Topografia e solo definindo a vegetação em escala local no ecótono cerrado - floresta amazônica

Abstract

The patterns of spatial distribution of species are influenced by environmental and biotic characteristics that determine the species' ability to establish themselves in specific environments. Thus, regional or local geoenvironmental conditions have contributed to the current configuration of the various Brazilian vegetation formations. We analyzed in this work the variation in vegetation composition and structure explained by physical variables such as topography, soil, climate and microclimate in contact areas, Cerrado and Amazon Rainforest. We tested the hypothesis that on a local scale variations in topography should better explain the distribution of species between Cerrado and Amazonian Forest formations. We performed the data collection in grids of 100x100m subdivided into plots 20x20m. We systematically sampled six plots in each formation with 3 spatial replicates: Cerrado 3 (areas 1, 2 and 3) and Forest 3 (Area 1, 2 and 3) and inclusion criteria were individuals with PAD (diameter at height of chest) at 1.30m of soil ≥ 10cm. We collected soil, microclimalocal (temperature and humidity) and climate (temperature and precipitation) data, as well as Declivity and Altitude data per plot. We performed exploratory analyzes of the data (similarity between samples using Cluster UPGMA), to verify the existence of difference in composition and structure between the two formations, and the Student 's T test to define the environmental variables that differed between the Cerrado and Forest formations. We tested the working hypothesis and the interaction of vegetation patterns and environmental factors through Canonical Redundancy Analysis (RDA) and the partition of the variance explained through partial redundancy analyzes with program R. The two formations are floristic and structurally distinct, without overlapping floristic composition denoting abrupt transition. The redundancy analysis explained 20.7% of the variation of the vegetation in the first two axes, being the variables Saturation in Bases, Effective Cationic Exchange Capacity more related to axis 1 and Altitude and Declivity more related to axis 2 of the analysis. Therefore our hypothesis was partially corroborated, since the studied area presented a fertility gradient of the forest areas for the Cerrado and the Declivity and Altitude act in a relevant way to distinguish between these formations in environments of ecological tension. Altitude and Declivity are factors that act in the distribution of the species in local scale, probably acting as modulating agents of the distribution of nutrients in the soil.