Category: invasive species

USFS invasive species report: Herculean effort that could have had greater impact

In February the USFS published a lengthy analysis of invasive species: Invasive Species in Forests and Rangelands of the United States. A Comprehensive Science Synthesis for the US Forest Sector (Poland et al. 2021; full citation at the end of the blog). More than 100 people contributed to the book; I helped write the chapters on legislation and regulations and international cooperation. The book is available for download at no cost here.

Chapters address impacts in terrestrial and aquatic systems; impacts on ecosystem processes; impacts on various sectors of the economy and cultural resources; interactions with climate change and other disturbances; management strategies for species and landscapes; tools for inventory and management. Each chapter evaluates the current status of knowledge about the topic and suggests research needs. There are also summaries of the invasive species situation in eight regions.

Miconia – one of many invasive plants damaging ecosystems in Hawai`i

I greatly appreciate the effort. Authors first met in 2015, and most chapters were essentially written in 2016. The long delay in its appearance came largely from negotiations with the publisher. The delay means some of the information is out of date. I am particularly aware that several experts – e.g., Potter, Guo, and Fei – have published about forest pests since the Aukema source cited. I wonder whether inclusion of their findings might change some of the conclusions about the proportion of introduced pests that cause noticeable impacts.

Since the report’s publication in February I have struggled with how to describe and evaluate this book. What is its purpose? Who is its audience? The Executive Summary says the report is a sector-wide scientific assessment of the current state of invasive species science and research in the U.S.

However, the Introduction states a somewhat different purpose. It says the report documents invasive species impacts that affect ecosystem processes and a wide range of economic sectors. This would imply an intention to enhance efforts to counter such effects– not just to shape research but also to change management. Indeed, the Conclusion of the Executive Summary (pp. xvi-xvii) is titled “An Imperative for Action”.

Tom Vilsack, Secretary of Agriculture

I am not the author to evaluate how effectively the book sets out research agendas. Regarding its usefulness in prompting policy-makers to do more, I regretfully conclude that it falls short.

Getting the balance right between an issue’s status and what needs to be done is difficult, perhaps impossible. I appreciate that the report makes clear how complex bioinvasion and ecosystem management and restoration are. Its length and density highlight the difficulty of making progress. This daunting complexity might well discourage agency leadership from prioritizing invasive species management.

On the other hand, summary sections sometimes oversimplify or bury important subtleties and caveats. The question of whether some key questions can ever be resolved by science is hinted at – but in detailed sections that few will read. The same is true regarding the restrictions imposed by funding shortfalls.

The Report Would Have Benefitted from Another Round of Editing

Editing this tome was a Herculean task. I feel like a curmudgeon suggesting that the editors do more! Nevertheless, I think the report would have been improved by the effort. One more round of editing – perhaps involving a wider range of authors – could have pulled together the most vital points to make them more accessible to policymakers. It could also have tightened the ecosystem-based descriptions of impacts, which are currently overwhelmed by too much information.

A precis for policymakers

A precis focused on information pertinent to policymakers (which the current Executive Summary does not) should contain the statement that the continued absence of a comprehensive investigation of invasive species’ impacts hampers research, management, and policy (mentioned only in §16.5, on p. 332). It should note situations in which insufficient funding is blocking recommended action. I note three examples: programs aimed at breeding trees resistant to non-native pests (resource issues discussed only in §§8.3.1 and 8.3.2, p. 195); sustaining “rapid response” programs (§6.4.3, p. 125); costs of ecosystem restoration, especially for landscape-level restoration (§16.4). I am sure there are additional under-funded activities that should be included!

cross-bred ash seedlings being tested for vulnerability to EAB; photo courtesy of Jennifer Koch

 Other important information that should be highlighted in such a precis includes the statement that many ecosystems have already reached a point where healthy functions are in a more tenuous balance due to invasive species (p. 51). Effective carbon storage and maintaining sustainable nutrient and water balance are at risk. Second, costs and losses caused by invasive forest pests generally fall disproportionately on a few economic sectors and households. They cannot be equated to governmental expenditures alone (p. 305).  Third, even a brief estimate of overall numbers of invasive species appears only in §7.4. Information about individual species is scattered because it is used as example of particular topic (e.g., impacts on forest or grassland ecosystems, or on ecosystem services, or on cultural values).

Ecosystem Impacts Overwhelmed

As noted above, the report laments the absence of a comprehensive investigation of invasive species’ impacts. Perhaps the editors intended this report to partially fill this gap. To be fair, I have long wished for a “crown to root zone” description of invasive species’ impacts at a site or in a biome. Concise descriptions of individual invasive species and their impacts are not provided by this report, but they can be found elsewhere. (The regional summaries partially address the problem of too much information – but they do not provide perspective on organisms that have invaded more than one region, e.g., emerald ash borer or white pine blister rust.) Another round of editing might have resulted in a more focused presentation that would be more easily applied by policymakers.

Welcome Straightforward Discussion of Conceptual Difficulties

I applaud the report’s openness about some important overarching concepts that science cannot yet formulate.  If supportable theories could be conceived, they would assist in the development of policies:

  • Despite decades of effort, scientists have not established a clear paradigm to explain an ecosystem’s susceptibility to invasion (p. 85). Invasibility is complex: it results from a dynamic interplay between ecosystem condition and ecological properties of the potential invader, especially local propagule pressure.
  • Scientists cannot predict how climate warming will change distributions of invasive species [see Chapter 4] and alter pathways. This inability hampers efforts to develop effective prevention, control, and restoration strategies (p. xi). Climate change and invasive species need to be studied together as interactive drivers of global environmental change with evolutionary consequences.

The Report’s Recommendations

Policy-oriented recommendations are scattered throughout the report. I note here some I find particularly important:

  • Measures of progress should be based on the degree to which people, cultures, and natural resources are protected from the harmful effects of invasive species.
  • Managers should assess the efficacy of all prevention, control, and management activities and their effect upon the environment. Such an evaluation should be based on a clear statement of the goals of the policy or action. [I wish the report explicitly recognized that both setting goals and measuring efficacy are difficult when contemplating action against a new invader that is new to science or when the impacts are poorly understood. Early detection / rapid response efforts are already undermined by an insistence on gathering information on possible impacts before acting; that delay can doom prospects for success.]
    • Risk assessment should both better incorporate uncertainty and evaluate the interactions among multiple taxa. Risk assessment tools should be used to evaluate and prioritize management efforts and strategies beyond prevention and early detection/rapid response.
    • Economic analyses aimed at exploring tradeoffs need better tools for measuring returns on invasive species management investments (§16.5).
  • Actions that might be understood as “restoration” aim at a range of goals along the gradient between being restored to a known historic state and being rehabilitated to a defined desired state. The report stresses building ecosystem resilience to create resistance to future invasions, but I am skeptical that this will work re: forest insects and disease pathogens.
  • Propagule pressure is a key determinant of invasion success. Devising methods to reduce propagule pressure is the most promising to approach to prevent future invasions (p. 115). This includes investing in quarantine capacity building in other countries can contribute significantly to preventing new invasions to the US.
  • Resource managers need additional studies of how invasive species spread through domestic trade, and how policies may differ between foreign and domestic sources of risk.

I appreciate the report’s attention to such often-ignored aspects as non-native earthworms and soil chemistry. I also praise the report’s emphasis on social aspects of bioinvasion and the essential role of engaging the public. However, I think the authors could have made greater use of surveys conducted by the Wisconsin Department of Natural Resources and The Nature Conservancy’s Don’t Move Firewood program.

Lost Opportunities

I am glad that the report makes reference to the “rule of 25” rather than “rule of 10s”. I would have appreciated a discussion of this topic, which is a current issue in bioinvasion theory. As noted at the beginning of this blog, the long time between when the report was written and when it was published might have hampered such a discussion

Also, I wish the report had explored how scientists and managers should deal with the “black swan” problem of infrequent introductions that have extremely high impacts. The report addresses this issue only through long discussions of data gaps, and ways to improve models of introduction and spread.

I wish the section on the Northwest Region included a discussion of why an area with so many characteristics favoring bioinvasion has so few damaging forest pests. Admittedly, those present are highly damaging: white pine blister rust, sudden oak death, Port-Orford cedar root disease, balsam woolly adelgid, and larch casebearer. The report also notes the constant threat that Asian and European gypsy moths will be introduced. (The Entomological Society of America has decided to coin a new common name for these insects; they currently to be called by the Latin binomial Lymatria dispar).

And I wish the section on the Southeast and Caribbean discussed introduced forest pests on the Caribbean islands. I suspect this reflects a dearth of research effort rather than the biological situation. I indulge my disagreement with the conclusion that introduced tree species have “enriched” the islands’ flora.

SOURCE

Poland, T.M., P. Patel-Weynand, D.M Finch, C.F. Miniat, D.C. Hayes, V.M Lopez, editors. 2021. Invasive species in Forests and Rangelands of the United States. A Comprehensive Science Synthesis for the US Forest Sector. Springer

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

“Rule of Tens” – Time to Refine It

are wood-borers examples of species more likely to “proceed through the steps of invasion” than the theory suggests?

Much of the literature about biological invasion has relied on the “tens rule”. First enunciated in the mid-1990s by Williamson and Fitter (1996), it was actually conceived a decade earlier by Williamson and Brown (1986).

The “tens rule” hypothesizes that about 10% of all species transported to a new environment will be released or escape and become introduced species. Subsequently, 10% of those introduced species establish viable populations in the wild. Finally, about 10% of the established species become highly damaging. That is, 1% of the number originally transported to the new environment is a highly damaging invader.

Is the “tens rule” supported by evidence?

Empirical support for the hypothesis has been mixed; the number of studies questioning it has increased over the decades (Jeschke and Pyšek 2018). So Jeschke and Pyšek (2018) decided to evaluate the basis for the hypothesis. First, they divided the hypothesis into two sub-hypotheses so they could separate the concept of impact from the process of introduction, establishment, and spread. They justified this separation by noting that novel species can have an impact at any stage. The two sub-hypotheses:

1st sub-hypothesis: At each of the three transitions between the invasion stages listed here the number of species completing the transition is reduced by 90% (invasion tens rule).

  • transport to exotic range

transition

  • introduction (release or escape into the environment)

transition

  • establishment of a least one self-sustaining population

transition

  • spread

2nd sub-hypothesis: about 10% of established non-indigenous species cause a significant detrimental impact. This sub-hypothesis applies to the transition from establishment (iii, above) to significant impact (iv). Stepping back to the earlier introduction, so as to consider the situation overall, about 1% of all introduced non-native species cause a significant detrimental impact; this sub-hypothesis thus relates to the transition from introduction (ii) to significant impact (iv).

Jeschke and Pyšek carried out a quantitative meta-analysis of 102 empirical tests of the tens rule drawn from 65 publications. They found no support for the “invasion tens rule”. Indeed, their analysis found that about 24% of non-native plant and 23% of non-native invertebrate species are successful in taking consecutive steps of the invasion process. Among non-native vertebrates, about 51% are successful in taking consecutive steps of the invasion process.

The “impact tens rule” is also not supported by currently available evidence. However, Jeschke and Pyšek decided that more data are needed before a reasonable alternative hypothesis can be formulated.

Findings

Jeschke and Pyšek state that the “tens rule” is not based on a model or other defensible concept. It is also hampered by confusion of terms. Thus, different authors define the invasion process differently. Particularly confounding is the mixing of “impact” with steps in the invasion process. At the same time, there have been few studies of the “impact tens rule” hypothesis.

Finally, the “tens rule’s” predictions are not adjusted to consider changes in temporal and spatial scales. That is, it does not recognize that more invaders will be detected in any given place during more recent times than in the past. Furthermore, more invaders will find suitable niches in large areas than small.

The note that analysis is hampered by the paucity of reliable data about establishment success – especially for taxa other than mammals and birds. They do not discuss how this lack might affect efforts to analyze proportions of entering species that succeed in becoming invasive, especially among the small and inconspicuous taxa such as insects and fungal organisms that concern thus of us that focus on threats to forests. This same data gap has limited other studies as well; see, for example, Aukema et al. (2010) – who restricted their discussion of pathogens to “high impact” species.

Although Jeschke and Pyšek (2018) do not specify which studies they relied on to determine the proportion of successful invaders among species belonging to particular taxa, it seems likely that they relied principally on Vila et al. (2010) in determining that on average 25% invertebrates that are introduced (that is, proceed to the second stage in the process given above) become invasive. Vila et al. analyze introductions to Europe. They found that 24.2% of terrestrial invertebrates caused recognized economic impacts.

Jeschke and Pyšek (2018) Results and Discussion

Considering the “invasion tens rule”, two-thirds of the empirical tests in the dataset focused on the “invasion tens rule”. The majority of these focused on the transition from introduction to establishment (the transition from (ii) to (iii). The observed average percentage of species making this transition is more than 40% – or greater than four times larger than the “tens rule’s” prediction.

At the next transition, from establishment to spread (from iii to iv), the observed percentage of species making the transition is  greater than 30% – or greater than three times the predicted value under the “tens rule”.

Considering the “impact tens rule”, on average a quarter of established non-indigenous species have a significant detrimental impact, which is again significantly more than the 1 out of 10 species predicted by the rule. Specifically by taxon, 18% of established plants have shown detrimental impacts. Among invertebrates and vertebrates that estimate is greater than 30%. All these observations are higher than predicted by the rule. However, sample sizes are low so more studies are needed to test whether these values hold true.

Regarding the fullest possible extent of the invasion process, 16 out of 100 species that were introduced (stage ii) had a significant impact. This is 16 times greater than the 1% predicted by the “tens rule”. Considering specific taxa, 6% of established plants and 15% of established invertebrates had a significant impact. Data were too poor to support an evaluation for vertebrates.

I note that the alarmingly high “impact” estimates for invertebrates are probably biased by scientists’ and funding entities’ lack of interest in species that don’t cause noticeable impacts.

Poor data preclude an analysis of the transition from transport (i) to introduced (ii).

Strengthening The Estimates

Might these introduction and impact estimates be tightened by analysis of additional sources, such as the studies led Seebens, forest pest impact analyses by Potter et al. (2019) and Fei (2019) and reviews of pest introduction numbers by Haack and Rabaglia (2013)? 

Is it worth pursuing efforts to refine the Jeschke and Pyšek (2018) estimates? I think it is. An underestimation of the risk of introduction might lead decision-makers to downplay the need for a response.

Some scientists have accepted the new “rule of 25” (Schulz, Lucardi, and Marsico. 2021. Full citation at end of blog; also cited by USFS report – Poland et al. 2021). Others have not. Venette and Hutchison (2021; full reference at end of blog) continue to cite the estimate of approximately one “invasion success” for every 1,000 attempts – that is, a low-probability, high-consequence event. This challenges those responsible for managing invasive species.

Or are there other conundrums of introduction, establishment, and predicting impacts that have more direct relationship to improving programs? I note that the recent Forest Service report on invasive species (Poland et al. 2021) does not address the “rule of tens”.

Other Reasons Why Bioinvasion Damage is Underestimated

Jaric´ and G. Cvijanovic´ (2012) note that scientists lack a full understanding of ecosystem functioning, so they probably often miss more subtle – but still important – impacts.

Jeschke and Pyšek (2018) note that the percentage of introduced or established species with a quantifiable impact is not always the most important information. A single introduced species can have devastating impact by itself. They cite the amphibian disease chytrid (Batrachochytrium dendrobatidis) and such mammals as rats and cats.

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

Brockerhoff, E.G. and A. M. Liebhold. 2017. Ecology of forest insect invasions. Biol Invasions (2017) 19:3141–3159

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. Liebhold. 2019. Biomass losses resulting from insect and disease invasions in United States forests. Proceedings of the National Academy of Sciences of the United States of America, 12 Aug 2019, 116(35):17371-17376

Haack, R.A. and R.A. Rabaglia. 2013 Exotic Bark and Ambrosia Beetles in the USA: Potential and Current Invaders. CAB International. 2013. Potential Invasive Pests of Agricultural Crops (ed. J. Pena)

Jaric´, I. and G. Cvijanovic´. 2012. The Tens Rule in Invasion Biology: Measure of a True Impact or Our Lack of Knowledge and Understanding? Environmental Management (2012) 50:979–981 DOI 10.1007/s00267-012-9951-1

Jeschke J.M. and P. Pyšek. 2018. Tens Rule. Chapter 13 of book by CABI posted at http://www.ibot.cas.cz/personal/pysek/pdf/Jeschke,%20Pysek-Tens%20rule_CABI%202018.pdf

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. (in press).

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

Schulz, A.N., R.D. Lucardi, and T.D. Marsico. 2021. Strengthening the Ties That Bind: An Evaluation of Cross-disciplinary Communication Between Invasion Ecologists and Biological Control Researchers in Entomology. Annals of the Entomological Society of America · January 2021

Seebens, H., T.M. Blackburn, et al. 2018. Global rise in emerging alien species results from increased accessibility of new source pools. www.pnas.org/cgi/doi/10.1073/pnas.1719429115

Vilà, M., C. Basnou, P. Pyšek, M. Josefsson, P. Genovesi, S. Gollasch, W. Nentwig, S. Olenin, A. Roques, D. Roy, P.E. Hulme and DAISIE partners. 2010. How well do we understand the impacts of alien spp on ecosystem services? A pan-European, cross-taxa assessment. Frontiers in Ecology and the Environment, Vol. 8, No. 3 (April 2010), pp. 135-144

Venette R.C. and W.D. Hutchison. 2021. Invasive Insect Species: Global Challenges, Strategies & Opportunities. Front. Insect Sci.1:650520. doi: 10.3389/finsc.2021.650520

Williamson M.H. and K.C. Brown. 1986. The analysis and modelling of British invasions. Philosophical Transactions of the Royal Society of London Series B 314:505–522

Williamson M. and A. Fitter. 1996 The varying success of invaders. Ecology 77(6):1661–1666

Early Warning Systems – Are They Helping Prevent Introductions?

symptoms of tomato brown rugose fruit virus; Wikimedia

The US Department of Agriculture (USDA) is making efforts to strengthen pest prevention by setting up “early warning” systems. As part of this effort, the USDA-funded regional Integrated Pest Management Center in Raleigh, NC, has published a review of existing systems. These are intended to inform national phytosanitary agencies, such as APHIS, about pest species that might pose a threat to natural or agricultural resources. The ultimate goal is providing information that empowers the agency to enact effective preventive measures. [Noar et al. 2021. A full reference to the study is posted at the end of this blog.]

The review looked at six early warning systems’ goals, as well as their procedures for obtaining and disseminating information about potential threats. With one exception, these systems focus on plant pests.

The review did not undertake a rigorous analysis of the various programs’ efficacy.

The article points to the high economic costs associated with invasive plant pests. As a consequence of the huge volume of international trade – which is the principal vector of plant pests’ introduction – national phytosanitary agencies need information on which pests are moving most frequently, and on what commodities, so they can target the most risky pathways. The early warning systems are intended to do this before the pests are introduced to a new region. The several systems use different methodologies and criteria to identify such potential pests. They also are intended to raise awareness about high risk pests and pathways – but for different audiences.

Several of the early warning systems were set up and are managed by national phytosanitary agencies or their regional organizations. These include PestLens and the EPPO and NAPPO alert systems (described below).  The article notes that these systems usually do not report diseases for which the causal agent has not been identified, because identification of the pathogen species is typically necessary before regulations can be adopted – and these are regulatory organizations. The authors do not analyze whether this constraint reduces the systems’ ability to provide timely warnings.

1. PestLens     

PestLens is an early warning system set up by APHIS. It therefore focuses on pests that might become quarantine pests – that is, subject to regulation under terms of the Plant Protection Act. Such pests must pose a defined threat to US agricultural and natural resources. PestLens monitors more than 300 sources, including scientific journals, reports from national phytosanitary agencies, Google alerts, newspapers, e-mail lists and other plant-health-related websites. PensLens staff evaluate the information for relevance to APHIS based on: a) whether the information is new to APHIS; b) whether the plant pest is of quarantine significance to the US; c) its potential economic impact if introduced; d) the likelihood of a pathway for introduction; and e) the likelihood that action by APHIS might be needed to prevent its introduction. Information considered relevant includes indication that a pest is associated with a previously unknown host, has been detected in a new location, or has been eradicated from a country. The information has not necessarily been confirmed by the country (warning included in PestLens notices).

When the PestLens criteria are met, the analysts write a brief article including the new information and any existing background, such as previously known host range and distribution. These articles are compiled into a weekly e-mail notification sent to PPQ employees and thousands of other subscribers. They are also archived on the PestLens website. APHIS staff evaluate the information and make decisions as to whether some regulatory action is appropriate.

I am puzzled because some of the five criteria appear to require a pest risk analysis. Pest risk analysis is a complex task that I do not believe PestLens is equipped to carry out – certainly not as quickly as is required by an alert system.

Update

A review of PestLens (Meissner et al. 2015; full citation at end of the blog) describes the system more fully. It found that during the period October 2012 – October, 2014, 73% of PestLens articles were based on articles in scientific journals; 17% on federal, state, or regional governmental sources; 8% fon news media sources; and 3% on other sources. The principal government pest reports used were from the web sites of IPPC, EPPO & NAPPO.

The majority of PestLens articles reporting new locations, interceptions, and new hosts came from journals. New pest descriptions, new reports of an organism as a pest, and articles on research of interest came exclusively from journals. Articles on pest detections, outbreaks, and eradications came largely from government sources.

Meissner et al. analyzed APHIS’ response to PestLens notices. They said that certain APHIS actions, such as the implementation of official control programs, initiation of research activities, or the formation of specliazed task groups were not captured in this analysis. They found that over a ten month period in 2014, APHIS used the PestLens notices to update its pest databases 350 times; updated pest datasheets or pest profiles on the PPQ website 16 times; evaluated a pest’s regulatory status (e.g., prepared a risk assessment) 11 times; and revised its regulations 4 times.

Meissner et al. consider that it is vital to maintain up-to-date databases, especially regarding pest host and distribution ranges. Another benefit from the PestLens system is a set of metrics to improve accountability, for example identifying duplication of efforts and providing permanent records of when actions are taken (or declined) and the rationale.  

2. EPPO Alert List and EPPO Reporting Service  

The European and Mediterranean Plant Protection Organization (EPPO) has 52 member countries stretching from Russia and Uzbekistan to Spain, Algeria, and Morocco, and including their off-shore islands. EPPO maintains a pest Alert List of species chosen by the EPPO Secretariat based on the scientific literature and suggestions by member’s phytosanitary agencies. Factors leading to a listing include newly described pests, reports of spread to new geographical locations, and reports of major outbreaks in the EPPO region. Each listed pest has a fact sheet which contains known hosts and distribution, the type of damage, the mode of dissemination, and potential pathways for spread. Some pests are selected for pest risk analysis (PRA). Once the PRA is completed, the pest might be placed on the EPPO A1/A2 lists, which are species recommended for regulation by the member states. Pests not selected for PRA stay on the EPPO Alert List temporarily, typically three years, then their information is archived.

The EPPO Secretariat also publishes a monthly Reporting Service newsletter, which details phytosanitary events that might threaten the EPPO region, including both officially designated quarantine pests as well as emerging ones. Information includes new hosts, new geographical locations, new pests, and new identification and detection methods.  

3. NAPPO Phytosanitary Alert System  

The North American Plant Protection Organization (NAPPO) comprises Canada, the United States and Mexico. It has a web-based alert system that provides official pest reports from member countries. NAPPO also puts out Emerging Pest Alerts that contain news about plant pests and pathogens not established in this region. Sources are public, including scientific journals, newspapers, records from port interceptions, and domestic plant pest surveys. Generally NAPPO does not confirm its reports with the corresponding country’s phytosanitary agency.

4. IPPC Pest Reports

The International Plant Protection Convention (IPPC) has been ratified by more than 180 countries. The member countries’ phytosanitary agencies submit official pest reports concerning the occurrence, outbreak, spread, or eradication of organisms that are quarantine pests in that country or for neighboring countries and trading partners. These pest reports are posted on the IPPC website.

5. International Plant Sentinel Network   

The International Plant Sentinel Network is a collaboration between the National Plant Diagnostic Network (NPDN) and the American Public Gardens Association. It is funded through cooperative agreements with APHIS under Section 10007 of the Farm Bill (Now Plant Protection Act §7721.) Launched in 2010, it has now grown to include more than 300 gardens across North America (information from the website).

The underlying premise is based on biogeography: plant-associated insects, fungi, and other pathogens introduced to plants that did not co-evolve with them (naïve plants) might cause unexpected damage. Since arboreta and botanical gardens cultivate many plant taxa outside their native range, they present an opportunity to observe new pest-host associations and the level of damage caused. Pests attacking native plants in North American botanical gardens might constitute “early detection” of a pest already in the country rather than a warning before the pest is introduced. Still, early detection is valuable.

6. ProMED   

The Program for Monitoring Emerging Diseases (ProMED) is a program of the International Society for Infectious Diseases (ISID). ProMED was launched in 1994 as an Internet service to identify unusual health events related to emerging and re-emerging infectious diseases and toxins affecting humans, animals and plants. It focuses on outbreaks in new geographic regions, newly described diseases, and diseases for which the causal agent is unknown. By its own estimation, ProMED is the largest publicly-available system conducting global reporting of infectious diseases outbreaks (information from the website). ProMED maintains several e-mail lists that disseminate information pertaining to disease outbreaks; subscribers can choose among lists to fit their areas of interest and their geographic region. ProMED has a much broader scope than the other early warning systems. Also, it uses informal and nontraditional sources, including local media, on-the-ground experts, and professional networks.

Stakeholders can access much of the information on these websites and use them to report findings of new alien species to phytosanitary agencies.

Gaps 

The review of early warning systems has disappointing gaps. First, I am puzzled that the authors looked only at the U.S.-based sentinel gardens effort and did not consider a parallel international network. The International Plant Sentinel Network was established in 2013. It is coordinated by the Botanical Garden Conservation Initiative, headquartered at Kew Gardens, United Kingdom. At present, 67 gardens and arboreta are participating; they are located in China, Australia and New Zealand, South Africa, South America, and Europe (including the Caucuses Mountains). After all, it is this international network that could inform APHIS about potential pests when they observe attacks on North American plants growing in their facilities. I confess that it is not clear to me whether participating gardens and arboreta would take the initiative to inform APHIS of pest attacks on North American plant species. It might be that APHIS would need to send inquiries to participants, probably focused on named pests. If these caveats are true, the network might not be a fully functional “early warning” body.

Update

Indeed, the USFS International Programs office is cooperating with the International Plant Sentinel Network to have some botanic gardens around the world monitor several North American species planted at their locations for disease and pest problems.  In June 2021 the USFS sought suggestions from contacts on which North American tree species should be monitored. Candidates could be tree species of high economic, ecological, or urban/landscape value. The candidate list would probably be limited to 10 species. They should represent a diverse range of conifers and hardwoods. 

Second, the articles authors make no mention of one of the principal sources of information on plant pests – CABI (Center for Agriculture and Bioscience International). CABI is a global source of information on organisms’ distribution. It is particularly strong in Commonwealth countries – which are important sources of plant material imported into the U.S.

Third, they apparently did not assess phytosanitary alert systems in place or anticipated in Australia, New Zealand, and South Africa.  This is a significant gap since these countries are leaders on phytosanitary issues. They are also potential sources of damaging pests.

Most disappointing is the lack of analysis of programs’ efficacy and weaknesses. The only step in this direction is contrasting ProMED’s willingness to report diseases for which the causal agent is unknown. PestLens, EPPO, and NAPPO refuse to do this. We desperately need an analysis of the extent to which this narrow concept of the task limits the ability of these systems to provide early warnings.

At least several of the networks, including PestLens and NAPPO, do not limit themselves to information that has been confirmed by countries – which might be reluctant to admit the presence of a damaging organism on their turf.

I suggest that it would have been particularly instructive to analyze the reasons why Australia’s early warning efforts failed to detect introduction of the myrtle rust pathogen sufficiently early to facilitate eradication.

This review did discuss how several of the networks tracked the global movement of the Tomato brown rugose fruit virus (ToBRFV). The virus was first detected in Jordan in 2015; this was reported by PestLens in 2016. PestLens reported the virus had spread to Israel 2017. The NAPPO system then reported the virus in Mexico in 2018. The virus was detected in the United States in 2018, although difficulties in taking official samples and diagnosing the virus probably delayed awareness of this outbreak. APHIS restricted imports of tomato and pepper seed, transplants and fruits from countries where the virus was known to be present in November, 2019. Still, APHIS acted after the virus had been detected in the country. ToBRFV has continued to spread; it is now found in Asia, Europe, the Middle East, and northern Africa. I am not completely convinced that this episode illustrates successful utilization of early warning networks. Did the apparently tardy action by APHIS arise from overconfidence that the virus would be limited to the Middle East? Or is it attributable to rules which limit agency actions until official confirmation of the detection? Another actor might have been delay in proving that the virus was being spread by the international seed trade; international phytosanitary rules require agencies to define the introductory pathway before regulating.

I hope other scientists will undertake a more comprehensive analysis of early warning systems. We need our phytosanitary systems to be made as effective as possible. Further evaluation of current efforts would provide valuable insight.

[A separate article reporting on the international sentinel gardens network from a British perspective is Marfleet, K. and S. Sharrock. 2020. The International Plant Sentinel Network: an update on phase 2. The International Journal of Botanic Garden Horticulture.]

SOURCES

Meissner, H., J. Fritz, L. Kohl, H. Moylett, J. Moan, S. Emerine, and A. Kaye. 2015. PestLens: An early-warning system supporting U.S. safeguarding against exotic plant pests. Bull. OEPP 45: 304-310

Noar, R.D, C.J. Jahant-Miller, S. Emerine, and R. Hallberg. 2021.  Early Warning Systems as a Component of IPM to Prevent the Intro of Exotic Pests.  Journal of IPM, (2021) 12(1): 16; 1–7 doi: 10.1093/jipm/pmab011

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

The South African Report as a Model: U.S. Falls Short

Ailanthus – one of the invasive species shared by South Africa and the U.S.

A few years ago, I posted a blog in which I pointed to a report on South Africa’s response to bioinvasion as a model for the U.S. and other countries. South Africa has published its second report. This report outlines the country’s status as of December 2019 and trends since the first report (i.e. since December 2016). (I describe the report’s findings on South Africa’s invasive species situation in a companion blog.) Again, I find it a good model of how a country should report its invasive species status, efforts, and challenges. In comparison, many U.S. efforts comes up short.

U.S. Reports Need to Be More Comprehensive

The South African report provides a national perspective on all taxa. Various United States agencies have attempted something similar a few times. The report issued by the Office of Technology Assessment in 1993  summarized knowledge of introduced species and evaluated then-current management programs.

The 2018 report by the U.S. Geological Service focused on data: the authors concluded that 11,344 species had been introduced and described the situation in three regions – the “lower 48” states, Alaska, and Hawai`i. However, the USGS did not evaluate programs and policies. The new USDA Forest Service report (Poland et al. 2021) describes taxa and impacts of invasive species in forest and grassland biomes, including associated aquatic systems. Again, it does not evaluate the efficacy of programs and policies.

The biennial national reports required by the Executive Order establishing the National Invasive Species Council (NISC) are most similar to the South African ones in intent. However, none has been comprehensive. For example, the most recent, issued in 2018, strives to raise concern by stating that invasive species effect a wide range of ecosystem services that underpin human well-being and economic growth. Some emphasis is given to damage to infrastructure. The report then sets out priority actions in six areas: leadership and prioritization, coordination, raising awareness, removing barriers, assessing federal capacities, and fostering innovation. NISC also issued a report in 2016 – this one focused on improving early detection and rapid response. NISC posted a useful innovation – a “report card” updating progress on priority actions — in October 2018.   It listed whether actions had been completed, were in progress, or were no longer applicable. However, the “report card” gave no explanation of the status of various actions; the most notable omissions concerned the actions dismissed as “not applicable”. Worse, no report cards have been posted since 2018. I doubt if those or any more comprehensive reports will be forthcoming. This reflects the increasing marginalization of NISC. The Council has never had sufficient power to coordinate agencies’ actions, and now barely survives.

U.S. Reports Need to Be More Candid

The authors of the South African report made an impressive commitment to honest evaluation of the country’s gaps, continuing problems, progress, and strengths. As in the first report, they are willing to note shortcomings, even of programs that enjoy broad political support (e.g., the Working for Water program).

It is not clear whether decision-makers have acted — or will act — on the report’s findings. That is true in many countries, including the United States. However, that is separate whether decision-makers have an honest appraisal on which to base action.

Assessment of South Africa’s Invasive Species Programs

Here is a summary of what the authors say about South Africa’s invasive species program. I want to state clearly that my intention is not to criticize South Africa’s efforts. No country has a perfect program, and South Africa faces many challenges. These have been exacerbated by COVD-19.  

The report identifies the areas listed below as needing change or improvement.

1) Absence of a comprehensive policy on bioinvasion. Such a policy would provide a vision for what South Africa aspires to achieve, clarify the government’s position, guide decision-makers, and provide a basis for coordinating programs by all affected parties (e.g., including conservation and phytosanitary agencies).

2) As in the first report, the authors call for monitoring program outcomes (results) rather than inputs (money, staffing, etc.) or outputs (e.g., acres treated). The authors also say data must be available for scrutiny. In those cases when data are adequate for assessing programs’ efficacy, they indicate that the control effort is largely ineffective.

3) Inadequate data in several areas. The report notes progress in developing and applying transparent and science-based criteria to species categorization as invasive (as distinct from relying on expert opinion). However, this change is taking time to implement, and sometimes results in species receiving a different rating. [I agree with the report that data gaps undermine understanding of the extent and impacts of bioinvasion, domestic pathways of spread, justification of expenditures, assessment of various programs’ efficacy (individually or overall), priority setting, and identifying changes needed to overcome programs’ weaknesses. However, I think filling these data gaps might demand time and resources that could better be utilized to respond to invasions – even when those invasions are not fully understood.]

4) Funding of bioinvasion programs by the National Department of Forestry, Fisheries, and the Environment has been fairly constant over 2012–2019, but this is a decline in real terms. The figure of 1 billion ZAR does not include spending by other government departments, national and provincial conservation bodies, municipalities, non-governmental organizations, and the private sector. Authors of the report expect funding to decrease in the future because of competing needs.

While at least 237 invasive species are under some management (see Table 5.1), funding is heavily skewed – 45% of funding goes to management of one invasive plant (black wattle); 72% to management of 10 species.

5) Need for policies to address the threat emerging from rising trade with other African countries, especially considering the probable adoption of the proposed African Continental Free Trade Area. Under this agreement, imported goods will only be inspected for alien species at the first port of entry, and most African countries have limited inspection capacity. [European pathologists Brasier, Jung, and others have noted the same issue arising in Europe, where imported plants move freely around the European Union once approved for entry by one member state.]

The authors of the South African report say programs’ efficacy would be considerably improved if species and sites were prioritized, and species-specific management plans developed. They warn that, in the absence of planning and prioritization, there is a risk that funding could be diluted by targeting too many species, leading to ineffective control and a concomitant increase in impacts.

In South Africa, regulations, permits, and other measures aimed at regulating legal imports of listed species are increasingly effective. However, there is still insufficient capacity to prevent accidental or intentional illegal introductions of alien species. There is also more enforcement of regulations requiring landowners to control invasive species. Six criminal cases have been filed and – as of December 2019, one conviction (guilty plea) obtained. However, the data do not allow an assessment of the overall level of compliance.

The report found little discernable progress on the proportion of pathways that have formally approved management plans. Management is either absent or ineffective for 61% of pathways. There has been no action to manage the ballast water pathway. On the other hand, in some cases, other laws focus explicitly on pathways, e.g., agricultural produce is regulated under the Agricultural Pests Act of 1983.

During the period December 2016 – December 2019, the Plant Inspection Services tested more than 12,000 plant import samples for quarantine pests and made 62 interceptions. The report calls for more detailed information from the various government departments responsible for managing particular pathways (e.g., the phytosanitary service), and for an assessments of the quality of their interventions.

The number of non-native taxa with some form of management has grown by 40% since December 2016 – although – as I have already noted — spending is highly skewed to a few plant species. The number and extent of site-specific management plans has also increased, apparently largely due to a few large-scale plans developed by private landowners. However, few of these plans have been formally approved by some unspecified overseer.

Citing the strengths and weaknesses described above, the current (second) report downgraded its assessment of governmental programs from “substantial” to “partial”.  

Comparison to U.S.

How does the United States measure up on the elements that need change or improvement?  I know of no U.S. government report that is as blunt in assessing the efficacy of our programs –individually or as a whole.

Nevertheless, each of the five weaknesses identified for South Africa also exist in the United States:

  1. Re: lack of a comprehensive policy, I think the U.S. also suffers this absence. This is regrettable since the National Invasive Species Council (NISC) was set up in 1999.
  2. Re: monitoring outcomes to assess programs’ efficacy, I think U.S. agencies do seem to be more focused on collecting data on programs’ results – see the Forest Service’ budget justification. However, I think too often the data collected focus on inputs and outputs.
  3. Re: data gaps, I think all countries – including the U.S. — lack data on important aspects of bioinvasion. I differ from the South African report, however, in arguing for funding research aimed at developing responses rather than monitoring to clarify the extent of a specific invasive species. Information that does not lead to action seems to me to be a luxury given the low level of funding.
  4. Re: funding, I find that, despite the existence of NISC, it remains difficult to get an overall picture of U.S federal funding of invasive species programs. Indeed, the cross-cut budget was dropped in 2018 at the Administration’s request. I expect all agencies are under-funded; I have often said so as regards key USDA programs. As in South Africa, funding is skewed to a few species that I think should be lower in priority (e.g., gypsy moth). 
  5. Re: upgrading invasive species programs to counter free-trade policies, I think U.S. trade policies place too high a priority on promoting agricultural exports to the detriment of efforts to prevent forest pest introductions. This imbalance might be present with regard to other taxa and pathways. See Fading Forests II here.

South African and U.S. agencies also face the same over-arching issues. For example, the U.S. priority-setting process seems to be a “black box.” Several USFS scientists (Potter et al. 2019) spent considerable effort to develop a set of criteria for ranking action on tree species that are hosts of damaging introduced pests. Yet there is no evidence that this laudable project influenced priorities for USFS funding.

SOURCES

Poland, T.M., P. Patel-Weynand, D.M Finch, C.F. Miniat, D.C. Hayes, V.M Lopez, editors. 2021. Invasive Species in Forests and Rangelands of the United States. A Comprehensive Science Synthesis for the US Forest Sector. Springer

Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S. 2019. Prioritizing the conservation needs of United States tree species: Evaluating vulnerability to forest P&P threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/j.gecco.2019.e00622.

SANBI and CIB 2020. The status of bioinvasions and their management in South Africa in 2019. pp.71. South African National BD Institute, Kirstenbosch and DSI-NRF Centre of Excellence for Invasion Biology, Stellenbosch. http://dx.doi.org/10.5281/zenodo.3947613

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

South Africa & Invasive Species: Threats to High Value Biodiversity and Human Well-Being

Protea repens and fynbos vegetation near Table Mountain; photo by Mike Wingfield

South Africa is a country of immense biological diversity. It is also one that recognizes the threat invasive species pose to its natural wealth – and to the economy and livelihoods of ordinary people.

Also, South Africans are trying hard to improve the country’s invasive species program. It recently released the second national report assessing how well it is curtailing introductions and minimizing damage. As I describe in a companion blog, I find these reports to contain exceptionally thorough and honest appraisals of South Africa’s invasive species programs. I address that value in the companion blog, where I compare the South African report — and its findings — to U.S. government reports on our invasive species programs.

In South Africa, bioinvasion ranks third – after cultivation and land degradation – as a threat to the country’s impressive biodiversity. Invasive species are responsible for 25% of all biodiversity loss. Certain taxa are at particular risk: native amphibians and freshwater fishes, and some species of plants and butterflies.

Particularly disturbing is the bioinvasion threat to the Fynbos biome. The report notes that 251 non-native species have been identified in this system. This finding causes concern because the Fynbos is a unique floral biome. In fact, it constitutes the principal component of one of only six floral kingdoms found on Earth: the Cape Floral Kingdom (or region). For more information, go here.

map of South Africa showing fynbos biome

Not surprisingly, invasive bird and plant species are most numerous around major urban centers. The report concludes that this is probably because most non-native birds are commensal with humans; most birds and plants were first introduced to urban centers; and there is greater sampling effort there. Indeed, the patterns of (detected) invasive plant richness are still highly sensitive to sampling effort.

South Africa is considered a leader on invasive species management. However, its record is spotty.

Successes

Biocontrol interventions are considered a success. South Africa has approved release of 157 biocontrol agents, including seven since 2016. All the recent agents (and probably most others) target invasive plants. The South African biocontrol community conducts a comprehensive review of their effectiveness at roughly 10-year intervals. The fourth assessment is currently under way. Also, the report considers eradication of non-native fish (primarily sport species) from several wetlands and river reaches to have been successful. (However, opposition by sport fishermen has delayed listing of some trout species as invasive.)

Failures

On the other hand, strategies to combat invasive plants, other than by biocontrol, appear to be having little success. Even the extent of plant invasions in national parks is poorly documented. Also, the report highlights ballast water as an inadequately managed pathway of invasion.

The report estimates that three new non-native species arrive in South Africa accidentally or illegally every year. Interestingly, reported species arrivals have declined in the current decade compared to the preceding one. The report’s authors consider this to probably be an underestimate caused by the well-known lag in detecting and reporting introductions. The apparent decline also is contrary to global findings. Table 1 in Seebens et al. 2020 (full citation at end of blog) projected that the African continent would receive approximately 767 new alien species between 2005 and 2050.

Even the introductory pathways are poorly known: the pathway for 54% of the taxa introduced to South Africa are unknown. Of the species for which the introductory pathway is known, horticultural or ornamental introductions of plants dominate – 15% of that total. A second important pathway – for accidental introductions – is shipping (5% of all introductions). Other pathways thought to be prominent during 2017–2019 are the timber trade, contaminants on imported animals, and natural dispersal from other African countries where they had previously been introduced.

PSHB symptoms on Vachellia sieberiana; photo by Trudy Paap

Polyphagous shothole borer

The report highlights as an example of a recent introduction that of the polyphagous shothole borer (PSHB, Euwallacea fornicatus). https://www.dontmovefirewood.org/pest_pathogen/polyphagous-shot-hole-borer-html/        http://nivemnic.us/south-africas-unique-flora-put-at-risk-by-polyphagous-shot-hole-borer/ See Box 3.1 in the report. This species is expected to have huge impacts, especially in urban areas. While most of the trees affected so far are non-native (e.g., maples, planes, oaks, avocadoes), several native trees are also reproductive hosts.  https://www.fabinet.up.ac.za/pshb  In response to the introduction, the government established an interdepartmental steering committee, which has developed a consolidated strategy and action plan. However, as of October 2020 the shot hole borer had not been listed under invasive species regulations, even on an emergency basis. It had been listed as a quarantine pest of agricultural plants (e.g., avocado) per the Agricultural Pests Act 1983.

As note in my blog assessing the report, the report bravely concludes that the government’s regulatory regime is only partially successful (whereas three years ago it graded it as “substantial”). The downgrade is the result of a more thorough evaluation of the regulatory regime’s effectiveness.

SOURCES

SANBI and CIB 2020. The status of bioinvasions and their management in South Africa in 2019. pp.71. South African National BD Institute, Kirstenbosch and DSI-NRF Centre of Excellence for Invasion Biology, Stellenbosch. http://dx.doi.org/10.5281/zenodo.3947613  

Seebens, H., S. Bacher, T.M. Blackburn, C. Capinha, W. Dawson, S. Dullinger, P. Genovesi, P.E. Hulme, M. van Kleunen, I. Kühn, J.M. Jeschke, B. Lenzner, A.M. Liebhold, Z. Pattison, J. Perg, P. Pyšek, M. Winter, F. Essl. 2020. Projecting the continental accumulation of alien species through to 2050. Global Change Biology. 2020;00:1 -13 https://onlinelibrary.wiley.com/doi/10.1111/gcb.15333

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

EAB Threat to Eastern Europe

The emerald ash borer (EAB) was first detected in European Russia in 2003, in Moscow. By 2020, EAB was recorded in 16 provinces [=‘oblast’] of European Russia, especially to the West of Moscow towards the borders with Belarus and Ukraine.  

Russian scientists have documented that the emerald ash borer is spreading faster in the southwest of the country and in neighboring Ukraine than in the northwest (near St. Petersburg and the Baltic countries).

Despite an abundance of ash [both green ash (Fraxinus pennsylvanica) – native to North America – and European ash F. excelsior], EAB population density in the northwest remains low and damage is in scattered clusters.

However, in September 2020 officials detected an isolated outbreak in a St. Petersburg suburb, 520 km away from the apparent edge of the principal Russian population. The authors believe this outbreak has been present since 2015. They think it is the result of transport of EAB either by “insect-hitchhiking” on vehicles or by movement of plants for planting or other commodities.

The Petersburg population is only 130 km from Estonia and Finland – the border with the European Union.

A thousand kilometers to the south, in southwest Russian eastern Ukraine, an outbreak was reported in June 2019. By the next summer, EAB were detected more than 100 km to the West. While this outbreak is still 800 km from Ukraine’s border with eastern Europe (Poland, Slovakia, Hungary, Romania), the authors note that rapid spread is likely since F. excelsior and F. pennsylvanica have been extensively planted along roads, railways, field shelter belts, and urban greenings.

The slower spread in the North is attributed to colder temperatures, the local abundance of food, and possibly pressure by the native parasitoid Spathius polonicus Niezabitowski (note that USDA APHIS has approved two Spathius species as biocontrol agents in the U.S.). On the other hand, the climate is milder in Saint Petersburg (along the coast) than it is inland; and ash woodlands are common along the Baltic coast.

Noting that ash dieback (Hymenoscyphus fraxineus)  has devastated more than 95% of European ash populations, the authors express concern about the future of ash.

SOURCE

Musolin, D.L.; Selikhovkin, A.V.; Peregudova, E.Y.; Popovichev, B.G.; Mandelshtam, M.Y.; Baranchikov, Y.N.; Vasaitis, R. North-Westward Expansion of the Invasive Range of Emerald Ash Borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) towards the EU: From Moscow to Saint Petersburg. Forests 2021, 12, 502. https://doi.org/10.3390/f12040502

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

Interior’s Invasive Species Plan: Let’s Implement It!

Posted by Scott J. Cameron, former Acting Assistant Secretary for Policy Management and Budget , US Department of the Interior

locations in Hawaii Volcanoes National Park where ohia trees were infected by rapid ohia death pathogen in 2017

In 2019 Congress passed the John D. Dingell, Jr. Conservation, Management, and Recreation Act. Among other things, it directed the Department of the Interior to “develop a strategic plan that will achieve, to the maximum extent practicable, a substantive annual net reduction of invasive species population or infested acreage on land or water managed by the Secretary.”  This provision triggered a year-long process of public involvement and inter-bureau coordination. The result was a plan published in January 2021.  It represents the first attempt by Interior at a Department-wide multi-taxa, multi-year approach to invasive species.  It has the potential to spur integration of invasive species work across the Department’s many bureaus and to focus each bureau’s efforts on a set of common goals, strategies, and performance metrics.

While Congress’ language is open-ended, any planning exercise is constrained by the most recent President’s budget and existing law.  It is up to those of us who are not, or at least no longer, executive branch employees to advocate for plans unbound by those constraints. 

In that spirit, I offer eight recommendations to improve invasive species management. Four are within existing authorities; four more are outside the current budgetary and statutory framework.  Many more ideas are without a doubt worth pursuing.

Opuntia (prickly pear) cactus – common plant in western National parks and on Bureau of Land Management lands; under threat by cactus moth

First, within existing funding and legal authorities, the Department has unfinished business that it can act on now.

  1. Secure approval of the package of categorical exclusions under the National Environmental Policy Act (NEPA) — now awaiting approval by the President’s Council on Environmental Quality (CEQ). Over many years agencies have documented how invasive species control improves, rather than harms, the environment.  Absent an applicable NEPA categorical exclusion approved by CEQ, though, each such action needs to run the time- and money-consuming gauntlet of NEPA compliance. In the meantime, the invasive plants germinate, the invasive animals reproduce, and what might have been a localized and inexpensive problem has expanded geographically and in terms of cost and complexity.  In the Fall of 2020 Interior submitted hundreds of pages of documentation on numerous practices proven to control invasive species without harming the environment.  Due to time and staffing constraints at CEQ, these categorical exclusions still await action.  Interior and CEQ should take prompt steps to finish them.
  • Allocate to the US Geological Survey at least $10 million of the roughly $90 million remaining available to the Secretary in CARES Act appropriations for research on invasive zoonotic diseases. These are diseases like COVID-19 and West Nile virus that can move from one species to another.  Many zoonotic diseases fit the definition of invasive species, since they are not native to the United States and endanger human health.  In the case of COVID-19 funding is available to the Secretary of the Interior, without need for further Congressional action, from funds appropriated by the CARES Act. The availability of these funds will expire at the end of September 2021, so Interior should provide this research funding to USGS as soon as possible. 
  • Join the existing Memorandum of Understanding between the Western Governors Association (WGA) and the US Department of Agriculture’s Forest Service. These groups have established “a framework to allow the U.S. Forest Service (USFS) and WGA to work collaboratively to accomplish mutual goals, further common interests, and effectively respond to the increasing suite of challenges facing western landscapes.”  This provides a forum to improve coordination between the States and the federal government on the management of invasive species, and Interior needs to be part of that team.
  • Interior should work with USDA to accelerate and intensify efforts to systematically improve coordination between the interagency Wildland Fire Leadership Council and the interagency National Invasive Species Council.  Both Councils have member agencies that practice vegetation management using similar tools and techniques, although for different purposes. The two Councils should identify a select number of initiatives in FY21 where their efforts would benefit both wildland fire management and invasive plant management .
swamp bay trees in Everglades National Park killed by laurel wilt; photo by Tony Pernas

Four steps to implement the strategic plan outside the scope of current law and the President’s Fiscal Year 2021 budget. I offer the following:

  1. Improve implementation of the Lacey Act program to list injurious species.  There are both legislative and administrative elements to this proposal.  

In a federal District Court decision on May 19, 2015, on a lawsuit filed by the Association of Reptile Keepers, the Court undid the longstanding Fish and Wildlife Service policy that the Lacey Act allowed FWS to ban interstate transport of injurious species. On April 7, 2017, the D.C. Circuit Court of Appeals upheld the District Court’s view. These rulings mean that FWS authority only applies to international commerce.  Unfortunately, the court’s interpretation of the law and legislative history are reasonable, so Congress needs to amend the law to make it clear that FWS is explicitly authorized to regulate interstate commerce in injurious species. The Department of the Interior should work with the Department of Justice and the Office of Management and Budget to develop the necessary bill language and submit it to Congress.

At the same time, the FWS injurious species listing process is notoriously slow, even causing Congress to occasionally list species legislatively.  The fact that these legislative initiatives have sometimes been promoted by Members of Congress who normally  are opposed to more federal regulation signals just how awkward the current FWS process is. Thus there might well be strong bipartisan support to amend the Lacey Act on the interstate commerce matter. Acting on its own authority, FWS should procure an independent third party review of the injurious species listing process and ask the contractor to make suggestions for “business process reengineering” to improve and streamline current practices, along with evaluating whether higher funding or new technology is needed.

  • The Bureau of Reclamation, Department of the Interior, and the Office of Management and Budget should develop legislative language to submit to Congress for the 2022 Water Resources Development Act, that explicitly authorizes an aquatic nuisance species program in the Bureau of Reclamation.  It could parallel the relatively new authority enjoyed by the Army Corps of Engineers and mandate increased coordination between the two water agencies.
  • Any climate change legislation pursued by Congress and the Administration should include provisions for addressing invasive species.  Climate change will make some North American habitats more suitable for foreign organisms, as cold-intolerant species might be able to survive in more northern latitudes in the U.S. than previously was the case. Second, the disruptive effect of climate change on North American ecosystem structure and trophic relationships at any latitude will make those ecosystems more vulnerable to invasion. Finally, the spread of invasive species may in and of itself exacerbate climate change, such as through the increased carbon dioxide emissions from rangeland wildfires aggravated by the dominance of invasive cheatgrass.
  • The Senate Committee on Environment and Public Works and the House Natural Resources Committee should each hold oversight hearings on how best to help state and local governments detect and respond to new invasive species that are not within the statutory purview of USDA/APHIS.  This is a complex topic, important for both ecological and financial reasons. Over the years several attempts to address it have failed.  A thoughtful review by Congress and the Administration, which perhaps would lead to passage of new statutory authority and funding, is worth exploring.

The Author:

Scott Cameron recently left the federal government, where he had served as Acting Assistant Secretary for Policy, Management and Budget at the U.S. Department of the Interior. In that capacity he oversaw Department-wide budget, invasive species, natural resource damage assessment and restoration, environmental compliance and numerous administrative functions of this $14 billion agency with 65,000 employees. Previously, Scott held other civil service job (e.g., at the White House Office of Management and Budget) & political appointments in the federal government, on the staff of the Governor of California, and on Congressional staffs. While not in government, Scott led formation of the Reduce Risk from Invasive Species Coalition.

CISP welcomes 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.

Further information on the plant pests mentioned in the photo captions can be obtained at www.dontmovefirewood.org; click the “invasive species” button.

Invasive Plants in National parks – Progress?

Japanese stiltgrass in Shenandoah National Park; photo by Jake Hughes, NPS

The recent appearance of a study by National Park Service (NPS) scientists quantifying the threat posed by invasive plants prompted me to seek updates on this issue. In May 2018, I blogged about NPS’ Invasive Plant Program Strategic Plan, which was issued in 2016. At the time, I got the impression that the program was struggling to gain support from NPS leadership in Washington, as well as leaders of individual parks. Has the situation improved since then?

The recent study, by Kathryn Miller and colleagues, focuses on National parks in the East, from Virginia to Maine. (I provide a full reference at the end of this blog.) I look forward to a planned follow-up article that will try to clarify drivers of invasion. 

The Miller study appears to have been undertaken to partially fulfill one of the goals of the NPS’ 2016  Invasive Plant Program Strategic Plan. One of the actions under Goal 1 in the Plan was to quantify the invasive plant threat, the effort needed to manage it, and then to communicate the gap between needs and available resources. Miller et al. have quantified the threat to National parks in one region (not the entire country). However, they have communicated the gap between effort and need in only the most general way.

Protecting the forests in eastern National parks is valuable from many perspectives. The forests in these parks are older and have higher stand-level tree diversity than surrounding unprotected forests. Protecting their long-term condition also corresponds to the National Park Service’s (NPS) stated mission, as established in its Organic Act.

The study relied on National Park Service Inventory and Monitoring Program data from 1,479 permanent forest plots covering 39 eastern NP units located from Virginia to Maine. The data were collected over 12 years, in three survey cycles (2007–2010, 2011–2014, and 2015–2018).

The authors note that in forest ecosystems, invasive plants can reduce native diversity, alter forest structure, suppress tree regeneration, alter nutrient cycling, and modify disturbance regimes.  Some – the shrubs and vines – also threaten human health by promoting increases in tick populations and associated Lyme disease risks.

Unsurprisingly, the data showed invasive plants to be widespread, and increasing. In 80% of the park units, there was a significant increase in at least one trend measuring abundance. Any decrease in plant invaders tended to be in herbaceous or graminoid species; that decrease was often counterbalanced by an approximately equivalent increase in invasive shrubs or vines. In 35 of the park units, more than half of the plots had at least one invasive plant species when the 2015-2018 survey began. In 10 parks (a quarter of those surveyed), every plot had at least one.

The most widespread species is Japanese stiltgrass (Microstegium vimineum). It is present in more than 75% of all park units and 30% of all 1,400 plots. This dominance is true despite the fact that stiltgrass does not extend north of Roosevelt-Vanderbilt National Historic Site in New York state (41o N latitude). Stiltgrass is also the most aggressive invader. 

The second most widespread invaders are a group of shrubs and vines, including most notably Japanese barberry (Berberis thunbergii), Japanese honeysuckle (Lonicera japonica), multiflora rose (Rosa multiflora), and wineberry (Rubus phoenicolasius). I note – although the articles does not – that several of these have been deliberately planted – either to “enhance” ecosystems (multiflora rose) or as ornamentals (barberry). [Lehan et al. 2013 (full reference at end of blog) found that 95% of 125 shrub species  introduced to the U.S. were introduced deliberately.] I know of no examples of deliberate planting of Japanese stiltgrass.

The most frequently detected non-grass herbaceous species is garlic mustard (Alliaria petiolata), which was detected in 20% of plots. Garlic mustard is found throughout the study area (Virginia to Maine). Tree-of-heaven (Ailanthus altissima) is the most common invasive tree. It is found in only 9% of plots and does not grow north of Roosevelt-Vanderbilt NHS. Again, both were intentionally introduced – and not noted as such in the article.

Because they could not identify the source populations for each plot, the study could not directly measure rates of establishment and expansion. The data did allow tracking rough trends in each park.

Parks with the highest abundance tended to be near densely populated areas. However, this pattern was not universal. For example, Prince William Forest Park in the outer Virginia suburbs of the District of Columbia metro area was one of two of the least invaded park units. 

Prince William Forest Park

(note the prevalence of beech – I fear for the arrival of beech leaf disease!)

Total invasives increased significantly in 21 of the 39 parks for at least one metric. In 10 parks (a quarter of all parks), total invasives increased significantly in two of the three metrics. Antietam National Battlefield experienced the steepest increases.

The authors note that invasive plants continue to establish and expand, even in already heavily invaded forests. Thus they found little evidence of saturation. This finding conflicts with invasion theory. They also found antagonistic interactions between invasive species to be common.

The authors said managers should prioritize efforts to control Japanese stiltgrass and the shrubs and vinesdue to their widespread occurrence, rapid expansion, ability to suppress tree regeneration and understory diversity, and – in the case of the shrubs and vines, link to ticks.

The authors noted the need to better understand the drivers and impacts of invasive plants in eastern forests. They mentioned the overabundance of white-tailed deer (Odocoileus virginianus), latitude, climate change, fragmentation and urbanization. I have urged them to include analysis of deliberate planting of various species on lands within the park units or nearby. They have said that they will do so in the planned follow-up article.

The authors propose that deferred management of natural resources receive attention and sustained commitment on par with the attention to deferred maintenance of the park units’ infrastructure. The maintenance backlog has been addressed through recent legislation: the Great America Outdoors Act which provided $6.5 billion over five years to address deferred maintenance projects in all 419 national park units. I believe that these projects will not address invasive species, which are managed under the “Natural Resources” budget account, not “Maintenance”. Some “Maintenance” projects probably will include control of invasive plants. A former Interior Department official has suggested that resource management activities might be funded under another section of the legislation, which provides $900 million under the Land and Water Conservation program. I hope this is true.

National Park Service’ Overall Invasive Plant Program Now

In response to the mandate in the John D. Dingell, Jr. Conservation, Management, and Recreation Act (Public Law 116-9), the Department of Interior has issued a department-wide invasive species strategy. Will issuance of the new strategy provide impetus to the NPS to seek funding to implement its 2016 invasive plant strategic plan? Will Congress provide funds for this purpose?

Finding out the current status of National Park Service took a little effort. The NPS’ website has “popular” information about the efforts of individual regional Invasive Plant Management Teams (see links at the end of this blog). These posts provide only the briefest overview of program achievements and do not compare those accomplishments to the goals in the 2016 plan.

However, Terri Hogan, Invasive Plant Program Manager in the Biological Resources Division, provided following information:

NPS leadership now supports the agency’s invasive plant effort. The national Invasive Plant Program (IPP) contributes to the annual Natural Resource Stewardship and Science Directorate (NRSS)’ Biological Resource Division (BRD) work plan. All is guided by the “Four Pillars to Guide Natural Resource Activities and Investments”, adopted in 2016. 

It is not clear that invasive species have the highest priority under this regime. The four “pillars” are

  • Holding the line – includes conserving biodiversity by removing invasive plants
  • Managing amid Continuous Change – includes conducting risk assessment and taking other actions to contain future exotic species
  • Leveraging for Conservation at Scale
  • Enhancing Stewardship and Science Access and Engagement

Cooperation with owners of neighboring private lands has been enhanced by engagement of the Western Governors Association and state and local political leaders. Many parks participate in Partnerships for Invasive Species Management (PRISMs), CISMS, and Cooperative Weed Management areas (CWMAs). This collaboration has been strengthened by adoption of the John D. Dingell, Jr. Act (see above).

In practice, the focus appears to still be on the Invasive Plant Management Teams (IPMTs). There are now 17 teams. Fifteen are funded through the national office. One is funded by an individual park; one funded through a regional office. Annual reports have been published for FYs 2017 and 2018. The FY19 report has been held up but should be posted soon.

The reports provide brief description of the overall program and vignettes of particular activities. There are more detailed – but still anecdotal – reports for each of the teams. It is difficult to determine whether there has been overall progress. For example, the reported total infested acreage increased from 133,658 acres in FY17 to 301,195 acres in FY18. This presumably reflects more intense monitoring as well as a probable increase in real infections. (The infested acreage figures do not address intensity of invasion on these acres.) The teams cumulatively treated 8,937 acres in FY 2017; 8,331 acres in FY 2018. They carried out inventory and monitoring projects on 169,057 acres in FY17, 210,000 acres in FY18.

Since the Miller article concerns the region from Virginia to Maine, I checked the FY17 and FY 18 reports from the Invasive Plant Management Teams from the Mid-Atlantic, National Capital Area, and Northeastern regions. The Mid-Atlantic team emphasized work on wavyleaf basketgrass and meadows in parks established to protect cultural or historic sites. The National Capital Area team emphasized partnerships and success eradicating Giant Hogweed (Heracleum mantegazzianum) on private land neighboring Rock Creek Park. The Northeastern Team serves 25 parks; the report emphasized leveraging resources and testing efficacy of pre-emergent herbicide for control of Japanese stiltgrass. With this exception, the teams do not appear to be prioritizing the species recommended for action by the Miller study.

Brief, “popular” articles about the NPS’ invasive plant effort are available here

Invasive Plant Management Teams – Biological Resources Division (U.S. National Park Service) (nps.gov)

NPS 20 Years of Invasive Plant Management 

20 Years of Action in 2020: Invasive Plant Management Teams 

20th Years of Action – The NPS IPMT Program 

SOURCES

Lehan, N.E., J.R. Murphy, L.P. Thornburn, and B.A. Bradley. 2013. Accidental Introductions are an Important Source of Invasive Plants in the Continental United States. American Journal of Botany 100(7): 1287–1293. 2013.

Miller, K. M., B. J. McGill, A. S. Weed, C. E. Seirup, J. A. Comiskey, E. R. Matthews, S. Perles, & J. Paul Schmit. 2020. Long-term trends indicate that invasive plants are pervasive and increasing in eastern national parks. Ecology. 00(00):e02239. 10.1002/eap.2239

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

Let’s shape the Biden Administration’s & New Congress’ Policies on Non-Native Forest Pests!

We have a great opportunity to shape future efforts to counter non-native forest pests and diseases. Administration officials are most open to new ideas when they first take office. The same is true of new Congressional leadership.

So now is the time to suggest needed changes!

The USDA Secretary-designate is Tom Vilsack. Of course, he was USDA Secretary during the Obama Administration … so he is not entirely “new” to the issues. However, perspectives and priorities have changed, so now is a good time to urge him to consider new approaches.  Furthermore, the Senate Agriculture Committee will hold confirmation hearings for him; we can ask the Senators to advocate for our views during this proceeding.

The House Agriculture Committee has a new Chair, David Scott – from the suburbs of Atlanta, Georgia. Again, this provides an opportunity to suggest new approaches and topics for hearings. 

I assume you all are knowledgeable about the numbers and impacts of non-native forest insects and pathogens in the United States, and of the pathways by which they are introduced and spread. If you are not, peruse my blogs about wood packaging or plants as vectors (click on the appropriate “categories” listed at the bottom of the archive of blogs). Or read Fading Forests III (see the link at the end of this blog) and the article I coauthored early this year on improving forest pest management programs.

On the basis of my long experience, I suggest that you encourage USDA Secretary-designate Vilsack, Senators on the Agriculture Committee, and House Agriculture Committee Chair David Scott to consider the following recommendations:

Actions Congress could take

  1. Congress could amend the Plant Protection Act [7 U.S.C. §7701, et seq. (2000)] to prioritize the protection of natural and agricultural resources over the facilitation of trade.  This might be done by amending the “findings” section of the statute to give higher priority to pest prevention.
  2. The Agriculture Committees of both the House and Senate could hold hearings on the importation of forest pests. They could determine if the USDA is doing an adequate job protecting the country from insect pests and diseases, and how our defenses could be strengthened. One component of the hearings could focus on whether current funding levels and mechanisms are adequate to support vigorous responses to new pest incursions.
  3. Congress could commission a study of the feasibility, costs and benefits of establishing a “Center for Forest Pest Control and Prevention” to coordinate research and policy on this issue.
  4. Congress could increase funding for the appropriate USDA APHIS and Forest Service programs and activities to enable vigorous containment and eradication responses targeting introduced forest pests and diseases.    
  5. Congress could increase funding for USDA research on detection of insects and pathogens in shipping; insect and disease monitoring/surveillance; biological control; alternatives to packaging made from wooden boards; management of established pests; and resistance breeding to enable restoration of impacted tree species.

Actions Secretary-designate Vilsack could initiate without legislative action (once he is confirmed)

Introductions of pests in the wooden crates, pallets, etc., goods come in

  1. APHIS could take emergency action to prohibit use of wood packaging by importers of goods from countries with a record of poor compliance with ISPM#15. This action is allowed under authority of the Plant Protection Act [7 U.S.C. §7701, et seq. (2000)] and Article 5.7 of the World Trade Organization’s Agreement on the Application of Sanitary and Phytosanitary Measures.
  2. APHIS could strengthen enforcement of current regulations by aggressively prosecuting repeat offenders.  For instance, APHIS could begin imposing administrative financial penalties on importers each time their wood packaging is non-compliant with ISPM#15.
  3. APHIS could work with Department of Homeland Security Bureau of Customs and Border Protection (CBP) to improve information available to U.S. importers about which foreign suppliers of SWPM and shippers have good vs. bad records of compliance with ISPM#15.
  4. DHS CBP could release information on country of origin and treatment facility for ISPM#15-stamped SWPM that is found to be infested with pests.
  5. USDA APHIS could begin a phased transition from solid wood packaging to alternative materials that cannot carry wood-boring pests. APHIS could initiate a pest risk assessment to justify making such an action permanent. Imports could be packaged in alternative materials, e.g., manufactured wood products (e.g. plywood), metal, or plastic.

Nursery Plant (“Plants for Planting”) Pathway

  1. APHIS could apply authorities under NAPPRA and other existing authorities to curtail imports of plants that pose a high risk of introducing insects and pathogens that would threaten tree species that are important in natural and urban forests in the U.S. At a minimum, APHIS should restrict imports of live plants that are in the same genus as native woody plants of the U.S.
  2. APHIS could work with the Agriculture Research Service and National Institute of Food and Agriculture to determine which taxa of woody vegetation native to the U.S. are vulnerable to pathogens present in natural systems of trade partners. Particularly important would be the many Phytophthora species found by Jung and colleagues in Vietnam, Taiwan, Chile, and other countries. Once the studies are sufficiently complete, APHIS could utilize authority under NAPPRA to prohibit importation of plants from those source countries until effective phytosanitary measures can be identified and adopted.

Other Actions

  1. APHIS could develop procedures to ensure the periodic evaluation of pest approach rates associated with wood packaging and imports of “plants for planting” and highlight areas of program strengths and weaknesses. A good place to start would be to update the study by Haack et al. (2014), which estimated the approach rate in wood packaging a decade ago.
  2. The USDA could expand early detection systems for forest pests, such as the APHIS CAPS program and the Forest Service EDRR program. These programs should be better coordinated with each other and should make better use of citizen observations collected through smartphone apps, professional tree workers such as arborists and utility crews, and university expertise in pest identification and public outreach.  An effective program would survey for a broad range of pests as well as for suspicious tree damage, and would be focused on high-risk areas such as forests around seaports, airports, plant nurseries, and facilities such as warehouses that engage in international trade.
  3. The USDA could initiate a “Sentinel Plantings“ network of US tree species planted in gardens abroad and monitored for potential pests and diseases. 

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

SOD – Regulations Should Reflect Disease’s Complexity

Syringa vulgaris Chmurka 2018-05-06 1352.jpg Wikimedia Commons

As we know, the SOD pathogen Phytophthora ramorum infects more than 100 plant species [APHIS host list posted here]. Some are killed, some not. Some support production of spores (=sporulation), and thus promote spread of the disease – either in nurseries and plantings, or in the wild. Conditions under which P. ramorum infects specific plant species also varies.

In both the ornamental plant industry and natural environments, transmission is driven mostly by foliar hosts.

Matteo Garbelotto and colleagues have carried out studies aimed at improving our understanding of the differences in host-pathogen interactions, and their meaning vis a vis persistence and spread of the disease – especially in wildland situations. The experiments were carried out five or more years ago, funded by the Farm bill Section 7721 funding. See the full reference at the end of this blog.

The team ranked 25 ornamental plant species representing ten families for susceptibility to P. ramorum and infectivity (spore production). They also tested potential differences among three of the genetic lineages of the pathogen—NA1 (prevalent in U.S. forests), NA2 (found in some nurseries in Pacific coast states), and EU1 (found in nurseries and – since 2015 – in some wildland forests in Oregon). The team also studied the effect of temperature on infectibility. Their goal was to help focus regulations so they will be more effective.

The studies clearly show that the relationship between P. ramorum and various hosts is complex – both susceptibility and infectibility vary depending on the host species, pathogen genetic lineage, and environmental conditions, especially temperature. Results of testing of leaves for the presence of the pathogen were affected by such experimental choices as the concentration of zoospores, temperature, plant host, pathogen genotype, and by the interaction between host and pathogen genotype. Stem results were mostly affected by host and host-pathogen genotype interaction.

Hosts bearing the most severe infections do not always support the highest levels of sporulation, so they are not necessarily the most likely to spread the disease.

Regulators also cannot always generalize re: the pathogen’s impact on plant hosts based on the hosts’ taxonomic relationship. Results were fairly similar for congeneric species within the genera Rosa, Prunus, and Syringa, but quite different for species within the genera Ilex, Gaultheria, and Osmanthus.

It is clear that basing regulatory or best management practices on any one pathogen-host-environment relationship is likely to lead to failure, leaving our forests inadequately protected

The findings that pertain most directly to early detection of infections and those that otherwise promote spread of the pathogen are my focus here.

Hosts that Support Sporulation / Spread of Disease

At least five host species are much more infectious than Rhododendron catawbiense. Hosts that support the highest levels of sporulation were Syringa vulgaris, Hamamelis intermedia, and Syringa meyeri. Hosts that support medium-high levels of sporulation were Rosa gymnocarpa and Syringa pubescens subsp. patula.  

Two of the Syringa species support high levels of sporulation, but rank low on overall susceptibility. Rosa gymnocarpa ranked fourth for levels of sporulation, but only fifteenth for overall susceptibility. At least six other species join this group of taxa that are highly infectious without displaying noticeable symptoms. Note than none of these top disease drivers is included in the so-called “filthy five” genera which are the focus of federal and state detection efforts. These genera are Rhododendron spp., Camellia spp., Viburnum spp., Pieris spp., and Kalmia spp.

One of the “filthy five” is Rhododendron catawbiense. It is often used as a standard against which to compare other species’ vulnerability. R. catawbiense supports a somewhat lower level of sporulation than do the species listed in the preceding paragraph. Again, disease severity is not a reliable cue to the likelihood of supporting sporulation and disease spread. Thus, the Hamamelis intermedia was the only species that scored high for both sporulation and susceptibility.

Temperatures Affect Infection Rates

A temperature of 20°C [68o F] was found to be ideal for maximum sporulation by all three genotypes. However, the NA1 genotype was a relatively good sporulator at 12oC [53oF]. The NA2 genotype sporulates prolifically at 25°C [77oF], but produces fewer sporangia than the other two genotypes at 12oC. These findings suggest which genotype might pose a greater risk in warmer or cooler regions than those supporting the current wildland infestations in California and Oregon. Thus, if NA2 spreads via the nursery trade to warmer regions, such as the area of the Southeast identified by various risk maps developed in the past [See maps on pages 14 – 16 in chapter 5 of Fading forests III, available here], it might pose a higher risk. This discovery intensifies concern arising from the fact that many of the P. ramorum-infected plants shipped to Indiana – and presumably other eastern states – in 2019 were of the NA2 lineage. States that received infected plants in 2019 included Alabama, Arkansas, Kentucky, Missouri, North Carolina, Tennessee, Virginia, and West Virginia.

Considering individual host species, Gaultheria shallon, R. catawbiense, Osmathus delayayi and Hamamelis intermedia supported good sporulation at the higher temperatures whereas Laurus nobilis, Syringa vulgaris, and Magnolia stellata supported better sporulation in cooler climates. Note that H. intermedia and S. vulgaris support prolific sporulation; the latter is a “symptomless superspreader”.

Garbelotto et al. note that Magnolia stellata is both highly susceptible and highly infectious at 12°C and thus able to spread the infection in colder areas. This advice to limit use of this species in cooler areas runs counter to horticultural experts’ guidance to plant this shrub in USDA Hardiness Zones 4–9 – which include virtually all the lower 48 except the most northern parts of Montana, North Dakota, and Minnesota. Clearly, star magnolia is a popular plant in colder regions. At the other end of the spectrum, Gaultheria shallon, Hamamelis intermedia, and Mahonia aquifolia were both highly susceptible and infectious at 25 °C, thus their use should be limited in warmer areas. All three include warm regions in their native ranges. 

Early Detection

There are two ways to carry out early detection surveys.

(1) The first is detection of infection in plants themselves. Garbelotto et al. determined that 14 plant species are highly or moderately susceptible to infection even with relatively limited inoculum sources. Intense monitoring of these species would be likely to detect new infestations. Three of the highly susceptiblespecies, namely Syringa meyeri, Syringa pubescens subsp. patula and Hamamelis intermedia, are potentially more susceptible than R. catawbiense.

Hamamelis x intermedia ‘Angelly’ 01.JPG Wikimedia Commons

Based on the relative ease of pathogen re-isolation from the following host species after they had been inoculated at low levels, Syringa meyeri, Syringa pubescens subsp. patula, Hamamelis intermedia, Syringa vulgaris, Osmanthus delavayi, and Magnolia grandiflora indicated that a larger number of plants in the production facility had become infected.

(2) A second approach to early detection monitoring would be to focus on those host taxa able to support the most robust sporulation when infected by low levels of inoculum. This approach emphasizes curtailing spread.

As I noted above, Garbelotto et al. conclude that five species could spur significantly faster disease spread due to higher transmission rates coupled with higher susceptibility rates. These five species are Syringa vulgaris, S. meyeri, and S. pubescens subsp. patula; Hamamelis intermedia; and Rosa gymnocarpa. Note than none of these disease drivers is included in the so-called “filthy five” genera on which regulators focus now detection efforts.

Several species appeared less diseased, but supported more vigorous sporulation (e.g., Syringa vulgaris, S. pubescens subsp. patula and Rosa gymnocarpa). Others were more diseased but supported less sporulation (e.g., Prunus laurocerasus and Prunus lusitanica). Therefore, nursery managers and regulators should not rely on visual assessment of disease intensity to judge spread risk.

Other Information

Comparing the three genotypes, EU1 was most aggressive in terms of disease incidence at both low and high inoculum loads. At low levels of inoculum, NA1 lineage was comparable in terms of disease severity.

However, at higher inoculum loads NA1 was clearly the most infectious based on the number of sporangia produced on infected hosts. Garbelotto et al. conclude that the co-mingling of the EU1 and NA1 lineages in Oregon forests might result in a highly destructive forest disease, as both virulence and transmission potential would be maximized. There is the further risk that the presence of the two genetic lineages, which have different mating types, might enable sexual reproduction/ genetic exchange between the two lineages.

Sources

Matteo Garbelotto, M., D. Schmidt, T. Popenuck. 2020. Pathogenicity and infectivity of Phytophthora ramorum vary depending on host species, infected plant part, inoculum potential, pathogen genotype, and temperature. Plant Pathology 2020;00.1

Phytophthora ramorum – a deadly forest pathogen, surviving and spreading as three strains in North America. “Plant Pathology” Highlight. https://www.bspp.org.uk/phytophthora-ramorum-a-deadly-destructive-forest-pathogen-surviving-and-spreading-as-three-strains-in-north-america-on-more-than-100-ornamental-hosts-from-leaf-to-stem-across-a-range-of-t/

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