黄河源区植被对活动层温度和水分的影响

植被和活动层水热关系是青藏高原冻土生态环境的重要组成部分，对气候变化和工程活动积极响应，是目前全球变化研究的热点之一.为了解植被差异对活动层水热过程的影响，以场地监测和植被调查数据为基础，分析了黄河源区高温高海拔多年冻土区同一地貌单元内局地条件相似而植被差异显著的3个场地活动层温度和水分变化.初步结果表明:植被盖度较低时，活动层水分含量也低，且含水量高值区趋于中下部；植被盖度较高时，冷季地气温差和温度位移都减小，暖季地气温差增大；随着植被盖度增大，冻融开始和结束时间明显滞后，冻融持续时间延长.初步揭示了黄河源区地表植被对活动层水分和温度的影响过程，对研究和保护高寒生态环境稳定具有重要意义. 

Responses of Surface Vegetation on Soil Temperature and Moisture of the Active Layer in the Source Area of the Yellow River

Relationships of the vegetation and active layer are the foci of global change study since the interaction between the vegetation and hydrothermal processes of the active layer are important part of Qinghai-Tibet Plateau permafrost ecosystems, and they are liable to react on the global warming and anthropogenic activities. Based on the analysis of soil temperature and unfrozen water content of the active layer, surveys of vegetation, the influences of vegetation on the variations of hydrothermal processes of the active layer in the source area of the Yellow River (SAYR) are studied. Preliminary results show that variations of unfrozen water content and soil temperature of the active layer are significantly affected by vegetation cover, above-ground biomass, and dominant species. The distribution unfrozen water content is consistent with the vegetation coverage. The offsets between the ground surface temperature and air temperature, which are affected by the vegetation cover, are higher in winter-time and lower in summer-time. The beginning of freezing is latter, the finishing of freezing is earlier, and the duration of freezing is longer for those sites with higher vegetation cover. With lowering of vegetation cover, zones with higher content of unfrozen water shift towards the bottom of the active layer. This study reveals the effects of variations of vegetation on soil temperature and unfrozen water content of the active layer for warm, and high-altitude permafrost in the SAYR, and will also facilitate the research and protection of cold eco-environments in the SAYR.