Brazil nut seedling establishment and autecology in extractive reserves of acre, Brazil

In the western Amazonian state of Acre, Brazil, extractive reserve residents are examining strategies to intensify their extraction-based system without compromising biological conservation. One such strategy is to increase production from their major source of income, Brazil nut (Bertholletia excelsa), by augmenting the species' density within the reserves. We evaluated the success of Brazil nut seedling establishment at three types of planting sites on extractivist landholdings: forest gaps, shifting-cultivation plots, and pastures. Nursery-grown seedlings were planted according to a randomized complete block design at five extractivist landholdings with planting sites as the main treatment. Average photosynthetic photon-flux density was approximately four times higher in shifting-cultivation plots and pastures than in forest gaps. Soil pH and extractable Ca, K, Mg, and P were the highest in shifting-cultivation plots. Pasture sites had the most compact soils and an intermediate pH value; forest-gap soils were the most acidic. There were no differences in total soil N, total soil C, and percent organic matter across the three sites. After two years, mean seedling height and diameter in the shifting-cultivation plots were almost double those of seedlings established in pastures and forest gaps, while seedling survival at all three sites was comparable, at approximately 40%. Seedlings in shifting-cultivation plots and pastures had higher predawn water potential values, foliar nutrient levels, and root biomass than seedlings in forest gaps. Although light, nutrients, and water resources were available in pastures, enrichment plantings in this site proved to be the least compatible with the overall extractivist system because of high labor inputs necessary for establishment, particularly if grazing animals were part of the system. Although forest gaps were appropriate enrichment sites from a socio-economic perspective, light availability was low, and both belowground resources, nutrients and water, appeared to be very limiting so that gap seedlings demonstrated slow growth. Shifting-cultivation plots were the best sites for Brazil nut enrichment plantings in extractive reserves. Light, nutrients, and water resources proved to be readily available, seedlings performed the best, and overall compatibility with the extractivist system was good.