The effects of drought and stocking density on vegetation productivity and the resilience of rangelands in Lesotho

Abstract

A significant portion of southern Africa is used for livestock production – both commercial and subsistence. The productivity of these natural grasslands depends, to varying degrees, on the soils and rainfall, as well as historical land management practices. Livestock farming practices may affect rangeland productivity, depending on the stocking rate, type of livestock and management activities. Moreover, these rangeland systems are also subject to periodic droughts, which can result in livestock mortality. How ecosystems respond to these droughts, and recover from these droughts, is likely to be, to an extent, affected by the previous history of stocking. Several studies on the effects of droughts on ecological processes in rangelands have been conducted and documented. However, the interactive effects of stocking practices and droughts on these rangelands are still poorly understood, despite the anticipated increase in both livestock populations and global change stressors such as droughts. Such a knowledge gap hampers development of effective mitigation strategies in these ecosystems. This study aims to investigate the relative impact of droughts (with reference to the 2015/2016 drought) and stocking densities on rangelands of Lesotho, and to determine the resilience of these ecosystems after perturbations. Such findings provide a conceptual framework for better understanding and appropriately managing ecosystems. The study was conducted in Lesotho, where long-term rainfall and stocking rates for different years were used to identify their combined effects on vegetation cover. The results show that droughts had a pronounced impact on vegetation productivity while the impacts of stocking rates were not really significant. However, a significant relationship between the altitude and stocking rates was observed (P= 0.032). In particular, the lowlands rangelands of Lesotho are relatively more heavily stocked than the mountain region. Similarly, vegetation loss was more evident in the lowlands region during drought episodes, although the mountain region showed a slower recovery after drought. This relatively slow recovery could possibly be related to low temperatures and shorter growing season in the mountain region.