Current challenges in distinguishing climatic and anthropogenic contributions to alpine grassland variation on the Tibetan Plateau

Abstract

Quantifying the impact of climate change and human activities on grassland dynamics is an essential step for developing sustainable grassland ecosystem management strategies. However, the direction and magnitude of climate change and human activities in driving alpine grassland dynamic over the Tibetan Plateau remain under debates. Here, we systematically reviewed the relevant studies on the methods, main conclusions, and causes for the inconsistency in distinguishing the respective contribution of climatic and anthropogenic forces to alpine grassland dynamic. Both manipulative experiments and traditional statistical analysis show that climate warming increase biomass in alpine meadows and decrease in alpine steppes, while both alpine steppes and meadows benefit from an increase in precipitation or soil moisture. Overgrazing is a major factor for the degradation of alpine grassland in local areas with high level of human activity intensity. However, across the entire Tibetan Plateau and its subregions, four views characterize the remaining controversies: alpine grassland changes are primarily due to (1) climatic force, (2) nonclimatic force, (3) combination of anthropogenic and climatic force, or (4) alternation of anthropogenic and climatic force. Furthermore, these views also show spatial inconsistencies. Differences on the source and quality of remote sensing products, the structure and parameter of models, and overlooking the spatiotemporal heterogeneity of human activity intensity contribute to current disagreements. In this review, we highlight the necessity for taking the spatiotemporal heterogeneity of human activity intensity into account in the models of attribution assessment, and the importance for accurate validation of climatic and anthropogenic contribution to alpine grassland variation at multiple scales for future studies.

Climate Variability Rather Than Livestock Grazing Dominates Changes in Alpine Grassland Productivity Across Tibet

“…Quantifying the key ecosystems' dynamics controlling factors is crucial for ecological management and adaptation (Li L. et al, 2018;Wei et al, 2020). Alpine grasslands in Tibet are one of the most vulnerable biomes to human activities and climate change in the world.…”

“…A better understanding of how ecosystem ANPP responds to climate change and human activities can help mitigate environmental damages and optimize ecosystem management (Zhou et al, 2018). A considerable volume of literature tried to identify and quantify the relative influences of climate change and human activities on ecosystem productivity with various methods (Paudel and Andersen, 2010;Erb et al, 2018;Li L. et al, 2018), such as manipulative experiments, traditional statistical analysis, and residuals-trend modeling (Li L. et al, 2018). Recently, random forest modeling, with high accuracy and robust efficiency, is increasingly being used to quantify predictors' relative importance (Gill et al, 2017;Huang and Xia, 2019).…”

Spatiotemporal Patterns of Vegetation Greenness Change and Associated Climatic and Anthropogenic Drivers on the Tibetan Plateau during 2000–2015

“…For example, growing season NDVI (GNDVI) derived from GIMMS 3g exhibited a decreasing trend from 2000 to 2012, however, the GNDVI from C5 products of MODIS Terra remained showing increasing trends for the same period on the TP [23][24][25]. Moreover, these inconsistencies of vegetation changing trends might further intensify the ongoing disputes over drivers for vegetation dynamics on the TP [24][25][26][27]. Studies based on GIMMS 3g NDVI, for example, have found a positive correlation between vegetation greenness and temperature [28,29], whereas studies based on MODIS Terra-C5 NDVI argued that climate warming adversely affected vegetation growth [24].…”

“…Such studies were mostly conducted within an individual factor perspective, e.g., road network and settlement locations. The role of human activities is becoming more and more important in influencing vegetation change [27]. Several studies even argued that anthropogenic activities were the primary contributors to changes in one-third alpine vegetation on the TP since 2000 [33,40].…”

Quantitative Analysis of the Research Trends and Areas in Grassland Remote Sensing: A Scientometrics Analysis of Web of Science from 1980 to 2020

“…The research methods mainly used the Carnegie-Ames-Stanford approach based on remote sensing [18], MODIS vegetation indexes, the random forest or random forest regression algorithm, modeling, and WorldView-2 imaging [97,98]. The research focused on the biophysical characteristics, phenological processes [12,74], and grassland management characteristics (degradation and grazing effects), and differentiated between the contributions of the influences of climate change and anthropogenic activities to NPP [99][100][101][102]. These can better predict future climate to help cope with the impact of global climate change on humans and to more quickly achieve sustainable development goals.…”