Drought limits large trees in African savannas with or without elephants
Drought limits large trees in African savannas with or without elephants
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干旱限制了非洲大草原上有或没有大象的大树
DOI：
10.1111/aec.13244
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发表时间：
2022
期刊：
影响因子：
1.5
通讯作者：
McCleery, Robert
中科院分区：
文献类型：
--
作者：
Jones, Maggie M.;Fletcher, Robert;Kruger, Laurence;Monadjem, Ara;Simelane, Phumlile;McCleery, Robert
消费者，包括大型食草动物和火灾，被认为是非洲稀树草原木本植物和树冠关闭的重要限制力量。然而，干旱等气候事件也可以在限制稀树草原上的树木和维持树与草的共存方面发挥重要作用。自上而下的控制（例如大型食草动物）和通过干旱和竞争进行的自下而上的资源限制相互作用，影响稀树草原树木死亡率和木本结构的程度尚不清楚。在这里，我们比较了有大象（Loxodonta africana）和没有大象的稀树草原严重干旱前后大树数量的变化。大象和干旱都限制了我们所在地大树的数量，但与我们的预测相反，这些驱动因素对树木密度的总体变化没有交互影响。然而，对占主导地位的树种塞内加尔黑树存在协同效应，因此与大象不在的地方相比，干旱后树木损失更大。因此，我们的结果表明，物种特异性的抗旱性差异以及密度依赖因素可能会影响干旱对稀树草原树木群落影响的严重程度。在稀树草原上，干旱有可能对树木的生存产生强有力的控制，并防止树冠关闭，从而部分填补了大型食草动物在缺乏消费者时限制大型树木的作用。由于预计未来干旱的严重程度和频率将会增加，干旱对稀树草原植被结构的影响变得越来越重要。
Consumers, including megaherbivores and fire, are considered important limiting forces for woody plants and canopy closure in African savannas. However, climatic events like drought can also play a significant role in limiting trees and maintaining tree‐grass coexistence in savannas. The extent to which top‐down control (e.g. megaherbivores) and bottom‐up resource limitation through drought and competition interact to influence savanna tree mortality and woody structure is unclear. Here, we compared the change in the number of large trees before and after a severe drought in a savanna with elephants (Loxodonta africana) and one without elephants. Elephants and drought both limited the number of large trees at our sites, but contrary to our predictions, there was no interactive effect of these drivers on overall changes in tree densities. However, there was a synergistic effect on the dominant tree species,Senegalia nigrescens, such that tree loss post‐drought was greater where elephants were present compared to where they were absent. Hence, our results suggest that species‐specific differences in drought resistance, as well as density‐dependent factors, likely impact the severity of drought effects on savanna tree communities. In savannas, drought has the potential to exert strong control on tree survival and prevent canopy closure, thus partially filling the role of megaherbivores in limiting large trees when these consumers are absent. As drought severity and frequency are predicted to increase in the future, the influence of drought on savanna vegetation structure becomes increasingly important to consider.
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