conservation priorities – Page 12 – Center for Invasive Species Prevention

Unique Black Ash Wetlands – Threatened by Emerald Ash Borer

Another unique ecosystem being severely damaged by non-native tree-killing pests are the wetlands dominated by black ash (Fraxinus nigra). Black ash typically grows in fens, along streams, or in poorly drained areas that often are seasonally flooded. Such swamps stretch from Minnesota to Newfoundland; in the three states of Michigan, Wisconsin, and Minnesota, they cover a total of over 2 million hectares (Kolka et al. 2018).

Recent research allows us to understand the impending loss to these unique ecosystems that will be caused by the emerald ash borer (EAB).

Hydrology is the dominant factor that influences a host of ecosystem functions in black ash wetlands. Water levels are largely determined by a combination of precipitation and evapotranspiration rates. Black ash can thrive in wetter areas than most other tree species (Slesak et al. 2014). Water tables in these swamps are typically above the surface throughout early spring, followed by drawdown below the surface during the growing season with periodic rises following rain events. Water table drawdown coincides with peak evapotranspiration following black ash leaf out, demonstrating the fundamental control that this species has on animal and other plant communities (Kolka et al. 2018; Slesak et al. 2014).

Ecological Importance

Black ash generally dominate the canopy of these wetlands. Ash density can range from about 40% to almost 100%. Several other tree species are present, including northern white cedar (Thuja occidentalis), red maple (Acer rubrum), American elm (Ulmus americana) (Kolka et al. 2018), quaking aspen (Populus tremuloides), American basswood (Tilia americana), and bur oak (Quercus macrocarpa) (Slesak et al. 2014), balsam fir (Abies balsamea), balsam poplar (Populus balsamifera), and speckled alder (Alnus incana) (Youngquist et al. 2020). Black ash, by maintaining low water levels during the growing season, creates conditions under which these other trees can live but not thrive (summary of study by B.J. Palik, USDA Forest Service, here. Most other species lack the physiological adaptations of black ash or face pathogenic constraints (e.g., Dutch elm disease on American elm Ulmus americana) (Kolka et al. 2018).

Ash trees in these swamps are uneven-aged with canopy tree ages ranging from 130–232 years (Slesak et al. 2014). This complexity provides important habitat for many wildlife species, including ground beetle community assemblages (Kolka et al. 2018) and an abundance of aquatic macroinvertebrates. These are characterized and dominated by mollusks (Sphaeriidae, Lymnaeidae, Physidae), annelids (Lumbriculidae, Hirudinea), caddisflies (Limnephilidae, Leptoceridae), and dipterans (Chironomidae, Culicidae) (Youngquist et al. 2020).

A major concern is that loss of trees – especially ash – might result in open marshes dominated by grasses, especially lake sedge (Carex lacustris). Conversion to sedge-dominated marshes has been observed in areas where trees have been removed as part of experiments to test various ecosystem responses to loss of the ash component (Slesak et al. 2014). Even if other trees took the place of ash, the substitutes might not support the same animal communities (see below).

Impact of Emerald ash borer and loss of black ash

Black ash is highly susceptibility to the EAB (Engelken and McCullough, 2020), so scientists expect severe impacts of the invasion in ash-dominated wetlands and – to a somewhat lesser extent — in forested stream systems’ riparian areas (Engelken and McCullough, 2020). They expect cascading impacts on 1) hydrology; 2) plant communities; 3) wildlife; 4) Native American cultures; and possibly even storage of carbon in vegetation and soils (Kolka et al. 2018).

1) Hydrology

Experiments suggest that loss of ash will cause higher water tables, especially during late summer and fall (Kolka et al 2018). This will result from reductions in evapotranspiration as large trees are replaced by shrubs and grasses (see below) (Kolka et al. 2018; Slesak et al. 2014). The higher water table might be exacerbated if higher annual precipitation levels predicted by climate change models occur. On the other hand, these models also predict a simultaneous increase in longer droughts, which might partially counteract higher precipitation and reduced evapotranspiration (Kolka et al. 2018). If they occur, these possible increases in drought length and frequency might enhance the establishment of less water-tolerant non-ash tree species in former black ash wetlands.

2) Plant Communities

Higher water tables are expected to reduce tree densities and promote conversion to open or shrub-dominated marshes. Several of the possible alternative tree species do not thrive as well as black ash under current conditions (Kolka et al. 2018). However, new hydrologic conditions might make forest restoration even more difficult because herbaceous plants transpire less water than trees, thus exacerbating the rising water tables (Slesak et al. 2014).

In upper Michigan, experiments which killed ash by cutting or girdling did not lead to an increase in growth rates of the remaining canopy species despite the increase in available resources (e.g., sunlight and nutrients) – presumably because of the raised water table (Kolka et al. 2081).

While some studies have found that black ash seedlings and saplings dominated the woody component of the swamp understory up to three years after ash were experimentally removed (Kolka et al. 2018), Engelken and McCullough (2020) found only eight saplings and a single seedling.

Scientists have planted several tree species in experiments to see which might be used to maintain the forested wetlands in the absence of black ash. The results are a confusing mix. Some species grew well once established – but had low levels of seedling establishment. Some trees planted on elevated microsites (hummocks) had the greatest survival and growth rates. (For specific data, see Kolka et al. 2018). A further consideration is tree species’ ability to adapt to warming temperatures already evident and expected to increase in coming decades (Slesak et al. 2014).

Consequently, Slesak et al. (2014) think it is likely that the EAB invasion will alter vegetation dynamics and cause a shift to an altered ecosystem state (e.g., open marsh condition) with higher water tables. They caution that the degree of ecosystem alteration will vary depending on site hydrology, annual precipitation, and period of time necessary for establishment of deeper rooted vegetation.

3) Wildlife

Moreover, any changes in vegetation will also affect the biota in more subtle ways through altered nutrient cycles. Black ash leaf litter is highly nutritious, having some of the highest nitrogen, phosphorus, and cation contents of any hardwood forest species (Kolka et al. 2018). Black ash leaves also decompose faster than most alternative tree species’ leaves (summary of Palik USDA Forest Service, here; Youngquist et al. 2018).

Youngquist et al. (2018) studied litter breakdown, litter nutritional quality, and growth of a representative invertebrate litter feeder – larvae of a shredding caddisfly (Limnephilus indivisus). They found that the larvae’s risk of death increased by a factor of three times or more when caddisflies were fed American elm, balsam poplar, or lake sedge leaves compared to black ash leaf litter. Even when the larvae lived – but matured more slowly because of the lower nutrition value of the leaves – they would still be vulnerable because they must reach metamorphosis before pond dry-down. In any planting done to maintain forested quality of wetlands, need to consider the nutritional quality of the leaf litter provided by replacements. Speckled alder was only apparently acceptable substitute; it was second to black ash in acceptability to caddisflies (Youngquist et al. 2020)

In fact, Youngquist et al. (2020) concluded that plant and detritivore biodiversity loss due to EAB invasion could alter productivity and decomposition at rates comparable to other anthropogenic stressors (e.g., climate change, nutrient pollution, acidification). The result will be altered biogeochemical cycles, resource availability, and plant and animal communities.

Scientists are also concerned about the impact of ash tree mortality on forest connectivity. Conversion of wooded swamps to shrub-and sedge-dominated wetlands will result in the loss of important micro-habitats that are already limited across the forested landscape and may also reduce availability of critical habitat for migrating birds. These changes will exacerbate on-going changes in land use in the Great Lakes region that are causing loss of forest habitat and forest homogenization. As yet, the magnitude of the impact on wildlife is unclear (Kolka et al. 2018).

black ash baskets – displayed at 2006 conference
photo by Faith Campbell

4) Cultural importance – baskets

Native Americans living in the range of black ash have utilized the wood to make baskets and other tools for thousands of years. Baskets had numerous uses, such as packs for carrying items, fish traps, and for preparing food and storing household items. Ash items also had ceremonial uses and they are highly sought as gifts and in trade. The skill needed to select a good tree and work the wood is handed down through the generations and is an important part of tribes’ culture (Benedict 2010).

Discussion of these cultural traditions can be found as Powerpoints here and here.

A video is posted here.

USFS Research Efforts

Concerned by the spread of EAB and probable impact on black ash swamps, the USDA Forest Service has initiated major research studies with the goal of filling in the numerous knowledge gaps and developing management recommendations. A large-scale study using various manipulations to simulate the EAB invasion was initiated in the Chippewa National Forest in northern Minnesota in 2009. A companion study began in the Ottawa National Forest in Michigan in 2010 (Kolka et al. 2018). The Slesak, Youngquist, and Kolka publications cited in this blog report results of some of the studies in this project. Other studies of black ash conditions, including regeneration, at various stages of the EAB invasion wave are being carried out by Deb McCullough, Nate Siegert, and others. They are working at sites from Michigan to New England (D.G. McCullough, pers. comm.).

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 great discussion of black ash basketweavers, see Anne Bolen, A Silent Killer: Black Ash Basket Makers are Battling a Voracious Beetle to Keep their Heritage Alive, American Indian Magazine, Spring 2020, available here.

SOURCES

Benedict, M. 2010. Ecology and the Cultural and Economic Importance of Black ash (Fraxinus nigra Marsh) for Native Americans May 2010 https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5191796.pdf

Engelken, P.J. and D.G McCullough. 2020. Riparian Forest Conditions Along Three Northern Michigan Rivers Following Emerald Ash Borer Invasion. Canadian Journal of Forest Research. Submitted

Kolka, R.K., A.W. D’Amato, J.W. Wagenbrenner, R.A. Slesak, T.G. Pypker, M.B. Youngquist, A.R. Grinde and B.J. Palik. 2018. Review of Ecosystem Level Impacts of Emerald Ash Borer on Black Ash Wetlands: What Does the Future Hold? Forests 2018, 9, 179; doi:10.3390/f9040179 www.mdpi.com/journal/forests

Slesak, R.A., C.F. Lenhart, K.N. Brooks, A.W. D’Amato, and B.J. Palik. 2014. Water table response to harvesting and simulated emerald ash borer mortality in black ash wetlands in MN, USA. Can. J. Forestry. Res. 44:961-968.

Youngquist, M.B., C. Wiley, S.L. Eggert, A.W. D’Amato, B.J. Palik, & R.A. Slesak. 2020. Foundation Species Loss Affects Leaf Breakdown and Aquatic Invertebrate Resource Use in Black Ash Wetlands. Wetlands. Society of Wetland Scientists

Posted by Faith Campbell

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

Calamity in Pacific Island Forests

We know the dire threats to Hawaiian forests from pathogens. Some threaten the most widespread tree – ohia. Others are insects threatening trees and shrubs in the remnant dryland forests.

The forests of smaller islands of the Pacific also appear to be facing severe threats – although I have been unable to find information on the current situation.

Guam and its Neighbors

The forests of Guam, Palau, and others in the Western Pacific are among those threatened.

They are geographically isolated and hard to reach, but that distance has not protected them from biological invaders. Their predicament illustrates the dominant role of global movement and trade in spreading pests. In this case, it’s mostly trade in ornamental plants.

These islands have unique flora and fauna. And true to invasive species experts’ expectations, they are vulnerable to bioinvaders. Guam’s most famous invasive species is the brown tree snake (Boiga irregularis), which over a few decades eradicated many bird species and the only native terrestrial mammal, the fruit bat.

Less known, but equally damaging, have been a group of insects that are decimating Guam’s native forest flora.

The most widespread arboreal species in the forests of Guam and neighboring islands is the Micronesian cycad, Cycas micronesica. Its range is Micronesia, the Marianas Group including Guam and Rota Islands; and several of the western Caroline Islands, e.g., Palau and Yap (Marler, Haynes, and Lindstrom 2010).

These forests have already absorbed severe habitat destruction as the sites of fierce fighting in World War II and – in some cases – construction of large military bases. Still, cycads were the most common species in the forest as late as 2002 (Moore, A., T. Marler, R. Miller, and L. Yudin. Date uncertain).

The Worst Pest: Asian Cycad Scale

The most severe current threat to the cycads are introduced insects, especially the Asian cycad scale Aulacaspis ysumatsui.

The cycad scale is native to Southeast Asia. It was first detected on Guam in 2003, when officials noticed that cycads planted near hotels had begun to die. However, this scale had already been spreading thanks to the trade in ornamental cycads. It was detected in Florida in 1996, on Hawai`i in 1998. It continued to spread rapidly in the western Pacific: to Rota in 2007, Palau in 2008 (University of Guam 2012). By late 2019, the scale had spread globally – numerous islands and neighboring mainland areas in the Caribbean (including Puerto Rico and US Virgin Islands), several US states in the Southeast, California, and Taiwan (Moore, Marler, Miller, and Yudin. Date uncertain.) and South Africa. (vanWilgen, et. al. 2020) Also, see the map prepared by CABI.

In every case, the scale has apparently been spread on nursery stock. It is difficult to contain by standard phytosanitary measures – visual inspection – because the scale is tiny and hides deep in the base of the plant’s stiff leaves and other crevices. (Marler and Moore 2010)

By 2005 the scale was killing the native cycad on Guam. Within four years, the millions of C. micronesica on Guam were reduced by more than 90% (Marler, T.E. and K.J. Niklas. 2011). The last time cycads on Guam reproduced in any significant number was in 2004 (Marler and Niklas 2018).

The severe impact of the scale was so rapid that the International Union for Conservation of Nature and Natural Resources (IUCN) changed its listing of C. micronesica from “near threatened” in 2003 to “endangered” in 2006. (IUCN Red List of Threatened Species Online 2008).

Scientists have made several attempts to introduce a biocontrol agent. However, the most promising – the lady beetle Rhyzobius lophanthae – has failed to control the scale, despite having become virtually ubiquitous on Guam. The beetle is too big to reach the significant proportion of scale insects living in small cracks and voids within the plant structures. Evidence from another cycad species indicates that the beetles also don’t prey on scale insects living beneath trichomes (fine hairlike structures on the leaves) or on parts of the plant close to the ground. (Moore, Marler, Miller, and Yudin. Date uncertain.).

Attempts to introduce a second biocontrol organism – the parasitoid wasp Aphytis lignanensis – were stymied by the presence of R. lophanthae (Moore, Marler, Miller, and Yudin. Date uncertain).

Micronesian cycad
photo by Lauren Gutierrez

Other Invasive Species Attacking Cycads

The cycad blue butterfly (Chilades pandava) was detected in 2005 and spread throughout Guam within months (IUCN 2009). Also, it’s been found on Saipan (1996) and Rota (2006). The butterfly is native to southern Asia from Sri Lanka to Thailand and Indonesia. High populations can cause complete defoliation of new foliage. Repeated defoliations can kill the plant. Cycads on Guam are particularly vulnerable because the scale has already caused loss of most of their leaves. Butterfly larvae are often protected by ants (Anonymous).

On cultivated plants the butterfly can be controlled by microbial insecticides containing Bacillus thuringiensis kurstaki (Moore). Scientists at the University of Guam are exploring use of injected insecticides (Moore). They have found an egg parasite, but parasitism levels are low. Any biocontrol agent targetting larvae would have to contend with the ants (Anonymous).

A longhorned beetle (Dihammus (Acalolepta) marianarum) and a snail (Satsuma mercatorius) are also feeding on the cycads (Marler 2010).

The Indo-Malayan termite Schedorhinotermes longirostris was detected in 2011. The termites weaken the cycad stems, which are then toppled by feeding by introduced deer. The termites are also damaging the cycad’s reproductive structures (megastrobili). Termite attacks on cycads surprised scientists since cycads do not form true wood. The termite had probably been introduced recently because, as of 2011, it had been detected only near the Andersen Air Force Base airport (Marler, Yudin, and Moore 2011).

More Isolated – but Still Overrun

Scattered across the Pacific are groups of atolls, including Palmyra and Rose.

Despite their distance from other islands, they have all been visited by mariners for centuries. As a result, they have non-native species, including insects that attack trees.

The tree most affected is pisonia – Pisonia grandis.

The principal insect is another scale, Pulvinaria urbicola. There are some reports that the scale is farmed by ants; species mentioned include several introduced species such as the yellow crazy ant, Paratrechina longicornis.

The scale is probably from the West Indies. Once it reached the Pacific, it might have been distributed to additional islands on seabirds, which travel long distances between the atolls.

The scale’s impact is unclear.

At first, in the mid-2000s, impacts seemed dire. It was reported to be causing widespread tree death on Palmyra and Rose atolls, islands around northeastern Australia, in the Seychelles, and possibly in Tonga.

However, in 2018, scientists reported that eradication of rats on Palmyra Atoll had resulted in an immediate spurt of reproduction of a tree. Numbers of “native, locally rare tree” seedlings (possibly but not explicitly said to be Pisonia grandis) jumped from 140 pre-eradication to 7,756 post-eradication (in 2016). The study made no mention of the scale.

Rose Atoll has only one small island (6.6 ha) with vegetation. Before 1970, it was dominated by Pisonia grandis, but by 2012, there were only seven trees on the island. Several possible causes of this decline have been suggested. Other than the scale, suggested causes include storms, drought, rising sea level / saltwater incursion, and imbalance of bird guano-derived nutrients in the soil. [All information about Rose Atoll is from Peck et al., 2014)

A survey carried out in April 2012 and November 2013 detected 73 species of arthropods from 20 orders on Rose Island, including nine ant species (all but one non-native). Two of these ants – Tetramorium bicarinatum and T. simillimum – were detected tending the scales on Pisonia.

The survey found no evidence of natural enemies of the Pulvinaria scales.

The scientists tested treatment of Pisonia with the systemic insecticide imidacloprid. This treatment apparently reduced scale populations considerably for several months, but then they began to build up again.

In contrast to Palmyra, Polynesian rats (Rattus exulans) were eliminated from Rose Atoll in 1990–1991 – so their role in destroying the trees had ended 20 years before the study. What does the continued decline of the Pisonia trees in subsequent decades suggest for the future of Pisonia trees on Palmyra?

I have sought updates on the tree-pest situations on Guam and the other Pacific islands, but my queries have not received a reply.

SOURCES

Anonymous. 2015. Cycad blue butterfly fact sheet.

Brooke, USFWS, pers. comm. June 3, 2005

CABI November 2019. Aulacaspis yasumatsui (cycad aulacaspis scale (CAS)) or the Asian cycad scale. https://www.cabi.org/isc/datasheet/18756 (was formerly Commonwealth Agricultural Bureaux (CAB) International; now apparently just uses acronym)

Marler, T.E. pers. comm. August 15, 2012

Marler, T.E. 2010. Cycad mutualist offers more than pollen transport. American Journal of Botany, 2010; 97 (5): 841. Viewed as materials provided by University of Guam, via EurekAlert; accessed 6 August, 2012.

Marler, T., Haynes, J. & Lindstrom, A. 2010. Cycas micronesica. The IUCN Red List of Threatened Species 2010: e.T61316A12462113. http://dx.doi.org/10.2305/IUCN.UK.2010-3.RLTS.T61316A12462113.en Accessed 22 April, 2020.

Marler, T.E., and A. Moore. 2010. Cryptic Scale Infestations on Cycas revoluta Facilitate Scale Invasions. HortScience. 2010; 45 837-839. Retrieved August 6, 2012 from www.eurekalert.org

Marler, T.E., L.S. Yudin, A. Moore. 1 September 2011. Schedorhinotermes longirostris (Isoptera: Rhinotermitidae) on Guam Adds to Assault on the Endemic Cycas micronesica. https://bioone.org/journals/florida-entomologist/volume-94/issue-3/024.094.0339/Schedorhinotermes-longirostris-Isoptera–Rhinotermitidae-on-Guam-Adds-to-Assault/10.1653/024.094.0339.full

Marler, T.E. and K.J. Niklas. 2011. Reproductive Effort and Success of Cycas micronesica K.D. Hill Are Affected by Habitat. International Journal of Plant Sciences, 2011; 172 (5): 700. Viewed as materials provided by University of Guam, via EurekAlert; accessed 6 August, 2012.

Moore, A. Cycad blue butterfly fact sheet. http://www.guaminsects.net/gisac2015/index.php?title=Cycad_blue_butterfly_fact_sheet accessed 20-4/24

Moore, A., T. Marler, R. Miller, and L. Yudin. Date? Biological Control of Cycad Scale, Aulacaspis yasumatsui, Attacking Guam’s Endemic Cycad, Cycas micronesica. Western Pacific Tropical Research Center University of Guam. Powerpoint http://guaminsects.myspecies.info/sites/guaminsects.myspecies.info/files/CycadScaleBiocontrolAustin.pdf

Peck, R., P. Banko, F. Pendleton, M. Schmaedick, and K. Ernsberger. 2014. Arthropods of Rose Atoll with Special Reference to Ants and Pulvinaria urbicola scales (Hemiptera: Coccidae) on Pisonia grandis trees. Hawaii Cooperative Studies Unit. University of Hawaii. Technical Report HCSU-057 December 2014

University of Guam (2012, August 2). Invasive insects cause staggering impact on native tree. ScienceDaily. Retrieved August 6, 2012, from www.sciencedaily.com-/releases/2012/08/120803094527.htm).

vanWilgen, B.W.,J. Measey, D.M. Richardson, J.R. Wilson, T.A. Zengeya. Editors. 2020. Bioinvasions in South Africa. Invading Nature. Springer Series in Invasion Ecology 14.

Posted by Faith Campbell

Pest Threats to Eastern Forests – Focus on the Mid-Atlantic

EAB-kiled ash tree in Shenandoah National Park in 2016
photo by F.T. Campbell

As we have known for years, forests of the eastern United States are under severe pressure from non-native forest insects and diseases. Several recent studies have put this fact into perspective.

Fei et al. (2019) found that the 15 most damaging introduced species threaten 41.1% of the total live forest biomass in the 48 conterminous states. Nine of the 15 species included in this calculation are pests of the eastern forest. Indeed, the greatest increase in biomass loss, as measured by USDA Forest Service Forest Inventory and Analysis (FIA) plot data occurred here. Compensatory growth in unaffected trees and the recruitment of new regeneration occurs only later – as much as two or more decades after the pest invasions began. Fei et al. (2019) expect these losses will be exacerbated in the future due in part to the likelihood that additional pests will be introduced.

Randall Morin found that non-native pests had caused approximately 5% increase in total mortality, by tree volume, nation-wide.

Most widespread pest threats in the East

Scientists have used several methods of measuring introduced pests’ impacts. One measure is the number of counties where the pest is present. A second measure is the proportion of the volume of the host that has been affected. Both metrics are used by Morin. A third method, used by the CAPTURE Project (Potter et al. 2019a), is the number of hosts affected by the pest.

Morin and colleagues found that the European gypsy moth has invaded 630 counties – or 29% of the volume of its principal host, oaks. (In both cases, the gypsy moth trailed white pine blister rust in extent of infestation. The latter is nationwide but having its greatest impacts in the West). The CAPTURE Project found that the gypsy moth affected the largest number of hosts – 65.

Using the “counties invaded” metric, Morin and colleagues found that dogwood anthracnose had invaded 609 counties in the East (and additional areas in the West); the emerald ash borer had invaded 479 counties at the time of analysis; the hemlock woolly adelged had invaded 432 counties. Using the number of hosts impacted measure, oak wilt (Bretziella fagacearum) affected the second largest number of hosts – 61 (Potter et al. 2019a). [All these pests are described briefly here.]

Project CAPTURE (Potter and colleagues 2019a) evaluated 339 serious pests threatening one or more of 419 native tree species in the continental US. They included both native and introduced pests. They analyzed 1,378 pest-host combinations. They found that:

54% of the host tree species (228) are infested by an exotic pest – although only 28% of the 1,378 host/agent combinations involved pests are known to be non-native in origin.
Exotic agents have, on average, considerably more severe impacts than native pests.
Non-native pests had greater average severity on angiosperms than on conifers. (As an earlier blog documented, Mech and colleagues have reached a similar – although tentative – conclusion.)
Their estimate of the threat posed by non-native pests to forests – especially for the East – is an underestimate because established pests could spread to additional vulnerable areas and there is a high likelihood that new pests will be introduced. The Southeast was consistently a “coldspot” – despite the near extirpation of one understory tree – redbay.

Potter et al. (2019a) ranked forest threats in two ways. Four host families were at highest risk to alien pests, as measured by both the numbers of tree species affected and by the most host/agent combinations: Fagaceae (oaks, tanoaks, chestnuts, beech); Pinaceae (pines); Sapindaceae (soapberry family; includes maples and buckeye); Salicaceae (willows, poplars, aspens). When host families were ranked by the severity of the host/pest threat, Fagaceae was still at greatest risk, and Sapindaceae was still in the top four; however, Ulmaceae (elms) and Oleaceae (includes Fraxinus) replaced pines and willows.

A very interesting study was published by scientists based in the Blue Ridge Mountains of Virginia (Anderson-Teixeira et al. 2020). They contend that their area is a good example of what is happening more broadly in the Mid-Atlantic region.

Anderson-Teixeira et al. (2020) found that non-native pests have substantially impacted at least 24% of the 33 tree genera (eight genera) recorded as present in their study plots. They estimated that over the century beginning with the appearance of chestnut blight in the region and ending with the expected extirpation of ash trees, net live aboveground biomass (AGB) loss among affected species totaled roughly 6.6–10 kg m -2. Forty to sixty percent of this loss started before the Park initiated quantitative surveys of permanent plots in 1987. The authors estimated that chestnut contributed up to 50% of estimated AGB losses over the century. Consequently, the estimate has very high uncertainty.

Despite these losses, Anderson-Teixeira et al. (2020) found that both total aboveground biomass and diversity within individual study plots had largely recovered through increases in non-vulnerable genera.

Average above ground biomass across the plots established in Shenandoah National Park increased as the forest recovers from logging, farming, and other disturbances before formation of the Park. These increases were due primarily to reproduction and growth of tulip poplar (Liriodendron tulipifera) and growth (but not reproduction) of oaks. Net AGB biomass was lost in oak- and hemlock-dominated plots. At plots established in the neighboring Smithsonian Conservation Biology Institute, pests had caused relatively minor impacts on AGB.

Diversity of tree species also did not change much. In the Park, the average number of genera per plot declined only 3% between 1991 and 2013. Diversity at the landscape scale increased by two genera – from 26 to 28. Many individual plots, though, lost three genera due to non-native pests – chestnut, redbud, and hemlock. A fourth genus was lost due to stochastic change. At the same time, the plots gained six native genera). This finding might be skewed by the short duration of the study period, which missed initial declines in several taxa and captured only the initial stages of decline in ash.

Several taxa were lost from the monitoring plots but were not completely extirpated from the region. Even those species not “lost” suffered elevated mortality rates and steep declines in abundance and above-ground biomass. These declines have not been reversed. The exception was some oaks, which regained above ground biomass, but not abundance, following the gypsy moth outbreak in the 1980s and early 1990s.

Taxa-specific findings

(Most of these pests are described briefly here.)

Fei et al. (2019) found that losses in biomass due to non-native pests – as measured by FIA plot data – was greatest for ashes, elms, beech trees, and hemlocks..

Morin and colleagues found annual mortality rates had increased three-fold above background levels for ash, beech, and hemlock. They also calculated the present mortality rates for several species for which the majority of loss occurred before their study (consequently, they could not calculate a pre-invasion “background” rate to which present rates could be compared). These included American chestnut (mortality rate of 7%), butternut (mortality rate of 5.6%), and elm trees (mortality rate of 3.5%).

The CAPTURE Project (Potter et al. 2019a) identified fifteen host-agent combinations with the highest severity. Ten of these species are found in the Mid-Atlantic region:

American chestnut (Castanea dentata)
Allegheny chinquapin (C. pumila)
Carolina ash (Fraxinus caroliniana) ,
pumpkin ash (F. profunda)
Carolina hemlock (Tsuga caroliniana)
butternut (Juglans cinerea)
eastern hemlock (Tsuga canadensis)
white ash (Fraxinus americana)
black ash (F. nigra)
green ash (F. pennsylvanica)

Four of these species are in genera included among the eight genera evaluated in the study conducted in the Blue Ridge (Anderson-Teixeira et al. 2020): American chestnut, butternut, eastern hemlock, green and white ash. The four other genera in the Blue Ridge study were elm (Ulmus), oak (Quercus), redbud Cercis, and dogwood (Cornus). All except redbud are recognized by other sources as heavily affected by non-native pests – confirming Anderson-Teixeira et al. (2020)’s conclusion that findings on the Blue Ridge reflect the wider situation.

Anderson-Teixeira et al. (2020) note that several of these tree species have been declared imperiled by the International Conservation Union (IUCN): American chestnut, butternut, American elm, eastern hemlock, and ash species.

Anderson-Teixeira et al. (2020) report data on three taxa previously important in the canopy of Blue Ridge forests – chestnut, elms, and butternut. Chestnuts larger than 10 cm DBH had disappeared from the future site of Shenandoah National Park by 1910. Short-lived sprouts continue to be present in plots in the low-elevation Smithsonian Conservation Biology Institute. Two elm species were described as ‘‘sparse’’ in the 1939 qualitative survey. Elms have persisted at low densities, low biomass, and increasingly small sizes. Butternut was ‘‘common’’ in 1939, but had disappeared from Shenandoah NP by 1987. On the Smithsonian’s property, butternut declined from four living individuals in 2008 to two in 2018. The near disappearance of butternut reflects the national picture: FIA data show the species has decreased about 58% across its U.S. range since the 1980s – which is decades after butternut canker started having a detectable impact in the Midwest.

In the Park, oak-dominated plots lost on average 24.9% of individuals and 15% of aboveground biomass. After 1995, when the gypsy moth was better controlled by spraying of Bacillus thuringiensis var. curstaki, oak aboveground biomass increased gradually, driven by individual tree growth rather than new recruitment. Continued declines in oak abundance are attributable to oak decline and management actions (or inactions) that do not promote regeneration.

In a separate study, a group of oak experts went through a process of queries to identify the greatest threat to oaks now and in the future (Conrad et al. 2020). They initially identified the following threats as most important currently (descending order): gypsy moth, oak wilt, oak decline, climate change, and drought. The top five future threats were initially identified as climate change, oak wilt, sudden oak death, oak decline, and some unknown new or emerging (non-native) pest or pathogen. By the third round, after the experts thought about their colleagues’ responses, oak decline had replaced gypsy moth as the most critical threat currently. Attack by an unknown new or emerging (non-native) pest or pathogen replaced climate change as the most critical future threat. While there was not a complete consensus, the consensus was stronger on the threat from a new pest.

remnant eastern hemlock at Linderlost, Shenandoah National Park
photo by F.T. Campbell

Anderson-Teixeira et al. (2020) reported that eastern hemlock was initially present in ten of Shenandoah plots, but was no longer recorded in the survey plots after 2007. (More than 20,000 insecticide-treated trees remain alive throughout Shenandoah NP).

Before arrival of the emerald ash borer, ash aboveground biomass was increasing in Shenandoah NP and stable on the Smithsonian Institute. EAB-caused mortality was first detected at the Smithsonian site in 2016 and accelerated steeply thereafter, exceeding 12.5% year by 2018. As of 2019, ash had lost 28% of individuals and 30% of aboveground biomass relative to 2016. Ninety-five percent of remaining live trees were considered “unhealthy’’ (Anderson-Teixeira et al. 2020).

eastern (flowering) dogwood; photo by F.T. Campbell

Unlike many studies, the Shenandoah study included understory species. Flowering dogwood declined by up to 90% from plots on the Smithsonian property; 2008–2019 mortality rates averaged 7.1%. Redbud declined by up to 76% from 1995 to 2018. The 2008–2019 mortality rates averaged 6.2% year.

Anderson-Teixeira et al. (2020) concede difficulty in estimating mortality due to less virulent or lethal pathogens, including Neofusicoccum spp. on redbud and Dutch elm disease on slippery elm.

Nevertheless, they believe their analysis probably underestimates the overall pest impacts because they did not analyze several other pest/host combinations known to be present in the Park: balsam woolly adelgid (Adelges piceae) on high-elevation populations of Abies balsamea; white pine blister rust (Cronartium ribicola) on eastern white pine (Pinus strobus); beech bark disease (Neonectria spp.) on American beech (Fagus grandifolia); thousand canker disease on walnut and butternut; and emerald ash borer on the novel host fringetree Chionanthus virginicus.

Another possible threat to oaks, winter moth (Operophtera brumata), is apparently now being controlled by the biocontrol agent Cyzenis albicans.

I am uncertain about the current status of two Diplodia fungi – Diplodia corticola and D. quercivora – link to blog which have been detected in both Florida and California. In Florida, almost all the symptomatic trees grow in cultivated settings where they are exposed to various stresses (Mullerin and Smith 2015).

However, host range studies indicate that 33 species of oaks and one species of chestnut that grow in the Southeast are vulnerable, to varying degrees, to D. corticola. Oaks in the red oak group (Section Lobatae) are more vulnerable than are white oaks (Section Quercus) (Mullerin and Smith 2015). In the test, the most vulnerable appear to be the following species native to the Southeast: Q. laurifolia, Q. virginiana, Q. geminata, Q. chapmanni, Q. laevis (turkey oak), Q. phellos, Q. pumila, and Q. incana (Dreaden et al. 2016).

What should we do?

Fei et al. (2019) noted that the losses to biomass would be exacerbated by the likely introduction of additional pests. They did not recommend any prevention actions.

Conrad et al. (2020) said their findings “lend support to national regulatory and awareness efforts to prevent the introduction and establishment of novel exotic insects and pathogens.”

Anderson-Teixeira et al. (2020) join others in declaring that future survival of the IUCN-listed species probably depends on conservation and restoration actions. They cite several sources, but not the CAPTURE Project – although the two studies reinforce each other. They specifically mention limiting invasive species’ spread through strengthened regulations and “enhanced plant biosecurity cyberinfrastructure”.

This last recommendation reinforces the message of Bonello et al. (2019) link to publication. We called for creation of a federal Center for Forest Pest Control and Prevention to implement end-to-end responses to forest pest invasions. One focus would be correcting the currently-inadequate focus on detection, development and deployment of genetic resistance while using modern techniques that allow for much faster breeding cycles.

Posted by Faith Campbell

SOURCES

Anderson-Teixeira, K.J., V. Herrmann, W.B. Cass, A.B. Williams, S.J. Paull, E.B. Gonzalez-Akre, R. Helcoski, A.J. Tepley, N.A. Bourg, C.T. Cosma, A.E. Ferson, C. Kittle, V. Meakem, I.R. McGregor, M. N. Prestipino, M.K. Scott, A.R. Terrell, A. Alonso, F. Dallmeier, and W.J. McShea. Date? Long-Term Impacts of Invasive Insects and Pathogens on Composition, Biomass, and Diversity of Forests in Virginia’s Blue Ridge Mountains. Ecosystems

Bonello, P. , F.T. Campbell, D. Cipollini, A.O. Conrad, C. Farinas, K.J.K. Gandhi, F.P. Hain, D. Parry, D.N. Showalter, C. Villari, and K.F. Wallin. 2019. Invasive tree pests devastate ecosystems – A proposed new response framework. Frontiers

Conrad, A.O., E.V. Crocker, X. Li, W.R. Thomas, T.O. Ochuodho, T.P. Holmes, and C. D. Nelson. 2020. Threats to Oaks in the Eastern US: Perceptions and Expectations of Experts. Journal of Forestry, 2020, 14–27

Dreaden, Black, Mullerin, and Smith. Poster presented at the 2016 USDA Invasive Species Research Forum

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. Liebhold. 2019. Biomass losses resulting from insect and disease invasions in United States forests. Proceedings of the National academy of Sciences.

Guo, Q., S. Feib, K.M. Potter, A.M. Liebhold, and J. Wenf. 2019. Tree diversity regulates forest pest invasion. PNAS. www.pnas.org/cgi/doi/10.1073/pnas.1821039116

Morin, R.S., K.W. Gottschalk, M.E. Ostry, A.M. Liebhold. 2018. Regional patterns of declining butternut (Juglans cinerea L.) suggest site characteristics for restoration. Ecology and Evolution.2018;8:546-559

Morin, R. A. Liebhold, S. Pugh, and S. Fie. 2019. Current Status of Hosts and Future Risk of EAB Across the Range of Ash: Online Tools for Broad-Scale Impact Assessment. Presentation at the 81^st Northeastern Forest Pest Council, West Chester, PA, March 14, 2019

Mullerin, S. & J.A. Smith. 2015. Bot Canker of Oak in FL Caused by Diplodia corticola & D. quercivora. Emergent Pathogens on Oak and Grapevine in North America. FOR318

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

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

Serious Invasive Species Damage to High-Elevation Sites in the West

Dream Lake, Rocky Mountain National Park, with limber pine
photo by F.T. Campbell

In this blog, I summarize two pest threats to the unique ecosystems on high-elevation mountain ridges in the West. At risk are several keystone tree species: the five-needle pines growing at high elevations (“high-five” pines) and subalpine fir. The invasive species causing this damage – white pine blister rust (WPBR; Cronartium ribicola) and balsam woolly adelgid (BWA; Adelges piceae) – are two of the most widespread non-native species threatening North American trees and affecting the highest proportion of host volumes (Morin).

The pines being killed by white pine blister rust are whitebark pine (Pinus albicaulis), limber pine (P. flexilis), Rocky Mountain bristlecone pine (P. aristata), foxtail pine (P. balfouriana), and southwestern white pine (P. flexilis var. reflexa). As of 2010, infestations had not been reported on Great Basin bristlecone pine (P. longaeva) and the Mexican white pine species. [Unless otherwise indicated, information on white pine blister rust is from a comprehensive review and synthesis published in the August 2010 issue of Forest Pathology (Vol. 40:3-4).]

As noted above, sub-alpine fir (Abies lasiocarpa) is also being affected – although less uniformly than the pines – by the balsam woolly adelgid.

Both of these pests arrived approximately a century ago, but they are still spreading and causing additional damage. White pine blister rust had spread widely throughout the West within 40 years of its introduction. Meanwhile, BWA spread among lowland and subalpine firs along the Pacific coast from California to British Columbia within 30 years of its first detection. Its spread eastward was slower, but relentless. It reached Idaho, Montana, Utah and interior British Columbia within 50 years. Also, BWA reached Alaska within 90 years of its introduction in California. These pests are perfect examples of how invasive species introduced long ago are dreaded “gifts that keep on giving”.

For a detailed discussion of these pests’ impacts, see the descriptions posted here. To summarize, though, WPBR is present in the ranges of eight of the nine vulnerable western white pines and has caused severe mortality to some species (Sniezko et. al. 2011). For example, 88% of the limber pine range in Alberta is affected (Dawe et al. 2020). WPBR is generally causing more damage to its hosts’ northern populations. Impact of the BWA are more subtle than WPBR. Also, impacts’ severity is linked to climatic conditions. For example, measurable decline on the Olympic Peninsula was greater on south-facing slopes. However, the study did not determine whether this reflected heat-loading and tree stress or more abundant subalpine fir on these slopes. An estimated 19-53% (average 37%) of subalpine fir trees had died on sample plots on one ridge over the 19 years since BWA was first detected there. Overall forest growth after 2007 could indicate partial recovery, a momentary pause in BWA invasion, or tree growth after severe weather events (Hutton 2015).

Ranges of Trees at Risk

Many of the host trees of these two pests are widespread; others are more narrowly endemic.

Limber pine reaches from Alberta and British Columbia south to mountain peaks in Arizona and New Mexico. Whitebark pine is found from Alberta and British Columbia to California and Nevada (USDA Plants database. Subalpine fir stretches from southeast Alaska along the Canadian Rockies coast into Washington, Oregon, east into Idaho, Montana, Wyoming, Colorado, Utah, even into scattered mountain ranges of Nevada and New Mexico (Hutton 2015).

Limber pine and subalpine fir are also found in a wide range of ecosystems within these ranges. Limber pine is found at both upper and lower tree lines in grassy, open forests; on exposed rocky slopes; and in dense, mixed-conifer stands. Subalpine fir is a pioneer species on ridges, alpine meadows, avalanche chutes, and lava beds (Ragenovich and Mitchell, 2006).

Before arrival of non-native pests or pathogens, these tree species have persisted for thousands of years under harsh conditions (Hutton 2015). Many of the individual trees were long-lived; some five-needle pines, e.g., bristlecone pines, have famously live for thousands of years. Core studies demonstrated that subalpine firs trees could live 272 years in the forests of Olympic National Park and 240 years in Glacier National Park (Hutton 2015). Surely loss of these trees – or even their conversion from large and old to small and short-lived – will result in significant destruction of these unique biomes.

All these trees play important roles in high altitude, unique ecosystems (Pederson et al. no date; Dawe 2020; Hutton 2015):

They retain ground water, slow the rate of snow melt, and maintain stream flow characteristics and water quality;
They curtail soil erosion and maintain slope stability; and
They provide high-value food and shelter to wildlife.

Whitebark and limber pines are famous for providing critical food for many wildlife species at high elevations —notably bears and nutcrackers (Compendium and Dawe 2020).

More Pest Threats

Other diseases, insects, and disturbances also pose serious threats to these tree species. The threats vary by region and age of the stand. They include – for the pines — mountain pine beetle (Dendroctonus ponderosae), dwarf mistletoe (Arceuthobium spp.), and various shoot, cone or foliage insects and pathogens. For subalpine fir, threats include western balsam bark beetle (Dryocoetes confusus), fir engraver (Scolytus ventralis), and the fir root bark beetle (Pseudohylesinus granulatus) (Hutton 2015). Trees are also damaged by bear and deer, seed predation by squirrels, wildfire, and biotic succession.

On Washington’s Olympic Peninsula, BWA initiates or predisposes subalpine fir for a novel disturbance complex. BWA-caused stress makes the trees more susceptible to moisture stress and endemic bark beetle attack. Surviving trees are subsequently subject to toppling by wind. A tree can die in a few years, survive with insects for up to 20 years, or recover, depending on duration, severity, and location of infestation, and local environmental conditions (Hutton 2015).

BWA study plots in the Cascade Range experienced subalpine fir mortality ranging from 7 to 79% (measured as stem counts, not basal area) over a 19 to 38 years study period. Higher mortality occurred at low-elevation, mesic sites. One stand experienced 40% mortality in 19 years, but lost the remaining 60% during a subsequent spruce budworm infestation. Most plots continued to show sporadic signs of adelgid presence and continued tree mortality. However, 41-69% of trees survived stem infestations (Hutton 2015).

How to Protect These Ecosystems

The seeds of both whitebark and limber pines are dispersed to newly disturbed, open areas by Clark’s nutcracker (Nucifraga columbiana). Furthermore, whitebark cones open to release seeds only after fire. This had led to expectations that prescribed fire could promote regeneration of these species. However, studies by Dawe (2020) and other have found that nutcracker seed caching behavior and seedling establishment are complex. Fire management might have to vary among regions, demanding consideration of stand characteristics,like openness and the presence of other tree species. For example, in the Colorado Front Range, limber pine can be replaced by subalpine fir when fire-free intervals are long. On the other hand, in Alberta, fire appeared to boost regeneration of the dominant tree species in the stands pre-fire. In the study areas, these were white spruce (Picea glauca) and lodgepole pine (Pinus contorta) (Dawe 2020). Dawe recommends protecting existing stands of limber pine through fire mitigation efforts, e.g., thinning and other fuel treatments, and supplementary planting of seedlings.

Efforts to find biocontrol agents to target the balsam woolly adelgid began in 1957; the original focus was on the insects’ damage to Fraser fir (Abies fraseri) in the southern Appalachians. More than 25 predatory species have been introduced from Europe and Asia. There was simultaneous research on native predators. None has had an impact on BWA populations in either the East or the West.

Neither white pine blister rust nor balsam woolly adelgid is considered a quarantine pest by federal officials, so there is no attempt to prevent their movement via interstate trade in Christmas trees, timber, or nursery stock. Hutton (2015) hypothesizes that the absence of regulatory measures targetting BWA arises from the pest’s gradual effect and the hosts’ not being commercially important as timber species (although several firs are important in horticulture and as Christmas trees). I think another factor is that the pests were introduced so long ago and are now widespread.

Efforts are under way to detect resistant genotypes to be used in breeding programs. Several of the lower-elevation five-needle pines vulnerable to WPBR have benefitted from extensive breeding efforts Whitebark pine has more recently been added to programs.

The eastern Fraser fir is the target of breeding – primarily for Christmas trees (APS). However, at least small-scale volunteer efforts have been carried forward by the Alliance for Saving Threatened Forests.

Hutton (2015) expresses hope that evolutionary pressure by BWA might enhance survival of more resistant forms of subalpine fir and lead to their gradual takeover. However, I ask, why leave it to chance?

In this context, I remind you of my involvement with a group (see Bonello et al. 2019) proposing creation of a federal Center for Forest Pest Control and Prevention to implement end-to-end responses to forest pest invasions – including overcoming the currently inadequate focus on detection, development and deployment of genetic resistance using modern techniques that allow for much faster breeding cycles.

I am puzzled that the Project CAPTURE places whitebark pine and subalpine fir only in Class A4.2, not among the highest priority species (Potter et al. 2019). As I blogged last spring, Project CAPTURE is part of a multi-partner effort to categorize and prioritize US tree species for conservation actions based on the threats and the trees’ ability to adapt to those threats. I find it puzzling because I am not sure I agree that these two species have a moderately high mean pest severity score – as required by the category. I am less puzzled by the assignment of a low adaptive capacity score.

Limber pine apparently ranks even lower in the Project CAPTURE priority process.

Posted by Faith Campbell

SOURCES

A comprehensive review and synthesis of the history, ecology, and management of white pines threatened by white pine blister rust see the August 2010 issue of Forest Pathology (Vol. 40:3-4).

American Phytopathological Society. Science Daily. December 9, 2019 https://www.sciencedaily.com/releases/2019/12/191209161314.htm?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+sciencedaily%2Fplants_animals%2Finvasive_species+%28Invasive+Species+News+–+ScienceDaily%29

Dawe, D.A., V.S. Peters, M.D. Flannigan. 2020. Post-fire regeneration of endangered limber pine (Pinus flexilis) at the Northern extent of its range. Forest Ecology and Management 457 (2020) 117725

Hutton, K.M. 2015. A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy. University of Washington. Available here

Morin, R. Presentation to the 81^st Northeastern Forest Pest Council Northeastern states forst agencies, Philadelphia, Pennsylvania, March 2019.

Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S. 2019. Prioritizing the conservation needs of US tree spp: Evaluating vulnerability to forest P&P threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/

Ragenovich, I.R. and R.G. Mitchell. 2006. Forest Insect and Disease Leaflet (FIDL) #118. http://www.na.fs.fed.us/pubs/fidls/bwa.pdf

Sniezko, R.A., M.F. Mahalovich, A.W. Schoettle, D.R. Vogler. 2011. Past and Current Investigations of the Genetic Resistance to Cronartium ribicola in High-elevation Five-needle Pines. In Keane, R.F., D.F. Tomback, M.P. Murray, and C.M Smith, eds. 2011. The future of high-elevation, five-needle white pines in Western North America. Proceedings of the High Five Symposium. 28-30 June, 2010. Missoula, MT.

Another New Pest Detected in California; Possible Threat to Native Shrubs

The California Department of Food and Agriculture (CDFA) is seeking comments on the appropriate pest rating for Leptosillia pistaciae, a recently discovered fungus that causes pistachio canker.

The Department’s draft pest ranking assigns the highest Economic Impact score – three. It assigns a medium Environmental Impact – two. This is because the pathogen can kill an important native shrub, with possible follow-on consequences of reduced biodiversity, disrupted natural communities, or changed ecosystem processes.

CDFA states that there is no uncertainty in its evaluation, but I see, and describe here, numerous questions about the possible true extent of the invasion and possible host range.

Comments are due on April 4, 2020.

The pathogen was detected in June 2019, when a habitat manager from an ecological reserve in San Diego County noticed multiple dead lemonade berry shrubs (Rhus integrifolia) in one of the parks. This is the first known detection of Leptosillia pistaciae in the United States and on this host. USDA APHIS has classified Leptosillia pistaciae as a federal quarantine pest. Rhus and Pistacia are in the same family, Anacardiaceae (cashews and sumacs).

According to the CDFA, Leptosillia pistaciae is the only member of this fungal genus known to be associated with disease symptoms on plants. Other species are endophytes or found in dead plant tissues. [It is not at all unusual for fungal species to be endophytes on some plant hosts but pathogenic on others. A California example is Gibberella circinata (anamorph Fusarium circinatum), which causes pitch canker on Monterey pine (Pinus radiata) but is an endophyte on various grass species (Holcus lanatus and Festuca arundinacea).]

(Reminder: this is the second new pest of native species detected in California state in 2019; I blogged about an ambrosia beetle in Napa County here. )

Rhus integrifolia (lemonade berry or lemonade sumac) is native to California. It grows primarily in the south, along the coast – from San Diego to San Luis Obispo. However, some populations are also found in the San Francisco Bay area. This and other sumacs are also sold in the nursery trade.

On pistachio trees in Italy, symptoms are observed in the winter and late spring. During the winter dormant season, trees had gum exudation and cracking and peeling of bark on trunks and branches. On trunks and large branches, cankers appeared first as light, dead circular areas in the bark; subsequently they became darker and sunken. Under the bark, cankers were discolored with necrotic tissues; in some cases, these extended to the vascular tissues and pith. During the active growing season, the symptomatic plants also showed canopy decline. Inflorescences and shoots, originating from infected branches or twigs, wilted and died. When the trunk was girdled by a canker, a collapse of the entire tree occurred.

On lemonade berry, large clumps of dead adult shrubs were observed on the edge of hiking trails. Some shrubs that had completely dead foliage were re-sprouting from their bases. Trunks of shrubs that were not completely dead were copiously weeping sap and fluids and showed foliage browning and die back with symptoms of stress.

It is thought that spores could be spread by wind, rain splashing, and the movement of dead or dying trees, greenwaste, and infected nursery stock. Contaminated pruning tools might also transport the spores. The possibility of a latent phase – or perhaps asymptomatic hosts – adds to the probability of anthropomorphically assisted spread.

I question how much effort has been put into detection surveys, especially in natural systems with native Rhus species. California has three other native sumacs: R. ovata, R. aromatica, and Malosma laurina (CNPS; full citation at the end of the blog). In addition, there are numerous other species in the family, including poison oaks (Toxicodendron spp.) and the widespread invasive plant genus Schinus.

Furthermore, some plants in the family (other than pistachios) are grown for fruit or in ornamental horticulture, including two of the native sumacs and two non-native species, Rhus glabra and R. lanceolata, cashew, mango, and smoke trees (Cotinus spp.).

Yet CDFA confidently states that there are only two hosts and that it has been detected in only one population – that in San Diego. This is because CDFA considers only official records identified by a taxonomic expert and supported by voucher specimens.

CDFA states that the pathogen is likely to survive in all parts of the state where pistachios are grown – primarily in the Central Valley. California supplies 98% of the pistachios grown in the United States; the remainder is raised in Arizona and New Mexico. California production occurred on 178,000 acres in 2012. A map is included in a flyer on production available at the url listed at the end of this blog.

In discussing spread potential, no mention is made of possible human-assisted spread.

The CDFA document includes instructions for submitting comments; the deadline is April 4.

Sources:

Rhus and related species native to California: California Native Plant Society

https://calscape.org/loc-california/Rhus(all)/vw-list/np-1?

Rhus species used in horticultural plantings in California: CalFlora https://www.calflora.org//cgi-bin/specieslist.cgi?where-genus=Rhus

Pistachio production information: https://apps1.cdfa.ca.gov/FertilizerResearch/docs/Pistachio_Production_CA.pdf

Posted by Faith Campbell.

Progress – Now Threatened – On Protecting Our Cacti

prickly pear cacti in Big Bend National Park
photo by Blake Trester, National Park Service

The cacti that are such important components of desert ecosystems across nearly 2 million square miles straddling the U.S.-Mexico border are under threat from non-native insects – as I have noted in earlier blogs. Of course, cacti are important in other ecoregions, too – I wrote recently about the columnar cacti in the dry forests of Puerto Rico.

Flat-padded prickly pear cacti of the genus Opuntia are threatened by the cactus moth, Cactoblastis cactorum.

In 1989, the cactus moth was found in southern Florida, to which it had spread from the Caribbean islands (Simonson 2005). Recently, the moth was found to have spread west as far as the Galveston, Texas, area and near I-10 in Columbus, Texas, about 75 miles west of central Houston (Stephen Hight, pers. com.) Two small outbreaks on islands off Mexico’s Caribbean coast have been eradicated.

In Florida, the cactus moth has caused considerable harm to six native species of prickly pear, three of which are listed by the state as threatened or endangered.

When the cactus moth reaches the more arid regions of Texas, it is likely to spread throughout the desert Southwest and into Mexico. In the American southwest, 31 Opuntia species are at risk; nine of them are endemic, one is endangered. Mexico is the center of endemism for the Opuntia genus. In Mexico, 54 Opuntia species are at risk, 38 of which are endemic (Varone et al. 2019; full citation at end of this blog).

The long-term effects of the cactus moth on these North American Opuntia are unknown because there may be substantial variations in tolerance. The attacks observed in the Caribbean islands have shown great variability in various cactus species’ vulnerability (Varone et al. 2019).

The Opuntia cacti support a diversity of pollinators as well as deer, javalina (peccaries), tortoises, and lizards. Prickly pears also shelter packrats and nesting birds (which in turn are fed on by raptors, coyotes, and snakes), and plant seedlings. Their roots hold highly erodible soils in place (Simonson 2005).

While scientists have been concerned about the possible impacts of the cactus moth since it was detected in Florida 30 years ago, a substantial response began only 15 years later. The U.S. Department of Agriculture began trying to slow the spread of the cactus moth in 2005 (Mengoni Goñalons et al. 2014), with a focus on surveys and monitoring, host (cactus) removal, and release of sterile males. This program was successful at slowing the moth’s spread and eradicating small outbreaks on offshore islands of Alabama, Mississippi, and Mexico.

Cactus moth damage to native cacti in Florida
photo by Christine Miller, UF/IFAS

However, the moth continued to spread west and the program never received an appropriation from Congress. The primary funding source was a US – Mexico Bi-National Invasive Cactus Moth Abatement Program. Both countries contributed funds to support the research and operational program to slow the spread in the U.S. Funds were provided through USDA Animal and Plant Health and Inspection Service (APHIS) and the Mexican Secretariat of Agriculture, Livestock, Rural Development, Fisheries and Food (SEGARPA). Unfortunately, funding was reduced by both entities and became inadequate to maintain the Bi-National Program.

Therefore, in 2012, APHIS abandoned its regional program and shifted the focus to biocontrol. This is now considered the only viable control measure in the desert Southwest where vulnerable cacti are numerous and grow close together. The biocontrol project has been funded since 2012 through the Plant Pest and Disease Management and Disaster Prevention program (which receives funding through the Farm Bill). It has received a total of slightly more than $2 million over seven years. More than half the funds went to the quarantine facility to support efforts to rear non-target hosts and verify the biocontrol agent’s host specificity. About a quarter of the funds supported complementary work of an Argentine team (both the cactus moth and the most promising biocontrol agent are native to Argentina). Much smaller amounts have supported U.S.-based scientists who have studied other aspects of the cactus moth’s behavior and collected and identified the U.S. moths being tested for their possible vulnerability to attack by a biocontrol wasp.

Here are details of what these dedicated scientists achieved in just the past seven years at the relatively low cost of roughly $2 million. Unfortunately, the project now faces a funding crisis and we need to ensure they have the resources to finish their work.

Some Specifics of the BioControl Program

After literature reviews, extensive collections, and studies in the cactus moth’s native habitat in Argentina (Varone et al. 2015), a newly described wasp, Apanteles opuntiarum (Mengoni Goñalons et al. 2014), has been determined to be host specific on Argentine Cactoblastis species and the most promising candidate for biocontrol. Wasps were collected in Argentina and sent to establish a colony in a quarantine facility in Florida to enable host specificity studies on North American Lepidoptera (Varone et al. 2015).

Quarantine host specificity studies and development of rearing technology has not been straightforward. Initially, it was difficult to achieve a balanced male/female ratio in the laboratory-bred generations; this balance is required to maintain stable quarantine laboratory colonies for host range testing. This difficulty was overcome. A second challenge was high mortality of the cactus-feeding insects collected in the Southwest that were to be test for vulnerability to the biocontrol wasp. These desert-dwellers don’t do well in the humid, air-conditioned climate of the quarantine facility! For these difficult-to-rear native insects, scientists developed a molecular genetics method to detect whether eggs or larvae of the cactus moth parasitoid were present inside test caterpillars after they were exposed to the wasps. For easy to rear test insects, caterpillars are exposed to the wasps and reared to adulthood. Host specificity tests have been conducted on at least five species of native U.S. cactus-feeding caterpillars and 11 species of non-cactus-feeding caterpillars (Srivastava et al. 2019; Hight pers.comm.).

To date there has been no instance of parasitism by Apanteles opuntiarum on either lepidopteran non-target species or non-cactus-feeding insects in the Florida quarantine or in field collections in Argentina (Srivastava et al. 2019; Varone et al. 2015; Hight pers.comm.).

The scientists expected to complete host-specificity testing in the coming months, then submit a petition to APHIS requesting the release of the wasp as a biocontrol agent. Unfortunately, the project’s request for about $250,000 in the current year was not funded. This money would have funded completion of the host specificity testing, preparation of a petition to APHIS in support of release of the biocontrol agent into the environment, and preparation of the release plan.

Meanwhile, what can we expect regarding the probable efficacy of the anticipated biocontrol program?

Some of the wasp’s behavioral traits are encouraging. The wasp is widely present in the range of the cactus moth, and persisted in these areas over the years of the study. The wasp can deposit multiple eggs with each “sting”. Multiple wasps can oviposit into each cactus moth without detriment to the wasp offspring. Unmated wasp females produce male offspring only, whereas mated females produce mixed offspring genders. In the field, female wasps attack cactus moth larvae in a variety of scenarios: they wait at plant access holes to sting larvae when they come outside to defecate; they attack larvae when they are moving on the surface of the pads; they can sting the youngest cactus moth larvae through the thin plant wall of mined the pads; and they enter large access holes created by older larvae and attack larger larvae. The wasps are attracted by the frass (excrement) left on the outside of the cactus pads by cactus moth larvae (Varone et al. 2020).

However, I wonder about the extent to which the cactus moth is controlled by parasitoids in Argentina. Cactoblastis eggs are killed primarily by being dislodged during weather events (rain and wind) and by predation by ants. First instar larvae are killed primarily by the native Argentine cactus plants’ own defenses – thick cuticles and release of sticky mucilage when the young larvae chew holes into the pads where they enter and feed internally. As larvae feed and develop inside the pads, the primary cause of mortality is natural enemies.

Of all the parasitoid species that attack C. cactorum, A. opuntiarum is the most abundant and important. When the larvae reach their final state (6^th instars), they leave the pads and find pupation sites in plant litter near the base of the plants. It is at this stage that the parasitism from A. opuntiarum is detected in the younger larvae that were attacked while feeding inside pads. As the moth larva begins to spin silk into which to pupate, larvae of the wasp erupt through the skin of the caterpillar and pupate within the silk spun by the moth. Predation by generalists (ants, spiders, predatory beetles) accounted for high mortality of the unprotected last instar and pupae (Varone et al. 2019).

Finally, the cactus moth has three generations per year when feeding on O. stricta in the subtropical and tropical coastal areas of the Americas and the Caribbean. In Argentina, on its native host, the moth completes only two generations per year (Varone et al. 2019).

How to Get the Program Support Needed

*Opuntia* in Big Bend National Park
Photo by Cookie Ballou,
National Park Service

To date, no organized constituency has advocated for protection of our cacti from non-native insect pests. Perhaps now that the Cactoblastis moth is in Texas, the threat it represents to our desert ecosystems will become real to conservationists and they will join the struggle. The first step is to resolve the funding crisis so that the agencies can complete testing of the biocontrol agent and gain approval for its release. So now there is “something people can do” – and I hope they will step forward.

I hope Americans are not actually indifferent to the threat that many cacti in our deserts will be killed by non-native insects. Many are key components of the ecosystems within premier National Parks, and other protected areas. Cacti also are beautiful treasures in botanical gardens. I hope conservationists will agree that these threats must be countered, and will help to ensure funding of the final stages of the biocontrol tests.

Sources

Mengoni Goñalons, C., L. Varone, G. Logarzo, M. Guala, M. Rodriguero, S.D. Hight, and J.E. Carpenter. 2014. Geographical range & lab studies on Apanteles opuntiarum (hymenoptera: braconiDae) in AR, a candidate for BC of Cactoblastis cactorum (Lepidoptera: Pyralidae) in North America. Florida Entomologist 97(4) December 2014

Simonson, S.E., T. J. Stohlgren, L. Tyler, W. Gregg, R. Muir, and L. Garrett. 2005. Preliminary assessment of the potential impacts and risks of the invasive cactus moth, Cactoblastis cactorum Berg, in the U.S. and Mexico. Final Report to the International Atomic Energy Agency, April 25, 2005 © IAEA 2005

Srivastava, M., P. Srivastava, R. Karan, A. Jeyaprakash, L. Whilby, E. Rohrig, A.C. Howe, S.D. Hight, and L. Varone. 2019. Molecular detection method developed to track the koinobiont larval parasitoid Apanteles opuntiarum (Hymenoptera: Braconidae) imported from Argentina to control Cactoblastis cactorum (Lepidoptera: Pyralidae). Florida Entomologist 102(2): 329-335.

Varone, L., C.M. Goñalons, A.C. Faltlhauser, M.E. Guala, D. Wolaver, M. Srivastava, and S.D. Hight. 2020. Effect of rearing Cactoblastis cactorum on an artificial diet on the behavior of Apanteles opuntiarum. Applied Entomology DOI: 10.1111/jen.12731.

Varone, L., G. Logarzo, J.J. Martínez, F. Navarro, J.E. Carpenter, and S.D. Hight. 2015. Field host range of Apanteles opuntiarum (Hymenoptera: Braconidae) in Argentina, a potential biocontrol agent of Cactoblastis cactorum (Lepidoptera: Pyralidae) in North America. Florida Entomologist — Volume 98, No. 2 803

Varone, L., M.B. Aguirre, E. Lobos, D. Ruiz Pérez, S.D. Hight, F. Palottini, M. Guala, G.A. Logarzo. 2019. Causes of mortality at different stages of Cactoblastis cactorum in the native range. BioControl (2019) 64:249–261

Posted by Faith Campbell

Hawaiian Dry Forests – Glimmer of Hope for one tree, Alarm for a shrub

wiliwili flower
photo by Forrest and Kim Starr, courtesy of creative commons

Hawaii’s dryland forest is a highly endangered ecosystem. More than 90% of dry forests are already lost due to habitat destruction and the spread of invasive plant and animal species. However, a new publication documents some recovery of wiliwili trees from one major pest. At the same time, a new pest is spreading and killing naio, a critical dryland shrub. Both pests originated in countries that have rarely if ever been a source of U.S. pests. This is worrying because phytosanitary agencies have their hands full with imports from the usual sources. The role of California as a source of invasive species in Hawai`i has long deserved federal attention – but as far as I know has not received it.

Hope for Wiliwili Trees

The Hawaiian endemic wiliwili tree, Erythrina sandwicensis, occurs in lowland dry forests on all the major islands from sea level to 600 m. Wililwili is a dominant overstory tree in these habitats. (Unless otherwise noted, the principal source is Kaufman et al. in press – full citation at end of blog.)

The tree has been severely affected by the introduced Erythrina gall wasp, Quadrastichus erythrinae (EGW). The gall wasp was detected on Oahu in 2005 and quickly spread to the other Hawaiian islands.

Arrival of the EGW on Oahu was part of the insect’s rapid global range expansion. Originally from East Africa, it was first detected in the Mascarene Islands and Singapore in 2003. At the time, it was unknown to science. Within a few years it had spread across Asia, many Pacific islands (including Hawai`i), and to the Americas, including Florida in 2006, Brazil in 2014 (Culik 2014), and Mexico in 2017 (Palacios-Torres 2017). Although apparently restricted to the Erythrina genus as host, it has lots of opportunities. This genus has 116 species distributed across tropical and subtropical regions: 72 species in the Americas, 31 in Africa, and 12 in Asia.

The severe damage to wiliwili (and to non-native Erythrina trees planted in urban areas and as windbreaks) prompted Hawaiian officials to immediately initiate efforts to find a classical biological control agent. The process moved rapidly. A candidate – a parasitic wasp species new to science, Eurytoma erythrinae – was found in East Africa in 2006. Host specificity testing was carried out. Scientists quickly learned to rear the parasitic wasp in laboratories. Release of the biocontrol agent was approved in November 2008 – only three and a half years after the EGW was detected on Oahu.

The biocontrol agent’s impact was quickly apparent. Establishment was confirmed within 1–4 months at all release locations throughout Hawai`i. Reduced pest impacts to trees were detected within two years. By 2018, only 33% of the foliage was damaged on the majority of wiliwili trees. Damage to non-native Erythrina had also declined.

Results of Biocontrol Agent’s Release

The biocontrol agent’s efficacy in reducing EGW’s impacts on trees has been evaluated for 10 years after the agent’s release. Monitoring was conducted at sites on four of the six main islands. (The monitoring program and its findings are described in Kaufman et al. in press).

I wonder how many other biocontrol agents have been monitored so closely for such a long time? Shouldn’t they all be?

Given the uniqueness and importance of such long-term assessment, it is worth looking at the data in detail.

1) Foliar Damage and Tree Health

In 2008, before release of the biocontrol agent, more than 70% of young shoots in wiliwili trees that were inspected were severely infested. The damage rating of “severe” fell from about 80% of trees in 2008 to about 40% in 2011. About 20% of trees surveyed – at sites on all islands – had no gall damage.

By three years after release of the biocontrol agent (2011), mortality rates attributed to stress from the EGW infestation for trees in natural areas fell to 21%. Mortality rates for trees in botanical gardens was somewhat higher – 34%. Kaufman et al. proposed several possible reasons: a) lingering presence of systemic insecticides that might have harmed the biocontrol agents early in the releases; b) year-round sustenance for the EGW as a result of the i) presence of alternative hosts and ii) supplemental irrigation which maintained fresh foliage on the trees.

Less intensive monitoring occurred during 2013 – 2018. It showed continuing substantial suppression of EGW damage on Erythrina foliage, although levels varied among locations. Sites with the lowest precipitation and higher temperatures throughout the year had the slowest recovery of wiliwili. Still, trees are now producing vegetative flushes and healthier canopies during non-dormant periods.

2) Flower and Seed Damage

Successful reduction of infestations in flowers and seedpods was less immediate. Still, by 2011, seed-set had increased from less than 3% of trees setting and maturing seed, to almost 30% with mature seed. The proportion of trees bearing inflorescences also increased, with more than 60% of trees blooming three years after introduction of the biocontrol agent. There was also a slow but steady increase in seed production.

However, in 2019, it remains unclear how infestation of seedpods will affect germination and therefore future plant recruitment.

More worrying, little recruitment was observed over the 10 years. Hawaiian authorities have completed tests on, and are preparing a petition for release of, a second biocontrol agent, Aprostocitus nites. It is hoped that it will further suppress EGW in flowers and seedpods.

Still, poor recruitment is likely due to the combined impacts of multiple invasive species in native environments. A significant factor is a second insect pest – a bruchid, Specularius impressithorax – which can cause loss of more than 75% of the seed crop. I hope authorities are seeking methods to reduce this insect’s impacts.

The Hawaiian species group of the IUCN has given the wiliwili tree the Reed Book designation of “vulnerable”.

Worries for Naio

naio in bloom
photo by Forrest and Kim Starr, courtesy of creative commons

Naio (Myoporum sandwicense)is an integral component of native Hawaiian ecosystems, especially in dry forests, lowlands, and upland shrublands. However, it is also found in mesic and wet forest habitats. Naio is found on all of the main Hawaiian Islands at elevations ranging from sea level to 3000 m. The loss of this species would be not only a significant loss of native biological diversity but also a structural loss to native forest habitats.

The invasive non-native Myoporum thrips, Klambothrips myopori, was detected on the Big Island (Hawai‘i Island) in 2009 – four years after it was first detected on ornamental Myoporum species in California. At the time of the California detection, the species was unknown to science. It is now known that this species is native to Tasmania.

The thrips feeds on and causes galls on plants’ terminal growth and can eventually lead to death of the plant.

For close to a decade, the Myoporum thrips was restricted to the Big Island. It has now been found on Oahu (Wright pers. comm.) Alarmed by the high mortality of plants in California, in September 2010, the Hawaii Department of Lands and Natural Resources Division of Forestry and Wildlife and the University of Hawai‘i initiated efforts to determine spatial distribution, infestation rates, and overall tree health of naio populations on the Big Island. Monitoring took place at nine protected natural habitats for four years. This monitoring program was supported by the USFS Forest Health Protection program. (See also the chapter on naio by Kaufman et al. 2019 in Potter et al. 2019 – full citation at the end of this blog.)

naio damaged by thrips
photo by Leyla Kaufman, University of Hawaii

The monitoring confirmed that the myoporum thrips has spread and colonized natural habitats on the leeward side of Hawai`i Island. Infestation rates increased considerably at all sites over the duration of the four-year sampling period. Trees experiencing high infestation levels also showed branch dieback.

Medium-elevation sites (between 500–999 m) had the highest infestations and dieback: over 70% of the shoots had the worst damage.. At two sites, over 70% of the monitored trees have died.

Even though flowers and fruits were still seen at all sites, little to no plant recruitment was observed at these sites. Thus another plant species important in this endangered plant community is in decline.

Few management strategies are available for this pest. They include preventing spread to other islands and early detection followed by rapid application of pesticides.

Implications and Conclusions

The Erythrina gall wasp and myoporum thrips are only two of the thousands of invasive species established in Hawai`i. Island ecosystems, especially Hawai`i, are well recognized as especially vulnerable to invasive species. It has been estimated that on average 20 new arthropod species become established in Hawai`i every year.

East Africa and Tasmania are new sources for invasive species. Phytosanitary agencies need to adjust their targetting of high-risk imports to recognize this reality. Regarding the Hawaiian introduction of the thrips, there was probably made an intermediary stop in California – which is not unusual. (See also ohia rust.)

I applaud Hawaiian officials’ quick action to counter these pests. I wish their counterparts in other states did the same.

There are multiple threats to Hawaii’s dry forests, including habitat modification and fragmentation; wild fires; seed predation by rodents; predation on seeds, seedling, and saplings by introduced ungulates (e.g. feral goats, pigs and deer); competition with invasive weeds; and damage by invasive insect pests and diseases.

With so much of Hawaii’s dry forests already lost, the release of biocontrol agents targetting specific pests is only one element of a much-needed effort. Long-term protection of wiliwili and naio depends on greater efforts to reduce all threats and to stimulate natural regeneration of this ecosystem. These programs could include predator-proof fencing to keep out ungulates; baiting rodents and snails; and active collection. Breeding, and planting of threatened plant species in an effort to protect both the individual species and the habitat.

SOURCES

Culik, M.P., D. dos Santos Martins, J. Aires Ventura & V. Antonio Costa. The invasive gall wasp Quadrastichus erythrinae (Hymenoptera: Eulophidae) in South America: is classical biological control needed?

Kaufman, L.V., J. Yalemar, M.G. Wright. In press. Classical biological control of the erythrina gall wasp, Quadrastichus erythrinae, in Hawaii.: Conserving an endangered habitat. Biological Control. Vol. 142, March 2020

Palacios-Torres, R.E., J. Malpica-Pita, A.G. Bustamante-Ortiz, J. Valdez-Carrasco, A. Santos-Chávez, R. Vega-Muñoz and H. Vibrans-Lindemann. 2017. The Invasive Gall Wasp Quadrastichus erythrinae Kim in Mexico. Southwestern Entomologist.

Potter, K.M. B.L. Conkling. 2019. Forest Health Monitoring: National Status, Trends, and Analysis 2018. Forest Service Research & Development Southern Research Station General Technical Report SRS-239

Kaufman, L.V, E. Parsons, D. Zarders, C. King, and R. Hauff. 2019. CHAPTER 9. Monitoring Myoporum thrips, Klambothrips myopori (Thysanoptera: Phlaeothripidae), in Hawaii

Wright, Mark. 2005. Assistant Professor and Extension Specialist, University of Hawaii. Personal communication.

NPS Report Published in Journal – Has it Been Implemented? Can it Be?

invasive lake trout in Yellowstone National Park

The National Park Service has a legal mandate to manage lands and waters under its jurisdiction so as to “preserve unimpaired” their natural and cultural resources (NPS Organic Act 54 U.S.C. § 100101, et seq.) Invasive species undermine efforts to achieve that mission. In 2000, the NPS adopted a program to coordinate management of invasive plants. It’s not as effective as needed – see the strategic plan.

However, only recently has NPS begun trying to prioritize and coordinate programs targetting the many animals and animal diseases which threaten Park resources. These organisms range from emerald ash borer and quagga mussels; to pythons, goats, and pigs; to diseases such as white nose syndrome of bats and avian malaria in Hawai`i.

In 2017, NPS released an internal study of the pervasive threat to Park resources posed by invasive animals and discussed steps to overcome barriers to more effective responses (Redford et al., 2017; full citation at end of this blog). The Chief of the Biological Resources Division initiated this report by asking a Science Panel to evaluate the extent of the invasive animal problem, assess management needs, review best practices, and assess potential models that could serve as a service-wide organizational framework. The report was to pay particular attention to innovative and creative approaches including, but not limited to, new genomic tools. I summarized the Panel’s findings and conclusions in a blog when its report appeared in 2017.

Significantly, the Panel’s final report states that “a general record of failure to control invasive species across the system” was caused principally by a lack of support for invasive species programs from NPS leadership.

This report has now appeared in the form of a peer-reviewed article in the journal Biological Invasions by Dayer et al. 2019 (full citation at end of this blog). Although nine of the ten authors are the same on both reports there are substantive differences in content. For example, the journal article reiterates the principal findings and conclusions of the Panel’s final report, but in less blunt language.

What’s Been Watered Down

The toning down is seen clearly in the statements some of the panel’s six key findings.

Finding #1

The panel’s report says: invasive animals pose a significant threat to the cultural and natural values and the infrastructure of U.S. national parks. To date, the NPS has not effectively addressed the threat they pose.

Dayer et al. says: the ubiquitous presence of invasive animals in parks undermines the NPS mission.

Finding #2

The panel’s report says: managing invasive animals will require action starting at the highest levels, engaging all levels of NPS management, and will require changes in NPS culture and capacity.

Dayer et al. says: coordinated action is required to meet the challenge.

Finding #4

The panel’s report states: effective management of invasive animals will require stakeholder engagement, education, and behavior change.

Dayer et al. says: public engagement, cooperation and support is [sic] critical.

Wording of the other three “key findings” was also changed, but these changes are less substantive.

Drayer et al. also avoid the word “failure” in describing the current status of NPS” efforts to manage invasive animal species. Instead, these authors conclude that the invasive species threat “is of sufficient magnitude and urgency that it would be appropriate for the NPS to formally declare invasive animals as a service-wide priority.”

Where the Documents Agree – Sort of

Both the Panel’s report and Dayer et al. state that invasive animal threats are under-prioritized and under-funded. They say that addressing this challenge must begin at the highest levels within the NPS, engage all levels of management, and will require investments from the NPS leadership. Even within individual parks, they acknowledge that staffs struggle to communicate the importance of invasive animal control efforts to their park leadership, especially given competition with other concerns that appear to be more urgent. And they admit that parks also lack staff capacity in both numbers and expertise.

Also, both the Panel’s report and Dayer et al. urge the NPS to acknowledge formally that invasive animals represent a crisis on par with each of the three major crises that drove Service-wide change in the past: over-abundance of ungulates due to predator control; Yellowstone fire crisis (which led to new wildfire awareness in the country); and recognition of the importance of climate change.

The Panel suggested ways to update NPS’ culture and capacity: providing incentives for staff to (1) address long-term threats (not just “urgent” ones) and (2) put time and effort into coordinating with potential partners, including other park units, agencies at all levels of government, non-governmental organizations, private landowners, and economic entities. Dayer et al. mention these barriers but does not directly mention changing incentives as one way to overcome them.

Both the Panel’s report and Dayer et al. suggest integrating invasive animal threats and management into long-range planning goals for natural and cultural landscapes and day-to-day operations of parks and relevant technical programs (e.g., Biological Resources Division, Water Resources Division, and Inventory and Monitoring Division).

What is Missing from the Journal Publication

The Panel’s final report noted the need for increased funding. It said that such funding would need to be both consistent and sufficiently flexible to allow parks to respond to time-sensitive management issues. It proposes several approaches. These include incorporating some invasive species control programs (e.g., for weeds and wood borers) into infrastructure maintenance budgets; adopting invasive species as fundraising challenges for non-governmental partners (e.g., “Friends of Park” and the National Park Foundation); and adopting invasive species as a priority threat. Dayer et al. do not discuss funding issues.

The final internal report envisioned the NPS becoming a leader on the invasive species issue by 1) testing emerging best management practices, and 2) educating visitors on the serious threat that invasive species pose to parks’ biodiversity. As part of this process, the authors suggest that the NPS also take the lead in countering invasive species denialism. Dayer et al. do not mention the issue of invasive species deniers.

Common Ground: Status of Invasive Animals in the Parks

The Panel’s report and Dayer et al. describe the current situation similarly:

More than half of the National parks that responded to the internal survey (245 of the 326 parks) reported problems associated with one or more invasive animal species.
The total number of species recorded was 331. This is considered to be an underestimate since staffs often lack the ability to thoroughly survey their parks – especially for invertebrates.
Invasive species threats to Parks’ resources have been recognized for nearly 100 years. The original report notes that 155 parks reported the presence of one or more exotic vertebrate species in 1977. At that time, exotic animals were the fourth most commonly reported source of threats. In 1991, parks identified 200 unfunded projects to address exotic species, costing almost $30 million.
Only a small percentage of non-native animal invasions are under active management. Dayer et al. stated that 23% have management plans at the park unit level, and only 11% are reported as being ‘‘under control”.
Individual parks have effective programs targetting specific bioinvaders (examples are described in Redford et al; a brief summary of these efforts is provided in my previous blog.

Common Ground on Some Solutions

The report and Dayer et al. promote the same steps to improve invasive animal management across the Service. Both note that the NPS is adopting formal decision support tactics to update and strengthen natural resource management across the board. More specific steps include

establishing a coordination mechanism that enables ongoing and timely information sharing.
mainstreaming invasive species issue across the NPS branches or creating a cross-cutting IAS initiative among the Biological Resources Division, Water Resources Division, Inventory and Monitoring Division, Climate Change Response Program, and the regional offices.

While both documents call on the NPS to develop and test emerging technologies, the Panel’s final report is more detailed, providing, in Table 5, a list of several areas of special interest, including remotely triggered traps, species-specific toxicants, toxicant delivery systems, drones, environmental DNA, and sterile-male releases. Dayer et al. mention eDNA and metabarcoding for ED/RR, biocontrol, and gene drives to control invasive pathogens. (Neither document discusses possible concerns regarding use of CRISPR and other gene-altering technologies, other than to say there would be public concerns that would need to be addressed.)

Both documents note the necessity of working with resource managers beyond park boundaries to detect and manage species before they arrive in parks. They note that developing and operationalizing such partnerships requires time and resources. Furthermore, invasive species prevention, eradication, and containment programs can be effective only with public support. They suggest strengthening NPS’ highly regarded public outreach and interpretation program to build such support, including through the use of citizen scientists.

The Panel’s final report said that the NPS should recognize that the condition of the ecosystem is the objective of efforts. Its authors recognized that achieving this goal might require reconsidering how ecosystem management is organized within NPS so interacting stressors (e.g., fire) and management levers (e.g., pest eradication/suppression, prescribed fire) would be addressed. For this, the NPS would need to create a focused capacity to address the pressing issue of invasive animals in such a way that fosters integrated resource management within parks, focusing on fundamental values of ecosystem states, and not eradication targets. Dayer et al. called for the same changes without specifically labelling “condition of the ecosystem” as the goal.

Publication of Dayer et al. prompted me to find out what progress the NPS has made in responding to the “key findings” in the Panel’s final report (neither publication calls them “recommendations”).

The National Park Service has acted on the recommendation to appoint an “invasive animal coordinator” within the Biological Resources Division. That person is Jennifer Sieracki. However, I wonder whether a person located in BRD is of sufficient stature to influence agency policy across all divisions. It is not clear whether there is active coordination with the national-level invasive plant coordinator.

Dr. Sieriaki responded to my query by noting the following new efforts 1) to improve outreach to partners and the public, and 2) to expand formal and informal partnerships with local, state, federal and tribal entities and local communities near parks.

NPS should soon finalize two formal partnerships with other agencies and organizations for outreach and management of invasive animal species.
NPS is working with researchers at the US Geological Survey to expand an existing modeling tool for identifying potential suitable habitat for invasive plant species to include invasive insects. This will help staff focus on the most likely locations for introductions and thus assist with early detection and control.
NPS has created a Community of Practice so NPS employees can seek each other’s advice on addressing invasive animal issues. A workshop of regional invasive species coordinators is planned for the coming months to guide direction of the service-wide program and identify other top priorities. (Seriacki pers. comm.)

I also wonder whether the NPS can achieve the top-level coordination and outreach to the public called for by both reports while complying with the terms of Public Law 116-9 – the John N. Dingle Jr. Conservation, Management, and Recreation Act, which was enacted a year ago. Title VII, Section 10(i) of this law limits spending to carry out invasive species program management and oversight to 10% of appropriated funds. Less than 15% may be spent on investigations (research), development activities, and outreach and public awareness efforts (Section 10(h)). The law does allow spending for investigations regarding methods for early detection and rapid response, prevention, control, or management; as well as inspections and interception or confiscation of invasive species to prevent in-park introductions.

For more information, see my previous criticism of NPS failure to address invasive species issues here.

Posted by Faith Campbell

See also my earlier discussion of the new legislation here.

SOURCES

Dayer, A.A., K.H. Redford, K.J. Campbell, C.R. Dickman, R.S. Epanchin-Niell, E.D. Grosholz, D.E. Hallac, E.F. Leslie, L.A. Richardson, M.W. Schwartz. 2019. The unaddressed threat of invasive animals in U.S. National Parks. Biol Invasions

https://doi.org/10.1007/s10530-019-02128-0

Redford, K.H., K. Campbell, A. Dayer, C. Dickman, R. Epanchin-Niell, T. Grosholz, D. Hallac, L. Richardson, M. Schwartz. 2017. Invasive animals in U. S. National Parks: By a science panel. Natural Resource Report NPS/NRSS/BRD/NRR—2017/1564. NPS, Fort Collins, Colorado. Commissioned by the NPS Chief of Biological Resources Division. https://irma.nps.gov/DataStore/DownloadFile/594922

Jennifer Sieracki, Invasive Animal Coordinator, Biological Resources Division, National Park Service

Solutions Suggested by 30 Years’ Work

Faith Campbell receives award for activism from National Association of State Foresters; 2016

For nearly 30 years I have documented bioinvasion threats and gaps, first in three Fading Forests reports (available here), then in five years of blogging. Here I pull together that information and suggest — in most cases reiterate — steps to address these threats and gaps. I list sources of discussion of the underlying issues – other than my reports and blogs – in references at the end of this blog.

My first premise is: robust federal leadership is crucial:

The Constitution gives primacy to federal agencies in managing imports and interstate trade.
Only a consistent approach can protect trees (and other plants) from non-native pests.
Federal agencies have more resources than state agencies individually or in any likely collective effort — despite decades of budget and staffing cuts.

My second premise is: success depends on a continuing, long-term effort founded on institutional and financial commitments commensurate with the scale of the threat. This requires stable funding; guidance by research and expert staff; and engagement by non-governmental players and stakeholders. Unfortunately, as I discuss below, funding has not been adequate or stable.

My third premise is that programs’ effectiveness needs to be measured, not just effort (see the NECIS document referenced at the end of the blog).

SPECIFICS

Preventing new introductions continues to be the most effective action. Mitigating options decrease and damages increase once a non-native pest has entered the country – much less become established (see Lovett et al. 2016 and Roy et al. 2014). I recognize that preventing new introductions poses an extremely difficult challenge given the volume and speed of international trade and the strong economic forces supporting free trade. These challenges have been exacerbated over several decades by the political zeitgeist – the anti-regulatory ideology, the emphasis on “collaborating” with “clients” rather than imposing requirements through regulations. Although the current “America First” policy might reduce import volumes and therefore reduce the invasive species threat to some extent, the anti-regulatory stance has only strengthened.

containers at the Port of Long Beach, California

Decades of cutting key agencies’ budgets and personnel are another factor. However, the damage to America’s natural systems is so great that we must try harder to find more effective strategies (See the Fading Forest reports; my previous blogs; Lovett et al. 2016; and APHIS annual reports – e.g., the 2019 report here)

Prevention

Despite adoption and implementation of new international and national regulations to stem pest introductions, introductions continue – although probably at a lower level than would otherwise be the case. Delays in adoption of regulations (documented in Fading Forests II and III and my two recent 30-years-in-review blogs have facilitated damaging introductions and spread.

Solutions

Stakeholders press USDA leadership to initiate rules intended to strengthen phytosanitary protection and expedite their completion
APHIS promote and facilitate analysis of current programs and policies by non-agency experts to ensure the agency is applying most effective strategies (Lovett et al. 2016).

Adoption of insufficiently protective regulations (documented in FFII, FFIII, two 30-years-in-review blogs) – adopted in part because APHIS is trying to “balance” trade facilitation and phytosanitary protection – has further contributed to damaging pests’ introduction and spread.

Solutions:

Boost priority of preventing pest introductions by amending the Congressional finding in the Plant Protection Act [7 USC 7701(3)] as follows

Existing language: “[I]t is the responsibility of the Secretary [of Agriculture] to facilitate exports, imports and interstate commerce in . . . commodities that pose a risk of harboring plant pests or noxious weeds in ways that will reduce, to the extent practicable, as determined by the Secretary, the risk of dissemination of plant pests and noxious weeds .… “

Amend to read as follows: “…. in ways that will ~~reduce~~ prevent, to the greatest extent ~~practicable~~ feasible, as determined by the Secretary, …” [emphasis added]

Adopt several actions to strengthen phytosanitary protections at the point of origin (Lovett et al. 2016)
Expand pre-clearance partnerships — as authorized for plants under Q-37 regulations and ISPM-36
Expand sentinel tree programs
Promote voluntary substitution of packaging made from materials other than solid wood.

APHIS doesn’t use the enforcement powers that it has under Plant Protection Act (see several of my past blogs)

Solutions:

CBP inspectors search for pests in a pallet; CBP photo

APHIS follow the lead of Customs and Border Protection and begin penalizing importers on the first instance of their wood packaging not being in compliance with ISPM#15 (see blog here).
APHIS prohibit use of wood packaging by countries and importers of categories of imports that – over the 13 years since implementation – have developed a record of frequent violations of ISPM#15.
APHIS use its authority per revised Q-37 regulations to negotiate with countries that export plants to the U.S. to establish “integrated measures” programs aimed at minimizing the risk of associated pests being transported to the U.S.
APHIS use its authority per revised Q-37 to place in the “Not Authorized for Import Pending Pest Risk Assessment (NAPPRA) “limbo” category genera containing North American “woody” plants (see Roy et al. 2014; Lovett et al. 2016).

Spread within the U.S.

The United States lacks a coordinated system to prevent pest spread within the country (see Fading Forests III Chapter 5). Even our strictest methods, like APHIS’s quarantines regulating interstate movement of goods, have failed to curtail spread of significant pests. The most obvious example is the emerald ash borer.

The regulations governing movement of the sudden oak death pathogen in the nursery trade have also failed: there have been periodic outbreaks in which the pathogen has been spread to nurseries across the country. Between 2003 and 2011, a total of 464 nurseries located in 27 states tested positive for the pathogen, the majority as a result of shipments traced from infested wholesalers. In 2019, plants exposed to the pathogen were again shipped to 18 states; eight of those states have confirmed that their plant retailers received infected plants (see my blog from summer here).

Another serious gap is the frequent failure of APHIS and states to adopt official programs targetting bioinvaders that will be difficult to control because of biological characteristics or cryptic natures – even when severe impacts are demonstrated. Recent examples include the laurel wilt disease complex, goldspotted oak borer, polyphagous and Kuroshio shot hole borers and associated pathogens, and even the spotted lanternfly (although the last has received significant funds from APHIS.)

redbay killed by laurel wilt disease, Georgia; photo by Scott Cameron

Solutions:

APHIS apply much more stringent regulations to interstate movement, based on a heightened priority for prevention in contrast to facilitating interstate trade. E.g., prohibit nurseries on the West Coast from shipping P. ramorum hosts to states where the pathogen is not established.
APHIS encourage states to adopt quarantines and regulations aimed at preventing spread of invasive pests to regions of the state that are not yet infested. For example, the sudden oak death pathogen in California and Oregon; the borers in southern California.
APHIS abandon plans to deregulate emerald ash borer and step up its support for state regulations on firewood.
APHIS stop dumping pests it no longer wants to regulate onto the states through the “Federally Recognized State Manage Phytosanitary (FRSMP) program”.
APHIS revise its policies so that the “special needs exemption” [7 U.S.C. 7756] actually allows states to adopt more stringent regulations to prevent introduction of APHIS-designated quarantine pests (see Fading Forests III Chapter 3).

To help fill the gaps, the states are trying to coordinate their regulations in some important areas. The most advanced example is the voluntary Systems Approach to Nursery Certification, or SANC program. APHIS has supported this initiative, including by funding from the Plant Pest and Disease Management and Disaster Program (see below). However, it is a slow process; USDA funds first became available in 2010. The states are trying to coordinate on firewood, but we don’t yet know what the process will be.

Funding shortfalls (See the three Fading Forests reports, my blogs about appropriations)
Increase APHIS’ access to emergency funds from the Commodity Credit Corporation by amending the Plant Protection Act [7 U.S.C. 7772 (a)] to include this new definition of “emergency”:

the term “emergency” means any outbreak of a plant pest or noxious weed which directly or indirectly threatens any segment of the agricultural production of the United States and for which the then available appropriated funds are determined by the Secretary to be insufficient to timely achieve the arrest, control, eradication, or prevention of the spread of such plant pest or noxious weed.

Although APHIS has the most robust prevention program of any federal agency, its funding is still inadequate. Stakeholders should lobby the Congress in support of higher annual appropriations.

The Plant Pest and Disease Management and Disaster Program (now under Section 7721 of the Plant Protection Act) has provided at least $77 million for tree-pest programs (excluding NORS-DUC & sentinel plant programs and other programs) since FY 2008. Much useful work has been carried out with these funds. However, these short-term grants cannot substitute for stable, long-term funding. I reiterate my call for stakeholders to lobby the Congress to provide larger appropriations to the APHIS Plant Protection program and Forest Service Forest Health Protection and Research programs.

Long-term Responses to Bioinvasive Challenge

More stakeholders are advocating raising the priority of – and providing adequate resources to – such long-term solutions as biocontrol and breeding trees resistant to pests and restoring them to our forests. Advocates include the state forestry agencies of the Northeast and Midwest, some non-governmental organizations, some academics, and individual USFS scientists. One effort resulted in inclusion of language in the 2018 Farm Bill (see blog here) – although this approach has apparently run into a dead end. The new emphasis on breeding has so far not been supported by agency or Congressional leaderships.

test planting of an American chestnut bred to be resistant to chestnut blight

Solutions:

USFS convene workshop of the federal, state, National Academy, academic, and NGO groups promoting resistance breeding in order to develop consensus on priorities and general structure of program.

Explicitly include evaluation of the CAPTURE Project’s (see blog here) efforts to set priorities to guide funding allocations and policies; and proposals for providing needed supportive infrastructure – facilities, trained staff in various disciplines. (See my blogs here.)

Report results of meeting to USDA leadership, Congress, and stakeholders

Then ensure implementation of the accepted approach by both Research and Development and Forest Health Protection programs. Include provisions to provide sustainable funding.

These proposed actions still do not address ways to correct the provisions of the international phytosanitary agreements (World Trade Organization and International Plant Protection Convention) that complicate – or preclude – efforts to prevent introduction of pests currently unknown to science. This issue is discussed in Fading Forests II. A current example is beech leaf disease (described here).

Continuing inadequate engagement by stakeholders

Most constituencies that Americans expect to protect our forests don’t press decision-makers to fix the problems I have identified above: inadequate resources, weak and tardy phytosanitary measures. Some of these stakeholders are other federal agencies, or state agencies – or their staffs. They face restrictions on how “political” they can be. But where are the professional and scientific associations, representatives of the wood products industry, forest landowners, environmental NGOs and their funders, urban tree advocates Efforts by me, USDA, and others to better engage these groups have had disappointing results.

As I have documented, groups of USFS scientists have made several attempts to document the extent of invasive species threats and impacts and to set priorities. So far, they have not gained much traction. Another USFS attempt, Poland et al. in press, will appear at the end of the year. Will this be more successful?

I detect growing attention to educating citizen scientists for early detection; but if there is an inadequate – or no – official response to their efforts won’t people become discouraged?

SOURCES

Lovett, G.M., M. Weiss, A.M. Liebhold, T.P. Holmes, B. Leung, K.F. Lambert, D.A. Orwig, F.T. Campbell, J. Rosenthal, D.G. McCullough, R. Wildova, M.P. Ayres, C.D. Canham, D.R. Foster, SL. Ladeau, and T. Weldy. 2016. NIS forest insects and pathogens in the US: Impacts and policy options. Ecological Applications, 26(5), 2016, pp. 1437–1455

National Environmental Coalition on Invasive Species “Tackling the Challenge.”

Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector. Springer Verlag. (in press).

Roy, B.A., H.M Alexander, J. Davidson, F.T Campbell, J.J Burdon, R. Sniezko, and C. Brasier. 2014. Increasing forest loss worldwide from P&Ps requires new trade regulations. Front Ecol Environ 2014; 12(8): 457–465

30 years of Analyzing Forest Pest Issues

dead whitebark pine in Crater Lake National Park
photo by F.T. Campbell

I began studying and writing about the threat to North America’s forests from non-native insects and pathogens in the early 1990s – nearly 30 years ago. I reported my analyses of the evolving threat in the three “Fading Forests” reports – coauthored by Scott Schlarbaum – in 1994, 2003, and 2014. These reports are available here.

So what has changed over those 30 years? What remains the same? Why have both the changes and the stasis occurred? What can we do to fix the gaps, close unaddressed pathways, strengthen flabby policies? I will address these issues in this and following blogs.

experimental American chestnut planted in Fairfax County, VA
photo by F.T. Campbell

What has changed since the early 1990s:

Adoption and implementation of significant new international and national regulations and programs aimed at preventing introductions of non-native invasive species.
Despite the welter of new regulations, an alarming increase in numbers of highly damaging forest pests established in the country. (By my count, about 50 new species have established on the continent, six on Pacific islands; see details below.)
Alarming spread of established pests to new geographic regions and new hosts (e.g., emerald ash borer in 35 states and 5 provinces; laurel wilt disease across the range of redbay and swamp bay; rapid ‘ōhi‘a death on three of the main Hawaiian islands).
Introductions via unexpected pathways and vectors far removed from phytosanitary agencies’ usual targets, e.g., ship superstructures, imported steel and stone …

What has remained the same since the early 1990s:

Inadequate resources provided to response and recovery efforts.
Available funding focused on only a few of the more than 90 species causing damage.
Adoption of insufficiently protective regulations that have failed to prevent introduction and spread of tree-killing pests.
Lengthy delays in implementing programs that tighten controls – another factor in continuing introductions and spread.
Continued importance of expected pathways – nursery stock and raw wood, especially crates, pallets, and other forms of wood packaging.
Federal and state agencies still choose not to take action on pests e.g., goldspotted oak borer, polyphagous and Kuroshio shothole borers, beech leaf disease.
Inadequate coordination despite several efforts to set priorities.
Spurts of attention by media and political decision-makers, contrasted by lengthy periods of inattention.
Failure of most stakeholders to support efforts to prevent and respond to introductions of tree-killing pests.

Details: The Situations Then and Now

(Many of the individual species mentioned here are described more fully here. Full citations of sources are at the end of blog.)

American elm on the National Mall, Washington, D.C.

photo by USDA Agricultural Research Service

In 1993:

The number of non-native forest pest species established in the U.S. was estimated at between 300 (Millers et al. 1993) and 380 (Mattson et al., 1994; Liebhold et al., 1995) .
The area suffering the greatest numbers and impacts was the Northeast.
Several highly damaging pests that had been established for decades, including chestnut blight, white pine blister rust, Port-Orford-cedar root disease, Dutch elm disease, hemlock woolly adelgid, butternut canker, and dogwood anthracnose were receiving some attention but continued to spread.
USDA Forest Service funding for management of exotic pest infestations was crisis-oriented, with “… priorities … set under political pressures for immediate answers, with too much regard for short-term problems and too little consideration for broader management objectives.” (NAS 1975)
Since few high-profile pests had been introduced in recent years, APHIS was not actively engaged. In FY92, APHIS spent $20 million on efforts to eradicate the Asian gypsy moth. The narrow focus is illustrated by the fact that in FY93, more than two-thirds of all USDA tree pest control funds were devoted to efforts to suppress or eradicate the European gypsy moth (See FFI).
Concern about possible new introductions had grown; it focused on proposals to import unprocessed wood from Siberia, New Zealand, and Chile. The USDA Forest Service, academic scientists, and therefore APHIS emphasized the risks of known Asian pests, e.g., Asian gypsy moth, to western coniferous forests (See FFI). While individual scientists had expressed concern about wood packaging material, there was little public discussion of this threat.
We would learn later that several of the most damaging pests were already present in the country but not yet recognized – Asian longhorned beetle, sudden oak death pathogen, probably emerald ash borer.

beech leaf disease

photo by John Pogacnik

In 2019:

Numbers of non-native insects and pathogens attacking trees in North America approach 500 species. (In Fading Forests III, I calculated that by the first decade of the 21^st Century, the number had risen to at least 475. Several more have been detected since 2014. More than 181 exotic insects that feed on woody plants had established in Canada. (Source: USDA APHIS. 2000. Wood packaging risk assessment.)
Of these, 91 are considered “serious” threats (Guo et al. 2019). This estimate excludes pests native to portions of North America that are causing severe damage in naïve hosts – e.g., goldspotted oak borer; pests of palms; and pests attacking trees on U.S. Pacific and Caribbean islands.
Introductions had continued.
- Between 1980 and 2016, at least 30 non-native species of wood- or bark-boring insects (Scolytinae / Scolytidae) were newly detected in the U.S. (Haack and Rabaglia 2013; Rabaglia et al. 2019). A few of these are highly damaging, e.g. redbay ambrosia beetle, polyphagous and Kuroshio shothole borers.
- In addition to these 30 new pests, other highly damaging tree-killing pests probably introduced since the 1980s include (on the continent):
  - Eight Cerambycids such as Asian longhorned beetle (Wu et al. 2017)
  - 7 Agrilus, including emerald ash borer and soapberry borer; plus goldspotted oak borer transported from Arizona to California (Digirolomo et al. 2019; R. Haack, pers. comm.)
  - Sirex woodwasp
  - Pests of palm trees, e.g., red palm mite, red palm weevil, South American palm weevil
  - Spotted lanternfly
  - Beech leaf disease
- Also not included in the above estimate and lists are tree-killing pests on America’s Pacific Islands :
  - ‘ōhi‘a rust
  - Cycad scale
  - Cycad blue betterfly
  - Erythrina gall wasp
  - two Ceratocystis pathogens that cause rapid ‘ōhi‘a death
  - Coconut rhinoceros beetle
- Authorities also carried out approximately 25 eradication programs targetting introductions of the Asian gypsy moth (USDA Pest Alert Asian Gypsy Moth plus additional outbreaks since 2014).
Impacts of exacerbated tree mortality rates linked to these introduced pests are seen across wide swaths of the country, and affect widespread species, genera, and families.

dead redbay in Claxton, Georgia
photo by Scott Cameron

I will discuss the risk of continuing new introductions in a separate blog.

Trying to Develop the Big Picture and Set Priorities

In recent years, USDA Forest Service scientists have made several attempts to provide nation-wide assessments of the impact of these pests and criteria for establishing priorities.

The National Insect and Disease Forest Risk Assessment predicted the loss of basal area to various pests over the 15-year time period 2012 – 2027. The assessment predicted the following losses for specific species: 90% for redbay; 60% for whitebark pine; more than 40% for limber pine; 24% for tanoak; 11% for coast live oak; 6% for eastern and Carolina hemlock; 27% for eight species of ash; 20% for American elm; 19% for red oak; 18% for American beech (Krist et al. 2014).

A separate group of scientists found that, nation-wide, non-native forest pests are causing an approximate 5% increase in total mortality by tree volume (Randy Morin at NEFPC). For details on Dr. Morin’s findings, see my blog here.

A third approach to developing a nation-wide picture, Project CAPTURE, (and my blog here) utilized FIA data to develop priorities for conservation action. Fifteen species were placed in the highest priority category, including Florida torreya (Torreya taxifolia), American chestnut and Allegheny and Ozark chinquapins, redbay, five species of ash, two species of hemlock, Port-Orford cedar, tanoak, and butternut (Potter et al. 2019(b).

According to Project CAPTURE, the non-native pests affecting the largest number of hosts are the European gypsy moth, which attacks 65 hosts; and oak wilt (Bretziella fagacearum), which infects 61 hosts. The Asian longhorned beetle attacks 43 hosts (Potter et al. 2019(b).

I note that several other non-native pests also have high numbers of host species. In the Project CAPTURE study, these pests are ranked lower because the project limited its evaluation to the five agents with the greatest effect on any particular host. Thus, of the 18 native tree species that host one or both of the invasive shothole borers and associated Fusarium disease complex (PSHB website), the project included only six. Of the 22 tree species listed by APHIS as hosts of Phytophtora ramorum, the project included 12 (K. Potter, pers. comm. April 17, 2019).

SOD-killed tanoak on the Big Sur peninsula, California
photo by Matteo Garbelotto, University of California Berkeley

More extensive discussions of non-native pests’ impacts are provided in Lovett et al. 2006, Lovett et al. 2016, and Potter et al. 2019. A book-length discussion of invasive species impacts – ranging from feral hogs to invasive plants, is expected in December; look for Poland et al. (in press).

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

Digirolomo, M.F., E. Jendek, V.V. Grebennikov, O. Nakladal. 2019. First North American record of an unnamed West Palaearctic Agrilus (Coleoptera: Buprestidae) infesting European beech (Fagus sylvatica) in New York City, USA. European Journal of Entomology. Eur. J. Entomol. 116: 244-252, 2019

Guo, Q., S. Fei, K.M. Potter, A.M. Liebhold, and J. Wenf. 2019. Tree diversity regulates forest pest invasion. Proceedings of the National Academy of Sciences of the United States of America. www.pnas.org/cgi/doi/10.1073/pnas.1821039116

Haack, R.A. and R.J. Rabaglia. 2013. Exotic Bark and Ambrosia Beetles in the USA: Potential and Current Invaders. CAB International 2013. Potential Invasive Pests of Agricultural Crops (ed. J. Peña)

Krist, F.J. Jr., J.R. Ellenwood, M.E. Woods, A. J. McMahan, J.P. Cowardin, D.E. Ryerson, F.J. Sapio, M.O. Zweifler, S.A. Romero 2014. National Insect and Disease Forest Risk Assessment. United States Department of Agriculture Forest Service Forest Health Technology Enterprise Team FHTET-14-01

Leung, B., M.R. Springborn, J.A. Turner, E.G. Brockerhoff. 2014. Pathway-level risk analysis: the net present value of an invasive species policy in the US. The Ecological Society of America. Frontiers of Ecology.org

Liebhold, A. M., W. L. MacDonald, D. Bergdahl, and V. C. Mastro. 1995. Invasion by exotic forest pests: a threat to forest ecosystems. Forest Sci., Monograph 30. 49 pp.

Lovett, G.M., C.D. Canham, M.A. Arthur, K.C. Weathers, and R.D. Fitzhugh. Forest Ecosystem Responses to Exotic Pests and Pathogens in Eastern North America. BioScience Vol. 56 No. 5 (May 2006)

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

Millers, I. United States Department of Agriculture, Forest Service Entomologist, Forest Health Protection Northeastern Area State and Private Forestry. Durham, NH. Personal communication to F.T. Campbell, 1993.

Morin, R. presentation at Northeastern Forest Pest Council 81st Annual Meeting, March 12 – 14, 2019, West Chester, Pennsylvania

National Academy of Sciences. 1975. Forest Pest Control. Washington, D.C.

Polyphagous shothole borer website https://ucanr.edu/sites/pshb/overview/About_PSHB/

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

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

Rabaglia, R.J., A.I. Cognato, E. R. Hoebeke, C.W. Johnson, J.R. LaBonte, M.E. Carter, and J.J. Vlach. 2019. Early Detection and Rapid Response. A Ten-Year Summary of the USDA Forest Service Program of Surveillance for Non-Native Bark and Ambrosia Beetles. American Entomologist Volume 65, Number 1

USDA, Animal and Plant Health Inspection Service. 2014. Asian gypsy moth pest alert https://www.aphis.usda.gov/publications/plant_health/content/printable_version/fs_phasiangm.pdf and pers. comm.

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

Wu,Y., N.F. Trepanowski, J.J. Molongoski, P.F. Reagel, S.W. Lingafelter, H. Nadel1, S.W. Myers & A.M. Ray. 2017. Identification of wood-boring beetles (Cerambycidae and Buprestidae) intercepted in trade-associated solid wood packaging material using DNA barcoding and morphology Scientific Reports 7:40316