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In the Guarani preservation area 100 ha of forest land was cut to evaluate harvest impact in natural subtropical forest. Two treatments were applied: “commercial logging” in which the logging contractor works in the traditional way, and “improved harvest” in which trees are selected and the skidding trails and landings planned. Forest structure and composition, seedlings and regenerations and soil physical parameters such as soil density, penetration resistance were measured before harvesting. The trees were cut by chainsaw and moved by a rubber tyred skidder to the landing area for loading on a truck. After harvesting, damage by cutting and by skidding was measured. All previous parameters were re-measured and traffic intensity in each plot calculated. The harvest yields were 9.9 m3 ha-1 for the improved harvesting and 16.4 m3 ha-1 for the commercial treatment. Trees felled were 6.8 trees ha-1 for improved harvest and 9.9 trees ha-1 for the commercial harvest. For canopy trees, commercial harvesting reduced the initial dominance 19.3%, while improved harvesting only decreased it 9.5% so forest structure is less affected by the improved harvesting. There was little change in abundance and species composition. Changes were observed in the order of importance of some species, e.g. Parapiptademia rigida was replaced by species of lesser importance. Regeneration after the commercial harvesting was less than in the improved harvesting method. Commercial harvesting had more (60%) traffic intensity (Mg km-1 ha-1) along all the skid trials in the plots.