近30年中国天然草地物候时空变化特征分析

Temporal and spatial variations in natural grassland phenology in China over the last 30 years

基于遥感的大面积长时序草地物候监测是物候生态学的重要领域,也是全球变化研究的重要方向。基于30年(1986-2015年)时间序列GIMMS 3g归一化植被指数(NDVI),利用Savitzky-Golay滤波法进行时间序列重建,并用动态阈值法提取中国天然草地物候参数[生长季始期(SOS)、生长季末期(EOS)、生长季长度(LOS)],然后以1998年为时间分界点,利用提取的3种物候参数对前后两个时间段内的草地物候特征的时间演化趋势及空间分异进行分析。结果表明:1)全国草地年平均SOS、EOS和LOS分别主要集中在第100~140天、260~290天和130~170天;2)物候趋势在30年时间尺度上没有显著变化,幅度为-0.3~0.3 d·yr^-1;3)在1998年之前,全国草地SOS平均提前速率为0.37 d·yr^-1,EOS平均推迟速率0.43 d·yr^-1,且空间差异较大,在1998年之后草地物候变化趋势出现转变,草地SOS变化幅度最大,平均推迟速率为0.28 d·yr^-1;4)高山亚高山草甸、山地草原、平地草原和高山亚高山平地草原在1998年后物候特征变化趋势出现与之前完全相反的转折。提取物候结果与观测资料和相关研究结果较为一致。

Long-term monitoring of grassland phenology in large-scale areas by remote sensing is an important area of ecological research and a core part of global change research.Based on the GIMMS 3 g Normalized Difference Vegetation Index(NDVI)of the 30-year(1986-2015)dataset,the Savitzky-Golay filtering method was employed to reconstruct the time series.A dynamic threshold method was used to extract phenological parameters of Chinese natural grassland(start of the growing season,SOS;end of the growing season,EOS;and length of the growing season,LOS).Then,1998 was selected as the time demarcation point to analyze the temporal trends in evolution and spatial differentiation of grassland phenological characteristics in the two time periods.It was found that:1)The national average annual SOS,EOS,and LOS were mainly concentrated around 100-140 days,260-290 days,and 130-170 days,respectively;2)Phenological trends have not changed significantly over the 30 years with a range of-0.3 to 0.3 d·yr^-1;3)Before 1998,the SOS of grassland was 0.37 d·yr^-1 earlier and the EOS was 0.43 d·yr^-1 later on average,and there was a big difference in the area of grassland.After 1998,grassland phenology began to change.The SOS of grassland showed the largest change with an average advance of 0.28 d·yr^-1;4)The phenological characteristics of alpine subalpine meadow,mountain grassland,flat grassland,and alpine subalpine flat grassland changed in a completely opposite direction after 1998.The time trends identified in this paper are consistent with observational data and the results of other studies.