2000—2017年东北森林NDVI时空动态及其驱动因子

Spatiotemporal dynamics of normalized difference vegetation index(NDVI)and its drivers in forested region of Northeast China during 2000-2017

森林是陆地生态系统的重要组成部分,调节着地表-大气间碳、水、能量交换,在减缓气候变化方面具有重要的作用。因此,理解森林生态系统动态及其驱动因子,对于预测气候变化下影响森林生态系统结构、功能的动态变化具有重要意义。本研究基于2000—2017年中分辨率光谱成像仪(MODIS)数据集,通过归一化植被指数(NDVI)逐像元计算分析东北森林植被动态变化趋势,并结合气象数据,分析气候因子对东北森林NDVI变化的影响。结果表明:东北森林NDVI在春季、夏季、秋季以及生长季均呈现了增长的趋势,其中秋季的增长速率最高,夏季的增长速率最低,整个生长季增长速率为0.0025 a-1(R2=0.77)。3种森林类型中,阔叶林NDVI增长速率最快,混交林次之,针叶林最慢。通过NDVI与气候因素的多因素相关性计算结果表明,干旱指数(Palmer drought severity index,PDSI)是驱动东北森林NDVI变化的主要因素。NDVI与PDSI呈显著的正相关关系,说明气候越湿润植被活动越强烈。气候变暖的背景下,气温升高可增加地表蒸发散,由此带来的干旱频率增加可能会成为影响东北森林植被活动和碳汇功能的主要因子。

Forest is a key terrestrial ecosystem type,and plays an important role in regulating the exchange of carbon,water and energy between land surface and atmosphere.Therefore,forest ecosystems are vital in mitigating climate change.Understanding the spatiotemporal dynamics of forest ecosystem and its drivers is important to predict its structure,function,and dynamics.Using normalized difference vegetation index(NDVI)dataset from Moderate Resolution Imaging Spectroradiometer(MODIS),we analyzed the vegetation dynamics and its climatic controls in forested region across Northeast China from 2000 to 2017.The results showed that NDVI increased in spring,summer,autumn and growing season from 2000 to 2017,with the highest increase rate in autumn and the lowest increase rate in summer.The increase rate of NDVI in the growing season was 0.0025 a-1(R2=0.77).Among the three forest types,broad-leaved forest had the highest interannual variability,followed by mixed forest and coniferous forest.Results of multiple regression analysis suggested that PDSI(Palmer drought severity index)was the major driver for the forests in Northeast China.PDSI was positively correlated with NDVI,indicating that higher water availability promoted stronger vegetation activity.Under climate warming scena-rio,increased evapotranspiration due to higher air temperature may increase drought frequency and become a dominant limiting factor for forest vegetation activity and carbon sink in Northeast China.