Quantitative Analysis Of Plant Communities In Sejila Mountain, Xizang

Surveying plentifully on community in Sejila Mountain, colligating multivariate statistical methods such as TWINSPAN,DCCA,DCA, circumfusing the response and relations between the changes of environmental gradient and the characteristics of vegetation quantity, we research on the vegetation classification, the relations between community distribution and environmental factors, community diversity, the law of community succession, and other characteristics of plant community. We gain the following major conclusions:(1) In Sejila Mountain community investigation, vascular plants were recorded 72 families, 238 genera, 504 species, of which, woody plants accounted for 135 species (26.73%), herbaceous plants accounted 370 species (73.27%). The average number in 900m2 quadrat is 20.65 species, up to 50, at least 3 species. In this 504 kinds of plants, phanerophytes occupied 25.40 percent (128 species), followed by hemicryptophytes (149 species, 29.56%), therophytes (130, 25.79%), cryptophytes (73, 14.48%) and chamaephytes (24, 4.76%). The proportion of all sorts of life-form species changed with the elevation gradients, and the approximate tendency was that the proportion of therophytes increased with the elevation increasing and the proportion of phanerophytes declined sharply, other types did not change obviously with the changes of elevation gradients.The species richness and species diversity indices of Sejila mountain communities showed the tendency that higher in high low altitude areas, lower in medium altitude with the elevation gradient changes to a certain extent.Species richness and diversity indices of most plant communities showed the characteristics that herb layer> shrub layer> tree layer, which resulted in herbaceous plants changes played a greater impact on the species diversity indices of different altitude plant communities. The species diversity indices of herb layer, shrub layer, tree layer varied on community gradients'form and extent.Viewing from the species'richness and diversity, the changing law with the altitude gradients of the same slope aspect's species diversity and richness conformed, but sunny and shady slopes changed differently. The distribution tendency of species richness and diversity indices were consistent with the elevation gradients, which better reflected the difference between different plant community types on species composition. Although the evenness index of tree layer, shrubs and herb layer fluctuated, there was no obvious changing trend overall.The value ofβ-diversity changed significantly with the elevation increasing, sunny and shady slope varied, but the general trend was gradually decreased, that is, community similarity increased with the elevation rising.(2) We carried through the mountain vegetation's quantity classification by TWINSPAN, divided 113 quadrates of Sejila Mountain into 23 associations, DCCA ordination was identical with TWINSPAN classification basically in the classification of plant communities, but TWINSPAN classification were slightly better than DCCA in the extent they matched the actual distribution of community.Environmental factors are the main factors that affect plant community's composition, structure, distribution and the succession. For Sejila Mountain, the spatial pattern of species number structure in plant communities was affected by various environmental factors. DCCA was used in this paper to put up ordination, which indicated that the gradients of mountain altitude and slope position were the primary determinants, followed by slope aspect gradients.(3) TWINSPAN and DCA were used to make out quantity classification and ordination for vegetation restoration succession of Sejila Mountain. The first ordination axis of DCA better reflected the succession series: herb→shrub→tree communities, and the community boundaries were marked. The region's succession series of communities were divided into nine stages, which showed the succession process: herb→shrub→tree communities. Linzhi spruce forests were the climax of succession for natural restoration succession. In succession series, family, genera and species of community took on a significant trend of growth: tree> shrub > herb communities. It indicated that species diversity and complexity of the community received a good recovery in the succession process with the extension of recovery time.The study on the changes of species diversity in community recovery process showed that: in its succession from unstable to stable phase, the changes of species diversity was fierce, diversity and stability were improved with the recovery time extension.The thickness of community litter and humus layer was growing, which had a relation with the strengthening of the community's complexity to a certain extent, particularly, the thickness of litter layer rose seriously with the emergence of trees.