A spreadsheet model for the assessment of sustainable stocking rate in semi-arid and sub-humid regions of Southern Africa

Focusing on the issue of veldt degradation and grazing pressure on rangelands, a simplified model was constructed for a sustainable stocking rate (SR) evaluation of the complex system of semi-arid and scab-humid regions in Southern Africa. The model considers the current activity in Southern Africa of multispecies herding, which allows a better utilization of vegetation and has a positive effect on plant and animal biodiversity. The model is intended as a practical and flexible tool supporting practical decision-making mainly at a local level, e.g. by extension services. It relies strongly on indigenous knowledge and flexibility. Users are therefore the main sources of information for the required inputs. The model combines the complexity of the range ecosystem with accuracy and precision of SR evaluation, while minimising input data requirements. The assessment of a grazing pressure compatible with the conservation of rangeland is based on a nutritional approach. Stocking rate (SR) is evaluated on the basis of the selected diet and total dry matter and energy intake. For a sustainable use of rangeland, forage availability is assumed to be the maximum consumption rate for each of the vegetation components (trees, shrub, grass) which does not endanger the long-term production of the vegetation. The whole model deals with a 12-month or a season period and it works on a regional :scale, a portion of land surface delimited by its intrinsic physical, biological and socioeconomical characteristics, with a minimum dimension of 100 km(2). The regional area under investigation is first divided into Grazing Unit Areas (GUA) homogenous in terms of their topography, soils, and vegetation cover. Results consist of three stocking rates (minimum, intermediate and maximum) calculated from a full consumption of the forage available on each of the vegetation components according to their respective levels of availability. After the discussion of the model, results of a case study are presented. (C) 1999 Elsevier Science B.V. All rights reserved.