Competitive effects of northern hardwoods on red pine seedling growth, nutrient use efficiency, and leaf morphology

To examine the competitive effects of northern hardwoods on red pine seedlings, a field study was implemented in 1988 in a recently disturbed ecosystem in western Maine. A complementary greenhouse study was designed to determine how varying levels of light, nitrogen, and phosphorus affected red pine seedlings under controlled conditions.; Growth and nutrient use efficiency were determined for red pine seedlings grown in the greenhouse experiment. Seedlings grown in high light (full greenhouse light) had four to five times more biomass than those in the low light (73% light exclusion) treatment. Nitrogen supply had a significant effect on total biomass as well as biomass components. Phosphorus supply did not have a significant effect on any of the biomass components or phosphorus use efficiency. Nitrogen use efficiency was significantly affected by light and N x P interaction. The results of the greenhouse study indicated that red pine seedlings can adjust their nutrient use efficiency, particularly for nitrogen, when light and nutrient availability are varied.; The effects of competition from seedlings of three northern hardwood tree species on red pine seedlings were examined on two clearcut sites in western Maine. The three species were striped maple (Acer pensylvanicum L.), red maple (Acer rubrum L.), and pin cherry (Prunus pensylvanica L.). These competitors were established at two densities (high and zero) with two levels of fertilization (0 and 224 g m{dollar}sp{lcub}-2{rcub}{dollar} of 10-10-10 NPK fertilizer). Plots were harvested at two time periods when pine seedlings were 2-years-old (1989) and 3-years-old (1990).; Red pine seedlings had higher specific leaf area, leaf area ratio, and nutrient use efficiencies of N, Ca, and Mg on competitor plots than on plots free of competition, suggesting a phenotypic response to resource depletion of light and nutrients. Red pine total leaf area and biomass were lower on the competitor plots. Fertilization decreased growth of red pine seedlings and decreased nitrogen use efficiency. Higher competitor biomass, leaf area index, and nutrient uptake explained the lower growth of red pine seedlings on competition plots. Pin cherry was the most significant competitor with striped maple being intermediate.