Population Structure of Brazil Nut (Bertholletia excelsa, Lecythidaceae) Stands in Two Areas with Different Occupation Histories in the Brazilian Amazon

Abstract

Here we hypothesize that the intensity of disturbances caused by human activities in Brazil nut stands (castanhais) is positively related with the regeneration of Brazil nut trees (Bertholletia excelsa H. B. K., Lecythidaceae) and consequently with a younger population structure of this species. In order to test this hypothesis we compared the population structure of Brazil nut trees in two areas of the Brazilian Amazon with different histories of land usage by humans. Archeological and historical data suggest that the region surrounding the Trombetas River was densely occupied in pre-Columbian times and experienced depopulation after European contact with Amerindian populations, especially in the 16th century. The 25 Brazil nut stands sampled in this region were dominated by old B. excelsa trees and had scarce recruitment in the understory. These very mature stands likely owe their origins to the interval between the depopulation of the indigenous peoples in the 16th-17th centuries and the establishment of quilombos at the beginning of the 19th century. The second study area was in the vicinity of the Madeira River (Capanã Grande Lake), where the castanhais were more accessible and disturbed. In this site, a younger population structure and abundant regeneration of B. excelsa were observed in the 10 sampled stands. Historical data from this region indicate that indigenous populations were replaced gradually beginning in the 18th century, with no evidence of severe depopulation. We suggest that the different historical and contemporary land use patterns contributed to the current contrasting population structures of the castanhais at the two locations. The data also support the idea that the castanhais, even the ones considered to be pristine and "native" forests, result from anthropogenic influences. We found no evidence to support restrictions on seed harvesting as a means to improve regeneration rates of Brazil nut stands. © 2011 Springer Science+Business Media, LLC.