The regeneration of Brazil nut trees in relation to nut harvest intensity in the Trombetas River valley of Northern Amazonia, Brazil

Abstract

This study examined the harvest of nuts from Brazil nut trees ( Bertholletia excelsa) in the valley of the Trombetas River, a 760-km tributary on the northern bank of the Amazon River in Pará state, Brazil. The region is characterised by old-growth forests dominated by Brazil nut trees. Demographic data were obtained from twenty-five 50-m × 1000-m transects with different harvest intensities (total area = 125 ha) established approximately along the trails used by Brazil nut harvesters. For each transect, correlations were calculated between regeneration indicators (seedling, sapling, and juvenile densities) and potential ecological and demographic variables. The Brazil nut populations in the region were characterised by a low proportion of juveniles (7.8% of trees had a 10 cm < diameter at breast height – DBH < 40 cm), a dominance of large trees (DBH > 100 cm), and a tendency towards old growth (25.5% of trees had a DBH > 160 cm). There were no seedlings in 52% of the transects, and 80% of the transects had no saplings. The low regeneration levels observed were independent of both harvest intensity and the dispersive activity of agoutis. An analysis of the regeneration indicators and the possible explanatory variables showed that harvests were not responsible for the low regeneration levels observed in the region. Furthermore, in areas with shorter distances between the points of harvest and first transport, the densities of saplings and juveniles were greater. We conclude that the restrictions on Brazil nut harvesting that are intended to improve the regeneration of Brazil nut trees are of little or no value. We propose the implementation of compensatory measures involving local communities and the promotion of seedling enrichment in gaps, forest edges, and disturbed areas, with the goal of promoting the growth of new generations of Brazil nut trees in the region.