Water sources in arid and semiarid ecosystems support humans, wildlife, and domestic animals, forming nodes of activity that sculpt surrounding plant communities and impact critical grazing and soil systems. However, global aridification and changing surface water supply threaten to disrupt these water resources, with strong implications for conservation and management of these ecosystems. To understand how effects of herbivore aggregation at water impact plant communities across contexts, we measured herbivore activity, plant height, cover (trees, grasses, forbs, and bare ground), diversity, and composition at 17 paired water sources and matrix sites across a range of abiotic factors in a semiarid savanna in Kenya. The effects of proximity to surface water and herbivore aggregation on plant communities varied substantially depending on soil and rainfall. In arid areas with nutrient-poor sandy soils, forb and tree cover were 50% lower at water sources compared to neighboring matrix sites, bare ground was 20% higher, species richness was 15% lower, and a single globally important grazing grass (Cynodon dactylon) dominated 60% of transects. However, in mesic areas with nutrient-rich finely textured soils, species richness was 25% higher, despite a 40% increase in bare ground, concurrent with the decline of a dominant tall grass (Themeda triandra) and increase in C. dactylon and other grass species near water sources. Recent rainfall was important for grasses; cover was higher relative to matrix sites only during wet periods, a potential indication of compensatory grazing. These findings suggest that effects of herbivore aggregation on vegetation diversity and composition will vary in magnitude, and in some cases direction, depending on other factors at the site. Where moisture and nutrient resources are high and promote the dominance of few plant species, herbivore aggregations may maintain diversity by promoting grazing lawns and increasing nondominant species cover. However, in arid conditions and sites with low nutrient availability, diversity can be substantially reduced by these aggregations. Our results highlight the importance of considering abiotic conditions when managing for effects of herbivore aggregations near water. This will be particularly important for future managers in light of growing global aridification and surface water changes.

中文翻译：

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水源中食草动物聚集对稀树草原植物的影响因土壤和气候梯度而异

干旱和半干旱生态系统中的水源支持人类、野生动物和家畜，形成活动节点，塑造周围植物群落并影响关键的放牧和土壤系统。然而，全球干旱化和不断变化的地表水供应有可能破坏这些水资源，对这些生态系统的保护和管理产生重大影响。为了了解食草动物聚集在不同环境中对植物群落的影响，我们测量了 17 个配对水源和基质地点的食草动物活动、植物高度、覆盖率（树木、草、杂草和裸地）、多样性和组成。肯尼亚半干旱稀树草原中的一系列非生物因素。接近地表水和食草动物聚集对植物群落的影响因土壤和降雨量而异。在营养贫乏的沙质土壤干旱地区，与邻近基质地点相比，水源处的杂草和树木覆盖率低 50%，裸地高 20%，物种丰富度低 15%，单一的全球重要牧草（Cynodon dactylon ) 占断面的 60%。然而，在营养丰富的细质地土壤的中产区，尽管裸地增加了 40%，但物种丰富度却高出 25%，同时优势草（Themeda triandra）的减少和C. dactylon 的增加和其他靠近水源的草种。最近的降雨对草很重要。仅在潮湿时期，覆盖率相对于基质地点更高，这是补偿性放牧的潜在迹象。这些发现表明，食草动物聚集对植被多样性和组成的影响会在幅度上有所不同，在某些情况下，方向也会有所不同，这取决于现场的其他因素。在水分和养分资源丰富并促进少数植物物种占优势的地方，食草动物聚集可以通过促进放牧草坪和增加非优势物种的覆盖来维持多样性。然而，在干旱条件和养分利用率低的地点，这些聚集会大大降低多样性。我们的结果强调了在管理靠近水的食草动物聚集影响时考虑非生物条件的重要性。鉴于全球干旱化和地表水变化不断加剧，这对未来的管理者来说尤为重要。