Fire and seed dormancy: a global meta-analysis

Fire-released seed dormancy (SD) is a key trait for successful germination and plant persistence in many fire-prone ecosystems. Many local studies have shown that fire-released SD depends on heat and exposure time, dose of smoke-derived compounds, SD class, plant lineage and the fire regime. However, a global quantitative analysis of fire-released SD is lacking. We hypothesized that fire-released SD is more prevalent in fire-prone than in non-fire-prone ecosystems, and in crown fire compared with surface fire ecosystems. Additionally, we expected to uncover patterns in the relationship between fire cues and SD classes at the global scale that mirror those identified in local or regional studies.

In total, 246 published germination studies from 1970 to 2022, encompassing 1782 species from 128 families, were used in our meta-analysis. Meta-analysis moderators included different fire cues, smoke application methods, smoke exposure duration and concentration, smoke compounds, fire-proneness, fire regimes and ecosystem types.

Heat released physical, and smoke released physiological and morphophysiological dormancies. For SD release, heat and smoke acted synergistically, and karrikinolide (KAR1) was the most effective smoke compound. Fire-released SD was more prevalent in fire-prone than in non-fire-prone regions, particularly under crown fire regimes. Fire-released SD occurred mainly in Mediterranean ecosystems, temperate dry forests and temperate warm ecosystems, whereas species from savannas and tropical grasslands, temperate grasslands and tropical rainforests generally responded negatively to fire.

Fire-released SD is strongly influenced by fire regimes, the latter having a significant role in shaping SD and germination patterns on a global scale. The synergistic effect of heat and smoke in dormancy release reveals more intricate interactions between fire cues than previously understood. Understanding these patterns is crucial in the context of shifting fire regimes driven by climate change, as they may disrupt plant life cycles, alter ecosystem functions, biodiversity and community composition, and provide key insights for biodiversity conservation and ecological restoration in fire-prone ecosystems.