Grazing gradient detection and assessment in arid rangelands of central Iran using remote sensing and soil-vegetation characteristics

摘要

One key tool to manage fragile ecosystems in arid lands is knowledge of land degradation. For this purpose, field-based soil and vegetation characteristics were related to remote sensing information extracted from Landsat OLI moving standard deviation index (MSDI), normalised difference vegetation index (NDVI), soil-adjusted vegetation index (SAVI) and modified soil-adjusted vegetation index (MSAVI) in degraded (watering points and livestock camps) and reference sites of arid rangelands of Iran. Values of spectral indices along grazing gradients at a distance of 50-1500 m from the centre of degradation were also extracted and analysed. Statistical analysis (t-test and ordination analysis) shows that MSDI is a sensitive index of landscape heterogeneity and, unlike other indices, exhibits a significant difference between degraded and reference sites. MSDI was sensitive to grazing gradients around watering points and livestock camps, and declined with increasing distance from these areas, although this varied between different sites due to grazing intensity and characteristics of soil and vegetation cover. Soil analysis showed that the amount of organic carbon, mean weight diameter (MWD), geometric mean diameter (GMD) and soil stability indicator (SSI) at reference sites were significantly higher than those at degraded areas. Ordination analysis confirmed the results of t-test regarding the high potential capability of MSDI in separating degraded areas. This simple and practical index can be used to determine ecological thresholds and investigating rangeland condition in arid ecosystems.