Invasive Soil Organisms and Their Effects on Belowground Processes

Invasive species have a wide range of effects on soils and their inhabitants. By altering soils, through their direct effects on native soil organisms (including plants), and by their interaction with the aboveground environment, invasive soil organisms can have dramatic effects on the environment, the economy and human health. The most widely recognized effects include damage to human health and economies, such as that caused by invasive fire ants and termites. Many other soil invasive species, however, have pervasive but poorly understood effects on terrestrial ecosystems. These species include the following: 1. Invasive plants and their symbionts (e.g., Falcataria in Hawaii). 2. Herbivores (e.g., root-feeding weevils). 3. Ecosystem engineers (e.g., earthworms). 4. Keystone species (e.g., terrestrial planaria). In addition, aboveground invasive species, notably herbivores and pathogens, can have major indirect effects on belowground processes by altering nutrient cycles, plant health, productivity and carbon (C) allocation patterns, demography, and community composition and function. Given the diversity of invasive soil organisms, there is a need for Forest Service Research and Development (R&D) to develop a prioritized list of invaders and research topics to help guide research and identify research gaps. Large gaps exist in our knowledge of the identity, distribution, abundance, and effects of most invasive soil organisms. Organisms with uncertain but potentially large ecosystem effects (e.g., invasive planaria) deserve more attention. In addition, we perceive several areas emerging as important research topics for Forest Service R&D. These topics include the widespread increase in propagule pressure of soil invasive species in urban areas and in the wildland-urban interface, the potential for additive and synergistic effects of suites of soil invasive species, the feedbacks between invasive species and soil microbial communities, and the interactions of soil invasive species with global change. All stages of management of soil invasive species are critical, and Forest Service R&D is poised to play a leadership role. In the prediction and prevention area, we are in need of a more coordinated effort. Forest Service R&D has the expertise to inform the U.S. Department of Agriculture (USDA), Animal and Plant Health Inspection Service (APHIS) and other organizations about gaps in their programs for excluding or limiting dispersal of soil invasive species, but, at present, no comprehensive program exists to generate such information. Some work is being done on biogeographic models of invasive distribution that could inform prediction and prevention efforts. In the detection and eradication, management and mitigation, and restoration and rehabilitation areas, we have scientists directly addressing major soil invasive species issues, including 1 Research Ecologist, Forest Service, Northern Research Station, Forestry Sciences Laboratory, 410 MacInnes Dr., Houghton, MI 49931. 2 Research Ecologist, Forest Service, Southern Research Station, Forestry Sciences Laboratory, 320 Green St., Athens, GA 30602–2044. 3 Bioclimatologist, Forest Service, Environmental Science Research Staff, Rosslyn Plaza, Building C, 1601 N. Kent St., 4th Floor, Arlington, VA 22209. 4 Botanist, Forest Service, Pacific Northwest Research Station, 3200 SW Jefferson Way, Corvallis, OR 97331. 5 Research Forester, Forest Service, Northern Research Station, c/o Pacific Northwest Research Station, 3200 SW Jefferson Way, Corvallis, OR 97331. 6 Research Ecologist and Director, Forest Service, Sabana Field Research Station, International Institute of Tropical Forestry, Jardín Botánico Sur, 1201 Calle Ceiba, San Juan, PR, 00926–1119. 7 Botanist, Forest Service, Northern Research Station, P.O. Box 1377, Luquillo, PR 00773–1377. 8 Entomologist, Forest Service, Forest Products Laboratory, One Gifford Pinchot Dr., Madison, WI 53726–2398. 9 Microbiologist, Forest Service, Forest Products Laboratory, One Gifford Pinchot Dr., Madison, WI 53726–2398.