Data from: A novel mechanism for grazing lawn formation: large herbivore-induced modification of the plant-soil water balance

1. Large herbivores play a key-role in creating spatial heterogeneity through the formation of grazing lawns. Recent research suggests that the currently accepted nutrient-based theory on the formation of these grazing lawns cannot universally explain their formation in all ecosystems where they are found. 2. We developed and investigated an alternative hypothesis on grazing lawn formation and maintenance based on herbivore effects on the plant-soil water balance. We propose that large herbivores change the soil water balance in grazing lawns through defoliation and soil compaction, causing a shift in vegetation composition towards a drought tolerant plant community. 3. Investigating this idea in a tropical savanna, we indeed found profound differences in grazing lawn soil properties and water balance. In particular, defoliation increased soil temperatures and potential evaporation rates while soil compaction increased bulk density and decreased water infiltration rates, especially on fine-textured soils. Soil moisture was therefore generally much lower in grazing lawns than in adjacent bunch grass areas. 4. Furthermore, we found that grazing lawn species show drought-tolerant traits, with higher leaf sodium levels, suggesting evolutionary adaptation to these herbivore-induced dry conditions. However, leaf water potentials did not differ between grazing lawn and bunch grass species. 5. Synthesis: This study shows that large herbivores might form grazing lawns through previously underestimated effects on water balance. Thus, future studies on large herbivore effects on vegetation should increasingly focus on additional pathways of soil compaction and defoliation. While nutrient-based processes driving grazing lawn formation may operate during the wet season in savannas, we suggest that water balance-based processes are additionally important during the dry season.

1. 大型草食动物通过形成啃食草坪（grazing lawn）在营造空间异质性方面发挥关键作用。近期研究表明，当前被广泛接受的基于营养机制的啃食草坪形成理论，无法在所有存在该类草皮的生态系统中普遍解释其形成过程。
2. 我们提出并验证了一项关于啃食草坪形成与维持的替代假说，该假说基于草食动物对植物-土壤水分平衡的影响。我们认为，大型草食动物可通过去叶作用与土壤压实作用改变啃食草坪内的土壤水分平衡，进而促使植被群落组成向耐旱型植物群落转变。
3. 我们在热带稀树草原中对这一假说开展验证，结果确实发现啃食草坪的土壤性质与水分平衡存在显著差异。具体而言，去叶作用会提升土壤温度与潜在蒸发速率，而土壤压实则会提高土壤容重并降低水分入渗速率，这一效应在细质地土壤中尤为明显。因此，啃食草坪内的土壤含水量通常远低于相邻的丛生草地区域。
4. 此外，我们发现啃食草坪的植物物种具有耐旱相关性状，其叶片钠含量更高，这表明这些植物已演化适应了草食动物诱导的干旱环境。不过，啃食草坪与丛生草本植物的叶片水势并无显著差异。
5. 综合分析：本研究表明，大型草食动物或可通过此前被低估的对水分平衡的影响作用形成啃食草坪。因此，未来针对大型草食动物对植被影响的研究，应愈发关注土壤压实与去叶作用这两条额外途径。尽管基于营养过程的啃食草坪形成机制可能在稀树草原的湿季发挥作用，但我们认为基于水分平衡的机制在旱季同样具有重要意义。