The influence of canopy gap size on natural regeneration of Brazil nut (Bertholletia excelsa) in Bolivia

To test whether Brazil nut (Bertholletia excelsa) requires a specific canopy gap size in order to regenerate, 50 gaps of varying size (25-712 m(2)) and 20 understorey sites (each of 141 m(2)) were sampled in tropical moist forest at Riberalta, Bolivia. The density of Brazil nut seedlings (<1.30 m in height) and saplings (>1.30 m) was assessed at each site, and the light environment was determined using hemispherical photography to estimate the global site factor (GSF), which represents the proportion of total above canopy irradiance that is received below the canopy. Saplings only occurred in gaps >95 m(2) or >10.48 GSF, whereas seedlings occurred throughout a range of gap sizes and in the forest understorey. Regression analysis showed a highly significant relationship between Brazil nut sapling density against both gap size and global site factor (GSF). These results may contribute to the development of plans for sustainable management of this species, by defining the appropriate canopy gap size required for the successful natural regeneration of Brazil nut. (C) 2000 Elsevier Science B.V. All rights reserved.