水分梯度下胡杨荒漠河岸林种内竞争及空间格局变化特征

为查明塔里木河下游不同水分梯度下胡杨种内竞争以及空间分布格局的变化规律，在塔里木河下游阿拉干断面选取3条样带，每条样带内依照水分梯度布设3个样方，采用Hegyi单木竞争模型与点格局等分析方法，探究了水分梯度下胡杨林种内竞争及空间格局变化特征。结果表明：1)塔里木河下游胡杨的最适竞争范围为10m; 2)胡杨竞争指数与胸径服从幂函数关系(P<0.001),胡杨竞争指数随对象木胸径的增加而逐渐减小，当对象木胸径达到20cm以上时，其竞争指数逐渐稳定，且维持在较低水平；3)随水分梯度的降低，胡杨林分竞争指数呈下降趋势；4)在塔里木河下游，胡杨空间格局主要为聚集分布，随空间尺度的增加，胡杨逐渐趋向于随机分布；5)随水分梯度的降低，胡杨空间格局由聚集分布逐渐转变为随机分布。水分是决定极端干旱区荒漠植被空间分布与结构的主要因子；在胡杨林分管理中，应充分考虑胡杨的种内竞争、空间格局及其与水分梯度之间关系，为塔里木河下游胡杨林的保护与更新提供科学依据。

Spatial distribution pattern and intraspecific competition of Populus euphratica riparian forests under different water gradients

Euphrates Poplar (Populus euphratica Oliv.) is a construction deciduous tree species in desert riparian forest and plays a vital role in ecological protection and sustainable floodplain management in arid regions. During a long period of time, the population growth structure has changed under the extreme drought environment under the water resources stress in the lower reaches of the Tarim River, and the forest stands spatial structure change is one of the obvious manifestations. Under the background of ecological water conveyance projects in this region over the past 20 years, it is necessary to find out the forest structure changes at present stage. Therefore, systematic study of the adaptability of P. euphratica population spatial distribution pattern and intraspecific competition under different water gradient conditions need to perform, which can deepen the understanding of the riparian forest adaptation mechanism to arid environment. In the present study, to investigate the intraspecies competition dynamics and spatial distribution patterns of P. euphratica under different water gradient conditions, three transects were selected at the Arghan area in the lower reaches of the Tarim River, NW China. Each transect was divided three research sites according to the water gradient. The results showed that:1) the optimum competition range of P. euphratica in the lower Tarim River was 10 m; 2) The competition index and diameter at breast height (DBH) obtained the power function model (P<0.001). The competition index of P. euphratica decreased with the increase of the DBH, the competition index of the target tree gradually stabilized and remained at a low level, when the diameter at breast height of the target tree reached 20 cm or more; 3) The competition index of P. euphratica stands decreased with the decrease of the water gradient; 4) In the lower reaches of the Tarim River, the spatial distribution pattern of P. euphratica was mainly aggregated pattern, and with the increase of spatial scale, the distribution pattern gradually tended to random pattern; 5) With the decrease of water gradient, the spatial pattern of P. euphratica gradually changed from the aggregated to random distribution pattern. Water was the main factor determining the spatial distribution and structure of desert vegetation in extreme arid zones; In P. euphratica stand management, the relationship between interspecific competition, the spatial pattern and water gradient should be fully considered to provide an important scientific basis for the conservation and regeneration of the riparian forests in the lower reaches of the Tarim River.