Conserving Dry Old-Growth Forest in Central Oregon, USA

Abstract

Logging and fire suppression have reduced the number of large old trees, increased the density of small shade-tolerant trees, and decreased forest resistance to fire, drought, insects, and disease in the interior Pacific Northwest. In Central Oregon, interim Old-growth definitions, the Deschutes Large Tree Layer, and the Gradient Nearest Neighbor (GNN) mapping tool are used to identify dry old-growth forests and guide forest planning. We used a recent characterization of dry old forests to evaluate interim old-growth definitions and GNN mapping. Historical old tree species composition should be used in old-growth definitions. The 21-in.-diameter harvest limitation maintains large trees but fails to protect smaller old individuals; it does not allow for removal of younger large shade-tolerant species more prevalent since fire suppression. GNN mapping accurately identified old forest based on abundance of large trees at a coarse landscape scale but was less accurate at a finer stand scale.