Mid-term effects of reduced-impact logging on the regeneration of seven tree commercial species in the Eastern Amazon

Reduced-impact logging (RIL) is a set of techniques aimed to maintain forest structure and functions of the harvested forest as similar as possible to pre-logging status, while reducing adverse impacts from logging activity on the remaining forest. We analysed the mid-term effects of RIL on the regeneration of the long-lived pioneers (LLP) Bagassa guianensis and Jacaranda copaia; the partially shade tolerant (PST) Hymenaea courbaril, Dipteryx odorata, and Carapa guianensis and the total shade tolerant species (TST) Symphonia globulifera and Manilkara huberi. This study was carried out in an intensive study plot in the 600,000-ha Tapajós National Forest, Eastern Amazon – Brazil (03°02′S and 54°56′W). Three transects split in 10 × 10 m plots, adding up to 2.37 ha were sampled in an area where RIL was applied, and compared with a same size sampling in an unlogged area. The regeneration of individuals ⩽20 cm in dbh was inventoried and measured before logging in 2003 and three times after logging (2004, 2006, and 2009). RIL modified the forest structure creating more gap-phase plots, with the consequences of such disturbance still remaining after 6 years. Densities of B. guianensis, J. copaia, and S. globulifera increased, while C. guianensis diminished. The positive effect on the density of LLP species was, however, ephemeral and disappeared 2 years after logging. RIL had a positive effect on the height growth rate of S. globulifera and on the dbh growth rate of C. guianensis. Plants growing in the gap-phase plots had higher height growth rates (ANOVA, F2;2980 = 33.3, p < 0.001) than plants growing in other phases, but the same difference was not observed for dbh growth rates (ANOVA, F1;364 = 0.9, p = 0.33). Crown position had positive effects on height and dbh growth rates: the higher the crown position, the faster the plant grows in height (ANOVA, F3;2979 = 148.4, p < 0.001) and dbh (ANOVA, F3;362 = 26.1, p < 0.001). The application of RIL following the Brazilian regulations, may be considered a silvicultural technique for increasing density and growth rates of commercial species, but additional silvicultural interventions, as liberation for example, might be required for maintaining the ecological outcomes of RIL in the long run.

► Effects of reduced-impact logging (RIL) on forest structure remain over 6 years.
► RIL is a treatment to increase recruitment and growth of marketable species.
► Desirable improvements of RIL on the regeneration disappear in the mid-term.
► Additional silvicultural treatments are needed to assure RIL benefits on regeneration.