Disturbance Level Determines the Regeneration of Commercial Tree Species in the Eastern Amazon

The effects of reduced-impact logging (RIL) on the regeneration of commercial tree species were investigated, as long-term timber yields depend partly on the availability of seedlings in a managed forest. On four occasions during a 20-month period in the Tapajós National Forest (Eastern Amazon, Brazil), seven commercial tree species were assessed as follows: the long-lived pioneers Bagassa guianensis and Jacaranda copaia; the partially shade-tolerant Hymenaea courbaril, Dipteryx odorata, and Carapa guianensis; and the totally shade-tolerant Symphonia globulifera and Manilkara huberi. In 2439 10 × 10 m plots, all individuals <20 cm diameter at breast height (dbh) were assessed over three intervals, before, during, and after the forest being logged. Before logging, the density of seedlings and saplings of the seven species did not change. Logged trees were spatially aggregated, with 9.2 percent of the plots being heavily impacted by logging. After logging, the recruitment rate increased more than the mortality rate, so that post-harvesting densities of seedlings and saplings increased. The increase in density was concentrated in logged plots with more disturbances. It is concluded that post-harvesting heterogeneity of micro-environments created by RIL may be an important component to be taken into account for sustainable forest management and conservation of commercial species.