塔里木河下游胡杨对输水的生态响应

对塔里木河下游不同离河距离成过熟胡杨和输水后更新胡杨胸径、地径、树高、冠幅、枯枝比以及优势胡杨百分比的调查表明:随离河距离增加(地下水埋深增加),胡杨(大树)枯枝比增加,优势胡杨百分比降低;胸径、树高、冠幅随离河距离增加,增减规律不明显。输水后萌蘖更新胡杨的树高、冠幅和地径均随离河距离增加而降低。以上调查指标确定胡杨输水后恢复等级,离河50~300 m胡杨整体恢复"优",离河300~500 m胡杨恢复"良",离河500~1 050m胡杨恢复"中",离河1 050~1 500 m胡杨对输水响应微弱,整体恢复"差"。胡杨具明显的随离河距离增加恢复等级降低的梯度响应特征,生态输水促进了河畔带胡杨的恢复,水是制约塔里木河下游胡杨生长与恢复的关键因子。

Ecological Responses of Populus Euphratica to Water Supply in the Lower Reaches of Tarim River

Investigations of the breast-width, the root diameter, the height, the cover of crown, the ratio of dead stems and the ratio of preponderance, the maturing and extra-maturing Populus euphratica which have different distances to the downstream of Tarim River revealed that the ratio of the dead stems increases and that of the preponderance decreases with the increase of the distance to the river. The increasing and decreasing trends indicated by the breast-width, the height and the cover of the crown are unapparent. The increasing and decreasing trends are less and less evident with the increase of the distance to the river. And the three indicators, i.e., the breast-width, the height and the cover of the crown of the renewed Populus euphratica after watering show the decline coincidently with the increase of the distance. In accordance with the investigations, we can classify the restoration class of the watered Populus euphratica with the distance to the river being 50-300m as "best", 300-500m as"good", 500-1050m as "medium" and 1050-1500m as"poor". The restoration class of Populus euphratica shows a gradual decrease with the increase of the distance to the river, and eco-water transfer accelerates the restoration of the Populus euphratica. Water is one of the key factors controlling the growth and renewal of Populus euphratica.