Abstract
The Three-River Headwaters region (TRHR) of China is an important part of the Qinghai-Tibetan Plateau. Although the TRHR is rich in grassland resources, the ecosystem of this area is extremely fragile. Natural and artificial interference have been key to the development of grassland ecosystem spatiotemporal heterogeneity, although the intensity and mode of their influence on ecological processes varies depending on scale; analyses in this area are therefore also scale-dependent. We use multi-scale nested data to analyze the mechanisms underlying the influence of climate change and human activities on grassland net primary productivity (NPP) by applying a multi-level modeling approach. The results of this study show that: (1) The annual grassland NPP of the TRHR has risen in a wavelike pattern over time, increasing by 39.88% overall; (2) Differences of 54.9% and 41.1% in temporal grassland NPP can be attributed to variations between these watersheds as well as county characteristics, and; (3) Although the ‘warm and moist’ climate trend seen over the course of this study has proved beneficial in enhancing grassland NPP, the rate of increase has tended to be faster in relatively dry and warm regions. Economic development and population growth have both exerted negative impacts on grassland NPP.
Highlights
Grassland ecosystems are important components of ecological communities on Earth[1,2], and perform key functions in carbon (C) cycling, climate regulation, and the maintenance of biological diversity[3,4,5,6]
Our multi-level linear model (MLM) analysis of grassland net primary productivity (NPP) changes within the Three-River Headwaters region (TRHR) shows that about 41.1% of variance can be explained at the county level, while the remaining 54.9% occurs at the level of small watersheds
The results of this study suggest that the long-term impact of NNRs on grassland NPP has not been significant, the productivity of these ecosystems within the TRHR has increased at a faster rate since the initiation of restoration projects and the previous rapid decline has been curbed
Summary
Grassland ecosystems are important components of ecological communities on Earth[1,2], and perform key functions in carbon (C) cycling, climate regulation, and the maintenance of biological diversity[3,4,5,6]. The approaches that are currently used to reveal the relationship between grassland NPP and underlying driving factors include field-based experiments[17,18], trend tests[12,19], and ecosystem modeling[20], and usually integrate ecological processes against the same background Because both natural and anthropogenic disturbances are spatially heterogeneous, a number of previous studies have demonstrated that ecological phenomena tend to manifest in the form of multi-level and multi-hierarchy structures[21,22]; this means that both the intensity and mode of a disturbance that results from either natural or anthropogenic factors will exhibit different characteristics depending on scale[23,24,25,26] and that there will be interactions between these different hierarchical levels[27]. Some previous research has shown that the implementation of these projects has contributed to grassland ecosystem restoration, in particular controlled degradation[45] as well as increased yields[43] and NPP42,46
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