Response of Understory Vegetation to Ponderosa Pine Thinning in Eastern Washington

Pine thinning caused highly significant increases in understory vegetation. After eight growing seasons, total understory yield increments ranged from 75 lb/acre on the unthinned plots to 417 lb under 26-foot pine spacing. The increase comprised 51% grasses, 37% forbs, and 12% shrubs. When pine canopy exceeded about 45%, forbs produced more than grasses; below 45%, grasses were superior producers. Shrubs were the least productive at all levels.