Study On Species Composition,Community Structure And Species Diversity Of Secondary Vegetation In Dagou

Minjiang River is an important branch of the upper reach of the Yangtze River.The upper reach of Minjiang River is situated in the region that connects Qinghai-Tibetan plateau and Sichuan basin. It has great and important ecological functions such as biodiversity conservation, water bolding and soil erosion controlling.But due to long-term disturbance of irrational human activities, especially the long-term extensive lumbering, the natural forests have degraded hably, and seriously ecological effects have arose. Based on the theories and methodologies of vegetation ecology, restoration ecology and biodiversity conservation, plots were designed in the shrub of the natural vegetation recovery and artificial forest of the manual recovery at Dagou valley in the Upper Reaches of Minjiang River, Southwest China. After detailed field investigation in the sample plot, community ecological characteristics such as community structure, species diversity , polulation structure, discuss the difference and effect of the natural vegetation recovery and manual recovery. The research results as follows:It was found that there was difference of the community structure of the three types of artificial forest.The mean density (2690n/hm~2) of nixed-forest was the highest and the mean tree diameter at breast height(10.39cm) and canopy closure(73%) of Pinus armandii forest were also the highest, while canopy closure(65%) of Pinus tabulaeformis forest was the lowest. The shrub layer of Pinus tabulaeformis forest showed the highest mean height, mean density and mean canopy closure.On the contrary , the mean height, mean density and mean canopy closure of Pinus armandii forest shrub layer were the lowest. Herb layer of mixed forest had the highest density while the herb layer of Pinus tabulaeformis forest had the highest canopy closure.Canopy closure of arbor layer showed significantly negative correlation with coverage of shrub, negative correlation with coverage of herbage, the coverage of shrub was negative correlation with coverage of herbage in the artificial forest community and secondary shrub community.The negative correlations also existed between the coverage of arbor layer and the diversity index of shrub layer,while this correlations also existed between the coverage of shrub layer and the diversity index of herb layer.But there was a significantly positive correlation between the richness index of herb layer and coverage of shrub layer of Quercus liaotungensis - Corylus heterophylla shrub. The reason might be that the presence of shrub stratum reduced the evaporation from soil surface thereby formed a well environment for the herb stratum.Three artificial forests showed higher richness and diversity of species than the secondary shrub-land. The shrub layer in Pinus tabulaeformis forest has the highest species richness and diversity index,the species richness is 11, while the shrub layer of Pinus armandi has lowest diversity index that is 7. The herb layer of mixed forest has the highest species richness and diversity index.The secondary shrub-land has higher species richness and diversity index. The species diversity index of the three kinds of secondary shrubs varied as follow: Quercus liaotungensis - Corylus heterophylla shrub-land >Fargesia nitida shrub-land >Rhododendron shrub-land.Changes of species diversity of three plantations communities under different layers of community were comparatively complex. All diversity indexes in Pinus tabulaeformis was shrub layer > herbage layer. At north slope, diversity index of Pinus armandi was herbage layer > shrub layer, but at south slope, diversity index manifested shrub layer > herbage layer. In the mixed forest with three slope directions, all diversity indexes manifested herbage layer > shrub layer. The species diversity variance of each layer of Quercus liaotungensis - Corylus heterophylla shrub-land and Fargesia nitida shrub-land communities are: shrub layer > herbage layer, but it reversed in Rhododendron shrub-land.Under similar altitude and slope, effects of slope on community structure and species diversity were greater. As a whole, structure index and diversity index of shade slope was greater than that of open slope, which might be the reason that evaporation of open slope is larger than that of shade slope's , temperature of open slope is higher than that of shade slope's and accumulation of organic matter of open slope is smaller than that of shade slope's . This characteristic reveal that environment of shade slope is better and vegetation renewal is easier than that of open slope...