气候变化和人为活动在宁夏草地变化中的相对作用

气候变化和人为活动是草地生态系统退化或恢复过程中的两大驱动因素。选取植被净初级生产力（NPP）为衡量指标，利用改进的Carnegie-Ames-Stanford Approach （CASA）模型、Thornthwaite Memorial模型以及残差趋势法分别计算了宁夏草地实际净初级生产力（ANPP）、潜在净初级生产力（PNPP）和人为活动影响的生产力（HNPP）及其变化趋势，定量评估了2001-2019年气候变化和人为活动在宁夏4种类型草地（温性草甸、温性草原、温性荒漠草原和温性草原化荒漠）动态变化中的相对作用。结果表明，2001-2019年宁夏草地实际净初级生产力增加的面积占宁夏草地总面积的97.84%；全区草地潜在净初级生产力均表现为增加趋势，表明气候变化有利于植被恢复。草地恢复过程中，气候变化引起的草地恢复面积占草地恢复总面积的61.68%，气候变化和人为活动共同作用引起的草地恢复面积占38.32%；人为活动是导致草地退化的绝对主导因素。4种类型草地动态变化的驱动因素存在差异，气候变化是促进温性草甸（68.94%）和温性草原化荒漠（70.51%）恢复的主导因素，气候变化和人为活动共同作用是促进温性草原恢复的主导因素（62.30%），温性荒漠草原的恢复是气候变化和人为活动共同作用的结果（97.93%）。水热条件好转，尤其是降水增加是宁夏草地恢复的主导气候因子，生态保护政策的实施是促进草地恢复的主要人为因素，对草地的不合理利用是导致草地退化的主要人为因素。

Assessment of relative effects of climate change and human activities on grassland dynamic in Ningxia

Climate change and human activity are two main factors driving vegetation dynamics during grassland recovery or degradation. In this study, the net primary productivity (NPP) was selected as the index, the improved Carnegie-Ames-Stanford Approach (CASA) model and Thornthwaite Memorial model were used to estimate actual net primary productivity (ANPP) and potential net primary productivity (PNPP) determined by climatic conditions, respectively. The residual trend analysis (RESTREND) method was applied to analyze the residuals of potential and actual net primary productivity and further identify non-climatic effects on vegetation dynamics in four types of natural grassland, including meadow steppe, warm steppe, desert steppe and warm steppe desert of Ningxia. Results showed that the ANPP in 97.84% of the grassland increased from 2001 to 2019 generally. The PNPP of the whole region presented an increasing trend, revealing that climate change had a positive effect on vegetation recovery across the study area. During the grassland restoration, 61.68% of the recovered grassland resulted from climate change, while 38.32% of the recovered grassland from the combined effects of climate change and human activity. Anthropogenic activities were considered as the absolutely dominant influencing factor for vegetation degradation. The driving factors of vegetation dynamic showed differences in the four types of grassland. Climate change was the dominant factor for the recovery of warm meadow (68.94%) and warm steppe desert (70.51%). The combined effects of climate change and human activities were the main factors for the recovery of warm steppe (62.30%). The recovery of warm desert steppe resulted from the combined effects of climate change and human activities (97.93%). The improvement of hydrothermal conditions, especially the increases in precipitation, was the main influencing factor for grassland restoration in Ningxia. The implementation of ecological protection policies produced significantly positive effects on the restoration of grassland, and the unreasonable occupation of grassland was the main anthropogenic factor leading to grassland degradation.