This 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...
Effects of tanoak (Lithocarpus densiflorus) on early
growth, morphology, and physiology of Douglas-fir
(Pseudotsuga menziesii) were studied to determine
developmental characteristics of young stands and
mechanisms of competition. Growth, leaf area, and biomass
of Douglas-fir, tanoak, and shrubs / herbs were monitored
for six years after establishing a gradient of...
Computer simulations and experiments were used to determine
the basis for skewness and inequality in size structures
(frequency distributions of Individual plant sizes) prior to
self-thinning mortality. In simulated stands, density-dependent
neighborhood heterogeneity caused variability in the growth rate
of individuals with the same size, and such variability caused
skewness...
Ungerminated seed and recent germinants from 39 open-pollinated Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco)
families were planted in each of three competitive environments in order to determine the degree to which growth differences among families are influenced by competitive environment, seed weight, and
date of emergence. The three competitive...
Competitive interactions between Douglas-fir seedlings (Pseudotsuga menziesii), and seedlings of a nitrogen-fixing hardwood
associate, red alder (Alnus rubra), were investigated in an addition series experiment. The primary objective of the research was to identify and quantify key processes underlying intra- and interspecific competitive interactions of Douglas-fir and red alder seedlings....
When Douglas-fir and red alder grow in mixture, interactions between the two species can be competitive, facilitative, or a combination of both over time. A number of factors have recently led to increased interest in managing these two species together for commercial production, and ongoing investigations are yielding important information...