[Impacts of Climate Change and Human Activities on Vegetation Restoration in Typical Grasslands of China].

Grasslands, as one of the key ecosystems relevant to the terrestrial ecosystem carbon and water cycles as well as the ecological security in China, are very sensitive to climate change and human activities. However, the relative contributions of climate change and human activities on the vegetation restoration in those regions are still controversial. Using ecosystem net primary production (NPP) as an ecological indicator, this study quantified the relative roles of climate change and human activities on vegetation restoration in Chinese typical grasslands (northern temperate grasslands and Qinghai-Tibet Plateau alpine grasslands) by comparing the trends of actual NPP derived from MODIS and potential NPP estimated by the Thornthwaite Memorial model during 2000-2020. The results showed that approximately 93% of the grasslands in the study area experienced a recovering tendency, with an average increase of NPP (carbon) by 2.12 g·(m2·a)-1(P<0.01). Therein, nearly half of the vegetation-restored areas were jointly-dominated by climate change and human activities, whereas approximately 36% and 10% of the restored areas were controlled individually by climate change and human activities, respectively. In addition, the share of climate-change dominated areas differed greatly by grassland types, characterized by a much larger area percentage in the alpine grasslands than that in the temperate grasslands and an increasing area share with a drying background climate. This study suggested that human activities were not primarily responsible for the vegetation restoration in northern temperate grasslands and Qinghai-Tibet Plateau alpine grasslands, but they could decrease and even cancel the possible vegetation degeneration caused by worsening climate in a few regions. Long-term monitoring of vegetation dynamics and a multi-method comparison are needed in future studies.

[Spatial-temporal Variations and Their Driving Forces of the Ecological Vulnerability in the Loess Plateau].

The Loess Plateau is one of the most eco-fragile regions in China, and therefore the scientific evaluation of its ecological vulnerability provides a premise for the effective implication of ecological protection and management practices. However, previous studies have mainly focused on the ecological vulnerability in a small region, which cannot reflect the overall picture of the ecological vulnerability in the Loess Plateau. Based on the "exposure-sensitivity-adaptation" framework, this study investigated the spatial-temporal patterns and their driving forces of the ecological vulnerability in the Loess Plateau from 2000 to 2015 through a combined use of the analytic hierarchy process, spatial principal component analysis, and Geodetector analysis. The results showed that the ecological vulnerability was overall at a moderate to high level, and the vulnerability was clearly higher in the northwestern part of the Loess Plateau than that in the southeastern counterparts. Additionally, the ecological vulnerability differed greatly by land use type. The ecological vulnerability decreased after an increase from 2000 to 2015 and in general decreased slightly throughout the study period. Therein, approximately 64% of the total land area experienced an upward or downward trend in the vulnerability. Vegetation coverage and precipitation were the two main factors contributing to the spatial-temporal variability in the ecological vulnerability, and there were significant interactions among all the used indicators. This study suggests that climate change and human activities may help reduce the ecological vulnerability over the Loess Plateau, although their contributions are limited.

[Impact of the Beijing and Tianjin Sand Source Control Project on the grassland soil organic carbon storage: a case study of Xilingol League, Inner Mongolia, China].

Understanding the impacts of eco-construction project on grassland soil carbon storage is crucial to assess the effectiveness of the project and its role in carbon cycling of the grassland ecosystems. Using IPCC carbon budget inventory method, this paper analyzed the influence of Beijing and Tianjin Sand Source Control Project (BTSSCP) on the grassland soil carbon storage between 2000 and 2006 in Xilingol League, Inner Mongolia, and evaluated the time needed to reach the maximal soil carbon density for three management practices (i. e. , sown pasture, aerial sowing pasture, and grazing exclosure). Results showed that the BTSSCP significantly increased soil carbon storage, with a carbon sequestration of 59.26 x 10(4) t C from 2000 to 2006. The rate and effectiveness of soil carbon sequestration varied significantly with management practices, with the highest rate in sown pasture (0.25 t C x hm(-2) x a(-1)) while a greater benefit of soil carbon sequestration in the grazing exclosure (63 million yuan). Compared with other grassland vegetations, lowland meadow and temperate meadow steppe both had higher carbon sequestration rates of 0.14 t C x hm(-2) x a(-1). Long time would be needed to reach the maximum soil carbon density in grassland under the three practices, yet shorter for sown pasture with average of 57.75 years.