Impacts of human activities and climate change on gross primary productivity of the terrestrial ecosystems in China

总初级生产力（GPP）是生态系统植被光合作用生成有机物的能力表征，是生态系统服务功能的基础，关系到区域社会经济可持续发展及区域生态安全。基于生态系统过程模型CEVSA2，应用中分辨率成像光谱仪（MODIS）卫星遥感的叶面积指数数据产品（MCD15A2H），以强迫法构建了遥感数据驱动的模型新版本——CEVSA-RS；基于CEVSA-RS模拟分析了气候变化和人类活动对中国陆地生态系统GPP时空变化的相对影响，从气候潜在总初级生产力（GPPCL）和现实总初级生产力（GPPRS）的大小和趋势两方面厘定了人类活动影响。2000至2017年全国平均潜在GPP （1016.36 gC m-2a-1）略高于对应现实GPP （962.85 gC m-2a-1），但存在明显的空间分异：长江以南大部、秦岭、太行山脉以东以及大兴安岭以东和长白山地区等森林植被覆盖区，现实GPP高于潜在GPP；而西部草地及灌丛等地区现实GPP低于潜在GPP。全国GPP呈显著增加趋势（P<0.05），其中现实GPP的增速（46.04 gC m-210a-1）高于潜在GPP的增速（41.46 gC m-210a-1），人类活动影响促进GPP增长，主要体现在华南地区和华北平原等地；内蒙古东部、东北平原北部、青藏高原西部等地人类活动呈负面影响。人类活动影响大于气候影响的区域可达全国陆地面积的53%，其中西部生态相对脆弱的草地区人类活动仍为负面影响，这些地区以草定畜，发展草牧业和保护生态，仍然任重道远。;Gross primary productivity (GPP) is the fundament of all ecological services that ecosystems can provide, and its change will influence the sustainable development of regional socio-economic and ecological security. Based on the ecosystem process model CEVSA2, this study applied the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite remote sensing data to construct a new version of the remote sensing data-driven model, CEVSA-RS. The relative impacts of climate change and human activities on the spatial and temporal changes of terrestrial ecosystem gross primary productivity were analyzed based on CEVSA-RS, and the impacts of human activities were determined in terms of both the magnitude and trends of potential gross primary productivity (GPPCL) driven by climate and actual gross primary productivity (GPPRS) driven by climate and remote sensing. According to the national average, potential GPP (1016.36 gC m-2a-1) was slightly higher than actual GPP (962.85 gC m-2a-1) from 2000 to 2017. However, there is an obviously spatial disparity:the actual GPP is higher than the potential GPP in forested vegetation cover areas such as most of the south of the Yangtze River, the east of the Qinling and Taihang Mountains, and the east of the Daxinganling and Changbai Mountain areas. Meanwhile, the actual GPP is lower than the potential GPP in areas such as grassland and shrubland over western China. The GPP of whole Chinese terrestrial ecosystems showed a significant increasing trend (P<0.05), and the increasing speed of actual GPP (46.04 gC m-210a-1) exceeded that of potential GPP (41.46 gC m-210a-1), which meant human activities positively contributed to the most area in South China and North China Plain, while negatively impacted the ecosystems in eastern Inner Mongolia, northern Northeast Plains and western Tibetan Plateau. The areas where the impacts of human activities are greater than the impacts of climate chang accounted for 53% of the total land area in China. Considering negative impacts of human activities in the western China, as an area of fragile eco-environment, there is a long way to protect its ecosystems while to develop grassland-based husbandry through determining livestock stocking rate according forage production.