Data and code for: microbial drivers of woody plant encroachment in fire-maintained grasslands and savannas

Woody plant encroachment into grasslands and savannas is a global phenomenon with wideranging consequences for people and nature, but we lack a comprehensive understanding of its drivers. Various factors can contribute to woody encroachment across ecosystems, but a notable commonality is that transitions from herbaceous to woody vegetation tend to be abrupt and difficult to reverse, suggesting that positive feedbacks play a role. Positive feedbacks are well-studied in the context of vegetation–fire dynamics, but growing evidence points to the potential importance of microbially mediated plant–soil feedbacks in woody plant encroachment. For example, ectomycorrhizal association, which often gives rise to positive feedback, is especially common among woody plants known to encroach into grass-dominated systems, while herbaceous plants tend to accumulate self-limiting microbial communities. To fill this gap, we developed a novel patch occupancy modeling framework for predicting microbial impacts on vegetation dynamics in fire-maintained grasslands and parameterized this model with empirically derived estimates of plant–microbe interactions from global meta-analyses. We find that, in fire-maintained grasslands, empirically measured microbial feedbacks necessitate especially frequent fire to maintain grassy communities. We also show that woody-favoring soil communities increase the duration of fire-based management necessary to recover grassland after encroachment and narrow the conditions under which such recovery is possible. In all, our model points to the overlooked yet consequential role of plant–soil feedbacks in driving changing vegetation patterns in firemaintained grass-dominated systems and the urgent need for empirical data testing this process.Data and code for this manuscript are provided along with a README.md file.木本植物侵占草原与稀树草原是一种全球性现象，对人类社会与自然生态均产生广泛影响，但目前我们对其驱动因子尚缺乏全面认知。不同生态系统中，木本植物侵占的成因多样，但存在一项显著共性：草本植被向木本植被的转变往往具有突发性且难以逆转，这表明正反馈机制在此过程中发挥了作用。正反馈机制在植被-火动态（vegetation–fire dynamics）领域已得到充分研究，但越来越多的证据表明，微生物介导的植物-土壤反馈（microbially mediated plant-soil feedbacks）在木本植物侵占过程中可能具有重要意义。例如，通常会产生正反馈的外生菌根共生（ectomycorrhizal association）现象，在已知会侵占草本主导生态系统的木本植物中尤为普遍；而草本植物往往会积累自我限制型微生物群落。为填补这一研究空白，我们构建了一种全新的斑块占据模型框架（patch occupancy modeling framework），用于预测火维持草原中微生物对植被动态的影响，并基于全球荟萃分析得到的植物-微生物相互作用的经验估计值对该模型进行了参数化。我们的研究结果表明，在火维持草原中，经经验测定的微生物反馈需要更为频繁的火干扰才能维持草本群落的存续。我们还发现，偏好木本植物的土壤群落会延长侵占发生后通过火管理措施恢复草原所需的时长，并缩小了此类恢复得以实现的环境条件范围。总体而言，我们的模型揭示了植物-土壤反馈在驱动火维持型草本主导生态系统植被格局变化中被忽视却至关重要的作用，并指出亟需开展实证研究以验证这一过程。本文稿配套的数据、代码及README.md文件均已提供。