Effects of Reduced Impact Logging on genetic diversity and spatial genetic structure of a Hymenaea courbaril population in the Brazilian Amazon Forest

Abstract

Levels of genetic diversity, inbreeding, and spatial genetic structure were investigated at different ontogenic stages for a population of Hymanaea courbaril, before and after Reduced Impact Logging (RIL) was applied, in a 546-ha plot in the Tapajós National Forest, in the Brazilian Amazon. The multilocus genotype of nine microsatellites loci was determined for 74 juveniles (dbh < 10 cm), 59 subadults (10 ≤ dbh < 50 cm), 76 adults (50 ≤ dbh < 100 cm), and 54 large adult trees (dbh ≥ 100 cm). The results show a clear tendency of increase in the levels of observed heterozygosity and decrease in the fixation index between juveniles and large adult trees. Although these results were not significant ( t-test, P > 0.05), they suggest the occurrence of inbreeding depression. All ontogenic stages showed spatial genetic structure at short distance classes (<200 m), but the levels are not constant among the subpopulations. The harvest of 61% of the reproductive trees caused a loss of 37 (25%) low frequency and rare alleles from the mature population. However, 24 of the “lost” alleles are present in juvenile and subadult populations which might allow their reintroduction into the population when these trees become reproductive. RIL also caused a reduction of the observed and expected heterozygosity of the unlogged reproductive population in comparison to the reproductive population, although these results were not statistically significant ( t-test, P > 0.05). Logging also reduced the distance of the spatial genetic structure in the reproductive population from about 800 to 200 m. In general, our results indicate that RIL affected the gene pool and spatial genetic structure of the reproductive population.