中文摘要：

在塔里木河上游垂直河岸设置样带,研究胡杨种群数量特征与空间格局沿地下水位梯度的动态及相互关系,探讨其生存发展的合理生态地下水位及胁迫水位。结果表明：胡杨具有伴河生长的特性,在距河道100m以内胡杨以幼苗为主,种群属进展型;随着离河道距离的增加,胡杨种群幼龄比例减少,胸径逐渐增大,远离河道区老龄个体占优势,种群结构呈倒金字塔形,趋向衰退。胡杨种群密度、幼苗比例、长势与林分郁闭度随离河道距离增加而降低,平均胸径、最大胸径与树冠疏失度则增加;密度、郁闭度与离河道距离（地下水位）呈显著负相关,平均胸径与离河道距离呈正相关。河岸带胡杨空间格局主要呈聚集分布,近河岸区则呈随机分布,随距离增加空间格局转为聚集分布,这是种群集群抵御干旱环境而采取的生态适应对策。地下水位是影响河岸带胡杨种群生长与分布的主要因素,而维系河岸带胡杨种群正常生长的合理地下水位应〈4.1m,胁迫临界地下水位为5.5m。

英文摘要：

Our objectives are to clarify ecological responses of Populus euphratica population to change in the groundwater level and determine the groundwater level depth needed for the survival of riparian forest,in order to provide theoretical basis for vegetation restoration and ecological water conveyance project.This experiment was done by setting 30m×30m transect plots at different distance from the channel,and adopted the method of combining the field investigation and statistical analysis to study the dynamics quantitative characteristics and spatial distribution pattern of P.euphraticapopulation along groundwater gradient and influence factors in riparian zone at the upper reaches of the Tarim River.Result shows that P.euphratica have a tendency to grow along the river bank.Within 100m of the river bank,the proportion of seedlings is the greatest,it belongs to progressive population.With increasing distance from the river,the proportion of young trees gradually decrease and DBH increase,and adult,old individuals are the greatest,it belongs to declining population with far away from river bank.The density,the proportion of young individuals,quantity,growth and stand canopy closure decrease,and average DBH,maximum DBH,and crown loss increase with increasing distance.The density,canopy closure and distance away from river bank is significant negative correlation,average DBH and distance are significant positive correlation.Spatial distribution pattern of P.euphraticapopulation conform to clumped distribution.Spatial pattern is random within 50 m and it turned to clumped distribution with increasing distance.This is the ecological adaptation strategy of P.euphratica population with aggregate distribution to resist drought environment and continue to live.Analysis based on above,groundwater depth（the distance from river bank）is the major influence factor for P.euphraticaforest growth and distribution in riparian zone.Thus,the optimum groundwater level for P.euphraticagrowth is〈4.1m and the threshold groundwater