October 2019 – Center for Invasive Species Prevention

New Study: Non-Native Pests Threaten 2/5ths of 48 States’ Forest Biomass

redbay in Georgia killed by laurel wilt
photo by Scott Cameron

In August I posted a blog summarizing information on pest introductions and impacts gleaned over my nearly 30 years of engagement. Already, I need to post an update, with an alarming estimate of introduced pests’ impacts across the continent.

Fei et al. 2019 (see the full citation is at the end of this blog) estimate that the 15 most damaging introduced species threaten 41.1% of the total live forest biomass in the 48 conterminous states.

In fact, this might be an underestimate of the pests’ impacts on biomass loss. Fei et al. (2019) note several limitations in their data that might result in such an underestimate. These include:

1) Mortality rates – and impacts – may increase over several decades following the initial invasion.

2) For pests already established throughout nearly all their potential ranges, pest-induced biomass loss could be substantially underestimated because most of their hosts died long ago, before the FIA data began to be collected. Consequently, the actual loss of these tree species from the forest is much greater than has been measured by the study’s methods.

3) Mortality rates vary among species and regions, which might introduce errors. They cite European gypsy moth, in which relatively small areas of heightened mortality due to repeated defoliations are swamped by lower mortality rates across the chosen measurement area.

4) They considered only tree mortality, not crown or root dieback or reductions in tree growth.

5) They did not estimate carbon release to the forest floor as a result of defoliation.

6) Pest-related mortality rates may be underestimated due to salvage – although the authors did not observe evidence of substantial salvage efforts for most of these pests.

7) The data did not include losses from urban tree mortality.

Fei et al. estimate that more than 450 pests are established in the 48 conterminous states. This study excluded pests attacking palms; trees on U.S. Pacific and Caribbean islands; and pests native to portions of North America that are causing severe damage in naïve hosts – e.g., goldspotted oak borer. I did include the latter groups in my slightly larger estimate laid out in my August blog.

Fei et al. base their analysis on 83 of the introduced pest species considered to cause substantial effects on tree health and productivity and sometimes extensive tree mortality. (In my August blog, I described findings by another study by Guo et al (2019) that counted 91 species in that category.)

Fei et al. build on studies by a group of USDA Forest Service (USFS) scientists that I described in an earlier blog.

This team found that, nation-wide, non-native forest pests are causing an approximate 5% increase in total annual mortality by tree volume. They based their studies on analysis of 92,978 long-term plots maintained by the USDA Forest Inventory and Analysis program.

As noted above, the article cannot capture the full range of mortality in species affected by pests introduced decades ago. Chestnut blight, white pine blister rust, Port-Orford-Cedar root disease, beech bark disease, butternut canker, dogwood anthracnose, and European gypsy moths had all killed millions of trees before the USFS forest inventory plots were established. Fei et al. do form a solid basis for measuring some of the current impacts and projecting future ones.

The focus of the new article is on the amount of carbon being transferred from live biomass to dead organic matter as a result of the increased mortality caused by the 15 species with the highest impacts. This is arguably a more quantifiable measure of pests’ impacts than others’ approaches. Here, I focus more narrowly on the documentation of exacerbated mortality as measured by the loss of biomass. Added together, these 15 species have caused an additional (i.e., above background levels) tree mortality rate of 5.53 TgC per year [defined as terragrams of carbon]. This estimate of annual conversion of live biomass to dead wood is similar in magnitude to that attributed to fire (5.4 to 14.2 TgC per year) (Fei et al. 2019). Yet the fire threat gets much more attention – for both prevention and management.

It is important to remember that conversion of living biomass to dead wood does not result in an immediate release of carbon to the atmosphere. Atmospheric releases take place through decomposition which is both gradual and takes place at varying rates. Some of the carbon will remain in the soil. And, over time, some of the carbon storage capacity will be restored by compensatory growth in unaffected trees and the recruitment of new regeneration – although this faster growth is delayed by as much as two or more decades after pest invasions begin (Fei et al. 2019).

American elm being killed by “Dutch” elm disease
photo by Cheryl Kaiser, University of Kentucky; bugwood.org

The 15 species of introduced pests used in this analysis are laurel wilt disease, chestnut blight, butternut canker, dogwood anthracnose, emerald ash borer (EAB), Dutch elm disease, red pine scale, beech bark disease, hemlock woolly adelgid, balsam woolly adelgid, European gypsy moth, white pine blister rust, green spruce aphid, sudden oak death, and Port-Orford cedar root disease. Of these, the highest elevation in biomass loss – as measured by FIA plot data – was caused by EAB, Dutch elm disease, beech bark disease, and hemlock woolly adelgid. We know that elms and beech, at least, began dying decades before the FIA data began to be collected. So the reported mortality rates are an underestimate. This is especially true because beech mortality is highest in the first decade after invasion by beech bark disease.

Annual levels of biomass loss are virtually certain to increase. First, pests will spread to new host ranges and infestations in already-invaded ranges will intensify. As a result, substantial amounts of the hosts’ biomass are at risk of exacerbated mortality. As I noted at the top of the blog, the total amount of host biomass at risk from these 15 species is estimated to be 5,197 TgC – or 41.1% of the total live forest biomass in the 48 conterminous states. Further exacerbating future losses is the likelihood that additional pests will be introduced. I would add that pests not included in this analysis – e.g., polyphagous and Kuroshio shot hole borers and possibly the spotted lanternfly – are also likely to contribute to losses of live forest biomass.

Fei et al. (2019) did not attempt to determine the economic value of this biomass loss or to address other types of losses to ecosystem services.

Remember that a separate set of studies reported by Potter et al. (2019) (the CAPTURE project) also relied on data from the FIA plots to evaluate the impact of introduced pests. These studies focused on identifying the host species at greatest risk rather than highest-impact pests or biomass loss. I find it reassuring that the Fei and Potter studies – using different approaches – resulted in very similar species rankings. See my discussion of the Potter studies here.

Together, the teams led by Potter and Fei set clear priorities for addressing the threats from non-native pests. What we need now is action! See my recommendations in my recent “solutions” blog.

U.S. Capitol – inform your representatives that you want action to protect trees!

SOURCES

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. 2019. Biomass losses resulting from insect and disease invasions in United States forests

Potter, K.M., M.E. Escanferla, R.M. Jetton, and G. Man. 2019a. Important Insect and Disease Threats to United States Tree Species and Geographic Patterns of Their Potential Impacts. Forests. 2019 10 304.

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

Congressional Funding for Key USDA Programs (Assuming it Ever Passes)

Fiscal Year 2020 began on 1 October. Congress has not yet passed funding bills (appropriations) for the full year. Agencies are operating now on a short-term continuing resolution which expires on November 21^st. Meanwhile, representatives of the House and Senate will meet to reconcile the differences between the two bodies’ appropriations bills in hope that a year-long bill can be finalized by that time.

(Disagreement between President Trump and the Congress about funding for the border wall might prevent adoption of full-year appropriations bills and lead to another government shutdown.)

I report here the differences between House and Senate bills funding the USDA APHIS and Forest Service programs that are vital to addressing non-native forest pests.

APHIS

Over the years, I have complained that inadequate funding is a major cause of shortfalls in APHIS’ efforts to detect new invasions by tree-killing pests and to respond to those invasions in effective ways.

While funding levels are still too low, at least Congress is holding funding steady for APHIS for Fiscal Year 2020 (which began three weeks ago, on October 1^st). Both House and Senate bills maintain funding for two crucial programs at the FY19 levels:

“tree and wood pests” program – $60 million (this matches the FY19 level; it is $4 million above the funding provided in previous years); and
“Pest Detection” – $27.4 million.

The House provided slightly higher funding than the Senate for two other programs:

“specialty crops” (including sudden oak death) – $186.5 million in the House bill, $186 million in the Senate bill; and
“methods development” – $21.686 million in the House bill, $20.686 million in the Senate bill.

In the report accompanying its bill, the House called for two additional funding options to address emergencies. First, it set up a contingency fund of $470,000 to control outbreaks of insects, plant diseases, animal diseases and pest animals and birds to meet emergency conditions. Second, the report repeated language from past reports that authorizes the Secretary to take “such sums as may be deemed necessary” from other USDA programs in order to counter pest emergencies threatening any segment of U.S. agricultural production.

The Senate report addressed several high-profile tree pests. It called for complete eradication of the Asian longhorned beetle; mandated that APHIS report on its efforts to eradicate ALB and spotted lanternfly and to minimize spread of the polyphagous and Kuroshio shot hole borers; and to assist states that have recently detected the emerald ash borer. (This language is helpful, but it falls short of what I previously advocated – that APHIS continue efforts to prevent EAB spread, especially through movement of firewood.) The Senate report also urged APHIS to maintain FY19 level funding addressing the sudden oak death pathogen, in particular to improve understanding of the two strains of the pathogen present in Oregon’s forests link to blog to inform control and management techniques in wildlands. (Actually, management in wildlands falls largely to the Forest Service, with scientific input from both Agriculture Research Service and – to some extent – the NORS-DUC research nursery managed by APHIS.)

For a lengthier justification of my funding requests, see my earlier blog on APHIS funding

Funding for Resistance Breeding through NIFA

As I pointed out in my blog in May, the 2018 Farm Bill included an amendment (Section 8708) that establishes a new priority for a grant program managed by the National Institute of Food and Agriculture. The amendment would support restoration to the forest of native tree species that have suffered severe levels of mortality caused by non-native insects, plant pathogens, or other pests. The amendment affects the Competitive Forestry, Natural Resources, and Environmental Grants Program under Section 1232(c)(2) of the Food, Agriculture, Conservation, and Trade Act of 1990 (16 U.S.C. 582A-8, as amended. However, this program has not been funded for more than a decade. In my blog, I asked you to support a $10 million appropriation to NIFA to fund a competitive grant program for such forests restoration.

Neither the House nor the Senate provided funding for this program.

USFS

The House bill provides $277,155,000 for USFS Research and Development – nearly $20 million more than the Senate bill ($257,640,000). The House report links this increase to the recognition of the increasing risk to urban, rural, and wildland forests from insect and disease outbreaks and invasive plant infestations. The report calls on the Forest Service to develop a research program that addresses several priorities critical to forest health, including preventing the spread of disease and invasive species.

USFS engagement on pest issues with other federal agencies and state, local government, and private land managers is carried out through the Forest Health Management program under the State and Private Forestry division. The Senate bill and report are confusing because they have separated out salaries and other expenses. As a result, I can’t compare its figures to those in previous years or to those from the House. Partly for this reason, I urge you to support the House bill, which is quite clear in appropriating $103,736,000 for Forest Health Management, which is a programmatic increase of $19 million above the FY19 level and $29,919,000 above the budget request. I am encouraged by the House’ report, which encourages the Forest Service to address high priority invasive species, pests, and diseases, including the emerald ash borer and bark beetle infestations.

For longer explanations, see my earlier blog on USFS funding.

These bills show an increasing awareness of forest pest issues in key funding committees in both the House and Senate. Let’s reinforce this message – and spread it to the rest of Congress. Please contact your senators and representative and ask them to support these funding levels.

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.

APHIS’ EIS on Importing Plant Pests: What it reveals about APHIS

APHIS has published a final Environmental Impact Statement (FEIS) as one of the final steps in modifying its regulations governing conditions for issuing permits for importation, interstate movement, and intrastate movement of plant pests – including biocontrol agents. Access it here.

The original proposal to modify the regulatory system was published in March 2017.

I find the rationale for modifying the regulations to be compelling: the current regulations:

date from 2001;
do not adequately reflect changes in APHIS’ mandate enacted by the Plant Protection Act; and
do not focus agency efforts on the permit applications that pose the highest risk.

The FEIS presents two alteratives: the “preferred alternative” and the “comprehensive risk mitigation program.” APHIS settles for the less protective actions that expose natural resources, especially, to risk from non-indigenous species

1) The FEIS reiterates — without discussion or rationale — APHIS’ acceptance of the vague word “acceptable” to describe the level of protection the agency strives to achieve (see pp. 2, 22, 45, 106 of the FEIS). The FEIS does not attempt to quantify the differences in the levels of protection provided by the two alternatives.

2) APHIS advocates a policy alternative that does not require post-release monitoring of biocontrol agents. The FEIS justifies adoption of this alternative despite putting a welcome emphasis on the importance of just such efforts to determine the actual impacts of biocontrol organisms on both target and non-target species (p. 67). On page 70, the FEIS notes that the paucity of documented examples of adverse effects on non-target species “may be the result of insufficient monitoring after release …” It goes on to note that “very few introductions included a careful evaluation of nontarget impacts …” The FEIS notes the paucity of funding for this research and – sometimes – the lack of authority to require such monitoring.

In the case of APHIS, I see no legal impediment to the agency requiring biocontrol permit applicants to carry out post-release monitoring.

Indeed, if APHIS chose the “comprehensive risk mitigation program”, the agency would require enhanced post-release monitoring. The goal would be to document “the extent of establishment, spread, and limit to expected hosts” of the introduced biocontrol organism (p. 43). Nevertheless, the FEIS accepts the “preferred alternative”, which does not require such monitoring. The reason given for this choice is that the comprehensive program would require too many resources. I note below that we can overcome this barrier by lobbying for increased appropriations and higher staffing levels.

3) APHIS dismisses risks associated with high levels of uncertainty. In justifying the less rigorous “preferred alternative”, the FEIS refers 20 times to the persistence of uncertainties in analyses of the potential impact of importation, interstate transport, or release of non-indigenous organisms. FEIS also says that given these inevitable uncertainties, APHIS should regulate most organisms “conservatively” – defined in the FEIS as “based on what is known” ( p. 74). Of course, APHIS long ago rejected the precautionary approach – which is a truly conservative approach.

4) The FEIS accepts APHIS’ current practice of evaluating risks only in the geographic area of approved introduction – despite conceding repeatedly that introduced organisms often spread beyond the original introduction site. It is true that the geographic area evaluated includes all continental states (whether Alaska is included is unclear). However, there is no discussion of the likelihood that organisms introduced to the continental states will be transported to U.S. islands in the Caribbean or Pacific – through either authorized or unauthorized mechanisms.

The FEIS Asserts Principles that APHIS Sometimes Fails to Live Up To

As I note above, the FEIS makes numerous references to the reality that an organism released into the environment might establish and spread to its maximum geographic range based upon host distribution, climate and other range-limiting factors. According to the FEIS, APHIS’ decisions about issuing a permit allowing release of non-native organisms must reflect that likelihood. For example:

“In principle, therefore, release of the biological control organism, at even one site, should be considered equivalent to release over the entire area in which potential hosts occur, and in which the climate is suitable for reproduction and survival.” (P. 67)

However, APHIS’ recent decision to allow introduction of a thrips (Pseudophilothrips ichini) in Florida to control Brazilian pepper (Schinus terebinthifolius) does not reflect this principle.

The environmental assessment (EA) that analyzed this proposed release reported that the thrips would both encounter a suitable climate in Hawai`i (pp. 11 and 19) and feed on two native Hawaiian species – Rhus sandwicensis and Dodonaea viscosa. The EA described the feeding damage on these non-target species as negligible and noted that P. ichini sustained only one generation on these non-target species (p. 27). Furthermore, the EA noted (p. 29) that the action being reviewed did not include release of P. ichini in Hawai`i. However, the EA did not discuss the frequency with which insects established on the Continent are transported – without authorization – to the Islands. In my view, if introduced to Hawai`i – by authorized or non-authorized transport – the thrips is likely to thrive because several good hosts are widespread. By feeding on these good hosts, the thrips could enjoy a “food subsidy” that would allow it to put constant pressure on the vulnerable Hawaiian species. [You can obtain a copy of my comments on the draft EA by contacting me via the “contact us” button, or by visiting the Federal Register site at the link given above.]

*Rhus sandwichensis*; photo by Forest & Kim Starr

The FEIS fails to address an important risk

*Amynthes agrestis* one of the invasive earthworms established in the U.S.
photo by National Park Service

The FEIS doesn’t recognize – or even mention – the impact of non-native earthworms on native ecosystems and native plants! The only discussion of risks associated with earthworms is on p. 26, where the sole concern is the risk that soil-dwelling worms could vector crop and livestock diseases present in the soil in the country of origin.

Yet the FEIS notes that APHIS’ mandate – and the purpose of the permit system – is to protect not only American agriculture but also our natural resources. I have blogged about the severe impact earthworms have on native flora here. Why did the authors of the EIS ignore the large and growing scientific literature on this issue?

Good Points in the FEIS

1) The FEIS notes the concern that biocontrol agents will attack non-target species, with results that “may not be easily reversed.” (pp. 66, 74) The FEIS cites several examples, including Cactoblastis cactorum on North American prickly pear (Opuntia) cacti – see my blogs here and the potential impact of Rhinocyllus conicus on native thistles. The FEIS notes that these particular biocontrol agents would not be approved for release under current policies. However, the FEIS also reports that a biocontrol agent released on thistles in Virginia in 1997 – that is, under criteria currently in use – had spread across the continent to California and Nevada within two years! While the FEIS reports the spread as by natural means, I wonder if some enterprising farmers might have taken infected plants/inoculum without authority.

2) The FEIS notes several indirect concerns arising from the environmental release of biocontrol organisms, including contamination, adaptation, interference, competition, and hybridization. When biocontrol organisms establish but don’t reduce populations of the target weed, they can provide a “food subsidy” to some organisms, thus disrupting the ecological balance. The example given is two gall flies (Urophora affinis and U. quadrifasciata), which failed to control knapweed and led to population explosions of deer mice – with repercussions for competition among small mammals, possibly reduced recruitment of native plant populations, and increased incidence of a serious disease of humans, Sin Nombre hantavirus. (Recall my similar concern re: a thrips if it reaches Hawai`i, above.)

3) The FEIS cites scientific publications demonstrating the low rate of success of biological control in controlling invasive plants or arthropods. One such discussion – on p. 53 – notes that an estimated 65% of introduced arthropods successfully establish for the purposes of weed control, 25 – 34% of those introduced to control arthropods. These figures are repeated on p. 59. However, on pp. 67-68, even lower success rates are presented, based on worldwide estimates. This is not a good record, given the risks involved. Furthermore, given my focus on non-native insects, I am concerned by the statement in the FEIS that the scientific study of potential risks of biocontrol targetting arthropods control is not thorough. (pp. 68-69)

The Center for Invasive Species Prevention hopes that other stakeholders will work with us to persuade APHIS to work toward adoption of the more protective approach described in the “comprehensive risk mitigation program”. A key factor will be lobbying the Administration and Congress to increase appropriations and personnel ceilings so that APHIS has the resources necessary to carry out the more protective program.