Effects of landslide erosion on subsequent Douglas-fir growth and stocking levels in the western Cascades, Oregon

Shallow, rapid landslides are common events in steep terrain of the Pacific Northwest. The effect of landslides on timber growth potential of forest land was estimated by examining a 30-yr history of clearcutting and landsliding in the western Oregon Cascades. The height growth of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] and stocking level of all commercial conifer species on naturally regenerated landslides were compared with the height growth and stocking level on nearby, artificially regenerated clear-cut units of similar aspect, elevation, ages, and slope position. Average height growth of Douglas-fir trees 5 to 18 years old on the landslides was reduced 62% compared to trees on clear-uts, and the average stocking level was reduced 25% from the clear-cut level. One-third of the landslide area was estimated to be nonstockable because of unstable or impenetrable substrate.