invasive species policy – Page 4 – Center for Invasive Species Prevention

Sobering News: Invasive Grasses, Trees, and Killer Pests in Hawai`i

At CISP, our hearts go out to all those affected by the terrible August fires on Maui. May the departed rest in peace. May the living find comfort and all that is needed for recovery.

Fire and Invasive Grasses

A fire in non-native grasses on Maui in 2009; photo by Forrest and Kim Starr

Major U.S. and international media continue to detail the fires’ devastation, especially in Lahaina. As time has passed, more news has highlighted the role that the widespread presence of introduced, fire-prone grasses played in the rapid growth and spread of Maui’s fires.

For example, The Washington Post devoted seven paragraphs in one story to the issue of grasses. The story quotes several experts: Alison Nugent, an associate atmospheric scientist at the University of Hawaii’s Water Resources Research Center; Jeff Masters, a meteorologist for Yale Climate Connections; and Clay Trauernicht, a fire researcher at the University of Hawaii.

These and others have been widely quoted in the many recent articles. I am glad that they – and the media – are making clear that climate change is not the sole factor causing damaging wildfires. It is clear that Maui’s recent weather patterns – including the high-velocity winds and drought – have been within the range of normal climate patterns. Fluctuations in the Pacific’s weather have also been normal, especially under the influence of the current El Niño.

The dangers caused by Hawai’i’s fire-prone grasses are also clear – and have been for years. Experts have identified policy weaknesses at the county and state level. Also, they have specified changes to land management that could better prevent or mitigate wildfires. There has been far too little action.

On the other hand, there are hopeful signs.

endangered ‘akikiki photo by Carter Atkinson, USGS

The Hawai’i Wildfire Management Organization, a nonprofit, is educating and engaging communities state-wide. Elizabeth Pickett, a Co-Executive Director, presented an overview of wildfire at the Hawai’i Invasive Species Awareness Month in February 2023. The Big Island Invasive Species Committee has successfully eradicated two species of pampas grass on Hawai’i Island – after 13 years’ work. A native species has been planted where pampas formerly grew.

Another Post article reported on efforts by staff and fire departments to protect the Maui Bird Conservation Center, which houses critically endangered Hawaiian birds found nowhere else on Earth, including some currently extinct in the wild. As I have blogged previously, the palila, kiwikiu, ‘akikiki, ‘alalā [Hawaiian crow; extinct in the wild] and other birds are dying from avian malaria, carried by nonnative mosquitoes. The Center on Maui and another on the Big Island are run by the San Diego Zoo Wildlife Alliance. Conservationists have completed field trials of a proposed mosquito suppression process for Maui and are seeking public comments for a similar program on Kaua’i. These programs represent groundbreaking and long-awaited progress on countering a principal threat to the survival of Hawai`i’s unique avifauna. Loss of the Center and its birds would have devastated post-suppression efforts to rebuild and restore bird populations in the wild.

The Post carried a second story about the effort to protect Hawai`i’s endangered birds – a full page of print, even longer – with many photos, on the web. The article mentions the “Birds, Not Mosquitoes” program and varying views about it. I rejoice that the dire situation for the Islands’ biodiversity is getting attention in the Nation’s capital. Again, see my earlier blog.

Plant Invasions in Hawaiian Forests

A team of scientists from the USDA Forest Service and Natural Resources Conservation Service, plus the Hawaii Division of Forestry and Wildlife, has carried out a new assessment of the extent of invasive plant species in forests on the Hawaiian Islands (Potter et al. 2023; full citation at end of blog).

The results of their analysis are – in their words – “sobering”. They portend “a more dire future for Hawai`i`s native forests.”

First, regarding the recent fires, Potter et al. found significantly higher cover by invasive grasses on Forest and Inventory Analysis (FIA) plots on Hawai‘i and Maui than on O‘ahu, Kaua‘i, and Lana‘i. Grass invasions were particularly high on the eastern coast of Maui – near Lahaina. Even so, the authors say their study’s methods resulted in a gross underestimate of areas invaded by fire-prone grasses. That is, most of Hawai’i’s xerophytic dry forests were converted to grasslands before the FIA program began. Therefore these grasslands are not included in FIA surveys.

*Psidium cattleyanum*; photo by Forrest and Kim Starr

The extent of current invasions in wetter forests is already significant – but trends point to an even more worrying future.

Naturalized non-native plant taxa constitute half of the Hawaiian flora.
56% of Hawaii’s 553,000 ha of forest land contained non-native tree species; about 39% of these forest lands are dominated by non-native tree species. Invasive plant species of particular concern were found in the understory of 27% of surveyed forest plots.
Across all islands, six of the ten most abundant species are non-native: Psidium cattleyanum, Schinus terebinthifolius, Leucaena leucocepahala, Ardisia elliptica, Psidium guajava, and Acacia confusa.
While less than one-third (29%) of large trees across the Islands are non-native, this proportion increases to about two-thirds of saplings (63%) and seedlings (66%). Potter et al. focus on the likelihood that plant succession will result in transformation of these forests’ canopies from native tree species to non-native species.
75% of forests in lower-elevation areas of all islands are already dominated by non-native tree species. “Only” 31% of higher-elevation forests are so dominated. These montane forests have been viewed as refugia for native species, but all are invaded to some extent – and likely to become more degraded.
Potter et al. say the high elevation forests might be more resistant to domination by non-natives. Such a result would be counter to well-documented experience, though. Even the authors report that the montane rainforests and mesophytic forests of O‘ahu and Kaua‘i are heavily invaded by non-native tree species. Such species constitute 86% or more of large trees, saplings, and seedlings in mesophytic forests; 45% of large trees and 66% of seedlings in their montane rainforests.
The most abundant tree species in Hawai`i is the invasive species Psidium cattleyanum (strawberry guava). It was recorded on 88, or37%, of 238 FIA plots. There are nearly twice as many P. cattleyanum saplings as Hawai`i’s most widespread native species, ‘ohi’a lehua (Metrosideros polymorpha).
Widescale replacement of native trees by non-native species is likely. Several factors favor these changes: 1) tree disease – rapid ‘ohi’a death has had drastic impacts on ‘ohi’a populations on several islands; 2) invasions by forbs and grasses; 3) soil damage and other disturbances caused by invasive ungulates; and 4) climate change. If succession conforms to these trends, non-native tree species could eventually constitute 75% or more of the forest tree stems and basal area on all islands and across forest types and elevations.

Loss of Hawai’i’s native tree species would be disastrous for biodiversity at the global level. More than 95% of native Hawaiian tree species are endemic, occurring nowhere else in the world.

The authors analyzed plant presence data from 238 FIA plots. Plots spanned the state’s various climates, soils, elevations, gradients, ownership, and management. However, access issues precluded inclusion of forests from several islands: Moloka‘i, Kaho’olawe, and Ni‘ihau. I know that Moloka‘i, at least, has a protected forest reserve (a Nature Conservancy property) at the island’s highest elevations.

Protecting Native Trees

Federal, state, and private landowners have carried out numerous actions to protect native forests. These efforts might be having some success. For example, forests on public lands, in conservation reserves, or in areas fenced to exclude ungulates were less impacted by non-native plants than unfenced plots, on average. However, the authors could not determine how much of this difference was the result of management or because protections were established in forests with the lowest presence of IAS species. Fencing did not prevent invasions by forbs and grasses – possibly because they are so widespread that seed sources are everywhere.

Hawaii’s two National parks (Hawai`i Volcanoes and Haleakala) have made major efforts to control invasive plants. Hawai`i Volcanoes, on the Big Island, began its efforts in the 1980s; Haleakala (on Maui) more recently. This might be one explanation for the fact that a smaller proportion of the forests on these two islands have been invaded. These efforts have not fully protected the parks, however. Low elevation native rainforests now have a high presence of non-native shrubs. Such forests on Hawai`i Island also have significant invasions by non-native woody vines, forbs and grasses.

More discouraging, intensive efforts have not returned lowland wet forest stands to a native-dominated state. Native tree species are not regenerating—even where there is plentiful seed from native canopy trees and managers have repeatedly removed competing non-native understory plants.

Potter et al. conclude that other approaches will be needed. They suggest deliberate planting of native and non-invasive non-native species or creation of small artificial gaps that might facilitate recovery of native tree species. In montane forests on Hawai`i and Maui, where native tree seedlings account for more than 70% of all tree seedlings, they propose enhancing early detection/rapid response efforts targetting invasive forbs. This would include both National parks.Certainly Haleakala National Park has this priority in mind. It launched a serious effort to try to eradicate Miconia calvescens when this tree first was detected.

Lloyd Loope, much-mourned scientist with US Geological Survey, attacking *Miconia* on Maui

Potter et al. note the challenge of managing remnant xerophytic dry forests, where natural regeneration of native plants has been strongly limited by invasive grasses; loss of native pollinators and seed dispersers; and the increasing frequency and intensity of droughts. They note that expanded management efforts must be implemented for decades, or longer, to be successful.

Native Trees at Risk to Nonnative Insects

Beyond the scope of the Potter et al. study is the fact that at least two dry forest endemic trees have faced their own threats from non-native insects.

The Erythrina gall wasp, Quadrastichus erythrinae, appeared in Hawai`i in 2005; it originates in east Africa. It attacks the endemic tree, wiliwili, Erythrina sandwicensis. I believe a biocontrol agent, Eurytoma erythrinae, first released in 2008, has effectively protected the wiliwili tree, lessening this threat.

The Myoporum thrips, Klambothrips myopori, from Tasmania, was detected on the Big Island in 2009. It threatens a second native tree. Naio, (Myoporum sandwicense), grows in dry forests, lowlands, upland shrublands, and mesic and wet forest habitats from sea level to 3000 m. The loss of this species would be both a signifcant loss of native biodiversity and a structural loss to native forest habitats. The thrips continues to spread; a decade after the first detection, it was found on the leeward (dry) side of Hawai`i Island with rising levels of infestation and tree dieback.

*Rhus sandwicensis* on Maui; photo by Forrest and Kim Starr

Two native shrubs, Hawaiian sumac Rhus sandwicensis and Dodonea viscosa, might be at risk from a biocontrol agent in the future. APHIS has approved a biocontrol for the highly invasive Brazilian pepper, Schinus terebinthifolia. Brazilian pepper is the second-most abundant non-native tree species in the State. It was found on 28 of 238 (12%) FIA plots. However, the APHIS-approved biocontrol agent is a thrips—Pseudophilothrips ichini. It is known to attack both of these two native Hawaiian shrubs. The APHIS approval allowed release of the thrips only on the mainland US. However, many insects have been introduced unintentionally from the mainland to Hawai`i. Furthermore, Hawaiian authorities were reported to be considering deliberate introduction of P. ichini to control peppertree on the Islands.

In Conclusion

In conclusion, Potter et al. found that most Hawaiian forests are now hybrid communities of native and non-native species; indeed, a large fraction are novel forests dominated by non-native trees. Business-as-usual management will probably mean that the hybrid forests – and probably those in which the canopy is currently dominated by native species—will follow successional trajectories to novel, non-native- dominated woodlands. This likelihood results in a more dire future for native plants in Hawaiian forests than has been previously described.

Potter at al. hope that their findings can guide research and conservation on other islands, especially those in the Pacific. However, Pacific islands already have the most naturalized species globally for their size—despite what was originally considered their protective geographic isolation.

SOURCE

Potter, K.M., C. Giardina, R.F. Hughes, S. Cordell, O. Kuegler, A. Koch, E. Yuen. 2023. How invaded are Hawaiian forests? Non-native understory tree dominance signals potential canopy replacement. Landsc Ecol https://doi.org/10.1007/s10980-023-01662-6

Posted by Faith Campbell

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

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

www.fadingforests.org

FY24 Appropriations for Key Programs: current status

In March I asked your help in asking Congress to fund USDA programs that protect forests from non-native insects and pathogens. The Congress has now taken major steps to specify funding for Fiscal Year 2024 – which begins on 1 October. Both the House and Senate Appropriations committees have adopted their bills. They differ substantially. When Congress returns from its August recess in September, it will face many difficulties in negotiating the final spending levels – not just the different funding levels but also attached “riders” dealing with social and political issues, most of which have nothing to do with invasive species. [Some of the riders to seek to restrict application of the Endangered Species Act to several species, e.g., sage grouse and grey wolf.]

USDA APHIS

As you know, USDA’s Animal and Plant Health Inspection Service (APHIS) is responsible for preventing introduction of pests that harm agriculture, including forests; and for immediate efforts to eradicate or contain those pests that do enter. While most port inspections are carried out by the Department of Homeland Security Bureau of Customs and Border Protection, APHIS sets the policy guidance. APHIS also inspects imports of living plants. In the table below, I provide information on funding for key APHIS programs in FY23, the Administration’s request for FY24, the funding level the Center for Invasive Species thought necessary, and the House and Senate funding levels.

The earlier blog link has additional information: the FY22 funding levels and a fairly long justification for funding these APHIS programs. I never posted a blog discussing USFS funding due to my trip to Europe.

Appropriations for APHIS programs (in $ millions)

Program	FY 2023	FY 2024 Pres.’ request	CISP ask	House bill	Senate bill
Tree & Wood Pest	$63	$64	$65	$55.6	$62.6
Specialty Crops	$216	$222	$222	$224.5	$217.9
Pest Detection	$29	$30	$30	?	?
Methods Development	$23	$23	$25	?	$21.8
Emerg. Preparedness	$44	$45.2	NA	$44.6	$48
Contingency fund	$514	$543		$514	$514

I have not seen a report from the House Committee so I don’t know whether that body prioritized any invasive species issues.

The Senate report included this statement re: Sudden oak death

“The European strain 1 [EU1] and the North American strain 1 [NA1] of the sudden oak death pathogen are major threats to western Douglas-fir/tanoak forests, resulting in quarantine restrictions that threaten U.S. forests and export markets for log shipments and lily bulbs. The Committee recommendation includes no less than the fiscal year 2023 funding level to improve understanding of EU1 and NA1 strains of the sudden oak death pathogen and treatment methods to inform control and management techniques in wildlands.”

Appropriations for USFS programs (in $ millions)

Program	FY 2023	FY 2024 Pres.’ request	CISP ask	House bill	Senate bill
Forest Health Protection
Federal Lands			$32		$17
Coop Lands			$51		$33
Research & Development		$349.1	$349.1	$275	$307.3
Forest Inventory		$30.2	$30.2	$32.2	$32.2
Work on 10 invasive spp	$.5	$4.4	$8.5*	0	0

* CISP ask was intended as first step to increasing funding for invasive species to 5% of R&D funds. See the March blog for an explanation.

SOD-killed tanoaks in southern Oregon; Oregon Department of Agriculture photo

Senate report = Sudden Oak Death. “Since 2001, USFS has been treating SOD infestations on public lands in Oregon and California, in cooperation with Bureau of Land Managemebt. The Committee expects USFS continue these efforts; it provides $3M for SOD treatments and partnerships with States and private landowners.”

Urban & Community Forestry.—”The bill provides $40 M for urban and community forestry. The Committee recognizes the critical need to restore and improve urban forests due to dominance of exotic invasive woody species. USFS should prioritize regional multi-organizational collaborations to support conservation efforts that help trees adapt to and offset climate change, which model best practices for effective urban and community forestry grants. The Committee also expects the program to prioritize tree-planting in socially disadvantaged and historically underserved communities with low canopy coverage, including Tribal communities.”

Summary of Justifications: The Costs of Introduced Pests

Introduced pests threaten many forest products and ecosystem services benefitting all Americans. Already, the 15 most damaging non-native pests threaten at least 41% of forest biomass in the “lower 48” states. In total, these 15 species have caused an additional annual conversion of live biomass to dead wood at a rate similar in magnitude to that attributed to fire (5.53 TgC per year for pests versus 5.4 to 14.2 TgC per year for fire). Fei et al.; full citation at end of blog.

These pests also impose significant costs that are borne principally by municipal governments and homeowners. As more pests have been accidentally introduced over time, these costs have risen.

Pathways of Introduction

The many tree-killing wood-boring pests arrive in inadequately treated crates, pallets, and other forms of packaging made of wood. The March blog presents 2023 data on import volumes and the findings of Haack et al. 2022. The point is, ISPM#15 has fallen short. [See blogs under “wood packaging” category on this site]

APHIS’ Tree and Wood Pests account supports eradication and control efforts targeting principally the Asian longhorned beetle and spongy (= gypsy) moth. Eradicating the ALB normally receives about two-thirds of the funds. The programs in Massachusetts, New York, Ohio, and South Carolina must continue until eradication succeeds. The emerald ash borer continues to spread since APHIS dropped regulations attempting to halt this. EAB was detected in Oregon in 2022; and on Colorado’s western slope in 2023.

Other pests—especially plant diseases like sudden oak death and sap sucking insects like hemlock woolly adelgid—come on imported plants. I noted that no studies have examined the risk of pests arriving on the ~5 billion plants we Americans now import annually (see March blog). The information gap is particularly alarming regarding pathogens. Evidence of failures:

the recent detection of two strains of Phytopthora ramorum that were formerly limited to Europe in forests of Oregon and California;
introduction of rapid ‘Ōhi‘a death in Hawai`i;
and the apparent introduction of the causal agent(s) of beech leaf disease.

APHIS manages damaging pests introduced on imported plants or other items through its Specialty Crops program. The principal example is its efforts to prevent spread of the SOD pathogen through the interstate trade in nursery plants. I am pleased that the Senate report calls on APHIS to focus on that pathogen’s growing genetic diversity.

Beech leaf disease has spread >700 miles since its first detection just 11 years ago

The Administration did not persuade the Congress to fund a $1 million emergency fund for APHIS – although they did fund both “emergency” and “contingency” programs. I am not certain about the difference.

Furthermore, both chambers of Congress included in their legislation – not in the report – language instructing the Secretary of Agriculture to use his authority to obtain emergency funds from other USDA agencies to address animal or plant health emergencies:

“Provided further, That in addition, in emergencies which threaten any segment of the agricultural production industry of the United States, the Secretary may transfer from other appropriations or funds available to the agencies or corporations of the Department such sums as may be deemed necessary, to be available only in such emergencies for the arrest and eradication of contagious or infectious disease or pests of animals, poultry, or plants, and for expenses in accordance with sections 10411 and 10417 of the Animal Health Protection Act (7 U.S.C. 8310 and 8316) and sections 431 and 442 of the Plant Protection 15 Act (7 U.S.C. 7751 and 7772), and any unexpended bal1ances of funds transferred for such emergency purposes in the preceding fiscal year shall be merged with such transferred amounts.”

The Congress has included this or similar language in appropriations reports for almost two decades, but it has not succeeded in freeing up many funds for countering plant pests. Perhaps placing the language in the legislation rather than the report will help … we will have to see.

In the meantime, I have been working with others to amend the Plant Protection Act to ensure that the emergencies so referenced include threats to forests. See §2 in H.R. 3174 link (Balint, Vermont) and S. 1238 (Welch, Vermont).

SOURCES CITED

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. 2019. Biomass losses resulting from insect and disease invasions in United States forests. PNAS August 27, 2019. Vol. 116 No. 35 17371–17376

Haack R.A., J.A. Hardin, B.P. Caton and T.R. Petrice .2022. Wood borer detection rates on wood packaging materials entering the United States during different phases of ISPM#15 implementation and regulatory changes. Front. For. Glob. Change 5:1069117. doi: 10.3389/ffgc.2022.1069117

Posted by Faith Campbell

www.fadingforests.org

Countering Non-Compliant wood packaging – is new study the 1st step?

infested wood bearing ISPM#15 mark; photo by Oregon Department of Agriculture

SWPM has been recognized as a major pathway for introduction of tree-killing pests since the Asian longhorned beetle was detected in New York and Chicago in late 1990s. As of 2014, 58 new species of non-native wood- or bark-boring insects had been detected – many probably introduced via wood packaging [Leung et al. 2014]. Other examples include the emerald ash borer, redbay ambrosia beetle, and, possibly, the invasive shot hole borers.

In response to recognition of the pest risk associated with wood packaging, countries adopted ISPM#15. This process was reviewed in the two articles by Haack et al. and my recent blog. I provided the broader context of the World Trade Organization (WTO) in my Fading Forests II report.

I have blogged often about the continuing poor compliance with wood packaging regulations, especially by China; and USDA APHIS’ insufficient efforts to fix the problems. The DHS Bureau of Customs and Border Protection (CBP) has tried much harder. See particularly my blog about Bob Haack’s re-evaluation of the pest approach risk in wood packaging. Given the high volumes of imports, pests infesting even a small proportion of incoming shipments can result in tens of thousands of pest-infested containers entering the U.S. or Canada each year. For an explanation of these calculations, see the “background” section of this blog.

Since 2010, CBP has discovered actionable pests in more than 700 shipments each year (pers. comm.). [APHIS reports half as many detections – 300 wood boring and bark beetles (Greenwood et al. citing APHIS report from 2021). Perhaps the difference arises from some of the actionable pests not being wood-borers, e.g., snails.] The persistence of pest presence has disappointed CBP staffers, because the agency has taken several actions intended to discourage violations. These include imposing fines and revoking the violators’ participation in the U.S. Trade Partnership Against Terrorism (C-TPAT) program. Greenwood et al. describe these consequences of non-compliance, as well as the expense of re-exporting the goods and associated wood packaging, as “significant”. Regardless of how significant they might be, so far these consequences have not reduced non-compliances substantially.

The fact is, countries cannot rely on the presence of the ISPM#15 mark or stamp to indicate that the wood packaging is pest-free. In both the United States and Europe, more than 90% of the SWPM found to be infested has born the ISPM#15 stamp (pers. comm.; Eyre et al. 2018). All the pest-infected shipments imported after 2006 discussed in the Haack et al. 2022 study were in wood packaging bearing the ISPM#15 mark. While many of the problems arise on shipments from Asia, findings occur sporadically with countries all across the globe- and notably, U.S. importers have also found serious problems with dunnage from Europe.

But that is the purpose of the standard!

Two outstanding questions that need answers

Continuing poor compliance with regulations by China. This is despite the fact that the U.S. and Canada have required treatment of wood packaging from China since December 1998 – nearly 24 years. Haack et al. found that the proportion of Chinese consignments with infested wood is five times greater than expected based on their proportion of the dataset. The rate of wood packaging from China that is infested has remained relatively steady: the Chinese infestation rate was 1.26% during 2003–2004, and ranged from 0.58 to 1.11% during the next three periods.

Why are the responsible agencies in the United States not taking more aggressive action to correct this long-standing problem? This is a matter of political will.

Despite the ISPM#15 mark being unreliable for more than a decade, countries have not carried out research to determine the root causes. Even now (i.e., Haack et al. 2022; Greenwood et al.) no one can say what proportion of these ISPM-marked but pest-infested pieces of wood results from the treatment not being effective in killing all pests; what proportion results from inadequate application of treatments that are per se effective; and what proportion from fraud (deliberate claims to have applied a treatment that was not done)?

Admittedly, answering these questions will not be easy. First, there is no independent test for whether treatments have been applied; the treatments do not alter the wood’s properties in measurable ways. Scientists need experiments to test the real-world efficacy of treatments in the specific contexts of solid wood packaging.

Second, each country is responsible for its own compliance. Countries differ in their capacity and political will to address this issue. However, success of ISPM#15 depends on determining the cause of continuing pest presence in wood marked as treated, and taking appropriate action to solve the underlying problem.

Greenwood et al. attempt to make progress toward carrying out this necessary task by describing the many steps in the wood packaging supply chain, associated opportunities for pests to infest the wood at each step, and actions exporters and importers can take to try to minimize the risk.

Again, as I discussed in the earlier blog, Haack et al. (2022) found several disturbing situations:

While the pest approach rate has fallen since U.S. implementation of ISPM#15, the extent of the decline has progressively decreased as time passes. The reduction during 2005–2006 was 61%; during 2007–2009, 47%; during 2010-2020 only 36%.
The 2010 – 2020 pest approach rate was calculated at 0.22%. This is more than double the rate based on 2009 data (0.1%, as stated in Haack et al. 2014). While we cannot directly compare these two data points (the two studies used different methods, as discussed in the blog), the bottom line is that the approach rate remains too high. Our forests continue to be exposed to the risk of introduction of highly damaging wood-boring pests. Furthermore, since the number of countries sending us infested wood packaging has increased, those potential pests include insects from a greater variety of countries (biomes).
The two most commonly intercepted families of wood borers are Cerambycidae and Scolytinae (Haack et al. 2022). These families include the Asian longhorned beetle, , redbay ambrosia beetle, and invasive shot hole borers. The 2009 amendment requiring debarking has not apparently resulted in substantial decreases in pest presence, although the proportion of pests that are true bark beetles has declined – from 100% of Scolytinae identified to genus or species detected before 2009 to only 23% in 2010–2020 period.

Michigan’s champion green ash killed by emerald ash borer

Haack et al. (2022) Recommendations

Haack et al. (2022) call for several improvements. Several pertain to how data are collected. Recording the number of infested pieces of wood instead of reporting only consignments would help clarify whether the numbers of insects reaching our borders has fallen, risen, or remained steady. Recording the presence of bark – and the size of any bark remnants – would help clarify whether pests are re-infesting treated wood.

They also note opportunities to improve ISPM#15 implementation and enforcement through training. However, compliance issues persist despite past educational efforts by APHIS and the IPPC.

The Wood Packaging Supply Chain Offers many Opportunities for Pests to Infest the Wood

Greenwood et al. describe each step in fabricating wood packaging material and the opportunities each step presents for unwanted organisms to enter that supply chain. They note that ensuring that these organisms are not then transported on wood packaging being used to carry goods requires that the pests be removed; rendered infertile, inactive, unable to complete development or reproduce; or killed.

The first step in fabricating wood packaging is to harvest trees. Those trees probably harbor various insects, fungi, nematodes, and other organisms that use trees as a resource — for food, shelter, or as a substrate for oviposition. Greenwood et al. mention that the multiplicity of organisms’ life histories pose different challenges for detection and management depending on size, type of tissue utilized, and other factors. The likelihood that a pest or pathogen will be present on or in tree tissues depends on several biotic and abiotic factors, including a species’ proclivity to experience periodic or episodic outbreaks; blow-down events (e.g., hurricanes, windstorms); and harvesting practices. Some of these factors can be controlled by people harvesting the wood.

One of the most frequent opportunities for pest infestation, escape, or cross-contamination is when the wood is stored in the environment. Such storage events happen after the tree is felled — at either the harvest site or processing facility; after the pallet or crate is built – either empty or after the goods have been packed; at the port of export before embarkation; at the importing port before inspection or onward transport; at distribution centers; at retailers; at “pallet graveyards” while awaiting repair or recycling. Retailers and customers have few resources for responsible handling of SWPM – and few incentives to be careful.

a “pallet graveyard”; photo by Adnan Prasad, then with Davey Tree

The risk is exacerbated if storage takes place near woodlands. photo from Savannah At ports and distribution centers, the presence of SWPM from many origins adds to the risk of cross-contamination. Enclosing the SWPM in containers does not completely eliminate the risk since organisms might enter through cracks or air vents. Greenwood et al. suggest management tactics to prevent or reduce pest interaction with the wood during these periods.

container storage near a treed area – Port of Savannah; photo by F.T. Campbell

One of the ISPM#15 requirements intended to minimize the pest risk is debarking the wood. This process removes most organisms that live in and just under the bark. However, debarked wood usually retains some patches of bark because trees are not perfectly round cylinders. Therefore ISPM#15 specifies that remaining bark must be less than 3 cm wide or, if the piece is longer than 3 cm, less than 50 cm² in area.

Greenwood et al. state that after debarking and treatments per ISPM#15, the risk that a pest will be present on the SWPM has been significantly reduced. However, other challenges appear as the newly-minted packaging is put into use – primarily through the possibility of contamination during storage – as described above. There are also risks associated with inadequate or insufficient treatment or fraud.

Once loaded onto a ship, containers and any SWPM, including dunnage, are very difficult to inspect. That means that the loading process presents that last opportunity for inspection and mitigation of contaminating pests. Greenwood et al. note that it is the shipper’s responsibility to ensure containers are “clean, free of cargo residues, noxious materials, plants, plant products and visible pests” before being loaded on the ship. However, the International Maritime Organization (IMO) provides only recommendations, not mandates. Australia has adopted more stringent requirements.

Arrival at the importing country’s port presents the first opportunity for non-indigenous organisms to escape and the first domestic opportunity for the receiving country to inspect the shipment. While U.S. and Canadian customs agencies have authority to board ships before they dock to inspect them, Mexican agencies do not. The most extensive pre-docking requirements are aimed at preventing arrival of moths in the Lymantria genus from Asia.

dunnage in Houston; photo by S. Useman, CBP

Greenwood et al. note that dunnage presents unique risks. After it is removed from ships during the unloading process it is often stored at the port. As noted above, storage in the open allows pests to escape to nearby trees or to cross-contaminate other SWPM. Ports struggle to manage these piles. In 2016 the U.S. revised its regulations to allow for the more rapid destruction of illegally deposited dunnage via incineration at the port. Since 2008 Canada has considered all shipborne dunnage to be non-compliant – regardless of whether it bears the ISPM#15 stamp. In the largest Mexican ports, dunnage is fumigated and destroyed. However, the dunnage might be stored in the open for considerable periods before being destroyed.

Worse, it is often impossible to assign chain of custody information and responsibility for either disposition of non-compliant dunnage or penalties for non-compliance. Dunnage or blocking pieces might be added immediately before shipping by entities other than the owners or brokers for the commodities being shipped. I have already noted that it is nearly impossible to inspect dunnage in a ship’s hold.

Unfortunately, studies have not clarified the level of infestation of dunnage in comparison to other wood packaging types made from multiple pieces of milled wood, such as pallets or spools.

Greenwood et al. describe the different fates of pallets, dunnage, crates, spools, and other types of SWPM. Wood pallets are frequently recycled or remanufactured in the U.S., although there are no data on the proportion of the recovery market that is composed of pallets initially manufactured overseas. In the U.S., most repairs are done with components from reclaimed pallets so they probably conform to ISPM#15 repair guidelines. However, contamination could happen while the pallets are in storage awaiting reuse. As SWPM ages, different types of pests might be attracted.

SWPM deemed not suitable for reuse is either destroyed in controlled settings (i.e., solid waste facilities, wood processing facilities, or landfills), used in recycling or downcycling markets, or reclaimed. It might be chipped and sold as mulch, soil amendment, or animal bedding; or it might enter the commercial fiber market and be manufactured into other wood products (e.g., paper, chipboard, fuel pellets). These dispositions present very low pest risk, due to the final dimensions of the wood products being too small to sustain pest development in most cases. However, some microorganisms and very minute arthropods might persist even on chipped or shredded material. There is little data on the final disposition of SWPM globally.

Greenwood et al. reiterate that the presence of hitchhiking or contaminating pests does not imply failure of ISPM#15 treatments, which do not target such organisms. Such pests can also be present on non-wood packaging material such as plastic and metal. Countries vary in their concern about these hitchhiking pests, which include dry wood borers and brown marmorated stinkbug (Halyomorpha halys). Since these pests are not addressed by ISPM#15, countries can implement their own management strategies to counter contaminating pests on all SWPM, containers, and conveyances. Indeed, Pennsylvania regulates the movement of SWPM and other high risk articles to prevent the spread of the non-specific hitchhiking pest, spotted lanternfly, Lycorma delicatula.

They also note that reuse, disposal, and recycling of packaging made from metal, plastic, or even paper requires very different processes and facilities than those used for wood.

Greenwood Recommendations

Greenwood et al. advocate additional research on several questions:

to test whether currently accepted ISPM#15 treatments are sufficiently effective within the newly proposed metrics found in Ormsby 2022.
to determine the risk profile and enforcement of dunnage, especially whether organisms in dunnage are more likely to survive treatment (dunnage pieces are often much larger than any component piece of a pallet or crate).
to develop new treatments – including to counter re-infestation later in the supply chain. Scientists will probably have to replace Probit9 as a standard because it is not practical to exposing tens of thousands of wood-infesting insects to the new treatment. This is also discussed in Ormsby 2022.
to develop ways to test whether treatments have been applied – needed to verify whether fraud has occurred.
social and economic motivations around compliance

Most of these studies will require international cooperation.

Other steps are also need. As U.S. importers of break-bulk cargo have found out, procuring apparently compliant SWPM does not protect them from legal, financial, and logistical consequences if that SWPM turns out to be non-compliant or otherwise infested with live actionable pests. Some importers have begun exploring options toward additional private inspection at the exporting port, beyond solely requiring the use of ISPM#15 compliant materials. Greenwood et al. suggest the possibility of third-party certification. They also supported calls for officials to release of information about which foreign facilities have a history of selling SWPM subsequently found to be non-compliant. This information would empower importers to procure pest-free SWPM – thus harnessing market incentives to improve compliance.

Managing all this + pest risks? Photo by Port Authority of Long Beach

Greenwood et al. say that reducing external contamination on conveyances – ships, airplanes, trucks, and trains – is challenging. It would require the cooperation of multiple entities who manage yards, equipment, and facilities. Improved management must make sense to people who have severe constraints on time, staffing, space, and safety protocols. Persuading them to act will probably depend on improved information (research) on the cost effectiveness of various strategies and real-world incidence of contamination in different storage scenarios (beyond Lymantria complex), plus development of new surveillance tools.

Greenwood et al. suggest that conducting a HACCP assessment of the supply chain could help identify how a systems approach might better mitigate pest risks of SWPM. They think systems approaches might be especially promising for reducing risks of contaminating organisms. NAPPO recently adopted a standard for designing and implementing systems approaches for wood commodities.

Finally, I remind you of my recommendations for immediate policy actions to hold foreign suppliers responsible for non-compliant wood packaging:

U.S. and Canada should refuse to accept wood packaging from foreign suppliers that have a record of repeated violations – whatever the apparent cause of the non-compliance. They should institute severe penalties to deter foreign suppliers from taking devious steps to escape being associated with their violation record.
I also support the suggestion (above) that phytosanitary agencies inform importers on which foreign treatment facilities have a record of poor compliance or suspected fraud – so the importers can avoid purchasing SWPM from them.
U.S. and Canada should encourage importers to switch to materials that won’t transport wood-borers. Cardboard and manufactured wood packaging (e.g. oriented strand board and compressed wood block) are wood fiber products that have near zero risk of wood-borer infestation. Plastic is also one such material. I note that Earth is drowning under discarded plastic.

APHIS and CFIA have the authority to take these action under the “emergency action” provision (Sec. 5.7) of the World Trade Organization’s Agreement on the Application of Sanitary and Phytosanitary Standards (WTO SPS Agreement). (For a discussion of the SPS Agreement, go to Fading Forests II, here.)

Longer-term Actions

APHIS and CFIA should exercise their right to set a higher “level of protection” to minimize introductions of pest that threaten our forests (described inter alia here.) They should prepare a risk assessment to justify adopting more restrictive regulations that would prohibit use of packaging made from solid wood – at least from the countries with records of high levels of non-compliance.

The studies needed to determine the cause of the continuing issue of the wood treatment mark’s unreliability, and appropriate actions to fix the problem, should be conducted with other countries. Appropriate entities would be the International Plant Protection Convention (IPPC) and International Forest Quarantine Research Group (IFQRG). However, if attempting such collaboration causes delays, APHIS and CFIA should begin unilaterally.

Meanwhile, what can we do?

Urge Congress to conduct oversight on APHIS’ failure to protect America’s natural resources from continuing introductions of nonnative insects and diseases. Note that the Mediterranean oak borer has apparently been introduced several times in recent years – despite ISPM#15.
Raise the issue with local, state, and federal candidates for office;
Urge Congress to include provisions of H.R. 3174 / S. 1238 in the 2023 Farm Bill;
Ask any associations of which you are a member to join in communicating these concerns to Congressional representatives and senators. These include:
- if you work for a federal or state agency – raise to leadership; they can act directly or through National Plant Board, National Association of State Departments of Agriculture, National Association of State Foresters, National Governors Association, National Association of Counties …
- scientific membership societies – e.g., Society of American Foresters, Entomological Society of America, Phytopathological Society;
- individual conservation organizations, either with state chapters or at the national level;
- woodland owners’ organizations, e.g., National Woodland Owners Association, National Alliance of Forest Owners, and their state chapters
- urban tree advocates
- International Forest Quarantine Research Group
Write letters to the editors of your local newspaper or TV news station.

SOURCES

Eyre, D., R. Macarthur, R.A. Haack, Y. Lu, and H. Krehan. 2018. Variation in Inspection Efficacy by Member States of Wood Packaging Material Entering the European Union. Journal of Economic Entomology, XX(X), 2018, 1–9 doi: 10.1093/jee/tox357

Greenwood, L.F., D.R. Coyle, M.E. Guerrero, G. Hernández, C.J. K. MacQuarrie, O. Trejo, M.K. Noseworthy. 2023. Exploring pest mitigation research and management associated with the global wood packaging supply chain: What and where are the weak links? Biol Invasions https://doi.org/10.1007/s10530-023-03058-8

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

Haack R.A., J.A. Hardin, B.P. Caton and T.R. Petrice. 2022. Wood borer detection rates on wood packaging materials entering the United States during different phases of ISPM#15 implementation and regulatory changes. Frontiers in Forests and Global Change 5:1069117. doi: 10.3389/ffgc.2022.1069117

Leung, B., M.R. Springborn, J.A. Turner, and E.G. Brockerhoff. 2014. Pathway-level risk analysis: the net present value of an invasive species policy in the US. Front Ecol Environ. 2014. doi:10.1890/130311

Posted by Faith Campbell

www.fadingforests.org

Introduced pests linked (again) to introduced plants; Prevention needs to recognize this nexus

I have blogged many times about the risk of pest introductions on imports of live plants [= “plants for planting” in USDA’s terms]. Last October I reviewed 14-year old data indicating that nearly 70% of 455 damaging tree pests introduced to the continental U.S. had probably been introduced via plant imports. These included 95% of sap feeding and 89% of foliage feeding insects and about half of the pathogens. The approach rate of pests on imported plants was apparently 12% (Liebhold et al. 2012) — more than 100 times higher than the 0.1% approach rate found by Haack et al. (2014) for wood packaging.

First, those analyses focus almost exclusively on insects (MacLachlan et al. 2022 focused on a single insect order, the Hemiptera!), despite the many pathogens probably introduced by the plant trade in recent decades. Examples I cited included several Phytophthoras, rapid ohia death, beech leaf disease, and boxwood blight. There have been repeated detections of the Ralstonia solanacearum Race 3 biovar 2.

SOD- infected rhododendrons; photo by Jennifer Parke, Oregon State University

Second, most studies analyzing the pest risk associated with plant imports use port inspection data – which are not reliable indicators of the pest approach rate – as explained by Liebhold et al. 2012 and Haack et al. 2014 (as it pertains to wood packaging).

Third, many of the studies are based on data from a decade or longer in the past. This means the studies do not address whether APHIS’ recent changes in its approach – including adoption of NAPPRA – have resulted in reduced introductions.

A complication is that, since insects are difficult to detect, those associated with the high volumes of plants imported in recent years might not be detected for years or decades after their introduction.

I have called for APHIS to update the Liebhold et al. 2012 study to determine the approach rate for all types of organisms that threaten North American tree species. Any such study should include trees on Hawai`i, Guam, Puerto Rico, and other U.S possessions and territories. These islands are nearly always excluded from analyses of imported pests. I concede that there are probably scientific and data-management challenges but these islands are immensely important from a biodiversity point of view, and they are parts of the United States!

eastern hemlocks killed by hemlock woolly adelgid; Linville Gorge; photo by Steven Norman, USFS

MacLachlan et al. (2022) estimated that new establishments – of insects in the order Hemiptera – per unit of additional plant imports have shrunk substantially. They attribute this decline to a combination of increased imports and the presence of a growing number of insect species introduced in the past. They found that introductions to the Asian Palearctic and Neotropic regions have been reduced by depletion of species pools. Other factors are thought to explain the substantial decline in establishment likelihood for the other regions. However, lag times in detecting insect introductions complicate this assessment.

However, despite that significant decrease in risk per unit of imports, MacLachlan et al. (2022) found that the number of establishments has remained relatively constant over the past century because of substantial increases in overall import levels and diversification of the origins of imports across regions, which exposed the U.S. to new source species pools.

MacLachlan et al. (2022) suggested that APHIS should target biosecurity resources to the specific commodity-country pairs associated with a higher relative risk of introducing additional insect species.

Recent studies are taking a welcome new stance: looking at links between introductions of non-native plant and insect species. I first raised this approach a year ago. Studies by teams led by Doug Tallany and Sara Lalk [Lalk et al.; articles by Tallamy] agree that:

Non-native plants – some of which are invasive – are altering ecosystems across broad swaths of North America and the impacts are insufficiently understood.
The invasive plant problem will get worse because non-native species continue to be imported, planted … and to invade.
Plant-insect interactions are the foundation of food webs – they transfer energy captured by plants through photosynthesis to other trophic levels, plus play a major role as pollinators. Consequently, changes to a region’s flora will have repercussions throughout ecosystems.

Dr. Tallamy studies the response of herbivorous insects to non-native woody plants – not just invasive plants, but also non-native plants deliberately planted as crops or ornamentals, or in forestry. Introduced plants have completely transformed the composition of plant communities in both natural and human-dominated ecosystems world-wide. The impacts can be significant: Burghardt et al. found that 75% of North American lepidopteran species and 93% of specialist species were found exclusively on native plant species.

monarch butterfly on milkweed; photograph by Jim Hudgins, USFWS

Lalk and colleagues studied the relationships between individual species of invasive woody plants and the full range of arthropod feeding guilds – pollinators, herbivores, twig and stem borers, leaf litter and soil organisms. They decry the absence of data on the complex interactions between invasive woody plants and arthropod communities at a time when invasive shrubs and trees are so widespread and causing considerable ecological damage. (See the blog for their specific research recommendations.)

Nor is the impact of non-native plants on insect fauna limited to North America. Outhwaite et al. found that the combination of climate warming and intensive agriculture is associated with reductions of almost 50% in the abundance and 27% in the number of species within insect assemblages relative to levels in less-disturbed habitats with lower rates of historical climate warming. These patterns were particularly clear in the tropics (perhaps partially because of the longer history of intensive agriculture in temperate zones). They found that high availability of nearby natural habitat (that is, native plants) can mitigate these reductions — but only in low-intensity agricultural systems.

Recognizing that plant diversity drives global patterns of insect invasion, Liebhold et al. (2023) compared various factors associated with numbers of invasive insect species in 44 land areas.They determined that the numbers of established non-native insect species are primarily driven by diversity of plants – both native and non-indigenous. Other factors, e.g., land area, latitude, climate, and insularity, strongly affect plant diversity; thus they influence insect diversity as a secondary impact. When I blogged about this study, I noted that the article appeared more than four years earlier, but has apparently had little influence on either policy formulation governing plant introductions or pest risk analysis applied to insects or pathogens that might be introduced. I suggested that we need a separate analysis of whether fungi, oomycetes, nematodes, and other pathogens show the same association with plant diversity in the receiving environment.

Studies of plant-insect relationships continue to be published. I welcome this!

Bonnamour et al. (2023) builds on the earlier studies. They also found that the presence of non-native plant species was a better predictor of insect invasions than such more widely discussed socioeconomic variables as trade volumes generally or even trade in plant products. However, detection of the associated insect invasions occurs years after detection of the plant invasions. Indeed, numbers of established non-native insect species corresponded more closely to plant introduction volumes in 1900 than current or recent import volumes.

Bonnamour et al. note that while the insect taxa that respond most directly to the non-native plant diversity are those that rely on those plants as hosts, pollinators, and plant visitors, over time those non-native herbaceous insects support introduced predators and parasites also.

Because of the “invasion debt” associated with that lag, Bonnamour et al. estimate that newly detected insect invasions will increase by 35% worldwide as a result of only recent plant introductions. They differentiate this “invasion debt” from “future invasions”, meaning the actual introduction of additional species resulting from future trade activities.

The model developed by Bonnamour et al. points to the highest numbers of newly introduced insect species occurring in areas with less capacity to deal with bioinvasions. Thus, the Afrotropics are anticipated to receive 869 new insect species, or a 10-fold increase over the number currently known to be established in the region. The Neotropics are projected to be invaded by 809 insect species, also a 10-fold increase. The Indomalayan region will probably detect 776 new insect species, a startling 20-fold increase. In reality, the “invasion debt” might not be quite this severe, since – as Bonnamour et al. note several times – the low numbers of introduced insects currently reported for these tropical regions probably partially reflect limited sampling. They note that already a high proportion of insect species intercepted by biosecurity services on imports arriving from Africa and South America are not yet recorded as established in the exporting regions.

Although both the European Palearctic and Australasia have already received many non-native insect species, their “invasion debt” is relatively high: 417 species for Europe, 317 species for Australasia.

The Neotropics are expected to be the greatest source of insect invasions in the future (904 exported species), followed by the European Palearctic (732 species).

Bonnamour et al. did not include non-native plant species used in agriculture, forestry, or ornamental horticulture. As noted above, these widespread deliberate plantings also affect insect fauna and higher trophic layers.

The greatest number of recorded insect introductions so far are in the Nearctic, Oceania (primarily Hawaii), Europe, and Australasia. While this imbalance is probably caused in part by the significantly limited sampling of non-native insect species in the Asian Palearctic and tropics, it is also true that these regions have received the majority of plant introductions through 1900. This factor has changed in the century since then; many non-native plant species have been recorded in the Afrotropics, Oceania, and Asia.

Eucalyptus plantation in Kwa-Zulu-Natal, South Africa; Kwa-Zulu-Natal Dept. of Transportation

Bonnamour et al. offer several potential explanations for the lag in detecting introduced insects compared to detecting introduced plants. First, it might be necessary for non-native host plants to reach a threshold of abundance before the associated insects are able to establish and spread. Second, reaching that threshold might require repeated introductions of the insect’s host plant species. Third, since only some of the imported plants are transporting insects, repeated imports of host plants might be necessary for the insect to achieve sufficient numbers to establish. Fourth, while their analysis included all non-native insect species, only some insect feeding guilds – herbivores and pollinators – are probably directly facilitated by introduced host plants. Fifth, plant species’ presence tends to be more quickly recorded than insects’ presence. Indeed, MacLaughlin et al. reported a median delay of 80 years between establishment and discovery of plant-feeding Hemiptera. This suggests that the actual time lag between plant and insect establishments might be shorter than the period discussed in Bonnamour et al.

Many insects from the European Palearctic have been introduced to the Nearctic; fewer insects have been introduced in the opposite direction. There is no consensus on the explanation. Thirty years ago Mattson et al. argued that there might be fewer niches for non-native insects in Europe due to the lower host plant diversity in this region caused by the Pleistocene/Holocene glaciations. On the other hand, more plant species from the European Palearctic to the Nearctic than the opposite.

Bonnamour et al. call for further research on:

1) time lags at the scale of individual insect species with their host plants.

2) effects of non-native plants used in agriculture, forestry, or ornamental horticulture.

3) whether time lags between plant and insect invasions vary among taxonomic groups, feeding guilds, or among regions.

4) effect of non-native plant abundance, rather than just species richness, on non-native insect establishment.

Recommendations

Writers about interactions of non-native plant species and insect introductions make a common plea: limit the introduction and spread of non-native plants in order to prevent future invasions of both plants and insects. Bonnamour et al. suggest including the risk of insect introductions in plant invasion risk screening tools. Earlier, the Tallamy and Lalk teams called for ending widespread planting of non-native plants.

Will policy-makers accept this advice?

I believe that these same interaction of plant host and “pest” introductions presumably applies to pathogens, too. I reiterate my frequent complaint that regulators have not responded to two or more decades of criticism of the failures of the international phytosanitary system re: insect and pathogen introductions via the international nursery trade. Examples include Brasier 2008; Liebhold el. al. 2012; Santini et al. 2013; Roy et al. 2014; Eschen et al. 2015; Jung et al. 2015; Meurisse et al. 2019; O’Hanlon et al. 2021.

As I have said earlier, I appreciate that some scientists are trying to reduce scientific uncertainty about the invasive potential of pathogens native to regions other than North America; I refer here to Jiri Hulcr (see Li et al.), Mech, and Schultz. Many more such studies are needed, addressing potential impacts on a wider variety of North American host trees and shrubs.

The late (& very much lamented!) Gary Lovett of the Cary Institute had advocated halting imports of plants that are congenerics of important North American tree species, in order to minimize the risk that pests that damage those genera will be introduced.

In January I suggested that at the global level we need:

National agricultural agencies, stakeholders, FAO & International Plant Protection Convention (IPPC) should consider amending the IPPC requirement that scientists identify a disease’s causal agents before regulating it. Experience shows that this policy virtually guarantees that pathogens will continue to enter, establish, & damage natural and agricultural environments.
National governments & FAO / IPPC should fund greatly expanded research to identify microbes resident in regions that are important sources of origin for traded plants, vulnerability of hosts in importing countries, and new technologies for detecting pathogens (e.g., molecular tools, volatile organic compounds [VOCs]).
Researchers & agencies should expand international “sentinel plants” networks; incorporate data from forestry plantations, urban plantings, etc. of non-native trees.
NPPOs should adopt regulations that apply the “systems approach” or HACCP programs outlined in ISPM#36. I had discussed these approaches in my Fading Forests III report – link at end of this blog.)

I suggested further that Americans need to

Evaluate the efficacy of current regulations – that is, implementing NAPPRA & Q-37 revision. This evaluation should be based on AQIM data, not port interception data. It should include arthropods, fungal pathogens, oomycetes, bacteria, viruses, nematodes. It should include threats to U.S. tropical islands (Hawai`i, Puerto Rico, Guam, etc.) which are centers of plant endemism.
Apply existing programs (e.g., NAPPRA, Clean Stock Network, post-entry quarantine) to strictly regulate trade in plant taxa most likely to transport pests that threaten our native plants; e.g., plants belonging to genera shared between North American trees & plants on other continents.
Recognize that plant nurseries are incubators for microbial growth, hybridization, and evolution; require nurseries to adopt sanitary operation procedures regardless of whether they sell in inter-state or intra-state commerce

SOURCES

Bonnamour, A., R.E. Blake, A.M. Liebhold, H.F. Nahrung, A. Roques, R.M. Turner, T. Yamanaka, and C. Bertelsmeier. 2023. Historical plant intros predict current insect invasions. PNAS 2023 Vol. 120 No. 24 e2221826120 https://doi.org/10.1073/pnas.2221826120

Burghardt, K. T., D. W. Tallamy, C. Philips, and K. J. Shropshire. 2010. Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities. Ecosphere 1(5):art11. doi:10.1890/ES10-00032.

Lalk, S. J. Hartshorn, and D.R. Coyle. 2021. IAS Woody Plants and Their Effects on Arthropods in the US: Challenges and Opportunities. Annals of the Entomological Society of America, 114(2), 2021, 192–205 doi: 10.1093/aesa/saaa054

Li, Y., C. Bateman, J. Skelton, B. Wang, A. Black, Y-T. Huang, A. Gonzalez, M.A. Jusino, Z.J. Nolen, S. Freeman, Z. Mendel, C-Y. Chen, H-F. Li, M. Kolařík, M. Knížek, J-H. Park, W. Sittichaya, T-H.

Pham, S. Itoo, M. Torii, L. Gao, A.J. Johnson, M. Lur, J. Sun, Z. Zhang, D.C. Adams, J. Hulcr. 2022. Pre-invasion assessment of exotic bark beetle-vectored fungi to detect tree-killing pathogens. https://apsjournals.apsnet.org/doi/full/10.1094/PHYTO-01-21-0041-R

Liebhold, A.M., E.G. Brockerhoff, L.J. Garrett, J.L. Parke, and K.O. Britton. 2012. Live Plant Imports: the Major Pathway for Forest Insect and Pathogen Invasions of the US. www.frontiersinecology.org

Liebhold, A.M., T. Yamanaka, A. Roques, S. August, S.L. Chown, E.G. Brockerhoff & P. Pyšek. 2018. Plant diversity drives global patterns of insect invasions. Sci Rep 8, 12095 (2018). https://doi.org/10.1038/s41598-018-30605-4

MacLachlan, M.J., A. M. Liebhold, T. Yamanaka, M. R. Springborn. 2022. Hidden patterns of insect establishment risk revealed from two centuries of alien species discoveries. Sci. Adv. 7, eabj1012 (2021).

Mattson, W. J., P. Niemela, I. Millers, and Y. Ingauazo. 1994. Immigrant phytophagous insects on woody plants in the United States and Canada: an annotated list. USDA For. Ser. Gen. Tech. Rep. NC-169, 27 pp.

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

Outhwaite, C.L., P. McCann, and T. Newbold. 2022. Agriculture and climate change are shaping insect biodiversity worldwide. Nature 605 97-192 (2022) https://www.nature.com/articles/s41586-022-04644-x

Richard, M., D.W. Tallamy and A.B. Mitchell. 2019. Intro plants reduce species interactions. Biol Invasions https://doi.org/10.1007/s10530-018-1876-z

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

Tallamy, D.W., D.L. Narango and A.B. Mitchell. 2020. Ecological Entomology (2020), DOI: 10.1111/een.12973 Do NIS plants contribute to insect declines? Conservation Biology DOI: 10.1111/j.1523-1739.2009.01202.x

Uden, D.R, A.M. Mech, N.P. Havill, A.N. Schulz, M.P. Ayres, D.A. Herms, A.M. Hoover, K.J. K. Gandhi, R.A. Hufbauer, A.M. Liebhold, T.D. M., K.F. Raffa, K.A. Thomas, P.C. Tobin, C.R. Allen. 2023. Phylogenetic risk assessment is robust for forecasting the impact of European insects on North American conifers. Ecological Applications. 2023; 33:e2761.

Posted by Faith Campbell

www.fadingforests.org

Support House & Senate bills to Enhance Response to Forest Pests

white ash: a species that might be restored under the programs envisioned in the proposed bills

Bills have been introduced into both the House and Senate to enhance USDA APHIS and Forest Service programs intended to curtail introduction and spread of non-native forest pests and disease and – especially – programs aimed at restoring pest-decimated trees to the forest.

The House bill is H.R. 3174; it was introduced by Reps. Becca Balint (VT).

The Senate bill is S. 1238; it was introduced by Senators Peter Welch (VT), Mike Braun (IN), and Maggie Hassen (NH). [Both senators Welch and Braun are on the Agriculture Committee – which will write the bill.]

CISP hopes that the contents of these two bills will be incorporated in the Farm Bill that Congress is expected to adopt this year or next. The proposals have the support of the Forests in the Farm Bill coalition. [Unfortunately, neither the “Consolidated Recommendations” nor “Summarized Recommendations appears to be posted on the internet at present.]

In the last Congress, a nearly identical bill introduced by then-Representative Peter Welch was endorsed by the organizations listed below. We hope they will endorse the new bills now! If you are a member of one of these organizations, please ask them to do so.

Organizations that endorsed the previous bill: Vermont Woodlands Association, American Forest Foundation, Center for Invasive Species Prevention, Reduce Risk from Invasive Species Coalition, National Woodland Owners Association (NWOA), National Association of State Foresters (NASF), The Society of American Foresters (SAF), the North American Invasive Species Management Association (NAISMA), the Ecological Society of America, Entomological Society of America, a broad group of university professors and scientists, The Nature Conservancy (TNC) Vermont, Audubon Vermont, the Massachusetts Forest Alliance, the New Hampshire Timberland Owners Association, the Maine Woodland Owners Association, and the Pennsylvania Forestry Association.

I seek your help in generating support for incorporating these proposals into the 2023 Farm Bill. Please urge your representative and senators to co-sponsor the bills or otherwise support that action.

beech in a breeding experiment at The Holden Arboretum; photo by Jennifer Koch

Key points of the two bills:

They strengthen APHIS’ access to emergency funds. APHIS has had the authority to access emergency funds from the Commodity Credit Corporation since 2000. However, the Office of Management and Budget has often blocked its requests. See § 2, of the bills, EMERGENCY AUTHORITY WITH RESPECT TO INVASIVE SPECIES.
It creates two separate but related grant programs.
- The first grant program – in § 3. FOREST RECLAMATION GRANTS – funds research addressing specific questions impeding the recovery of tree species that are native to the US and have suffered severe levels of mortality caused by non-native plant pests or noxious weeds.
- The second grant program – in § 4. FOREST RESTORATION IMPLEMENTATION GRANTS – funds implementation of projects to restore these pest-decimated tree species to the forest. These projects must be part of a forest restoration strategy that incorporates a majority of the following components:

(1) Collection and conservation of native tree genetic material.

(2) Production of propagules of the target tree species in numbers sufficient for landscape-scale restoration.

(3) Preparation of planting sites in the target tree species’ former habitats.

(4) Planting of native tree seedlings.

(5) Post-planting maintenance of native trees.

§ 5 states that the absence of a national policy on addressing nonnative forest pests has resulted in their receiving a low priority within all Federal agencies. It then mandates a study to analyze agencies’ available resources, raise the issue’s priority, and improve coordination among agencies. This study is to be carried out by an independent institution, for example the National Academy of Sciences. The authors are to consult with specialists in entomology, genetics, forest pathology, tree breeding, forest and urban ecology, and invasive species management.
Funding for all three action components – the emergency response and both grant programs – would come from the Commodity Credit Corporation, so it would not be subject to the vagaries of annual appropriations bills.

Forest Restoration Alliance volunteers potting hemlock seedlings; photo provided by Fred Hains

Entities which could apply for the research grants (§ 3 of the bills) include Federal agencies; State cooperative institutions; academic institutions offering degrees in the study of food, forestry, and agricultural sciences; and non-profit organizations exempt from taxes under §501(c)(3) of the tax code. Types of research funded could include:

‘‘(A) biocontrol of nonnative pests & diseases or noxious weeds severely damaging native tree species [the bill does not specify, but Project CAPTURE identifies many qualifying species; see also my earlier blog];

‘‘(B) exploration of genetic manipulation of the plant pests or noxious weeds;

‘‘(C) enhancement of pest-resistance mechanisms of hosts; and

‘‘(D) development of other strategies for restoring individual tree species.

The maximum amount of such grants is $400,000 per year.

Entities which could apply for the implementation grants (§ 4 of the bills) include a cooperating forestry school; a land-grant college or university; a State agricultural experimental station; a 501(c)(3) organization. Funding would begin at $3 million for FY 2023 and rise to $10 million for FY 2026.

The Secretary of Agriculture would be guided in implementing these programs by two committees. One – the committee of experts – would constitute representatives of the USFS, APHIS, ARS & State forestry agencies. The second – the advisory committee – would be composed of representatives of land-grant colleges and universities and affiliated State agriculture experiment stations, forest products industry, recreationists, and professional forester, conservation, and conservation scientist organizations.

Port-Orford cedar seedlings at USFS Dorena Center – a model for success! Photo provided by Richard Sniezko

Please contact your Member of Congress (Representative) and senators to urge them to support inclusion of these provisions in the Farm Bill. [Remember: they work for us!] Telling them of your support for these bills is especially important if your Representative or Senator is on the Agriculture Committee. I list those legislators here:

State	HOUSE AGRIC COMM	SENATE AGRIC COMM
AL	Barry Moore	Tommy Tuberville
AR	Rick Crawford	John Boozman
CA	Doug Lamalfa John Duarte Jim Costa Salud Carbajal
CO	Yadira Caraveo	Michael Bennet
CT	Jahana Hayes
FL	Kat Cammack Darren Soto
GA	Austin Scott David Scott Sanford Bishop	Raphael Warnock
HI	Jill Tokuda
IA	Randy Feenstra Zach Nunn	Joni Ernst Charles Grassley
IL	Mike Bost Mary Miller Nikki Budzinski Eric Sorensen Jonathan Jackson	Richard Durbin
IN	Jim Baird	Mike Braun
KS	Tracey Mann Sharice Davids	Roger Marshall
KY		Mitch McConnell
MA	Jim McGovern
ME	Chellie Pingree
MI	Elissa Slotkin	Debbie Stabenow
MN	Angie Craig	Amy Klobuchar Tina Smith
MO	Mark Alford
MS	Trent Kelly	Cindy Hyde-Smith
NC	David Rouzer Alma Adams
ND		John Hoeven
NE	Don Bacon	Deb Fischer
NJ		Cory Booker
NM	Gabe Vasquez	Ben Ray Lujan
NY	Marc Molinaro Nick Langworthy	Kirsten Gillibrand
OH	Max Miller Shontel Brown	Sherrod Brown
OK	Frank Lucas
OR	Lori Chavez-Deremer Andrea Salinas
PA	Glenn Thompson	John Fetterman

SD	Dusty Johnson	John Thune
TN	Scott Desjarlais Brad Finstad
TX	Ronny Jackson Monica de la Cruz Jasmine Crockett
VA	Abigail Spanberger
VT	Peter Welch
WA	Marie Gluesenkamp Perez
WI	Derrick van Orden

Posted by Faith Campbell

www.fadingforests.org

New Tool for Evaluating Insect Pests’ Possible Impacts: One Test Shows Great Potential for Identifying the Greatest Threats to our Forests

red spruce (*Picea rubens*) — the conifer at greatest risk; This grove is in Great Smoky Mountains National Park; photo by Famartin via Wikimedia Commons

Scientists have incorporated into the widely-used urban tree management tool, i-Tree, a tool to help predict the damage that an insect species little known in North America might cause to trees growing in a specific area if it is introduced. This tool is available to all here.

I rejoice that predictive tools are becoming widely available. The tool is obviously the result of a lot of work by participating scientists – who are listed below. I hope many of you will try it out! Perhaps you and your students can join efforts by the tool-development team, especially in analyzing insect species from Central America and Asia that have not yet arrived in North America? If you are interested in helping, contact Katheryn Thomas, Angela Mech, or Ashley Schulz; you can obtain their contact information by visiting their institution’s website. You might choose which insect species to evaluate by consulting your own or colleagues’ research, reviewing the refereed and grey literature, APHIS and CFIA interception databases, databases maintained by several countries, websites such as CABI, EPPO, etc.

The new tool might help create a more effective “early warning” system. Whether this happens depends on what others do now. Anyone – perhaps a staffer of a federal or state agency, or a city tree manager, or an academic – can apply the tool to meet his/her own objectives. If a more effective national or continental “early warning” system is to be created, someone needs to set up a process for conveying the findings to responsible federal or state/provincial agencies or even the scientific societies, e.g., Entomological Society (and, in the case of beetles transporting associated fungi, American Phytopathological Society). Perhaps the most challenging issue is to find an entity willing to receive these communications, review their accuracy, and – at a minimum – make the results accessible to phytosanitary agencies, interested public, etc. One possible entity is “PestLens”, a web-based early-warning system maintained by APHIS. The project’s objective is to provide early-warning information and facilitate a prompt, coordinated, and appropriate safeguarding response. PestLens posts alerts once a month. These are visible to anyone who subscribes. However, it remains unclear how often APHIS and state agencies act on the notices. The North American Plant Protection Organization (NAPPO) also hosts an alert system, but it records only official notices, leading to some absurdities. (E.g., NAPPO reported Mexico’s designation of the invasive shot hole borers as quarantine pests – without mentioning that they are well-established in California because neither APHIS nor California Department of Food and Agriculture has designated the insects as officially regulated.)

Those applying the tool need to have some knowledge and access to a range of scientific resources (including, in my view, people who can check the accuracy of the data entered into the system). Users must have appropriate skills to conduct some research into the insect and what it feeds on. Information required for the tool includes the following:

taxonomic information for the insect (Order, Family, Genus, Species)
the feeding guild of the insect (i.e., foliovore, gall, reproductive, root, sap, wood)
climate in the native range of the insect (i.e., Tropical, Dry, Temperate, Continental, Polar)
native range of the insect (i.e., Afrotropical, Australasian, Indomalayan, Neotropical, Oceanian, Palearctic Asia, Palearctic Europe)
the host trees of the insect in its native range (scientific name [Genus species]). The tool warns participants to include the full range of potential tree hosts – by listing either all or a representative sample. The tool will use this information to estimate the evolutionary distance between known native hosts and potential North American hosts using comprehensive phylogenetic tree of plants.

Clearly, those using the tool have their work cut out for them! The tool does provide definitions, descriptors, and drop-down lists for most of the factors, including insect orders and families, tree genera, geographic origins, and climate types. Users are now anticipated to be employees of federal and presumably state agencies; academics – even students!—and others who have the capacity to research what an insect feeds on in its native range.

This tool is intended to predict the probability that an insect species of concern – either newly detected in the country or thought likely to invade based on port detections or other reasons — will become a high impact invader. I rejoice that they are inclusive – the tool can test the vulnerability of 50+ conifer species and 360+ hardwood species native to North America. Assuming the assessor can enter accurate information for the categories outlined above, the tool can then provide a list of probabilities for each relevant North American host tree.

The tool is based on the findings of two studies, Mech et al. and Schulz et al. (full citations at the end of this blog). I discussed these studies in earlier blogs. They were also incorporated into the broader effort to identify predictive traits carried out by Raffa et al. (full citations at the end of this blog) and discussed in a separate blog. See the section titled “Potential” to see the exciting results of an application of the Mech et al. findings and methods.

To develop the tool, project scientists synthesized data on traits and factors representing four types of drivers: (1) insect traits, (2) tree traits (especially those associated with host defenses), (3) the relatedness between the insect’s native and North American tree hosts, and (4) the relatedness between the non-native insect and North American insects on the same tree. They tested key hypotheses, e.g., defense free space and enemy release. The team tested the tool with researchers from USDA APHIS and Canadian Food Inspection Agency (CFIA), Northeast Plant Diagnostic Network, and National Invasive Species Council.

Norway spruce (*Picea abies*) — host of 30 of the 62 insect species analyzed in Uden *et al*.; photo by Marzena via Pixabay

The research group hopes this tool will stimulate development of a global database of insects which will utilize the results of basic research on phytophagous insects and what they eat. Basic research on insects native to North America is also important and can benefit other countries that might want to develop a similar tool for their own phytosanitary needs.

The Tool’s Potential

Many of the scientists who developed the i-Tree tool have participated in an analysis of the threat to North American conifer species posed by insects native to Europe that have not yet been introduced to North America (Uden et al.). They applied the methodology from Mech et al., which is comparable to, although not identical to, the i-Tree system. They (1) created a list of 62 European insect species that appear to pose a risk to 47 species of North American conifers; (2) identified and compared the predicted likelihoods of high-impact invasion under each of four phylogenetic systems datasets; and (3) evaluated risk and vulnerability trends among insects & conifer hosts, respectively. In total they evaluated 2,914 insect–novel host pairs.

Fraser fir (*Abies fraseri*) in Great Smoky Mountains National Park; photo by James St. John via Flickr

Among their findings are the following:

Of the 2,914 pairs examined, 302 (10.4%) had a predicted risk of high impact. These pairs included 41 (66%) of the insect species and 20 (41.7%) of the conifer species. The proportion of potential invasions posing a significant risk is higher than those indicated by earlier studies.
The insect species posing a risk of high-impact invasion were spread among insect orders, with relatively high levels concentrated in Lepidoptera and Coleoptera, fewer in the Hymenoptera and Hemiptera.
Consistent with Mech et al., they found a “Goldilocks” period of evolutionary divergence of hosts exposing the North American tree species to the highest risk. Thus, if a North American conifer shared a common ancestor with the insect’s native European host ~2–10 million years ago, it was predicted to be more vulnerable to a high-impact invasion by a conifer specialist.
North American fir (Abies) and spruce (Picea) species are more vulnerable to the introduction of European conifer-specialist insects than are pines (Pinus). [Mech et al. found that trees with high shade tolerance and low drought tolerance are more vulnerable. These traits also fit fir and spruce; but not pine.] The most vulnerable tree species was red spruce (Picea rubens).

Uden et al. also say Fraser fir (Abies fraseri) and Carolina hemlock (Tsuga caroliniana) are highly vulnerable to European insect species. They identified 17 high-risk insect species for Fraser fir. Of course, both are already severely depleted by non-native insect pests (Balsam woolly adelgid and hemlock woolly adelgid, respectively). They have also been identified by the Potter et al. “Project CAPTURE” process as having high priorities for conservation efforts.

I worry that fir and spruce are less important as timber species than pines; I hope this does not result in agencies and important stakeholders assigning this risk finding a lower priority.

Uden et al. assert that their study shows that this system can identify vulnerable tree species in the absence of information about which particular insect might invade. This information helps managers focus biosecurity and management program programs on protecting the most vulnerable tree species. However, 57% of the North American conifers (27 species) were found to be vulnerable under at least one of the insect-host pairs. To further set priorities, they suggest combining predictions from this analysis with USFS Forest Inventory and Analysis (FIA) data to identify vulnerable biogeographic regions and vegetation communities. (Fraser fir and Carolina hemlock rank high under this process.) Scientists could also apply species importance indicators, such as the NatureServe Explorer plant community descriptions. They suggest linking these criteria to the USFS Early Detection Rapid Response surveillance program, link to website which currently targets specific insect species.

red pine (*Pinus resinosa*) – the pine species at greatest risk; photo by Charles Dawley via Flickr

Uden et al. also warn that their analysis focused on a narrow range of possible introduced species: insects from Europe that feed on conifers exclusively. They caution that no one should assume that tree species that have a low “vulnerability” rank in this study should be considered at low risk for all possible introduced insects. They suggest researchers should identify tree species from the wider Palearctic that are within the high-impact “Goldilocks” zone of divergence times in relation to specific North American tree species, and then identify the insects that feed on those Palearctic trees to determine the species that would have the highest predicted risk of causing a high impact on those North American conifers.

Of course, many North American tree species are not conifers! Applying the methods in Schulz et al. – now integrated into the i-Tree tool – would facilitate similar predictive findings for the angiosperms.

Participants

The importance of this project is seen in the impressive array of funders supporting it. They include:

U.S. Geological Survey John Wesley Powell Center for Analysis and Synthesis for a working group titled “Predicting the nest high-impact insect invasion: Elucidating traits and factors determining the risk of introduced herbivorous insects on North American native plants;”
USDA Forest Service National Urban and Community Forestry Advisory Council funded a working group titled “Forecasting high-impact insect invasions by integrating probability models with i-Tree from urban to continental scales”;
Nebraska Cooperative Fish and Wildlife Research Unit;
University of Washington;
USDA Forest Service Eastern Forest Environmental Threat Assessment;
National Science Foundation Long-Term Ecological Research program;
USDA Forest Service International Programs; and
USDA National Institute of Food and Agriculture (Hatch and McIntire-Stennis projects).

Scientists who created this tool:
Kathryn A. Thomas (USGS – Southwest Biological Research Center)
Travis D. Marsico (Arkansas State University)
Daniel A. Herms (The Davey Tree Expert Company)
Patrick C. Tobin (University of Washington)
Andrew Liebhold (U.S. Forest Service)
Nathan Havill (U.S. Forest Service)
Angela Mech (University of Maine)
Ashley Schulz (Mississippi State University)
Matthew Ayres (Dartmouth College)
Kamal Gandhi (University of Georgia)
Ruth A. Hufbauer (Colorado State University)

Kenneth Raffa (University of Wisconsin) Daniel

Uden (University of Nebraska-Lincoln)

Carissa Aoki (Maryland Institute College of Art)

Scott Maco (The Davey Tree Expert Company)

Angela Hoover (University of Arizona)

SOURCES

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

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

Raffa, K.F., E.G. Brockerhoff, J-C Gregoire, R.C. Hamelin, A.M. Liebhold, A. Santini, R.C. Venette, and M.J. Wingfield. 2023. Approaches to Forecasting Damage by Invasive Forest P&P: A Cross-Assessment. BioScience Vol. 73 No. 2: 85–111 https://doi.org/10.1093/biosci/biac108

Posted by Faith Campbell

www.fadingforests.org

Let’s Not Dismiss Conservation of Biodiversity While Seeking Carbon Storage in Forests

red deer on farm in New Zealand; photo by Bernard Spragg via Flickr

Among the non-native species damaging forest systems are mammals – introduced deer, goats and sheep, and swine, … These animals have the greatest impacts on island systems that are sufficiently isolated that they have no native terrestrial mammals, e.g., Hawai`i and New Zealand. Several New Zealanders have published a study of their impacts (Allen et al.; full citation at end of the blog). The focus of their analysis is the native forests’ ability to sequester carbon and thus mitigate climate change. The scientists are well aware, however, that forests provide many other ecosystem values and services, including biodiversity, water supply and quality, etc.

Introduced ungulates can have many direct effects: reduction and damage to understory biomass, depletion of seedling regeneration, exacerbated soil erosion, and local nutrient imbalances. Mammals’ browsing can modify the composition of plant communities by favoring abundance of unpalatable species. Changes also can alter ecosystem functions associated with nutrient cycling, e.g., by reducing nutrient returns to the soil and altering rates of litter decomposition

In these ways, introduced ungulates exert long-term impacts on forests’ capacity to store carbon.

Allen et al. aimed to determine the extent of these effects on forests’ capacity to store carbon, both above- and below-ground, and on forest structure and diversity. The authors compared data from 26 pairs of sites across New Zealand – half with ungulate exclosures and half adjacent unfenced control plots. The ungulate exclosures had all been established for at least 20 years. All the sites were in species-rich communities of conifers and broadleaved evergreen angiosperm trees. These forests (1) cover about one-third of the country’s remaining mature natural forest; (2) contain tree species of a wide range of palatability to ungulate herbivores; and (3) have been named a conservation priority for forest carbon management. The ungulates present on the plots were European red deer (Cervus elaphus), fallow deer (Dama dama), sika deer (Cervus nippon), and feral goats (Capra hircus).

They assert that New Zealand is a good place to do this type of study because ungulate introductions are relatively recent so their impacts are well documented.

Allen et al. found that managing invasive ungulates makes valuable contributions to conserving biodiversity but not to carbon sequestration. They found little difference in total ecosystem carbon between ungulate exclosures and unfenced control plots. Most of the difference they did find was explained by the biomass of the largest tree within each plot. As they point out, these large trees have been unaffected by invasive ungulates introduced during the last 20–50 years. However, they believe ungulate-caused changes in understory biomass, species composition, and functional diversity might result in major shifts in the diversity and composition of regenerating species. Hence, longer term consequences for both ecosystem processes and storage of forest carbon storage can be expected.

Indeed, excluding ungulates did increase the abundance and diversity of saplings and small trees. The basal area of the smallest class of tree size was 70% greater. Species richness of small trees and saplings was 44% and 68% higher, respectively. This difference had little impact on overall carbon storage, however, because the small trees and saplings store only about 5%. In contrast, the largest tree size class (dbh =/>30 cm), with their roots, contributed 44% of total ecosystem carbon in both exclosure and control plots. The largest effects of exclosures on carbon stocks were in early successional stands, e.g., those affected by such major disturbances as windthrow, volcanic activity, or landslides.

Climate change is expected to cause surprising interactions among forest productivity, herbivory, disturbance. Allen et al. suggest that authorities should focus on excluding ungulates on these highly productive regenerating forests rather than old-growth forests. I am disturbed by this suggestion. It exposes the most biologically diverse forests to continuing damage.

Data gaps

New Zealand has many long-lived, slow-growing tree species. Recruitment of understory trees is already low across both main islands. This situation has been attributed to ungulate browsing. Over centuries, this might result in shifts in the canopy composition. Allen et al. call for additional research to increase our understanding of how browsing and other short-and long-term drivers affect the regeneration of large trees. Also, data on soil CO₂ emissions needs better integration.

Australian brushtail possum; photo by Peter Firminger via Flickr

The study did not consider the impact of other introduced mammals, such as feral pigs (Sus scrofa), rodents, and Australian brushtail possum (Trichosurus vulpecula). The possum is known to damage New Zealand trees. The scientists did not explain this omission; I assume it might have been the result of either lack of resources to support a broader study or differences in management strategies – or both?

I note that the study also did not address the extent to which non-native pathogens threaten these large trees. In response to my query, Kara Allen said that their plots did not include many kauri (Agathis australis) trees, so the severe dieback disease caused by Phytophthora agathidicida did not affect their results. Naturally regenerating kauri is limited to a small area of warm temperate rainforests located at the top of the North Island. So kauri potentially play a relatively small role in terms of overall carbon stocks in New Zealand’s forests. On the other hand, Allen says that myrtle rust (Austropuccinia psidii) could have a major impact on New Zealand forests’ carbon storage. Trees in the host family, Myrtaceae, are ecologically important across both islands. Also, they comprise a large portion of overall forest carbon stocks (ranked in the top 5 largest families for above- and belowground biomass). An example is southern rata (Mterosideros umbellata), which are preferentially fed on by Australian brush possum.

Bernd Blossey, (free access!) who has long studied the role of high deer populations in North American forests, praises the study’s attempt to measure data, not just rely on models, and its inclusion of soil. However, he notes other limitations of the New Zealand study:

The small exclosures (20 x 20 m) are subject to edge effects. Some of Blossey’s exclosures occupy 2 hectares.
Twenty years is too short a time for analysis of such long-term processes as carbon sequestration and regeneration of slow-growing trees. Therefore, any results must be considered preliminary. Furthermore, no one recorded any differences in carbon sequestration of the paired plots at the time the exclosures were set up.
There’s no mention of possible impacts by introduced earthworms.

Dr. Blossey recognizes that the current study’s authors cannot re-do actions taken decades in the past. Still, the data gaps reduce the value of the findings.

I conclude that uncertainties continue due to: the long timelines of species’ regeneration and growth to full sizes; the requirement for large exclosures; the complexity of factors affecting carbon sequestration; and probably other influences.. Managers trying to maximize carbon sequestration are forced to act without truly knowing the best strategy or how their actions will affect the future.

For more about invasive mammals’ impacts in U.S. forests, also see the study by USFS scientists, Poland et al. (full citation listed in sources). One can enter “mammal” in the search box for the on-line PDF.

SOURCES

Allen, K., P.J. Bellingham, S.J. Richardson, R.B. Allen, L.E. Burrows, F.E. Carswell, S.W.Husheer, M.G. St. John, D.A. Peltzer, M. Whenua. 2023. Long-term exclusion of invasive ungulates alters tree recruitment and functional traits but not total forest carbon. Ecological Applications. 2023; e2836. https://onlinelibrary.wiley.com/r/eap

Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector. Springer Verlag. The on-line version as at https://link.springer.com/book/10.1007/978-3-030-45367-1

Posted by Faith Campbell

www.fadingforests.org

Global Overview of Bioinvasion in Forests

black locust – one of the most widespread invasive tree species on Earth; photo via Flickr

In recent years there has been an encouraging effort to examine bioinvasions writ large see earlier blogs re: costs of invasive species – here and here. One of these products is the Routledge Handbook of Biosecurity and Invasive Species (full citation at end of this blog). I have seen only the chapter on bioinvasion in forest ecosystems written by Sitzia et al. While they describe this situation around the globe, their examples are mostly from Europe.

Similar to other overviews, this article re-states the widely-accepted attribution of rising numbers of species introductions to globalization, especially trade. In so doing, Sitzia et al. assert that the solution is not to curtail trade and movement of people, but to improve scientific knowledge with the goal of strengthening biosecurity and control programs. As readers of this blog know, I have long advocated more aggressive application of stronger restrictions on the most high-risk pathways. Still, I applaud efforts to apply science to risk assessment.

Sitzia et al. attempt to provide a global perspective. They remind readers that all major forest ecosystems of Earth are undergoing significant change as a result of conversion to different land-uses; invasion by a wide range of non-native introduced species—including plants, insects, and mammals; and climate change. These change agents act individually and synergistically. Sitzia et al. give greater emphasis than other writers to managing the tree component of forests. They explain this focus by asserting that forest management could be either the major disturbance favoring spread of non-native species or, conversely, the only way to prevent further invasions. They explore these relationships with the goal of improving conservation of forest habitats.

Japanese stiltgrass invasion; photo by mightyjoepye via Flickr

Sitzia et al. focus first on plant invasions. They contend that – contrary to some expectations – plants can invade even dense forests despite competition for resources. They cite a recent assessment by Rejmánek & Richardson that identified 434 tree species that are invasive around Earth. Many of these species are from Asia, South America, Europe, and Australia. These non-native trees can drive not only changes in composition but also in conservation trajectories in natural forests. However, the example they cite, Japanese stilt grass (Microstegium vimineum) in the United States, is not a tree! Sitzia et al. note that in other cases it is difficult to separate the impacts of management decisions, native competitive species, and non-native species.

Sitzia et al. note that plant invasions might have a wide array of ecological impacts on forests. They attempt to distinguish between

“drivers” of environmental change – including those with such powerful effects that they call them “transformers”;
“passengers” whose invasions are facilitated by other changes in ecosystem properties; and
“backseat drivers” that benefit from changes to ecosystem processes or properties and cause additional changes to native plant communities.

An example of the last is black locust (Robinia pseudoacacia). This North American tree has naturalized on all continents. It is a good example of the management complexities raised by conflicting views of an invasive species’ value, since it is used for timber, firewood, and honey production.

Sitzia et al. then consider invasions by plant pathogens. They say that these invasions are one of the main causes of decline or extirpations in tree populations. I applaud their explicit recognition that even when a host is not driven to extinction, the strong and sudden reduction in tree numbers produces significant changes in the impacted ecosystems.

American chestnut – not extinct but ecological role gone; photo by F.T. Campbell

Sitzia et al. contend that social and economic factors determine the likelihood of a species’ transportation and introduction. Specifically, global trade in plants for planting is widely recognized as being responsible for the majority of introductions. Introductions via this pathway are difficult to regulate because of the economic importance (and political clout) of the ornamental plants industry, large volumes of plants traded, rapid changes in varieties available, and multiple origins of trade. As noted above, the authors seek to resolve these challenges by improving the scientific knowledge guiding biosecurity and control programs. In the case of plant pathogens, they suggest adopting innovative molecular techniques to improve interception efficiency, esp. in the case of latent fungi in asymptomatic plants.

The likelihood that a pathogen transported to a new region will establish is determined by biogeographic and ecological factors. Like other recent studies, Sitzia et al. attempt to identify important factors. They name a large and confusing combination of pathogen- and host-specific traits and ecosystem conditions. These include the fungus’ virulence, host specificity, and modes of action, reproduction, and dispersal, as well as the host’s abundance, demography, and phytosociology. A key attribute is the non-native fungus’ ability to exploit micro-organism-insect interactions in the introduced range. (A separate study by Raffa et al. listed Dutch elm disease as an example of this phenomenon.) I find it interesting that they also say that pathogens that attack both ornamental and forest trees spread faster. They do not discuss why this might be so. I suggest a possible explanation: the ornamental hosts are probably shipped over wide areas by the plant trade.

surviving elms in an urban environment; photo by F.T. Campbell

Sitzia et al. devote considerable attention to bioinvasions that involve symbiotic relationships between bark and ambrosia beetles and their associated fungi. These beetles are highly invasive and present high ecological risk in forest ecosystems. Since ambrosia beetle larvae feed on symbiotic fungi carried on and farmed by the adults inside the host trees, they are often polyphagous. Bark beetles feed on the tree host’s tissues directly, so they tend to develop in a more restricted number of hosts. Both can be transported in almost all kinds of wood products, where they are protected from environmental extremes and detection by inspectors. Sitzia et al. specify the usual suspects: wood packaging and plants for planting, as ideal pathways. These invasions threaten indigenous species by shifting the distribution and abundance of certain plants, altering habitats, and changing food supplies. The resulting damage to native forests induces severe alterations of the landscape and causes economic losses in tree plantations and managed forests. The latter losses are primarily in the high costs of eradication efforts – and their frequent failure.

Eucalyptus plantation in Kwa-Zulu-Natal, South Africa; photo by Kwa-Zulu-Natal Department of Transportation

Perhaps their greatest contribution is their warning about probable damage caused by invasive forest pests in tropical forests. (See an earlier blog about invasive pests in Africa.) Sitzia et al. believe that bark and ambrosia beetles introduced to tropical forests threaten to cause damage of the same magnitude as climate change and clear cutting, but there is little information about such introductions. Tropical forests are exposed to invading beetles in several ways:

1) A long history of plant movement has occurred between tropical regions. Sitzia et al. contend that the same traits sought for commercial production contribute to risk of invasion.

2) Logging and conversion of tropical forests into plantation forestry and agriculture entails movement of potentially invasive plants to new areas. Canopies, understory plant communities, and soils are all disturbed. Seeds, insects, and pathogens can be introduced via contaminated equipment.

3) Less developed nations are often at a disadvantage in managing potential invasion. Resources may be fewer, competing priorities more compelling, or potential threats less obvious.

Sitzia et al. call for development of invasive species management strategies that are relevant to and realistic for less developed countries. These strategies must account for interactions between non-native species and other aspects of global environmental change. Professional foresters have a role here. One clear need is to set out practices for dealing with conflicts between actors driven by contrasting forestry and conservation interests. These approaches should incorporate the goals of shielding protected areas, habitat types and species from bioinvasion risk. Sitzia et al. also discuss how to address the fact that many widely used forestry trees are invasive. (See my earlier blog about pines planted in New Zealand.)

planted forest in Sardinia, Italy; photo by Torvlag via Flickr

In Europe, bark beetle invasions have damaged an estimated ~124 M m²between 1958 and 2001. Sitzia et al. report that the introduction rate of non-native scolytins has increased sharply. As in the US, many are from Asia. They expect this trend to increase in the future, following rising global trade and climate change. Southern – Mediterranean – Europe is especially vulnerable. The region has great habitat diversity; a large number of potential host trees; and the climate is dry and warm with mild winters. The region has a legacy of widespread planting of non-native trees which are now important components of the region’s economy, history and culture. These include a significant number of tree species that are controversial because they are – or appear to be – invasive. Thus, new problems related to invasive plants are likely to emerge.

Noting that different species and invasion stages require different action, Sitzia et al. point to forest planning as an important tool. Again the discussion centers on Europe. Individual states set forest policies. Two complications are the facts that nearly half of European forests are privately owned; and stakeholders differ in their understanding of the concept of “sustainability”. Does it mean ‘sustainable yield’ of timber? Or providing multiple goods and services? Or sustaining evolution of forest ecosystems with restrictions on the use of non-native species? Resolving these issues requires engagement of all the stakeholders.

Sitzia et al. say there has recently been progress. The Council of Europe issued a voluntary Code of Conduct on Invasive Alien Trees in 2017 that provides guidelines on key pathways. A workshop in 2019 elaborated global guidelines for the sustainable use of non-native tree species, based on the Bern Convention Code of Conduct on Invasive Alien Trees. The workshop issued eight recommendations:

Use native trees, or non-invasive non-native trees;
Comply with international, national, and regional regulations concerning non-native trees;
Be aware of the risk of bioinvasion and consider global change trends;
Design and adopt tailored practices for plantation site selection and silvicultural management;
Promote and implement early detection and rapid response programs;
Design and adopt practices for invasive non-native tree control, habitat restoration, and for dealing with highly modified ecosystems;
Engage with stakeholders on the risks posed by invasive NIS trees, the impacts caused, and the options for management; and
Develop and support global networks, collaborative research, and information sharing on native and non-native trees.

SOURCE

Sitzia, T., T. Campagnaro, G. Brundu, M. Faccoli, A. Santini and B.L. Webber. 2021 Forest Ecosystems. in Barker, K. and R.A. Francis. Routledge Handbook of Biosecurity and Invasive Species. ISBN 9780367763213

Posted by Faith Campbell

www.fadingforests.org

Analysis of Methods to Predict a New Pest’s Invasiveness: Which Work Best Under What Conditions?

spotted lanternfly – could we have predicted its arrival? Its Impacts? Photo by Holly Ragusa, Pennsylvania Department of Agriculture

As readers of my blogs know, I wish to prevent introduction and spread of tree-killing insects and pathogens and advocate tighter and more pro-active regulation as the most promising approach. I cannot claim to have had great success.

Of course, international trade agreements have powerful defenders and the benefit of inertia. And in any case, prevention will be enhanced by improving the accuracy of predictions as to which specific pests are likely to cause significant damage, which are likely to have little impact in a naïve ecosystem. This knowledge would allow countries to can then focus their prevention, containment, and eradication efforts on this smaller number of organisms.

I applaud a group of eminent forest entomologists and pathologists’ recent analysis of widely-used predictive methods’ efficacy [see Raffa et al.; full citation at the end of this blog]. I am particularly glad that they have included pathogens, not just insects. See earlier blogs here, here, here, and here.

I review their findings in some detail in order to demonstrate their importance. National and international phytosanitary agencies need to incorporate this information and adopt new strategies to carry out their duty to protect Earth’s forests from devastation by introduced pests.

Raffa et al. note the usual challenges to plant health officials:

the high volumes of international trade that can transport tree-killing pests;
the high diversity of possible pest taxa, exacerbated by the lack of knowledge about many of them, especially pathogens;
the restrictions on precautionary approaches imposed by the World Trade Organization’s Sanitary and Phytosanitary Agreement (the international phytosanitary system) – here, here, and here.
the high cost and frequent failure of control efforts.

ash trees killed by emerald ash borer; Mattawoman Creek, Maryland; photo by Leslie A. Brice

The Four Approaches to Predicting Damaging Invaders

At present, four approaches are widely used to predict behavior of a species introduced to a naïve environment:

(1) pest status of the organism in its native or previously invaded regions;

(2) statistical patterns of traits and gene sequences associated with high-impact pests;

(3) sentinel plantings to expose trees to novel pests; and

(4) laboratory tests of detached plant parts or seedlings under controlled conditions.

Raffa et al. first identify each method’s underlying assumptions, then discuss the strengths and weaknesses of each approach for addressing three categories of biological factors that they believe explain why some organisms that are relatively benign, sparse, or unknown in their native region become highly damaging in naïve regions:

(1) the lack of effective natural enemies in the new region compared with the community of predators, parasites, pathogens, and competitors in the historical region (i.e., the loss of top-down control);

(2) the lack of evolutionary adaptation by naïve trees in the new region compared with long-term native interactions that select for effective defenses or tolerance (i.e., the loss of bottom-up control); and

(3) novel insect–microbe associations formed in invaded regions in which one or both members of the complex are non-native, resulting in increased vectoring of or infection courts for disease-causing pathogens (i.e., novel symbioses). I summarize these findings in some detail later in this blog.

Most important, Raffa et al. say none of these four predictive approaches can, by itself, provide a sufficiently high level of combined precision and generality to be useful in predictions. Therefore, Raffa et al. outline a framework for applying the strengths of the several approaches (see Figure 4). The framework can also be updated to address the challenges posed by global climate change.

Raffa et al. repeatedly note that lack of information about pests undercuts evaluation efforts. This is especially true for pathogens and the processes determine which microbes that are innocuous symbionts in co-evolved hosts become damaging pathogens when introduced to naïve hosts in new ecosystems.

Findings in Brief

Raffa et al. found that:

Previous pest history in invaded environments provides greater predictive power than population dynamics in the organism’s native regions.
Models comparing pest–host interactions across taxa are more predictive when they incorporate phylogenies of both pest and host. Traits better predict a pest’s likelihood of transport and establishment than its impact.
Sentinel plantings are most applicable for pests that are not primarily limited to older trees. Ex patria sentinel plantations are more likely to detect pest species liberated by loss of bottom-up controls than top-down controls, i.e., most fungi and woodborers but not insect defoliators.
Laboratory tests are most promising for pest species whose performance on seedlings and detached parts (e.g., leaves) accurately reflects their performance on live mature trees. They are thus better at predicting impacts of insect folivores and sap feeders than woodborers or vascular wilt pathogens.

Raffa et al. also ask some fundamental questions:

How realistic is it to expect reliable predictions, given the uniqueness of each biotic system?
When should negative data – lack of data showing a species is invasive – justify decisions not to act? Especially when there are so many data gaps?
Who should make decisions about whether to act? How should the varying values of different social sectors be incorporated into decisions?

Raffa et al. identify critical areas for improved understanding:

1) Statistical tools and estimates of sample size needed for reliable forecasts by the various approaches.

2) Reliability, breadth, and efficiency of bioassays.

3) Processes by which some microorganisms transition from saprophytic to pathogenic lifestyles.

4) Procedures for scaling up results from bioassays and plantings to ecosystem- and landscape-level dynamics.

5) Targetting and synergizing predictive approaches and methods for more rapid and complete information transfer across jurisdictional boundaries.

I am struck by two generalizations:

While most introduced forest insects are first detected in urban areas, introduced pathogens are more commonly detected in forests. I suggest that more intensive surveys of urban trees and “sentinel gardens” might result in detection of pathogens before they reach the forest.
Enemy release is rarely documented as the primary basis for pathogens that cause little or no impact in their native region but become damaging in an introduced region. Enemy release appears generally more important with folivores and sap feeders than with woodborers.

Detailed Evaluation of Predictive Methodologies

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

Empirical assessment of pest status in previously occupied habitats

This is the most commonly applied method now, partly because it seems to follow logically from the World Trade Organization’s requirement that national governments provide scientific evidence of risk to justify adopting phytosanitary measures. The underlying assumption is that species that have caused damage in either their native or previously invaded ranges are those most likely to cause damage if introduced elsewhere. The corollary is that species that have not previously caused damage are unlikely to cause significant harm in a new ecosystem.

As noted above, Raffa et al. found that a species’ damaging activity in a previously invaded area can help indicate likely pest status in other regions. However, its status — pest or not — in its native range is not predictive. See Table 1 for numerous examples of both pests and non-pests. For example, Lymantria dispar has proved damaging in both native and introduced ranges. Ips typographus has not invaded new territories despite being damaging in its nature range and frequently being transported in wood. White pine blister rust is not an important mortality source on native species in its native range but is extremely damaging in North America.

Raffa et al. also note the importance of whether effective detection and management strategies exist in determining a pest’s impact ranking. Insects are more easily detected than pathogens; some respond to long distance attractants such as pheromones or plant volatiles. These methods can include insect vectors of damaging pathogens.

Re: the difficulty of assessing insect–microbe associations, they name several examples of symbionts which have caused widespread damage to naïve hosts: laurel wilt in North America; Sirex noctilio and Amylosterum areolatum around the Southern Hemisphere; Monochamus spp. and Bursaphelenchus xylophilus in Asian and European pines. Dutch elm disease illustrates a widespread epidemic caused by replacement of a nonaggressive native microorganism in an existing association with a non-native pathogen. Beech bark disease resulted from independent co-occurrence of an otherwise harmless fungus and harmless insect.

In sum, “watch” lists are disappointingly poor at identifying species that are largely benign in their native region but become pests when transported to naive ecosystems. Many of our most damaging pests are in this group. Raffa et al. note that this is not surprising because naïve systems lack the very powerful top-down, bottom-up, and lateral forces that suppress pests’ populations in co-adapted system. Countries often try to overcome this uncertainty by shifting to pathway mitigation and other “horizontal measures” – as I have often advocated. Raffa et al. emphasize that such approaches are costly to implement and constrain free trade.

Predictive models based on traits of pests and hosts

Predictive models provide the most all-encompassing and logistically adaptable of the forecasting approaches. Typically, models consider various components of risk, e.g. probability of transport, probability of establishment, anticipated level of damage.

The overriding assumption is that patterns emerging from either previous invasions or basic biological relationships can provide reliable predictions of impacts that might result from future invasions. However, Raffa et al. note that the models’ reliability and specificity are hampered by small sample sizes and data gaps.

They found that specific life history traits have proved to be more predictive of insect — and to a lesser extent fungal – establishment than of impact. Earlier studies [Mech et al. (2019) and Schulz et al. (2021)] found no association between life history traits and impacts for either conifer-feeding or angiosperm-feeding insects.

Some traits of pathogens have been linked to invasion success, e.g., dispersal distance, type of reproduction, spore characteristics, and some temperature characteristics for growth and parasitic specialization. Raffa et al. say that root-infecting oomycete pathogens have a broader host range and invasive range than those that attack aboveground parts. Oomycetes that grow faster and produce thick-walled resting structures have broader host ranges. Phenotypic plasticity is also important. Raffa et al. say that those organisms that require alternate hosts can be limited in their ability to establish. However, they don’t mention that – once introduced — they can have huge impacts, as the example of white pine blister rust illustrates.

Raffa et al. say that phylogenetic distance of native and introduced hosts is more predictive for foliar ascomycetes than for basidiomycete and oomycete pathogens with broad host ranges. They suggest predictive ability can be improved by incorporating other factors, e.g., feeding guild. They note that the findings of Mech et al. and Schulz et al. (see links above) show the importance of both host associations with pests and phylogenetic relationships between native and naïve hosts for predicting impacts.

Geography is important: while there is a greater chance of Northern Hemisphere pests invading in the same hemisphere, this is not universal, as shown by Sirex (of course, the woodwasp is attacking hosts native to the Northern Hemisphere – pines).

Genomic analyses have been used more often with pathogens. There are two general approaches:

trees killed by chestnut blight; USDA Forest Service photo

1) Comparing the genomes of different species to identify the determinants associated with certain traits or lifestyles. For example, a post hoc analysis of the genus Cryphonectria could distinguish nonpathogenic species from the chestnut blight fungus C. parasitica.

2) Using genomic variation within a single species to identify markers associated with traits. Genome sequencing of a worldwide collection of the pathogens that cause Dutch elm disease revealed that some genome regions that originated from hybridization between fungal species contained genes involved in host–pathogen interactions and reproduction, such as enhanced pathogenicity and growth rate.

Raffa et al. point out that the growth of databases will facilitate genomic approaches to identify important invasiveness and impact traits, such as sporulation, sexual reproduction, and host specificity.

At present, Raffa et al. believe that models based on traits, phylogeny, and genomics offer potential for a rapid first pass to predicting levels of pest damage. However, assessors must first have a list of candidate pest species and detailed information about each. Plus there is still too much uncertainty to rely exclusively on the models.

Sentinel trees

Raffa et al. say that sentinel trees can potentially provide the most direct tests of tree susceptibility and the putative impact of introduced pests. Three types of plantations offer different types of information:

In patria sentinels [= sentinel nurseries] = native trees strategically located in an exporting country and exposed to native pests. The intention is to detect problematic hitchhikers before they are transported to a new region. These plantings are useful for commodity risk assessment. However, all the taxa associated with the sentinel trees must be identified to ascertain whether they can become a threat to plants in the new ecosystem.

Ex patria plantings [= sentinel plantations] = trees from an importing country are planted in an exporting country with the aim of assessing new pest–host associations. These plantings are most useful for identifying threats that arise primarily from lack of coevolved host tree resistance (i.e., loss of bottom-up control). They cannot predict the effects of lack of co-adapted natural enemies in the importing region (i.e., loss of top-down control). Plantings are thus more helpful in predicting impacts by pathogens and woodborers than folivores and sap feeders. However, ex patria plantings cannot predict pest problems that arise from novel microbial associations, or increased susceptibility to native pests.

Trees in botanic gardens, arboreta, large-scale plantations, and urban parks and yards can provide information on both existing native-to-native associations and new pest–host associations. Analyzing these plantings can be useful for studying host-shift events and novel pest–host associations. Again, all the taxa associated with the sentinel trees must be identified to ascertain whether they can become a threat to plants in the new ecosystem. Monitoring these planting have detected previously unknown plant–host associations (such as polyphagous shot hole borer and tree species in California and South Africa), and entirely unknown taxa. Pest surveillance in urban areas can also facilitate early detection, thereby strengthening the possibility of eradication.

PSHB attack on *Erythrina caffri*; photo by Paap

Sentinel tree programs are limited by 1) small sample sizes; 2) immature trees; and 3) the fact that trees planted outside their native range might not be accurate surrogates for the same species in native conditions. Some of these issues can be reduced by establishing reciprocal international agreements among trading partners; the International Plant Sentinel Network helps to coordinate these collaborations.

Botanic gardens and arboreta have the advantage of containing adult trees; this is important because pest impacts can vary between sapling to mature trees. However, they probably contain only a few individuals per plant species, usually composed of narrow genetic base.

Large-scale plantations of exotic tree species, e.g., exotic commercial plantations, comprise large numbers of trees planted over large areas with varied environmental conditions, and they stand for longer times. Still, they commonly have a narrow genetic base that might not be representative of wild native plants. Also, only a few species are represented in commercial plantations.

Raffa et al. report that experience in commercial Eucalyptus plantations in Brazil alerted Australia to the threat from myrtle rust (Austropuccinia psidii). However, in an earlier blog I showed that Australia did not act quickly based on this knowledge.

Laboratory assays using plant parts or seedlings

Laboratory tests artificially challenge seedlings, plant parts (e.g., leaves, branches, logs), or other forms of germplasm of potential hosts to determine their vulnerability. These tests are potentially powerful because they are amenable to experimental control, standardized challenge, and replication. They also avoid many of the logistical constraints of sentinel plantings. Finally, they can be performed relatively rapidly.

The key underlying assumption is that results can be extrapolated to predict injury to live, mature trees under natural conditions. The validity of this assumption depends on the degree to which exogenous biotic and abiotic stressors affect the outcomes. Raffa et al. report that environmental stressors tend to more strongly influence tree interactions with woodborers than folivores.

These assumption are more likely to be met by pathogens that infect shoots or young tissues, such as the myrtle rust pathogen Austropuccinia psidii, ash dieback pathogen Hymenoscyphus fraxineus, and the sudden oak death pathogen Phytophthora ramorum.

The host range of and relative susceptibilities to insects is usually tested on twigs bearing foliage for defoliators and sap suckers; bark disks, logs, or branches for bark beetles, ambrosia beetles, and wood borers. These methods do not work as well for bark beetle species that attack mature trees in which active induced responses and transport of resins through established ducts are critically important.

The major advantages of laboratory tests is that they readily incorporate both positive (known hosts) and negative (known nonhosts) controls, can provide a range of environmental conditions, can be performed relatively rapidly, are statistically replicable at relatively low costs, and can test multiple host species and genotypes simultaneously. The ability to statistically replicate a multiplicity of environmental combinations and species is particularly valuable for evaluating relationships under anticipated future climatic conditions.

However, there are several important limitations. In testing pathogens, environmental conditions required for infection are often unknown. Choice of non-conducive conditions might result in false negatives; choice of too-conducive conditions might result in exaggerating the likelihood of infection. Results of tests of insect pests can vary depending on whether the insects are allowed to choose among potential host plants. Other complications arise when the pest being evaluated requires alternate hosts. In addition, seedlings are not always good surrogates for mature trees – especially as regards pathogens and bark, wood-boring and root collar insects. Folivores are less affected by conditions. Plus, the costs can be significant since they involve maintaining a relatively large number of viable and virulent pathogen cultures, insects, and candidate trees in quarantine.

Finally, although lab assays are well suited for identifying new host associations, results might not be amenable to scaling up to predict a pest’s population-level performance in a new ecosystem. Scaling up is especially problematic for those insect species whose dynamics are strongly affected by trophic interactions.

SOURCE

Posted by Faith Campbell

www.fadingforests.org

Eradicating Invasive Species: You need “social license” to succeed

spread of non-native conifers in mountains of New Zealand; photos by Richard Bowman; New Zealand government website

As those of us who want to “do something” to counter bioinvasions struggle to mobilize both the resources and the political will necessary, I rejoice that more studies are examining what factors affect “social license” [= public approva] for such programs. One such study was recently published in New Zealand — Mason et al. (full citation at the end of the blog). New Zealand enjoys a greater appreciation of the uniqueness of its biology and awareness of invasive species’ impacts than the United States. However, their findings might provide useful guidance in the US and elsewhere.

Mason et al. sought to understand motivations of, and constraints on, those local groups responsible for controlling the spread of non-native conifers into New Zealand’s remnant native ecosystems. Non-forest ecosystems across much of the country are at risk of rapidly transforming into exotic conifer forests. For these reasons, authorities are pressing for timely removal of existing seed sources, that is, mature non-native conifer trees of several species. The blog I posted earlier apparently describes effects of conifer invasions in lowland ecosystems, whereas the Programme described here is focused on high-elevation systems.

The eradication effort in the study is the National Wilding Conifer Control Programme, establishedin 2016. A large increase in funding provided during the COVID-19 lockdown made it practical to try to eradicate seed sources from large swathes of vulnerable land. The Programme coordinates control efforts across the country, working across property and land-tenure boundaries. Landowners are expected to cover 20% of the cost of removing conifers from their land. Since removing all seed sources of high-risk conifer species from the landscape is key to achieving long-term goals, success is unlikely if significant seed sources are allowed to persist.

Mason et al. combined workshops, questionnaires, and site visits to gather data on particular aspects of this Programme. They found that social resistance, rather than lack of scientific knowledge, was often the main barrier to success in managing widespread invasive species. The authors do not address whether the fact that only 30 people provided information for their study might undermine the reliability of their findings.

map of conifer wilding sites; adapted from *Wilding conifers – New Zealand history and research background*, a presentation by Nick Ledgard at the “Managing wilding conifers in New Zealand – present and future” workshop (2003)

The authors suggest that the main benefit of scientific information might be to increase stakeholders’ support for management interventions — rather than to guide manager’ decisions about which strategies to pursue. To support social license, invasive species research programs might need to focus not only on cost-effective control technologies and strategies, but – perhaps especially — the benefits (both tangible and intangible) of invasive species control for society.

Mason et al. found that people were motivated to combat conifer invasions by impacts with direct influence on humans or human activities (e.g., reduced water yield, damage to infrastructure from wildfires, reduced tourist activities due to landscape transformation) and also by impacts affect ecosystems (e.g., impacts on biodiversity, aquatic ecosystems and landscapes).

People objected to control or eradication programs primarily because of social concerns. These included the unwillingness of landowners to participate and regulatory frameworks that had perverse incentives.

Mason et al. called for greater efforts by scientists to persuade stakeholders [p1] to allow removal of “wilding” conifers from private land and development of more appropriate regulations. They found that forecasting models were particularly effective in persuading people to support these efforts. It seems to me that outreach teams might need “translators” to convert scientists’ findings to information that would be more useful by stakeholders.

The authors concede that the “wilding conifer” situation has unique attributes. First, invading conifers present a stark, easily seen difference between native and invaded ecosystems. Second, some – but not all—stakeholders appreciate the uniqueness of New Zealand’s biomes. Third, the impacts of conifer invasion are sufficiently well known that they can be described succinctly and accurately.

Do these unique attributes undercut the relevance of this study to North America? It is still true that ongoing support from local stakeholders (including landowners and community groups) influences the effectiveness or profitability of managing invasive species. .It is also true that groups’ varying values affect willingness to support the activities.

Mason et al. think through the issue of stakeholders’ conflicting perspectives on the value of particular invasive species and the values threatened by that invader. These can include ethical or safety concerns around management methods, particularly regarding toxins and genetic modification. Economoic costs are also a factor – especially if the landowner must pay all or some of them.

I find it interesting that the government simultaneously funded a 5-year research program to study various issues regarding the spread, ecosystem impacts, and control of wilding conifers. The result is the Mason et al. study discussed here. I wish the U.S. funded independent analyses of its invasive species programs!

*Pinus contorta* – the most rapidly growing Pinus introduced to New Zealand; photo by Walter Siegmund / Wikimedia

More Details, Policy Suggestions

Workshop attendees unanimously identified landscape impacts as a reason for controlling wilding conifers. This primarily concerned the loss of New Zealand’s visual heritage or cultural identity rather than loss of native species’ habitats. When the landowner was raised in Europe, these cultural or heritage values sometimes had the opposite effect, since they see conifer forests as important components of “natural” landscapes.

Currently, landowner funding and permission is required for conifer removal. Some individual landowners want to establish new forestry plantings. Some resist removal of existing forestry plantations (which provide income) and shelter belts (which provide shelter for livestock in high country landscapes). Some landowners were unwilling to pay their 20% of removal costs. Or they objected to certain conifer control methods—particularly helicopter spraying of herbicides. New Zealand’s regulatory process also requires years of negotiating to remove standing trees – further delaying any action. In theory, landowners who resist removal could be prosecuted under the Biosecurity Act. However, this approach has never been tried for removing wilding conifers.

Mason et al. suggested several changes in policy to overcome some of these barriers.

First, forestry consultants can “game” the wilding conifer “risk calculator” to obtain government approval to establish conifer plantations in high-risk environments. The authors suggest that authorities create a “liability calculator.” Under this system, landowners wishing to retain conifers on their land for whatever reason would be liable for any subsequent containment costs. However, developing such a tool requires more finely-scaled models of conifer spread.

Second, given the high costs of combatting invading conifers if seed sources are allowed to persist, they suggested that it might be more cost-effective for the control program to pay for plantation removal under New Zealand’s Emissions Trading Scheme.

Given the overwhelmingly social and regulatory nature of barriers to success, the primary role for scientific information is providing assessments of outcomes in the absence of wilding conifer control. Preferred messages were return-on-investment estimates and forecasts of ecosystem impacts, particularly relating to biodiversity loss, water yield reduction, and wildfire hazard. Forecasts were key to demonstrating that management interventions reduced future control costs and avoided environmental impacts which large sections of the community value (i.e. biodiversity loss, reduction in water yield and agricultural productivity, increased wildfire risks). Practitioners felt that forecasting models might also channel research toward areas of high uncertainty. Mason et al. recognize the difficulties presented by inherent complexity of ecological systems. However, they think “good practice” guidelines on forecasting are emerging.

The authors find that information content and presentation need to be tailored to the various audiences – most of whom lack experience in interpreting data from environmental forecasting models. They suggest that outreach materials focus on clear illustration of the tangible and intangible benefits of wilding conifer management rather than detailed explorations of scenarios. Participants suggested ways to improve the web tool to make it more accessible to a non-expert audience.

Mason et al. mention aspects that require balancing, but don’t suggest criteria for making these choices. They say it is important to include all relevant stakeholders in invasive species management governance bodies. The absence of stakeholders with positive attitudes to wilding conifer invasions led to unanticipated external social resistance to the Programme. They recognize that including stakeholders with conflicting interests might obstruct the decision-making process. Also, in areas where there has been success in containing conifers’ spread, people can’t see invading trees, so they don’t recognize the problem. They also note that existing data do not adequately recognize risks of spread from deliberately planted seed sources such as shelter-belts, plantations and amenity plantings. The authors do not discuss how to integrate these data into analyses and public outreach.

Finally, Mason et al. recognize that many other factors strongly influence stakeholders’ willingness to support invasive species control programs, especially the level of trust and strength of relationships between bioinvasion program staff and stakeholders.

Also, they suggest topics for future research: assessing how well forecasting models are integrated with communications with stakeholders; how qualitative and quantitative research methods in different fields might support one another; and empirical tests to measure the relative effects on social license of a) involving stakeholders in developing models, b) using forecasts to assess the consequences of different management decisions and, c) the usefulness of different methods for incorporating scientific information in stakeholder engagement.

SOURCE

Mason, N.W.H., Kirk, N.A., Price, R.J. et al. Science for social license to arrest an ecosystem-transforming invasion. Biol Invasions 25, 873–888 (2023). https://doi.org/10.1007/s10530-022-02953-w

see also https://www.doc.govt.nz/nature/pests-and-threats/weeds/common-weeds/wilding-conifers/

Posted by Faith Campbell

What do YOU think about the role “social license” plays in US invasive species programs? 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.