Fire as a stimulant of shrub recruitment in northwestern Patagonian (Argentina) grasslands

One strategy of plant survival during post-fire succession is to persist and regenerate by recruiting new individuals from a fire-resistant seed bank. The heat, smoke, and charcoal released during plant combustion may act (individually or in combination) as a cue for post-fire seed germination. Fabiana imbricata is a shrub that forms persistent seed banks in the northwestern Patagonian grasslands and shows a high recruitment from seeds during post-fire succession. Mathematical models showed that this species is advancing over the grasslands in response to fires. To corroborate these findings, we studied the role of fire on F. imbricata seed germination. In order to achieve this, a factorial experiment was designed in laboratory conditions to study the effect of heat, charcoal, smoke, scarification, and their interactions on F. imbricata seed germination. Seeds treated with the higher temperatures required a longer period of time to germinate, thus, significantly affecting the mean germination time. Total germination percentages in F. imbricata were significantly enhanced by smoke and scarification, but the interaction of heat, smoke, and scarification was more important than the effect of each fire factor alone. The positive response to fire cues exhibited by F. imbricata indicates that this species would have an adaptive advantage to colonize these grasslands if fire frequency increased, as predicted for this environment. Hence, fire will contribute to the grassland encroachment by this species and, therefore, to the loss of biodiversity and productivity of northwestern Patagonian grasslands.