Resumo. This research took place in a semi-deciduous forest fragment in secondary succession stages on Morro doCerrito in the municipality of Santa Maria, in the state of Rio Grande do Sul. The aim was to determinethe floristic groups in the study area by quantifying the sociology of main species and theirrelationship with geomorphologic and pedological compartments. Permanent plots measuring 10m2 were continuouslyallocated along the topographical gradient of the hill, beginning at the base and going to thetop. All trees with diameter at breast equal or larger than 5 cm height were measured. Grouping analysis was performedby (Twinspan), having as variables the number of individuals of the species and characterizedthe sites of groups by testing in the field of geomorphological compartments and morphological andchemical analysis of soils. Three ecological groups were found evenly distributed along the gradient as a result of differentsuccessions and environmental conditions that were due mainly to the substrate, the soilclasses, and landscape positions.