Environmental drivers of above-ground biomass in semi-arid rangelands

Abstract

Above-ground biomass (AGB), as a key biophysical and functional parameter of rangeland ecosystems, plays an important role in ecosystem carbon (C) stocks. The aim of this study was to explore the important environmental drivers of AGB in an arid rangeland by using structural equation modelling (SEM). Vegetation and soil (physical and chemical properties) were sampled using randomised-systematic methods within sampling plots. The topographic (elevation, slope, aspect, hillshade (i.e. a technique for showing the topographical shape of hills and mountains to indicate relative slopes and mountain ridges)) and climatic (mean temperature (MT), mean precipitation (MP), actual evapo-transpiration (AET) and land-surface temperature (LST)) properties were extrapolated using a raster-based digital elevation-model (DEM) map, and their values extracted at each sampling plot. SEM was then applied to assess the direct and indirect impacts of environmental factors on AGB. The AGB was directly affected by soil (41%, P < 0.05) and climatic properties (34%, P < 0.05). The effect of topographical factors on AGB was non-significant (P > 0.05). However, climatic properties were directly affected by topographical properties, with a path coefficient of 34%. Among soil properties, nitrogen, phosphorus and potassium concentrations, silt content and soil pH were the key factors affecting AGB. Climatic variables (MT, MP) were equally effective in explaining the climate latent variable (with loading factors of −0.97 and 0.99 respectively) and AGB changes. This study highlighted the importance of soil and climatic properties in AGB variation. SEM simplified and revealed the complex relationships among ecosystem components affecting AGB, which could assist proper management of rangelands.