| At present, the ecosystem is suffering from severe persecution, among which, as one of the biggest terrestrial ecosystem, forest comes to be the core part of ecological system and can resist the ecological environment problems. However, the forest ecosystem is facing persecution and management defects, which has resulted in reducing natural forest area, the decline of the plantation quality as well as the forest ecological function. Thus, it is of great significance to improve forest quality and its ecological function. In our study, having taken the fixed sample with 4 hm~2 of conifer and broad-leaved mixed forest community in Taiyueshan Shanxi Province as the research object, the characteristics of forest community structure, species abundance distribution pattern and species diversity were separately analyzed by the method of classical community investigation combined with the precious research results.(1) Characteristics of forest community structure:on the basis of 400 quadrats with 100m~2, the characteristics of forest community structure, including their species composition, vertical structure, species diversity, dominant species and diameter class structure were analyzed. It was concluded that there were 88 kinds of plants in total, attaching to 34 families and 72 genuses in the conifer and broad-leaved mixed forest community. Its vertical structure could be divided into tree, shrub and herb layers from top to bottom with each species of 20,33 and 48, respectively. Meanwhile, the sequence of species diversity in each layer was herb layer> shrub layer> tree layer. In addition, the diameter class structure of Quercus liaotungensis and Betula platyphylla showed a stable growth, while on account of the few individual seedlings of Pinus tabuliformis, it presented a recession mode. Dominant species in tree layer were Quercus liaotungensis, Betula platyphylla and Pinus tabuliformis, in shrub layer were Spiraea pubescens, Forsythia suspense and Swida bretschneideri, while in herb layer were Carex lanceolate, Achnatherum extremiorientale and Polygonatum sibiricum.(2) Species abundance distribution pattern:In order to reveal the influence of scale variation on species abundance distribution pattern, the building mechanism of abundance pattern and its ecological process were explored by the method of broken stick model (BSM), preemption model (NPM), lognormal distribution model (LN), Zipf model, Zipf-Mandelbrot model as well as neutral model (NT). Meanwhile, the optimal model was determined according to the chi-square test and Akaike information criterion (AIC) value based on the data fitting of 11 species abundance distribution patterns. It was obtained that the plants in conifer and broad-leaved mixed forest community have different optimal model matched to corresponding scale, namely scale have big influence on specoes formation mechanism. For example, as the sample scale was 10m×10m or20 m x 20 m, each model was accepted, as it was increased to 40 m*40 m, BSM was rejected and LN comed to be the optimal model. When the sample scale was 60 mx60 m,120 m×120 m or 160 m×160 m,200 mx200 m, Zipf-Mandelbrot model was the most suitable model. While as the sample scale became 80 mx80 m or 180 m×180 m, NPM was the fitted model. When it was sampled in 140 m×140 m, Zipf model was the optimal model. In general, each sampling scale has its own corresponding suitable model. Therefore, when fitting the species abundance distribution model, the influence of spatial scale couldn't be ignored. Among the whole scales, especially in large scales, NT model had the better fitting effect and species were distributed as the neutral model mechanism.(3)Species diversity:In our study, cross-validation multivariate regression tress (MRT) was applied to classify the 400 samples, and the classification results were revised to make samples in conformity with the space continuity. Simultaneously, Margalef, Shannon-Wiener Index, Simpson Index as well as Pielou Index were used to analyze species diversity of Taiyueshan conifer and broad-leaved mixed forest community. The results showed that Margalef diversity index in Quercus liaotungensis was the largest, which explained that its ecological environment was good and the ecological niche of three layers were reasonable. The richness index and diversity index were generally represented as herb layer> shrub layer> tree layer, and the evenness of herb layer was less than the tree layer and shrub layer, indicating the community was complex with large species diversity. |
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