关键词: 胡杨林, 种群结构, 数量动态, 衰退演替, 瓜州绿洲

Abstract: 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.

Key words: Populus euphratica, population structure, quantitative dynamics, decline succession, Guazhou Oasis