Fogo e dinâmica da comunidade lenhosa em cerrado sentido restrito, Barra do Garças, Mato Grosso , in Area 1, tree mortality was lower (2.0%) and recruitment (3.7%) higher than that observed Area 2 (4.3% and 0.05% respectively). Plant mortality decreased with increasing size class. In Area 2, there was a reduction in plant size (height and diameter). The resprouting pattern after fire was related to plant size. Smaller size classes had higher proportions of resprouting at the base of the stem while the larger size classes had more resprouts at the tree crown. In Area 2, species richness was reduced (estimated by Jacknife and Chao 2). Our results suggest that the tolerance of adult trees and smaller plants due to resprouting may explain the persistence of the woody cerrado community submitted to a fire regime interval over five years.

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RESUMO(Dinâmica da comunidade arbórea em uma floresta estacional semidecidual sob queimadas recorrentes). Os efeitos do fogo sobre a mortalidade de árvores podem alterar a composição e estrutura da vegetação, dependendo da intensidade, frequência e duração das queimadas. Monitoramos áreas de floresta sujeitas a diferentes frequências de fogo no Parque Estadual da Serra Azul, Barra do Garças, MT: 0,9 ha queimaram em 2007 (Q1) e 0,9 ha em 2005 e 2007 (Q2). A dinâmica foi referente ao intervalo médio de 2,02 anos, de forma que o primeiro levantamento (T1) ocorreu em outubro/2006-maio/2007 e o segundo levantamento (T2) em março/2009, considerando indivíduos com PAP ≥ 15 cm. A diversidade (H') e a riqueza de espécies (estimada por Jackknife) foram maiores em Q2, nos dois levantamentos. Ocorreu a diminuição significativa na densidade em Q1 e Q2, mas a proporção de indivíduos mortos foi maior em Q1. Os parâmetros da dinâmica baseados no número de indivíduos e na área basal não diferiram entre Q1 e Q2. O aumento da diversidade na área sujeita a maior frequência de queimadas pode ser explicada pela hipótese de distúrbio intermediário. Entretanto, apesar da mortalidade e recrutamento não terem diferido entre Q1 e Q2, as altas taxas de mudança, independentes da frequência do fogo, sugerem futuras alterações florísticas e estruturais na floresta, caso as queimadas continuem ocorrendo na área. Palavras-chave: dinâmica florestal, distúrbios, incêndios florestais, mortalidade ABSTRACT(Tree community dynamics in a semideciduous forest under recurrent fires). The effects of fire on tree mortality can change floristic and forest structure depending on intensity, frequency and the length of a fire. Areas of semideciduous forest in Parque Estadual da Serra Azul, Barra do Garças (MT, Brazil), exposed to different frequencies of fire, were monitored: 0.9 ha burned in 2007 (Q1) and 0.9 ha in 2005 and 2007 (Q2). The dynamics were based on the average interval of 2.02 years between T1 (outubro/2006-maio/2007) and T2 (March/2009), including individuals with PAP ≥ 15 cm. Diversity (H') and species richness (estimated by Jackknife) were higher in Q2, in both at T1 and T2. The decrease of tree density between surveys was significant for Q1 and Q2, but the proportion of deaths was higher in Q1. There were no differences in the dynamic parameters between Q1 and Q2 when considering both the number of individuals and basal area. The increase of diversity in Q2 may be partially explained by the hypothesis of intermediate disturbance. However, despite the absence of differences in recruitment and mortality between Q1 and Q2, the high turnover rates, independent of fire frequency, suggest future changes in the flora and structure of the forest if fire continues to be frequent in the area.

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The tropical vegetation growing in dystrophic soils is capable of recycling nutrients through litterfall and thus maintaining soil fertility. However, climate changes can alter this production and, consequently, the litter layer over the soil, affecting the carbon cycle and the integrity of the ecosystem. In this study, we investigated whether a reduction in rainfall increased the litterfall and the litter layer (stock) and, if so, whether the effects are more evident in degraded environments. We compared the litterfall and the litter layer in years with higher (1575.3 mm) and lower (1360.8 mm) rainfall rates in three environments: ''cerradão'' (CD; savanna woodland), typical ''cerrado'' (savanna-like vegetation) and successional area (SA). We recorded increasing litterfall in the SA and in the litter layer in the three environments during the year with lower rainfall rates. We also detected alterations to the seasonal variation in the litter layer and the production of reproductive parts. The reduction in rainfall increased the return of carbon to the soil, especially in open areas. Our results indicate that climatic extremes (e.g., reduced rainfall) can modify the availability of nutrients and their absorption by plants and therefore compromising important ecosystem functions, such as carbon cycle.