Biomass estimation of alpine grasslands under different grazing intensities using spectral vegetation indices

Abstract

We measured and analyzed the spectral reflectance characteristics and biophysical properties such as biomass and vegetation cover of purple feather-grass (Stipa purpurea) alpine steppe grassland under different grazing intensities (no grazing, light, moderate, and heavy grazing) during the growing season. We investigated the effects of grazing intensities on the spectral reflectance and red edge parameters of S. purpurea alpine steppe grassland and established potential models of biomass estimation based on the relationship of spectral vegetation indices and measured alpine grassland biomass in Northern Tibet, China. The results indicated that the spectral reflectance of alpine grassland is similar to the spectral characteristics of typical green vegetation. Reflectance in the near-infrared region of the no grazing treatment was higher than the grazing treatments, while the reflectance of the no grazing treatment in the visible light region was weaker than the grazing treatments. With enhanced grazing intensity, the spectral reflectance of grass canopy followed an increasing trend; the red edge position moved to longer wavelengths, and the amplitude of the red edge decreased in alpine grassland. A significant relationship of measured aboveground biomass and vegetation indices was caculated based on spectral reflectance. Hence, the optimized soil adjusted vegetation index is prefered for the estimation of aboveground biomass of S. purpurea alpine steppe in Northern Tibet, China.