瓜州绿洲胡杨种群结构与动态研究

在瓜州四工和桥子天然胡杨林区设置两个样方,采用相邻格子法进行每木调查,建立胡杨种群年龄结构和存活曲线,分析其动态量化特征。结果表明,研究区胡杨种群的年龄结构不完整,大体呈偏正态分布型,为衰退种群。不同生境胡杨种群年龄结构差异显著。其中,桥子缺失幼苗和Ⅷ-Ⅺ级大树、老树,幼树较多,中树最多,占总数的84.91%,林分年轻,十分稠密、相对矮小;四工幼苗和Ⅲ级中树缺失,幼树甚少,中、大树比例高,分别占总数的51.27%和45.57%,林分偏大,相对稀疏、高大。胡杨种群存活曲线基本接近Deevey I型,为下降种群;幼、中树存活率较高,大树、老树存活率很低。桥子的存活率明显高于四工。胡杨种群发育过程存活数量的动态量值计算表明,幼、中树的动态量值为负值,变化幅度大;大、老树为正值,变化幅度小,种群总体为衰退的结构动态关系。总之,研究区胡杨种群未来因幼苗缺乏而趋于衰退演替,且以四工胡杨种群的演替速度更快。

Structure and Dynamics of Populus Euphratica Population in Guazhou Oasis,Northwest China

Based on statistical investigation of Populus euphratica population plants in Sigong and Qiaozi sampling plots in Guazhou Oasis of Gansu Province in 2009,size and age structure and survival curves of P.euphratica population were created by using continuous grid quadrat survey,and its quantitative dynamics was also analyzed in the paper.Results showed that the size and age structure of P.euphratica population was not intact and belonged to partial normal distribution,which indicated P.euphratica population was declining.There was obvious difference between age structures of P.euphratica population in different habitats in the study area.There were not seedlings and Ⅷ-Ⅺ class big and old age trees in Qiaozi,and young trees were relatively more,and the middle age trees were the most,accounting for 84.91% of the total plant number.So the P.euphratica population was very dense and short in Qiaozi plot because of its young age structure.There were not seedlings and Ⅲ class middle age trees in Sigong,and young trees are relatively less,and the middle age trees and large trees were a lot,accounting for 51.27% and 45.57% respectively.So the P.euphratica population was relatively sparse and high in Sigong plot because of its relatively old age structure.The survival curves of the population clearly conformed to the type of Deevey I,and the survival rates of young trees and middle age trees were relatively high,and the survival rates of large and old trees were relatively low,indicating a declining population.The survival rate was higher in Qiaozi than in Sigong.The statistical results of quantitative dynamics of the population indicated that the dynamic indices of young trees and middle age trees were negative values with big change extent,and the dynamic indices of large and old trees were positive values with small change extent.It also displayed a declining structure of P.euphratica population.In a word,P.euphratica population will tend to a decline status because of lacking seedlings,and the speed of the decline succession in Sigong plot will be faster than in Qiaozi plot in future.