As a result of recent fire history and decades of even-aged forest management,
many coniferous forests in western Oregon are composed of young (20-50 yrs), densely stocked Douglas-fir stands. Often these stands are structurally
simple - a single canopy layer with one or two overstory tree species - and have a relatively sparse understory. The lack of structural complexity in these stands may limit the availability of key habitat components for several species of vertebrates, including birds.
Thinning may increase structural diversity by reducing competition among
overstory trees and increasing the amount of sunlight reaching the forest floor,
thereby increasing development of understory vegetation. Existing old-growth
forests may have developed under lower densities than is typical of contemporary
plantations. Thus, thinning also may be a tool for accelerating the development of late-successional forest conditions in some circumstances. In addition to the
potential increases in structural and biological diversity, thinning frequently is used to optimize wood fiber production and to generate timber revenue.