Composição florística e estrutura de uma floresta densa de terra firme explorada seletivamente no município de Moju, Pará.

Abstract

Dynamics in the floristic composition and in the structure of a terra firme forest (2° 07‟ 30‟‟ - 2° 12‟ 06‟‟S and 48° 46‟ 57‟‟ - 48° 48‟ 30‟‟W) in the municipality of Moju, state of Para, Brazilian Amazon, was evaluated in a 9-year period after reduced impact logging. All individuals 5 cm dbh (diameter at 1.3 m above ground) and above were identified and measured in a 1.8 ha sample area. During the study period 219 species belonging to 50 families were recorded. Leguminosae, Sapotaceae and Moraceae were the most important families. Species richness increased immediately after logging and species diversity was high over the study period. Rinorea guianensis Aubl. and Lecythis idatimon Aubl. were the most important species considering abundance, frequency and basal area of individuals during the entire study period. The number of individuals decreased from the lower to the bigger size classes, with understorey (85% - 88,5%) being the most abundant followed by the low layer (9,5% - 10,5%), medium layer (2,0% - 2,8%) and the upper forest layer (0,67% - 0,9%). Diameter distribution of the individuls showed a reverse J-curve during the entire study period. Regarding to the ecological groups, the intermidiate species group was the richest (28.3%) follwed by shade tolerant species group (11.4%) and by the light-demanding species group (1.4%). Annual mortality rate was 1.34% and the annual ingrowth rate was 2.44%, so there was more ingrowth than mortality, suggesting that the forest is in its construction phase. Mortality rate was higer in the lower diameter classes and in the shade tolerant species group. Rinorea guianensis, Cecropia sciadophylla and Lecythis idatimon had higher mortality rates, while Rinorea guianensis, Protium pilosum and Lecythis idatimon had higher ingrowth rates. Richness, high diversity and forest structure are kept similar during the entire period, suggesting that reduced impact logging has contributed to the forest dynamics.