Fire as a regeneration filter: contrasting effects of heat and smoke on Arctic seed germination. Data and code

The rapid warming of the Arctic is increasing the frequency, intensity, severity, and spatial extent of fires. Because fire has historically been rare in this region, most Arctic plant species are unlikely to have evolved traits that confer tolerance to fire, and the consequences for early life-history stages such as seed germination remain largely unknown. Here, we experimentally tested the effects of two key fire-related cues, heat shock and smoke exposure, on the germination traits of 25 widespread Arctic plant species. Seeds collected across the Arctic were subjected to four treatments: (i) high-heat (110 °C for 4 min, simulating surface fire exposure); (ii) low-heat (50 °C for 10 min, simulating soil seed bank conditions); (iii) smoke water produced from Arctic plant biomass; and (iv) a combination of low-heat and smoke water. We analysed germination responses at three levels: overall, across functional groups (forbs, graminoids, and woody species), and at the species level. High-heat treatment almost completely inhibited germination, reducing the final percentage of germination from ~78% to ~2%, with graminoids being least affected and only three species germinating at all. Low-heat treatment produced no overall or functional group changes in final germination but reduced germination speed and synchrony in some species. Smoke water did not alter final germination percentage but consistently accelerated germination speed by ~9–11%. Together, these results suggest that most Arctic species are not adapted to survive the temperatures experienced at or near the soil surface during fires. However, buried seeds may remain viable after low heating and be stimulated by smoke, creating a filter that favours species with persistent soil seed banks or traits that promote seed burial. As Arctic fires become more frequent, seed-based regeneration will likely play a growing role in shaping post-fire recruitment and the diversity and composition of plant communities.