Postfire seed bank dynamics in semiarid grasslands

Abstract

We evaluated the combined effects of fire after drought on the seed bank composition and its role in the postfire recovery of NW Patagonia grasslands. During three years, we monitored the seed bank and the aboveground vegetation. Species were arranged in functional groups and Detrended Correspondence Analysis was used to separate sites according to species and functional groups. Similarity between aboveground vegetation and seed bank was calculated with SØrensen Index. In the first year, the seed density was similar in the control and burned sites and was lower than following years in all the sites. The species that survived the high temperatures were all annuals with the exception of the perennial species Fabiana imbricata and Rumex acetosella. In the second postfire year, the diversity and seed density increased due to the contribution of fugitive species (rare in the community) and exotic annual species. Seed bank of perennial species was the most affected by fire and just recovered in the third year. Drought did not affect the similarity between the seed bank and vegetation. Fire had low impact on the total seed bank, probably due to the heat buffering nature of the soil, whereas drought reduced significantly seed bank size and richness. Seed bank contributes to grassland richness maintenance.

Fire cue effects on seed germination of six species of northwestern Patagonian grasslands

“…These species are not only directly affected by fire, but can also benefit from other postfire gap-related cues, such as temperature and light fluctuations and the reduction of competition. The brief temporary presence of the fugitive species in the vegetation causes important changes in the early postfire community, such as increase in diversity and species' richness (Gonzalez and Ghermandi, 2008). Finally, the seedling recruitment in these grasslands could be affected by other factors like the competition and facilitation with other plants, the availability of safe sites (Franzese et al, 2009;Gonzalez et al, 2010), and fire, as shown in the present study.…”

“…Moreover, likely direct fire cues are not a sufficient stimulus for the dormant fraction of seeds, thus other cues may be necessary. The removal of biomass and litter by fires became the postfire environment into the "big gap" (Gonzalez and Ghermandi, 2008), where space and resources such as light and temperature fluctuation increase and the competition is reduced (Bond and van Wilgen, 1996). Moreover, since in general species of the genus Nicotiana have physiological dormancy, their seeds probably require the occurrence of dormancy-breaking factors like stratification in order to germinate (Finch-Savage and Leubner-Mezger, 2006).…”

“…We studied perennial grasses and shrubs which predominantly resprout after fires and their seeds do not accumulate a seed bank (Gonzalez and Ghermandi, 2008). We have no records of postfire massive germination of species of these two functional groups.…”

“…We have no records of postfire massive germination of species of these two functional groups. Another postfire phenomenon in these grasslands is the massive seedling recruitment of annual fugitive herbs from the soil seed bank (Gonzalez and Ghermandi, 2008). Occasionally these species may germinate with other intense disturbances, such as soil removal.…”

Spatial dynamics of <I>Fabiana imbricata</I> shrublands in northwestern Patagonia in relation to natural fires

“…The flowering period extends from September to January. This species forms persistent seed pools in the soil (Gonzalez and Ghermandi, 2008) and its regeneration after a fire depends on seedling production (obligate seeder). The aerial parts of F. imbricata are used for medicinal purposes as a diuretic, digestive agent and to relieve kidney ailments (Razmilic et al, 1994) but it has no value as forage specie for cattle and sheep breeding.…”