Niche Characteristics of Main Tree Populations in the EvergreenBroad-Leaved Forest in Simian Mountain, Chongqing

The niche breadths and overlaps of 20 main tree populations in the evergreen broad-leaved forest in Simian Mountain, were measured by using the formulas described by Levins ,Hurlbert and PianKa ,and the relationships among niche breadth, niche overlap and interspecific association were discussed in this paper. The results show that the niche breadths of main dominant species were greater. The niche overlaps among the species with the same or similar environment requirements were great , while those between the species with broad niche breadth and other species were much greater. The more intense the positive association was, the larger the value of niche overlap was；and the more intense the negative association was, the smaller the value of niche overlap was.