Quantitative Classification And Species Diversity Of Forest Communities In Simian Mountains, Chongqing

Based on the field survey of 50 plant quadrates, a quantitative classification of the forest communities in Simian Mountains, Chongqing is performed with TWINSPAN (Two way indicator species analysis) and DCCA (Detrended canonical correspondence analysis) methods; Species diversity of the forest communities are studied in this paper by using richness index, Shannon-Wiener index, Simpson index and Pielou evenness index. The main conclusions are as follows:50 plots collected from Simian Mountains are classified into 14 types, representing 14 formations by TWINSPAN. The result of classification sums up the forest vegetation types of Simian Mountains comprehensively.14 formations are all subtropical nature of the secondary vegetation types. The gathered groups of plant plots in the space of DCCA ordination are consistent with the result of TWINSPAN, all the 14 formations resulted from TWINSPAN have their corresponding distribution in the two-dimensional sorted map DCCA, but there are no obvious boundaries between different plant communities. This reveals a relationship between plant formations and environmental gradients. The integrated gradient of soil moisture and temperature determined by the elevation is the main environmental factors which determine the distribution pattern of plant communities in Simian Mountains, and slope degree and slope position impact the distribution in some extent. In addition, human disturbance also plays an important role in the distribution of plant communities.The amount of species in Simian Mountains is abundant, but different communities have different species diversity indices. Different layers in the communitiy show different species diversity indices. The trend of the richness index in plant communities is shrub layer> tree layer> herb layer. The species diversity index of the shrub layer is the largest. The order of diversity index is not the same in tree layer and herb layer in different communities, but they are smaller than shrub layer. The species diversity index of the tree layer and the shrub layer reach its peak in the range of 1000-1200m elevation, the species diversity index decrease below or above this altitude range. The trend of the species diversity index of the herb layer is downward with altitude. The evenness indexes at all levels are complex and have no clear trendency.With the change of species diversity, the herb layer is the most sensitive layer along environmental gradient, followed by the shrub layer, and the tree layer is the least. Elevation is also the major habitat factor affecting plant species diversity in Simian Mountains.