Abstract

For millions of years the distribution of the world's biota has been restricted by oceans and other natural barriers. During the last 100 yr, human activities, especially international travel and trade, have circumvented these barriers, and species are invading new continents at an increasing rate. Biological invasions of insect, plant, and fungal pest species often cause substantial disturbance to forest ecosystems as well as severe socioeconomic impacts. The invasion process is composed of three phases: arrival, establishment, and spread. Arrival occurs when a species is initially transported to the new area (e.g., transportation to a new continent). Establishment is essentially the opposite of extinction; it is the process by which a population becomes abundant enough to prevent extinction. Spread is the process by which a species expands its range into adjoining uninfested areas. Management of pest invasions focuses on preventing arrival, establishment, or spread. We present case histories that illustrate the invasion process via details of the arrival, spread, impact, and management of selected exotic forest pests. Biological invasions are probably the most significant environmental threat to the maintenance of natural forest ecosystems in North America and elsewhere. The magnitude of this problem necessitates increased efforts to reduce the incidence and impacts of pest invasions. For. Sci. Monogr. 30:1-49.