Responses of green fractional vegetation cover of alpine grassland to climate warming and human activities

The alpine grassland ecosystem is sensitive to climate warming and human activities. Estimation of green fractional vegetation cover (GFVC) is important for acquiring the growing condition of vegetation and assessing the effects of restoration of degraded grassland. At present, the most popular method for estimating GFVC on the ground is to acquire it from digital pictures. This method estimates GFVC from multispectral pictures and it is relatively accurate and effective. In this study, we used the Agricultural Digital Camera (ADC) to estimate GFVC of alpine grassland on different succession stages and in those grazebanning and tillage zones over the growing season of the source region of Shule River. We improved the thresholdmethod for estimating GFVC by using different thresholds in different plots. Main results are as follows: 1) There is no significant difference between the results estimated from the new threshold method and real values (P=0.219), while the results processed by the old threshold method are significantly different from real values (P=0.001). 2) Different types of grassland in different succession stages has different GFVC, and the GFVC of swamp meadow is higher than others. However, all of them reach the highest value in July. 3) In the permafrost regions, where the productivity of grassland is low, effects of grazebanning is not obvious in a short term, and tillage can even further reduce the GFVC of alpine grassland.