Pests (e.g., insects, pathogens) affect forest communities through complex interactions with plants, other animals, and the environment. While the effects of exotic (non-native) pests on trees received broad attention and were extensively studied, fewer studies addressed the ecosystem-level consequences of these effects. Related studies so far mostly only targeted a very few dominant pests (e.g., hemlock woolly adelgid—HWA, beech bark disease—BBD, and spongy moth—SM) and were limited to aspects of the complex situation such as (1) pests’ direct physical disturbance to forest ecosystems, (2) altered geochemical elements of soils, water, and air (e.g., excretion), and (3) feedback effects from the alteration of ecosystems on plants, native insects, and present and future pest invasions. New studies also show that, in general, planted forests appear to be more prone to exotic pest invasions and thus suffer greater impacts than natural forests. Integrated studies are critically needed in the future to address (1) direct/indirect interactions of pests with ecosystem elements, (2) both short- and long-term effects, and (3) feedback effects. We discuss the implications of the new findings and corresponding management strategies.