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.

Keywords: Tibetan Plateau; alpine grassland; climate change; degradation; human activity intensity; validation.

Figure 1

Spatial distribution of topographic feature (a) and typical vegetation types (b) on the Tibetan Plateau

Figure 2

Spatial distribution of attributions for alpine grassland NPP change during (a) 1982–2001 (Chen et al., 2014), (b) 2002–2011 (Chen et al., 2014), (c) 2000–2013 (Wang, Zhang, et al., 2016), and (d) 2000–2004 and 2004–2012 (Xu et al., 2016). Human footprint pressure was mapped in (e) 1993 and (f) 2009 (Venter et al., 2016a, 2016b). In abbreviations in the legends of a‐d panels, I indicates an increase in NPP, D indicates a decrease in NPP, C indicates a change in NPP due to climatic factors, and H indicates a change in NPP due to human activities

Figure 3

Comparison of the mean growing season (May–September) NDVI on the Tibetan Plateau from different sources. Pixels with growing season NDVI lower than 0.10 are not considered

Figure 4

Conceptual graph of climatic and anthropogenic impacts on alpine grassland variation. In wilderness areas, such as northwest Tibetan Plateau, climate change plays a leading role, while in some regions close to roads, settlements, and urban areas, human disturbance determines grassland variation. In addition to human disturbance and climate change, other attributions still exist, for example, the consumptions of wild animals, both in wilderness areas and human‐disturbed areas

Figure 5

Assessment framework for determining the attributions to alpine grassland change at multiple scales