Species diversity based on sample size in a Pinus tabulaeformis mixed forest

Species diversity is a key indicator of community composition with its spatial pattern and basic causes being important components of species diversity research. To study changing trends in species diversity on various scales, for characteristics of species diversity at all forest layers based on different scales, and for relationships between tree structure and species diversity of undergrowth vegetation, a 1 hm2 plot of Pinus tabulaiformis mixed forest on Huanglong Mountain was utilized. Analysis was conducted with Richness, Pielou, Simpson, and Shannon-Wiener Diversity Indexes. Also, the relationship between density and mingling degree of tree layers as well as species diversity indexes of shrub and herb layers were analyzed with a grey relational analysis. Results showed that （1） as the scale increased, the Richness had no clear trend, whereas Simpson, Shannon-Wiener and Pielou Diversity Indexes all stabilized after a certain scale, with their spatial variation decreased. （2） At scales of 5 000 m2 and larger, diversity index relationships between varying layers remained unchanged with the shrub layer having the greatest species diversity. The herb layer had the lowest species richness with higher uniformity for species distribution than tree layers. （3） The grey relational analysis showed that the structure of the tree layer was related to species diversity of the shrub and herb layers. The results showed that sampling scale should be taken into account when studying species diversity in a Pinus tabulaeformis mixed forest.［Ch, 2 fig. 3 tab. 30 ref.］