On modelling the relationship between vegetation greenness and water balance and land use change

Abstract

Here we sought a biologically meaningful, climate variable that captures water-energy availability and is suitable for high resolution (250m×250m) modelling of the fraction of photosynthetically active radiation intercepted by the sunlit canopy (FV) derived from a 10-year (July 2000 – June 2010) time series of Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized diference vegetation index (NDVI) satellite imagery for Australia. The long-term mean annual evaporation defcit, and mean annual water availability indices all yielded strong linear relationships with mean FV (FV, %). We hypothesised whether some of the scatter about the relationships was related to land-use changes that have disrupted the vegetation-climate-soil equilibrium. Using continental-scale spatial data layers of protected area status and vegetation condition classes we repeated our analyses with restricted datasets. FV of intact native vegetation within protected areas was greater than all modifed vegetation classes. There was a consistent decline in the slopes of the regression relationships with increasing intensity of woody vegetation clearing and livestock grazing. Where native vegetation has been transformed by land use there was a 25% reduction in predicted FV.