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 f...1. 大型食草动物（Large herbivores）通过形成放牧草坪（grazing lawns），在塑造空间异质性（spatial heterogeneity）方面发挥核心作用。近期研究表明，当前主流的基于养分的放牧草坪形成理论，无法普遍解释所有存在放牧草坪的生态系统中的草坪形成过程。2. 本研究提出并验证了一种基于食草动物对植物-土壤水分平衡（plant-soil water balance）影响的放牧草坪形成与维持替代假说（alternative hypothesis）。我们认为，大型食草动物可通过去叶作用（defoliation）与土壤压实（soil compaction）改变放牧草坪内的土壤水分平衡，进而促使植被群落组成向耐旱植物群落转变。3. 在热带稀树草原（tropical savanna）中对该假说开展验证后，我们确实发现放牧草坪的土壤特性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（bulk density）并降低水分入渗速率（water infiltration rates），尤其在……