Enrichment planting of Bertholletia excelsa in secondary forest in the Bolivian Amazon:: effect of cutting line width on survival, growth and crown traits

Enrichment planting is commonly used for enhancing the density of desired tree species in secondary forests. Bertholletia excelsa is one of the most important economic species of northern Bolivia, and there is interest in increasing its density in secondary forests. The aim of this study was to evaluate the effect of line planting on the survival, height growth and crown traits of Bertholletia plants growing in a secondary, forest. Seedlings were planted randomly to five different treatments: cutting lines of 2, 4, and 6 m wide, total clearing of the vegetation, and untouched vegetation; each with four replications. Light levels were estimated twice during the experiment using hemispherical photographs. Survival and height growth were measured for a period of 4 years, while crown traits were measured once. Cutting lines with different widths resulted in significantly different canopy openness (range 16-55%). The reduction in canopy openness above the plant crown through the study period ranged from 32 to 54% depending on the treatment. Survival rate of Bertholletia plants was lower in the untouched vegetation (86.5% per year) than in the other treatments (97% per year). After 4 years, mean plant height ranged from 0.7 to 3.9 m. Height growth rate was higher during the period 1995-1996 than during 1998-1999, and it was higher in the more open treatments, Crown traits of the Bertholletia plants varied with plant size, and were not affected by treatment. There was no effect of line width on survival of Bertholletia plants, but plants grew better in height in the 6 m line width and the total clearing of the vegetation. These results indicate that for enrichment planting of secondary forests with Bertholletia, it is necessary to open and to maintain line widths that allow for a canopy openness in the range of 25-40% to guarantee high rates of height growth. (C) 2002 Elsevier Science B.V. All rights reserved.