近13 a来黄河源区高寒草地物候的时空变异性

以8 d合成的500 m空间分辨率的MODIS [NDVI]时序数据为基础，利用非对称高斯函数拟合法和比值阈值法对2000-2012年黄河源区高寒草地生长季始期（SOG）、生长季末期（EOG）、生长季长度（LOG）的时空变化进行了研究。结果表明：黄河源区高寒草地多在第126～140 d开始生长，到第277～290 d逐渐停止生长，LOG多集中在140～160 d。由东南向西北，随水热条件变化，SOG 逐渐推迟，EOG逐渐提前，LOG逐渐缩短。物候的海拔分异明显，随海拔升高，SOG逐渐延迟，EOG逐渐提前，LOG逐渐缩短。2000-2012年，黄河源区高寒草地SOG显著提前，EOG基本不变，LOG显著延长。SOG提前、EOG推迟、LOG延长的区域主要分布在黄河源区西北部和西南部，而SOG推迟、EOG提前、LOG缩短的区域主要分布在黄河源区中部，其中LOG延长和缩短区域分别占植被区面积的82.77% 和17.23%。黄河源区高寒草地物候的年际变化在不同海拔上分异显著。高海拔地区SOG与LOG变化幅度均超过了低海拔地区，而EOG变化幅度相当。春季、秋季气温升高可能是引起黄河源区高寒草地SOG提前和EOG推迟的主要原因。

Spatial-temporal pattern variations of alpine grassland phenology in source region of the Yellow River from 2000 to 2012

Vegetation phenology is the best indicator in monitoring the influence of climate on vegetation. More and more remote-sensing image time series are now available to monitor vegetation phenology dynamics over large areas. Based on the Asymmetric Gaussians Filtering and Dynamic Threshold Method，the spatial-temporal pattern variations of alpine grassland phenology in source region of the Yellow River were analyzed using EOS-MODIS [NDVI] data from 2000 to 2012. The results showed that alpine grassland phenology in the study area generally started from late April to early May，and ended in late September to early October. The spatial patterns of alpine grassland phenology were significantly different. Start of growing season（SOG） of alpine grassland phenology in the southeast started earlier than the northwest，and end of growing season （EOG） ended later. Therefore，long of growing season（LOG） in the southeast was longer than those in the northwest influenced by variations of thermal and hydrological conditions. Alpine grassland phenology was closely related with altitude. SOG delayed，EOG advanced，LOG prolonged with altitude increasing．Inter-annual linear tendency of SOG，EOG，LOG in the region from 2000 to 2012 was -10.38 d/10 a（R=-0.65，p=0.017），0.07 d/10 a（R=0.01，p=0.95），10.46 d/10 a（R=0.72，p=0.005）. The trends of alpine grassland phenology had certain spatial discrepancy，which expressed that the LOG prolonged in northwest，southwest areas and shorten in central areas covering about 82.77% and 17.23% of total areas respectively．The spatial patterns of alpine grassland trends were altitude dependent. The magnitude of the trend in SOG and LOG increased in higher altitudes contrasted with lower altitudes，while EOG had no significant change. It was inferred that alpine grassland in higher altitudes was more sensitive to climate change. Increasing in spring and fall temperature mainly caused SOG advancing and LOG extending of alpine grassland in source region of the Yellow River. The phenology of alpine grassland extracted using EOS-MODIS [NDVI] datasets in this paper was generally concordant with many reported researches. This paper can provide a reference for the evaluation and protection of ecological environment in source region of the Yellow River.