干旱区生态环境知识资源中心

A new approach was developed to evaluate the implications of the spatiotemporal variability of green vegetation for the dispersion of livestock that is required to access quality forage in semi-arid Africa. Maximum NDVI (Normalized Difference Vegetation Index) at 1 km(2) resolution was determined for concentric rings (0-31 km radii) around 227 individual sample locations within the study area for 14 dates (between 1 April to 1 November) annually over the 2000-2010 period. A sigmoidal curve was fitted to points within the maximum NDVI x distance radii space to determine the asymptote distance (AD) - the radius at which further dispersion from the sample location does not lead to significant gains in access to green forage. AD was found to: increase with latitude (or increasing aridity); decline as the rainy season proceeds; and show no trend over the 2000-2010 period. These results introduce much-needed empirical data to current debates surrounding the scales of governance to support livestock mobility.