Could drought constrain woody encroachers in savannas?
Could drought constrain woody encroachers in savannas?
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干旱能否限制稀树草原上的木本入侵者？
DOI：
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
A. Carla Staver
中科院分区：
文献类型：
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作者：
M. F. Case;B. Wigley;C. Wigley;A. Carla Staver
由于气候变化，干旱预计将变得更加频繁和严重，对稀树草原植被造成不确定的后果。在一些稀树草原上观察到了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有多大，或者是什么决定了物种之间在干旱脆弱性上的差异，人们知之甚少。在这里，我们研究了哪些特征最独特的树种，这些树种最近在南非克鲁格国家公园受到的干旱影响最大。对非结构性碳水化合物的投资相对较低的木本植物、根部吸食物种的死亡率最高。特别令人感兴趣的是Dichrostachys cinerea，它是南部非洲大草原广泛木本植物入侵的显著贡献者，那里遭受了很高的干旱死亡率。利用雨量图和植被调查数据，我们发现克鲁格国家公园灰飞虱的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，而干旱发生频率较高的地区树干密度较低，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。木质侵袭者，如黄花木兰，可能面临促进繁殖和耐旱性之间的权衡，而更频繁和更严重的干旱可能会越来越限制它们的传播。
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.