solution: requiring that imported plants be produced under clean stock or critical control point production programs. See ISPM#36 and RSPM#24 and USDA APHIS’ revision of the Q-37 regulation. Use of critical control point approaches has been suggested by Campbell and Schlarbaum (2014). It is also part of the comprehensive program called for by Jung et al. (2015). Jung et al. (2015) note the need for rigorous enforcement as well as campaigns to develop consumer awareness, creating an incentive for the nursery industry to distribute only clean stock. However, the non-governmental authors advocate application of critical control point programs to far more plant taxa than the phytosanitary officials have envisioned, so apparent agreement between advocates and officials is illusory. Attempts to create such a program are more advance domestically, for example see Swiecki, et al, 2021.

New Ways to Fix the System?

Unwilling to challenge the WTO/IPPC system directly, national phytosanitary officials are instead adopting approaches and technologies aimed at reducing the number of species that remain “unknown”. New molecular identification techniques are facilitating rapid identification of difficult-to-distinguish microbes at ports or as part of screening or monitoring programs. This advance is cheered by scientists [e.g., Eschen, Roques and Santini (2015); Jung et al. (2015)] as well as phytosanitary officials.

Authorities are also attempting to improve inspection at the border by targetting shipments thought to be of high risk.

Both these actions have limited efficacy, however. Eschen, Roques and Santini (2015) still say that given the difficulty of reliably identifying fungi and fungal-like organisms, authorities should reject any consignment with disease symptoms. Furthermore, greater certainty in identifying organisms does not overcome information gaps about their invasibility or possible virulence.

Targetting based on past interceptions, a mainstay of inspection programs, is increasingly considered unreliable – scientists warn about the “bridgehead effect”. That is, when non-native pests establish in new countries and then are transported from there [see Bertelsmeier and Ollier (2021); although this article concerns ants].

Others are exploring strategies to improve authorities’ ability to evaluate poorly known species’ possible impacts. There is enthusiastic endorsement of the concept of “sentinel” plantings. These are a tool to detect pests that attack tree species growing outside the host tree’s natural range. Others are trying to identify species traits or other factors that can be used to predict impacts, as explored below.

Scientists’ Efforts in North America

loblolly pine (*Pinus taeda*) — one of the pines tested by Li *et al*. photo by Dcrjsr, via Wikimedia

One team assessed 111 fungi associated with 55 Asian and European scolytine beetle species. None was found to be virulent pathogens on two pine species and two oak species native to the Southeastern U.S. (defined as having an impact similar to Dutch elm disease or laurel wilt). Twenty-two fungal species were minor pathogens (Li et al. 2021).

Mech et al. (2019) are trying to rank threats by non-native insects pose to North American tree species. (They did not evaluate pathogens). They evaluated the probability of a non-native insect causing high impact on a novel North American host as a function of the following: (a) evolutionary divergence time between native and novel hosts; (b) life history traits of the novel host; (c) evolutionary relationship of the non-native insect to native insects that have coevolved with the shared North American host; and (d) the life history traits of the non-native insect. The team has published its analyses of insects that specialize on conifers and hardwoods; they will publish on generalist insect pests in the near future. The insects evaluated were those identified in studies by Aukema et al. (2010) and Yamanaka et al. (2015).

Regarding conifers, the factors driving impacts were found to be:

1) The time (in millions of years) since a North American host tree species diverged from a coevolved host of the insect in its native range.

2) The tree host species’ shade and drought tolerance.

3) The presence or absence of a closely related native herbivore in North America.

None of the insect life history traits examined, singly or in combination, had predictive value.

There are interesting differences when considering hardwoods. Schultz et al. (2021) find that the most important predictive factor is an insect trait: being a scolytine beetle. Two tree-related factors are moderately predictive: moderate density of the wood, and divergence time between native and novel hardwood hosts.While this last factor is shared with the analysis of insects on conifers, the divergence period itself differs. For hardwood trees there is no predictive value tied to whether a related native insect attacks the North American host.

[For details, see also the blogs posted here and here.]

In a report issued earlier this year, in response to §10110 of the Agriculture Improvement Act (Farm Bill) of 2018 (USDA 2021), APHIS claims that recent changes to managing plant imports has cut interceptions via the plants for planting pathway to 2% of total forest pest interceptions during the period 2013 – 2018. The contributing agency actions are listed as

• Developing an offshore greenhouse certification program that gives U.S. producers a more reliable supply chain of healthy plant cuttings;

• Implementing risk-based sampling to focus port inspections on higher-risk shipments [but note questions about this approach raised by Eschen, Roques and Santini (2015)].

• Began using of molecular diagnostics at ports to detect high-risk pests that physical inspection would miss;

• Restricting imports of some plants under authority of the NAPPRA program; and

• Increasingly applying standardized systems approaches.

APHIS says its preclearance programs span 23 countries and cover 68 different types of commodities. In addition, APHIS has certified 25 offshore facilities in 12 countries. However, the report does not say how many of these agreements cover production of woody plants – those most likely to transport forest pests.

APHIS has had a greenhouse certification program with Canada since 1996. A high proportion of U.S. woody plant imports comes from Canada. The recent report (USDA 2021) lists source countries for the highest numbers of pest interceptions for plants for planting – although not in order of detections. Canada is listed – in bold type. The meaning of this highlight is not explained. (China is also listed in bold.) More disturbing, the report makes no mention of the suspicion that at least some of the plants infested by Phytophthora ramorum that were shipped to 18 states in spring 2019 originated in a British Columbia nursery.

Scientists’ Efforts in Europe

The focus in Europe appears to be on pathogens, specifically the Phytophthora genus. Europeans are responding to several recently-introduced highly damaging diseases caused by species in the genus that were unknown to science before introduction. Barwell and colleagues (full reference at end of the blog) sought to explain the species’ impact as measured by traits such as number of countries invaded, latitudinal limits, and host range. They evaluated factors they thought would be easily discerned, such as species’ traits, phylogeny and time since description (as a proxy for extent of scientific understanding of the species’ behavior). The most predictive traits were thermal minima, oospore wall index and growth rate at optimum temperature. They found that root-attacking species of Phytophthora were reported in more countries and on more host families than foliar-attacking species.

Japanese larch plantation in Britain killed by *Phytophthora ramorum*; photo from UK Forest Research

Progress – but Still Incomplete Solution to the SPS/IPPC Conundrum

Perhaps these efforts to close information gaps earlier in the invasion process will be accepted by the phytosanitary agencies and the findings will be incorporated into their decision-making. If this happens, scientists’ efforts might contribute substantially to overcoming the challenges created by the SPS/IPPC system. Presumably acting on scientific findings is more acceptable than the more radical approach that I and others have suggested. Still, there remain the “unknown unknowns” – and the SPS/IPPC system continues to hinder measures that might be effective in preventing their introduction.

Meanwhile, the British are pursuing both a nursery certification/accreditation program and a coordinated strategy for early detection of Phytophthora pathogens in the nursery trade. Green et al. (2021) found that nursery owners could not justify the cost of adopting best management practices if they were aimed at preventing the presence of Phytophthora alone. They could if the program sought to curtail the presence and spread of numerous plant pathogens. A decade ago in the U.S., The Nature Conservancy explored a possible structure combining a clean stock system with insurance. The latter would reimburse participating nurseries for inventory lost to pests as long as the nursery used prescribed pest-avoidance strategies. The SANC program attempts to incentivize adoption of clean stock systems by the American nursery industry. However, it does not include the insurance concept.

Another helpful step would be to change the pest risk assessment process by assessing the risks more broadly. Perhaps the analysis could evaluate the risks associated with – and determine effective measures to counter – certain organisms, i.e.:

(a) pests associated with any bare-root woody plants from a particular region, for example East Asia; (b) pests associated with roots or stems, without limiting the study to particular kinds of plants or geographic regions of origin; or

(c) single types of pests, such as a fungal pathogen without regard to its species, on any imported plant (regardless of taxon or country of origin), especially learning how to prevent their presence.

SOURCES

Aukema, J.E., D.G. McCullough, B. Von Holle, A.M. Liebhold, K. Britton, & S.J. Frankel. 2010. Historical Accumulation of Nonindigenous Forest Pests in the Continental United States. Bioscience. December 2010 / Vol. 60 No. 11

Barwell, L.J., A. Perez-Sierra, B. Henricot, A. Harris, T.I. Burgess, G. Hardy, P. Scott, N. Williams, D.E. L. Cooke, S. Green, D.S. Chapman, B.V. Purse. 2021. Evolutionary trait-based approaches for predicting future global impacts of plant pathogens in the genus Phytophthora. Journal of Applied Ecology 2021; 58:718-730

Bertelsmeier, C. and S. Ollier. 2021. Bridgehead effects distort global flows of alien species. Diversity and Distributions https://onlinelibrary.wiley.com/doi/full/10.1111/ddi.13388

Brasier C.M. 2008. The biosecurity threat to the UK and global environment from international trade in plants. Plant Pathology 57: 792–808.

Eschen, R., A. Roques and A. Santini. 2015. Taxonomic dissimilarity in patterns of interception and establishment of alien arthropods, nematodes and pathogens affecting woody plants in Europe. Journal of Conservation Biogeography Diversity and Distributions (Diversity Distrib.) (2015) 21, 36–45

Jung, T., et al. 2015. Widespread Phytophthora infestations in European nurseries put forest, semi-natural and horticultural ecosystems at high risk of Phytophthora diseases. Forest Pathology. November 2015.

Jung, T., A. Pérez-Sierra, A. Durán, M. Horta Jung, Y. Balci, B. Scanu. 2018. Canker and decline diseases caused by soil- and airborne Phytophthora species in forests and woodlands. Persoonia 40, 2018: 182–220

Klapwijk, M.J., A.J. M. Hopkins, L. Eriksson, M. Pettersson, M. Schroeder, A. Lindelo¨w, J. Ro¨nnberg, E.C.H. Keskitalo, M. Kenis. 2016. Reducing the risk of invasive forest pests and pathogens: Combining legislation, targeted management and public awareness. Ambio 2016, 45(Suppl. 2):S223–S234 DOI 10.1007/s13280-015-0748-3

Li, Y., C. Bateman, J. Skelton, B. Wang, A. Black, Y. Huang, A. Gonzalez, M.A. Jusino, Z.J. Nolen, S. Freeman, Z. Mendel, C. Chen, H. Li, M. Kolařík, M. Knížek, J. Park, W. Sittichaya, P.H. Thai, S. Ito, M. Torii, L. Gao, A.J. Johnson, M. Lu, J. Sun, Z. Zhang, D.C. Adams, J. Hulcr. 2021. Pre-invasion assessment of exotic bark beetle-vectored fungi to detect tree-killing pathogens. Phytopathology. https://doi.org/10.1094/PHYTO-01-21-0041-R

Roy, B.A., H.M Alexander, J. Davidson, F.T. Campbell, J.J. Burdon, R. Sniezko, and C. Brasier. 2014. Increasing forest loss worldwide from invasive pests requires new trade regulations. Frontiers in Ecology and the Environment 12(8), 457-465

Swiecki, T. J., Bernhardt, E. A., Frankel, S. J., Benner, D., & Hillman, J. (2021). An accreditation program to produce native plant nursery stock free of Phytophthora for use in habitat restoration. Plant Health Progress, PHP-02. https://apsjournals.apsnet.org/doi/abs/10.1094/PHP-02-21-0025-FI

United States Department of Agriculture Animal and Plant Health Inspection Service and Forest Service. 2000. Pest Risk assessment for Importation of Solid Wood Packing Materials into the United States.

Yamanaka, T., Morimoto, N., Nishida, G. M., Kiritani, K. , Moriya, S. , & Liebhold, A. M. (2015). Comparison of insect invasions in North America, Japan and their Islands. Biological Invasions, 17, 3049–3061. 10.1007/s10530-015-0935-y

Posted by Faith Campbell

New Asian Defoliator – a Threat to Elms?

symptomatic feeding by EZM larva; photo by Gyorgy Csoka via Bugwood

The elm zigzag sawfly (EZM; Aproceros leucopoda) was reported in the Western Hemisphere for the first time in Quebec in July 2020.

In 2021, only a year later, the sawfly was confirmed in northern Virginia [David Gianino, State Plant Regulatory Official (SPRO) of Virginia, pers. comm.]

There is 700 miles between Quebec and Virginia.

In September 2022, the sawfly was detected in St. Lawrence County, New York — just across the St. Lawrence River from Canada, where the insect has been known for two years. There is no information yet on impacts. [Brynda, S. “New pest affecting elm trees in St. Lawrence County.” October 3, 2022.

Impact in Europe

Elm zigzag sawfly is native to Eastern Asia — Japan and China for certain and, possibly Far Eastern Russia. There it is considered a minor pest. Serious localized defoliation, though, has been reported at least once, on the island of Hokkaido (Blank et al. 2021).

The sawfly was first detected outside its native range in Hungary and Poland in 2003. By 2010, the outbreak was revealed to be present over an area of 1,700 km, from eastern Ukraine to Austria. Other countries reporting the sawfly were Hungary, Poland, Romania, and Slovakia (Blank et al. 2010). Spread continued. By 2013 or 2014 elm zigzag sawfly was also reported in Belgium, Netherlands, and Germany — apparently the result of separate instances of human-assisted transport. German scientists calculated a natural spread rate of 45–90 km/yr. By 2018 the insect had reached the United Kingdom.

Severe localized defoliation by the species has been recorded on elms in a variety of situations across Europe. In some countries, defoliation has reached 74% or higher, even 100%. However, in other countries, such as Bulgaria, defoliation rates appear to be much lower (1-2%). Aproceros leucopoda showed no preference for host trees of a particular age. Heavily defoliated trees in Hungary did not seem to be dying (Blank et al. 2010).

The fear – in Europe and North America – is that elms already severely depleted by Dutch elm disease will be unable to sustain any decline in vigor caused by defoliation (Blank et al. 2010)

Probable Hosts

On the European continent, the sawfly has fed on several elms, including Ulmus minor, U. pumila and U. pumila var. arborea, U. glabra, and possibly. U. laevis (Blank et al. 2010). In the United Kingdom, it has fed on English elm (Ulmus procera), wych elm (U. glabra) and field elm (U. minor).

In Japan, collaborators in the Blank et al. (2010) study collected sawfly larvae on U. japonica and U. pumila.

In Virginia, larvae were collected from Chinese elm (U. parvifola). However, all species of elm trees native to North America are considered at risk. Also threatened are the native elm-browsing insects which might be out-competed by elm zigzag sawfly.

How the Sawfly Is Moved

Some have suggested that the EZS is transported on plants for planting, but they have not reported observations. Because elms are usually moved while dormant, it is more likely that the cryptic wintering cocoons are transported in leaf litter accompanying the trees rather than on the trees themselves.

American elms in Arlington County, Va; photo by F.T. Campbell

Worrying Traits

The elm zigzag sawfly matures very rapidly. The total time from oviposition to emergence of mature individuals is 24–29 days (Blank et al. 2010). They can produce up to six or seven generations per year. The sawfly is also parthenogenic, so it can reproduce in the absence of males. As a result, populations can build up rapidly. No specific predators are known. The impact of generalist native parasitoids in Europe has not yet been studied.

Also, EZS tolerates a wide range of climates. Conditions on Hokkaido are similar to those in Central Europe. However, Hokkaido’s winters are usually colder, summers warmer, and annual precipitation higher. Blank et al. (2010) did not know limiting temperature and humidity but thought it probable that this species could spread into northern and south-western Europe wherever elms grow. In North America, the Canadian Food Inspection Agency expressed concern that EZS would be able to withstand temperatures as low as –30 °C which includes much of Canada.

While the elm zigzag sawfly was on the Alert List on the European and Mediterranean Plant Protection Organization (EPPO), in 2015 it was removed since no EPPO member country had requested international action (Blank et al. 2010).

SOURCES

Blank, S.M., H. Hara, J. Mikulas, G. Csoka, C. Ciornei, R. constantineanu, I. Constantineanu, L. Roller, E. Altemhofer, T. Huflejt, G. Vetek. 2010. Aproceros leucopoda (Hymenoptera: Argidae): An East Asian pest of elms (Ulmus spp.) invading Europe. European Journal of Entomology · March 2010

DOI: 10.14411/eje.2010.045

Blank, S.M., T. Köhler, T. Pfannenstill, N. Neuenfeldt, B. Zimmer, E. Jansen, A. Taeger, A.D. Liston. Zig-zagging across Central Europe: recent range extension, dispersal speed and larval hosts of Aproceros leucopoda (Hymenoptera, Argidae) in Germany. https://jhr.pensoft.net/articles.php?id=4395

Sinon, S. First confirmed sighting of a new invasive in North America: elm zigzag sawfly – Invasive Species Centre. https://www.invasivespeciescentre.ca/first-confirmed-sighting-of-a-new-invasive-in-north-america-elm-zigzag-sawfly/

(United Kingdom) Forest Research Elm zigzag sawfly (Aproceros leucopoda) https://www.forestresearch.gov.uk/tools-and-resources/fthr/pest-and-disease-resources/elm-zigzag-sawfly/

Posted by Faith Campbell

New Study on Forest Carbon and Pests: The Picture is Ugly

lodgepole pines killed by mountain pine beetle in British Columbia; photo courtesy of Wikipedia

Natural systems, especially forests, could provide as much as 37% of the near-term mitigation necessary to meet Paris global climate goals. In the US, conservation, restoration, and improved land management could provide carbon sequestration equivalent to an estimated 21% of current net annual emissions.

However, the current U.S. forest carbon sink, which includes soils and standing and downed wood as well as live trees, might be in jeopardy due to increasing levels of disturbance, conversion, and/or declining sequestration rates in old growth stands.

Insects and plant diseases are one such disturbance agent. Acting alone or in combination with other forest stressors, they can damage or kill large numbers of trees in short periods of time, thereby reducing carbon sequestration and increasing emissions of stored carbon through decomposition of wood in dead or injured trees.

Historically, native and introduced insects and diseases have impacted an estimated 15% of the total U.S. forest cover annually. This impact is likely to increase. One study (Fei et al., 2019) found that an estimated 41% of the live forest biomass in the contiguous U.S. could be impacted by the 15 most damaging introduced pests already established in the U.S. Continuing introductions of new pests and exacerbated effects of native pests associated with climate change portend worsening losses of live trees. These rising impact of pests, combined with more frequent and severe fires and other forest disturbances, are likely to negate efforts to improve forests’ carbon sequestration capacity.

Sources of information about introduced pests’ impacts is available from, inter alia Campbell and Schlarbaum Fading Forests II and III, Lovett et al 2016, Poland et al. 2021, many blogs on this site, and pests’ profiles posed here under “invasive species” tab. Chapter 4 of Poland et al. (2021) provides a summary of what is known about interactions between invasive species and climate change – both climate impacts on bioinvaders and bioinvaders’ effect on carbon sequestration.

The United States and other major polluting countries have certain advantages. Their strong economies have the scientific and financial resources needed to implement effective invasive species prevention and forest management strategies. At the same time, many of them receive the most new forest pests – because they are major importers. These introduced pests pose the most serious and urgent near-term ecological threat to their forests and all the ecosystem services forests provide.

So, reducing insect and disease impacts to forests can simultaneously serve several goals—carbon sequestration, biodiversity conservation, and protecting the myriad economic and societal benefits of forests. See the recent IUCN report on threatened tree species.

A Major New Study

A new study by Quirion et al. (2021) takes another step in quantifying the threat to U.S. forests’ ability to sequester carbon by analyzing data from National Forest Inventory plots. Unfortunately, the re-measurement data for the period 2001 – 2019 are not available in the NFI for the Rocky Mountain states, which represents a critical data gap in the NFI program. This gap might not have had a significant impact on the national findings, however, because while the insect damage level (measured by an earlier inventory round) was quite severe in the Rocky Mountain States, the relatively slow growth of trees in that region means carbon sequestration rates are low.

Forest stand productivity – and carbon sequestration — will typically decline immediately after pest outbreaks, then recover or even increase beyond pre-outbreak levels depending on the productivity and maximum achieved biomass of replacement plant species and related soil characteristics. However, when prevalence of the disturbance increases, by, for example, more frequent pest outbreaks, carbon stocks in standing trees and sequestration rates can be reduced for extended periods.

Findings

Nationally, insects and diseases have decreased carbon sequestration by live trees on forest land by 12.83 teragrams carbon per year. This equals ~ 9% of the contiguous states’ total annual forest carbon sequestration and equivalent to the CO₂ emissions from over 10 million passenger vehicles driven for one year.
This estimate includes the impacts of both native and introduced insects and diseases, because the NFI database does not distinguish between them.
Insect-caused mortality had a larger impact than disease-caused mortality (see below). Forest plots recently impacted by insect disturbance sequestered on average 69% less carbon in live trees than plots with no recent disturbance. Plots recently impacted by disease disturbance sequestered on average 28% less carbon in live trees than plots with no recent disturbance.
Ecoprovinces in which the greatest annual reductions in live tree carbon sequestration due to pests were the Southern Rocky Mountain Steppe, Cascade Mixed Forest, Midwest Broadleaf Forest, and Laurentian Mixed Forest. (Ecoprovinces are outlined – but not named – in Quirion et al. 2021; more complete information is provided in the supplementary material.)

If this study had been carried out in the 1920’s, when chestnut blight and white pine blister rust were spreading across vast areas and killing large trees, the impact of diseases would have been much higher. Today, the most widespread impacts of diseases are on either small trees (e.g., redbay succumbing to laurel wilt) or slow-growing, high-elevation trees (e.g., whitebark and limber pine to white pine blister rust). As long as no equivalents of those earlier diseases are introduced, insects will probably continue to have the larger impacts.

western white pine killed by blister rust; photo from National Archives

Quirion et al. 2021 note that their estimates should be considered conservative. The USFS’s inventory records only major disturbances. That is, when mortality or damage is equal to or exceeds 25% of trees or 50% of an individual tree species’ count on an area of at least 0.4 ha. This criterion largely excludes less severe pest disturbances, including those from which trees recover but which might have temporary negative effects on carbon sequestration.

The study’s authors note that their work has important limitations. The dearth of data from the Rocky Mountain states is one. Other factors not considered include transfers of carbon from live biomass to dead organic matter, soils, and salvaged or preemptively harvested wood products. As trees die from pests or diseases, their carbon becomes dead wood and decays slowly, producing a lag in the carbon emissions to the atmosphere. A small fraction of the carbon in dead wood might be incorporated into soil organic matter, further delaying the emissions. A full accounting of the carbon consequences of pests and diseases would require assessment of these lags, probably through a modeling study.

affects of mountan pine beetle on lodgepole pine in Rocky Mountain National Park, Colorado photo from Wikimedia

Actions to Maintain Carbon Sequestration

Quirion et al. (2021) outline several actions that would help protect the ability of America’s forests to sequester carbon. These suggestions address both native and introduced pests, since both contribute to the threatened reduction in capacity.

Concerning native pests, the authors call for improved forest management, but warn that measures must be tailored to species and environmental context.

Concerning introduced insects and pathogens, Quirion et al. (2021) call for strengthening international trade policies and phytosanitary standards, as well as their enforcement. The focus should be on the principal pathways: wood packaging (click on “wood packaging” category for on this blog site) and imported plants (click on “plants as vectors” category for on this blog site). Specific steps to reduce the rate of introduction of wood-boring insects include enforcement to increase compliance with the international treatment standard (ISPM#15), requiring trade partners – especially those which have repeatedly shipped infested packaging – to switch to packaging made from alternative materials. Introductions via the plant trade could be reduced by requiring foreign shippers to employ integrated management and critical control point systems (per criteria set by the U.S.) and using emergency powers (e.g., NAPPRA) to further restrict imports of the plants associated with the highest pest risk, especially plant species that are congeneric with native woody plants in North America. See Lovett et al 2016; Fading Forests II & III

As backup, since even the most stringent prevention and enforcement will not eliminate all risk, the authors urge increased funding for and research into improved inspection, early detection of new outbreaks, and strategic rapid response to newly detected incursions.

To reduce impacts of pests established on the continent – both recently and years ago – they recommend increasing and stabilizing dedicated funding for classical biocontrol, research into technologies such as sterile-insect release and gene drive, and host resistance breeding.

Thinning is useful in reducing damage by native bark beetles to conifers. However, it has not been successful in controlling introduced pests for which trees do not have an evolved resistance. Indeed, preemptive harvesting of susceptible species can harm forest ecosystems directly through impacts of the harvesting operation and indirectly as individual trees that may exhibit resistance are removed, reducing the species’ ability to develop resistance over time.

Further research is needed to clarify several more issues, including whether introduced pests’ impacts are additive to, or interact with, those of native species and/or other forest stressors.

SOURCE

Quirion BR, Domke GM, Walters BF, Lovett GM, Fargione JE, Greenwood L, Serbesoff-King K, Randall JM & Fei S (2021) P&P Disturbances Correlate With Reduced Carbon Sequestration in Forests of the Contiguous US. Front. For. Glob. Change 4:716582. [Volume 4 | Article 716582] doi: 10.3389/ffgc.2021.716582

SOURCES of additional information

Campbell, F.T. and S.E. Schlarbaum. Fading Forest reports at http://treeimprovement.utk.edu/FadingForests.htm

Lovett, G.M., M. Weiss, A.M. Liebhold, T.P. Holmes, B. Leung, K.F. Lambert, D.A. Orwig, F.T. Campbell, J. Rosenthal, D.G. McCullough, R. Wildova, M.P. Ayres, C.D. Canham, D.R. Foster, S.L. Ladeau, and T. Weldy. 2016. Nonnative forest insects and pathogens in the United States: Impacts and policy options. Ecological Applications, 26(5), 2016, pp. 1437-1455

Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector. Springer Verlag. Available for download at no cost at https://www.fs.usda.gov/treesearch/pubs/61982

Posted by Faith Campbell