Old-growth forest structure in Eastern Oregon and Washington
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Old-growth forest structure is an important issue in managing for forest health and productivity in eastern Oregon and Washington, USA. Old-growth forest structure is estimated to be as little as 3% of presettlement levels; what remains is in isolated patches and is at risk of loss from less frequent but more severe fires. Low-elevation ponderosa pine (Pinus ponderosa) and Douglas fir (Pseudotsuga menziesii) stands are more densely stocked with increased fuel, and often represent compositional shifts to more lodgepole pine (Pinus contorta) and grand fir (Abies grandis). The changes are attributed to changes in natural disturbance regimes as a result of management of fire, grazing, timber harvest, wildlife, insects, and disease. Treatments that can accelerate development of old-growth forest structure include thinning to accelerate growth on residual stems, returning fire to fire-dependent ecosystems, and maintaining large trees and snags. These methods have risks: prescribed fire may not mimic frequency and severity of historical fire, thinning may activate dormant stem decay, increased connectivity may increase susceptibility to stand-replacement fire, insects, and pathogens. Models for multiple species and interactions of treatments, insects, and disease are not available.