关键词: 疏勒河中下游, 胡杨林, 种群结构, 衰退演替

Abstract: Based on the investigated and selected research plots of 6.8524 hm² of Populus euphratica which were divided into 566 subplots in 2009 in the middle and lower reaches of the Shule River Basin Oasis, Hexi Corridor, all the trees whose stems are over 2.5 cm in DBH were identified, measured, tagged and mapped by using quaclrat method and every-tree measuring method. The size and age structure and the survival curves were created and the dynamics quantitative estimate was analyzed with field data. The results indicated that the characteristics of the size and age structure of Populus euphratica population were obviously different under different habitats in the middle and lower reaches of the Shule River Basin. In the middle reaches saplings were lack, with a few springwood and old trees, the population of the middle age trees was the biggest, occupying 72.15% of the total; more big trees and less old trees made the age structure present a normal distribution type; the forest stand is young, very dense and tall and the total of Populus euphratica per hectare is 13.45 times that of the lower reaches. In the lower reaches saplings were lack, with few springwood, more middle and old age trees, the population of big and old trees occupied 62.54% of the total, presenting an inverse pyramid type in age structure; the forest stand is older, very sparse, and dwarfish. They are both declining population in the study area. The survival curves of the population conformed to the type of Deevey I, a type of degressive population. The survival ratio was high in the springwood and middle age trees, low in the big and old age trees. The average survival ratio in the middle reaches was higher than that in the lower reaches, the highest in Qiaozi plot of the middle reaches and the lowest in plot of the lower reaches. The result of the dynamics quantitative estimate indicated that the survival amount in springwood and middle age trees of the population showed a negative value, and a plus value in Ⅶ-Ⅺ size class big and old age trees of the population. A general tendency was a dynamics structure relation of declining population. In a word, the trend is that Populus euphratica population, owing to lack of saplings, will be tending to a decline succession in the study area and the rate of succession in the lower reaches will be faster than that in the middle reaches.

Key words: middle and lower reaches of the Shule River Basin, Populus euphratica, population structure, declining succession