In the Nama-Karoo, South Africa, rainfall and grazing by livestock are two important drivers of botanical composition. Summer rains are advantageous particularly to the grass layer, whereas the characteristic dwarf shrubs survive better than grasses during drought, and benefit from rainfall during cool months. Heavy grazing by livestock during summer reduces the abundance of grasses, whereas winter grazing increases it. This study examined the influences of season of grazing (summer vs winter) and rainfall on botanical composition at two long-term grazing trials at Grootfontein in the eastern Karoo from 1949 to 1967. Severe summer grazing strongly reduced grass abundance and slightly increased the abundance of both palatable and unpalatable dwarf shrubs. High previous-season rainfall strongly promoted short-lived grasses. Dwarf shrubs and grasses declined in response to a decline in annual rainfall over the study period, except for the creeping grass Tragus koelerioides that increased in abundance, possibly in response to decreased competition and an increase in available gaps in the vegetation layer. Results indicate that grazing systems that exclude repeated summer-only grazing maintain ecological health, and that rainfall is the main driver of composition unless extreme grazing systems are employed.

中文翻译：

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放牧季节和降雨对南非东部卡鲁植被的长期影响

在南非的纳马卡鲁，降雨和牲畜放牧是植物组成的两个重要驱动因素。夏季降雨对草层特别有利，而特征性矮灌木在干旱期间比草更能存活，并在凉爽月份受益于降雨。夏季牲畜大量放牧减少了草的丰度，而冬季放牧则增加了草的丰度。本研究于 1949 年至 1967 年在卡鲁东部格鲁特方丹的两次长期放牧试验中检查了放牧季节（夏季与冬季）和降雨对植物成分的影响。严重的夏季放牧强烈降低了草的丰度，并略微增加了草的丰度。可口和不可口的矮灌木。前一季的高降雨强烈促进了短命草的生长。矮灌木和草在研究期间随着年降雨量的减少而减少，但匍匐草 Tragus koelerioides 的丰度增加，这可能是由于竞争减少和植被层中可用间隙的增加。结果表明，排除重复夏季放牧的放牧系统保持生态健康，除非采用极端放牧系统，否则降雨是构成的主要驱动因素。