Abstract Biome boundaries are expected to be sensitive to changes in climate and disturbance, because it is here that ecological communities are at environmental, ecological or disturbance limits. Using palaeoecology to study ecosystem dynamics at biome boundaries provides opportunities for understanding ecosystem resilience or sensitivity at ecologically meaningful timescales, and under varying climatic and disturbance conditions. The fynbos biome is a megadiverse Mediterranean type shrubland, found only in South Africa, that is threatened by climate change, land-use change and invasion by alien species. We used palaeoecological records from the semi-arid and mesic boundaries of the fynbos biome to test hypotheses regarding ecosystem resilience over timescales of centuries to millennia. We hypothesised that fynbos would expand at its mesic boundary at the expense of afrotemperate forest under drier and / or more fire prone conditions. In contrast, we hypothesised that at the semi-arid boundary, fynbos would expand at the expense of succulent karoo under wetter and cooler and / or more fire-prone conditions. Contrary to our expectations, the fossil pollen record at both biome boundaries showed remarkable stability at centennial - millennial timescales. To explain our results, we generated new hypotheses exploring possible mechanisms that might confer resilience. At the mesic (temperate) boundary, we suggest that decreased seasonality of rainfall during drier phases favoured fire and fynbos persistence, while in wetter periods, increased seasonality of rainfall resulted in enhanced summer drought stress, inhibiting forest expansion. At this boundary, internal reorganisation from grassy to proteoid fynbos states conferred resilience through resistance. At the succulent karoo boundary, we suggest that increased aridity was offset by less seasonality of rainfall, which enhanced biomass and allowed fire to persist, favouring persistence of fynbos. At this boundary, fynbos sensu stricto retreated during arid phases but recovered during climate amelioration, consistent with resilience through recovery. In both cases, this mega-diverse, disturbance-adapted flora provided a range of traits that enabled fynbos to persist despite environmental perturbation. Our findings agree with general observations that for ecosystems in regions of ample resource availability (i.e. at the mesic boundary), biotic interactions and disturbance tend to become more important in ecosystem dynamics, whereas in regions of scarce resources (in this case water scarcity at the semi-arid boundary) abiotic stress is more important. Our findings contribute to debates over the mechanisms that confer resistance and resilience to environmental change. Understanding and conserving the processes and mechanisms underpinning its resilience will be critical to effective conservation planning.

中文翻译：

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南非种类繁多的荒地 fynbos 中等和半干旱边界的恢复力对比机制

摘要 生物群落边界预计对气候变化和干扰很敏感，因为在这里生态群落处于环境、生态或干扰的极限。使用古生态学研究生物群落边界的生态系统动态，为了解生态系统在具有生态意义的时间尺度以及不同气候和干扰条件下的恢复力或敏感性提供了机会。fynbos 生物群落是一个种类繁多的地中海型灌木丛，仅在南非发现，受到气候变化、土地利用变化和外来物种入侵的威胁。我们使用来自 fynbos 生物群落的半干旱和中等边界的古生态记录来测试关于几个世纪到数千年时间尺度内生态系统恢复力的假设。我们假设 fynbos 会在其中间边界扩张，但会在更干燥和/或更容易发生火灾的条件下以牺牲非洲温带森林为代价。相比之下，我们假设在半干旱边界，fynbos 会在更潮湿、更冷和/或更容易着火的条件下以多汁的 karoo 为代价扩张。与我们的预期相反，两个生物群落边界的化石花粉记录在百年至千禧年的时间尺度上都表现出显着的稳定性。为了解释我们的结果，我们提出了新的假设，探索可能赋予弹性的机制。在中（温带）边界，我们认为干燥阶段降雨季节性的降低有利于火灾和 fynbos 的持久性，而在湿润时期，降雨的季节性增加导致夏季干旱压力增强，抑制森林扩张。在这个边界上，从草类到蛋白质类 fynbos 状态的内部重组通过抵抗赋予了弹性。在多汁的 karoo 边界，我们认为干旱的增加被降雨的季节性减少所抵消，这增加了生物量并允许火灾持续存在，有利于 fynbos 的持续存在。在这个边界上，fynbos sensu stricto 在干旱阶段撤退，但在气候改善期间恢复，与恢复过程中的恢复力一致。在这两种情况下，这种种类繁多、适应干扰的植物群提供了一系列特征，使 fynbos 能够在环境扰动的情况下持续存在。我们的研究结果与一般观察结果一致，即对于资源充足地区（即在中间边界）的生态系统，生物相互作用和干扰在生态系统动态中往往变得更加重要，而在资源稀缺的地区（在这种情况下，半干旱边界缺水）非生物压力更为重要。我们的发现有助于对赋予环境变化抵抗力和恢复力的机制的辩论。了解和保护支撑其恢复力的过程和机制对于有效的保护规划至关重要。