Climate change as the major driver of alpine grasslands expansion and contraction: A case study in the Mt. Qomolangma (Everest) National Nature Preserve, southern Tibetan Plateau

To assess the spatial patterns of alpine grassland changes (expansion and contraction) and their responses to climate changes in the context of global change in recent years on the southern Tibetan Plateau, the Mt. Qomomagma National Nature Preserve (QNNP), covering an area of 36 594 km2 and located on the southern Tibetan Plateau was selected as the study area. Alpine grassland cover was obtained by image reclassification of more than five pairs of remote sensing images taken in 1976–2006. Expansion and contraction were determined by cover changes in alpine grassland and expressed as binary variables. Logistic regression was then used to analyze the impacts of climatic-, neighborhood-, and topographic-related variables on alpine grassland changes. In the study period, the area of alpine grassland increased by 84.3 km2. The expansion rate is significantly higher on the gentle slopes with higher mean annual temperature (MAT), inter-annual variability trend of temperature (IVT), and inter-annual variability trend of precipitation (IVP), and also in areas close to lakes and distant from roads. While most contraction is found on the gentle slopes and in areas close to streams, lakes, and roads; the MAT is also a significant driven impact factor. Alpine grassland expansion and contraction in the QNNP were significantly affected by MAT but not by mean annual precipitation (MAP). The IVT and IVP had significant effects on alpine grassland expansion but not on contraction. The results contradict the prevailing view that climate changes, such as increased temperature with decreased precipitation, would exacerbate grassland degradation on the Tibetan Plateau. This study indicated that climate changes have different effects on alpine grassland changes in different areas of the Tibetan Plateau.