Droughts are expected to become more frequent and severe, due to climate change, with uncertain consequences for savanna vegetation. Drought-driven tree mortality has been observed in some savannas, but little is known about how tolerant savanna trees are to drought, or what determines differences among species in drought vulnerability. Here, we examine which characteristics best distinguished tree species that were most negatively affected by a recent drought in Kruger National Park, South Africa. Woody-encroaching, root-suckering species, which tended to have relatively low investments in non-structural carbohydrates, had the highest mortality rates. Of particular interest was Dichrostachys cinerea, a notable contributor to widespread woody encroachment across southern African savannas, which suffered high drought mortality. Using rainfall maps and vegetation survey data, we show that D. cinerea distributions in Kruger National Park are limited to areas with higher mean annual rainfall and lower past drought frequency, and stem densities are lower where droughts have occurred more frequently, suggesting that past droughts have had lasting impacts on the distribution and abundance of this species. Woody encroachers, such as D. cinerea, may face a trade off between traits promoting proliferation vs. drought tolerance, and more frequent and severe droughts could increasingly limit their spread.

中文翻译：

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干旱会限制热带稀树草原的木本侵占者吗？

由于气候变化，干旱预计将变得更加频繁和严重，对热带稀树草原植被造成不确定的后果。在一些稀树草原中已经观察到干旱导致的树木死亡，但关于稀树草原树木对干旱的耐受性如何，或者决定物种之间干旱脆弱性差异的因素知之甚少。在这里，我们研究了哪些特征最能区分受南非克鲁格国家公园最近干旱影响最大的树种。对非结构性碳水化合物的投资往往相对较低的木本侵占、吸根物种的死亡率最高。尤其令人感兴趣的是 Dichrostachys cinerea，它是导致非洲南部热带稀树草原大面积木本侵占的显着贡献者，干旱死亡率很高。使用降雨图和植被调查数据，我们表明克鲁格国家公园的 D. cinerea 分布仅限于年平均降雨量较高和过去干旱频率较低的地区，并且在干旱发生频率较高的地区茎密度较低，这表明过去的干旱对该物种的分布和丰度产生了持久的影响。木质侵染者，如 D. cinerea，可能面临促进增殖与耐旱性之间的权衡，更频繁和更严重的干旱可能会越来越多地限制它们的传播。表明过去的干旱对该物种的分布和丰度产生了持久的影响。木质侵染者，如 D. cinerea，可能面临促进增殖与耐旱性之间的权衡，更频繁和更严重的干旱可能会越来越多地限制它们的传播。表明过去的干旱对该物种的分布和丰度产生了持久的影响。木质侵染者，如 D. cinerea，可能面临促进增殖与耐旱性之间的权衡，更频繁和更严重的干旱可能会越来越多地限制它们的传播。