The U.S. Geological Survey (USGS) has published an updated register of introduced species in the United States. The master list contains 14,700 records, of which 12,571 are unique scientific names. The database is divided into three sub-lists: Alaska, with 545 records; Hawai`i, with 5,628 records; and conterminous (lower 48) United States, with 8,527 records.
The project tracks all introduced (non-native) species that become established, because they might eventually become invasive. The list includes all taxa that are non-native everywhere in the locality (Alaska, Hawai`i, or 48 conterminous states) and established (reproducing) anywhere in that locality.
Each record has information on taxonomy, a vernacular name, establishment means (e.g., unintentionally, or assisted colonization), degree of establishment (established, invasive, or widespread invasive), hybrid status, pathway of introduction (if known), habitat (if known), whether a biocontrol species, dates of introduction (if known; currently 47% of the records), associated taxa (where applicable), native and introduced distributions (when known), and citations for the authoritative source(s) from which this information is drawn.
The 2022 version is more complete re: plant pathogens than earlier iterations; I thank the hard-working compilers for their efforts!
Hawai`i
wiliwili tree (Erythrina sandwicensis); photo by Forest and Kim Starr
Among the non-native species listed as being in Hawai`i are 3,603 Arthropods, including the following about which I have blogged:
eight species of mosquito in the Hawaiian islands, including the Culex and Aedes species that vector the diseases that have caused extinction of numerous endemic bird species on the Islands.
Also listed are 95 mollusk species and 20 earthworm species. I wonder who is studying the worms’ impacts? I doubt any is native to the Islands.
The Hawaiian list contains 1,557 non-native plant species. Families with largest representation are Poaceae (grass) – 223 species; Fabaceae (beans) – 156 species; and Asteraceae – 116 species. About a third of the plant species – 529 species – are designated as “widespread invaders”. This number is fifteen times higher than the numbers in lists maintained by either the Hawaiian Ecosystems At Risk project (106 species) [HEAR unfortunately had to shut down a decade ago due to lack of funds]; or Hawaiian Invasive Species Council (80 species). Furthermore, some of the species listed by HEAR and HISC are not yet widespread; the lists are intended to facilitate rapid responses to new detections. We always knew Hawai`i was being overrun by invasive species!
Among the 529 most “widespread invaders” are the following from the most introduced families:
Other families have fewer introduced species overall, but notable numbers of the most widespread invaders:
Euphorbiaceae – 8 spp. of Euphorbia
Cyperaceae – 6 spp. of Cyperus
Myrtaceae – Melaleuca quinquenervia, 2 Psidium, Rhodomyrtus tomentosa rose myrtle, 3 Syzygium [rose myrtle has been hard-hit by the introduced myrtle rust fungus]
Zingiberaceae – 3spp. Hedychium (ginger)
Anacardiaceae — Schinus molle (Peruvian peppertree); USGS considers congeneric S. terebinthifolia to be somewhat less widespread.
Plus many plant taxa familiar to those of us on the continent: English ivy, privet, castor bean, butterfly bush, Ipomoea vines … and in more limited regions, Japanese climbing fern Lygodium japonicum.
Rhus sandwicensis; photo by Forest and Kim Starr
I learned something alarming from the species profiles posted on the HISC website: the Hawaiʻi Division of Forestry and Wildlife and Hawaiʻi Department of Agriculture are considering introduction of a species of thrips, Pseudophilothrips ichini, as a biocontrol agent targetting S. terebinthifolia. I learned in early 2019, when preparing comments on Florida’s proposed release of this thrips, that Pseudophilothrips ichini can reproduce in low numbers on several non-target plant species, including two native Hawaiian plants that play important roles in revegetating disturbed areas. These are Hawaiian sumac Rhus sandwicensis and Dodonea viscosa. The latter in particular is being propagated and outplanted in large numbers to restore upland and dryland native ecosystems. While the environmental assessment prepared by the USDA Animal and Plant Service says the thrips causes minimal damage to D. viscosa, I am concerned because of the plant species’ ecological importance. Of course, the two Schinus species are very damaging invasive species in Hawai`i … but I think introducing this thrips is too risky. [To obtain a copy of CISP’s comments, put a request in comments section. Be sure to include your email address in your comment; the section algorithm does not include email addresses (how inconvenient!).]
Continental (lower 48) states
Among the 8,500 species listed in the USGS Register for the 48 continental states are 4,369 animals, among them 3,800 arthropods; 3,999 plants; and just 89 fungi. Among the arthropods, there are 1,045 beetles and 308 lepidopterans. The beetles listed include 12 Agrilus (the genus which includes emerald ash borer and goldspotted oak borer.) It does not include the elm zig-zag sawfly USGS staff have not found any publications documenting its U.S. occurrences. Among the microbes are six Phytophthora (P. cinnamomi, P. lateralis, P. pseudocryptogea, P. quercina, P. ramorum, P. tentaculata). Profiles of several of these species are posted at www.dontmovefirewood.org; click on “invasive species”, then scroll using either Latin or common name.
elm zig-zag sawfly; photo by Gyorgy Czoka via Bugwood
Citation:
Simpson, Annie, Pam Fuller, Kevin Faccenda, Neal Evenhuis, Janis Matsunaga, and Matt Bowser, 2022, United States Register of Introduced and Invasive Species (US-RIIS) (ver. 2.0, November 2022): U.S. Geological Survey data release, https://doi.org/10.5066/P9KFFTOD
United States Register of Introduced and Invasive Species;US-RIIS ver. 2.0, 2022
If you would like to contribute to future versions of the US-RIIS, please email the project leaders at us-riis@usgs.gov.
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
In a new paper, “Forest Resources of the World: Present Status and Future Prospects,” Singh et al. affirm the importance of forests for terrestrial biodiversity, provision of multiple ecosystem services, and supporting the economic well-being of approximately 1.6 billion people directly. This equals about a quarter of Earth’s population. The authors conclude that achieving global Sustainable Development Goals (SDGs), including poverty reduction, food security, and mitigating and adapting to climate change — all depend on sustaining forests.
According to the 2020 Global Forest Resource Assessment, Earth’s forested area comprises ~4.06 billion hectares, or 31% of the total land surface.More than half (54%) of all global forest area is found in five countries: the Russian Federation, Brazil, Canada, the United States, and China. Tropical forests constitute 45% of this total; boreal forests, 27%; temperate forests, 16%; and subtropical forests, 11%. An estimated 93% (3.75 billion ha) regenerate through natural processes; 7% (290 million ha) is planted forest.
The extent of global forest area has been declining for decades but the rate of loss slowed significantly between 1990 and 2020. This reflects decreased deforestation in some countries and an increase in forest area in others. The latter is due to both afforestation and also natural forest growth. However, conversion of tropical forests to agriculture continues apace. From 2010 to 2020, the net loss of forest area was highest in Africa (3.9 million ha) and South America (2.6 million ha). Increases in net forest area occurred in Asia, Oceania and Europe. The status of the top 10 countries or territories in global forest resources as of 2020 is given in Table 1.2 of the chapter. [News sources document that rapid deforestation continues in Brazil, at least.]
Several trends are concerning to those of us who value primary or undisturbed forests. First, the area of naturally regenerating forest has decreased, while the area of planted forest has expanded – but only by 123 million ha. In the last decade, the rate of increase in the area of planted forests has also slowed.
Second, total carbon stock in forests declined from 668 gigatons to 662 gt in 1990–2020. This is only 6%, but it is trending in the wrong direction. As we know, forest conservation counters climate change in two ways: conserved forests are a carbon sink, while degraded or destroyed forests are a significant source of atmospheric CO2. In fact, forests are the 2nd largest storehouses of carbon, after oceans. Global forests sequester about one-third of total CO2 emission from the combustion of fossil fuels. Almost all forest carbon is found in living biomass (44%) and soil organic matter (45%).
Costa Rican rainforest; photo by eflon via Flickr
Third, primary forests are already severely reduced and continue to shrink. Primary forests are those composed of native species, and supporting relatively undisturbed ecological processes. They are irreplaceable for sustaining biological diversity. These forests are already severely reduced – they cover only ~ 1 billion ha. Since 1990, the extent of primary forest has decreased by 81 million ha. More than half are in Brazil, Canada, and Russia.
Singh et al. report that only about 10% of the world’s forests are set aside for biodiversity conservation. Again, trends are in the wrong direction. The rate of increase in the area of forest designated largely for biodiversity conservation has slowed. On the other hand, forest areas designated for other non-extractive purposes have increased: soil and water conservation, recreation, tourism, education, research, and the protection of cultural and spiritual sites.
Singh et al. are cheered by the fact that more than 2 billion hectares are under management with well-defined management plans. The extent of forests under management plans has increased by 233 million ha since 2000.
Singh et al. say that continuously increasing anthropogenic pressure is the main cause of deforestation and forest degradation in unmanaged forests. Citing projections that the world’s population will reach almost 10 billion by 2050, they say this growth will make reconciling the need for forest conservation with the basic requirements of humans for food, shelter, and fuel more difficult than ever.
I appreciate this honesty. Too many experts interviewed on the day that the global population was estimated at 8 billion made optimistic statements about the consequences. They mentioned Earth’s carrying capacity only in reference to First World people demanding excessive resources. There was minimal discussion of humanity’s carbon footprint and no reference to ever-increasing threats to biological diversity. Nor to the fact that people in developing countries want to raise their standards of living – which entails higher demand for resources, including energy. For an example, see The Washington Post editorial, here.
On the other hand, Ruby Mellen in the Post on 15 November mentioned that, according to the World Wildlife Fund, 75% of Earth’s ice-free land has been significantly altered by people, and two-thirds of mammal, fish, reptile, and amphibian species have become endangered in the last ~50 years. Unfortunately, the on-line version of the paper doesn’t have this specific article!
fires in Siberian forest in 2016; European Space Agency
Threats to Forests: Fire
Singh et al. rank fire as the most disastrous threat, affecting biodiversity and carbon sequestration potential. According to the U.N. Food and Agriculture Organization, about 29% of the total geographical area in the world was affected by forest fires during 2001–2018; more than two-thirds of these fires occurred in Africa. U.S. media, however, focused on fires in the Amazon, temperate areas (U.S., Europe), and, sometimes, boreal forests or Australia. Singh et al. say that areas that are frequently affected by fire are prone to other types of disturbances like drought and outbreaks of insect pests.
tanoaks killed by Phytophthora ramorum in Oregon; photo by Oregon Department of Forestry
Threats to Forests: Diseases and Pests
I am glad that Singh et al. recognize the damage to forest productivity caused by disease and pest infestations. In doing so, they cite familiar sources – Clive Brasier, Peter Vitousek, Juliann Aukema, Gary Lovett, Sandy Liebhold, Kerry Britton, Bitty Roy, Hanno Seebens – regarding surges in pest attacks; the growing diversity of damaging pests; resulting changes in forest species composition and structure that impede ecosystem functions and productivity. Singh et al. follow these sources in calling for improved hygiene in nurseries, adoption of scientific silvicultural practices reducing physical damage to the vegetation, selection of genotypes that are resistant, and reinforcing national and international policies on quarantine and biosecurity measures to minimize pest impacts in the future. They also mention adoption of remote sensing technologies to detect the trees under stress and use of sentinel plantings. They list the 10 most important international agreements dealing with invasive species issues as the International Plant Protection Convention, Ramsar Convention, Convention on International Trade in Endangered Species of Wild Fauna and Flora, Convention on Migratory Species, Convention on Biological Diversity and its Cartagena Protocol on Biosafety, IUCN Invasive Species Specialist Group, World Trade Organization Agreement on Sanitary and Phytosanitary Measures, Global Invasive Species Program, and International Civil Aviation Organization, and Cartagena.
slash and burn agriculture in Bolivia; photo Neil Palmer
Threats to forests: Development Projects
Singh et al. consider development projects to be the third threat to forest conservation. Their roads, powerlines, and other linear developments cause habitat loss and fragment landscapes. In their view, environmental impact assessments and other similar requirements are not yet sufficient to safeguard sustainable use of forest resources.
Policy Responses
Singh et al. call for more inclusive forest management structures to respond to the threat climate change poses to forests, industries, and forest-dependent communities. They all for partnerships that bring together researchers from several disciplines with forest managers and local stakeholders. Geoffrey M. Williams and others (including me) advocate for similar conservation approaches. (See pre-print here.)
In this context, Singh et al. mention several reports, plans, and agreements aimed at global forest conservation. Participants in global fora have recognized the importance of forests in contributing to food security and sustainable development. Among agreements mentioned are the UN’s Strategic Plan for Forests 2030 and recommendations of the International Institute for Sustainable Development (IISD) published in 1994. The former tries to generate greater coherence, collaboration, and synergy across UN programs aimed at encouraging volunteer forest conservation by countries, international, regional, and local organizations, partners, and stakeholders. Unfortunately, they do not discuss the extent to which the 30-year old IISD recommendations have – or have not – been implemented.
They also describe Forest Landscape Restoration as an effective strategy to restore the functionality of forests.Again, the focus is on a collaborative approach aimed at integrating efforts by all forestry-related stakeholders, e.g., scientific and academic organizations, local communities, indigenous peoples, and private sectors, including forest-based enterprises and NGOs.
Also praised is rising attention to trees outside forest. This includes fostering use of trees in agroforestry systems ranging from home gardens to farm forestry systems, shelterbelts, and woodlots. This approach helps to sustain the livelihoods of rural communities and maintain a stable and secure food supply. Meanwhile, it reduces dependence on natural forests
Singh et al. say community forest management and decentralized governance have gained acceptance. They describe examples from Gambia and Rwanda. They concede that such decentralization has its own risks and challenges. For example, e the most marginalized sections of the community must be ensured adequate capacity for robust conflict resolution.
Singh et al. advocate that all nations seek to increase their forest cover; affluent countries that are hampered by physical and climatic conditions should aid poorer nations in increasing and upgrading their forest cover. They suggest “recognition” and encouragement of countries that maintain forest cover above 30% of territory.
Singh, M., N.N. Shahina, S. Das, A. Arshad, S. Siril, D. Barman, U. Mog, P. Panwar, G. Shukla, and S. Chakravarty. 2022. Forest Resources of the World: Present Status and Future Prospects. In Panwar, P., G. Shukla, J.A. Bhat, S. Chakravarty. 2022. Editors. Land Degradation Neutrality: Achieving SDG 15 by Forest Management; ISBN 978-981-19-5477-1 ISBN 978-981-19-5478-8 (eBook)
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
In an earlier blog about tree extinctions, I commented that less drastic impacts by pests can also be important. I mentioned specifically that clumps of beech root sprouts cannot duplicate the quantities of nuts and cavities provided by mature beech trees.
This thought prompted me to search for information about use of tree cavities by wildlife. The articles I have found are decades old and largely focus on implications for management of forests for timber. Timber production conflicts with a goal of ensuring the presence of large (“overmature”), trees, especially those with dead branches, and completely dead trees (“snags”). These articles were written too long ago to address the possible impacts of non-native insects and pathogens – although there is some discussion of widespread mortality of pines caused by the mountain pine beetle.
These sources make clear that species that make cavities are keystone species. Many other wildlife species depend on them — birds, bats and terrestrial animals – mammals and herps. Furthermore, these cavity-associated species require forests with significant numbers of large, old, declining trees. When non-native insects or pathogens kill those trees, there might be a short-term bonanza of dying trees – suitable for nesting and foraging; and wood-feeding insects to provide food. But afterwards – for decades or longer – there will probably be small-diameter trees, and different species. Can the cavity-dependent species find habitat or food under these circumstances?
[By coincidence, the PBS program “Nature” broadcast an episode on woodpeckers on the 2nd of November! The title is “The Hole Story”. ]
Cavities provide a variety of habitats for many species – including some not usually thought of as “forest” species. Among the 85 North American bird species identified by Scott et al. as associated with cavities are seven species of ducks, two vultures, three falcons, 12 owls, two swifts, six flycatchers, two swallows, purple martin, seven chickadees, three titmice, four nuthatches, brown creeper, five wrens, three bluebirds, and two warblers. They point out that the majority of these birds are insectivores. Woodpeckers are especially important predators of tree-killing bark beetles.
Goodburn and Lorimer found that more than 40 species of birds and mammals in hardwood forests of Wisconsin and Michigan use cavities in snags and dead portions of live trees for nest sites, dens, escape cover, and winter shelter. Bunnell reported that 67 vertebrate species commonly use cavities in the Pacific Northwest. Chepps et al., Daily et al., and Wiggins focus on specific species in the Rocky Mountains. (Full citations for all sources are at the end of the blog.)
While Scott et al. (published in 1977) do not address the impact of non-native pests, their profiles of individual bird species sometimes name specific types of trees favored. Several of these tree taxa have been decimated by such non-native pests, or face such attack in the near future. Thus, concern appears warranted for:
pileated woodpecker; photo by Jo Zimni via Flickr
birds nesting in American elm, including two that are quite large so they require large trees to accommodate their nests: common goldeneye (a duck) and pileated woodpecker (larger than a crow).
the pileated woodpecker also nests in ash and beech and here
How many species depended on American chestnut, which – before the blight — grew to diameters up to 5 feet, heights of 70 to 100 feet, and had hollow centers (USDA 2022)?
In the West, some nesting tree species are under imminent threat from invasive shot hole borers, goldspotted oak borer, or sudden oak death. Detection of the emerald ash borer in Oregon portends a longer-term threat. Birds likely to feel these impacts include the acorn woodpecker, ash-throated flycatcher, and purple martin. The golden-fronted woodpecker is associated with oaks in parts of Texas where oak wilt is severely affecting live oaks.
ash-throated flycatcher; photo by Mick Thompson via Flickr
At the beginning of the 21st Century – before widespread mortality caused by the emerald ash borer — densities of snags in the managed forests in the Lake States were apparently already insufficient to sustain population densities of cavity nesting birds. Pileated woodpeckers and chimney swifts both prefer snags greater than 50 cm dbh, which are significantly less abundant in harvested stands. For six of eight bird species studied, the number of breeding pairs was significantly higher in old-growth northern hardwood stands than in those under management (Goodburn and Lorimer).
Strong Primary Excavators are Keystone Species
Cavity nesters are commonly divided into:
1) primary excavators that excavate their own cavities. These are further divided into strong excavators – those species that forage by drilling, boring, or hammering into wood or soil; and weak excavators – those species that probe or glean bark, branches, and leaves to acquire prey.
2) secondary cavity users, that use holes made by primary cavity excavators (Bunnell).
Strong primary excavators tend to be large, e.g., most woodpeckers, sapsuckers, and the northern flicker. Weak excavators are mostly smaller species, such as chickadees and nuthatches; plus those woodpeckers that forage primarily by probing and gleaning, extracting seeds, or capturing insects in flight [e.g., acorn woodpecker (Melanerpes formicivorus), downy woodpecker (Picoides pubescens)] (Bunnell).
Bunnell considers strong excavators to be keystone species because so many other cavity users depend on them. Their loss would seriously disrupt forest ecosystems. For example, in the Pacific Northwest, only nine of 22 avian primary excavators are strong excavators. Another 45 species are secondary cavity users. These include waterfowl, tree swallows, and some mammals such as flying squirrels. Some cavity nesters support an even wider group of species: in the Pacific Northwest, at least 23 bird species, six mammal species, and numerous arthropods (nine orders and 22 families) feed on sap and insects collected at holes drilled by sapsuckers (Bunnell). [I discuss sapsuckers’ ecosystem role in greater detail later.]
Tree Characteristics
There is general agreement that animals dependent on tree cavities “prefer” (actually, require) trees that are large – tall, of large circumference, and sturdy – while having decayed interiors.
Size:
As Bunnell notes, larger snags provide more room and tend to stand longer without breaking, so they provide greater opportunities for cavity use. They also tend to be taller, so they offer higher nest sites that provide better protection from ground-dwelling predators. While larger-diameter trees remain standing longer regardless of the cause of mortality, snags created by fire usually fall sooner than do other snags. Beetle-killed trees are more attractive to cavity nesters that tend to excavate nest sites in trees on which they have foraged.
In the upper Midwest, cavity trees were a scare resource, even in unmanaged forests. Mean diameters for live cavity trees were twice as large as the mean diameter of the live trees in stands under a management regime. Such larger-diameter snags were more numerous in old-growth than in managed stands, especially in mixed hemlock-hardwood stands (Goodburn and Lorimer).
The Importance of Decay
Excavating a cavity demands considerable energy, so birds seek sites where a fungal infection has softened the interior wood. The exterior wood must remain strong to prevent collapse of the nest. These rots take time to develop, so they appear more often in older, even dying, trees. Bunnell, Scott et al., Chepps et al., and Goodburn and Lorimer all emphasize the role of decay in providing suitable cavity sites. Chepps et al. compared the aspen trees used by four species of cavity-nesting birds in central Arizona. Not only were nest trees softer than neighboring trees; they were softer at the spot where the nests were excavated than at other heights. [Spring (1965) provides a fun discussion of different species’ adaptations to the energy demands of hard pecking and climbing vertical trunks.]
Live v. Dead Trees
However, the need for decay does not necessarily mean birds prefer dead trees. Goodburn and Lorimer found that in Wisconsin and Michigan, a large percentage of all cavities found were in live trees.
Bunnell found that strong excavators select trees with less visible signs of decay. Where possible, secondary users will also use live trees. However, intense competition often forces them to use dead trees.
Hardwoods v. Conifers
Bunnell states that deciduous trees more often contain internal rot surrounded by a sound outer shell than do conifers (at least this is true in the Pacific Northwest). He found that cavity nesters chose hardwoods for 80–95% of their nest sites even where hardwoods comprised only 5–15% of the available tree stems. He concluded that availability of living hardwoods had a significant influence on strong excavators in the West, although probably was less important in hardwood stands in the East.
Taxa Dependent on Other Types of Cavity
Some species depend on cavities created by forces other than bird excavations, such as decay or fire. These include most of the mammals, especially the larger ones e.g., American martens, fishers, porcupines, and black bears. These natural cavities are often uncommon. Vaux’s swifts nest and roost in hollow snags large enough that they can fly in a spiral formation to enter and leave (Bunnell).
little brown bat Myotis sp. photo by S.M. Bishop via Wikimedia Commons
Bats are a special case. Bats are unique among mammals of their size in having long lives, low reproductive rates, and relatively long periods of infant dependency. They also play a key ecological role as the major predators of nocturnal flying insects (van den Driesche 1999). Also many species are in perilous conservation status: half of the 16 bat species in British Columbia were listed as threatened or endangered as of 1998 (van den Driesche). This was before the deadly disease whitenose syndrome had been detected in North America.
Bats require larger trees. In the Pacific Northwest at least, that choice often means conifers (Bunnell). Roosts are difficult to find, so samples are small. A study on the west coast of Vancouver Island (van den Driessche), located only nine roosts despite searching during three summers. Five roosts were in large-diameter (old) western red cedar, with dead tops and extensive cracks.
Brown creepers and some amphibians and reptiles nest or seek cover under slabs of loose bark, which are typically found on dead or dying trees. The same large, mature and old-growth conifer trees also provide preferred foraging habitat, since there is a higher density of arthropod prey on their deeply furrowed bark. While Wiggins (2005) studied bird populations in the Rocky Mountains, he cited studies in the eastern United States, specifically in the Blue Ridge and Allegheny mountains, that have found similar results. Goodburn and Lorimer found that in National forests in Wisconsin and Michigan, only 15% of trees consisted of the necessary snags with loose bark plates. Suitable trees were most frequent old-growth hemlock-hardwood stands, and on larger-diameter snags. A high proportion of the snags with loose bark were yellow birch (Betula alleghaniensis).
Importance of foraging sites
As Bunnell points out, a bird must feed itself before it can nest. Foraging trees and snags are usually smaller than nesting trees. Furthermore, birds need many more foraging sites than nesting sites. The situation perhaps most pertinent to our usual focus on invasive pests concerns bird species’ response to mountain pine beetle outbreaks. Red-breasted nuthatches and mountain chickadees increasing dramatically in apparent response to the beetle epidemic. When most of the conifers had been killed, and numbers of beetles diminished, numbers of these bird species also declined–despite the increased availability of conifer snags for nesting. Indeed, the birds continued to nest primarily in aspen during the epidemic.
Bunnell reiterates that snags of all sizes are needed; they provide perching, foraging, and hawking sites for bird species beyond cavity nesters as well as sustenance for bryophytes, insects, and terrestrial breeding salamanders. He says more than 200 studies reported harvesting of standing dead trees in beetle-killed forests had negative effects on bird, mammal, and fish species.
Other Dependencies – Food Sources
yellow-bellied flycather; photo by Dennis Church via Flickr
A few studies looked at the role of cavity-creating birds in providing food sources. The focus was on sapsuckers. They drill sapwells into trees’ phloem; sap flowing into these wells attracts many other species. In Michigan, Rissler determined that yellow-bellied sapsuckers’ sapwells attracted insects in seven orders and 20 families, especially Coleoptera, Diptera (other than Tephritidae), bald-faced hornets, and Lepidoptera. Daily et al. (1993) cites other studies showing that ruby throat and rufous hummingbirds have extended their breeding ranges by relying on these sapwells for nutrition in early spring before flowers open. [The “Nature” program covers this behavior.]
In a subalpine ecosystem in Colorado, Daily et al. found that red-naped sapsuckers support other species in two ways. First, they excavate nest cavities in fungus-infected aspens that are utilized by at least seven secondary cavity nesting bird species. When they feed, they drill sapwells that nourish more than 40 species – including hummingbirds, warblers, and chipmunks. Daily et al. called this a keystone species complex comprised of sapsuckers, willows, aspens, and a heartwood fungus. Disappearance of any element of the complex could cause an unanticipated unraveling of the community.
Goodburn and Lorimer looked at the availability of downed wood but did not discuss the implications of the presence of only small-diameter coarse woody debris.
Efforts to Accommodate Biodiversity Needs
Scott et al. reported in 1977 that the USDA Forest Service had required staff at regional and National Forest levels to develop snag retention policies. Twenty years later, Goodburn and Lorimer noted that Forest Service management guidelines for some Wisconsin and Michigan National forests since the early 1980s have called for the retention of all active cavity trees and 5-10 snags (larger than 30 cm dbh)/ha. However, as I noted above, they fear that these recommended snag retention levels might still be too limited to support cavity nesters. They found that two species that prefer snags greater than 50 cm dbh, pileated woodpeckers and chimney swifts, were significantly more abundant in old-growth than in selection stands. Furthermore, the number of breeding pairs of six species was at least 30% higher in old-growth northern hardwood than in selection stands and more than 85% higher in selection cuts than even-aged.
Goodburn and Lorimer cited others’ findings that removal of some live timber and snags in an Arizona ponderosa pine forest reduced cavity-nesting bird populations by 50%. Species affected were primarily violet-green swallows, pygmy nuthatches, and northern three-toed woodpeckers.
Female mountain bluebird by Jacob W. Frank. Original public domain image from Flickr
As I noted, none of these experts has addressed the impacts of wide-spread pest-caused tree mortality. If I may speculate, it seems likely that when the first wave of mortality sweeps through a forest, the result might be an expansion of both nesting opportunities (in dead or dying trees) and food availability for those that feed on wood borers. These would probably be more plentiful even in trees killed by pathogens or nematodes. Sapsuckers and those that depend on them might experience an immediate decline in sap sources. Over the longer term it seems likely that all cavity-dependent species will confront a much lower supply of large mature trees. I note that many deciduous/hardwood tree species are being affected by introduced pests.
Are there current studies in Michigan, where so many ash have died?
SOURCES
Bunnell, F.L. 2013. Sustaining Cavity-Using Species: Patterns of Cavity Use and Implications to Forest Management. Hindawi Publishing Corporation. ISRN Forestry. Volume 2013, Article ID 457698
Chepps, J., S. Lohr, and T.E. Martin. 1999. Does Tree Hardness Influence Nest-Tree Selection by Primary Cavity Nesters? The Auk 116(3):658-665, 1999
Daily, G.C., P.R. Ehrlich, and N.M. Haddad. 1993. Double keystone bird in a keystone species complex. Proc. Natl. Acad. Sci. USA Vol. 90, pp. 592-594, January 1993 Ecology
Goodburn, J.M. and C.G. Lorimer. 1998. Cavity trees and coarse woody debris in old-growth and managed northern hardwood forests in Wisconsin and Michigan. Can. For. Res. 28: 427.438 (1998)
Rissler, L.J., D.N. Karowe, F. Cuthbert, B. Scholtens. 1995. Wilson Bull., 107(4), 1995, pp. 746-752
Spring, L.W. 1965. Climbing and Pecking Adaptations in Some North American Woodpeckers.
United States Department of Agriculture, Animal and Plant Health Inspection Service. Draft Enviromental Impact Statement. 2022. State University of New York College of Enviromental Science and Forestry Petition (19-309-01p) for Determination of Nonregulated Status for Blight-Tolerant Darling 58 c’nut (Castanea dentata)
van den Driessche, R., M. Mather, T. Chatwin. 1999. Habitat use by bats in temperate old-growth forests, Clayoquot Sound, British Columbia
Wiggins, D.A. (2005, January 27). Brown Creeper (Certhia americana): a technical conservation assessment. [Online]. USDA Forest Service, Rocky Mountain Region. Available: http://www.fs.fed.us/r2/projects/scp/assessments/browncreeper.pdf [date of access].
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
Australian Eucalypts; photo by John Turnbull via Flickr
I congratulate Australian scientists for bringing about substantial improvements of their country’s biosecurity program for forest pests. While it is too early to know how effective the changes will be in preventing new introductions, they are promising. What can we Americans learn from the Australian efforts? [I have previously praised South Africa’s efforts – there is much to learn there, too.]
Australia has a reputation of being very active in managing the invasive species threat. However, until recently biosecurity programs targetting forest pests were minimal and ad hoc. Scientists spent 30 years trying to close those gaps (Carnegie et al. 2022). Their efforts included publishing several reports or publications (listed at the end of the blog) and an international webinar on myrtle rust. Scientists are hopeful that the new early detection program (described below) will greatly enhance forest protection. However, thorough pest risk assessments are still not routinely conducted for forest pests. (Nahrung and Carnegie 2022).
The native flora of Australia is unique. That uniqueness has provided protection because fewer of the non-native insects and pathogens familiar to us in the Northern Hemisphere have found suitable hosts (Nahrung and Carnegie 2020). Also – I would argue – the uniqueness of this flora imposes a special responsibility to protect it from threats that do arise.
Only 17% of Australia’s landmass is covered by forests. Australia is large, however; consequently, these forests cover 134 million hectares (Nahrung and Carnegie 2020). This is the 7th largest forest estate in the world (Carnegie et al. 2022).
Australia’s forests are dominated by eucalypts (Eucalyptus, Corymbia and Angophora). These cover 101 million ha; or 75% of the forest). Acacia (11 million ha; 8%); and Melaleuca (6 million ha) are also significant. The forest also includes one million ha of plantations dominated by Pinus species native to North America (Carnegie et al. 2022). A wide range of native and exotic genera have been planted as amenity trees in urban and peri-urban areas, including pines, sycamores, poplars, oaks, and elms (Carnegie et al. 2022). These urban trees are highly valued for their ecosystem services as well as social, cultural, and property values (Nahrung and Carnegie 2020). Of course, these exotic trees can support establishment and spread of the forest pest species familiar to us in the Northern Hemisphere. On the positive side, they can also be used as sentinel plantings for early detection of non-native species (Carnegie et al. 2022 and Nahrung and Carnegie 2020).
Despite Australia’s geographic isolation, its unique native flora, and what is widely considered to be one of the world’s most robust biosecurity system, at least 260 non-native arthropods and pathogens of forests have established in Australia since 1885 (Nahrung and Carnegie 2020). [(This number is about half the number of non-native forest insects and pathogens that have established in the United States over a period just 25 years longer (Aukema et al. 2010).] As I noted, forest scientists have cited these introductions as a reason to strengthen Australia’s biosecurity system specifically as it applies to forest pests.
What steps have been taken to address this onslaught? For which pests? With what impacts? What gaps have been identified?
Which Pests?
Nahrung and Carnegie (2020) compiled the first comprehensive database of tree and forest pests established in Australia. The 260 species of non-native forest insect pests and pathogens comprise 143 arthropods, 117 pathogens. Nineteen of them (17 insects and 2 fungal species) had been detected before 1900. These species have accumulated at an overall rate of 1.9 species per year; the rate of accumulation after 1955 is slightly higher than during the earlier period, but it has not grown at the exponential rate of import volumes.
While over the entire period insects and pathogens were detected at an almost equal rate (insects at 1.1/year; pathogens at 0.9/year), this disguises an interesting disparity: half of the arthropods were detected before 1940; half of the pathogens after 1960 (Nahrung and Carnegie (2020). By 2022, Nahrung and Carnegie (2022) said that, on average, one new forest insect is introduced each year. Some of these recently detected organisms have probably been established for years. More robust surveillance has just detected them recently. I have blogged often about an apparent explosion of pathogens being transported globally in recent decades.
In a more recent article (Nahrung and Carnegie, 2022), gave 135 as the number of non-native forest insect pests. The authors don’t explain why this differs from the 143 arthropods listed before.
damage to pine plantations caused by Sirex noctilio; photo courtesy of Helen Nahrung
Eighty-seven percent of the established alien arthropods are associated with non-native hosts (e.g., Pinus, Platanus, Populus, Quercus, Ulmus) (Carnegie et al. 2022). Some of these have escaped eradication attempts and caused financial impact to commercial plantations (e.g., sirex wood wasp, Sirex noctilio) and amenity forests (e.g., elm leaf beetle, Xanthogaleruca luteola) (Carnegie and Nahrung 2019).
About 40% of the alien arthropods were largely cosmopolitan at the time of their introduction in Australia (Carnegie et al. 2022). Only six insects and six fungal species are not recorded as invasive elsewhere (Nahrung and Carnegie 2020). Of the species not yet established, 91% of interceptions from 2003 to- 2016 were known to be invasive elsewhere. There is strong evidence of the bridgehead effect: 95% of interceptions of three species were from their invaded range (Nahrung and Carnegie 2022). These included most of the insects detected in shipments from North America, Europe and New Zealand. These ubiquitous “superinvaders” have been circulating in trade for decades and continue to be intercepted at Australia’s borders. This situation suggests that higher interception rates of these species reflect their invasion success rather than predict it (Nahrung and Carnegie 2021).
I find it alarming that most species detected in shipments from Africa, South America, and New Zealand were of species not even recorded as established in those regions (Nahrung and Carnegie 2021; Nahrung and Carnegie 2022).
Arhopalus ferus, a Eurasian pine insect often detected in wood from New Zealand; photo by Jon Sullivan – in New Zealand; via Flickr
Half of the alien forest pests established in Australia are highly polyphagous. This includes 73% of Asian-origin pests but only 15% of those from Europe (Nahrung and Carnegie 2021). Nahrung and Carnegie (2022) confirm that polyphagous species are more likely to be detected during border inspections.
PATHWAYS
As in North America and Europe, introductions of Hemiptera are overwhelmingly (98%) associated with fresh plant material (e.g. nursery stock, fruit, foliage). Coleoptera introductions are predominantly (64%) associated with wood (e.g. packaging, timber, furniture, and artefacts). Both pathways are subject to strict regulations by Australia (Nahrung and Carnegie 2021).
Eradication of High-Priority Pests
Eight-five percent of all new detections were not considered high-priority risks. Of the four that were, two had not previously been recognized as threats (Carnegie and Nahrung 2019). One high-priority pest – expected to pose a severe threat to at least some of Australia’s endemic plant species – is myrtle rust, Austropuccinia psidii. Despite this designation, when the rust appeared in Australia in 2010, the response was confused and ended in an early decision that eradication was impossible. Myrtle rust has now spread along the continent’s east coast, with localized distribution in Victoria, Tasmania, the Northern Territory, and – in 2022, Western Australia. `
Melaleuca quinquenervia forest; photo by Doug Beckers via Wikimedia
There have been significant impacts to native plant communities. Several reviews of the emergency response criticized the haste with which the initial decision was made to end eradication (Carnegie and Nahrung 2019). (A review of these impacts is here; unfortunately, it is behind a paywall.)
A second newly introduced species has been recognized as a significant threat, but only after its introduction to offshore islands. This is Erythina gall waspQuadrastichus erythrinae (Carnegie and Nahrung 2019). DMF Although Australia is home to at least one native species in the Erythrina genus, E. vespertilio,, the gall wasp is not included on the environmental pest watch list.
Four of the recently detected species were considered to be high impact. Therefore eradication was attempted. Unfortunately, these attempts failed in three cases. The single success involved a pinewood nematode, Bursaphelenchus hunanesis. See Nahrung and Carnegie (2021) for a discussion of the reasons. This means three species recognized as high-impact pests have established in Australia over 15 years (Nahrung and Carnegie (2021). In fact, Australia’s record of successful forest pest eradications is only half the global average (Carnegie and Nahrung (2019).
Carnegie and Nahrung (2019) conclude that improving early detection strategies is key to increasing the likelihood of eradication. They discuss the strengths and weaknesses of various strategies. Non-officials (citizen scientists) reported 59% of the 260 forest pests detected (Carnegie and Nahrung 2019). Few alien pests have been detected by official surveillance (Carnegie et al 2022). However, managing citizen scientists’ reports involves a significant workload. Futhermore, surveillance by industry, while appreciated, is likely to detect only established species (Carnegie and Nahrung 2019).
Interception Frequency Is Not an Indicator of Likelihood of Establishment
Nahrung & Carnegie (2021) document that taxonomic groups already established in Australia are rarely detected at the border. Furthermore, only two species were intercepted before they were discovered to be established in Australia.
Indeed, 76% of species established in Australia were either never or rarely intercepted at the border. While more Hemiptera species are established in Australia, significantly more species of Coleoptera are intercepted at the border. Among beetles, the most-intercepted family is Bostrichid borers (powderpost beetles). Over the period 2003 – 2016, Bostrichid beetles made up 82% of interceptions in wood packaging and 44% in wood products (Nahrung and Carnegie 2022). This beetle family is not considered a quarantine concern by either Australian or American phytosanitary officials. I believe USDA APHIS does not even bother recording detections of powderpost beetles. Nahrung and Carnegie (2021) think the high proportion of Bostrichids might be partially explained by intense inspection of baggage, mail, and personal effects. While Australia actively instructs travelers not to bring in fruits and vegetables because of the pest risk, there are fewer warnings about risks associated with wood products.
Nahrung & Carnegie (2021) concluded that interception frequencies did not provide a good overall indicator of likelihood of risk of contemporaneous establishment.
Do Programs Focus on the Right Species?
Although Hemiptera comprise about a third of recent detections and establishments, and four of eight established species are causing medium-to-high impact, no Hemiptera are currently listed as high priority forestry pests by Australian phytosanitary agencies (Nahrung & Carnegie (2021). On the other hand, Lepidoptera make up about a third of the high-priority species, yet only two have established in Australia over 130 years. Similarly, Cerambycidae are the most frequently intercepted forest pests and several are listed as high risk. But only three forest-related species have established (Nahrung and Carnegie 2020). (Note discussion of Bostrichidae above.).
Unlike the transcontinental exchanges under way in the Northern Hemisphere, none of the established beetles is from Asia; all are native to Europe. This is especially striking since interceptions from Asia-Pacific areas account for more than half of all interceptions Nahrung and Carnegie (2021).
Interestingly, 32 Australian Lepidopteran and eight Cerambycid species are considered pests in New Zealand. However, no forest pests native to New Zealand have established in Australia despite high levels of trade, geographic proximity, and the high number of shared exotic tree forest species (Nahrung and Carnegie 2020).
STRUCTURE OF PROGRAM
The structure of Australia’s plant biosecurity system is described in detail in Carnegie et al. (2022). These authors call the program “comprehensive” but to me it looks highly fragmented. The federal Department of Agriculture and Water Resources (DAWR,[recently renamed the Department of Agriculture, Fisheries, and Forestry, or DAFF) is responsible for pre-border (e.g., off-shore compliance) and border (e.g., import inspection) activities. The seven state governments, along with DAFF, are responsible for surveillance within the country, management of pest incursions, and regulation of pests. Once an alien pest has become established, its management becomes the responsibility of the land manager. In Australia, then, biosecurity is considered to be a responsibility shared between governments, industry and individuals.
Even this fragmented approach was developed more recently than one might expect given Australia’s reputation for having a stringent biosecurity system. Perhaps this reflects the earlier worldwide neglect of the Plant Kingdom? Carnegie and Nahrung (2019) describe recent improvements. Until the year 2000, Australia’s response to the detection of exotic plant pests was primarily case-by-case. In that year Plant Health Australia (PHA) was incorporated. Its purpose was to facilitate preparedness and response arrangements between governments and industry for plant pests. In 2005, the Emergency Plant Pest Response Deed (EPPRD) was created. It is a legally-binding agreement between the federal, state, and territorial governments and plant industry bodies. As of 2022, 38 were engaged. It sets up a process to implement management and funding of agreed responses to the detection of exotic plant pests – including cost-sharing and owner reimbursement. A national response plan (PLANTPLAN) provides management guidelines and outlines procedures, roles and responsibilities for all parties. A national committee (Consultative Committee on Emergency Plant Pests (CCEPP) works with surveys to determine invaded areas (delimitation surveys) and other data to determine whether eradicating the pest is technically feasible and has higher economic benefits than costs..
Austropuccinia psidii on Melaleuca quinquenervia; photo by John Tann via Flickr
Even after creation of EPPRD in 2005, studies revealed significant gaps in Australia’s post-border forest biosecurity systems regarding forest pests (Carnegie et al. 2022; Carnegie and Nahrung 2019). These studies – and the disappointing response to the arrival of myrtle rust – led to development of the National Forest Biosecurity Surveillance Strategy (NFBSS) – published in 2018; accompanied by an Implementation Plan. A National Forest Biosecurity Coordinator was appointed.
The forest sector is funding a significant proportion of the proposed activities for the next five years; extension is probable. Drs. Carnegie and Nahrung are pleased that the national surveillance program has been established. It includes specific surveillance at high-risk sites and training of stakeholders who can be additional eyes on the ground. The Australian Forest Products Association has appointed a biosecurity manager (pers. comm.)
This mechanism is expected to ensure that current and future needs of the plant biosecurity system can be mutually agreed on, issues identified, and solutions found. Plant Health Australia’s independence and impartiality allow the company to put the interests of the plant biosecurity system first. It also supports a longer-term perspective (Carnegie et al. (2022). Leading natural resource management organizations are also engaged (Carnegie, pers. comm.).
Presumably the forest surveillance strategy (NFBSS) structure is intended to address the following problems (Carnegie and Nahrung 2019):
Alien forest pests are monitored offshore and at the border, but post-border surveillance is less structured and poorly resourced. Australia still lacks a surveillance strategy for environmental pests.
Several plant industries have developed their own biosecurity programs, co-funded by the government. These include the National Forest Biosecurity Surveillance Strategy (NFBSS).
Some pilot projects targetting high risk sites were initiated in the early 2000s. By 2019, only one surveillance program remained — trapping for Asian spongy (gypsy) moth.
The states of Victoria and New South Wales have set up sentinel site programs. Victoria’s uses local council tree databases. It is apparently focused on urban trees and is primarily pest-specific – e.g., Dutch elm disease. The New South Wales program monitors more than 1,500 sentinel trees and traps insects near ports. This program is funded by a single forest grower through 2022.
Dr. Carnegie states: “With the start of the national forest biosecurity surveillance program in December 2022, the issues and gaps identified by Carnegie et al. 2022 are starting to be addressed. The program will conduct biosecurity surveillance specifically for forest pests and pathogens and be integrated with national and state biosecurity activities. While biosecurity in Australia is still agri-centric, a concerted and sustained effort from technical experts from the forest industry is changing this. And finally, the new Biosecurity Levy should ensure sustained funding for biosecurity surveillance.”
There is a separate National Environmental Biosecurity Response Agreement (NEBRA), adopted in 2012. It is intended to provide guidelines for responding, cost-sharing arrangements, etc. when the alien pest threatens predominantly the environment or public amenity assets (Carnegie et al. (2022). However, when the polyphagous shot hole borer was detected, the system didn’t work as might have been expected. While PSHB had previously been identified as an environmental priority pest, specifically to Acacia, the decision whether to engage was made under auspices of the the Emergency Plant Pest Response Deed (EPPRD) rather than the environmental agreement (NEBRA). As a result, stakeholders focused on environmental, amenity and indigenous concerns had no formal representation in decision-making processes; instead, industries that had assessed the species as a low priority (e.g., avocado and plantation forestry) did (Nahrung, pers.comm.).
Additional Issues Needing Attention
Some needs are not addressed by the National Forest Pest Strategic Plan (Carnegie et al. 2022) (Nahrung, pers. comm.):
1) The long-term strategic investment from the commercial forestry sector and government needed to maintain surveillance and diagnostic expertise;
2) Studies to assess social acceptance of response and eradication activities such as tree removal;
3) Studies to improve pest risk prioritization and assessment methods; and
4) Resolving the biosecurity responsibilities for pests of timber that has been cut and used in construction.
In 2019, Carnegie and Nahrung (2019) called for developing more effective methods of detection, especially of Hemiptera and pathogens. They also promoted national standardization of data collection. Finally, they advocated inclusion of technical experts from state governments, research organizations and industry in developing and implementing responses to pest incursions. They note that surveillance and management programs must be prepared to expect and respond to the unexpected since 85% of the pests detected over the last 20 years—and 75% of subsequently mid-to high-impact species established—were not on high-priority pest list. See Nahrung and Carnegie 2022 for a thorough discussion of the usefulness and weaknesses of predictive pest listing.
SOURCES
Aukema, J.E., D.G. McCullough, B. Von Holle, A.M. Liebhold, K. Britton, & S.J. Frankel. 2010. Historical Accumulation of Nonindigenous Forest Pests in the Continental United States. Bioscience. December 2010 / Vol. 60 No. 11
Carnegie A.J. and H.F. Nahrung. 2019. Post-Border Forest Biosecurity in AU: Response to Recent Exotic Detections, Current Surveillance and Ongoing Needs. Forests 2019, 10, 336; doi:10.3390/f10040336 www.mdpi.com/journal/forests
Carnegie A.J., F. Tovar, S. Collins, S.A. Lawson, and H.F. Nahrung. 2022. A Coordinated, Risk-Based, National Forest Biosecurity Surveillance Program for AU Forests. Front. For. Glob. Change 4:756885. doi: 10.3389/ffgc.2021.756885
Nahrung H.F. and A.J. Carnegie. 2020. NIS Forest Insects and Pathogens in Australia: Establishmebt, Spread, and Impact. Frontiers in Forests and Global Change 3:37. doi: 10.3389/ffgc.2020.00037 March 2020 | Volume 3 | Article 37
Nahrung, H.F. and A.J. Carnegie. 2021. Border interceps of forest insects estab in AU: intercepted invaders travel early and often. NeoBiota 64: 69–86. https://doi.org/10.3897/neobiota.64.60424
Nahrung, H.F. & A.J. Carnegie. 2022. Predicting Forest Pest Threats in Australia: Are Risk Lists Worth the Paper they’re Written on? Global Biosecurity, 2022; 4(1).
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
plants for sale in UK; Evelyn Grimak via Geograph what pests could be here?
There has recently been a series of studies trying to use port detection data to determine which types of insects are most likely to arrive and possibly establish in the country. These studies – and related sources – are listed at the end of this blog. Some of the studies focus on the U.S. experience, but not all. Their – and my – conclusions are meant to be relevant around the globe.
I agree with Nahrung et al. (2022) as a correct definition of the problem:
“… despite decades of research on and implementation of [biosecurity] measures, insect invasions continue to occur with no evidence of saturation, and are even predicted to accelerate.”
I also think the issue they raise applies more broadly. As these experts point out, forest pests have received considerable attention, are the subject of a specific international regulation (ISPM#15), and the pest risks to a range of forests is relatively well understood and appreciated. So what does failing to control this group of pests – as I say the international phytosanitary system is – imply for other pests and pathways?
I appreciate these experts’ efforts to improve the many elements of excluding pests: prediction, pest risk analysis, targeted phytosanitary measures, enforcement actions, and early detection. However, we have a long way to go before we can confidently apply port data to determine pest approach rates as well as the efficacy of phytosanitary measures.
Problems with the Quality of the Port Detection Data
inspection by APHIS
There is general agreement that detection data are not a reliable indicator of the true pest approach / arrival rate. Even Turner et al. (2022) – who titled their article “Worldwide border interceptions provide a window …” — concede this, although they try to find ways to apply the detection data anyway. According to pages 2 and 15 of Turner et al., true arrival rates of potentially invading species are usually difficult to estimate and probably exceed the number reported in the article. Allison et al. (2021) agree.
Turner et al. and Nahrung & Carnegie both note that many insect species established in the destination country are never or rarely detected. Turner et al. cite as an example spotted lanternfly, Lycorma delicatula, which appeared only once out of almost 1.9 million interceptions recorded in the combined global data. Nahrung & Carnegie note that 76% of species established in Australia were either never or rarely intercepted at the border.
Turner et al. explain that interception frequencies are a function of both the true arrival rates and the probability of (1) being detected during inspections (which depends on how these are carried out) and (2) being recorded. They say the data are more reliable when they report detections at the family-level. . The authors call on countries to base port inspections on a statistically based sampling program that would better reflect pest approach rates than do data biased by inspection priorities.
The issue of data quality might be broader. Certain kinds of pests travelling in certain types of imports might be sufficiently cryptic as to be rarely detected by even the best border inspections. Liebhold et al. (2012) found that APHIS inspectors detected actionable pests in only 2.6% of incoming shipments of plants, whereas a statistically valid audit determined that the actual approach rate was 12%. It is probable that many pests are never or rarely reported in official port detection data.
See a thorough discussion of the issues undermining use of interception data in Nahrung and Carnegie 2022, cited at the end of this blog.
Problems Due to Narrow Taxonomic Range of Pests Studied
Protection of our forests requires preventing introductions of many taxonomic groups, e.g., nematodes, fungal and other pathogens, viruses, and arthropods other than ambrosia beetles and Hemiptera.
I recognize that it is much more difficult to study and manage organisms other than common beetles. But the impacts of some introduced organisms in other categories have been devastating. I list some of the pathogens that have been introduced to the United States in recent decades, probably on imported plants: several Phytophthoras, ohia rust (Austropuccinia psidii), rapid ohia death (Ceratocystis lukuohia and C. huliohia), beech leaf disease, and the boxwood blight fungi. See Garbelotto and Gonthier (2022) for a thorough discussion of impacts of introduced forest pathogens.
boxwood hedge at Longwood Gardens; photo by F.T. Campbell
Points of Agreement
I agree with Nahrung et al. that:
Biosecurity successes are probably under-recognized because they are difficult to see whereas failures are more evident. They call this the “Biosecurity Paradox”: the more successful biosecurity is, the fewer new species establish so the less important it appears.
Uncertainty regarding the costs and benefits of forest border biosecurity measures appears to have led to under-regulation and wait-and-see approaches. Some recent reviews (Cuthbert et al.) show that delay substantially increases the costs associated with bioinvasion. 297https://www.nivemnic.us/?p=3209
Helping “weakest links” improve their performance is crucial. (see Geoff Williams et al.
We need to revise international and national biosecurity practices. However, my proposals differ from those cited on page 221 of Nahrung et al.; see my “Fading Forests” reports [links at end of this blog] and earlier blogs here and here. A new complication is that pathologists complain that proposed systems proposed by various invasive species experts don’t reflect realities of managing plant pathogens (Paap et al. 2022).
I wish Nahrung et al. had suggested bolder interim steps that go beyond data management and research.
I appreciate that the Canadian report on forest biosecurity (Allison et al.) notes that claiming most introduced forest pests are reported to cause no measurable impact probably reflects our ignorance. I wish others who repeat this assertion, e.g., Nahrung et al. 2022, would explore this claim’s truth more carefully.
Points of Disagreement
Customs and Border Protection officers inspecting infested pallet
I also found other statements about the efficacy of existing efforts to be too uncritical. So yes, ISPM#15 has resulted in decreased arrivals of bark- and wood-boring insects, as stated by Nahrung et al. 2022. However, the 36-52% decrease documented by Haack et al. (2014) is not sufficient to protect forests, in my view. Many publications have documented continuing introductions of damaging pests via the wood packaging pathway. For example, there have been 16 outbreaks of the Asian longhorned beetle (ALB) detected around the globe between 2012 and 2015 (Wang). Before we conclude that ISPM#15 has been a success, let’s see what the just-completed new study by Haack and colleagues shows. In addition, there has been controversy for a decade or more about what causes continuing introductions, that is, whether they result from treatment inadequacy v. sloppy application of treatments v. fraud. Why have scientists and regulators not collaborated to clarify this issue during this time?
I note – again – that many pathogens have been introduced widely over the last couple of decades. This is a global problem. My recent blogs have discussed introductions of tens of species of Phytophthora to countries around the world. Other examples include myrtle rust (Austropuccinia psidii) to 27 countries and the two causal agents of boxwood blight to at least 24 countries in Eurasia, New Zealand, and North America. Most of these species were unknown to science at the time of their introduction. Other species were known – but not believed to pose a threat because, in their native regions, their co-evolved hosts are not harmed.
Rhodomyrtus psidioidis in Australia killed by myrtle rust; photo by Peter Entwistle
I think Helen Nahrung (Nahrung et al.) exaggerates when she says that Australia has one of the strictest biosecurity systems in world. Several publications – some coauthored by her! – cite numerous shortfalls in applying the country’s phytosanitary programs to forest pests (Carnegie et al 2022). This latter group’s efforts have determined that at least 260 non-native arthropods and pathogens of forest hosts have established in Australia since 1885 (Nahrung and Carnegie 2020). True, this number is about half the number of non-native forest insects and pathogens that have established in the United States over a period just 25 years longer (Aukema et al. 2010). However, it is enough – and they have had sufficient impact – to prod these scientists to spend 30 years pushing for improvements.
Lessons Learned
Still, we can learn from these studies. Turner et al. compared insect interception data from nine regions over a 25-year period (1995 to 2019) – at ports in New Zealand, Australia, South Korea, Japan, Canada, mainland United States, Hawai`i, United Kingdom, and the region united under European Plant Protection Organization (EPPO) – Europe and the Mediterranean region.
They found that 174 species (2% of the total) were “superinvaders.” They were intercepted more than 100 times, and constituted 81% of all interceptions across all regions. Most of the same types of insects – even the same species – are arriving at ports around the world. The three species most frequently intercepted are all sap-feeding insects commonly associated with widely traded plants. In a separate study, Australian scientists found the same: about 40% of the alien pests detected at Australian borders were already widely introduced at the time of their introduction in Australia (Carnegie et al. 2022). The Australians report strong evidence of the bridgehead effect [that is, species being spread from locations to which they have been introduced] (Nahrung and Carnegie 2021). In fact, they conclude that higher interception rates might confirm invasion success rather than predict it.
Most of the species, however, are intercepted rarely. Turner et al. found that 75% of species reported in their nine regions were intercepted in only a single region. In fact, 44% of all species were intercepted only once (= “singletons”). Such singletons made up about half of individual species in five insect orders; the exception was Thysanoptera – 29% of those species were intercepted only once.
The 75% of all species that were intercepted in only one region included both species rarely intercepted anywhere and species intercepted numerous times – but only in that one region. The authors note that several possible factors might explain these differences. Some species are less likely to be intercepted, so it is not odd that they are detected infrequently, especially if all the regions have the same blind spots. Countries also have their unique approaches to data collection and inspection prioritization that could introduce biases in the data. Finally, countries vary in the sources of goods they import. Unfortunately, some of the data sets Turner at al. analyzed said nothing about the source country, pathway, or commodity. Consequently, they were unable to evaluate the influence of these factors.
Improving Our Understanding of the Current Risk to the U.S.
Dendrobium officinale via Wikipedia; Fusarium stilboides has been detected on this orchid in China; F. stilboides is reported to attack pine trees
As I noted in a previous blog, U.S. imports of plants have increased by more than 400% since the 1960s; 35% in just the last 15 years (MacLachlan et al. 2022). In 2011, APHIS adopted an important new policy: temporary prohibition of plant taxa determined to be “Not Authorized for Importation Pending Pest Risk Assessment” (NAPPRA). Now we have a decade of experience with NAPPRA. Given that, and because the “plants for planting” pathway is among the most risky, APHIS should update the Liebhold et al. 2012 study to determine the current approach rate for all types of organisms that threaten North American tree species. Unlike the previous study, the update should include trees on Hawai`i, Guam, Puerto Rico and the other U.S possessions and territories. Finally, the study should try to evaluate the difference in risks associated with various types of plants and – possibly – also source regions.
Hawaiian native plant naio; photo by Forrest and Kim Starr
Unknown Unknowns
As I noted above, problems curtailing introduction of tree-killing pests are not limited to the U.S. For more than a decade, scientists have noted that the international phytosanitary system has failed to prevent the rapid worldwide spread of significant pathogens 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. One of the principal concerns is the fact that most species of microorganisms have not been named by science, much less evaluated for their potential impacts on naïve hosts. This issue was raised by Sarah Green of British Forest Research at the annual meeting of the Continental Dialogue on Non-Native Forest Insects and Pathogens. She asked the APHIS representative whether the agency’s phytosanitary procedures (described here) are working to prevent introductions. She pointed to the issues raised by numerous scientific experts: pest risk analyses address only known organisms, so they cannot protect importers from unknown organisms.
U.S. scientists are beginning to address the issue of “unknown unknowns”. Some studies have taken a stab at evaluating traits of insects that are more likely to damage conifers (Mech et al.) and hardwoods (Schultz et al.). Jiri Hulcr – of the University of Florida — assessed the threat posed by 55 insect-vectored fungi to two species of oak and two species of pines. However, the forests of the southeastern U.S. comprise many other tree genera! He also set a very high bar for defining a threat as serious: the damage to the host must be equivalent to that caused by Dutch elm disease or laurel wilt. We urgently need APHIS, USDA/Forest Service, and academia to sponsor more similar studies to evaluate the full range of risks more thoroughly.
SOURCES
Allison J.D., M. Marcotte, M. Noseworthy and T. Ramsfield. 2021. Forest Biosecurity in Canada – An Integrated Multi-Agency Approach. Front. For. Glob. Change 4:700825. doi: 10.3389/ffgc. 2021.700825 Frontiers in Forests and Global Change July 2021 | Volume 4 | Article 700825
Carnegie A.J. and H.F. Nahrung. 2019. Post-Border Forest Biosecurity in AU: Response to Recent Exotic Detections, Current Surveillance and Ongoing Needs. Forests 2019, 10, 336; doi:10.3390/f10040336 www.mdpi.com/journal/forests
Carnegie A.J., F. Tovar, S. Collins, S.A. Lawson, and H.F. Nahrung. 2022. A Coordinated, Risk-Based, National Forest Biosecurity Surveillance Program for AU Forests. Front. For. Glob. Change 4:756885. doi: 10.3389/ffgc.2021.756885
Garbelotto M. and P. Gonthier. 2022. Ecological, evolutionary, and societal impacts of invasions by emergent forest pathogens. Chapter 7, Forest Microbiology. Elsevier 2022.
Li, Y. C. Bateman, J. Skilton, B. Wang, A. Black, Y-T. Huang, A. Gonzalez, M.A. Jusino, Z.J. Nolen, S. Freemen, Z. Mendel, C-Y. Chen, H-F. Li, M. Kolarik, M. Knizek, J-H. Park, W. Sittichaya, P.H. Thai, S-I. Ito, M. Torii, L. Gao, A.J. Johnson, M. Lu, J. Sun, Z. Zhang, D.C. Adams, J. Hulcr. 2021. Pre-invasion assessment of exotic bark beetle-vectored fungi to detect tree-killing pathogens. Phytopathology. https://doi.org/10.1094/PHYTO-01-21-0041-R
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
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).
Mech, A.M., K.A. Thomas, T.D. Marsico, D.A. Herms, C.R. Allen, M.P. Ayres, K.J. K. Gandhi, J. Gurevitch, N.P. Havill, R.A. Hufbauer, A.M. Liebhold, K.F. Raffa, A.N. Schulz, D.R. Uden, & P.C. Tobin. 2019. Evolutionary history predicts high-impact invasions by herbivorous insects. Ecol Evol. 2019 Nov; 9(21): 12216–12230.
Nahrung, H.F. and A.J. Carnegie. 2020. NIS Forest Insects and Pathogens in Australia: Establishment, Spread, and Impact. Front. For. Glob. Change 3:37. doi: 10.3389/ffgc.2020.00037 Frontiers in Forests and Global Change | www.frontiersin.org 2 March 2020 | Volume 3 | Article 37
Nahrung, H.F. and A.J. Carnegie. 2021. Border interceptions of forest insects established in Australia: intercepted invaders travel early and often. NeoBiota 64: 69–86. https://doi.org/10.3897/neobiota.64.604
Nahrung, H.F. & A.J. Carnegie. 2022. Predicting Forest Pest Threats in Australia: Are Risk Lists Worth the Paper they’re Written on? Global Biosecurity, 2022; 4(1).
Nahrung, H.F., A.M. Liebhold, E.G. Brockerhoff, and D. Rassati. 2022. Forest Insect Biosecurity: Processes, Patterns, Predictions, Pitfalls. Annu. Rev. Entomol. 2023.68.
Paap, T., M.J. Wingfield, T.I. Burgess, J.R.U. Wilson, D.M. Richardson, A. Santini. 2022. Invasion Frameworks: a Forest Pathogen Perspective. FOREST PATHOLOGY https://doi.org/10.1007/s40725-021-00157-4
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.
Turner, R. M., E. G. Brockerhoff, C. Bertelsmeier, R. E. Blake, B. Caton, A. James, A. MacLeod, H. F. Nahrung, S. M. Pawson, M. J. Plank, D. S. Pureswaran, H. Seebens, T. Yamanaka, and A. M. Liebhold. 2021. Worldwide border interceptions provide a window into human-mediated global insect movement. Ecological Applications 31(7):e02412. 10.1002/eap.2412
Wang, Q. (Ed.). 2017. Cerambycidae of the world: biology and pest management. Boca Raton, FL: CRC Press
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
area devastated by EAB; photo by Nathan Siegert, USFS
The emerald ash borer (EAB; Agrilus planipennis) is the most damaging forest insect ever introduced. In late June 2022 it was detected in Forest Grove, Oregon — 26 miles from Portland. This is the first confirmation of EAB on the West Coast – a jump of over 1,000 miles from outbreaks in the Plains states. The infested ash trees were immediately cut down and chipped (see Oregon Department of Agriculture website; full link at end of blog). See my earlier blog on EAB’s threat to ash-dominated riparian wetlands in Oregon.
ash-dominated swamp along the Willamette River in Oregon; photo by William Wyatt, ODF
Oregon has been preparing for the EAB:
The state finalized its response plan in March 2021; see reference at end of blog.
The state sought and received funds from USDA APHIS to initiate a biocontrol program. The funds were not from APHIS’ operational budget, but from the agency’s Plant Pest and Disease Management and Disaster Prevention Program (PPDMDPP) (Farm Bill money).
State and federal agencies have begun collecting seeds for resistance screening and a possible breeding program.
EAB: Why Quarantines Are Essential
As you might remember, in January 2021 APHIS dropped its federal regulations aimed at curtailing EAB’s spread via movement of wood and nursery plants. This shifted the responsibility for quarantines to state authorities. Instead, APHIS reallocated its funding to biological control. I raised objections at the time, saying the latter was no substitute for the former.
A new academic study shows that APHIS’ action was a costly mistake.
Hudgins et al. (2022; full citation at end of this blog) estimate EAB damage to street trees alone – not counting other urban trees – in the United States will be roughly $900 million over the next 30 years. These costs cannot be avoided. Cities cannot allow trees killed by EAB to remain standing, threatening to cause injury or damage when they fall.
ash fallen onto house in Ann Arbor, Michigan; photo courtesy of former mayor John Hieftje
The authors evaluated various control options for minimizing the number of ash street trees exposed to EAB. They assessed the trees’ exposure in the next 40 years, based on management actions taken in the next 30 years.
In their evaluation of management options, Hudgins et al. tried to account for the fact that the effect of management at any specific site depends on the effects of previous management. Additional complexity comes from the facts that the EAB is spread over long distances largely by human actions (i.e., movement of infested wood); and that biocontrol organisms also disperse.
They conclude that efforts to control spread at the invasion’s leading edge alone – as APHIS’ program did – are less useful than accounting for urban centers’ role in long-distance pest dispersal via human movement. Cities with infested trees are hubs for pest transport along roads. Hudgins et al. say that quarantine programs need to incorporate this factor.
Hudgins et al. concluded that the best management strategy always relied on site-specific quarantines aimed at slowing the EAB spread rate. This optimized strategy, compared to conventional approaches, could potentially save $585 million and protect an additional 1 million street trees over the next 40 years. They also found that budgets should be allocated as follows: 74-89% of funds going to quarantine, the remaining 11% to 26% to biocontrol.
In other words, a coherent harmonized quarantine program – either through reinstatement of the federal quarantine or coordination of state quarantines — could save American cities up to $1 billion and protect 1 million trees over several decades. Since street trees make up only a small fraction of all urban trees, up to 100 million urban ash trees could be protected, leading to even greater cost savings.
Unfortunately, such a coordinated approach seems unlikely. States continue to have very different attitudes about the risk. For example, Washington has no plans to adopt EAB regulations, despite it being detected in Oregon. To the north, Canada already has EAB quarantines and Hudgins et al. advise that they be maintained.
The authors recognize that quarantines’ efficacy is a matter of debate. Quarantines require high degrees of compliance from all economic agents in the quarantine area. Also they need significant enforcement effort. Some argue that meeting either requirement, let alone both, is unrealistic. However, under Hudgins et al.’s model, use of quarantines was always part of the optimal management method across a variety of quarantine efficiency scenarios. Again, these models point to allocating about 75% of the total budget to quarantine implementation. In all scenarios, reliance solely on biocontrol led to huge losses of trees compared to a combined strategy.
Hudgins et al. asked their model for optimal application of both quarantines and biocontrol agents. For example, quarantine enforcement could focus on limiting entry of EAB at sites that: 1) have many ash street trees, 2) currently have low EAB propagule pressure, but 3) are vulnerable to receiving high propagule influx from many sites. Seattle is a prime example of such a vulnerable city with many transportation links to distant cities with significant ash populations.
On the other hand, quarantine enforcement could strive to limit outward spread (emigration) of EAB from which high numbers of pests could be transported to multiple other locales, each with many street trees and low propagule pressure. These sites would be along the leading edge of the invasion and where the probability of long-distance pest dispersal is high.
Authorities should be prepared to adjust quarantine actions in response to changing rates and patterns of invasion spread.
Biocontrol agents should be deployed to sites with sufficient EAB density to support the parasitoids, especially sites predicted to be hubs of spread.
Hudgins et al. concede that they did not explicitly account for:
1) The impact of uncertainty regarding EAB spread on the model;
2) Alternative objectives that might point to other approaches, e.g., minimizing extent of invaded range, or reducing the number of urban and forest trees exposed to EAB;
3) Impacts of predators, such as woodpeckers, on EAB populations;
4) Synergistic impacts from climate change, which by exacerbating stress on ash trees will probably increase tree mortality from EAB infestations; and
5) Variation in management efficiency depending on communities’ capacities.
In the future, Hudgins et al. hope to test their model on other species to determine whether there is a predictable spatial pattern for all wood boring pests, that is, should quarantines always be focused on centers of high pest densities as probable sources of spread. Determining any patterns would greatly assist risk assessment and proactive planning.
dead ash near major road in northern Virginia; photo by F.T. Campbell
In an earlier study, Dr. Hudgins and other colleagues projected that by 2050, 1.4 million street trees in urban areas and communities of the United States will be killed by introduced insect pests – primarily EAB. This represents 2.1- 2.5% of all urban street trees. Nearly all of this mortality will occur in a quarter of the 30,000 communities evaluated. They predict that 6,747 communities not yet affected by the EAB will suffer the highest losses between now and 2060. However, they evaluated risks more broadly: the potential pest threat to 48 tree genera. Their model indicated that if a new woodboring insect pest is introduced, and that pest attacks maples or oaks, it could kill 6.1 million trees and cost American cities $4.9 billion over 30 years. The risk would be highest if this pest were introduced via a port in the South. I have blogged often about the rising rate of shipments coming directly from Asia to the American South
SOURCES
Hudgins, E.J., J.O. Hanson, C.J.K. MacQuarrie, D. Yemshanov, C.M. Baker, I. Chadès, M. Holden, E. McDonald-Madden, J.R. Bennett. 2022. Optimal emerald ash borer (Agrilus planipennis) control across the U.S. preprint available here: https://doi.org/10.21203/rs.3.rs-1998687/v2
Hudgins, E.J., F.H. Koch, M.J. Ambrose, B. Leung. 2022. Hotspots of pest-induced US urban tree death, 2020–2050. Journal of Applied Ecology
Members of this team published an article earlier that evaluated the threat from introduced woodborers as a group to U.S. urban areas; see E.J. Hudgins, F.H. Koch, M.J. Ambrose, B. Leung. 2022. Hotspots of pest-induced US urban tree death, 2020–2050. Journal of Applied Ecology
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
TACF back-crossed chestnut growing in southern Fairfax County, Virginia
same chestnut, dying in 2021; probably from Phytopthora root rot
In the first half of the 20th Century, American chestnut (Castanea dentata) was functionally extirpated from US forests east of the Mississippi River by chestnut blight, caused by a fungus from Asia, Cryphonectria parasitica. Today, only 10% of the pre-blight chestnut population remains, most as root sprouts less than 2.5 cm dbh (Dalgleish et al. 2015; full citation at the end of the blog).
Volunteer organizations — with recent help from federal and state agencies – have worked for more than a century to develop chestnut trees resistant to the blight. Their aim is to restore the species to the forest. Their decades of hybridization efforts now appear unlikely to produce a highly blight-resistant chestnut with a genome that is predominantly American, so TACF now plans to incorporate the use of transgenic techniques to enhance resistance to the blight fungus.
However, restoration of chestnut requires addressing a second Asian pathogen: Phytophthora cinnamomi, which causes a fatal root disease. Several studies indicate that up to 80% of seedlings are killed. The pathogen is widespread in soils south of 40o North Latitude, which falls just north of the Maryland-Pennsylvania line. Thus, P. cinnamomi occupies the southern half of American chestnut’s former range. Scientists expect this pathogen to move north in response to the warming climate; indeed, some project that the root disease could reach throughout the entire current chestnut rangeby 2080.
historic range of American chestnut
Gustafson et al. 2022 modelled chestnut’s vulnerability to P. cinnamomi to current and expected environmental conditions in two state forests in the Appalachians of western Maryland to evaluate the probable impact of the root disease on efforts to restore the tree species.
They found that root rot greatly reduced chestnut biomass on the landscape, even when resistance to root rot was at the target level for selection of root rot-resistant chestnut families using traditional breeding methods.
Gustafson et al. 2022 recommend that chestnut restoration apply the following strategies:
Locate restoration plantings at latitudes, elevations, and sites where root rot is not expected to be present well into the future. This probably means sites in the Northeastern US and Canada (Burgess et al. 2017)
Enhance the planting stock’s resistance to P. cinnamomi through breeding.
Identify soil conditions, including soil microbes, that suppress the pathogen or protect tree roots.
Since planting stock – both bareroot and containerized – can transmit P. cinnamomi, either raise seedlings in nurseries located outside the pathogen’s current range or rely on direct seeding. These strategies have their own downsides. Restricting locations of nurseries might complicate efforts to ensure seedlings are adapted to local conditions in the restoration area and seeds would need to be protected from seed predators.
The authors specify these additional important conditions:
Planting locations: while Canada is currently outside the range of American chestnut, the same climatic warming that will facilitate northward spread of P. cinnamomi will probably allow the tree to thrive farther north (Barnes and Delborne 2019). Perhaps the tree’s range will shift farther north than the pathogen’s.
Breeding: some resistance to Phytophthora root rot has been found in families providing blight resistance used in The American Chestnut Foundation (TACF) breeding program. TACF now plans to cross individuals from those families with transgenic blight-resistant chestnut to combine both resistances.
Soils: P. cinnamomi is favored by compacted soils with poor aeration or that tend to remain saturated. These include heavy clay soils and those highly disturbed by agriculture or mining. Restoration sites should be non-disturbed, well-drained sites. (This recommendation contradicts others’ proposals that chestnuts be planted on reclaimed mining sites.) Silvicultural management should also minimize environmental stresses.
that dying chestnut trying to reproduce!
Restoring chestnut will be challenging in any case: successful restoration requires chestnut trees that can compete successfully in the forest and adapt to conditions which are now quite different from those a century ago when the species was dominant. These include abiotic factors, e.g., climate and atmospheric CO2 levels; and biotic factors, e.g., different forest pests and invasive plant species.
In an earlier publication, Gustafson and colleagues (Gustafson et al. 2018) modelled the effects of warmer temperature and elevated atmospheric CO2 levels on chestnut’s growth and competition and the tree’s adaptation to natural and anthropogenic disturbances. They concluded that aggressive restoration programs – involving clearcutting, then planting chestnuts – could restore chestnut as an important component of forested ecosystems in the Appalachian Mountains.
However, this earlier study did not consider the effects of Phytophthora root rot. The 2022 study demonstrates that these recommendations are probably applicable only to the northernmost portion of former chestnut range, outside the areas infested by Phytophthora root rot, unless breeding is successful in substantially increasing resistance to root rot.
Several studies indicate American chestnut is highly susceptible to P. cinnamomi; rates of root rot induce mortality of 80% or higher have been documented. TACF has found that hybrid chestnut families selected for root rot resistance have a mortality rate of about 45%. Even with this level of tolerance, the model shows that chestnut could not regain anything approaching its former abundance on the landscape. Since the threat of P. cinnamomi to chestnut restoration has become evident, TACF is assessing how to integrate increased tolerance to root rot into their larger blight resistance breeding program (Westbrook et al. 2019).
Soil properties – texture, land use, drainage, waterlogging, drought, temperature, and water-holding capacity – influence infection. So does weather: a single heavy rain event might saturate soil sufficiently to facilitate a P. cinnamomi infection. For these reasons, climate change is expected to exacerbate its geographic spread and pathogenicity.
The sites used in both studies are at the center of chestnut’s former range, which is also at the northern edge of the root rot pathogen’s range. However, the two sites differ in important ways, especially in rainfall and soils. The researchers considered one a mesic site and the other, xeric.
Their 2022 model showed that root rot caused a dramatic reduction in chestnut biomass on both the mesic and xeric sites. Apparently temperature and wetness levels offset each other. That is, higher soil temperatures intensified P. cinnamomi virulence at the xeric site sufficiently to overcome its relative soil dryness. At the mesic site, soil temperature sometimes dropped to levels that are lethal to Phytophthora. On the whole, then, climate change is expected to intensify P. cinnamomi infection rates on both sites and reduce the number of sites where the pathogen is absent.
Gustafson et al. (2022) discuss several assumptions and data gaps that require further study.
SOURCES
Barnes, J.C. and Delborne, J.A., 2019. Rethinking restoration targets for American chestnut using species distribution modeling. Biodiversity and Conservation, 28(12), pp.3199-3220.
Burgess, T.I., Scott, J.K., Mcdougall, K.L., Stukely, M.J., Crane, C., Dunstan, W.A., Brigg, F., Andjic, V., White, D., Rudman, T. and Arentz, F., 2017. Current and projected global distribution of Phytophthora cinnamomi, one of the world’s worst plant pathogens. Global Change Biology, 23(4), pp.1661-1674.
Dalgleish, H.J., Nelson, C.D., Scrivani, J.A. and Jacobs, D.F., 2015. Consequences of shifts in abundance and distribution of American chestnut for restoration of a foundation forest tree. Forests, 7(1), p.4.
Gustafson, E.J., B.R. Miranda, T.J. Dreaden, C.C. Pinchot, D.F. Jacobs. 2022. Beyond blight: Phytophthora root rot under climate change limits populations of reintro Am chestnut Ecosphere. 2022;13:e3917.
Gustafson, E.J., A.M.G. De Bruijn, N. Lichti, D.F. Jacobs, B.R. Sturtevant, D.M. Kashian, B.R. Miranda, and P.A. Townsend. 2018. “Forecasting Effects of Tree Species Reintroduction Strategies on Carbon Stocks in a Future without Historical Analog.” Global Change Biology 24: 5500–17. https://doi.org/10.1111/gcb.14397
Westbrook, Jared W., et al. “Resistance to Phytophthora cinnamomi in American chestnut (Castanea dentata) backcross populations that descended from two Chinese chestnut (Castanea mollissima) sources of resistance.” Plant disease 103.7 (2019): 1631-1641.
Posted by Faith Campbell
[An earlier version of this blog has now been corrected, with additional sources added. I think Cornelia Pinchot, USFS, for the corrections.]
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
Phytopthora cinnamomi on manzanita in California; photo courtesy of Ted Swiecki/Phytosphere
While I blog often about wood packaging the fact is that imports of live plant [= “plants for planting” in USDA’s terms] have historically posed a higher risk of introducing tree-killing pests. In 2012, Liebhold et al. found that nearly 70% of 455 damaging pests introduced to the continental U.S. as of 2006 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. Imported plants not only carry a greater variety of pests than wood packaging; they also carry many more.
Introductions on imported plants for planting is not a rare event. An analysis of data in the Agriculture Quarantine Inspection Monitoring (AQIM) during 2009 found that 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. This alarming statistic receives less attention than warranted because APHIS objected to the accuracy of other aspects of the study.
APHIS has adopted changes to its phytosanitary system for plants for planting in the decade since 2009. The question is, have these changes reduced the known risks associate with live plant imports – especially given skyrocketing imports? Are more measures necessary? Current data and analyses cannot provide a scientifically valid answer.
ohia rust on endangered Hawaiian native plant Eugenia koolauensis
First, most studies focus on insects – they even exclude pathogens. Among pathogens introduced in recent decades, probably by the plant trade, are several Phytophthoras, rapid ‘ōhi‘a death, beech leaf disease, boxwood blight. (I am assuming that the Fusarium dieback disease vectored by Euwallacea beetles was introduced via wood packaging.) There have been repeated detections of the Ralstonia solanacearum Race 3 biovar 2, a bacterium that attacks a range of herbaceous plants, despite APHIS requiring specific integrated pest management programs in producing nurseries located in Central America. Examples of recently introduced leaf feeders include the European beech leaf-mining weevil and elm zigzag sawfly.
I concede that it is difficult to study introduced pathogens. It is nearly impossible to compile a complete list of introduced fungi and related organisms since only the most damaging are typically detected and their native ranges are frequently undeterminable. However, European forest pathologists are much more active on these questions. Why? What can we do to focus Americans on the threats these organism pose?
Second, most studies analyzing the pest risk associated with plant imports use port inspection data. However, port inspection data 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). Thus, most of the analyses carried out by Liebhold et al. and MachLachlan et al. (2022) are based on the pests found by APHIS inspectors: actionable pests were detected on only 2.6% of the incoming plants that they inspected.
Here I discuss two recent discussions of the risk associated with imported plant for planting. One is an analysis of establishments of one order of insects in the United States over 200 years (MacLachlan et al. 2022; full citation at the end of the blog). Again, the focus is on insects! The other is a discussion of the pathway during the recent annual meeting of the Continental Dialogue on Non-Native Forest Insects and Diseases. link to posting of presentations This discussion raised some of the key questions, although no answers were provided.
U.S. imports of plants have increased by more than 400% since the 1960s; 35% in just the last 15 years (in 2007 the U.S. imported approximately 3.7 billion plants [Liebhold et al. 2012]; in 2021 it was about 5 billion [MacLachlan et al. 2022]. Yet establishments of new non-native insects associated with this pathway have not risen commensurately. MacLachlan et al. (2022) attempt to answer why this is so. However, pests are often not detected for several years or a decade after their introduction. Furthermore, I doubt that an analysis based on inspection data, not the more reliable AQIM data, can provide an accurate assessment.
To clarify the pest risk associated with plant imports, studies of some insect types, excluding pathogens, is not sufficient. Again, APHIS should update the Liebhold et al. 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 usually excluded from analyses of imported pests, including Liebhold et al. 2012. 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!
Cycas micronesica endemic to Guam; threatened by cycad scale & cycad blue butterfly; photo courtesy A. Gawel
MacLachlan et al. (2022) focused their analysis on the insect order Hemiptera, including the so-called true bugs, including cicadas, aphids, planthoppers, and leafhoppers. This is the insect order most frequently transported with imported plants. In addition, establishments of Hemiptera can be attributed to plant imports rather than to wood or other vectors. Of the 3,500 species of non-native insects established in North America (including the contiguous U.S. states, Alaska, and Canada), about 27% are Hemiptera. Many are serious pests, e.g., hemlock woolly adelgid and balsam woolly adelgid). Complicating the analysis, however, is the fact that some Hemiptera are inconspicuous so they are difficult to detect. In fact, MacLaughlan et al. 2022 estimate the median delay between introduction and detection to be 80 years! They believe that many introduced species remain undiscovered, ranging from 21% for Eurasian regions to 38% for the Neotropics and 52% for Australasia.
eastern hemlocks killed by hemlock woolly adelgied; Linville Gorge, NC; photo by Steven Norman, USFS
MacLachlan et al. (2022) compare the relationship between plant imports and discoveries of Hemiptera from 1800 to the present in an attempt to answer the puzzle of why new Hemiptera establishments have remained relatively steady despite quadrupled plant imports. Perhaps the pool of novel insect species in the source region has been depleted. Or other factors might have changed, such as
the commodities imported (plant species or types; or geographic source)
phytosanitary measures applied by the U.S.
MacLachlan et al. (2022) tracked plant imports since 1854 from seven ecological regions: Afrotropic, Asian Palearctic, Australasia, European Palearctic, Indomalaya, Nearctic, Neotropic. In the early decades, both imported plants and introduced Hemiptera detected in the U.S., came predominantly from European and Asian Palearctic regions. Now, however, almost no new Hemiptera species are being introduced on plants imported from the European and Asian Palearctic regions. Since the 1950s, estimated establishments from the Indomalaya region have remained relatively stable. Establishments from the Neotropic and Afrotropic regions rose following World War II and have remained relatively high. After also declining in the first half of the 20th century, establishments of new species from Australasia have recently increased.
Generally, the regions associated with declining establishments of new species (Eurasia) are experiencing relatively gradual increases in their exports to the U.S. Those regions which contribute relatively steady or increasing establishments (Neotropics, Indomalaya, Australasia, and Afrotropic) have each undergone rapid increases in exports to the U.S.
Establishment Risk Among Regions
Source regions vary in the type of plants they export (e.g., rootless cuttings v. whole plants) and in the volume of exports. They also differ in the composition of their indigenous and introduced insect populations. Imports from areas with an abundance of species capable of establishing and adapted to environmental conditions in North America pose greater establishment risk, although it is challenging to determine the risk associated with individual species.
Establishment risk of shipments from a particular region also changes over time. The number of potential new species of invaders might shrink as more and more arrive in North America. (This situation has no effect on the continued introduction of insect species already established in North America. These reintroductions might arrive in new areas – so expanding the area at risk; or their increasing number contributes to propagule pressure at establishment sites.) Another factor might be phytosanitary policies. Strengthening of phytosanitary measures might suppress the number of organisms that travel with the plant shipment, enter North America, and establish. The opposite might happen if phytosanitary measures are relaxed or if the sourcing or type of imports diversifies in ways that connect additional species in source regions with trade pathways.
Considering all regional plant sources, MacLachlan et al. (2022) estimate that establishments per unit of additional imports – of Hemipterans – have shrunk because of a combination of increased imports, accumulated introductions associated with past imports, and the passage of time. These decreases are substantial – between 75.2% and 99.8% for the various regions from 1962 to 2012. For the Asian Palearctic and Neotropic regions, MacLachlan et al. (2022) determined that depletion of species pools is a contributing factor. Other factors are thought to explain the substantial decline in establishment likelihood for the other regions. However, note the caveats above re: lag times in detecting introductions.
However, despite that significant decrease in risk per unit of imports, the number of establishments has remained relatively constant over the past century. MacLachlan et al. (2022) attribute this pattern to the decreases in marginal risk from additional imports being offset by 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) suggest that APHIS should target biosecurity resources to the specific commodity-country pairs associated with a demonstrated higher relative risk of introducing additional insect species.
MacLachlan et al. (2022) are unable to evaluate the efficacy of APHIS’ most important policy change: creation of the “Not Authorized for Importation Pending Pest Risk Assessment” (NAPPRA) program because it was adopted in 2011 and they analyzed data only through 2012. A decade later this policy restricts imports of about 250 taxa (Regelbrugge to Continental Dialogue). It is certainly time to evaluate its efficacy through a new study of pest approach rates in the “plants for planting” trade.
I do not think that U.S. phytosanitary policy should be based on an analysis of just one of at least three types of pests that travel via the pathway. We need analysis of the risk from pathogens, nematodes, viruses … and other orders of arthropods.
The Continental Dialogue on Non-Native Forest Insets and Pathogens
The Continental Dialogue on Non-Native Forest Insects and Pathogens hosted a discussion of the risk of pest introduction via the plant trade during its recent annual meeting. Participants asked: How can the international phytosanitary system curtail introductions of unknown organisms when it is based on risk assessments that address only species that are fully known and – usually – have proven to be invasive elsewhere.
Rhodomyrtos psidioides in eastern Australia killed by myrtle rust; photo by Peter Entwistle
In recent decades, tens of species of Phytophthora have been introduced to countries around the world. Myrtle rust (Austropuccinia psidii) has been introduced to 27 countries from the U.S. to Australia and South Africa. The two causal agents of boxwood blight has been introduced to at least 24 countries in three geographic areas: Europe and western Asia; New Zealand; and North America. The ash decline fungus has been introduced across Europe. Most of these species were unknown to science at the time of their introduction. Other species were known – but not believed to pose a threat because, in their native regions, their co-evolved hosts are not harmed.
For more than a decade, scientists have noted that the international phytosanitary system has failed to prevent this rapid worldwide spread of significant pathogens 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.
During the Continental Dialogue discussion, Craig Regebrugge, Vice President of AmericanHort (the principal nursery trade association) noted the economic importance of greenhouse and nursery production and the importance of offering novel plants to their customers. Also, he noted that U.S. retail nurseries import primarily unrooted plant cuttings. In so doing, they have a strong incentive to ensure that they are pest-free in order to avoid delays arising during inspections. Those delays would probably kill these highly perishable products. Most U.S. imports of “finished” plants come from Canada. There have been pest problems; one of the most recent examples is a moth that attacks boxwoods (Buxus), which is the top-selling shrub crop in the U.S. Earlier there was confusion over whether plants shipped from British Columbia had been infected by the sudden oak death pathogen.
Regelbrugge noted that the industry’s voluntary integrated pest management program – Systems Approach to Nursery Certification (SANC) – currently has about two dozen participating nurseries. Hoped-for adoption by more of the hundreds of production nurseries in the country has been delayed by COVID-related travel restrictions, but he hopes to restore momentum. The industry is looking for opportunities to strengthen the program through marketing messages.
Regelbrugge and a second speaker, Rebecca Epanchin-Niell of the University of Maryland, warned that prohibitions on imports will stimulate smuggling. Both raised concerns about direct-to-consumer sales by e-commerce vendors and sought ideas on how to change the behavior of both exporters and consumers.
Later Sarah Green of British Forest Research asked the APHIS representativewhether the agency’s import procedures are working to prevent introductions. She pointed to the issues raised by the scientific sources I cited above: pest risk analyses address only known organisms, so this process cannot protect importers from unknown organisms. She noted that the United Kingdom is struggling to contain a number of introductions of previously unknown pathogens. Gary Lovett of the Cary Institute noted that this weakness of pest risk assessments also hampers U.S. attempts to prevent introductions – especially of pathogens. He called on the Dialogue to focus on the resource at risk – native and urban forests – and change our phytosanitary programs on this basis. He has 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.
an American elm that has survived DED – at Longwood Gardens; photo by F.T. Campbell
Jiri Hulcr of the University of Florida tried to reassure Dialogue participants by stating that recent research has substantially reduced the threat from “unknown unkowns”. I applaud Dr. Hulcr’s efforts to reduce scientific uncertainty about the invasive potential of pathogens native to regions other than North America. His study might be the largest attempted by U.S.-based scientists. However, I note that his study assessed the threat posed by 55 insect-vectored fungi to two species of oak and two species of pines. The forests of the southeastern U.S. comprise many other tree genera! He also set a very high bar for defining a threat as serious: the damage to the host must be equivalent to that caused by Dutch elm disease or laurel wilt. Both have devastated their respective hosts. I believe U.S. phytosanitary policy must aim at protecting the full range of native species. Furthermore, levels of damage that affect the host’s role in the ecosystem – not just rapid mortality — should not be acceptable.
Li, Y. C. Bateman, J. Skelton, B. Want, A. Black, Y-T. Huang, A. Gonzalez, M.A. Jusino, Z.J. Nolen, S. Freemen, Z. Mendel, C-Y. Chen, H-F. Li, M. Kolarik, M. Knizek, J-H. Park, W. Sittichaya, P.H. Thai, S-I. Ito, M. Torii, L. Gao, A.J. Johnson, M. Lu, J. Sun, Z. Zhang, D.C. Adams, J. Hulcr. 2021. Pre-invasion assessment of exotic bark beetle-vectored fungi to detect tree-killing pathogen. Phytopathology. https://doi.org/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
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).
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
Oregon-ash dominated swamp in the Ankeny National Wildlife Refuge, Willamette Valley, Oregon; photo by Wyatt Williams, Oregon Department of Forestry
In April 2022 I blogged about efforts on the West Coast to prepare for arrival of the emerald ash borer (EAB).
That blog focused on Oregon ash (Fraxinus latifolia), which is an important component of riparian forests. I alerted you to the availability of ODA/ODF EAB 2018 Response Plan.
I also mentioned Oregon’s active participation in “don’t move firewood” campaigns.
California has long inspected incoming firewood. In 2021 it establishment of a state quarantine in response to APHIS ending the federal quarantine. Washington State operates a statewide trapping program for invasive insects but does not regulate firewood.
Contributions from the Tualatin Soil and Water Conservation District enabled the USDA Forest Service Dorena Genetic Resource Center to begin testing Oregon ash for resistance to EAB and related genetics work. Other funding came from the USFS Forest Health Protection program.
EAB has now been detected in Oregon — in the Willamette Valley! (See photo above, by Wyatt Williams) Concerned stakeholders have established a new newsletter to keep people informed and promote cooperative efforts.
The newsletter is “Ash across the West”.
The first issue of the newsletter provides the following information:
there are eight ash species in the West; all are vulnerable to the emerald ash borer (EAB)
Single-leaf ash (Fraxinus anomala) CA, NV, AZ, UT, NM, CO, WY
Fragrant ash (Fraxinus cuspidata) NV, AZ, NM, UT
Calif ash (Fraxinus dipetala) CA, NV, AZ, UT
Fresnillo (Fraxinus gooddingii) AZ
Gregg’s ash (Fraxinus greggii) AZ
OR ash (Fraxinus latifolia) WA, OR, CA
Chihuahuan ash (Fraxinus papillosa) AZ, NM, TX
Velvet ash (Fraxinus velutina) CA, NV, AZ, UT, NM, TX
EAB Risk Map for OR: based upon known occurrences of ash & corresponding human activities associated with known pathways of EAB introduction and establishment.
2022 status of the two field trials
the Dorena Genetic Resource Center (DGRC): planted 600 seedlings from 27 families; 85% survival in 2022; controlling competing vegetation
Washington State University Puyallup Research Center: planted seedlings from 26 of these families; 95% survival rate. Possible complication from a foliar disease.
Seedlings from 17 Oregon ash families (including 14 of those in the DGRC field trial) sent to Dr. Jennifer Koch (USFS) in Ohio) for EAB resistance/susceptibility testing.
Seed collections began in 2019; interrupted by COVID-19 in 2020 but resumed in 2021 and continue in 2022. Several consortia are involved in Oregon and Washington. In California and the other states, The Huntington Botanical Gardens will lead the collecting effort. Funding is from USFS Forest Health Protection. Seeds are stored for gene conservation; some are used for the field trials in Oregon and Washington and the initial EAB-resistance studies going on in Ohio.
Penn State Ash Genomic Project: Dr. Jill Hamilton is trying to create a ‘genomic passport’ for Oregon ash populations for use in establishing genotype-environment associations to inform seed transfer guidelines. If you would like to help Dr. Hamilton collect leaves for sampling, contact: Dr. Jill Hamilton at jvh6349@psu.edu
To help with seed collection, ash monitoring, documenting the importance of ash to various communities, and other activities; or to get on the mailing list for the newsletter, contact Richard Sniezko at Richard.sniezko@usda.gov
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
I have posted nearly 40 blogs about wood packaging (SWPM) since 2015. [You can view these by scrolling below archives to find category “wood packaging”.]
I first raised the need for APHIS to authorize Robert Haack to update his study analyzing pest “approach rates” in wood packaging in July 2018.
Why?
SWPM has delivered our worst forest pests.
SWPM has been recognized as a major pathway of introduction of wood-boring insects for 30 years. Examples include the Asian longhorned beetle, emerald ash borer, redbay ambrosia beetle, and, possibly, the invasive shot hole borers.
For decades, pest-infested wood packaging has come primarily from the same countries: Mexico, Italy, China, and, more recently, Turkey. Many of our most damaging invaders have come from Asia so growing import volumes from Vietnam and other Asian countries also raise concern.
2) The U.S. and Canada have required that wood be treated to kill pests for at least 16 years.
The U.S. and Canada fully implemented the international standard on wood packaging (ISPM#15) in early 2006 – nearly 17 years ago. They had earlier (1999) required treatment of SWPM from China – nearly 24 years ago.
3) Even old analyses concluded that more than 11,000 incoming containers harbored wood pests each year.
The U.S., Canada, and Mexico import more than 31 million shipping containers per year (see “Background” below). Applying decade-old estimates to this number, we conclude that 11,600 of these containers are probably transporting a quarantine wood-boring pest. About 80% of the containers – and probably the pests! – come to U.S. ports. This pest risk is not limited to the West Coast; expansion of the Panama Canal and congestion at West Coast ports mean that an increasing number of ships are travelling directly to ports on the East and Gulf coasts. These region have already been demonstrated to be highly vulnerable to pests from Asia (ranging from Dutch elm disease and Asian longhorned beetle to laurel wilt and beech leaf disease.)
dead redbay trees – killed by redbay ambrosia beetle + laurel wilt fungus – introduced from Asia to Savannah, Georgia
4) Efforts to reduce the pest “approach rate” have not worked yet.
Meantime, administrative efforts to reduce the numbers of containers carrying pests have not been successful. The Bureau of Customs and Border Protection (CBP) has tried. CBP began penalizing individual shipments that are not in compliance with ISPM#15 in 2017 — 5 years ago.
As of the first three-quarters of Fiscal Year 2022 (John Sagle pers. comm. and Crenshaw-Nolan of CBD to Continental Dialogue on Non-Native Forest Insects and Diseases, September 2022), CBP has issued 510 Emergency Action Notifications (EAN) for noncompliant SWPM. About 38% (194) were issued because actionable pests had been discovered. The rest were issued because the ISPM#15 stamp (attesting to the wood having been treated) was either missing or fraudulent. The full-year interception rate will probably be comparable to interceptions in recent years: in FY2021, 548 EANs; in FY2020, 509; in FY2019, 746. CBP staff are disappointed that interceptions have not declined.
CBP agents inspecting SWPM
5) APHIS has avoided stricter enforcement.
APHIS has not adopted an enforcement stance. It has not stiffened penalties. The agency did not raise these phytosanitary issues when it negotiated a major agriculture trade agreement with China in 2020. The agency continued to insist that ISPM#15 is working – but agreed to work with Robert Haack to re-evaluate the approach rate only in 2021.
Correction: I became alarmed when the study had not been released four months after the analysis was completed (in May). I have since learned that the findings had not yet been completely written up and that internal reviews were proceeding. I apologize for the criticism in the original version of this blog. I impatiently await the study’s release, which I hope will be in a few weeks or months.
In the meantime, APHIS has also hired the Entomological Society to carry out an extensive study that includes analysis of interception data from five ports over a period of five years and rearing insects extracted from incoming wood packaging. I don’t want to postpone action aimed at curtailing introductions via this pathway for another five years!
APHIS has instead tried to improve foreign suppliers’ and phytosanitary agencies’ compliance with ISPM#15 through education. In partnership with Canada and Mexico, APHIS has supported two regional education workshops sponsored by the North American Plant Protection Organization (NAPPO). APHIS is now expanding its outreach to smaller companies, industry associations, and foreign suppliers. APHIS and CBP are now collaborating with an industry initiative to train inspectors that insure other aspects of foreign purchases. In addition, the International Plant Protection Convention (IPPC) is developing a “guidance document”. These educational efforts are supported by the U.S. pallet trade association, National Wooden Pallet and Container Association.
For all of these reasons we urgently need the updated data on the pest approach rate in the analysis by Haack and colleagues. Until we see these results, we can’t know the current level of risk associated with growing volumes of imports or assess the effectiveness of new policies. For example, CBP incorporated compliance with ISPM#15 into its government-importer partnership aimed at ensuring cleanliness of supply chains (C-TPAT) in February 2021. Only by comparing the results of the “approach rate” study with future data collected using the same techniques will it be possible to know how effective this action has been. I greatly appreciate CBP’s efforts.
There is still the issue of untrustworthy stamps.
Past data indicate a high proportion – 87% – 95% — of the SWPM found to be infested bore the ISPM#15 stamp. The same proportion was found in a narrower study in Europe (Eyre et al. 2018). Nor are all problems associated with Asia – importers in Houston have complained that stamps on dunnage from Europe also cannot be trusted.
While there are questions about whether this breakdown results from treatment inadequacy (i.e., 56oC for 30 minutes does not kill the larvae), failure of application, or of fraud –
What matters is that neither regulators nor importers can rely on the stamp to identify pest-free wood packaging.
infested wood packaging bearing ISPM#15 mark; photo courtesy of Oregon Department of Agriculture
(True: ISPM#15 was never intended to prevent pest introductions, only to “reduce the risk of introduction and spread of quarantine pests associated with the movement in international trade of wood packaging material made from raw wood.” Still, we should be trying to minimize pest introductions which threaten our wildland, rural, and urban forests.)
CPB’s experience indicates that cracking down on individual shipments will not be sufficient.
Immediate actions to hold foreign suppliers responsible
U.S. and Canada refuse to accept wood packaging from foreign suppliers that have a record of repeated violations – whatever the apparent cause of the non-compliance. Institute severe penalties to deter foreign suppliers from taking devious steps to escape being associated with their violation record.
APHIS and CBP and their Canadian counterparts provide guidance to importers on which foreign treatment facilities have a record of poor compliance or suspected fraud – so they can avoid purchasing SWPM from them. I am hopeful that the voluntary industry program described here will help importers avoid using wood packaging from unreliable suppliers in the exporting country.
Encourage rapid switch to materials that won’t transport wood-borers. Plastic is one such material. While no one wants to encourage production of more plastic, the Earth is drowning under discarded plastic. Some firms are recycling plastic waste into pallets.
APHIS and CFIA have the authority to take these actions 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.)
APHIS should also release the findings of the 2021-2022 study of approach rates by Haack and colleagues. Then the agency should invite stakeholders to discuss the implications, then develop and implement protective strategy reflecting its findings.
Longer-term Actions
APHIS and CFIA should cite their need for setting a higher “level of protection” to minimize introductions of pest that threaten our forests (described inter alia here.) They should then 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.
Michigan champion green ash killed by emerald ash borer
APHIS and CFIA should also undertake the studies needed to determine the cause of the continuing issue of the wood treatment mark’s unreliability, then act to resolve it. Preferably, this work should be conducted with other countries and such international entities as the IPPC & International Forest Quarantine Research Group (IFQRG). However, if attempting such collaboration causes delays, they should begin unilaterally. Upcoming opportunities to address this issue include:
FAO International Day of Forests in 2023
FAO global assessment of forests & health – pest & disease outbreaks
Of course, these steps should be based on the findings of Haack and colleagues.
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.
These hearings should be in the context of drafting the 2023 Farm Bill.
Raise the issue with local, state, and federal candidates for office;
Urge Congress to include provisions of H.R. 1389 in the 2023 Farm Bill;
Ask any associations of which we are members 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, American 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 (NAFO) 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.
BACKGROUND: Calculation of the Number of Infested Containers Entering U.S.
As of 2020 (when trade was greatly depressed by the COVID-19 pandemic), nearly 31 million TEUs [a standardized measure for containerized shipment; defined as the equivalent of a 20-foot long container] entered North America. Ports in the U.S. received 80% (24.5 million); Canada 11.5% (3.5 million); Mexico ~9% (2.7 million). U.S. imports have grown substantially since 2020; during the first quarter of 2022 U.S. imports from Asia each month were 20 to 30% higher than in 2019 before COVID-19 disrupted supply chains (blog #292). The U.S. is projected to handle ~26 million TEUs in 2022 [sources here and here.
A “TEU” equals a 20-feet container. Most containers now are twice as large – 40-feet. Several steps are involved in applying findings of Haack et al. 2014 and Meissner 2009 estimates:
divide estimated number of containers (26 million) in half = 13 million.
Assume that three-quarters of that number (13 million) contain wood packaging (based on Meissner) = 9.75 million.
If 1 out of each thousand of these containers with wood packaging is transporting a pest = 9,750 containers / year.
I performed the same calculation for North America-wide estimate of 31 million TEUs discussed at the beginning of the blog.
container being offloaded at Savannah harbor; photo by F.T. Campbell
A separate study (Hudgins et al. 2022) projected that introduction of a new woodboring insect pest that attacks maples or oaks it could kill 6.1 million trees and cost American cities $4.9 billion over 30 years. The risk would be highest if this pest were introduced via a port in the South. I have blogged often about the rising rate of shipments coming directly from Asia to the American South.
An analysis of fungi associated with Eurasian bark and ambrosia beetles reached a conclusion that the authors consider to be more optimistic. Li et al. (2021) found that none of the 111 fungi was sufficiently virulent to trigger tree mortality after a single-point inoculation. This level of lethality was considered analagous to Dutch elm disease DMF or laurel wilt DMF. Thirty-eight percent of the fungi were considered to be weak or localized pathogens that could kill trees under certain conditions. However, they tested the fungi against only two oak and two pine species. They did not evaluate fungi that might be lethal when the vector beetle engages in mass attacks. Finally, I think phytosanitary agencies should act promptly when a pathogen threatens levels of mortality somewhat below Dutch elm disease and laurel wilt!
SOURCES
Hudgins, E.J., F.H. Koch, M.J. Ambrose, B. Leung. 2022. Hotspots of pest-induced US urban tree death, 2020–2050. Journal of Applied Ecology 59(5): 1302-1312.
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
