中文摘要：

以澜沧江中游小湾水库库周为研究区,在1997年（小湾水库建设前）澜沧江中游小湾水库下游3个样地[输电区（1号样地）、变电站和进站公路区（2号样地）和水库移民区（3号样地）]植被调查基础上,2010年（小湾水库建设后）分别对3个样地进行植被组成、盖度和优势种观测,评估了水坝工程对澜沧江中游陆地植物的生态风险.结果表明：3个样地上优势种的总和优势度在水坝建设前后均发生了明显变化.本研究根据物种类型（优势种和非优势种）及物种总和优势度变率将生态风险划分为无风险/极低风险（0）、低风险（Ⅰ）、中风险（Ⅱ）、高风险（Ⅲ）、极高风险（Ⅳ）5个等级.研究区处于Ⅲ级生态风险（高风险）的物种数量最多,部分物种处于Ⅳ级生态风险（极高风险）;3号样地处于Ⅲ级（高风险）和Ⅳ级（极高风险）生态风险的物种比例明显高于1、2号样地.水坝建设导致的物种水平生态风险主要表现为原生物种减少、外来物种大量入侵等.应采取有效的保护措施降低陆生植物物种水平水坝生态风险.

英文摘要：

Taking the surrounding areas of Xiaowan Reservoir in the middle reach of Lancangjiang River as study area,and based on the vegetation investigation at three sites including electricity transmission area（site 1）,electricity-transfer substation and roadsides to the substation（site 2）,and emigration area（site 3） in 1997（before dam construction）,another investigation was conducted on the vegetation composition,plant coverage,and dominant species at the same sites in 2010（after dam construction）,aimed to evaluate the ecological risk of the dam construction for the terrestrial plant species in middle reach of Lancangjiang River.There was an obvious difference in the summed dominance ratio of dominant species at the three sites before and after the dam construction.According the types of species（dominant and non-dominant species） and the changes of plant dominance,the ecological risk（ER） for the plant species was categorized into 0 to IV,i.e.,no or extremely low ecological risk（0）,low ecological risk（Ⅰ）,medium ecological risk（Ⅱ）,high ecological risk（Ⅲ）,and extremely high ecological risk（Ⅳ）.As affected by the dam construction,the majority of the species were at ER Ⅲ,and a few species were at ER Ⅳ.The percentage of the plant species at ER Ⅲ and ER Ⅳ at site 3 was higher than that at sites 1 and 2.The decrease or loss of native plants and the increase of alien or invasive plants were the major ecological risks caused by the dam construction.Effective protection strategies should be adopted to mitigate the ecological risk of the dam construction for the terrestrial plants at species level.