Quantitative monitoring of grazing intensity in the temperate meadow steppe based on remote sensing data

摘要

Grazing intensity (GI) is difficult to measure accurately because of the diversity of grazing livestock, their mobility in the grazing space and the uncertainty of grazing times. Thus, GI monitoring is often only qualitative, while quantitative monitoring is scarce. In this study, models correlating GI, the normalized difference vegetation index (NDVI) and aboveground biomass (AGB) were established based on a controlled GI experiment. The GI derived from NDVI was evaluated using the GI derived from AGB samples, under the principle that AGB is similar for the same GI in the same grassland type. The results showed that the appropriate time to build the model in the study area was from July to August, when there was a negative correlation between GI and NDVI. The simulated GI derived from NDVI was similar to GI derived from AGB, and the R-2 (coefficient of determination) values for fresh weight and dry weight were 0.3770 and 0.4292, respectively; the root mean square error (RMSE) were 0.2302 and 0.1953 animal units (AU) ha(-1) (1AU=500kg of adult cattle); and the relative error from -20% to 20% accounted for 62.07% and 72.41% of the total samples. Most of the study area was under heavy grazing according to monitoring results from 2010 to 2016, except for a few pastures with rational utilization (0.23AU ha(-1) - 0.46AU ha(-1)), and continuous heavy grazing often occurred for many years without rest grazing.