Malan Forest Plant Community Species Abundance Study

Due to the soil and groundwater depletion, the ecosystem of Loess Plateau is seriously degraded.In this way, to accelerate the recovery and restoration of degenerative ecosystem of this region is not only significant in improving the ecological environment of this region but also significant in promoting the ecological productivity of the whole northwestern region. Malan forest region, which is located at the south tip of Ziwuling Mountain, is one of the relative intact natural forests on the Loess Plateau. Malan forest region has great impact on adusting the climate of this region, maintaining ecological balance and also promoting economical and ecological sustainable development on the Loess Plateau. It can provide scientific proof for the restoration of vegetation, the establishment of plantation forest, the protection and regulation of biological diversity by elucidating the variation mechanism of species abundance patterns in the process of vegetation restoration,by discussing the variation and causes of the species abundance distribution pattern of community and also by revealing the changes in community structure and the utilization of resources at the succession process of forest community in the Loess Plateau.Based on the comprehensive research of vegetation on Loess Plateau, this thesis systematically studies the pattern variation of plant community at different succession stages, the relationship between the community abundance pattern and diversity and the influence of environmental factors in a way of analyzing the distribution pattern of species abundance. The characteristics of the main species abundance distribution pattern of this region have been grasped, and then the environmental factors which influence the vegetation pattern distribution have been chosen. The following is the results:(1)By using species abundance statistical models (logarithmic series distribution model and lognormal distribution model) and niche models (broken stick model, overlapping niche model and random assortment model), this thesis studies the variation in the species abundance distribution pattern of three forest communities at different succession stages in Malan forest region of Ziwuling Mountain on the Loess Plateau. The study with species abundance statistical models showed that in the Betula platyphylla community of early succession stage, the species were rich but distributed unevenly, in the natural Pinus tabulaeformis community of middle succession stage, P. tabulaeformis was dominant, and the understory shrub and herb species were less and in centralized distribution, in the climax Quercus liaotungensis community, the species had a uniform and centralized distribution, and many gaps were formed by the standing dies. These three forest communities fitted the species abundance niche models well, indicating that in the process of succession, the species distribution was affected by many natural and anthropogenic factors, and it was unwise to only choose one niche model to study the species abundance of forest community.(2) This thesis analyzes the variation of species diversity of three forest communities at different succession stages by adopting different species diversity index, such as Shannon-Wiener diversity index, Margalef's evenness index and Simpson's dominance index. The results can be shown as follows:ⅰ) the species diversity is shown in an increased order of shrub layer, herbaceous layer and arbor layer in three communities;ⅱ) The index of statistical model(logarithmic series model and lognormal model)can be used as community diversity index, which can explain the species constitution and structure of community.(3)Using the method of substituting spatial difference for time change, this thesis studies the variation of abundance distribution pattern of these seven plant communities which are Artemisis argvi grassland, Elymus dahuricus Turcz grassland, Rosa husonis shrub, Ostryopsis davidiana shrub and the forest community of Betula platyphylla,Pinus tabulaeformis and Quercus liaotungensis at natural succession stages in Malan forest region of Ziwuling Mountain on the Loess Plateau by using species abundance statistical models (logarithmic series model and lognormal model) and niche models (broken stick model, overlapping niche model, random assortment model and niche preemption model). The result shows in the following way:The Species constitution and distribution of communities has changed greatly.the niche model which fits the community pattern variation has a transition trend from broken stick model, overlapping niche model and random assortment model to niche dominant model after studies on pecies abundance distribution pattern of community in the process of succession,the species constitution and structure of communities have great changes at different succession stages; the species abundance distribution pattern of community can reveal the process of community's development and changes very well.(4) By using the forward selection method and Monte Carlo's outstanding examine, this thesis selects the environmental factors which have great impact on the species constistution at different succession, and also it analyzes the relationships between species abundance of seven communities and environmental factors by the method of CCA sequence method. The results shows in the following way:i)the environmental factors which influence the community of Artemisis argvi grassland is soil moisture, providing thirty percent of the environmental information; there is no influential environmental factor in the community of Elymus dahuricus Turcz grassland, Betula platyphylla arbor and Pinus tabulaeformis arbor; the environmental factors which influence the community of Ostryopsis davidiana shrub is slope position, providing twenty percent of the environmental information; the environmental factors which influence the community of Rosa husonis shrub is slope degree, providing twenty-four percent of the environmental information; the environmental factors which influence the community of Quercus liaotungensis arbor is slope aspect, providing twenty-five percent of the environmental information; the environmental factors which have significant influences on these seven plant community pattern are organic matters, pH value, canopy shelter, slope aspect and salinity, providing twenty percent, thirteen percent, forty percent, eight percent and eight percent of the environmental information respectively;ⅱ) the plant communities at different succession stages showing on the CCA plots have great differences between each other, taking up different niches, and the change of illumination is one of the main reasons why niche variate.In conclusion,it is shown that species abundance pattern changes with the process of succession in the region:The highest species evenness consist in community at herb stage, in which the distribution of individuals is more concentrated; with so many common species in community at shrub stage, the abundance of dominant species didn't show any superiority to other species; In community at forest stage, the dominant species has higher abundance, while for the species richness of all shrub and herb plants from Betula platyphylla arbor to Pinus tabulaeformis arbor then to Quercus liaotungensis arbor, the tendency was that it was more at first, then becoming less and at last more. The study of community abundance pattern has an important role in imitating community variation in space and time. By combining it with the explanation of diversity index and environmental factors, the constitution of community can be reflected better and the pattern system of species diversity also can be revealed effectively, which can provide proof for the protection of vegetation.