The importance of large trees for grazing ungulates in African savannas

非洲稀树草原利用不同种类的植被结构，容纳了高度多样化的野生动物物种。不同的降雨模式和土壤肥力创造了一个连续的草本层，点缀着巨大的稀树草原树。这些树木可以增加其林下植被的营养含量，从而为放牧野生动物提供有吸引力的觅食场所。然而，由于伐木活动的增加和一些保护区大象密度的增加，大面积的树木覆盖率正在下降。这可能会导致食草性有蹄类动物的数量减少，这些有蹄类动物通过选择高质量的饲料来优化它们的食物摄入量。我们汇编了在东部和南部非洲收集的植物营养含量的数据，以及对野生有蹄类物种最低营养需求的估计。我们将比较树冠下的草和开阔草原地区的草的营养质量，并使用线性优化模型来确定树木环境对放牧有蹄类物种的重要性。我们推测，由于周围稀树草原饲草料的质量较低，这些物种最好在树冠下觅食。我们将把沿降雨量和土壤养分含量梯度的不同稀树草原的信息与非洲的地理地图结合起来。然后我们可以确定野生动物在树冠下的使用量应该很高的地区。因此，我们可以根据不同稀树草原类型的树木覆盖预测未来野生动物丰度的模式，以便相应地应用管理和保护决策。

African savannas accommodate a high diversity of wildlife species utilising a mosaic of heterogeneous vegetation structure. Varying rainfall patterns and soil fertility create a continuous herbaceous layer, interspersed by large savanna trees. These trees can increase the nutrient content of their understorey vegetation and thereby generate attractive feeding sites for grazing wildlife. Large tree cover, however, is declining due to increased logging activities and elevated elephant densities in some protected areas. This may lead to a decline in the abundance of herbivorous ungulates that optimise their food intake by choosing high quality forage. We compile data on plant nutrient contents collected in Eastern and Southern Africa, together with estimates about minimal nutrient requirements of wild ungulate species. We will compare the nutrient quality of grasses underneath canopies with grasses in open savanna areas and use linear optimisation models to identify the importance of tree environments for grazing ungulate species. We hypothesize that these species will preferably feed beneath canopies due to the low quality of fodder grasses in surrounding savanna grasslands. We will combine information on different savannas along a gradient of rainfall and soil nutrient content with geographic maps of Africa. We then can identify areas where wildlife use underneath canopies should be high. Hence, we can predict future patterns of wildlife abundance with respect to tree cover in different savanna types such that management and conservation decisions can be applied accordingly.