Effects of Anthropogenic Disturbance on Community Structure and Species Diversity of a Secondary Machilus nanmu Forest in Xiejia Mountain, Northwest Sichuan

Using the typical sample plot method, a comparative study was done of effects of anthropogenic disturbance varying in intensity, low, moderate and high, on community structure and species diversity of a secondary Machilus nanmu forest. Species richness index(D), Simpson dominance index(H'), Shannon-Wienner diversity index(H), and Pielou evenness index(J_SW) of the forest were measured and used to evaluate comprehensively its level of species diversity. Results show that(1) plots of the forest under high anthropogenic disturbance were the lowest in number of species in various community level;(2) community structure varied within the forest with intensity of anthropogenic disturbance; and in the plot low in disturbance, trees, 4.0-8.0 cm in DBH(d_b,h), peaked in number, reaching 74, while in the plot moderate in disturbance, trees, 8.0-12.0 cm in d_b,h, did, reaching 62, and in the plot high in disturbance, trees, 12.0-16.0 cm in d_b,h, did, reaching 66;(3) with intensifying disturbance, species importance value mainly concentrated on a few species, such as Machilus nanmu, Pistacia chinensis, and Perilla frutescens; and(4) with intensifying disturbance the biodiversity indices of shrub and herbaceous communities rose first and then declined, regardless of disturbance degree, but in the plot moderate in disturbance, they increased obviously, while the index of the tree community decreased in all plots.