Data from: Fire after a mast year triggers mass recruitment of slender mulga (Acacia aptaneura), a desert shrub with heat-stimulated germination

PREMISE OF THE STUDY: Fire typically triggers extensive regeneration of plants with heat-stimulated germination by causing short periods of intense soil heating. If plants with heat-stimulated germination are also subject to seed predation and display mast-seeding cycles, postfire recruitment may be contingent on the seedfall density of prefire masts, and on whether granivores are satiated at the time of fire.

METHODS: We conducted a longitudinal seedbank study and a mensurative field experiment in central Australia to examine whether fire and the variation in seedfall density across sites in a mast year interact to influence recruitment of slender mulga (Acacia aptaneura), an iteroparous masting shrub with heat-stimulated germination.

KEY RESULT: The seedbank study showed seedbank pulsing after masting, with mean seed counts in the upper 4-cm soil layer being 132.8 seeds/m2 12-mo after a dense seedfall, but only 3.8 seeds/m2 following a year with no seed production. Consistent with this, recruitment increased postfire at sites where denser seedfall had occurred during the preburn mast year. Conversely, little recruitment occurred at unburnt populations, irrespective of prefire seedfall density.

CONCLUSIONS: We attribute our findings to: (1) elevated soil temperatures during fires stimulating germination of heat-cued seeds; and (2) granivore satiation following masting facilitating assimilation of seeds into the soil seedbank. These results highlight the importance of rare seed-input events for regeneration in fire-prone systems dominated by masting plants, and provide the first example from an arid biome of fire interacting with masting to influence recruitment.

研究背景：野火通常会引发短期的强烈土壤升温，从而促使依赖热激发种子萌发（heat-stimulated germination）的植物实现大规模植株更新。若这类依赖热激发萌发的植物同时面临种子捕食压力，且存在大年结实（mast-seeding）周期，那么野火后的植株更新可能取决于火前大年的种子沉降密度，以及野火发生时食种子动物是否处于饱和状态。

研究方法：我们在澳大利亚中部开展了一项长期种子库研究（longitudinal seedbank study）与一项观测性野外实验（mensurative field experiment），以探究野火与大年结实年份不同样地的种子沉降密度的交互作用，是否会影响细叶姆尔加金合欢（Acacia aptaneura）的植株更新——该物种为一种多次结实（iteroparous）型大年结实灌木，其种子萌发依赖热激发。

主要结果：种子库研究显示，大年结实后土壤种子库出现脉冲式变化：在密集种子沉降发生后的12个月内，表层4厘米土壤中的平均种子密度为132.8粒/平方米，而在无种子产出的年份仅为3.8粒/平方米。与此结果一致的是，在火前大年发生过密集种子沉降的样地，野火后的植株更新率显著提升；相反，未遭受火烧的种群几乎未出现植株更新，无论其火前种子沉降密度如何。

结论：我们将本次研究结果归因于两点：其一，野火期间升高的土壤温度可激发热触发型种子的萌发；其二，大年结实后食种子动物的饱和状态，可促进种子融入土壤种子库。本研究结果凸显了稀有种子输入事件在以大年结实植物为主的易火生态系统中，对植株更新的重要意义，同时也是干旱生物群区内野火与大年结实交互作用影响植株更新的首个研究案例。