Data from: Are forest‐shrubland mosaics of the Cape Floristic Region an example of alternate stable states?

The idea of alternate stable states (ASS) has been used to explain the juxtaposition of distinct vegetation types within the same climate regime. ASS may explain the co‐existence of relatively inflammable closed‐canopy Afrotemperate Forest patches (“Forest”) within fire‐prone open‐canopy Fynbos in the Cape Floristic Region (CFR) on sandstone‐derived soils. We evaluated the hypothesis that although fire and local topography and hydrology likely determined the paleogeographic boundaries of Forest, present‐day boundaries are additionally imposed by emergent edaphic properties and disturbance histories. We studied vegetation and edaphic properties of Forest‐Transition‐Fynbos vegetation at two sites within the CFR on sandstone‐derived soils and tracked historical change using aerial photography. Whereas Forest and Fynbos have changed little in extent or density since 1945, Transition vegetation increased into areas formerly occupied by Fynbos. Forest soils were ubiquitously more nutrient‐rich than Fynbos soils, with Transition soils being intermediate. These edaphic differences are not due to geological differences, but instead appear to have emerged as a consequence of different nutrient cycling within the different ecosystems. Soil nutrients are now so different that a switch from Fynbos to Forest is unlikely, in the short term (i.e. decades). Floristically and nutritionally, Transitional vegetation is more similar to Fynbos than Forest and may be less resilient to changes in exogenous drivers (e.g., fire). Our findings are consistent with the idea that geologically Forest and Fynbos are largely fire‐derived long‐term ASS, with the stability of each state reinforced by marked soil nutrient differences. In contrast, the intermediate Transitional vegetation that might switch states is unlikely to be stable.交替稳定态（alternate stable states, ASS）这一概念被用于解释同一气候体系下不同植被类型的毗邻分布格局，其可解释在砂岩衍生土壤发育的开普植物区（Cape Floristic Region, CFR）内，易受火灾干扰的开阔冠层凡波斯（Fynbos）群落中，相对难燃的封闭冠层非洲温带森林（Afrotemperate Forest）斑块（下称"森林"）的共存现象。我们验证了如下假说：尽管火灾、局地地形与水文或曾决定了森林的古地理边界，但当前的分布边界还额外受到逐渐形成的土壤属性与干扰历史的调控。我们在开普植物区两处砂岩衍生土壤样地中，开展了森林-过渡带-凡波斯植被的群落调查与土壤属性分析，并借助航空摄影记录了植被的历史变化。自1945年以来，森林与凡波斯的分布范围与冠层密度均未发生明显变化，而过渡带植被则向原本由凡波斯占据的区域扩张。森林土壤的养分含量普遍高于凡波斯土壤，过渡带土壤的养分水平则介于二者之间。这类土壤养分差异并非源于地质背景不同，而是不同生态系统间养分循环模式差异所导致的结果。当前土壤养分的显著差异使得短期（数十年尺度内）从凡波斯向森林的植被转换几乎无法实现。从区系组成与养分特征来看，过渡带植被与凡波斯的相似性高于森林，且其对外源驱动因子（如火灾）的恢复力可能更弱。我们的研究结果支持如下观点：从地质演化角度而言，森林与凡波斯本质上均为长期形成的、受火灾调控的交替稳定态，二者的稳定性均通过显著的土壤养分差异得以强化；反之，具备状态转换潜力的过渡带植被则难以维持长期稳定。