Rangelands of arid ecosystems are driven by internal and external environmental controls. Grazing pressure is an important anthropogenic driver, but stochastic environmental events such as rainfall variability and prolonged drought can have profound effects on arid vegetation. We investigated the effect of a prolonged drought and initial high grazing pressure on range condition, perennial vegetation cover, life form cover, vegetation composition and vegetation diversity at five monitoring sites in a conservation area in arid Succulent Karoo vegetation. The response of the rocky mountainous vegetation to drought and grazing differed notably from the response of the sandy plains vegetation. Range condition and perennial vegetation cover reduced drastically in all habitats, although the extent of deterioration was less in the mountainous habitats. Annual vegetation cover was associated with inter-annual rainfall variability. Species richness decreased at three of five sites, whereas species evenness increased at three of five sites. Shannon-Wiener index of diversity and Simpson's diversity index trends were inconsistent. Vegetation composition changed directionally from a quasi-stable state in all five monitoring sites as the drought persisted. The extent of the change was less in mountainous habitats indicating potentially higher resilience than in plains habitats, though grazing pressure was lower in the mountains than on the plains over the study period. The existence of quasi-stable states, together with the observed directional changes in vegetation composition in response to both drought and grazing, indicated that both equilibrium and non-equilibrium vegetation dynamics apply.

干旱生态系统的牧场受到内部和外部环境控制的驱动。放牧压力是一个重要的人为驱动因素，但降雨量变化和长期干旱等随机环境事件可能对干旱植被产生深远影响。我们在干旱多肉卡鲁植被保护区的五个监测点调查了长期干旱和初始高放牧压力对牧场条件、多年生植被覆盖、生命形式覆盖、植被组成和植被多样性的影响。岩石山地植被对干旱和放牧的反应与沙质平原植被的反应明显不同。所有栖息地的范围状况和多年生植被覆盖都急剧减少，尽管山区栖息地的恶化程度较小。年度植被覆盖度与年际降雨量变化相关。五个地点中的三个的物种丰富度下降，而五个地点中的三个的物种均匀度增加。Shannon-Wiener多样性指数与Simpson多样性指数趋势不一致。随着干旱的持续，所有五个监测点的植被组成都从准稳定状态发生了方向性变化。尽管在研究期间山区的放牧压力低于平原，但山区栖息地的变化程度较小，表明其恢复能力可能高于平原栖息地。准稳定状态的存在，以及观察到的植被组成响应干旱和放牧的方向变化，表明平衡和非平衡植被动态都适用。