Invasive Species

More than 400 species of non-native (aka alien or exotic) invasive forest insects and diseases are established in the United States. Some of these insects have become invasive, spreading rapidly and causing significant economic and ecological impacts to the nation's forest and urban trees. Northeastern and North Central cities have historically been “entry ports” for most invasive pests and continue in this dubious distinction. Because of this, Northern Research Station (NRS) entomologists and plant pathologists have a long history of research on the biology and ecology of non-native forest pests and also on methods for control and eradication. NRS scientists conduct research to understand tree diseases in order to develop management strategies and planning tools for achieving the goal of healthy woodlands, forest plantations, and urban landscapes.

Current research topics on invasive species include prediction and prevention, detection and monitoring, management and restoration. Specific insects currently being studied by NRS scientists include the Asian longhorned beetle (ALB), emerald ash borer (EAB), hemlock woolly adelgid (HWA), and gypsy moth (GM). Specific diseases caused by invasive pathogens include sudden oak death (SOD), white pine blister rust, butternut canker, red pine shoot blight, oak wilt, and armillaria root disease; beech bark disease is a combination of infestation by certain scale insects and infection with a fungus. Other, stress-related diseases such as oak and sugar maple declines are also being studied.

Selected Research Studies

Managing Invasive Forest Insect Pests with Bacillus thuringiensis
Research on the mode of action of Bt has revealed that activated Cry toxins bind to specific receptors on the cellular lining of the gut in larvae and then insert into the membrane, creating pores. Until recently, it was generally accepted that the effect of Cry toxins was due to pore formation and subsequent lysis of gut cells.

Is Housing a Factor in the Distribution of Invasive (Aggressive, Nonnative) Plants?
We analyzed the relationship between housing and distribution of invasive exotic plants in forested areas at coarse and fine scales. Specifically, we tested the influence of housing compared with other environmental and human factors in explaining exotic invasive plant distribution.

Development of the Euproctis chrysorrhoea Baculovirus as a Microbial Control for the Browntail Moth
The browntail moth, Euproctis chrysorrhoea, is a nonnative pest of forested and urban landscapes on Cape Cod, Massachusetts and the Casco Bay area of Maine.  Browntail moth larvae cause significant and at times complete defoliation in infested areas and severe rashes and breathing problems in people contacting larval hairs.  Infested areas in Maine are being treated with chemical insecticides to control browntail moth.  However, due to the shellfish and lobster industries in these areas the preferred control agent is nonchemical.  No control measures are being employed on Cape Cod.

Biopesticides for Control of Douglas-fir Tussock Moth
TM Biocontrol-1 is a viral biopesticide produced by the U.S. Forest Service that is used, along with various commercial Bacillus thuringiensis (Bt) products, for the control of the Douglas-fir tussock moth (DFTM), Orgyia pseudotsugata, in the Pacific Northwest. Improving the efficacy of these products involves bioassay in a standard (Goose Lake) strain of tussock moth that is reared to maintain vigor and provide an on-demand larval resource for research and evaluation of a variety of biological products.

FRAME: Forest FRAgments in Managed Ecosystems
We designed this research program as a long-term study of conditions in forest fragments across the mid-latitude temperate forests of the world. The core sites are located in northern Delaware, in an area surveyed of fragments in 1965 in a joint project of the University of Delaware and the U.S. Forest Service. One of these sites has been continuously monitored since 1973.

Effects of Nonnative Plants on Bird Communities in Suburban Forest Fragments
The objective of this project is to study the effects of nonnative plants on bird populations in suburban forest fragments.

Soil Chemistry and Exotic Plant Invasions in Riparian Corridors of Varying Width
Our research was designed to explore relationships between the width of riparian corridors in human-dominated landscapes and their ability to buffer streams from runoff and invasion.

Development of DNA Based Markers to Identify Beech Bark Disease-resistant trees in natural stands
In northern hardwood stands that have been long affected by beech bark disease, large numbers of severely deformed American beech trees persist.  Stand management practices are complicated by the initiation of root sprouts by beech trees in decline due to BBD.  Such sprouts can result in the formation of “thickets” of diseased, deformed beech trees of small diameter that prevent the establishment of other more desirable species yet offer little ecological or economical value.  Silvicultural approaches are needed to reduce the number of susceptible trees and increase the number of resistant beech trees. 

Development of an American Beech Breeding Program
There are American beech trees that remain disease-free in forests long affected by beech bark disease.  Insect challenge experiments have demonstrated that such trees are resistant to the scale insects and extensive fungal infections typically are not observed without prior scale infestation. 

Dutch Elm Disease
The American elm was once widely distributed throughout the eastern United States and was a preferred tree for use along city streets and in the yards of many homeowners.  The Dutch elm disease (DED) fungal pathogen, Ophiostoma ulmi, was introduced into the United States in Cleveland and Cincinnati, OH in 1930, and spread to destroy millions of American elm trees in urban and forested landscapes. 

Identification and Utilization of Ectomycorrhizal Fungi for Restoration of the American Chestnut in Reclaimed Mined Lands
The American chestnut, once the third most dominant tree in eastern United States forests, has been almost eliminated by an invasive fungus, Cryphonectria parasitica. The fungus was first introduced to North America in 1904. It quickly spread into its new and defenseless host population as happens with many other nonnative pest introductions. As a result, American chestnuts are being reduced to mere susceptible shrubs instead of being one of the most dominant tree species.

Hemlock woolly adelgid
The hemlock woolly adelgid (HWA) is a tiny sap-sucking insect first noted in the eastern United States around 1950 on nursery stock in Richmond, Virginia. It spread slowly on ornamentals until it reached the forests of the Appalachian Mountains, where hemlocks are an important part of stream-side and moist shady ecosystems. When this happened, around the late 1980s, the spread rate took off and HWA is now recognized as a serious forest pest. It has now spread as far as the Smoky Mountains and southern Maine. A heavily infested hemlock usually dies within 5-7 years, unless treated by methods that are not practical for wildland trees. NRS entomologists and their cooperators are working to find natural enemies of the HWA (mostly lady beetles from China) and are also investigating host plant differences (hemlocks in Asia and the West Coast are not killed by HWA infestations).

Alien Forest Pest Explorer
Alien Forest Pest Explorer is maintained as a portal for the exploration of spatial data relating to non-indigenous forest pests. It can be used to generate customized maps that depict historical and future range expansion, historical damage and forest susceptibility. Currently, the Explorer contains data for 72 forest pests in the eastern US. Plans are underway to include data from other pests as well as selected invasive plants.

Ailanthus and Prescribed Fire Study
While prescribed fire can favor oak regeneration, its use may also risk the invasion and expansion of non-native plant species.  Ailanthus altissima (tree-of-heaven) is a shade-intolerant tree that is widely distributed in the eastern U.S. and can be highly invasive.  It invades disturbed habitats through wind-dispersed seed and can persist and expand through root sprouts.  Ailanthus is present in many oak forest landscapes throughout the eastern US; however, little is known about the effects of fire on Ailanthus and its observed expansion in recently burned forests.

SILVAH NNIS
As we have planned to increase our SILVAH training and decision support in Ohio, several of our partners suggested that ignoring NNIS was not an option.  Pending development of better guidelines for recognizing when NNIS are abundant enough to pose a threat to management objectives and treatment options, SILVAH currently provides a format for recording presence absence and frequency data about several NNIS that are important in Ohio and elsewhere in the mixed hardwood forests of the east.  SILVAH flags the presence of such species and encourages users to investigate treatment options for NNIS before undertaking the silvicultural treatments that SILVAH recommends. 

Tropical Forest Mycology
The Center for Forest Mycology Research (CFMR, part of the Northern Research Station of the US Forest Service) leads critical research on the biology of tropical fungi native to Hawaii, US territories in the Caribbean (Puerto Rico and the US Virgin Islands) and to other countries in the Caribbean Basin.

Collections at the Center for Forest Mycology Research
Forest fungi are critically important for forest health and productivity. Of the estimated 1.5 million species of fungi worldwide, only about 5% have been described and named. Key characteristics used to identify species and the relationships among species are in a critical period of change. 

Saving the Butternut
The butternut canker disease is killing butternut and threatening the future of this important hardwood species throughout its range in North America.

Oak Wilt
Oak wilt, caused by the exotic fungus, Ceratocystis fagacearum, is one of the most serious diseases of oaks (Quercus) in the Midwest and kills tens to hundreds of thousands of oak trees every year.  Infection by the fungus causes clogging of water conducting vessels, leading to wilt and death of infected trees. 

Mediterranean Pine Engraver for Eastern Forests
The Mediterranean pine engraver is new to the United States. It was first detected here in 2004. This bark beetle has a history of causing extensive mortality in pines elsewhere in the world, but it is uncertain whether the beetle could feed on conifers in the northeastern United States. Information is needed to better predict and prevent the spread of the beetle to the rest of the country.

Technical Innovations to Reduce Impacts of Invasive Species
Technology that is available to manage invasive species and increase productivity of short rotation woody crops (SRWC) is often too expensive, difficult to operate, cumbersome, and/or impractical. There is a need for technical innovations that help to achieve these objectives while meeting specific experimental needs.

Earthworm Invasion
Populations of exotic European earthworms have been expanding into formerly worm-free forests in the north central and northeastern United States.  These earthworms consume the organic horizons of the forest floor, often removing leaf litter within several years of invasion.  This leads to changes in soil carbon, nutrients (e.g. nitrogen and calcium), soil microclimate, hydrology, soil organisms, and plant community assemblages. 

Impacts of Beech Bark Disease
In 2000, very high populations of the beech scale (Cryptococcus fagisuga) were observed when ground-truthing these areas of discoloration on the Tionesta Scenic and Research Natural Area. In anticipation of mortality, a small number of American beech trees were selected for continued monitoring. These trees were selected to mirror existing long term BBD monitoring plots elsewhere in its range. With beech mortality reaching 52% in 5 years it became obvious that the impact of BBD on old growth American beech-eastern hemlock forest required a more in-depth evaluation.

Fire and Fire Surrogate Treatments: The Central Appalachian Plateau Site
Current forests in many fire-dependent ecosystems of the United States are denser and more spatially uniform, have many more small trees and fewer large trees than did their presettlement counterparts. Causes include fire suppression, past livestock grazing and timber harvests, and changes in land use. The results include a general deterioration in forest ecosystem integrity and the threat of losing important, widespread forest types. Such conditions are prevalent nationally, especially in forests with historically short-interval, low- to moderate-severity fire regimes, such as the upland oak forests of the central hardwoods region.   

Aspen FACE Experiment
The Aspen FACE (Free-Air Carbon Enrichment) Experiment is a multi-disciplinary study to assess the effects of increasing tropospheric ozone and carbon dioxide levels on the structure and function of northern forest ecosystems.

Tracing the movement of an invasive insect using stable isotopes
To better understand the response of insect populations to increasing environmental pollution, we are using stable isotope analysis to trace the movement of an invasive insect in mixed tree communities grown under different air quality conditions.

Asian gypsy moth
The main focus of this gypsy moth work is on the type with flight-capable females, generally referred to as the “Asian” gypsy moth because of the origin of the original interceptions.  For regulatory purposes, the United States Department of Agriculture refers to any type/subspecies of Lymantria dispar possessing female flight capability as the Asian gypsy moth. 

Asian longhorned beetle
The Asian longhorned beetle (ALB) arrived here as larvae boring in solid-wood packing material from China. The first beetles were detected in trees in several suburban towns on Long Island and in Brooklyn, Manhattan, and Chicago. Later, ALB were found in northern New Jersey, Toronto, and Sacramento, CA. These outbreaks have triggered major eradication efforts that included inspection of ALL trees in designated quarantine areas. ALB have also been detected as larvae in warehouses and are destroyed. In its native habitat in China, the ALB is a normal, relatively harmless member of the forest insect fauna but it has infested poplars and other plantation-grown trees that were made into packing and dunnage materials. Laws now require that all such materials be treated kill any insect larvae. NRS researchers are instrumental in researching the growth habits of the ALB in the Forest Service=s only mainland quarantine laboratory and also working on detection methods with cooperators at the Oak Ridge National Laboratories.

Emerald ash borer
The emerald ash borer (EAB), an exotic pest relatively new to North America, attacks and kills all ash species growing here. The EAB probably first entered Michigan at least 10 years ago, presumably in solid-wood packing materials from China. EAB has since been found in Ontario, Ohio, Indiana, and Illinois and has also traveled to Maryland and Virginia on infested nursery stock. At this point, the only eradication treatment is cutting down, chipping, and burning the trees. Because ash species were planted in many urban areas as replacements for the elms that were killed by Dutch elm disease, many of our streets and yards are once again sadly bare. About 15 million ash trees in urban and forested settings have been killed by the EAB. Quarantines in the United States and Canada restrict the movement of ash trees, logs, and firewood to prevent new introductions. NRS scientists have been in the forefront of research to understand the biology and ecology of the EAB and to develop methods for prevention of spread, trapping, detection, monitoring, and management.

Nun moth
The nun moth, Lymantria monacha (nun moth), is closely related to gypsy moth in appearance and behavior.  It is a major pest in Central and Eastern Europe and southeastern Siberia, as well as Spain.  Its establishment in North America would be disastrous because of its polyphagous feeding habits, ability to colonize new habitats, and capacity to be spread rapidly by vagile adults.

Ecosystem Management Study: Restoration of Mixed-oak Forests with Prescribed Fire
Historically, fire was a frequent disturbance process in the mixed-oak forests of the central hardwoods region. Fire control has altered forest structure and composition. Forests are more dense and the sustainability of oak and hickory dominance is now threatened by an abundance of shade-tolerant and fire sensitive tree species such as red maple, sugar maple, and beech. Prescribed fire has been advocated to promote and sustain open-structured mixed-oak forests and the plants and animals that have adapted to these communities. However, long-term research on fire effects is lacking.

Plant Diversity in Managed Forests
The great majority of plant diversity in forests is contained in the herbaceous layer, comprised of both herbaceous and woody species.  We seek a better understanding of how forest management activities affect plant diversity.  NRS-2 scientists are investigating the direct and indirect effects of timber harvesting, prescribed burning, herbicide application, and deer browsing (alone and in combination) on plant composition and diversity in mixed oak, Allegheny, and Northern Hardwood forests.

Site, Stress, Nutrition, and Forest Health Interactions
A range of stressors including defoliating insects, pathogens, droughts, inadequate soil base cations, and changing climate have interacted to affect the health and regeneration of selected northern and central hardwood forest species. In the 1980s and 1990s sugar maple dieback and mortality was extensive across the unglaciated Allegheny Plateau in northern Pennsylvania. 

Gypsy moth
Gypsy moth (GM) caterpillars have defoliated oak and mixed hardwood forests, spreading out from Boston, where they were accidentally introduced around 1869. Because the adult females are flightless, the line of advance moves annually only as far as the early-instar caterpillars can “parachute” in the wind or the eggs are moved around by human activities. The line now reaches from North Carolina to Michigan. As well as studying the basic biology of the GM, NRS scientists have developed most of the products and application techniques used in recent decades by the “Slow the Spread” Program: these include Bt (Bacillus thuringiensis, which infects GM) and two general-use biopesticides that are registered by the EPA: Gypchek (a nucleopolyhedrovirus product for GM) and Neochek-S (a related product for European pine sawfly). An improved virus-production method for possible industrial-scale use have been developed by other NRS scientists. Natural disease agents such as viruses, bacteria, fungi, and microsporidia are being tested on insect populations to develop strategies for enhancing their effectiveness in mitigating damage by pests.

Sudden oak death

Oak ramorum blight (aka sudden oak death, or SOD) is a non-native fungal disease that is killing oaks and tanoaks in California and Oregon, as well as infesting a large number of shrub species but not killing them. Unfortunately, some of these shrubs (rhododendrons, mountain-laurels, pieris, and others) are grown horticulturally in this same area and they could vector the disease to the East Coast. Indeed, some incidents have already happened. NRS scientists who have been researching the rates and mode of spread of GM and HWA have applied their expertise to make risk rating maps for SOD. Oak species are major components of eastern and midwestern hardwood forests and the host shrubs mentioned earlier are common understory components.