The spatial heterogeneity of vegetation in a communal grazing system provides pastoralists with a range of grazing sites to select for their livestock. When fencing spatially constrains herds, there is reduced access to ecological heterogeneity, which may have a negative impact on livestock and the grazing resource. This study investigated temporal and spatial changes in stocking densities and distribution within the six major vegetation types of the Leliefontein pastoral area in Namaqualand, South Africa. This semi-arid, biodiverse area of about 2000 km² supports a spatially-constrained mobile pastoral system based on small stock production. Over the data period from 1999 to 2006, the location of 256 small stock herds, their temporal occupancy and herd size were used to determine stocking densities within the daily grazing radius of herds. These grazing radii were overlaid using GIS to produce stocking density distributions over the landscape. The density and location of herds were unevenly distributed when assessed monthly and annually. Parts of the study area were consistently overstocked whereas others remained ungrazed. We argue that the recommendation of fixed stocking rates within this variable environment is inappropriate because forage availability and quality fluctuate within and between years and within drought cycles. We conclude that development interventions should rather focus on reducing stocking densities during and after drought periods. This would benefit pastoralists through reduced livestock mortalities and the vegetation would recover more quickly from the impacts of drought.

公共放牧系统中植被的空间异质性为牧民提供了一系列放牧地点以供其牲畜选择。当围栏在空间上限制畜群时，会减少获得生态异质性的机会，这可能对牲畜和放牧资源产生负面影响。本研究调查了南非纳马夸兰 Leliefontein 牧区六种主要植被类型的放养密度和分布的时空变化。这个半干旱、生物多样性的区域约 2000 平方公里²支持基于小牲畜生产的空间受限的移动牧区系统。在 1999 年至 2006 年的数据期间，使用 256 个小畜群的位置、它们的时间占有率和畜群规模来确定畜群每日放牧半径内的放养密度。使用 GIS 覆盖这些放牧半径，以产生整个景观的放养密度分布。每月和每年评估时，畜群的密度和位置分布不均。研究区域的部分地区持续积压，而其他地区则没有放牧。我们认为，在这种可变环境中推荐固定放养率是不合适的，因为草料的可用性和质量在年份之间和年份之间以及干旱周期内波动。我们得出的结论是，发展干预应更侧重于减少干旱期间和之后的放养密度。这将通过减少牲畜死亡率而使牧民受益，并且植被将更快地从干旱的影响中恢复。