Seed germination and seedling recruitment of Dimorphandra mollis Benth. in a Neotropical savanna subjected to prescribed fires

Recruitment in savanna environments represents a high-risk step in a plant's life cycle. Dimorphandra mollis Benth (Fabaceae) is a savanna tree species which produces dry fruits holding coat-imposed dormant seeds dispersed late in the dry season. We investigated fire effects on fruit dehiscence, seed dormancy breaking and seed viability, and also monitored seedling recruitment and survival for 44 months in a savanna area subjected to biennial controlled fires in central Brazil. Fruits were laid aboveground, and seeds were buried before and after an experimental fire set in August 1999. Fruits started to open after the experimental fire up to the following rainy season. Around one fourth of the seeds removed from these fruits were viable but required scarification to imbibe, indicating that fruits do not totally insulate seeds, and fire does not break seed dormancy. No seedling emerged from buried seeds during the first rainy season after the fire, but fourteen seedlings emerged during the second rainy season. Half of the seedlings died and the other half resprouted after a second experimental fire set during the third dry season. In the third rainy season, thirteen new seedlings emerged, but two died in the fourth dry season. We found that fire was a more determinant constraint to seedling survival than the dry season itself. After 44 months we recovered 27 viable seeds from those initially buried, suggesting that seeds of D. mollis have the potential to establish a persistent seed bank. As expected for savanna trees, we found that D. mollis seeds and seedlings may persist in environments periodically disturbed by fires.