Field-burn vs. fire-related cues: germination from the soil seed bank of a South American temperate grassland

Abstract

Fire and grazing are large-scale disturbances that shape the structure and function of open habitats. In temperate grasslands of southern South America, fire is used as a management tool to control tussock grasses and improve forage quality. In this study, we examined if fire and two of its components (heat and smoke) affect germination from the soil seed bank of a temperate grassland in Uruguay. Soil samples were extracted from a recently burned site and from an adjacent area that had not been burned for at least 4 years. The latter was subjected to four treatments: (1) heat shock, (2) smoke, (3) heat shock and smoke and (4) control. The samples were placed in a germination chamber and germination was recorded for 140 days. Field burn was the treatment that differed most from the control. This treatment produced a significant increase in density and richness of germinants and the germination peak preceded those of the remaining treatments. The three treatments involving fire-related cues did not affect the seedling richness and density, but the germination of some individual species was enhanced by some of them, mainly those in which the seeds were smoked. Our results show that fire and its components stimulate the germination of some species of the Río de la Plata grasslands, contrary to what had been observed previously in the region. We also suggest that, unlike Mediterranean-type systems, other fire cues, alone or in combination with heat and smoke, may promote germination after a fire event.