Comparação florística e estrutural entre florestas de igapó e campinarana ao longo de gradientes hidro-edáficos na Reserva de Desenvolvimento Sustentável do Uatumã, Amazônia Central

Abstract

Amazonian igapó and campinarana are considered low-productivity systems and contain forests located upon soils with low nutrient availability and subject to periodical floods. Their species composition, diversity, forest structure and biomass may be equally limited by nutrient availability and some studies suggest a close relationship between their floras. The aim of this study was to describe and to compare the species composition, diversity, forest structure and biomass in an igapó and a campinarana in Central Amazonia and to test its dependence on soil texture, soil nutrients and hydric factors. We inventoried all individuals ≥ 10 cm DBH, distributed along six 0.5 ha plots in each ecosystem. We also calculated trees heights and basal areas. We estimated the above ground wood biomass (AGWB). Tree biomass was estimated based on two allometric models, which consider DBH, wood specific density (ρ) and tree heights, while palm biomass was estimated using an allometric model that considers only individual s height. We sampled 2163 individuals in the igapó and 1849 in the campinarana. Both ecosystems are characterized by high acidity and nutrient-poor soils, being the soil clayish in the igapó and sandy in the campinarana. Mean duration of flooding in igapó plots varied between 10 and 202 days year-1. Mean water table depth in campinarana plots varied between 39.7 and 245.5 cm during the rainy season and between 92.0 and 315.7 cm during the dry season. Although the campinarana was richer in tree species, mean Fisher s alpha diversity was not significantly different between both ecosystems. Floristic similarity between both ecosystems was extremely low (Bray-Curtis dissimilarity index 0.97). Floristic patterns were neither related to edaphic or hydric gradients in both ecosystems. Amanoa cf. guianensis was the most important species in igapó while Aldina heterophylla was the most important species in campinarana. Both ecosystems are similar in structure, with dominance of individuals of low heights and small diameters. They are also similar on biomass: AGWB amounted to 141 - 152 Mg ha-1 in the igapó and to 152 - 164 Mg ha-1 in the campinarana. Flood duration was negatively related to the biomass accumulation in the igapó. In both ecosystems, no dependence of biomass on edaphic gradients was detected. The low biomass found for the igapó and the campinarana when compared to other Amazonian ecosystems, seems to reflect the nutrient-poor soils.