Ziwuling Malan Forest Plant Community Complexity And Stability Analysis

It is imperative under the situation to accelerate the recovery and restoration of degenerative ecosystem on loess plateau, because the ecosystem is seriously degraded due to soil and groundwater depletion. Malan forest area is situated in the northeast of Xunyi County, Shaanxi province. It belongs to the south of Ziwuling in the middle part of the Loess Plateau. Malan forest, a relative intact natural secondary forest on the Loess Plateau, is important water conversation and ecological availability forest for Loess Plateau central area. Malan forest region has crucial effect on adjusting regional climate, maintaining ecological balance and promoting ecologically sustainable economic development on the Loess Plateau. So the research of the community complexity and stability has significant ecological meaning for recovery and restoration of degenerative ecosystem.In this paper, the studies on the community stability, the complexity and structure of the main communities, for example, Quercus liaotunagensis community, Pinus tabulaeformis community and Betula platyphylla community etc., the effect on the soil factors to the community was carried on. The results as follows:(1) Structure of communities by studied was simple in the mass, and they can be divided into three layers, namely tree, shrub and herb layers. Upper species of the B. platyphylla community is sparse, the species of B. platyphylla community distributes mainly shrub and herb layer of community medium and lower layer, Because of too large of density, the more P. tabulaeformis plant of P. tabulaeformis community is self-thinning death. The quantity of species was gradually decreased from lower to upper layer in Q. liaotungensis community. The dissimilarity index of total and shrub layer was the highest in B. platyphylla community and the Q. liaotungensis community was the lowest, which is opposite with the dissimilarity index of tree layer. The distribution of herb in each community is complex, because the dissimilarity index of herb layer is the highest.(2) Ten correlative indexes such as Shannon-Weiner Index of the Arbor, shrub and herbaceous, the quantity proportion of seeding, saplings and adults, humus thickness, and so on, which could describe the community stability were chosen in order to reveal the relationship between stability and some characters of community. The results showed that the species diversity of B. platyphylla community was the highest and the Q. liaotungensis community was the lowest. While the Q. liaotungensis community was the steadiest and the B. platyphylla community was the worst steady in all of the arbor communities. And the species diversity was decreased in order of shrub layer, herb layer and tree layer in all communities. The total community complexity expressed that the complexity of P. tabulaeformis community was higher than that of Q. liaotungensis community, and the complexity of B. platyphylla community was the lowest. The most stable was not the most complicated; the diversity was not equal to the complexity, too. So, the community stability, complexity and diversity were interconnected and different.(3) Species diversity and life stage are both the importantly influence factors in the each principle components analysis of communities. The stability of the Q.iaotungensis community which is the climatic climax in Ziwuling Mountain is the highest and the Shannon-Weiner Index is the most important factor. But, Due to the interaction of other factors, we couldn't ascertain the stability of community only according to the diversity index. The studies displayed that it will be more exact to estimate the stability of the forest community by combining the diversity index of every layer structure with age distribution of dominant species in community. The average tall of tree is important to community stability, but it isn't significantly different in three communities.(4) Ecological niche differentiation of species embodies the utilization of environmental resources in some extent. The Mean of niche breadth of Q. liaotungensis community is the highest and the P. tabulaeformis community is the lowest, while, the Mean of niche overlap in B. platyphylla community is the highest and the P. tabulaeformis community is the lowest in all of the arbor communities, the ecological niche differentiation in Q. liaotungensis community is higher. According to above analysis, it is showed that the resource is abundant in B. platyphylla community, limited in P. tabulaeformis community and adequately used in Q. liaotungensis community.(5) There was no obvious correlation between community complexity and the content of Availale Kalium and pH in the soil environment, but there was a significant negative correlation between community complexity and the content of available phosphate. This explains that the available phosphorus has important effect on community complexity of the region, and is the main factor of restricting community complexity. Through soil nutrient status of the community and the characteristics of tree species niche, it could analyze the status quo of community complexity well.To sum up, B. platyphylla community is unstable, because it is the initial stage of succession, and has abundant shrub and herb, the age distribution of the inverted pyramid-shape and low total community complexity. P. tabulaeformis community isn't very stabile because it has limited resource, the distribution of species isn't homogeneous, shrub layer and tree layer are major, and spatial structure of community is become complex. But it is stabile in a certain period, because the proportion of P. tabulaeformis in community is large, seedling is major in age distribution—community is well regenerated. Q. liaotungensis community is unstable, because its index of species diversity and dissimilarity is the lowest, species reduce from shrub layer to tree layer little by little, moreover the niche breathe is wide , but the niche overlap is middle, which the species don't fiercely compete to soil nutrition.The stability and complexity of communities reflected synthetically the characteristics of communities. So, for the analysis of the communities' stability and complexity, we would know the actual state of communities, explain reasonably the species growth and communities' development, put forward to the scheme of communities' governing and provide the scientific basis for local forest restoration at last.