Study On The Structural Characteristics Of Picea Schrenkiana Var.Tianschanica Communities In Xinjiang

Picea schrenkiana var.tianschanica is a kind of forest which distribute wideliest and has biggest forest stock volume in Xinjiang mountain forest. Mt. Tianshan forests contribute irreplaceable functions for water resource conservation, soil conservation, buiding ecosystem and maintaining banlance of ecosystem. Therefore, this paper takes the Picea schrenkiana var.tianschanica community as the research object in Tianshan Mountain Forest Ecosystem Research Station. By the plots investigation, the structural characteristics of Picea schrenkiana var.tianschanica community are studied in some aspects, including species composition, species diversity, size class, spatial distribution pattern, as well as natural regeneration capacity. The results are as follows:The floristic elements of seed plants are intricate. There are 401 vascular plants species in the community of Picea schrenkiana var.tianschanica. It includes 393 seed plants species, which are classified into 47 families and 194 genera. The dominant families consist of Compositae, Gramineae, Labiatae, Rosaceae, and Ranunculaceae, accounting for 47.58% of the total sum of the species. Families with few genera or only one occupy the most percent amounted to 89.36%. Temperate elements amounted to 44.68%, which occupy the dominant status in the flora and the structure of vegetation. This phenomenon reflects a rule that the vegetation adapted to the local climate zone, geographical location and change of geological history primely. Although temperate elements make a large part, it forms dominance difficultly because of the arid desert climate. Only the cosmopolitan families can occupy dominance in this habitat execrable area because of enormous species and adaptation ability.The species richness and species diversity indices are lower, evenness and dominance indices are bigger. Arboreal layer richness index is only 3 and the ecological dominance index amounted to 0.6073, which is the biggest. Through long-term competition and succession, the broadleaved trees were replaced, Tianshan mountain natural forest community, Picea schrenkiana var.tianschanica community, comes into zonal climax community. Currently, over 2 000 m altitude, Picea schrenkiana var.tianschanica forest is not easily replaced by other tree species without external destruction. Herbage richness, diversity, ecological dominance indices doesn't change notably with altitudinal gradients.The size class of Picea schrenkiana var.tianschanica population is a typical pyramid shape, with distribution in each class. Seedlings in this area are abundant, accounted for 25.37%. The survival curve belonged to be Deevey-III, namely a developing population. In the early period, mortality rate was bigger while the population is stationary in the late period. The spatial distribution pattern of population shows on aggregative distribution, but aggregative intensity is different in every growth stage, grade I II III IV aggregativeintensity is quite strong, K is less than 1. Grade I is the least and K amount to 0.104, which indicates it has stongest aggregative intensity. Aggregative intensity of Grade V descend rapidly and K is more than 1 amounted to 1.105. From I to V, M*/M descends from 10.619 to 1.905, which trend to dispersion gradually, and the dispersion trend of grade I-MI-* III is clear. The result shows that Picea schrenkiana var.tianschanica population is aggregated intensively in the period of seedling because of the influence of population breeding and habitat heterogeneity. With the growth of trees, the effects of self-thinning and unself-thinning will strengthen. This affect will result of a lot of trees to die, and the aggregative intensity will weaken gradually. In the period of mature, the distribution trend is less aggregation and random distribution. The seedlings need moderate shade according to the survey. With the growth constantly, the need of PAR will increase. When the trees become large, it will need total sunlight. Provided that all trees grow under the shade long time enough, its growth will stop and even die. In pure forest which has high canopy density, the regeneration will be worse, or none regeneration. The regeneration is better in the area of forest gap, parts of forest margin and open forest land. Natural regeneration is affected by many factors, especially the livestock that make the regeneration ability descend, increase the frangibility of forest, and debase the stability.