Environmental variables, floristics, diversity, and species distribution in an Urban Alluvial Forest

The Alluvial Forest occurs along the margins of watercourses, as well as in wet lowlands and temporarily flooded zones. This study established correlations between the arboreal vegetation and environmental variables, to discover the main factors that influence the species distribution in fragments of the urban Alluvial Mixed Ombrophilous Forest (Guarapuava, Paraná, Brazil). The floristic survey was conducted in three transects (subdivided into 42 sample subunits of 100 m2), covering the water gradient across the riverbed. The tree species that presented Diameter at breast height (DBH) ≥ 5 cm were measured and identified. The variables measured were: piezometric level, volumetric and gravimetric soil moisture, penetration resistance, and chemical and granulometric soil analysis. The species abundance data were processed using the multivariate technique TWINSPAN, with subsequent phytosociological analysis; the environmental variables were then correlated with the abundance data (ind ha-1) through the Canonical Correspondence Analysis (CCA). Four groups were formed: (1) well drained soils; (2) moderately drained soils (intermediate characteristics); (3) soils with water saturation and (4) soils with greater hydromorphy. Subunits with higher water influence showed the lowest diversity values and the highest dominance values. The canonical correspondence analysis showed that the distribution of Gymnanthes klotzschiana, Ligustrum lucidum, and Allophylus edulis are related to soil water saturation, while the distribution of Matayba elaeagnoides and Ocotea puberula is correlated with well drained soils. The other species showed a preference for moderately drained soils. The groups separated the species according to environmental characteristics, indicating that hydromorphism influences the establishment of the forest community.