Effects of reduced impact logging (RIL) on the floristic composition and structure of a dense ombrophylous forest in the Brazilian Amazon

This study aimed to evaluate the changes that occurred in floristic composition, species diversity and forest structure after subjecting the forest to reduced impact exploration in the Tapajos National Forest, Para. The data were obtained in permanent plots (2500 m(2)) installed in 3 Annual Production Units (APU n degrees 2, 3 and 5) that were explored in 2007, 2008 and 2010 in APUs. The Inventories occurred on 4 occasions: the first before logging and the remaining after each logging. Data collected were the diameter at breast height, measured at 1.3 m above the soil (dbh) equal to or greater than 10 cm. Subsequently the floristic composition and diversity was evaluated using the Shannon-Wiener index (H') by phytosociological estimators (Density, Basal Area and Volume). Analyses of variance (ANOVA) of the analyzed variables were calculated between the successive settings to 95% of probability; where significant differences were found the Tukey test (alpha=0.05) was applied. Throughout the evaluated period, an average of 135, 160, 159 species were recorded in APUs 2, 3 and 5, respectively. The family with the greatest floristic wealth was Fabaceae in all registrations in the 3 APUs. The diversity index (H') was considered high even after the EIR with values ranging from 4.10 to 4.35. After logging, the estimators obtained dropped in values, recovering over the years. The ANOVA indicated a significant difference only in the tree density (tree.ha(-1)) in the APUs 2. The logging applied in the APUs minimized the damage to the remaining trees due to the moderate cutting intensity. The behavior of the forest allows us to infer that its recovery to pre-sustainability EIR values, is achieved ahead of the next cutting cycle; therefore not compromising the timber production.