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.

从北极苔原到热带稀树草原的放牧生态系统（grazing ecosystems）通常以植食动物偏好斑块与避食斑块的小型镶嵌格局为特征，可维系植物生物多样性并提升生态系统恢复力。关于放牧生态系统中双稳态斑块格局（bistable patchiness）的三大主流解释分别为：其一，植食动物驱动的养分循环；其二，干旱条件下植物生长与水分入渗的反馈机制；其三，植食动物诱导的不可逆本地非生物胁迫（表层土壤侵蚀、盐渍化）。然而，上述解释未能充分阐释高生产力生境中放牧镶嵌格局的高时间动态与广泛分布特征。本文提出第四类解释路径：交替分布的斑块由两类核心生物过程的交互作用调控——一类是土壤动物群落（soil fauna）介导的生物扰动（bioturbation），该过程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），该过程会局部破坏土壤条件，进而催生低矮草本群落。本文综述了阐释生物扰动主导斑块与生物压实主导斑块之间快速转变的相关机制，并绘制了该机制适用的全球分布图谱。通过构建简单模型，本文证明这第四类机制可拓展放牧镶嵌格局得以存续的环境条件范围。最后本文指出，放牧生态系统对全球变化（如生态退化或极端干旱）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。