Community Dynamic And Influenceing Factors Of 8ha Dynamics Plots In Picea Schrenkiana Forest In Tianshan Mountains

The construction of large-scale dynamic monitoring plots and its network has been rapidly spreaded all over the world since 1980 promoted by Stephen Hubbell. Researches carried out a lot of investigates on the dynamic monitoring plot and have explained many key scientific problems of biological diversity such as the construction of community and mechanism of maintenance. Tianshan Picea schrenkiana forest, located in the northern arid area, is the rational plots to study the population dynamics and mechanism change of pure forest, because it has sample community composition, and P. schrenkiana is the single dominant species of the forest with sparse shrubs undergrowths. Based on the investigates data of 2009 and 2014 on an 8-ha P. schrenkiana forest plot, we made statistical analysis of community species composition, size structure and population dynamics. Then discusseed the relationship between some enviornment factors that effect on the community dynamics, for example the geography shape, the soil characters and so on.. Besides, we used "case- control" method to verified the community density dependent effects. The main results are showed below:1. In the 8 ha forest dynamics plot in the middle of Tianshan Mountains, kinds of woody plants reduced to six from eight, and number of individuals with DBH≧1cm reduced to 11050 from 11835 in 2009-2014. During the 5 years, the number of dead was 1044, and the mortality rate was 8.82%, while the number of recruitment was 259, and the recruitment rate was 2.19%.2. Size class structure of four woody plants(Picea schrenkiana, Berberis, Lonicera hispida and Sorbus tianschanica) showed apparent inverted "J" type, indicating that the Tianshan P. schrenkiana forest is in growth stage, and the update is good. The mortality rate of P. schrenkiana individuals were highest when DBH was 2.5cm-5cm, and with DBH increased, mortality rate gradually reduced; when DBH≧22.5cm, the mortality rate is 0. So DBH≧22.5cm is the critical value that P. Schrenkiana can growth stable.3. According the analysis of soil samples in the plots, we found that soil nutrient and soil enzyme were in great variation. The Pearson correlation coefficient of soil total nitrogen and total phosphorus were highest(R2=0.672, P<0.01), followed by soil urease activity and catalase activity(R2=-0.421, P<0.01).Soil nutrient and soil enzyme present different distribution through the analysis of Kriging difference.4. RDA analysis result of population dynamic characteristics of P. schrenkiana and environmental factors was significant, and the cumulative explanation of first two ordination axes on the population dynamics and environmental factors up to 96.1%, canopy density, elevation and cellulase activity significantly affected population dynamic characteristics. Stepwise linear regression analysis showed that the plot slope, canopy density and elevation were the most important environment factors that affect the P. schrenkiana individual survival, and the death of P. schrenkiana individual was mainly affected by canopy, while the recruitment were connected with elevation and soil nitrogen.5. We used Point-pattern to analysis the spatial distribution pattern of dominant species P. schrenkiana. When do not eliminate habitat heterogeneity, young and medium-aged P. schrenkiana trees presented an aggregation distribution with a scale of 0–40 m, and the aggregation intensity decreased as the scale increased. When eliminate the habitat heterogeneity by using "Case- control" design method, young and mediumaged trees presented extra aggregation relative to the adult trees, and this extra aggregation decreased gradually with the increase of the DBH. That is density dependent effects, indicating that spatial pattern of P. schrenkiana was affected by density dependent effects. And through the study on different life history stages of spatial association,we found that young trees and adult trees, medium trees and adult trees both showed negative spatial association in 0-40 m scalesTo sum up, the study in this work can provide a help to deeply understand the community construction and the mechanism of maintenance about forest. and also making an important supplement and improvement to key scientific theory of biological diversity.