Efeito da topografia na florística em uma floresta de terra firme na Amazônia Oriental

Abstract

Understanding soil-plant interactions is important to generate information about forest ecosystems. The study was carried out at the Ferreira Penna Scientific Station (ECFPn), located inside the Caxiuanã National Forest, between the municipalities of Portel and Melgaço, Pará. The aim of the study is to test whether there is variation in the richness, diversity, and species composítion of the natural regeneration of the terra firme forest in relation to the platôs and baixios areas. Seventy-five plots of 2m x 2m were established in each of the two topographic zones in three locations. Within each plot, all individuals were counted and identified. Soil moisture in each plot was obtained with hidrosense. The floristic similarity between the plots was analyzed by NMDS (Nonmetric Multidimensional Scaling). 214 species were identified in natural regeneration, 162 species recorded in the platôs with 1164 individuals in forty-eight families, being Fabaceae Sapotaceae, Rubiaceae, Burseraceae, Lecythidaceae and Marantaceae the most representative. In the baixios we found sixty species with eight hundred individuals in thirty-two families, with the Cyperaceae, Poaceae, Rutaceae, Apocynaceae, Fabaceae and Araceae families being the most representative. The soil moisture of the terra firme forest was significantly lower in the platôs zones (x=17.9; dp=3.9) compared to the baixios zones (x=80.7; dp=18.5) (t=25.67; p=0.0001). The number of species of the natural regeneration plant community was significantly lower in the baixios compared to the platôs (t=-4.63; p=0.0001). The density of individuals of natural regeneration plants was significantly lower in the baixios (x=10.7; dp=4.2) compared to the platôs (x=15.5; dp=5.9) in the three areas inventoried in this study (t=-5.79; p= 0.0001). The NMDS analysis showed that there is a clear separation of the species composítion of the natural regeneration of the terra firme forest between the platôs and baixios plots (R=0.29561) (F=12.086; p=0.001). The natural regeneration plots in the platôs zones did not separate between the three sampling sites, while the plots in the three baixios areas did not separate sharply. The life forms that most influenced the separation of the species composítion between platôs and baixios were the arboreal, herbaceous and grass life forms. The results of this study are very important, as they demonstrate that even on a small geographic scale, a large partition of the species composition of the natural regeneration of the terra firme forest is observed between the two topographical zones and between the sampled shallows.