Data from: Biotically driven vegetation mosaics in grazing ecosystems: the battle between bioturbation and biocompaction

Grazing ecosystems ranging from the arctic tundra to tropical savannas are often characterized by small-scale mosaics of herbivore-preferred and herbivore-avoided patches, promoting plant biodiversity and resilience. The three leading explanations for bistable patchiness in grazed ecosystems are: i) herbivore-driven nutrient cycling, ii) plant growth-water infiltration feedback under aridity, and iii) irreversible local herbivore-induced abiotic stress (topsoil erosion, salinity). However, these insufficiently explain the high temporal patch dynamics and wide-ranging distribution of grazing mosaics across productive habitats. Here we propose a fourth possibility where alternating patches are governed by the interplay of two important biotic processes: bioturbation by soil fauna that locally ameliorates soil conditions, promoting tall plant communities, alternating with biocompaction by large herbivores that locally impairs soil conditions, and promotes lawn communities. We review mechanisms that explain rapid conversions between bioturbation- and biocompaction-dominated patches, and provide a global map where this mechanism is possible. With a simple model we illustrate that this fourth mechanism expands the range of conditions under which grazing mosaics can persist. We conclude that the response of grazing systems to global change, as degradation or catastrophic droughts, will be contingent on the correct identification of the dominant process that drives their vegetation structural heterogeneity.

从北极苔原（arctic tundra）到热带稀树草原（tropical savannas）的各类放牧生态系统，普遍呈现出植食动物偏好生境与避食生境构成的小型镶嵌格局，该格局可促进植物生物多样性并增强生态系统恢复力。当前针对放牧生态系统双稳态镶嵌格局的三大主流解释分别为：① 植食动物驱动的养分循环；② 干旱条件下植物生长与水分入渗的反馈机制；③ 不可逆的局部植食动物诱导的非生物胁迫（表层土壤侵蚀、盐渍化）。然而，上述理论无法充分解释放牧镶嵌格局的高时间动态特征，以及其在高生产力生境中的广泛分布现象。本文提出第四种可能性：交替出现的斑块格局由两类关键生物过程的相互作用调控——一类是土壤动物（soil fauna）介导的生物扰动（bioturbation），可局部改善土壤条件，促进高大植物群落发育；另一类是大型植食动物介导的生物压实（biocompaction），会局部破坏土壤条件，进而催生草本草坪群落。本文综述了可解释生物扰动主导型斑块与生物压实主导型斑块间快速转换的相关机制，并绘制了该机制可行的全球分布地图。通过构建简易模型，本文证实该第四种机制可拓宽放牧镶嵌格局得以维持的环境条件范围。本文最终得出结论：放牧生态系统对全球变化（如生态退化或极端干旱事件）的响应，将取决于能否准确识别驱动其植被结构异质性的主导过程。