Our mission is to provide the basic biological and ecological knowledge and innovative management strategies required for management and control of native and non-native insect pests, disease pathogens and invasive plants in changing forest ecosystems.
Justification and Problem Areas
The mission of the Forest Service is to sustain the health, diversity, and productivity of the Nation’s forests and grasslands to meet the needs of present and future generations. As identified in the Forest Service 2013 National Strategic Framework for Invasive Species Management, non-native invasive insects, pathogens, and plants are among the most significant environmental and economic threats to fulfilling this mission. Although a relatively small percentage of all species introduced from parts of the world become damaging pests, some introduced species populations proliferate dramatically due to their escape from coevolved natural enemies, and/or lack of resistance or competitive ability among our native hosts and associates. In forests, invasive species degrade or threaten ecosystem services and resources, including water quality, wood products, recreational opportunities, and wildlife habitat. More than forty percent of all federally-listed threatened and endangered species are considered at risk primarily due to negative effects of invasive species. Such adverse effects can be exacerbated by interactions with fire, native pests, weather events, human actions, and environmental change. In the US alone, three groups of invasive forest insects (borers, sap-feeders, and defoliators) are estimated to cost nearly $5 billion annually in government and household expenditures, property value losses, and timber losses. In addition to invasive species, native pests continue to pose forest management challenges in the context of changing climates, environmental and forest conditions, land-use patterns, and markets. To protect resources, sustain ecosystem services, rehabilitate natural landscapes, and minimize taxpayer costs, a strong research effort to address insect, disease and invasive plant issues is critical to implementing the Forest Service mission.
Problem 1. Insects
Southern U.S. forests face numerous challenges associated with native and non-native insects. Due to the abundance of mature and densely-stocked pine forests, the southern pine beetle (Dendroctonus frontalis) and other native bark beetles of southern conifers continue to be persistent and destructive pests in the region. At endemic levels, bark beetles serve as natural mortality agents in weakened trees, but at epidemic levels they cause great economic damage and disruption of resource management practices. Projected forest conditions in the South indicate that large acreages will continue to be of high hazard for southern pine beetle (SPB) outbreaks. At the same time, changing timber markets, land development, and land ownership/management patterns are making traditional silvicultural techniques for bark beetle prevention and control (e.g., thinning, suppression harvests, etc.) increasingly difficult to implement in many areas. These factors, coupled with recent outbreaks of SPB outside the Southern region, point to a continued need to develop novel management strategies and tools for native bark and wood-boring insects. Furthermore, insect pests of seed orchards, seedling nurseries, and young forests (including tip moths, reproduction weevils, acorn weevils, coneworms, and seedbugs) can hinder efforts to regenerate and restore forests with high-quality trees. The dynamics of some native pests and their associates may well change in unexpected ways in response to a changing climate.
The threats to Southern forest health and sustainability by non-native invasive insect pests are as acute as ever. Hemlock woolly adelgid (Adelges tsugae) has spread through nearly the entire Southern Appalachian range of eastern hemlock and is steadily removing this keystone species from riparian forests. To date, the emerald ash borer (Agrilus planipennis) has invaded more than half of the 13 Southern states and threatens to functionally eliminate all Fraxinus species. Movement of infested wood products are likely responsible for the arrival and establishment of the walnut twig beetle (Pityophthorus juglandis) and its fungal associate, which are now killing the economically and ecologically valuable eastern black walnut in Virginia and Tennessee. Although it has not yet been a damaging pest in the Northeastern US, the European wood wasp (Sirex noctilio) is still considered a serious threat to the Southern region due to its destructive impacts in overstocked pine plantations (including loblolly pine) in other countries. The continual intra- and international movement of wood products and live plants increase the likelihood that new destructive forest insects will become introduced and established in the Southern region in the coming decades. There is a pressing need for strategies and tools for prevention, detection, suppression, and integrated management of invasive forest insects to meet economic, ecological, aesthetic, and recreational forest management objectives.
Despite the threats posed by certain pest insects, the ecological services and benefits provided by various native insect groups are substantial. Worldwide, dead wood in forests is recognized as one of the three most important habitats for insect and fungal diversity, and it is estimated that as many as one third of all forest insects are saproxylic (directly or indirectly dependent on dead wood). Pollinating insects have been in decline in recent years and yet are critical to the reproduction of numerous plant species including food crops. The effects of various forest management practices, as well as invasive species introductions, on decomposers, pollinators, and other beneficial insects are still poorly understood.
Problem 1a. Ecology, biology and management of bark beetles and other native insects.
A lack of economic incentives for harvesting pine timber, coupled with loss of numerous synthetic pesticides for control of bark beetles, has created a need for the development of alternative management and control tactics for bark and wood boring insects. Semiochemicals (whether attractant, anti-aggregant, or anti-feedant) have shown some promise for managing bark beetles and invasive insects, as have systemic and new pesticides. However, few of these strategies have been adequately tested, deployed or optimized, thus limiting their potential use.
Problem 1b. Detection, biology and management of non-native insects.
The steady influx of non-native insect species calls for development of improved detection and monitoring strategies for important forests pest groups. Rapid detection can play a key role in preventing the establishment of new pest species. Established populations of non-native insects often spread quickly and can be extremely difficult to control. When this is due, at least in part, to a lack of effective natural enemies in the introduced range, classical biological control can be a useful long-term strategy for reducing pest populations. Because invasive insects also often encounter limited resistance from naïve host plants, classical biological control often cannot succeed in isolation. A truly integrated management approach (i.e., combining biological, chemical and cultural control methods with host plant improvement), informed by basic biological research, will be needed to combat some of the most aggressive invasive pest problems.
Problem 1c. Effects of forest management and species invasion on insect biodiversity and ecosystem processes.
Many questions remain about how native forest insect communities are impacted by management practices and invasion by exotic plant species. Two insect groups are of particular concern due to the ecosystem services they provide, their importance to biodiversity, and documented population declines. The importance of bees and butterflies to the pollination of crops is widely acknowledged, for instance, but it remains largely unknown how these organisms are affected by forest management or invasion. There is an urgent need for research in this area given documented declines in pollinator populations. Similarly, saproxylic insects (i.e., species directly or indirectly dependent on dead wood) account for about one third of all forest insect species and are also suffering population declines in many parts of the world. Although the ecosystem services provided by saproxylic insects remain largely unstudied, these organisms may contribute importantly to wood decomposition, nutrient cycling and pest control, thus promoting forest health and resilience.
Problem 2. Diseases
As dramatically illustrated by the historical demise of species like American chestnut, American elm, and butternut, non-native tree pathogens have the potential to functionally eliminate tree species and drastically alter forest landscapes. Like invasive insects, forest diseases can cause substantial negative economic, ecological, cultural and aesthetic impacts. The causal factors of forest diseases can be complex and may be characterized by multiple predisposing, inciting or contributing factors. The widespread impact of laurel wilt disease, which has killed millions of redbay and sassafras trees from North Carolina to Texas over the last decade, was not anticipated even after the non-native insect vector was detected and identified. Careful study of the causal agents, pathogen genetic variability, host range, epidemiology, vector interactions, and host responses are important to the development of management strategies for forest and nursery diseases.
Problem 2a. Insect-microbial associations and insect-pathogen disease complexes.
The laurel wilt disease pathogen (Raffaelea lauricola) exemplifies the potential for fungal symbionts of traditionally secondary insects (e.g. ambrosia beetles) to cause catastrophic effects when introduced into novel ecosystems. Additional research on the identity, relationships and functional roles of fungi and other microorganisms associated with insects such as bark beetle (e.g. walnut twig beetle) and wood wasps (e.g. Sirex noctilio or native Siricidae) are needed to understand the epidemiology of certain diseases and determine appropriate management strategies for potential introductions of insect-pathogen complexes in the South.
Problem 2b. Other diseases of forest ecosystems.
In addition to diseases caused by insect-pathogen complexes, other forest disease occurrences or epidemics may occasionally demand research attention due to their complex diagnosis or impact on local or regional ecosystems, forest resources or communities.
Problem 2c. Forest nursery diseases.
Historically, a variety of fungal pathogens and plant parasitic nematodes have impacted seedling production in forest tree nurseries. The introduction of fumigation with methyl bromide in the 1950’s provided a means for broad spectrum control of many soil borne pest problems. Methyl bromide has been identified as an ozone depleting chemical and its use is being phased-out under the terms of the Montreal Protocol. We plan to continue our work on the influences of nursery cultural practices on pathogenic fungi and plant parasitic nematodes to minimize subsequent disease development and increase seedling production. As methyl bromide is phased out, we will continue to assess application methods, distribution, efficacy and fate of alternative soil fumigants and other pesticides.
Problem 3. Invasive Plants
Non-native invasive species represent one of the most serious challenges to sustainable forest health and management in the United States and around the globe. Invasive plant species such as cogongrass, invasive privets, Chinese tallowtree, Japanese and Old World climbing ferns, and non-native honeysuckles are altering and degrading native plant communities, negatively impacting forest biodiversity and ecosystem function, and hindering management objectives in forests. The inhibition of ecosystem services by plant community shifts is under-researched, poorly understood, or poorly integrated in Forest Service research. Moreover, other non-native forest pest organisms (e.g., emerald ash borer, hemlock woolly adelgid) can threaten to largely eliminate major tree species or genera from North America, and may cause significant shifts in the plant and animal assemblages, successional trajectories, community dynamics, and ecosystem services provided by forests. Combined effects characterized by the invasional meltdown hypothesis (whereby invasion by one non-native species initiates a cascade of invasions by other non-native species from varied guilds), may occur more frequently in forest types that are of conservation or management concern.
In recent decades, substantial research progress was made in determining types, rates, and application methods of herbicides appropriate for effective extirpation of invasive plants in forest ecosystems. Newly released or reformulated herbicides require comparative testing. However, many invasive plant species remain persistent due to variable applications and/or efficacy, differential reproduction potentials and strategies, persistent propagule pressure, inter- and intraspecific hybridization, and potential novel evolutionary selection pressures or release from natural enemies, among many other ecological factors contributing to invasion success in plant species.
Problem 3a. Prevention, detection, and characterization of invasive plant species.
Research is needed to contribute to prevention of entering invasive propagules, efficient detection of nascent establishing populations, and the identification and characterization of invasive plant populations.
Problem 3b. Invasive plant species control and management.
Additional research is needed to optimize the types, rates, methods, timing, and frequency of herbicide applications for persistent invasive plant problems (e.g., cogongrass) under varied forest types and management. Significant research gaps exist in the integration of chemical control with other management methods including manual, mechanical, biological and silvicultural tactics. Even when a target invasive plant is eradicated or suppressed, few methods exist to rehabilitate or restore communities and the ecosystem services therein to pre-invasion levels, or at least recoup some of the losses.