Forest Structure: A Key to the Ecosystem

Forest structure is both a product and driver of ecosystem processes and biological diversity. It has become apparent in recent years that changes in forest structure as a result of management for timber production have undesirable consequences for other components of forest ecosystems. The objective of this paper is to provide an overview of what we have learned about the ecological roles of forest structure in the Pacific Northwest and how forest structure changes as a result of disturbance and succession. Forests are structurally diverse, but many structures derive from the same processes of disturbance and growth. Consequently, measurements on a few structural attributes can be used to estimate many other structural conditions. Particularly important components of forest structure include live-tree sizes, vertical foliage distributions, horizontal variation in canopy density, and coarse woody debris. Knowledge of the ecological roles of these structures has increased in recent years and we now have a general understanding of how these structures change during succession. Although the ecological values of forest structures are now more widely appreciated, we still have many significant knowledge gaps including the ecological roles of belowground structure, woody debris, and landscape pattern.