Research on Structure and Species Diversity of Larix gmelinii Community in Orqohan

The species distribution pattern of Larix gmelinii in Orqohan County was analyzed by means of variance (v) / mean (m) method, and the species diversity was studied by species richness, diversity index and evenness index. The results showed that sample plotⅠwas mainly composed of Larix gmelinii, mixed with some Betula platyphylla and Populus davidiana; sample plot Ⅱ and sample plot Ⅲ were also mainly composed of Larix gmelinii and mixed with little Betula platyphylla. The density differed greatly among the sample plots, which was in the order as sample plot Ⅰ(1740 tree/hm2)＞sample plot Ⅲ(1080 tree/hm2)＞sample plot Ⅱ(910 tree/hm2). The distribution pattern of sample plotⅠand sample plot Ⅲ was aggregated distribution, while sample plot Ⅱ was random distribution. The complexity of species composition of the three plots was ordered as sample plot Ⅰ(23 species)＞sample plot Ⅲ (21 species)＞ sample plot Ⅱ(19 species). Species richness and species diversity indexes in the vertical community structure were both indicated as herb layer > shrub layer > arbor layer. Evenness index of the sample plots was mainly as herb layer > shrub layer > arbor layer, except for that the Pielou index (Jsw) of both sample plot Ⅰ and sample plot Ⅲ, and the Alatalo index of sample plot Ⅲ was shrub layer > herb layer > arbor layer.