Comparação da vegetação lenhosa entre borda e interior de uma mancha de mata de restinga na resex mar Caeté-Taperaçu, Bragança, Pará.

Abstract

This study analyses the vegetation of patch of forest (33 ha) within the Marine Extractivist Reserve Caeté-Taperaçu, Bragança district, Pará. Along transects between margin and interior of the patch, topography, salinity, ground water levei and soil charactehstics along this gradient were evaluated. 12 transects of 100 m length were laid out around the patch. Woody vegetation with breast height diameter (dbh) of 2.5 cm was mapped in a 100x10 m plot along each transect, recording for each tree distance from the margin, diameter and height. Elevation profiles along the transects were produced by topographic measurements. The maximum range of tidal inundation was recorded at the lowest point of each transect by tracking the highest high water levei duhng March and September equinoxes. Changes in ground water levei were monitored fortnightly along two of the transects by checking the water levei in groups of three wells reaching depths of 0.5, 1 and 2 m, respectively, inserted side by side; three of these groups were installed at stations at the forest border, in the middle and at the end of the transect. Superficial soil layers were examined by taking 1-m-depth corer samples every 10 m along each transect, recording soil colour and texture. The vegetation sampling included 1040 individual plants (38 families, 62 genera and 83 species). The Burseraceae Protium heptaphyllum showed the highest frequency (50%) and the highest density (105±94 trees ha'1). The Lauraceae Aniba citrifolia showed the highest basal area values (2.4±1.7 m2 ha'1). The médium sub-plot density of ali species amounted to 844±216 trees ha'1, the corresponding basal area to 20.3±4.7 m2 ha'1. The mean dbh was 0.13±0.02 m, the average height was 9.0±0.8 m (maximum value: 24 m). No significant changes in basal area and tree density were detected along transects. No distinctive species community for the margin cr the forest interior could therefore be identified. Ground water levei showed charactehstic, rainfall dependent seasonal changes but water levei dynamics at "margin", "middle" and "interior" well stations did not differ. Soil samples showed predominantly sandy soil layers of different texture and with vahation in A horizon thickness; no margin-intehor pattern was identified. The study site shows an unusually high diversity and well-developed forest structure when compared to other woody restinga vegetation of north Brazil. The small vahation of abiotic gradients margin to the interior may be responsible for uniform vegetation structure and species composition.