Burning the seed bank: Seed response of eight species to different fire intensities in Patagonian steppe

Abstract

Questions: Fire intensity influences the soil seed bank in fire-prone environments. The aim of this investigation was to study the effects of fire intensity on seed germination and seedling growth of native species which belong to three functional groups (grasses, shrubs, and fire ephemerals). We addressed the following questions: (1) How does fire intensity affect the seed germination and seedling growth of the functional groups? Are there differences among species within each functional group? (2) How do seed traits (shape, size, protection structures of seeds, and embryo position) influence the resistance to high temperatures? (3) What conclusions at the community level can we infer from our results?. Location: Northwestern Patagonian grasslands, Argentina. Methods: We performed two experimental burns using different amounts of grassland biomass to simulate low and high fire intensities on sowed seeds of eight native species (four grasses, two shrubs, and two fire ephemerals). We calculated the frequency of seed germination, mean germination time, and estimated seedling growth by weighing the dry biomass (roots and leaves). We examined the relationship of seed mass, length, and shape to the percentage of seed germination in low- and high-temperature treatments. Results: Both temperature treatments negatively affected the seed germination of all functional groups and species, except for the fire ephemeral Boopis gracilis with protected linear embryos. Among grasses, the presence of protective structures in Pappostipa speciosa seeds and of hairs in Poa lanuginosa seeds probably provides resistance to high temperatures. Root growth of seedlings of the grasses Pappostipa speciosa and Festuca pallescens was stimulated by high-temperature treatment ensuring post-fire establishment. Conclusions: Our results suggest that fire intensity influences the post-fire seed germination and seedling growth of the three dominant functional groups of northwestern Patagonian grasslands. In addition, we can affirm that the species of these functional groups have adaptations to resist wildfires and are capable of exploiting post-fire resources.