Resource use efficiency as a function of species richness and stand composition in upper montane conifer forests of the Sierra Nevada.

摘要

Questions: 1. Does resource use efficiency increase with increased species richness in conifer forests? 2. Do patterns found in resource use support niche differentiation/complementarity between species, or is any increase indicative of a selection effect? Location: All data were collected from upper montane (2200-2600 m a.s.l.) conifer forests of the Desolation Wilderness in the central California Sierra Nevada, USA. Methods: We established 281 plots of varying levels of conifer richness throughout the wilderness area. Within each plot we used hemispherical photos to measure canopy closure and LAI, total soil carbon and nitrogen from the A-horizon, and stand basal area. We used linear regression and ANOVA to analyse the relationship between stand species richness and resource availability. Results: We found no correlation of either soil nitrogen or carbon with stand biomass. Nor did soil nitrogen and carbon levels change with species richness. Canopy closure increased with species richness but also varied significantly between pure stands of different species. Pure Pinus monticola stands had the lowest canopy closure, Tsuga mertensiana stands the highest. Composition explained more canopy cover variation than did species richness. We found evidence supporting both the sampling effect and niche differentiation models at different stages of stand development. Conclusions: During initial stages of stand development, the interaction between the shade-intolerant Pinus species and shade-tolerant Abies magnifica and T. mertensiana followed the niche differentiation model, but switched to the sampling effect model during the competitive-exclusion stage. In contrast, interaction between A. magnifica and T. mertensiana followed the niche differentiation model..