北方地区典型林草地物候时空变化特征及其对气象因子的响应

为探究北方地区典型植被林地、草地物候特征及其对气候变化的响应，本文基于1982—2015年的GIMMS NDVI 3gv1数据集和气象资料，采用动态阈值法提取植被物候，应用线性回归和偏相关分析法分析林、草地物候时空变化特征及其与气候变化的关系。结果表明：(1)林地生长季长度(LOS)以0.32d/a的速率极显著延长，整体表现为生长季始期(SOS)以-0.18d/a极显著提前，生长季末期(EOS)以0.14d/a极显著推迟。林地SOS提前、EOS推迟和LOS延长的区域面积占比分别为93.3%、90.4%和96.3%。(2)草地LOS以-0.01d/a的速率不显著缩短，表现为SOS以-0.09d/a不显著提前，EOS以-0.10d/a不显著提前。SOS提前、EOS提前和LOS缩短的区域占比为67.5%、69.1%和50%。(3)林地SOS主要受冬末春初的气温升高和降水增加而提前，EOS受夏季气温升高、秋季以及冬末春初降水增加而推迟。(4)草地SOS主要受春季气温升高和短波辐射减少而提前，EOS受秋季气温升高和短波辐射减少而提前，草地物候与气象因子的响应时长小于林地。

Spatio-temporal variations of typical woodland and grassland phenology and its response to meteorological factors in Northern China

To reveal the phenological characteristics of typical vegetation woodland and grassland and its response to climate change in Northern China, adopting the GIMMS data and meteorological data from 1982 to 2015, the woodland and grassland phenology were extracted by using a dynamic threshold method, and the spatio-temporal variations of phenology and its response to climate change were identified by linear regression and partial correlation analysis methods. The results can be summarized as follows. (1) The woodland length of season (LOS) was significantly extended with a rate of 0.32d/a, while the start of season (SOS) was significantly advanced with rate at -0.18d/a and the end of season (EOS) was obviously delayed with rate at 0.14d/a. The advanced SOS, delayed EOS, and extended LOS areas covered 93.3%, 90.4%, and 96.3% of the whole woodland area, respectively. (2) The grassland LOS was insignificantly shortened with a rate of -0.01d/a, while the SOS was insignificantly advanced with rate at -0.09d/a and the EOS was insignificantly advanced with rate at -0.10d/a. The advanced SOS and EOS areas covered 67.5% and 69.1% of the whole grassland area, respectively. And, the LOS was shortened in 50% of the areas. (3) The advanced woodland SOS was mainly influenced by the increase in temperature and precipitation in late winter and early spring, and the delayed EOS was affected by the increased temperature in summer and precipitation in autumn, late winter, and early spring. (4) The advanced grassland SOS was mainly related to the increase in temperature and the decrease of short-wave radiation in spring, and the advanced EOS was affected by the increase in temperature and the decrease of short-wave radiation in autumn. The response time of grassland phenology and meteorological factors was shorter than that of woodland.