Study on Spatial Distribution Pattern and Dynamics of Primary Population in Populus euphratica Natural Forest in Tarim Basin,Xinjiang

One 50 m×50 m standard plot was sampled in natural forest of Populus euphratica in Awati County,which is situated at the edge of Tarim Basin,Xinjiang Uygur Autonomous Region,and the field investigation was conducted with contiguous grid quadrate method.By means of t-test of variance/mean value ratio,aggregation intensity index and theoretical distribution models,the spatial distribution pattern and the dynamics of primary populations in P.euphratica forest were studied.The results showed that the spatial distribution pattern of two dominant arbor populations conformed to clumped distribution.The aggregation intensity of P.euphratica population was higher than that of P.pruinosa population.The spatial distribution pattern of two companion plant populations in the shrub layer also conformed to clumped type,though the aggregation intensity of Tamarix chinensis was higher.In the herb layer, the distribution patterns of Glycyrrhiza uralensis and Asparagus persicus conformed respectively to clumped pattern and random pattern.The tested results of Taylor power method and Iwao's M-X regression model also verified that both P.euphratica and P.pruinosa populations belonged to clumped pattern.Although the distribution pattern of P.pruinosa population at different development stages all belonged to clumped distribution pattern,the aggregation intensity dropped gradually along with age development.The distribution patterns of P.euphratica population at different development stages changed from random type to clumped type,and further to random type.The differences in spatial distribution pattern of different populations at different development stages were related not only to ecological and biological characteristics of each species in the communities in the light of competitive exclusion principle among the populations,but also closely related to the habitats in which the species lived in.