Assessing light to moderate grazing effects on grassland production using satellite imagery

Abstract

Understanding the influences of grazing intensity on grassland production is essential for grassland conservation and management improvement. Grazing at light to moderate intensity theoretically enhances grassland production, thus benefiting grassland ecosystems. However, inconsistent results of the beneficial effects of light to moderate grazing on grassland production were reported due to the lack of accurate and repeatable techniques for discriminating grazing effects from other abiotic factors. Advanced remote-sensing techniques provide a promising tool for filling this gap in grazing effects research due to their high spatial and temporal resolution. In this article, the influences of light to moderate grazing on grassland production in mixed grasslands were investigated for the period 1986–2005, using spectral data derived from satellite images. The effects of precipitation on the detection of grazing-induced production change were also analysed. The results revealed that the normalized canopy index (NCI) showed superior performance in quantifying grassland production in mixed grasslands. Significant differences in grassland production between grazed and ungrazed treatments occurred in the three years with above-average and average growing-season precipitations (April–August), but not in the dry years. Most of the variation in production (75%) was explained by growing-season precipitation for both grazed and ungrazed sites. Our results demonstrate the feasibility of using remote-sensing data to monitor long-term light to moderate grazing effects and the important role of precipitation, especially growing-season precipitation, in modulating production in mixed-grassland ecosystems.