Fifth-year growth responses of Douglas-fir to crowding and other competition

Graduation date: 1984This thesis examines the competitive aspects of Douglas-fir trees growing with two commonly associated competitors--red alder and grass--at varying densities. Two Nelder plots in three different environments in the Oregon Coast Range were studied. The sites represented the warm, dry climate of the Willamette Valley; the warm, moist climate of the valleys of the mid-range; and the cool, moist climate found along the fog belt a few miles from the Pacific Ocean. Plots ranged in spacing from 300 to 15250 cm²/tree and consisted of six "pie-shaped" treatments. The plots had been previously planted in the spring of 1978 with 2-0 bare root Douglas-fir nursery stock. Two sections were interplanted with red alder, and two sections were broadcast seeded with grass the following year. Measurements indicate that Douglas-fir growth is inhibited by red alder and grass competition as well as competition from other Douglas-fir. Grass competition is severe only during the initial years of the plantation, while red alder competition becomes more pronounced with time. Growth is a function of density, competitor type, and site, and significant interactions occur among the three. Leaf area per tree of Douglas-fir under competition can be predicted by leaf weight, stand density, and competitor type. The formation of shade needles in response to density and competitor type increases the leaf area:leaf weight ratio. Growth efficiency (stemwood volume production/unit of leaf area) is not highest for the most vigorous trees. On a per hectare basis, high productivity is correlated with high leaf area index, but the relation is reversed on a per tree basis