Effects of forest patch type and site on herb-layer vegetation in a temperate forest ecosystem. (Special Issue: Shaping forest management to climate change.)

摘要

Development of strategies and schemes for adaptive forest management requires sound understanding on the controls and contributing factors of forest productivity and biological conservation. Understanding the factors determining the distribution of understory plants is important for biological conservation because the herb-layer vegetation represents the largest component of biodiversity in most forest ecosystems. We examined the effects of tree canopy and site on herb-layer vegetation in 40 plots representing three contrasting forest patch types, i.e. Pinus tabuliformis Carr (pine forest), Quercus liaotungensis Koidz (broadleaf forest), and P. tabuliformis-Q. liaotungensis mixture (mixed-wood forest), at elevations ranging from 1542 m to 1734 m in a temperate forest of North China. The importance of the overstory and other biotic and site factors in controlling understory species composition and diversity was quantitatively assessed by the method of constrained ordination (CCA). Analysis with multi-response permutation procedure (MRPP) reveals significant differences in species composition of the herb-layer among the three contrasting forest patch types; each forest patch type supports a distinct plant community in the herb-layer as assessed by composition and importance value of the representative species. Forward variable selection shows that litter mass, aspect, and canopy openness are most important in explaining species composition and diversity of the herb-layer. Both species richness and Shannon-Wiener index (H') increase as the aspect orients southward and the sampling plot moves higher on slope. To a lesser extent, increasing canopy openness is associated with slightly decreasing species diversity in the herb-layer. Mixed-wood forest is found to have highest species richness and lowest Whittaker's measure of inter-site variability in species composition (i.e. beta -diversity) in the herb-layer among the three forest patch types, highlighting the ecological significance of the mixed-wood forest in maintaining biodiversity and community stability in temperate forest ecosystems. The outcome of this study suggests that management practices should consider retaining the natural intermix of canopy patches for conservation of biodiversity in the herb-layer of forest ecosystems.