Absence Of Zonation In A Mangrove Forest In Southeastern Brazil

Abstract

The mangrove forest of the estuarine system of Santos, Brazil, occupies 71 km2 - an area consisting of a complex system of canals and rivers forming a predominantly depositional environment. The climate provides high rainfall, with no water deficit and minimum temperatures above 18oC. In this environment, 3,870 mangrove trees, distributed on 20 random transects, were identified, counted and measured and the litterfall measured. The phytosociological data (density, height and basal area) were measured in parcels at different distances from the waterline. Three species of trees were identified: Rhizophora mangle, Avicennia schaueriana and Laguncularia racemosa. The data showed large variability between stands but with no zonation perpendicular to the fringe in relation to phytosociological descriptors, the distribution of the tree species and litterfall production. This phenomenon is attributed to the low energy subsidy occurring as a function of the microtidal regime, the reduced velocity of the water in the innermost regions of the estuarine system, the homogeneous sediment (silt) and mostly the absence of any water deficit in the region. All these factors reduce the environmental gradient from the fringe to the interior of the basin. Some stands also showed immature features which were attributed to the anthropogenic impacts of many kinds, mainly over the last 60 years, that have been preventing the mangroves from attaining their full development.