Caracterização microclimática, ecofisiológica e fitossociológica em uma floresta estacional semidecidual secundária, em Viçosa, MG / Microclimatic, ecophysiological and phytosociological characterization of a secondary semideciduous seasonal forest, in Viçosa, MG, Brazil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

A study in the domain of the Atlantic Forest was carried out in ten sites with different slope, aspect and topographic position at the Estação Experimental Mata do Paraíso, in Viçosa, Minas Gerais State, Brazil (20o45 Latitude South, 42o55 Longitude West and an average altitude of 690 m). The spatial and temporal characterization of the photosynthetically active radiation (PAR) and leaf area index (LAI) were measured in four occasions: April 23 to May 16; July 31 to August 20; November 26 to December 21, 1999 and February 26 to March 31, 2000. A detailed microclimatic and ecophysiological study was also done in three of these areas, and in an open area close to the forest, in two periods of the year: September 02 to 26, 1999, at the end of the dry season, and January 08 to February 14, 2000, in the middle of the rainy season. The phytosociological analysis was carried out using natural regeneration data, which included all plants with DBH less than 5 cm. The mean transmissivity of the PAR in the forest fragment was 4.1%, and the LAI was 4.5. Some species shed the leaves in the cold and dry period of the year (July/August) which caused a temporal oscilation of the forest LAI from 3.8 (July/August) to 5.1 (February/March). The temporal changes of the LAI values and the apparent movement of the sun caused variations in the mean annual PAR transmissivity in the forest, which varied from 2.8% (April/May) to 6.5% (November/December). The mean soil temperature (at 2 cm depth) inside the forest was 5.6oC lower than at the open area, although a seasonality was observed in relation to the energetic availability, soil moisture and LAI. The greater differences of soil and air temperatures, and air moisture between the interior of the forest and the open area outside of the forest were most evident on clear day, specially at the warmest hours of the day. An ecophysiological study showed that the species growing under open canopies, in relation to those under closed canopies, presented higher values of net photosynthesis, luminic saturation, stomatal conductance and transpiration. Sunflecks were important for carbon assimilation by the understory plants. The floristic and phytosociological composition analysis showed the occurrence of 128 species, distributed among 43 families with an remarkable variation in floristic diversity among the ten areas. The canonical correspondence analyses distinguished the areas in three groups. The correlation between natural regeneration index and PAR transmissivity allowed to determine the tolerance of the species to shade.

ASSUNTO(S)

silvicultura ecofisiologia vegetal comunidades vegetais florestais mata atlântica regeneração natural mata atlântica natural regeneration forest microclimatology microclimatologia florestal plant communities vegetal ecophysiology

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