Simulated post-fire temperature affects germination of native and invasive grasses in cerrado (Brazilian savanna)

Background: Although fire is an important factor in determining cerrado vegetation, information about its effect on seed banks is sparse. Cerrado fires are rapidly moving surface fires with low residence time, producing only short-term heating of the uppermost centimetres of the soil. However, the reduction in vegetation cover and deposition of ashes increases the daily amplitude of soil temperature by as much as 35 degrees C. Aims: To assess the effect of post-fire daily soil temperatures on the germination of one alien and nine native grasses. Methods: Seeds were stored at alternating temperatures of 45 oC/10 oC (10h/14h) for 7d or 30d, simulating two different storage times in the soil seed bank before the onset of the rainy season. Germination was monitored over 30d. Results: The variation in temperature had a significant effect on the rate of seed germination in some species, either enhancing it (Aristida setifolia) or reducing it (Schizachyrium sanguineum). Increased storage time reduced the viability of S. sanguineum and Echinolaena inflexa. The invasive Melinis minutiflora had the highest germination rate and it also showed the best toleration of post-fire conditions (45 oC/10 oC) after 7d, with significant reduction in the germination time after 30d. Conclusions: Fire seems to have a significant effect in the early life of cerrado grasses. Some native species responded positively to temperature oscillation, suggesting that they should be better prepared to compete with alien species after a fire, with more of their seeds germinating and/or at a more rapid rate.