Monodominância em bosques de mangue como consequência de tensores ambientais

Abstract

In the area of the extractive reserve of Iguape Bay there are untouched mangrove areas (highly preserved), but also woodland sites affected by human activities as they are near urban areas. In this ecological study, it was applied the study of the vertical structure of a forest in two mangrove areas that present different usage and occupation history aiming to compare and investigate the factors that when put together make a species monodominant in mangrove areas. In order to achieve this goal, it was allocated 26 plots in grids of 10x10m in both mangrove sites, located at opposite riverbanks of the Paraguaçu River estuary. A total of 362 individuals were registered in area 1, the most disturbed area, being 331 of Laguncularia racemosa species, 14 of Avicennia shaueriana species and 9 individuals of Rizhophora mangle species, thus confirm the monodominance of Laguncularia racemosa in this site. In area 2, a site of difficult access, possible to arrive only by boat, located on the opposite of the riverbank of area 1, it was registered 735 individuals, 41 of Avicennia shaueriana species, 454 Laguncularia racemosa species and 240 Rizhophora mangle species. Although most of the collected and identified individuals belonged to Laguncularia racemosa, the phytosociology parameters presented different results in relation to area 1. The relative frequency revealed a coexistence among Laguncularia racemosa and Avicennia shaueriana species (37,14%). About the relative density, there was a highlighted species inversion: Rizhophora mangle (32,6%) and Avicennia shaueria (5,6%). The average density of this area was 3,84 ind. m2.ha− 1 and the basal area achieved 0,438 m2.ha− 1. The mangrove sites were classified in different succession stages, considering that mangrove area 1 was highly damaged by the incessant human activities. The species distribution occurred due to the phenology plasticity of Laguncularia racemosa, which is more resistant to altered environments, and also due to the resistance of Avicennia shaueriana to restrictive conditions of environmental equilibrium.