You Might Be Surprised By Who is Authorized to Manage Wildlife on Federal Lands

mountain goats – introduced onto USFS-managed lands in the Columbia River Gorge at state initiative; in Utah, the state introduced mountain goats on lands adjacent to a USFS Research Natural Area


The journal Environmental Law has just published a 135-page article that debunks a common myth of wildlife management – a piece that the U.S. Forest Service tried to quash. The authors’ analysis could affect the introduction of potentially invasive non-native species – and the reintroduction of native ones – on federal lands.

Nie, M., C. Barns, J. Haber, J. Joly, K. Pitt & S. Zellmer. 2017. Fish and Wildlife Management on Federal Lands; debunking state supremacy. Environmental Law, Vol. 47, no. 4 (2017).

The article reviews the legal authority of federal and state governments to manage wildlife on federal lands.  The authors examined wildlife-related provisions within the National Park System, National Wildlife Refuge System, National Forest System, Bureau of Land Management, the special case of Alaska, the National Wilderness Preservation System, and the Endangered Species Act. They also reviewed cases where federal and state agencies came into conflict over wildlife management on federal lands.

Citing the U.S. Constitution, federal land laws, and relevant case law, the authors assert that federal agencies have an obligation, not just the discretion, to manage and conserve fish and wildlife on lands and waters under their management. They say that the often-cited statement that “the states manage wildlife and federal land agencies only manage wildlife habitat” is wrong from a legal standpoint. This is the myth that the article debunks.

Furthermore, the authors find that federal agencies frequently apply their powers in an inconsistent and sometimes even unlawful fashion. Due to political pressures, they may back down when confronted by states wanting to manage wildlife to achieve their own goals – even when the state’s goals conflict with the legally-mandated purposes of the federal land under question. Such goals might include ensuring maximum populations of “game” animals or introduction of species to new habitats – regardless of the potential impact on native plants and animals.

The authors note that federal land and wildlife laws provide ample opportunities for constructive intergovernmental cooperation in wildlife management. They call for truly mutual collaboration by federal, state, and tribal authorities in managing wildlife. However, such cooperation is blocked in part by states choosing to challenge the constitutional powers, federal land laws, and U.S. government supremacy. In addition, the authors contend, most states have not put together programs that address their own conservation obligations. These obligations are inherent in the widely recognized doctrine of wildlife being a public trust to be managed for the present and future benefit of the people, not the government or private individuals.

According to the website of the Forest Service Employees for Environmental Ethics,  posting of a draft of this article on the University of Montana website (where lead author Martin Nie teaches) led the U.S. Forest Service to pressure the university to withdraw the article. The university refused, and the Forest Service ended its contract with Nie and his research center.

The paper can be downloaded here. 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.

Posted by Faith Campbell

“Invasive Species Denialism” Increases Exponentially


Anthony Ricciardi and Rachael Ryan have analyzed 77 articles published from 1994 to 2016 in scholarly journals and the mainstream media that express some level of “invasive species denialism”. Denialist articles appearing in these publications have increased exponentially over the past three decades, most notably in the mainstream popular press – and they have the graph, fitted to a curve, to prove it.

The authors cite Diethelm and McKee (2009) in defining “science denialism” as “the use of rhetorical arguments to give the appearance of legitimate debate where there is none, with the ultimate goal of casting doubt on scientific consensus.” Similar strategies have appeared in disputes over the dangers of tobacco smoking and climate change.

Ricciardi and Ryan say that “[u]nlike normal scientific debates, which are evidence based, this discourse typically uses rhetorical arguments to disregard, misrepresent or reject evidence in attempt to cast doubt on the scientific consensus that species introductions pose significant risks to biological diversity and ecosystems….” In their view, the “denialist” articles assert an absence of damage from bioinvasion “despite peer-reviewed research that shows otherwise ….”  One example of evidence ignored by the contrarians are several analyses of the causes of endangerment or extinction of vertebrate species listed on the Red List maintained by the IUCN [as reported in my blog from May 2016 link]

Furthermore, these claims are almost always made in the absence of peer review – either in popular media or as opinion articles in scholarly journals. Many of the writers are social scientists and philosophers, not natural scientists. Only five of the 77 articles, or 6%, were published in natural science journals.

Ricciardi and Ryan say that unlike genuine scientific debate, “denialists” reject scientific evidence while repeating claims that have already been refuted in the scientific arena. Often, “contrarians” link invasion biology to xenophobia and latent racism, or otherwise impugn the motives of those engaged in the invasion biology field.

Ricciardi and Ryan consider possible reasons for the rise in “denialist” articles. Possible reasons include anti-regulatory ideologies, distrust of scientific institutions, conflicting values and perceptions of nature, even individuals’ desire for attention. They note that despite the absence of a true scientific controversy, the “denialists’” assertions gain credibility because science reporters think they need to present “both sides” of the argument.

Unlike the situation in the contrived controversies over climate change and risks from tobacco, we at CISP have not found a powerful industry backing the contrarians.

Ricciardi and Ryan express concern that the growing number of articles rejecting decades of research on invasive species might undermine policy initiatives at a time when invasion biology’s relevance to biosecurity, conservation, and ecosystem management is increasing. Gaining public support is critical to the success of such policies.

This concern is especially well-founded given that the authors’ results underestimate the extent of invasive species denialism. That is, they omitted from their analysis articles from internet blogs – known to be major platforms for promoting “science denialisms” – and websites that specifically attack invasion biology.

While Ricciardi and Ryan published this as a “note,” it is packed with information, e.g., references on science denialism, in general; and, in supplementary information, a table citing the 77 denialist articles.



INVASION NOTE. Ricciardi, A. & R. Ryan The exponential growth of invasive species denialism. Biological Invasions. Published online 12 September 2017


Invasive “hot spot” study confirms vulnerable places, causes of introductions

removing Miconia from Hawaiian forest; courtesy of the Nature Conservancy of Hawai`i

A recent article by Wayne Dawson and 24 coauthors (see reference at the end of this blog) provides the first-ever global analysis of established alien species. They studied the diversity of established alien species belonging go eight taxonomic groups – amphibians, ants, birds, freshwater fish, mammals, reptiles, spiders and vascular plants – across 609 regions (186 islands or archipelagos, and 423 mainland regions).

The analysis found that the highest numbers of established alien species in these taxonomic groups were in the Hawaiian Islands, New Zealand’s North Island and the Lesser Sunda Islands of Indonesia. The Hawaiian Islands have high numbers of invasive species in all of the eight groups studied. In New Zealand, the highest numbers were invasive plants and introduced mammals that prey on the native birds.

Florida is the top hotspot among mainland regions. Florida is followed by the California coast and northern Australia.

Burmese python in the Florida Everglades; photo by U.S. Fish & Wildlife Service


 Invasive species hotspots were found mainly on islands and in coastal regions of mainland areas. The lead author, Dr. Wayne Dawson, a researcher at Durham University’s Department of Biosciences, suggested that the greater invasive species richness in coastal regions probably results from higher rates of species introductions to port areas compared to interior regions.

Island regions have, on average, higher cross-taxon invasive species richness. This cross-taxon richness on islands tends to be higher for those islands further from continental landmasses. The authors suggest that such oceanic islands might be more likely to import large quantities of goods from foreign sources than islands close to continents, thus experiencing higher propagule pressure.



Regions with greater wealth (measured as per capita GNP), human population density, and area have higher established alien richness. These effects were strongest on islands. The authors suggest that wealth and human population density might correlate with higher numbers of species being brought to the region through trade and transport.

On mainlands, cooler regions have higher richness. I think this might reflect history – centuries of colonial powers importing plants and animals. However, colonial powers also introduced species to tropical regions.  In contrast, on islands warmer and wetter regions have higher richness of invasive species.



The authors conclude that cumulative numbers of invasive species at a particular location are driven to a greater extent by differences in area and propagule pressure than by climate. The model that best explains cross-taxon invasive species richness combines per capita GDP, population density and sampling effort. Other important factors are area of the region, mean annual precipitation, and whether a region is on a mainland or island(s).

The study results show that, per unit increase in area, per capita GDP, and population density, invasive species richness increases at a faster rate on islands than on mainlands. This might be confirmation of the longstanding belief that islands are more readily invaded than mainlands, although the authors caution that a rigorous test of this explanation would require data on failed introductions.

The authors call for additional research to understand whether these effects arise because more species are introduced to hotspot regions, or because human disturbance in these regions makes it easier for the newcomers to find vacant spaces and opportunities to thrive.


I think it would be helpful to compare the findings on invasive species richness in specific regions to data on historic patterns of trade and colonization to strengthen our understanding of the importance of propagule pressure in determining invasion patterns.


Increasing Confirmation of Significance and Breadth of Invasive Species Threat

The Dawson et al. study is the latest in a series of analyses of global or regional patterns in invasive species. I have blogged previously about several of these:

  • Bradshaw et al. 2016 concluded that invasive insects alone cause at least $77 billion in damage every year, a figure they described as a “gross underestimate”.
  • A study by Hanno Seebens and 44 coauthors showed that the rate of new introductions of alien species has risen rapidly since about 1800 – and shows no sign of slowing down. Adoption of national and international biosecurity measures have been only partially effective, failing to slow deliberate introductions of vascular plant species, birds, and reptiles, and accidentally introduced invertebrates and pathogens. Like Dawson et al, Seebens et al. found a strong correlation between the spread of bioinvaders introduced primarily accidentally as stowaways on transport vectors or contaminants of commodities (e.g., algae, insects, crustaceans, molluscs and other invertebrates) and the market value of goods imported into the region of interest.
  • Liebhold et al. 2016(see reference below) studied insect assemblages in 20 regions around the world. They found that an insect taxon’s ability to take advantage of particular invasion pathways better explained the insect’s invasion history than the insects’ life-history traits. (The latter affect the insect’s ability to establish in a new ecosystem.)
  • Maartje J. Klapwijk and several colleagues note that growing trade in living plants and wood products has brought a rise in non-native tree pests becoming established in Europe. The number of alien invertebrate species has increased two-fold since 1950; the number of fungal species has increased four-fold since 1900.
  • Jung et al. (2015) studied the presence of Phytophthora pathogens in nurseries in Europe. They found 59 putatively alien Phytophthora taxa in the nurseries. Two-thirds were unknown to science before 1990. None had been intercepted at European ports of entry when they were introduced. Nor have strict quarantine regulations halted spread of the quarantine organism ramorum.
  • A report by The World Conservation Union (IUCN) on World Heritage sites globally found that invasive species were second to poaching as a threat to the sites’ natural values. Of 229 natural World Heritage sites examined, 104 were affected by invasive species. Island sites – especially in the tropics – were most heavily impacted.
  • Another report by IUCN found that invasive species were the second most common cause of species extinctions – especially for vertebrates.


These studies demonstrate that

  • Invasive species have become a significant threat to biological diversity and ecosystem services around the world – one that continues to grow.
  • The recent spate of studies originating in Europe probably reflects recent recognition of the continent’s vulnerability – as seen, inter alia, in the proliferation of tree-killing Phytophthoras.
  • Human movement of species – propagule pressure – whether deliberately or due to inadequate efforts to manage trade-related pathways – explain the bulk of “successful” introductions.
  • Economic activity drives introductions, so areas at highest immediate risk are urban areas and other centers receiving high volumes of imports and visitors. Among troubling trends in the future is rapid global urbanization – along with rising economic interdependency.
  • Efforts to curb these movements – at the national, regional, and international levels – have failed so far to counter the threat posed by invasive species of nearly all taxonomic groups.

In my view, the requirements that phytosanitary measures “balance” pest prevention against trade facilitation results in half measures being applied – and half measures achieve halfway results. For example, the U.S. does not require that packaging be made from materials that cannot transport tree-killing pests. The USDA has moved far too slowly to limit imports of plant taxa that pose a risk of either being invasive themselves or of transporting pests known to be damaging.


Conservationists should focus on building political pressure to strengthen regulations and other programs intended to curtail this movement. No other approach will succeed.



Bradshaw, C.J.A. et al. Massive yet grossly underestimated global costs of invasive insects. Nat. Commun. 7, 12986 doi: 10.1038/ncomms12986 (2016). (Open access)

Dawson, W., D. Moser, M. van Kleunen, H. Kreft, J. Perg, P. Pyšek, P. Weigelt, M. Winter, B. Lenzner, T.M. Blackburn, E.E. Dyer, P. Cassey, S.L. Scrivens, E.P. Economo, B. Guénard, C. Capinha, H. Seebens, P. García-Díaz, W. Nentwig, E. García-Berthou, C. Casal, N.E. Mandrak, P. Fuller, C. Meyer and F. Ess. 2017. Global hotspots and correlates of IAS richness across taxon groups. Nature Ecology and Evolution Vol. 1, Article 0186. DOI: 10.1038/s41559-017-0186 |


Jung,T., L. Orlikowski, B. Henricot, P. Abad-Campos, A.G. Aday, O. Aguin Casa, J. Bakonyi, S.O. Cacciola, T. Cech, D. Chavarriaga, T. Corcobado, A. Cravador, T. Decourcelle, G. Denton, S. Diamandis, H.T. Doggmus-Lehtijarvi, A. Franceschini, B. Ginetti, M. Glavendekic, J. Hantula, G. Hartmann, M. Herrero, D. Ivic, M. Horta Jung, A. Lilja, N. Keca, V. Kramarets, A. Lyubenova, H. Machado, G. Magnano di San Lio, P.J. Mansilla Vazquez, B. Marais, I. Matsiakh, I. Milenkovic, S. Moricca, Z.A. Nagy, J. Nechwatal, C. Olsson, T. Oszako, A. Pane, E.J. Paplomatas, C. Pintos Varela, S. Prospero, C. Rial Martinez, D. Rigling, C. Robin, A. Rytkonen, M.E. Sanchez, B. Scanu, A. Schlenzig, J. Schumacher, S. Slavov, A. Solla, E. Sousa, J. Stenlid, V. Talgø, Z. Tomic, P. Tsopelas, A. Vannini, A.M. Vettraino, M. Wenneker, S. Woodward and A. Perez-Sierra. 2015. Widespread Phytophthora infestations in European nurseries put forest, semi-natural and horticultural ecosystems at high risk of Phytophthora disease. Forest Pathology.


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


Liebhold, A.M., T. Yamanaka, A. Roques, S. Augustin, S.L. Chown, E.G. Brockerhoff, P. Pysek. 2016. Global compositional variation among native and nonindigenous regional insect assemblages emphasizes the importance of pathways. Biological Invasions (2016) 18:893–905


Seebens, H. et al., 2017. No saturation in the accumulation of alien species worldwide. Nature Communications. January 2017. [ ]



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.


Posted by Faith Campbell



CISP Starts Focus on Emerging Wildlife Diseases in Large Collaboration


A new CISP effort is underway: we are pleased to announce support for our work on emerging wildlife diseases. Funding for this collaborative effort was provided by the BAND Foundation, a charitable foundation whose mission includes conservation of wildlife and plant species and combatting wildlife diseases. The grant, managed by the Association of Fish & Wildlife Agencies (AFWA), will provide support through 2017 and 2018. The scope of the project is described in the following AFWA announcement. We will provide more information on the project as it develops.


Washington D.C. (May 4, 2017) – The Association of Fish & Wildlife Agencies is pleased to announce a partnership focused on fish and wildlife health, in collaboration with Bat Conservation International, the Amphibian Survival Alliance, the Amphibian and Reptile Conservancy, the Center for Invasive Species Prevention, and five universities in the United States.

 Disease is rapidly emerging as a major threat to wildlife globally. While wildlife diseases are not new, human actions are dramatically increasing their spread and impact. The partnership between the BAND Foundation and the Association will lead to more effective responses to emerging wildlife diseases.  Three specific emerging pathogens that affect bats (White-nose syndrome (WNS)), salamanders (Batrachochytrium salamandrivorans (Bsal)) and sea stars (Sea Star Wasting Disease (SSWD)) are of immediate concern in the United States. These families of animals play vital roles as ecosystem engineers across a range of habitats from agricultural landscapes to forests to intertidal zones. This project provides funding for critical research and monitoring to better understand the diseases that threaten them, aims to catalyze a public policy framework for tackling wildlife disease more broadly and strategically, and seeks to leverage additional dollars to address this critical issue.

 “State fish & wildlife agencies are on the front lines of wildlife disease prevention. This much needed funding will go a long way to prevent and prepare for disease outbreaks through the United States,” said Nick Wiley, President of the Association of Fish & Wildlife Agencies.

A conference to bring together experts in science and management of various wildlife diseases will be convened in 2018, to help further identify needs and improve communication and responses.

at: file:///C:/Users/Owner/Downloads/PR-%20AFWA%20Partners%20with%20the%20BAND%20Foundation.pdf .


Posted by Peter Jenkins

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.



Bill aimed at controlling invasive species on the ground advances

whitebark pine in Crater Lake National Park killed by white pine blister rust; photo by F.T. Campbell

In the first days of April, the Senate Environment and Public Works Committee  adopted the Wildlife Innovation and Longevity Driver Act (S. 826) (the WILD Act).

Title II of this legislation would amend the Fish and Wildlife Coordination Act by inserting language very similar to the Federal Land Invasive Species Control, Prevention, and Management Act (S. 509).  I blogged last year about that  bill and a hearing about it here.

Our concerns at the time focused on:

  • The provision allowing invasive control projects to proceed without first being evaluated by an environmental impact statement or environmental assessment. Lack of careful analysis could expose the environment to additional damage. For example, use of herbicides or grazing to control invasive plants can lead to suppression of native forbs. Suppressing invasion by one set of plants – whatever the strategy used – often facilitates a secondary invasion.
  • The mandatory funding allocations – which severely limit funds available to support research, outreach, and strategic planning and coordination – could undercut activities crucial to development and implementation of effective strategies and management tools.
  • The mandatory goal of reducing invasive species populations by 5% per year is unrealistic.
  • New requirements on reporting and coordination might divert already-thin resources and delay needed action.
  • Priority-setting. Managing invasive species on national lands should reflect national goals and perspectives, not be set by states’ governors.

Caroline Murphy of The Wildlife Society and I have reviewed Title II of the new WILD Act and find that it differs from last year’s invasive species control bill in several important ways:

  • The bill now applies to a wider range of agencies. The Secretary of the Army (who supervises the Corps of Engineers) is included explicitly; he joins the secretaries of Interior and Agriculture (as supervisor of the Forest Service). In addition, the bill also applies to the head of “any federal agency” having duties related to planning or treatment of invasive species “for the purpose of protecting water and wildlife on land and in water.”
  • Most important, projects are no longer granted a “Categorical Exclusion” from preparing environmental impact analyses. Instead, under an “Expedited Action” provision, the Secretaries are instructed to use all existing legal tools and flexibilities to expedite projects and activities.
  • The bill still requires that 75% of invasive species funds be allocated to “on-the-ground control and management of invasive species.” But such activity now may include “the use of appropriate methods to remove invasive species from a vehicle or vessel capable of conveyance.” I wish the language also included efforts to prevent invasive species from being present in or on the vehicle or vessel.
  • The bill has dropped the requirement that invasive species’ populations be reduced by 5% annually. The bill now requires the Secretaries to develop a strategic plan “to achieve, to the maximum extent practicable, a substantive annual net reduction of invasive species populations or infested acreage on land or water” that the Secretary manages. It is still not clear whether that reduction should apply to some or all of the invasive species there.

I am still concerned that

  • Projects are to use least-cost methods. This requirement is likely to favor reliance on chemical controls, which could have significant non-target impacts and might not provide lasting control. This incentive might be counter-balanced by the requirement that the methods be effective, based on sound scientific data. However, the bill’s focus on measuring annual results rather than long-term efficacy will add to pressures to rely on short-term approaches that could undermine long-term effectiveness.
  • Leadership of the projects – especially setting priorities – will be in hands of state governments, not the federal agencies which have the responsibility under federal law to manage the lands and waters that are to be protected. A partial counter-balance is the requirement that the appropriate federal agency Secretary determine which lands or waters need immediate action to address the invasive species risk.  Furthermore, the expedited actions are to be carried out in accordance with agency procedures, including any applicable land or resource management plan

I welcome the requirement that the Secretaries, in developing their strategic plans, must take into consideration the ecological as well as the economic costs of acting or not acting.

As before, the projects are to be carried out through collaboration with wide range of partners, including private individuals and entities – apparently including non-governmental organizations such as state or local invasive plant coalitions.

The rest of the WILD Act would reauthorize the Partners for Fish and Wildlife Program, some Multinational Species Conservation Fund Programs, and create several conservation-related competitive grant programs to be managed by the National Fish and Wildlife Foundation, one of which is for the management of invasive species.

Now that these provisions are incorporated into a wider bill, and Senator Barasso is chairman of the full committee, adoption of some version of this legislation now seems more likely than I thought last year.  Apparently there is still no action in House on the parallel bill.

While I am heartened by some of the changes in the bill since last year, I continue to think that America’s public lands would be better protected by a more comprehensive approach that includes prevention, mapping, early detection, research, prioritization, coordination and outreach aimed at engaging key stakeholders.  Such an approach was outlined in a document developed a couple of years ago by the National Environmental Coalition on Invasive Species (NECIS) – available here.

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.

The New Year – Where We Are & What Needs to be Done


dying ash tree, Fairfax County, Virginia; photo by F.T. Campbell

According to Aukema et al. 2010 (see references at the end of this blog), by the first decade of the 21st Century, the number of non-native insects and pathogens damaging our forests had risen to at least 475.  Sixty-two of the insects, and all of the 17 pathogens, were judged to have “high impact”, with both economic and ecological ramifications. More than 181 exotic insects that feed on woody plants are established in Canada (USDA APHIS 2009). Especially hard-hit is the eastern deciduous broadleaf forest — there is an exotic pest threat to nearly every dominant tree species in this ecosystem type.

The situation is actually worse than this article and others based on it depict. Aukema et al. 2010 did not include several highly damaging forest pests that are native to regions of North America (e.g., goldspotted oak borer, thousand cankers disease); nor did they include pests on U.S. islands, such as `ohi`a rust and Erythrina gall wasp in Hawai`i. Aukema et al. 2010 also did not include pests that attack palms or cycads – which are significant components of some ecosystems on the continent as well as on America’s tropical islands. Finally, some invaders have come to our attention since the database on which these authors relied was compiled, e.g., polyphagous and Kuroshio shot hole borers and the rapid ohia death pathogen. (For a list of pests detected since 2003, see page 7 of Fading Forests III, available here; this list was compiled in 2014, so it does not include the most recently detected pests, such as rapid ohia death. For descriptions of most invaders discussed in this blog, go here.)

Of course, more important than numbers are impacts. Lovett et al. 2016 provide a summary of those impacts … but let’s get specific. Note that some of these species occupy wide ranges; it is not only the narrow endemics that are under threat.

  • Several tree species are severely depleted throughout their ranges: American chestnut, Fraser fir, Port-Orford cedar, butternut, Carolina hemlock, redbay and swamp bay, cycads on Guam
  • Other species or genera are already severely reduced in significant portions of their ranges and the causal agents are spreading to the remaining sanctuaries: whitebark pine.
  • In some cases, the causal agent has not yet spread, but threatens to: `ohi`a.
  • Some tree or shrub taxa are under severe attack across much of their ranges: ashes, eastern hemlock, American beech, dogwoods, tanoak, viburnums …

Many of America’s 300 species of oak face a variety of threats:

  • in the East, European gypsy moth, oak wilt, and – in some areas – winter moth;
  • in the South, oak wilt and Diplodia;
  • on the West coast, sudden oak death, goldspotted oak borer, the polyphagous and Kuroshio shot hole borers, Diplodia, and foamy bark canker.

(For more about threats to oaks, see my blog from last April.)

Other threats are – so far – confined to relatively small areas, but they could break out. These include the multi-host insects Asian longhorned beetle; polyphagous and Kuroshio shot hole borers; and spotted lanternfly. Tree genera containing species at risk to one or more of these insects include maple, elm, willow, birch, sycamore, cottonwood and poplar, sweet gum, oak. Only ALB and the lanternfly currently are the focus of federal and state programs aimed at eradication or containment. The widespread invasive tree, Ailanthus or tree of heaven, could support spread of at least the polyphagous shot hole borer and spotted lanternfly.

Of course, additional pests are likely to be introduced (or detected) in the future. Known threats include the various Asian subspecies of gypsy moth and ash dieback (Hymenoscyphus fraxineus – previously  called Chalara fraxinea). If history is any guide, we are likely to be surprised by a highly destructive invader that we have either never heard of or dismissed based on its behavior elsewhere. See my earlier blogs for discussions of what should be done to reduce the introduction risk associated with wood packaging and imports of living plants.


What Should We Do?

2017 brings a new Administration and a new Congress. At a minimum, we need to educate all these decision-makers about both the high costs imposed by tree-killing insects and pathogens and effective strategies to minimize those costs. How will our concerns be received? We don’t know yet.

We might have opportunities arising from the skeptical attitude toward trade voiced during the campaign. Will newly elected or appointed agency and Congressional staffers be open to re-considering the plant health threats associated with international trade? On the other hand, will mainstream agriculture’s traditional strong support for exports continue to overwhelm calls to strengthen phytosanitary measures? Even if our message about risks associated with trade gains a hearing, will officials be willing to consider more rigorous regulations? Or higher funding levels for agencies responsible for plant pest prevention and response?

I hope you will join the Center for Invasive Species Prevention and others in coordinated efforts to take these messages to the next Secretary of Agriculture (who has not yet been named!) and key members of the Senate and House of Representatives. Opportunities in the Congress include Senate confirmation of the new Secretary and the three Under Secretaries that oversee APHIS, USFS, and ARS; annual appropriations bills; and early consideration of possible amendments to the Farm Bill (which is due for renewal in 2019).

See my post from a week ago for more suggestions for how Congress could improve U.S. invasive species management programs.

Expect to hear from me often in the coming year!



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

Lovett, G.M., M. Weiss, A.M. Liebhold, T.P. Holmes, B. Leung, K.F. Lambert, D.A. Orwig , F.T. Campbell, J. Rosenthal, D.G. McCullough, R. Wildova, M.P. Ayres, C.D. Canham, D.R. Foster, S.L. LaDeau, and T. Weldy. 2016. Nonnative forest insects and pathogens in the United States: Impacts and policy options. Ecological Applications, 0(0), 2016, pp. 1–19. DOI 10.1890/15-1176.1

U.S. Department of Agriculture, Animal and Plant Health Inspection Service.  2009.  Risk analysis for the movement of SWPM (WPM) from Canada into the US.


Posted by Faith Campbell

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


What the new President & Congress Can Do re: Invasive Species

 White House


A new President and Congress take office in January.  And outgoing President Obama recently amended the Executive Order on invasive species.

What might the new leaders do to improve America’s invasive species programs?

Here are a group of actions that I think would improve programs significantly:

  • amend the Lacey Act to strengthen controls over introduction and spread of invasive animals and animal diseases;
  • raise the political profile of invasive species issues by holding more frequent oversight hearings;
  • increase funding for invasive species prevention, containment, and control programs;
  • support proposals to amend the 2019 Farm Bill to strengthen on-the-ground programs, policies, and research aimed at minimizing invasive species introduction, spread, and damage;
  • during the confirmation process, Senators should ask President Trump’s nominees to leadership positions in the Departments of Agriculture and Interior about how they will address invasive species challenges.

Do we need new legislation mandating that federal land-managing agencies do X or Y with regard to invasive species? This was the focus of a hearing in May at which I testified.

Federal land-managing agencies are already authorized and – in some cases required – to act to control invasive species on lands and waters under their jurisdiction.  Some of the existing statutes even authorize the agencies to apply fees paid by people who use the public lands for some purpose (e.g., livestock grazing, recreation) to management of invasive species.

Most of the statutes authorizing invasive species management incorporate that activity into the agency’s broader management goals for protection of wildlife, habitat, natural resources, historic or cultural sites, etc.  For example, the USFS Manual §2900 lists 21 laws and 6 regulations or policies that govern the USFS’ management of invasive species.  Some of these laws apply to all federal land-managing agencies, including:

  • Endangered Species Act (ESA) of 1973 (16 U.S.C. §§1531 et seq.)
  • Surface Mining Control and Reclamation Act of 1977 (30 U.S.C. 1201, 1201 (note), 1236, 1272, 1305). §515
  • North American Wetland Conservation Act 1989 (16 U.S.C. 4401 (note), 4401-4413, 16 U.S.C. 669b (note)). §9 [U.S.C. 4408]
  • Sikes Act (Fish and Wildlife Conservation) of September 15, 1960 (16 U.S.C. 670g-670l, 670o, P.L. 86-797), as amended. §201
  • National Historic Preservation Act of 1966 [16 U.S.C. §§470 et seq.]
  • Wilderness Act of 1964 (16 U.S.C. §§1131 et seq.

Other statutes apply only to resource management authorities of the USDA Forest Service; these include:

  • Organic Administration Act of 1897 (16 U.S.C. §§ 473 et seq.).
  • Fish and Wildlife Coordination Act (16 U.S.C. § 661 et seq.).
  • Knutson-Vandenberg Act of June 9, 1930 (16 U.S.C. 576, 576a-576b). §3 [16 U.S.C. 576b]
  • Bankhead-Jones Farm Tenant Act of 1937 (7 U.S.C. §§1010 et seq.)
  • Anderson-Mansfield Reforestation and Revegetation Act of October 11, 1949 (16 U.S.C. 581j (note), 581j, 581k)
  • Multiple-Use Sustained-Yield Act of 1960 (16 U.S.C. §§528 et seq.)
  • Forest and Rangeland Renewable Resources Planning Act (RPA) of 1974 as amended by the National Forest Management Act (NFMA) of 1976. §6
  • International Forestry Cooperation Act of 1990 (16 U.S.C. § 4501)
  • Healthy Forests Restoration Act of 2003 (H.R. 1904), [16 U.S.C. 6501-6502, 6511-18, 6541-42, 6571-78]
  • Wyden Amendment (P.L. 109-54, Section 434).
For brief descriptions of all these statutes, see the references and links at the end of this blog posting.

Advocates have tried before to legislate a specific requirement that federal agencies combat invasive species.  The Federal Noxious Weed Act of 1974 (7 U.S.C. § 2801 note; 7 U.S.C. § 2814) was amended in 1990 to add §15, “Management of Undesirable Plants on Federal Lands”.  This section requires each federal agency to

1) designate an office or person adequately trained to develop and coordinate an undesirable plants management program for control of undesirable plants on federal lands under the agency’s jurisdiction, and

2) establish and adequately fund an undesirable plants management program through the agency’s budgetary process,

3) complete and implement cooperative agreements with state agencies regarding the management of undesirable plant species on federal lands, and

4) establish integrated management systems to control or contain undesirable plant species targeted under cooperative agreements.

This approach hasn’t worked – no one is satisfied by the federal agencies’ “weed” management efforts.



What is missing is a political demand for action – and support for necessary staff and funding. Agencies under the secretaries of Agriculture and Interior bear most of the responsibility for managing invasive species.  As long as these officials are not being pressed by key Congressional committees, the media, and key stakeholders to take more aggressive and effective action to curtail species introductions and suppress established populations of bioinvaders, they will continue to focus their attention on issues that do generate these kinds of political pressure.

I am not saying that the principal statutes governing invasive species management could not be improved.  As noted above, several proposals have been put forward to strengthen laws which are the foundation for preventing introduction of invasive species.  I will blog about specific proposals in the new year.



USFS Invasive Species Manual

ANSTF/NISC report “Federal Policy Options Addressing the Movement of Aquatic Invasive Species Onto and Off of Federal Lands and Waters. 2015.  Committee on the Movement of Aquatic Invasive Species both onto and off of Federal Lands and Waters.

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.

On the Road to Extinction, Invasive Plants Do Have Significant Impacts

Lantana camarata

No studies have documented extinction of a native plant species caused by invasive ones. This has led to questions about whether invasive plants have truly significant impacts. (Of course, species extinction is not the only important impact).

These questions have been answered in a recent article by Paul Downey (of the Institute for Applied Ecology, University of Canberra) and David Richardson (of the Centre for Invasion Biology at Stellenbosch University, South Africa). A link to the article is provided at the end of this blog.

Downey and Richardson argue that studies have documented instances of invasive plant species putting native plants on the path – or trajectory – to extinction. Furthermore, plants go extinct more slowly than animals, often over centuries. As result, current approaches to analyzing impacts of invasive plants underestimate the damage that non-native species cause because they assume extinction will not result.

The authors name six “thresholds” along the trajectory to plant extinction. Each is affected by invasive plants:

  1. Plants die more quickly than they can be replaced by their offspring in some locations.
  2. Plants disappear from some locations entirely, but seeds or spores remain that could regenerate a new cohort of individuals.
  3. Some locations lose both individual plants and their propagules. This is a local extinction.
  4. The last locations hosting a species lose their individual plants, but in some places seeds or spores remain in the soil.
  5. The species is entirely lost in the wild with no individuals or propagules. The only survivors are held in botanic collections.
  6. Extinction. The remaining plants are lost, and the remaining seeds or spores are no longer capable of becoming new plants.

By focusing purely on full extinction — step six — plant conservationists lose sight of the threats to species as they occur and accumulate at each stage of the process. Without such attention we fail to act on opportunities to protect the species and counter the wider impacts of its disappearance.

Downey and Richardson note that plant invasions affect each component of a plant species’ population dynamics:  fecundity (seed production); death; immigration; and emigration (dispersal). Yet they could find no studies that have explored the effects of alien plants for all four components collectively.

A second explanation for scientists’ not documenting any extinctions caused by invasive plants is that it is extremely difficult to prove that every last individual or propagle of a plant species is dead . Many plant species have long-lived seed banks in the soil, or can regenerate from underground structures – so it is hard to know when that species is truly gone. This is especially true since seed banks are rarely monitored.

Furthermore, many of the conditions needed to demonstrate that alien plants have caused the extinction of native plant species have either not been measured, or have been examined for too short a time. The IUCN definition of extinction requires that data be collected over “a period that is appropriate for the life cycle of the species” (IUCN. 2014. Guidelines for using the IUCN Red List categories and criteria. Version 11. Prepared by the Standards and Petitions Subcommittee. Switzerland). Given the long persistence of plant species, the “appropriate period” exceeds the timeline almost all of even the few long-term studies in invasion ecology.


Downey and Richardson say that relying on changes in species richness to assess the impacts of alien plants will not adequately predict or describe the effects of invasion. Such analysis especially will not provide evidence for a species crossing from Threshold 1 to 2 or 3 . Indeed, they assert, collective species richness measures could mask losses of some species in instances where additional species are also recorded (i.e. the losses are off-set by additions).


The authors have found abundant evidence of invasive plants driving native plants along this extinction trajectory. They cite several examples of an invasive plant causing a “threshold effect” – that is, increases in alien plant cover or density result in decreased native plant species diversity or richness. They define this as the native species crossing from Threshold 1 to 2. Among the examples provided are several species in Australia and New Zealand and Lonicera maackii in the United States.


The authors also provide examples of species causing “extinction debts” – that is, a significant time lag between the introduction of an alien species initiating a native species’ movement along the trajectory and its actual extinction. One mechanism is by reducing native plants’ seed production. Again, Lonicera maackii is cited.

Downey and Richardson also note the potential downsides of invasive plant control measures.

In the end, the authors urge that scientists “… shift attention away from the end point of the extinction trajectory … to give due consideration of the full series of processes that drive declines of populations of native species.”

As Richardson has said in an interview with Oxford University Press, “… There is absolutely no doubt that alien plant invasions are eating away at native plant biodiversity. Many native plant species — probably HUNDREDS of species — are precariously close to being functionally extinct and survive as the ‘living dead’.’”


Source: Downey, P.O., D.M. Richardson. 2016. Alien plant invasions and native plant extinctions: a six-threshold framework. AoB Plants, 2016; 8: plw047 DOI: 10.1093/aobpla/plw047 ; open access, available at


Posted by Faith Campbell

Invaders Put Another Bird at Risk


i`iwi; photo by James Petruzzi; courtesy of American Bird Conservancy

As noted in an earlier blog (“When Will Invasive Species Get the Respect They Deserve?” May 2016),  invasive species can cause extinctions – especially on islands.  I have posted other blogs about the invasional meltdown in Hawai`i (“Hawaii’s unique forests now threatened by insects and pathogens” October 2015).

A further demonstration of the meltdown is the decision by the US Fish and Wildlife Service (USFWS) to propose listing  another Hawaiian honeycreeper (bird) – the i`iwi (Drepanis (Vestiaria) coccinea) as a threatened species.  Already, some 20 Hawaiian forest birds are protected under the Endangered Species Act.  Many, although not all, are threatened by the same factors as the i`iwi.

The proposal, which summarizes an extensive supporting report, is available here.  USFWS is accepting comments on the proposal that are submitted to the USFWS’  website before November 21.

The proposal documents the tragedy of Hawai`i. The i`iwi was once almost ubiquitous on the islands, from sea level to the tree line. Today the bird is missing from Lanai; and reduced to a few individuals on Oahu, Molokai, and west Maui. Remaining populations of i`iwi are largely restricted to forests above ~ 3,937 ft (1,200 m) on Hawaii Island (Big Island), east Maui, and Kauai.

In the past, hunting for the bird’s striking red feathers and agricultural conversion doubtless affected the i`iwi’s populations. Since the early 20th Century, though, the threats have all been invasive species.

The USFWS has concluded that the principal threat is disease: introduced avian malaria  — caused by the protozoan Plasmodium relictum and vectored by introduced mosquitoes (Culex quinquefasciatus). A second disease, Avian pox (Avipoxvirus sp.), is also present but scientists have not been able to separate its effects from those of malaria. Both vectored by the southern house mosquito.

I`iwi are very susceptible to avian malaria; in lab tests, 95% of birds died.


I’iwi on `ohi`a blossom at Hakalau NWR; photo by Daniel J. Lebbin; courtesy of American Bird Conservancy

I`iwi alive now have survived because they live in forests at sufficiently high elevations; there, cooler temperatures reduce the numbers of mosquitoes, and thus transmission of the disease.  However, the birds must fly to lower elevations in certain seasons to find flowering plants (the i`iwi feeds on nectar) – and then becomes exposed to mosquitoes.

Worse, climate change has already caused warming at higher elevations, and is projected to have a greater impact in the future.  The rising temperatures predicted to occur – even if countries meet their commitments from the December 2015 meeting of the UN Framework Convention on Climate Change – will result in upslope movement of mosquitoes. As a result, according to three studies reviewed by the USFWS, the i`iwi will lose 60 – 90% of its current (already limited) disease-free range by the end of this century, with significant effects occurring by 2050.

I`iwi occur primarily in closed canopy, montane wet or montane mesic forests composed of tall-stature `ohi`a (Metrosideros polymorpha) trees or in mixed forests of `ohi`a and koa (Acacia koa) trees. The i`iwi’s diet consists primarily of nectar from the flowers of `ohi`a  and several other plants, with occasional insects and spiders.



Hakalau National Wildlife Refuge; USFWS photo

The i`iwi’s dependence on `ohi`a creates another peril, because `ohi`a trees are vulnerable to alien diseases – both ohia rust and, especially, rapid ohia death or Ceratocystis ohia wilt. (Read descriptions of both diseases here.  As of September 2016, rapid ohia death has been found only on Hawai`i – the “Big Island”. However, 90% of all i`iwi currently reside on the Big Island! Worse, in future the relatively large area of high-elevation `ohi`a dominated forest on the Big Island was expected to be the principal refuge of the i`iwi from the anticipated climate-driven up-slope movement of malaria. However, as just noted, the Big Island’s trees are now being killed by disease. If rapid ohia death continues to spread across the native `ohi`a forests – on Hawai`i and potentially on the other islands – it  will directly threaten i`iwi by eliminating the limited, malaria-free native forest areas that remain for the species.

Rapid `ohi`a death (ROD) is caused by two distinct strains of the widely introduced pathogen Ceratocystis fimbriata.  It was first detected in the Puna District of Hawai`i in 2012. The disease has since been detected across a widening area of the Big Island, including on the dry side of island in Kona District (See map here.  The total area infested has increased rapidly, from ~6,000 acres in 2012 to 38,000 acres in June 2016.  Since symptoms do not emerge for more than a year after infection, the infested area is probably larger.  ROD kills `ohi`a in all size and age classes. There is no apparent limit based on soil types, climate, or elevation. O`hi`a growing throughout the islands appears to be vulnerable, from cracks in new volcanic areas to weathered soils; in dry as well as mesic and wet climates. The pathogen is probably spread by spores sticking to wood-boring insects and – over short distances – wind transport of insect frass.

Federal and state agencies are spending $850,000 on research on the disease, possible vectors, and potential containment measures.  Additional funds would be needed to implement any strategies, and to expand outreach  to try to limit human movement of infected plants or soil.

The Hawaii Department of Agriculture adopted an interim rule in August, 2015  which restricts the movement of `ohi`a plants, plant parts, wood, and frass and sawdust from Hawai`i Island to neighboring islands. Soil was included in the interim rule with an effective date of January 1, 2016. In March 2016, HDOA approved permit conditions for movement of soil to other islands. The interim rule is expected to be made permanent at a meeting of the Board of Agriculture on 18 October.

Other invasive species threatening the i`iwi are feral ungulates, including pigs (Sus scrofa), goats (Capra hircus), and axis deer (Axis axis).  All degrade `ohi`a forest habitat by spreading nonnative plant seeds and grazing on and trampling native vegetation. Their impact is exacerbated by the large number of invasive nonnative plants, which prevent or retard regeneration of `ohi`a forest. Drought combined with invasion by nonnative grasses have promoted increased fire frequency and the conversion of mesic `ohi`a woodland to exotic grassland in many areas of Hawaii.

The feral pigs pose a particular threat because by wallowing and overturning tree ferns (Cibotium spp.)  they create pools of standing water in which the mosquitoes breed.  The US FWS has concluded that management of feral pigs – across large landscapes – might be a strategic component of programs aimed at managing avian malaria and pox.

One possible source of hope: research into genetic manipulation of the mosquito disease vector by using tools from synthetic biology and genomics (see draft species status report . Considerable research is probably necessary before such a tool might be implemented.

Threat of Plant Pest Threat to Endangered Animals is Not Limited to Hawai`i

The USFWS is struggling to deal with the threat posed by plant pests to listed species. In San Diego, California, FWS personnel are trying to decide how to address the threat posed by the Kuroshio shot hole borer (read description here  to willows which constitute essential riparian habitat for the least Bell’s vireo.

Numerous cactus species that have been listed as endangered or threatened might be attacked by two insects from Argentina, the cactus moth and Harissia cactus mealybug (see my blog from October 2015; or read descriptions here .


Endangered Species Agencies Need to Coordinate with Phytosanitary Agencies

A growing number of species listed under the Endangered Species Act are being threatened by damage to plants from non-native plant insects and pathogens. This growing damage affects not just listed plants – such as the cacti mentioned in this and the October blogs; but also plants that are vitally important habitat components on which listed animals depend. The USFWS needs to engage with other federal and state agencies and academic institutions which are working to prevent introduction of additional plant pests, slow the spread of those already in the United States, and develop and implement strategies intended to restore plant species that have been seriously depleted by such pests. The USFWS should, therefore, work more closely with USDA Animal and Plant Health Inspection Service and Forest Service. USFWS must, of course, continue to work with experts in wildlife and wildlife disease.

Similarly, state wildlife agencies also need to coordinate their efforts with their counterparts in state departments of Agriculture and divisions of Forestry.

Many agencies in Hawai`i play crucial roles in protecting the Islands’ unique plant and animal communities:

  • U.S. Department of the Interior: Fish and Wildlife Service, National Park Service, United States Geological Service Biological Resources Division
  • US. Department of Agriculture: APHIS, Forest Service, Agriculture Research Service, National Institute of Food and Agriculture
  • US. Department of Homeland Security Bureau of Customs and Border Protection.
  • Hawai`i State Department of Agriculture and Department of Land and Natural Resources

Hawaiians of all types – federal and state employees and agencies, academics, and conservationists – deserve our thanks for promptly taking action of rapid ohia death.  All parties should make every effort to obtain the remainder of the funds needed to carry forward crucial research on ROD and avian malaria.  Those of us from the mainland need to support and help their efforts.


Posted by Faith Campbell

Invasive Earthworms Need Action!

 worm_medAmynthes agrestis; National Park Service photo


Earthworms have been largely ignored as a class of invaders. But evidence is accumulating that their numbers and impacts are too significant to ignore.


Non-indigenous earthworms began arriving in the Americas with the first European colonists and they are now widespread. One study (see summary of Reynolds and Wetzel 2008 here) found 67 introduced species among the 253 earthworm species in North America (including Mexico, Puerto Rico, Hawaii, and Bermuda).  In Illinois, 20 of the 38 species are introduced. Nuzzo et al. 2009 recorded a total of 11 earthworm species – all nonnative – at 15 forest sites in central New York and northeastern Pennsylvania.


Earthworms are good invaders – they reproduce quickly and are easily transported to new places – both carelessly and deliberately for bait, composting, or other uses.


As ecosystem engineers, invasive earthworms cause significant impacts to the soil and leaf litter, as well as to plants and animals dependent on those strata.  However, they are little studied and few efforts been made to address their threat.  Wisconsin is the pioneer (see below).


Ecosystem Engineers: Impacts on Soil, Plants, and Animals


Invasive alien earthworms cause enormous damage in forest environments. (I have seen no information about the damage they might cause in other natural systems.)  Earthworms can change soil chemistry, soil structure, and the quantity and quality of the litter layer on the soil surface. Changes include rapid incorporation of leaf litter into the soil, alteration of soil chemistry, changes in soil pH, mixing among soil layers, and increased soil disturbance. Such changes have been shown to harm native plant species – both herbaceous ones on the forest floor as well as the regeneration of woody vegetation, including trees.  See the review just published by Craven et al. 2016 and Hale and Nuzzo references below).


Craven et al. (2016) conducted a meta-analysis of 645 observations in earlier publications. They sought to measure the effects of introduced earthworms on plant diversity, cover of plant functional groups, and cover of native and non-native plants. Sites with a higher the diversity of invading earthworms – with associated variety in behaviors (see below) – had greater declines in plant diversity.  Higher earthworm biomass or density did not reduce plant diversity but did change plant community composition:  cover of sedges and grasses and non-native plant species significantly increased, and cover of native plant species (of all functional groups) tended to decrease. The increase in non-native plant cover in areas with higher earthworm biomass is thus an example of ‘invasional meltdown’ as propounded by Simberloff and Von Holle in 1999.


Craven et al. 2016 propose several direct and indirect mechanisms by which introduced worms might affect plant species. These include ingestion of seeds or seedlings, burying seeds, and alteration of water or nutrient availability, mycorrhizal associations, and soil structure. European and Asian plant species that co-evolved in the presence of earthworms could better tolerate earthworms’ presence.


Important Questions


Craven et al. 2016 note that the interaction of the invader-related factors with other site-related conditions such as deer browsing, fire history, forest management, and land-use history require further study to disentangle. Many other questions need to be answered, too.

Although Craven et al. (2016) do not specify the geographic range of the studies analyzed, I believe most were conducted in the northern and northeastern regions of the United States and some parts of Canada. It would be interesting to see if these studies’ findings differed from those carried out in Great Smoky Mountains National Park on the Tennessee-North Carolina border. The latter is an area where – unlike the northern states – earthworms were not wiped out by the most recent glaciation.  (See references by Bruce Snyder and Jeremy Craft, below.)


The finding that worm species diversity is associated with decreased plant species diversity seems to indicate that worms’ impacts might vary depending on the behavior of the worm in question – especially whether the worms remain on or near the soil surface and — if not — how deeply they burrow.  Are studies under way to clarify these differences?


Furthermore, do the impacts of European worms – the subjects of most of the studies carried out in Minnesota, New York, and Pennsylvania – differ substantially from the impacts of Asian earthworms? Or are any differences explained better by the species’ activity in the soil (e.g., depth of burrows) than their origins?


Impacts of earthworms on wildlife are less studied and perhaps less clear.  Several studies have focused on salamanders because of their known dependence on leaf litter. In a study of 10 sites in central New York and northeastern Pennsylvania, Maertz et al. 2009 found that salamander abundance declined exponentially with decreasing volume of leaf litter. They suggested that the salamander declines were a response to declines in the abundance of small arthropods, a stable resource.

A study by Ziemba et al. (2016) in Ohio involved Asian worms (genera Amynthas and Metaphire) rather than the European worms most often included in studies carried out in Minnesota, New York, and Pennsylvania.  These authors found a complex picture: earthworm abundance was negatively associated with juvenile and male salamander abundance, but had no relationship with female abundance.

Craft (2009) found that reduced leaf litter mass in invaded areas of Great Smoky Mountains National Park diminished habitat for both salamanders and salamander prey.

Others have studied millipedes – a largely unappreciated example of biological diversity in the Southern Appalachian Mountains – in Great Smoky Mountains National Park. Snyder and colleagues (2013) found that earthworms in the genus Amynthas altered soils by decreasing the depth of partially decomposed organic horizons and increasing soil aggregation. The result was a significant decrease in millipede abundance and species richness – probably as a result of competition for food.

Results from a study of earthworms’ effects on the Park’s food web by Anita Juen and Daniela Straube, begun in 2010, have not yet been published (pers. comm. from GRSM staff).

Even birds might be affected by worm invasions. One study in Wisconsin found that hermit thrush and ovenbird populations are lower in areas infested by worms. Possible reasons for the decline are that nests (on the ground) are more vulnerable to predation when located in the grasses promoted by worms, and a reduction in invertebrates fed to nestlings.


Expanding Risks

Several non-native earthworm species have been collected (so far) only from greenhouses or other places of indoor cultivation.  But can we be sure that they are not being spread to yards, parks, and other places halfway to natural systems through movement of plants and mulch?


Earthworms are extremely difficult to manage once established.

Are these challenges the reasons why few official efforts to control earthworm spread have been adopted? Or is it the animals’ public image – they are widely regarded as “good” critters that enrich the soil and facilitate composting. Or is it that trying to control worms will require enhanced regulation of the nursery and green waste industries?

worms1Amynthes photo; from Wisconsin DNR website

Wisconsin Is the Policy Pioneer

Wisconsin stands out for trying to address the issue! The state’s conservation and phytosanitary officials became alarmed when they detected Amynthas species in the University of Wisconsin Arboretum in 2013.  This is the site of regular plant sales,a likely pathway for spread.  Wisconsin now knows this genus of worms to be present in 21 counties, mainly along urban corridors.  They have not yet been found in the state’s forests.

Wisconsin is acting to protect its forests despite Amynthas worms having been present in the United States for over a century: Snyder, Callaham and Hendrix 2010 say several species of Amynthas were documented in Illinois and Mississippi by the 1890’s.  Some 15 species are recorded as established and widespread across the eastern United States (Reynolds and Wetzel 2004).


Wisconsin has classified the Amynthas genus as “restricted” – so their movement is now regulated. The risk of spread appears to be greatest through mulch produced from leaves collected in residential communities. The state held a workshop during which the regulated industry developed best management practices to address that risk. The Wisconsin Department of Natural Resources has posted a web page with information about identifying the worms and the BMPs. (Wisconsin DNR has also been a leader in tackling the firewood pathway.) The Wisconsin Department of Agriculture put the worm issue on the agenda of the National Plant Board in August 2016 and urged other states to take action.

The Wisconsin DNR webpage has

  • ID cards and other information to aid identification, g., photos of worms and the “coffee ground” soil they create;
  • a brochure with the state’s new “best management practices”
  • educate yourself and others to recognize jumping worms;
  • watch for jumping worms and signs of their presence;
  • ARRIVE CLEAN, LEAVE CLEAN – Clean soil and debris from vehicles, equipment and personal gear before moving to and from a work or recreational area;
  • only use, sell, plant, purchase or trade landscape and gardening materials and plants that appear to be free of jumping worms; and
  • only sell, purchase or trade compost that was heated to appropriate temperatures and duration following protocols that reduce pathogens.

What’s Up Where You Are?

What is your state doing to slow the spread of invasive earthworms?

  • Do nursery inspectors look for earthworms when approving plant shipments? Craven et al. 2016 findings re: higher impacts on plants as number of worm species rises demonstrate the importance of slowing spread of new species even into areas that already have some non-native earthworms.
  • Are professional associations of nurserymen and green waste recyclers educating their members about the damage caused by invasive earthworms and steps they can take to minimize worms’ spread to new areas?
  • Are organizations of anglers and gardeners in your state educating their members about the damage caused by invasive earthworms and steps they can take to minimize worms’ spread to new areas?
  • Are ecologists studying earthworm invasion impacts in other parts of the country? In non-forested ecosystems?
  • Are conservation organizations initiating or joining outreach efforts?
  • Can worm-education efforts be joined with h more robust public and private outreach focused on aquatic invaders, invasive plants, or firewood?



Bohlen, P.J., S. Scheu, C.M. Hale, M.A. McLean, S. Migge, P.M. Groffman, and D. Parkinson. 2004.  Non-native invasive earthworms as agents of change in northern temperate forests. Front Ecol Environ 2004; 2(8): 427–435

Craft, J.J. 2009. Effects of an invasive earthworm on plethodontid salamanders in Great Smoky Mountans National Park. Thesis prepared at Western Carolina University.

Craven, D., M.P. Thakur, E.K. Cameron, L.E. Frelich, R.B. Ejour, R.B. Blair, B. Blossey, J. Burtis, A. Choi, A. Davalos, T.J. Fahey, N.A. Fisichelli, K. Gibson, I.T. Handa, K. Hopfensperger, S.R. Loss, V. Nuzzo, J.C. Maerz, T. Sackett, B.C. Scharenbroch, S.M. Smith, M. Vellend, L.G. Umek, and N. Eisenhauer. 2016.The unseen invaders: intro earthworms as drivers of change in plant communities in No Am forests (a meta-analysis). Global Change Biology (2016), doi: 10.1111/gcb.13446 available here.

Hendrix, P.F. 2010. Spatial variability of an invasive earthworm (Amynthas agrestis) population and potential impacts on soil characteristics and millipedes in the Great Smoky Mountains National Park, USA. Biological Invasions DOI 10.1007/s10530-010-9826-4

Maertz, J.C., V. Nuzzo, B. Blossey.  2009. Declines in Woodland Salamander Abundance Associated with Non-Native Earthworm and Plant Invasions. Conservation Biology Volume 23, Issue 4 August 2009  Pages 975–981

Nuzzo, V.A., J.C. Maerz, B. Blossey. 2009. Earthworm Invasion as the Driving Force Behind Plant Invasion and Community Change in Northeastern North American Forests. Conservation Biology Volume 23, Number 4, 966-974.

Simberloff, D.  and Von Holle, B. 1999. Positive interactions of nonindigenous species: invasional meltdown? Biological invasions 1, 21-32

Snyder, B.A., M.A. Callaham, C.N. Lowe, P.F. Hendrix. 2013. Earthworm invasion in North America: food resource competition affects native millipede survival and invasive earthworm reproduction. Soil Biology and Biochemistry 57, 212-216

Ziemba JL, Hickerson C-AM, Anthony CD. 2016. Invasive Asian Earthworms Negatively Impact Keystone Terrestrial Salamanders. PLoS ONE 11(5): e0151591. doi:10.1371/journal.pone.0151591


See also:

Global picture:

Great Lakes Wormwatch website:  

Illinois Natural History Survey webpage:

Wisconsin  DNR

Information on western Canada:

Native Earthworms of British Columbia Forests:


Posted by Faith Campbell