Challenges in disentangling the influence of climatic and socio-economic factors on alpine grassland ecosystems in the source area of Asian major rivers

摘要

Climate change and human activities affect ecosystems simultaneously. To distinguish their respective roles, we analyzed the relative impacts of climate change and human activities on alpine grasslands in Northern Tibet, which are the source area of Asian major rivers. The changes and their causes were determined using Normalized Difference Vegetation Index (NDVI) and climatic and socio-economic factors at different intensities of human activity within sampling plots (including depopulated land without human influences) from 1981 to 2006. Mann-Kendall test (MK) was used to test the trend of NDVI change and Pearson correlation analyses was utilized in multiple regressions between NDVI and the influencing factors. Abrupt changes of NDVI occurred at different times in plots that differed in human activity. Regional climate change has produced more negative than positive changes on alpine grasslands. The alpine grasslands significantly benefited under a moderate intensity of grazing activities. With the increased human activity, negative changes in NDVI were pervasive in Northern Tibet.