Explaining variation in Brazil nut fruit production
Kainer K; Wadt L; Staudhammer C
Forest Ecology and Management
Brazil nut is widely recognized as the cornerstone of the Amazonian extractive economy. Tight linkages between Brazil nut production regional income and intact mature forests have thrust this species into focus as a key component of Amazonian conservation and income generation strategies. Nonetheless a comprehensive synthesis of factors explaining Brazil nut fruit production variation is lacking. We aimed to address this knowledge gap asking: (1) What are the rates and annual variation of Bertholletia excelsa fruit production at individual and population levels? (2) What factors explain B. excelsa production variation focusing on spatial and temporal variables diameter at breast height (dbh) crown attributes liana loads and soil attributes? and (3) Does liana cutting affect fruit production? Our model explained 73% of the variability in fruit production by 140 trees over 5 years. Dbh alone explained >50% and trees in the middle diameter range (100 cm ‚â§ dbh < 150 cm) produced best. Top-producing trees were loosely grouped spatially. Cation exchange capacity and P also explained production variation. The liana load variable was only weakly significant for explaining production variation and there were no direct significant effects of liana cutting. Cutting however did improve crown forms‚Äîanother highly significant model variable. This coupled with a weakly significant interaction of liana cutting by year suggests that liana cutting could improve production over time. In any given year approximately 25% of the trees produced 72% of the total population production. Annual variation of fruit production at the individual level was relatively high and at the population level was extremely low with annual production departing from average only in a year of delayed and reduced rainfall. These results coupled with low synchronicity of fruiting confirm long-term observations of harvesters that Brazil nut populations exhibit relatively constant fruit production. Results suggest that fruit productivity at the individual tree level could be increased possibly through experimental liana cutting and/or P amendments. At the population level Brazil nut collectors could potentially increase efficiency by concentrating collection efforts on consistently high producers and possible production ‚Äúhotspots‚Äù.