Aspectos silviculturais da castanha-do-brasil (Bertholletia excelsa) em sistemas agroflorestais na Amaz\uf4nia Central

Este estudo avaliou o desempenho da castanha-do-brasil (Bertholletia excelsa) em sistemas agroflorestais implantados em ecossistema de terra firme na Amazônia Central. Foram avaliados 3 sítios de sistemas agroflorestais multi-estratificados, implantados em 1992, em áreas de pastagens degradadas, situadas no km 54 da BR-174, no Campo Experimental da Embrapa Amazônia Ocidental, em Manaus (AM). Os sistemas foram implantados após o processo tradicional de derruba e queima da vegetação secundária estabelecida em pastagens submetidas por 6 anos ao pastejo intensivo e abandonadas por 4 anos, em média, ao processo de regeneração natural. O desempenho da espécie com 12 anos de idade foi avaliado por meio do diâmetro à altura do peito (DAP), da altura total, da taxa de sobrevivência e das variáveis morfométricas "Diâmetro da Copa", "Proporção de Copa", "Grau de Esbeltez", "índice de Saliência", "índice de Abrangência" e "Forma de Copa". Os indivíduos atingiram altura total média de 20,9 m e DAP de 37,9 cm, com incremento médio anual de 1,74 m e 3,16cm, respectivamente. A porcentagem média de sobrevivência foi de 78%, cuja mortalidade foi relacionada às ventanias e raios. Os resultados indicaram a eficiência dessa espécie para reabilitar áreas degradadas e confirmaram-na como uma espécie adequada para formar sistemas agroflorestais.This study evaluated the development of Brasil nut (Bertholletia excelsa) in agroforestry systems established on non-flooding plateaus in Central Amazonia. Three multi-strata agroforestry systems established in 1992 in degraded pastures, located at the Experiment Station of Embrapa Amazonia Ocidental, BR-174 highway, km 54, Manaus, Amazonas, were evaluated. The area had been intensively managed as pasture for six years, then abandoned for four years, and reopened with traditional slash and burn practices to plant the agroforestry systems. Species development was evaluated with measurements of survival rate, trunk diameter at breast height (DBH), total tree height, crown diameter, canopy proportion, degree of slenderness, prominence index, inclusion index and crown shape. At 12 years of age, the trees had a mean total height of 20.9 m and DBH of 37.9 cm, with an annual mean increment of 1.74 m and 3.16 cm, respectively. Mean survival was 78%, with mortality due windstorms and lightening. These observations confirm the suitability of this species to help rehabilitate degraded areas and be included in agroforestry systems

Allometric regressions for improved estimate of secondary forest biomass in the central Amazon

Estimates of the sequestering of carbon by secondary forests - which occupy almost half the deforested area of the Brazilian Amazon - will be improved by the use of accurate allometric relationships for non-destructive measurement of standing biomass and by an evaluation of the suitability of existing equations for application in secondary forest. Species-specific and mixed-species regressions for estimating total above-ground dry weight (DW) were therefore developed using eight abundant secondary forest tree species in the central Amazon. Using only DBH as the input variable, the species-specific equations estimated DW of individual trees with an average error of 10-15%. For the mixed-species equations, developed using 132 trees from seven of the eight species (excluding Cecropia), average error in estimating DW of individual trees was 19.8% using only DBH and 15.0% using DBH plus specific density of the wood (SD). Average SD for each species can be substituted without increasing the error of the estimate. Adding total tree height (H) as an input variable provided only a slight reduction in error to 14.0%. Previously published mixed-species biomass regression models, based on primary and secondary forest trees of the Amazon, were also cross-validated against the trees of this study. Two of these models, based on primary forest plots and using only DBH as an input, overestimated biomass by 10-60% for central Amazonian secondary forest trees in the size range 5-25 cm. The overestimate was greatest for the larger trees. Including Cecropia in the test group will make the overestimate even greater. Those published equations using DBH, H and SD as inputs, whether from secondary or primary forest plots, showed better agreement with the sample-derived regressions and lower average errors in estimation of individual tree dry weights