2001–2020年黄土高原光合植被时空变化及其驱动机制

Spatiotemporal variation and its driving mechanism of photosynthetic vegetation in the Loess Plateau from 2001 to 2020

为揭示实施退耕还林(草)政策20年后黄土高原植被盖度的最新演变趋势及区域差异,定量分析气候和人类活动对该区植被盖度变化的贡献率及空间分布。该研究以光合植被(PV)盖度为植被生长状况指标,基于2001–2020年PV数据及同期气象数据,采用Mann-Kendall检验、Sen分析和残差分析等方法,分析了黄土高原2001–2020年植被覆盖的时空演变特征及其驱动要素。主要结果:20年中黄土高原植被盖度呈显著增加趋势,增速为每年0.8%。全区植被盖度呈增加趋势的区域面积比例为90%,呈显著增加的区域面积占比为71%;对全区植被盖度增加的贡献,主要是黄土丘陵区(约2/5),其次为风沙丘陵区(约1/4)和石质山区(约1/5);不同地貌分区内,黄土丘陵区中陕西榆林和延安两市区境内植被盖度增加迅速,风沙丘陵区中内蒙古鄂尔多斯市植被盖度变化最快;研究时段内人类活动和气候变化对黄土高原植被增加的贡献率分别为76%和24%;人类活动对植被盖度贡献较大区域主要分布在陕西延安以北、山西太原以南、宁夏同心以南和甘肃平凉和庆阳等丘陵、台塬和风沙丘陵等政府生态工程实施较好的地区。

Aims The objectives of this study were to reveal the changing trends and regional differences of vegetation fractional coverage on the Loess Plateau 20 years after the implementation of the“Grain for Green(GFG)”policy,and to quantify the contribution of climate and human activities to the change of vegetation fractional coverage and its spatial distribution in the region.Methods The spatial and temporal variation of photosynthetic vegetation(PV)fractional coverage on the Loess Plateau from 2001 to 2020 and its drivers and contributions were analyzed based on MODIS-PV and meteorological data,and using the methods of the Mann-Kendall method,the Sen estimator,and multivariate residual trend analysis.Important findings Regional vegetation fractional coverage increased from 40%in 2001 to 60%in 2020.Vegetation fractional coverage of the Loess Plateau showed a significant increasing trend over 20 years,with an increasing rate of 0.8%·a-1.The proportion of the area with an increasing trend of vegetation fractional coverage for the entire region was 90%,and the proportion of the area with a significant increase was 71%.The contribution to the increase of vegetation fractional coverage in the region was mainly in the loess hilly region(2/5),followed by the sandy hilly region(1/4)and the rocky mountain region(1/5).Within the different geomorphology divisions,vegetation fractional coverage in the loess hilly region increased rapidly in Yulin and Yanʼan in Shaanxi.Vegetation fractional coverage in Ordos,Nei Mongol,changed the fastest in the sandy hilly region.Human activities and climate change contributed 76%and 24%,respectively,to the increase of vegetation fractional coverage on the Loess Plateau during the study period.The areas where human activities contributed positively to vegetation fractional coverage were mainly located in the loess hilly and sandy hilly regions in the northern part of Yanʼan in Shaanxi,the southern part of Taiyuan in Shanxi,the southern part of Tongxin in Ningxia,and the hills and plateaus of Pingliang and Qingyang in Gansu where the ecological projects funded by the Chinese government have been well implemented.