The Species Diversity And Stability Of Sub-alpine Plantation Communities In The Upper Reach Of Minjiang River

In this paper, the population structure, species diversity and community stability of the main plantation community types in sub-alpine area were studied and analyzed. The results were as follows:The distribution of Patrick index, Simpson index, Shannon-wiener index, Pielou index and Alatalo index in community gradient among subalpine vegetation showed a more consistent trend. The primeval forest communities had the highest richness index, and the shrub communities had the lowest richness index. The plantation communities had the highest diversity and evenness index, the secondary and primeval forest communities had lower index while the shrub communities had lowest. Among them, mixed Larix mastersiana-Picea asperata forest, mixed Pinus tabulaeformis-Quercus liaotungensis forest, Picea asperata-Betula albo-sinensis evergreen-deciduous coniferous-broad-leaved forest, Picea purpurea coniferous forest and Abies faxoniana coniferous forest with higher diversity index.Within the communities, the richness index of species for different growth form of vegetation was different. Between tree and shrub layers, the difference was significant. Between tree and herb layers, and between shrub and herb layers, the difference was more significant. In most communities, herb layers had the highest Simpson and Shannon-wiener index values. Tree layers had the lowest. That indicates herb layers contribute more to the species diversity. The values of diversity index for different growth form of vegetation present more significant difference, but it is not for the evenness index. There was irregularity on community gradient of evenness index. The evenness of shrub layers was higher than herb layers, and the tree layer evenness was the lowest.Among the four plantation communities, there were no clear boundaries between main layers and sub layers of mixed Larix mastersiana-Picea asperata forest and mixed Pinus tabulaeformis-Quercus liaotungensis forest, and with more natural regeneration seedlings and uniform distribution of individual tree. Simple species composition for Picea asperata plantation and mixed Betula platyphylla-B.albo-ainensis forest leads an unreasonable population structure.Among the four plantation communities, the values of richness and diversity index of mixed Larix mastersiana-Picea asperata forest and mixed Pinus tabulaeformis-Quercus liaotungensis forest were higher than Picea asperata plantation and mixed Betula platyphylla-B.albo-ainensis forest. And mixed Betula platyphylla-B.albo-ainensis forest had the highest evenness index values.The diversity index of herb layers in different plantation communities was higher than tree and shrub layers. Within a community, the indexes had less difference among the three layers. Only for Shannon-wiener index between tree and herb layers, the difference was significant. Mixed Larix mastersiana-Picea asperata forest had the highest total values for each index and Picea asperata plantation had the lowest.The analysis of M.Godron index resulted: intersection coordinates for the four plantation communities were away from the point of 20/80 an indicator of stability, showed their instability. The relative distance from the indicator identifying that Picea asperata plantation was the most stable community. And the diversity analysis showed different trend.