invasion of wild/black mustard Brassica nigra; photo by carlbegge via Flickr
A California state legislator has proposed a bill to expand state efforts to counter invasive species. Should we support it – and others like it in other states?
The bill is Assembly Bill 2827 introduced by Assembly Member (and former Majority Leader) Eloise Reyes of the 50th Assembly District. She represents urban parts of southwestern San Bernardino County, including the cities of Rialto, Colton, and Fontana.
According to media reports, Reyes was prompted to act by the current outbreak of exotic fruit flies, which as of some months ago resulted in detections in 15 California counties.
The bill is much broader than agricultural pests, however. It would find and declare that it is a primary goal of the state to prevent the introduction, and suppress the spread, of invasive species within its borders. I applaud the language of the “findings” section:
(a) Invasive species have the potential to cause extensive damage to California’s natural and working landscapes, native species, agriculture, the public, and economy.
(b) Invasive species can threaten native flora and fauna, disrupt ecosystems, damage critical infrastructure, and result in further loss of biodiversity.
Paragraph (c) cites rising threats associated with increased movement of goods, international travel, and climate change — all said to create conditions that may enhance the survival, reproduction, and spread of these invasive species, posing additional threats to the state.
(d) It is in the best interest of the state to adopt a proactive and coordinated approach to prevent the introduction and spread of invasive species.
California sycamore attacked by invasive shot hole borer; photo by Beatriz Nobua-Behrmann
The bill calls for
The state agencies, in collaboration with relevant stakeholders, to develop and implement pertinent strategies to protect the state’s agriculture, environment, and natural resources.
The state to invest in research, outreach, and education programs to raise awareness and promote responsible practices among residents, industries, and visitors.
State agencies to coordinate efforts with federal, local, and tribal authorities.
However, the bill falls short when it comes to action. Having declared that countering bioinvasion is “a primary goal of the state”, and mandated the above efforts, the bill says only that the California Department of Food and Agriculture (which has responsibility for plant pests) is to allocate funds, if available, to implement and enforce this article. Under this provision, significant action is likely to depend on holding agencies accountable and providing increased funding.
removing coast live oak killed by goldspotted oak borer; photo by F.T. Campbell
Would this proposed legislation make a practical difference? I have often complained that CDFA has not taken action to protect the state’s wonderful flora. For example, CDFA does not regulate firewood to prevent movement of pests within the State. It has not regulated numerous invasive plants or several wood-boring insects. These include the goldspotted oak borer; the polyphagous and Kuroshio shothole borers; and the Mediterranean oak borer.
On the other hand, CDFA is quick to act against pests that might enter the state from elsewhere in the country, e.g., spongy moth (European or Asian), emerald ash borer and spotted lanternfly.
I hope Californians and the several non-governmental organizations focused on invasive species will lobby the legislature to adopt Assembly Bill 2827. I hope further that they will try to identify and secure a source of funds to support the mandated action by CDFA and other agencies responsible for managing the fauna, flora, and other taxa to which invasive species belong.
I applaud Ms. Reyes’ initiative. I hope legislators in other states will consider proposing similar bills.
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
At CISP, our hearts go out to all those affected by the terrible August fires on Maui. May the departed rest in peace. May the living find comfort and all that is needed for recovery.
Fire and Invasive Grasses
A fire in non-native grasses on Maui in 2009; photo by Forrest and Kim Starr
Major U.S. and international media continue to detail the fires’ devastation, especially in Lahaina. As time has passed, more news has highlighted the role that the widespread presence of introduced, fire-prone grasses played in the rapid growth and spread of Maui’s fires.
For example, The Washington Post devoted seven paragraphs in one story to the issue of grasses. The story quotes several experts: Alison Nugent, an associate atmospheric scientist at the University of Hawaii’s Water Resources Research Center; Jeff Masters, a meteorologist for Yale Climate Connections; and Clay Trauernicht, a fire researcher at the University of Hawaii.
These and others have been widely quoted in the many recent articles. I am glad that they – and the media – are making clear that climate change is not the sole factor causing damaging wildfires. It is clear that Maui’s recent weather patterns – including the high-velocity winds and drought – have been within the range of normal climate patterns. Fluctuations in the Pacific’s weather have also been normal, especially under the influence of the current El Niño.
The dangers caused by Hawai’i’s fire-prone grasses are also clear – and have been for years. Experts have identified policy weaknesses at the county and state level. Also, they have specified changes to land management that could better prevent or mitigate wildfires. There has been far too little action.
On the other hand, there are hopeful signs.
endangered ‘akikiki photo by Carter Atkinson, USGS
The Hawai’i Wildfire Management Organization, a nonprofit, is educating and engaging communities state-wide. Elizabeth Pickett, a Co-Executive Director, presented an overview of wildfire at the Hawai’i Invasive Species Awareness Month in February 2023. The Big Island Invasive Species Committee has successfully eradicated two species of pampas grass on Hawai’i Island – after 13 years’ work. A native species has been planted where pampas formerly grew.
Another Postarticle reported on efforts by staff and fire departments to protect the Maui Bird Conservation Center, which houses critically endangered Hawaiian birds found nowhere else on Earth, including some currently extinct in the wild. As I have blogged previously, the palila, kiwikiu, ‘akikiki, ‘alalā [Hawaiian crow; extinct in the wild] and other birds are dying from avian malaria, carried by nonnative mosquitoes. The Center on Maui and another on the Big Island are run by the San Diego Zoo Wildlife Alliance. Conservationists have completed field trials of a proposed mosquito suppression process for Maui and are seeking public comments for a similar program on Kaua’i. These programs represent groundbreaking and long-awaited progress on countering a principal threat to the survival of Hawai`i’s unique avifauna.Loss of the Center and its birds would have devastated post-suppression efforts to rebuild and restore bird populations in the wild.
The Post carried a second story about the effort to protect Hawai`i’s endangered birds – a full page of print, even longer – with many photos, on the web. The article mentions the “Birds, Not Mosquitoes” program and varying views about it. I rejoice that the dire situation for the Islands’ biodiversity is getting attention in the Nation’s capital. Again, see my earlier blog.
Plant Invasions in Hawaiian Forests
A team of scientists from the USDA Forest Service and Natural Resources Conservation Service, plus the Hawaii Division of Forestry and Wildlife, has carried out a new assessment of the extent of invasive plant species in forests on the Hawaiian Islands (Potter et al. 2023; full citation at end of blog).
The results of their analysis are – in their words – “sobering”. They portend “a more dire future for Hawai`i`s native forests.”
First, regarding the recent fires, Potter et al. found significantly higher cover by invasive grasses on Forest and Inventory Analysis (FIA) plots on Hawai‘i and Maui than on O‘ahu, Kaua‘i, and Lana‘i. Grass invasions were particularly high on the eastern coast of Maui – near Lahaina. Even so, the authors say their study’s methods resulted in a gross underestimate of areas invaded by fire-prone grasses. That is, most of Hawai’i’s xerophytic dry forests were converted to grasslands before the FIA program began. Therefore these grasslands are not included in FIA surveys.
Psidium cattleyanum; photo by Forrest and Kim Starr
The extent of current invasions in wetter forests is already significant – but trends point to an even more worrying future.
Naturalized non-native plant taxa constitute half of the Hawaiian flora.
56% of Hawaii’s 553,000 ha of forest land contained non-native tree species; about 39% of these forest lands are dominated by non-native tree species. Invasive plant species of particular concern were found in the understory of 27% of surveyed forest plots.
Across all islands, six of the ten most abundant species are non-native: Psidium cattleyanum,Schinus terebinthifolius, Leucaena leucocepahala, Ardisia elliptica, Psidium guajava, and Acacia confusa.
While less than one-third (29%) of large trees across the Islands are non-native, this proportion increases to about two-thirds of saplings (63%) and seedlings (66%). Potter et al. focus on the likelihood that plant succession will result in transformation of these forests’ canopies from native tree species to non-native species.
75% of forests in lower-elevation areas of all islands are already dominated by non-native tree species. “Only” 31% of higher-elevation forests are so dominated. These montane forests have been viewed as refugia for native species, but all are invaded to some extent – and likely to become more degraded.
Potter et al. say the high elevation forests might be more resistant to domination by non-natives. Such a result would be counter to well-documented experience, though. Even the authors report that the montane rainforests and mesophytic forests of O‘ahu and Kaua‘i are heavily invaded by non-native tree species. Such species constitute 86% or more of large trees, saplings, and seedlings in mesophytic forests; 45% of large trees and 66% of seedlings in their montane rainforests.
The most abundant tree species in Hawai`i is the invasive species Psidium cattleyanum (strawberry guava). It was recorded on 88, or37%, of 238 FIA plots. There are nearly twice as many P. cattleyanum saplings as Hawai`i’s most widespread native species, ‘ohi’a lehua (Metrosideros polymorpha).
Widescale replacement of native trees by non-native species is likely. Several factors favor these changes: 1) tree disease – rapid ‘ohi’a death has had drastic impacts on ‘ohi’a populations on several islands; 2) invasions by forbs and grasses; 3) soil damage and other disturbances caused by invasive ungulates; and 4) climate change. If succession conforms to these trends, non-native tree species could eventually constitute 75% or more of the forest tree stems and basal area on all islands and across forest types and elevations.
Loss of Hawai’i’s native tree species would be disastrous for biodiversity at the global level. More than 95% of native Hawaiian tree species are endemic, occurring nowhere else in the world.
The authors analyzed plant presence data from 238 FIA plots. Plots spanned the state’s various climates, soils, elevations, gradients, ownership, and management. However, access issues precluded inclusion of forests from several islands: Moloka‘i, Kaho’olawe, and Ni‘ihau. I know that Moloka‘i, at least, has a protected forest reserve (a Nature Conservancy property) at the island’s highest elevations.
Protecting Native Trees
Federal, state, and private landowners have carried out numerous actions to protect native forests. These efforts might be having some success. For example, forests on public lands, in conservation reserves, or in areas fenced to exclude ungulates were less impacted by non-native plants than unfenced plots, on average. However, the authors could not determine how much of this difference was the result of management or because protections were established in forests with the lowest presence of IAS species. Fencing did not prevent invasions by forbs and grasses – possibly because they are so widespread that seed sources are everywhere.
Hawaii’s two National parks (Hawai`i Volcanoes and Haleakala) have made major efforts to control invasive plants. Hawai`i Volcanoes, on the Big Island, began its efforts in the 1980s; Haleakala (on Maui) more recently. This might be one explanation for the fact that a smaller proportion of the forests on these two islands have been invaded. These efforts have not fully protected the parks, however. Low elevation native rainforests now have a high presence of non-native shrubs. Such forests on Hawai`i Island also have significant invasions by non-native woody vines, forbs and grasses.
More discouraging, intensive efforts have not returned lowland wet forest stands to a native-dominated state. Native tree species are not regenerating—even where there is plentiful seed from native canopy trees and managers have repeatedly removed competing non-native understory plants.
Potter et al. conclude that other approaches will be needed. They suggest deliberate planting of native and non-invasive non-native species or creation of small artificial gaps that might facilitate recovery of native tree species. In montane forests on Hawai`i and Maui, where native tree seedlings account for more than 70% of all tree seedlings, they propose enhancing early detection/rapid response efforts targetting invasive forbs. This would include both National parks.Certainly Haleakala National Park has this priority in mind. It launched a serious effort to try to eradicate Miconia calvescens when this tree first was detected.
Lloyd Loope, much-mourned scientist with US Geological Survey, attacking Miconia on Maui
Potter et al. note the challenge of managing remnant xerophytic dry forests, where natural regeneration of native plants has been strongly limited by invasive grasses; loss of native pollinators and seed dispersers; and the increasing frequency and intensity of droughts. They note that expanded management efforts must be implemented for decades, or longer, to be successful.
Native Trees at Risk to Nonnative Insects
Beyond the scope of the Potter et al. study is the fact that at least two dry forest endemic trees have faced their own threats from non-native insects.
The Erythrina gall wasp, Quadrastichus erythrinae, appeared in Hawai`i in 2005; it originates in east Africa. It attacks the endemic tree, wiliwili, Erythrina sandwicensis. I believe a biocontrol agent, Eurytoma erythrinae, first released in 2008, has effectively protected the wiliwili tree, lessening this threat.
The Myoporum thrips, Klambothrips myopori, from Tasmania, was detected on the Big Island in 2009. It threatens a second native tree. Naio, (Myoporum sandwicense), grows in dry forests, lowlands, upland shrublands, and mesic and wet forest habitats from sea level to 3000 m. The loss of this species would be both a signifcant loss of native biodiversity and a structural loss to native forest habitats. The thrips continues to spread; a decade after the first detection, it was found on the leeward (dry) side of Hawai`i Island with rising levels of infestation and tree dieback.
Rhus sandwicensis on Maui; photo by Forrest and Kim Starr
Two native shrubs, Hawaiian sumac Rhus sandwicensis and Dodonea viscosa, might be at risk from a biocontrol agent in the future. APHIS has approved a biocontrol for the highly invasive Brazilian pepper, Schinus terebinthifolia. Brazilian pepper is the second-most abundant non-native tree species in the State. It was found on 28 of 238 (12%) FIA plots. However, the APHIS-approved biocontrol agent is a thrips—Pseudophilothrips ichini. It is known to attack both of these two native Hawaiian shrubs. The APHIS approval allowed release of the thrips only on the mainland US. However, many insects have been introduced unintentionally from the mainland to Hawai`i. Furthermore, Hawaiian authorities were reported to be considering deliberate introduction of P. ichini to control peppertree on the Islands.
In Conclusion
In conclusion, Potter et al. found that most Hawaiian forests are now hybrid communities of native and non-native species; indeed, a large fraction are novel forests dominated by non-native trees. Business-as-usual management will probably mean that the hybrid forests – and probably those in which the canopy is currently dominated by native species—will follow successional trajectories to novel, non-native- dominated woodlands. This likelihood results in a more dire future for native plants in Hawaiian forests than has been previously described.
Potter at al. hope that their findings can guide research and conservation on other islands, especially those in the Pacific. However, Pacific islands already have the most naturalized species globally for their size—despite what was originally considered their protective geographic isolation.
SOURCE
Potter, K.M., C. Giardina, R.F. Hughes, S. Cordell, O. Kuegler, A. Koch, E. Yuen. 2023. How invaded are Hawaiian forests? Non-native understory tree dominance signals potential canopy replacement. Landsc Ecol https://doi.org/10.1007/s10980-023-01662-6
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
Dead ash along Mattawoman Creek in 2019; Mattawoman Creek is a Maryland tributary of the Potomac River, hence of the Chesapeake Bay. Photo courtesy of Leslie A. Brice
In this blog I describe one state’s forest health efforts – Virginia. The pertinent lesson is the importance of external funding, especially that provided by USFS Forest Health Protection program, in supporting states’ efforts. Is your state’s forest health program as dependent upon federal funding as Virginia’s is? If so, there is a role for everyone: lobby your Congressional representative and senators to increase funding for this program!
I have based most of this blog on the Virginia Department of Forestry’s annual report for 2022.
Forests grow on more than 16 million acres in Virginia, or 62% of the Commonwealth’s land area. Eighty percent of these forests are hardwood or hardwood-pine. They break down as follows: 61% oak-hickory; 11% oak-pine; 5% bottomland hardwood; and 2% maple-beech-birch. A fifth of the forest is pine, composed of pine plantation (14%) and natural pine (7%). The long term trend is growth, especially among hardwoods.
The report devotes much of its attention to the agency’s programs to advise private landowners (individuals own 80% of the Commonwealth’s forestland); fire management (including prescribed burns); and state and federal conservation programs (e.g., easements). A major program shares reforestation costs on harvested pine lands. In 2022, this program assisted reforestation practices on 74,702 acres. Virginia has an impressive tree-raising program. VDOF grows more than 40 species, including longleaf and shortleaf pine, several spruce species, and dozens of hardwoods. The aim is to provide stock suited for the Commonwealth’s soils and climate. Many of the hardwood species are grown from acorns and seeds collected and donated by volunteers.
VDOF also helps to protect and improve the Commonwealth’s water quality through tree planting and sound forest management. VDOF has an unusual responsibility: enforcing the Virginia Silvicultural Water Quality Law.
The report also summarizes several urban and community forestry programs focused on education, community engagement, tree selection, and grants for tree planting to ensure canopy retention & management.
Slightly over 1 million acres was mapped by aerial surveys in FY22. I believe the funding for these surveys came largely from the USFS. The surveys detected heavy to moderate defoliation by the spongy moth on 24,493 acres (almost twice the area detected in FY21). The spongy moth infestation is primarily in counties on the western side of the state, in the mountainous region, which has the highest densities of oaks and other hardwoods.
The spotted lanternfly (SLF) was detected in Virginia early – in 2018 in Winchester at the northern end of the Shenandoah Valley. Winchester is connected to central Pennsylvania by Interstate 81, so rapid movement of SLF to Virginia from outbreaks slightly to the east of I-81 in Pennsylvania doesn’t surprise me. SLF has been spreading south along the mountains and over the Blue Ridge to Loudoun and Fairfax counties (in 2022). Fairfax County has announced a four-year, $200,000 effort to try to slow SLF spread by eradicating high densities of its preferred host, Ailanthus, from two county parks in the far south and north ends of the county. Ailanthus removal requires not just cutting the trees, but applying herbicide to prevent sprouting from the roots. This work is funded by the county, the local park authority and a $20,000 grant from the regional energy company, Dominion Energy Charitable Foundation.
Virginia has six species of ash: white and green (both common), and smaller populations of black, blue, pumpkin and Carolina. EAB is now confirmed in 84 counties – most of the Commonwealth except the far southeast. The Department of Forestry treats 130 – 150 trees per year – half or more on state lands. At least in FY21, the funding came from federal sources. The report also notes outreach efforts at two minor league baseball games. Virginia recently adopted a priority of protecting the Chesapeake Bay watershed by promoting tree planting in riparian forest buffers. The EAB threatens this goal; see the photo (at top) of ash mortality along a Maryland tributary of the Bay. In 2021, EAB was detected in Gloucester County – a peninsula east of the York River that has Bay shoreline on the eastern side, tributary on the west (see photo).
Gloucester Point – Virginia Institute of Marine Sciences “living shoreline”; EAB was detected in Gloucester County in 2021, threatening riparian areas. Photo courtesy of the Chesapeake Bay Program
Threats to Beech
Beech bark disease is present in the western mountainous parts of the Commonwealth. One new county – Augusta – was detected in 2022. Three other counties are infested with the scale, but the fungal pathogen has not yet been detected. The alarming new threat, beech leaf disease, was detected in Prince William County in 2021. In 2022, it was confirmed in neighboring Fairfax County. The source of funding is not specified.
beech in a typical northern Virginia second-growth forest; photo by F.T. Campbell
I am pleased that the Commonwealth is paying attention to laurel wilt disease, which has been spreading north on sassafras. The closest outbreaks are in Tennessee, to the southwest of Virginia. The Commonwealth hosted a detection training program attend by 26 participants from six agencies from three states. The report does not specify the source of the funding.
Southern Pine Beetle
Virginia has also utilized funding from the USFS FHP program to manage the southern pine beetle. Since the program’s inception in 2004, Virginia has thinned pines on more than 70,000 acres, including 4,240 acres in FY22.
Invasive Plants
USFS FHP invasive species grants funded control treatments of invasive plants on somewhat less than 1,300 acres of state lands. Different figures on different pages of the report cause confusion. However, it is clear that nearly all the funds came from the USFS FHP program. Ailanthus was the main target; other species mentioned are privet, mimosa, autumn olive and Miscanthus.
State Funding of Conservation Initiatives; Will They Continue?
While the state’s government was controlled by Democrats, the governor and state legislature launched new programs with broader conservation goals. It is unclear whether they will continue now that Republicans have won the governorship and control of the House of Delegates.
Among the programs enjoying increased funding from the state budget during the current two-year cycle are
Efforts to restore depleted populations of two groups of tree taxa, shortleaf and longleaf pines. The emphasis has shifted to longleaf pine: the number of projects and acreages rose from 220 acres in FY21 to 1,212 acres in FY22. Restoration of shortleaf pine forests was limited to slightly over 600 acres in both years.
Programs to improve management of hardwood stands. These projects included crop tree release, control of “invasive species” (I think probably targetting invasive plants), prescribed burning and commercial thinning. There were also several demonstration projects on state-owned lands, a small land-owner planning assistance program, and training of state foresters and private consulting foresters in hardwood management. Apparently these aspects had been largely ignored in the past.
Creation of a dedicated Watershed program focused on increasing riparian forest buffers. This section of the report does not mention the threat posed by loss of ash to the emerald ash borer (EAB) [see EAB section above]
Urban forestry projects, many linked to protecting surface and ground water (including Chesapeake Bay watershed).
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
nearly dead ash in Shenandoah National Park; photo by F.T. Campbell
I participated in the annual USDA Interagency Invasive Species Research Forum in Annapolis in January 2023; as usual, I learned interesting developments. I focus here on updates re: efforts to protect ash and hemlock
Hopeful Developments re: countering EAB to protect ash
There are hopeful results in both the biocontrol and resistance breeding programs. The overall goal is to maintain ash as a viable part of the North American landscape.
Biocontrol
Juli Gould (APHIS) reminded us that the agency began a classical biocontrol program targetting emerald ash borer (EAB) in 2003 – only a year after EAB had been detected and much earlier than is the usual practice. [Thank you, former APHIS PPQ Deputy Administrator Ric Dunkle!] By 2007 scientists had identified, tested, and approved three agents; a fourth was approved in 2015.
Nicole Quinn (University of Florida) stressed that the egg prarasitoid, Oobius — if it is effective — could prevent EAB from damaging trees. However, it is so small that it is very difficult to sample. One small study demonstrated that Oobius will parasitize EAB eggs laid in white fringe trees (Chionanthus virginicus) as well as in ash. This is important because it means this secondary host is not likely to be a reservoir of EAB.
The numbers
According to Ben Slager (APHIS), more than 8 million parasitoids have been released at 950 sites since the program began in 2007. These releases have been in 418 counties in 31 states, DC, and four Canadian provinces. Still, these represent just 28% of infested counties. Parasitoids have been recovered in 21 states and two provinces.
Rafael de Andrade (University of Maryland) specified that these releases included more than 5 million Tetrastichus in 787 sites; ~2.5 million Oobius in 828 sites in 30 states; ~500,000 Spathius agrili – lately only north of the 40th parallel. Releases of Spathiusgalinae began in 2015; so far ~ 470,000 in 395 sites.
Impact
Several presenters addressed questions of whether the agents are establishing, dispersing, and – most important – improving ash survival. Also, can classical biocontrol be integrated with other management techniques, especially use of the pesticide emamectin benzoate.
Dispersal
Several studies have shown that the four biocontrol agents disperse well (with the caveat that Oobius is very difficult to detect so its status is much less certain).
Implementation considerations
De Andrade found that the longer the delay between the date when EAB was detected and release of Oobius, the less likely Oobius will be recovered. Tetrastichus surprised because the higher the numbers released, the fewer were recovered. He could determine no association between recovery of S. agrili and variations in release regime [numbers released; delay in releasing biocontrol agents; or frequency of releases]. He said it is too early to assess Sp. galinae since releases began only in 2015, but he did see expected relationship to propagule pressure – the more wasps released, the higher the number that were recovered. Sp. galinae did surprise in one way: it seemed to perform better at lower latitudes. De Andrade noted he was working data from less than half of release sites. He asked collaborators to submit data!!!!
Initial signs of ash persistence and recovery
Claire Rutledge (Connecticut Agriculture Experiment Station) determined that
More large trees were surviving in plots where the biocontrol agents were released
EAB density was lower at long-invaded sites
Parasitism rates were similar across release age treatments and release/control plots
Gould focused on protecting saplings so they can grow into mature trees which could be sources of seeds to establish future generations. She noted that there are many “aftermath” forests across the northern United States – those dominated by ash saplings.
In Michigan, at a site of green ash, as of 2015 – 2021, EAB populations are still low, parasitism rate by Tetrastichus and S. galinae high. The percentage of saplings that remained healthy was greater than 80%. There were similar findings in white ash in New York: very low EAB larval density; and more than 70% of ash saplings had no fresh galleries. Gould reported that Tetrastrichus impcts could be detected within three years of release.
So, EAB are being killed by the biocontrol agents combined with woodpecker predation; but in their fourth instar, after considerable damage to the trees.
downy woodpecker in Central Park, NYC. photo by Steven Bellovin, Columbia University
Jian Duan reported on two long-term studies in green & white ash in Michigan and New England. His team used the most labor-intensive but best approach to determine EAB larval mortality and the cause – debarking trees – to determine whether the EAB larva were parasitized, were preyed on by woodpeckers, or were killed by undetermined cause, such as tree resistance, disease, or competition. In Michigan, he linked a crash of EAB population in 2010 was caused by Tetrastichus; EAB tried to recover, but crashed again, due to S. galinae. EAB larval densities had been reduced to 10 / m2. Predation by abundant woodpeckers and the native parasitoid Atanycolus was also important.
In New England, EAB has also declined from 20-30 larvae /m2 to ~ 10 m2.
In Michigan, healthy ash with dbh of larger than 5 inches were much more plentiful in sites where parasitoids had been released. Their survival/healthy rate also was much higher in release sites but the difference declined as years passed. In New England there were growing numbers of healthy trees in 2021-22; (almost none in 2017). Duan conceded that he could not prove a direct link but the data points to recovery.
Tim Morris (SUNY-Syracuse) found that white ash saplings continued to die in large numbers, but the mortality rate was significantly below the rate in 2017. Canopy conditions varied; some trees that were declining in 2013 were recovering in 2017. Forty percent of “healthy” ash in 2013 continued recovering in 2021. Few living trees were declining; trees were either healthy or dead. He thinks probably a combination of genetics and presence of parasitoids explains which trees recover. Morris also reported some signs of regeneration.
beaver feeding on ash saplings, Fairfax County, Va; photo by F.T. Campbell
At this point, I noted that in parts of northern Virginia, beavers have killed ash saplings. Morris reported finding the same in some sites in New York. Perhaps others have, also; my comment was greeted by laughter.
Theresa Murphy (APHIS) looked at integration of biocontrol and insecticide treatment in urban and natural sites. A study of black and green ash in Syracuse, NY Naperville, IL, and Boulder, CO found continued high parasitism by Tetrasticus and S. galinae and woodpecker attacks in trees treated with emamectin benzoate. Researchers could not detect Oobius. By 2020, most of the untreated trees had died but treated trees remained healthy.
Murphy has begun studying integration of biocontrol and pesticides in green and black ash forests. The goal is to protect large trees to ensure reproduction; the biocontrol agents do not yet protect the large trees. This is especially important for black ash because it declines very quickly after EAB invades. Sites have been established in New York, through collaboration with New York parks, Department of Environmental Conservation, and the Mohawk tribe. She is still looking for sites in Wisconsin – where EAB is spreading more slowly than expected.
1 of the infested ash in Oregon; photo by Wyatt Williams, ODF
Max Ragozzino of the Oregon Department of Agriculture reported on imminent release of biocontrol agents targetting the recently detected outbreak there. I am encouraged by the rapid response by both the state and APHIS.
EAB resistance in ash
Jennifer Koch (USFS) said the goal is not to produce populations where every seedling is fully EAB-resistant, but to develop populations of ash trees with enough resistance to allow continued improvement through natural selection while retaining sufficient genetic diversity to adapt to future stressors (changing climate, pests, diseases). The program has developed methods to quantify resistance in individuals.. Initial field selections of “lingering ash” were shown to be able to kill as many as 45 % of EAB larvae. Already green ash seedling families have been produced by breeding lingering ash parents. This first generation of progeny had higher levels of resistance, on average, than the parent trees. Each generation of breeding can increase the proportion of resistance. Although the bioassays to test for EAB-resistance are destructive (e.g., cutting and peeling to count numbers of surviving larvae), the potted ash seedling stumps can resprout. Once the new sprouts are big enough they are planted in field trials to correlate bioassay results with field performers. Poor performers are culled; those with higher levels of resistance remain and become sources of improved seed.
To ensure preservation of local adaptive traits, this process must be repeated with new genotypes to develop many seed orchards from across the species’ wide range. To support this work, concerned scientists are building multi-partner collaborative breeding networks. These organizations provide ways for citizens and a variety of partners to engage through monitoring and reporting lingering ash, making land available for test planting, and helping with the work of propagation.
Resistance levels in some of the first generation progeny were high enough for use in horticulture, where it is important that trees can remain healthy in challenging environments (street trees, city parks, landscaping, etc.). Koch hopes to develop about a dozen cultivars comprising the best-performing trees, appropriate for planting in parts of Ohio, Michigan, Indiana, and Pennsylvania. Local NGO partners are planting some of these promising genotypes in Detroit to see how they withstand EAB attack.
a black ash swamp; photo via Flickr
The threat to black ash is especially severe, and this species presents unique difficulties. While scientists found several seedlings from unselected seedlots had killed high levels of larvae, those deaths did not always result in better tree survival. Koch thinks the tree’s defense response becomes detrimental to tree by blocking transport of water and nutrients. She is working with experts in genomics and others, such as Kew Royal Botanic Gardens, to try to identify candidate trees for breeding programs. The genomics work has been supported by APHIS and the UK forest research agency, DEFRA. Michigan and Pennsylvania have supported the breeding work. USFS Forest Health Protection has supported work with black and Oregon ash (see below) (J. Koch, USFS, pers. comm.).
Koch has also begun working with Oregon ash, in collaboration with the USFS Dorena Genetic Resource Center (located in Cottage Grove, Oregon) and other partners.
dead hemlock in Massachusetts; photo by Ian Kinahan, University of Rhode Island
Scientists are still trying to find the right combination of biocontrol, chemical treatments, and silvicultural manipulation.
For several years, hope has focused on two has been on two predatory beetles, Laricobius nigrinus and L. osakiensis. Scott Salom (Virginia Tech) reports that release of these beetles over the past 20 years has had a significant impact on HWA density and tree photosynthetic rate and growth. However, Laricobius aredifficult to rear and they attack only the sistens generation of the adelgid. Ryan Crandall (University of Massachusetts) reports it has been difficult to establish these beetles in the Northeast. He links this difficulty is caused by temporary drops in HWA populations after cold snaps.
Scientists now agree that need to find predators that attack HWA during other parts of its lifecycle. Hope now focuses on silverflies — Leucotaraxis argenticollis and Le. piniperda. While both species are established in eastern North America, the clades in the east feed almost exclusively on pine bark adelgid, and have not begun attacking HWA. Biocontrol practitioners therefore collect flies in the Pacific Northwest for release in the east. Salom is increasing his lab’s capacity to rear silverflies and exploring release strategies.
Preliminary evidence indicates that the western clades of Leucotaraxis are establishing, although data are not yet definitive (Havill, USFS).
Detecting the presence of biocontrol agents presents several challenges. Tonya Bittner (Cornell) described efforts to use eDNA analysis for this. Some puzzles have persisted; e.g., at some sites, she detected eDNA but caught no silverflies. This raised the question of long eDNA associated with the original release might persist. Another problem is that the assay cannot separate the introduced western L. nigrinus from the native congener, L.rubus (which also does not feed on HWA). She continues efforts to improve this technique.
Others explored interactions of the biocontrol agents with insecticides. Salom is studying the impact of soil-applied insecticides on Laricobius populations, which aestivate in the soil. Preliminary results showed significant reduction in the beetle’s population under soil drench application but not under soil injection. He has not yet analyzed all the data.
Michigan is trying to prevent spread of HWA from five counties along the eastern shore of Lake Michigan (where HWA was introduced on nursery stock) to widespread hemlock forests in northern part of the state. Phil Lewis (APHIS) is studying persistence of systemic insecticides in hemlock tissues, particularly twigs and needles. The pesticides involved are imidacloprid, dinotefuran, and Olefin. He has found that pesticide levels are highest 18 – 22 months after treatment, then decline. They are significantly higher after trunk injection compared to bark spray or soil treatments. Imidacloprid had higher residues in twigs; dinotefuran in needles. This difference affects the likelihood of adelgids actually ingesting the toxin.
healthy hemlock in experimental gap; Jefferson National Forest, VA; photo by Bud Mayfield, USFS
Bud Mayfield (USFS) reported on his study of silvicultural strategies to support healthier hemlocks. While hemlocks normally thrive in shade, it has been determined that sunlight assists small trees reducing HWA sufficiently to counter the tree’s leaf-level stress. Small sapling hemlocks grown in sunlight fix more carbon and convert it to growth in shoots and trunk diameter.
Mayfield found promising immediate suppression of HWA in large gaps in Georgia and Tennessee. By the third year the saplings were still growing, although their faster growth had attracted more HWA. These findings were less clear farther north in central Virginia and western Maryland – Mayfield thinks because HWA pressure there is lower. However, managers must maintain the gaps by cutting rapidly-growing competing woody species. He plans to test this strategy farther north in Pennsylvania. He is still trying to determine the optimal size of the gap.
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
The Nature Conservancy (TNC) and Clemson University have analyzed how to persuade people not to move firewood – and the tree pests that can accompany it. (Full citation at the end of this blog) Their study is based on five surveys conducted by TNC between 2005 and 2016. These surveys guided TNC’s “Don’t Move Firewood” campaign and its outreach efforts since the beginning in 2008
As Solano et al. note, wood-boring pests continue to enter the country and spread, causing immense damage. Firewood transport by campers is a significant contributor to that spread. Millions of individuals decide whether to move firewood. Yet the scientific literature is quite limited regarding their behavior and TNC’s survey data has never been published.
The patchwork of state and federal quarantines is largely reactive and has failed to prevent continuing spread. The regulatory regime has been further fragmented by APHIS’ deregulation of the emerald ash borer. As a consequence, limiting the spread of pests depends even more on educating campers to behave responsibly – voluntarily.
The TNC’s surveys each focused on different geographic areas and asked different questions in each. So their compilation cannot show trends in awareness or other measures. Nevertheless, the authors find:
Most people in the United States don’t know firewood can harbor invasive forest insects and diseases, but when targeted by effective education they can learn and are likely to change their behavior.
The two best ways to reach the public is through emails confirming campsite reservations and flyers handed out at parks. Web-based information seemed less effective. However, most of the surveys were done before 2011, the year when 50% of adults reported using internet media.
Forestry-related public agencies (especially state forestry departments) are the most trusted sources of information about forest health issues.
It works better to “push” information, not expect people to seek it on their own.
Messages should focus on encouraging the public to make better choices, including how they, themselves, will benefit. Positive, empowering calls to action, like “Buy it Where You Burn It” or “Buy Local, Burn Local” are better than negative messages, such as “Don’t Move Firewood”.
People respond to messages that emphasize protecting forest resources, e.g., ecosystem services like clean water. They response less to messages about forest threats.
Hungerford Lake Recreation Area at Equestrian Campground. Original public domain image from Flickr
Solano et al. describe the ways that different socioeconomic groups differ in their awareness of forest pests and in how they respond to various statements about forests, pests, and messengers. The focus is on how to overcome four psychological barriers to changing behavior that had been identified in a study of climate change. In the firewood context, those barriers were: 1) lack of awareness; 2) mistrust and negative reactions to the messengers; 3) habit; and 4) social comparison, norms, conformity, and perceived poor quality of purchased firewood.
From this work, the authors suggested further work::
Development of education and outreach programs that target those with lower education levels, since, on average, ~60% of people who camp did not graduate from college. Further research is probably needed to identify the most effective messengers and messages.
While 80% of the survey respondents were over 40, the proportion of campers made up of Gen X and millennials is increasing. Managers need to improve outreach for younger audiences. This includes engaging the messengers they trust: scientists, environmentalist politicians, peer networks, and social media.
While women trust the USDA Forest Service and conservation organizations, 55% of campers in a given year are men. Further research is needed to clarify the most effective messengers and messages for men. The outreach agencies should select the messengers that both sexes trust.
Levels of awareness should be assessed both before and after implementing new educational strategies so that the strategies’ effectiveness can be determined.
Since 80% of the respondents were white, determining the most effective messages and messengers for other ethnic groups also seems necessary, although the authors did not address this.
SOURCE:
Solano, A., Rodriguez, S.L., Greenwood, L., Rosopa, P.J., and Coyle, D.R. 2022. Achieving effective outreach for invasive species: firewood case studies from 2005-2016. Biological Invasions. https://link.springer.com/article/10.1007/s10530-022-02848-w
To request a copy of this study from the author, contact the lead author at Clemson University.
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
Asian giant hornet; photo by Yasunori Koide; Wikimedia commons
They’re still here … and perhaps more widespread than thought last year.What officials have learned is that colonies are often high up in trees, not in the ground, as expected based on behavior in Asia. This makes detection and control especially difficult.
In June a citizen found a dead Asian giant hornet (AGH) male in Snohomish County. This county in the Seattle metropolitan area is separated from Whatcom County (site of last year’s detections) by a third county, Skagit County. The Washington State Department of Agriculture (WSDA) responded by setting up traps in Snohomish and King counties, and urging citizens to be alert and report any hornet sightings.
Equally worrying, the dead wasp was determined by appearance and genetics to be unrelated to the colonies detected in 2019 and 2020 in Washington and British Columbia. Trapping in the areas found no additional specimens (S. Spichiger pers. comm.)
In July, WSDA designated the hornet genus Vespa as a quarantine pest; this action confirms WSDA authority to control access to nest sites.
nest eradication; WSDA photo
Nests Found and Destroyed
Starting in late summer, citizens began reporting sightings and officials succeeded in tracking hornets to their nests. However, it was not easy! Eradicating Asian giant hornets demands lots of resources and commitment. While all these nests were in Whatcom County – site of last year’s detections — it is clear that several colonies had been established. It seems to me highly unlikely that they have all been detected.
Detection of the first nest in 2021 came in August, following several visual detections of the hornets attacking nests of paper wasps. WSDA staff captured and tagged three hornets over a couple of days. They succeeded in tracking the third hornet when it reappeared a week later. The nest was destroyed (after removal of all hornets) on August 25th. This nest held nine layers of comb with 292 eggs, 422 larvae, and 563 prepuae. Nearly 200 adult hornets were killed. One queen was found. [Hornet Herald 21.07 Sept. 8 2021] The nest was at the base of a dead alder tree in rural Whatcom County, east of Blaine, just 400 metres south of the Canadian border.
The second and third nests were detected on September 8 and 10, 2021. In these cases, tagging and tracking the hornets was easier than in August. Nest eradication was not easy, however. Both nests were high inside dead alder trees, making access difficult. Both nests held multiple combs with hundreds of larvae, eggs, and pupae. Fortunately, only one queen was found in each. [Hornet Herald 21.08; October 5, 2021]
No detections have occurred since these.
WSDA also collected data on foraging behaviors of wasps in the third nest. Data include information on periods during the day when the wasps are active, and what materials they bring back to the nest – which includes wood pulp for nest comb construction and insect thoraces for feeding the pupae. [Hornet Herald 21.08; October 5, 2021]
It is encouraging that only one queen was found in each nest; in 2020, the single nest officials destroyed held 200 queens!
Trapping in British Columbia
Although British Columbia officials increased the number of traps in 2021, and urged citizens to also set out traps, no confirmed AGH finds were made in British Columbia until early November, when one was caught in a trap set for Japanese beetles. This hornet was on the border with Washington, so officials are trying to determine whether it came from one of the nests already discovered there.
There were a couple of unconfirmed sightings. On October 22 a single, aged specimen was found in a Japanese beetle trap about 1.2 km north of the first hornet nest extracted this year in Washington. The beetle trap had been serviced one month earlier. Canadian government entomologists are analyzing the DNA of this specimen to see if it was related to the Washington State nests.
At least one citizen said he had seen an Asian giant hornet in July, but officials said they could not investigate until they had either a picture or a specimen.
Asian giant hornet with radio tag developed by USDA APHIS scientists
Intriguing wrinkle
Mattila et al. (2021) describe an “impressive array of strategies” Asian honey bees use to protect nests from attacks by hornets in the genus Vespa, including a previously unknown use of auditory and perhaps chemical signals to warn nest mates. The authors suggest that this diverse alarm repertoire is similar to alarms issued by socially complex vertebrates such as primates and birds.
Giant hornet (Vespa soror) attacks trigger frenetic antipredator signalling in honeybee (Apis cerana) colonies. R. Soc. Open Sci. 8: 211215. https://doi.org/10.1098/rsos.211215
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 tree-killing 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
