The purpose of this study was to characterize the floristic composition and horizontal structure of an Alluvial Araucaria Forest remain, located in the Guarapuava Municipality, PR; to evaluate the forest dynamics during the period of 2007 to 2011; as well as to analyze the influence of environmental variables over the arboreal vegetation along an environmental gradient. The floristic, phytosociology and the forest dynamics were evaluated in 6 permanent sample plots with 500 m2 divided into 30 subplots with 100 m2 each, totaling 0.3 ha of sampled area. Plots were set in 2007 and trees with DBH ≥ 5 were measured, identified and marked for the future evaluations. In 2011 trees were measured again and mortality and recruitment were counted. Studying the correlations between environmental variables and vegetation, were used 3 transects (A, B and C) along an environmental gradient. Transects were divided into 100 m2 subplots, where trees with DBH ≥ 5 were measured and identified. Soil samples were collected from each subplot for the chemical and physical analysis, and compaction were measured using a digital penetrometer. Forty-four species were identified in both evaluations and the Shannon Diversity Index ranged from 2.62 in 2007 to 2.67 in 2011. Sebastiania commersoniana was the most representative specie of the arboreal community, presenting the highest values for the Density, Dominance, Frequency parameters, and consequently, the Importance Value on both moments (22.20% and 22.72%, respectively), followed by Matayba elaeagnoides, Prunus myrtifolia e Ilex theezans. The forest presented an average basal area increment of 0.86 m2.ha.year-1 and average diameter increment of 0.24 cm.year-1. Mortality rates were higher than the recruitment rates (3.77% year-1 e 2.88% year-1, respectively). The results of chemical soil analysis showed soils with high acidity, high Al+3 concentration and low bases saturation, indicating soils with low fertility. The physical analysis showed the predominance of clay texture in all the subplots and the compaction analysis did not show the presence of significantly compacted soils. According to the cluster analysis and edaphic gradient was evidenced on the transects B and C and the principal component analysis identified the pH and Ca as the most determinants among the variables. The canonical correspondence analysis evidenced the preferential occurrence of Sebastiania commersoniana, Allophylus edulis and the exotic specie Ligustrum lucidum at places with high Ca, Mg and P concentrations, and places with high basal area. Conversely, Prunus myrtifolia and Vitex megapotamica occurred preferentially at places with low pH and, consequently, high Al+3 concentrations, and more compacted soils. As conclusions, the low floristic diversity of the forest, high predominance of few species and instability between the mortality and recruitment rates, as observed at the study area, might be consequence of the constraining environmental factors taking place on alluvial forests. The establishment and development of the arboreal species is more related to the soil drainage and groundwater level than the soil fertility.
