Changes in climate may allow some nonnative plant species, insect pests, and pathogens to expand their ranges farther north as the climate warms and the region loses some of the protection offered by a traditionally cold climate and short growing season. The abundance and distribution of some nonnative plant species may be able to increase directly in response to a warmer climate and also indirectly through increased invasion of stressed or disturbed forests. Similarly, forest pests and pathogens are generally able to respond rapidly to changes in climate and also disproportionately damage-stressed ecosystems. Thus, there is high potential for pests and pathogens to interact with other climate-mediated stressors. Unfortunately, we lack basic information on the climatic thresholds that apply to many invasive plants, insect pests, and pathogens. Further, there remains a limited ability to predict the mechanisms of infection (in the case of pests and diseases), dispersal, and spread for specific agents, as well as which specific nonnative species, pests, or pathogens may enter the region during the 21st century.