橡胶坝对西安灞河河道湿地旱柳群落的影响

Influence of Rubber Dams on the Salix matsudana Community in the Bahe River Wetland of Xi′an

分析探讨灞河河道湿地部分区段旱柳大量死亡的问题,提出解决方法及对策,指导橡胶坝的运行及管理。调查区段为西安灞河下游A橡胶坝(浐灞河汇合处)至B橡胶坝(灞河南三环大桥)。该区段中游频繁受到水淹,旱柳死亡严重;上游临近B坝受水淹较少,旱柳长势良好。对这2处长势差异较大的旱柳群落的胸径等级结构、倒伏、树皮开裂以及生存状况进行了比较和分析。结果表明旱柳倒伏、树皮开裂以及死亡状况差异显著;倒伏与旱柳树皮开裂、死亡均正相关;树皮开裂个体数与柳树存活个体数呈显著的负相关。倒伏和树皮开裂是旱柳死亡的直接原因,采取降低橡胶坝水位、减少蓄排水频率和减缓蓄排水速度的措施能够形成较为稳定的河流湿地生态系统,可减少旱柳死亡。

Bahe River is the main river of the Chan-Ba National Ecological District in Xi’an.The Salix matsudana community has been an important vegetation type and representative landscape in the Bahe River basin since ancient times.To develop water-oriented eco-tourism,a number of cascaded rubber dams were built in the Bahe River basin to raise the water level and improve the landscape,but increased flooding frequency in some sections has sharply decreased the area inhabited by S.matsudana.The objective of this study was to determine the reasons for S.matsudana decline and recommend countermeasures to guide rubber dam operation and wetland management.The investigation was carried out between rubber dams A and B in early June and late August of 2014.Diameter at breast height(DBH),lodging,bark cracking and survival rate of S.matsudana were measured and found to differ significantly in different sections of the study area.While S.matsudana grew well in the upper reach of the study area,where the willows are not affected by the operation of rubber dams,the S.matsudanacommunity in the middle and lower reaches of the study area was in crisis,with serious lodging,bark cracking and high mortality rate.The mortality rate of S.matsudana was positively correlated with lodging and bark cracking and these are the direct cause of the high mortality of S.matsudana.Therefore,stabilizing the wetland ecosystem would benefit S.matsudana and reduce the mortality.Specific recommendations include decreasing the water level,lengthening the water storage-drainage cycle and reducing water velocity during drainage.