Response of vegetation to fire disturbance: short-term dynamics in two savanna physiognomies

Fire is a constitutive ecological force in savanna ecosystems, but few studies have monitored its short-term effects on plant community dynamics. This study investigated changes in plant diversity in the South American savanna (Cerrado) after severe disturbance by fire. We monitored 30 permanent plots (10 m × 5 m) distributed in two Cerrado physiognomies (típico: more forested; ralo: grass-dominated), being 10 plots in the area disturbed by fire, and five in a preserved control area (undisturbed). From August 2010 to June 2011, we evaluated changes in species richness, abundance and composition of savanna vegetation. Monitoring started one week after the fire; disturbed plots were surveyed monthly, while control plots were surveyed every two months. We observed rapid reassembling in both physiognomies: plots affected by fire showed rapid increase in species richness and plant density during the first four months after the disturbance. Concerning species composition, disturbed plots in the cerrado típico tended to converge to control plots after one year, but each local assemblage followed particular temporal trajectories. A different pattern characterized cerrado ralo plots, which showed heterogeneous trajectories and lack of convergence between disturbed and control plots; the structure of these assemblages will likely change in next years. In conclusion, our results showed that fire significantly affected plant diversity in the two savanna physiognomies (cerrado típico and ralo), but also indicated that community reassembling is fast, with different dynamics between Cerrado physiognomies

Seed germination performances of Styrax species help understand their distribution in Cerrado areas in Brazil

In this descriptive paper, we described germination responses of Styrax pohlii, S. camporum and S. ferrugineus seeds at 5, 10, 15, 20, 25, 30, 35, 40 and 45 degrees C. We also assessed the percentage germination (% G) of S. pohlii seeds with different seed water contents because, as a forest species, it seems to have recalcitrant seed behavior. Intrigued by the capacity of seeds of this species to germinate directly from puddles formed on poorly drained soils of riparian forests, where it typically occurs, we also tested the effect of de-pulping fruits on germination of S. pohlii seeds under hypoxia and normoxia conditions. In addition, we checked whether distinct concentrations of gibberellic acid (GA(3)) could break S. ferrugineus seed dormancy, a typical seed behavior of Cerrado species. No germination occurred at 5, 40 and 45 degrees C, regardless of the species. The optimal temperature for germination was 20 degrees C for S. pohlii and 25 degrees C for S. camporum. However, S. ferrugineus seeds showed a very low % G, regardless of the temperature, and GA(3) could not consistently break possible physiological seed dormancy. For S. pohlii seeds, the higher the seed desiccation the lower the % G, and fruit pulp removal showed to be essential for seed germination. S. pohlii seeds germinated independently of oxygenation conditions.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Univ Estadual Paulista UNESP, Inst Biociencias, Dept Bot, BR-13506900 Rio Claro, SP, BrazilUniv Estadual Paulista UNESP, Inst Biociencias, Dept Bot, BR-13506900 Rio Claro, SP, BrazilCNPq: 306119/2011-