Efeitos do fogo sobre a vegetação em duas áreas de campo rupestre na Chapada Diamantina, Bahia, Brasil

Abstract

The fire is considered one of the factors determining the structure and composition of grasslands and tropical savannas, exerting great influence on their faces and compositions floristics. The high frequency of fire in the Chapada Diamantina is worrying because it is an important center of diversity of mountains in Brazil, with high numbers of endemic plants. This study aimed to detect changes resulting from the floristic and structural vegetation burned in rural community and to detect patterns of vegetation cover over the rocky and sandy substrates. It was studied an area of rocky fields burned in November 2008 (12 ° 27'50, 9 "- 12 ° 27'52, 5" S and 41 ° 25'50, 7 "- 41 ° 26'02, 6" W) APA-Marimbus located in Iraq, and another area used as a control, with last burned in October 2005 (12 ° 28'00, 5 "- 12 ° 28'01, 4" S and 41 ° 26'03, 8 "- 41 ° 26'05 .1 "W) located in the Chapada Diamantina National Park. We randomly selected 16 units divided into subunits 10x10m 2x2m, from which the percentage of coverage and height of the species were estimated. The importance of the types of regeneration was measured by the proportion of individuals with growth or regrowth from seed and forms of life Raunkiaer. Were related to 128 species in 92 genera and 40 families, with 45% of families were represented by only one species. Of the species recorded in the floristic survey, 83 occurred in the burned areas and 56 control areas. Families with higher coverage in the burned areas of bedrock were Poaceae, Leguminosae and Bromeliaceae, whereas in areas of sandy substrate were Poaceae, Leguminosae and Cyperaceae. Despite the changes observed, eighteen months after the fire occurred in November 2008, the field area affected by fire showed rock composition and structure of families similar to the area of vegetation control. The reduction in range of species that have grown by seed, which could not be established after the fire, and regrowth of most predominant species in the area may be possible explanations for this result. It was found that the number of species and average height of vegetation in the burned area increased progressively and similarly in both types of substrate, but eighteen months was not sufficient to restore the coverage area of vegetation in rocky fields, since areas of sandy soil regeneration was only 46% of the vegetation in the control, while in the area of rock outcrop that regeneration was 67%. Hemicryptophyte species are more common on disturbed by fire, regardless of the substrate. The number of species able to resprout is higher in the bedrock, whereas species that appear to seeds, are most common on sandy soil. However, species that use the two strategies of growth showed a larger area of coverage throughout the study in both types of burned substrates, showing that this is the most efficient strategy of occupation, as it stays in place previously established (regrowth) and occupies open new areas (seed).