青海湖流域植被物候格局时空动态变化及其与植被退化的关系

本研究利用2000-2014年期间MODIS 16 d合成EVI 数据,选用阈值法模型提取了青海湖流域逐年的植被关键物候期,分析了物候时空动态变化特征及其与植被退化的关系。结果表明,青海湖流域内植被陆续在4月中旬-6月中旬进入返青阶段,8月中旬-10月中旬进入枯黄期,生长季长度在100~150 d之间。植被陆续进入返青期的时间在流域整体空间上呈现由东南向西北延迟的水平地带性变化趋势,多高山分布区域的植被进入返青期时间表现出垂直非地带性特征。植被进入枯黄期的时间与进入返青期早晚的时间在空间格局上相反,生长季长短空间格局与植被进入返青时间早晚的空间格局一致。气候变化趋势下,流域植被物候时空动态变化存在空间异质性,返青期均值年际变化趋势不明显,枯黄期均值提前6.4 d,生长季均值缩短8.9 d。流域内植被物候除受气候因子影响外,与植被退化也有密切关系。植被生长趋于茂盛,返青期呈现延迟趋势;植被生长退化趋势,返青期呈现提前倾向。枯黄期与植被退化的关系较复杂,整体上未表现出明显一致的相关性。植被生长季与植被退化呈现强负相关,即植被生长呈现茂盛趋势的区域,生长季缩短。

Spatial-temporal variation of vegetation phenology and their relationships with vegetation degradation in a Qinghai Lake watershed

This paper presents a threshold method to examine the vegetation phenology in a Qinghai Lake watershed based on a time-series analysis of a MODIS EVI dataset from 2000 to 2014 using 16-day intervals. The spatio-temporal variation of vegetation phenology and the relationship with vegetation degradation were also analyzed. The results showed that the beginning of the vegetation growing season (BGS) occurred from mid-April to mid-June and the end of growing season (EGS) from mid-August to mid-October; growing season (GS) was between 100 to 150 days. The BGS spatial pattern was embodied by a transition from southeast to northwest; vertical zonation in the mountainous region showed a contrary trend in EGS and GS. Spatio-temporal variation of vegetation phenology at the whole watershed level showed spatial heterogeneity under climate change, but mean BGS trends were not pronounced during the study period. EGS was advanced approximately 6.4 days and GS prolonged by 8.9 days. Vegetation phenology was also affected by vegetation degradation. BGS tended to be later when vegetation flourished and advanced when vegetation was degraded. The relationship between annual EGS date and vegetation degradation was relatively complex. EGS and vegetation degradation were significantly negatively correlated indicating EGS was earlier where the vegetation was in good condition.