Dinâmica de cobertura de dossel de povoamentos de clone de Eucalyptus grandis W. Hill ex-Maiden submetidos a desrama artificial e desbaste

Abstract

A dinâmica de copa foi avaliada através do índice de área foliar (IAF), transmitância da radiação fotossinteticamente ativa (t%) e índice de cobertura do dossel (ICD), entre 55 e 68 meses de idade, em povoamentos de clone de Eucalyptus grandis desramados entre 16 e 45 meses de idade até a altura de 6 m. Esses povoamentos foram submetidos a desbaste (0 e 35% do número total de mudas plantadas), aos 55 meses de idade, em Abaeté, MG. Não foi observada diferença significativa (P≥0,05) entre os tratamentos de desrama, para IAF, t% e ICD, entre 55 e 68 meses de idade, em razão da elevada capacidade de recomposição de copa desse clone. Porém, observou-se mudança significativa (P≤0,05) nesses parâmetros entre as idades de avaliação, e houve redução de IAF e ICD e aumento de t% imediatamente após o desbaste, tendo havido pronta recomposição da copa seis meses após o desbaste, nas três idades de primeira intervenção de desrama. Aos 68 meses de idade, o IAF e o ICD do povoamento desbastado foram significativamente (P≤0,05) maiores, enquanto t% foi significativamente menor do que do povoamento não-desbastado. Os resultados de IAF e t% indicaram que essas informações podem ser utilizadas para avaliação da dinâmica de copa, sendo os dados de IAF mais consistentes do que os de t%. A utilização de fotografia digital apresenta potencial para avaliar a dinâmica de cobertura do dossel, em razão de ser um método de uso fácil e barato, embora ainda requeira aperfeiçoamentos.

Crown dynamic based on leaf area index (LAI), photosynthetic active radiation transmitancy (t %) and crown cover index (CCI) of Eucalyptus grandis clone stands was studied in southeastern Brazil. Plants were submitted to various pruning intensities and frequencies, starting at the age of 16, 20 and 28 months, up to 45 months, to reach 6 m pruned trunk. Thinning was applied at the age of 55 months by removing 0% (control) and 35% of the total number of planted trees. There was no significant (P ≥ O.05) difference among pruning treatments for LAI, t% and CCI. LAI decreased from 2.75 to 1.98, immediately after thinning. A significant LAI recovery (P≤ O.05) was verified six months after thinning. LAI of the control was 29.3% higher than that of the thinned forest, at the age of 68 months indicating that by the age thinning was applied, the trees were still capable of expanding their crown. Photosynthetic active radiation transmitancy increased from 11.9 to 22.7%, shortly after thinning, reducing to 16.8% at the age of 68 months due to leaf recover. In the non-thinned forest, t% was 9.6%, value significantly (P≥0.05) smaller than that observed in the thinned forest (16.8 %). CCI (digital photograph method), at the age of 55 months reduced after thinning, from 0.83 to 0.69, and to 0.70 at the age of 68 months, showing that this method was less sensitive to evaluate crown dynamics, if compared to LAI and t%. In the non-thinned forest, CCI was 0.79, significantly (P≥0.05) higher than that observed for the thinned forest at the age of 68 months. The overall results indicated that LAI and photosynthetic active radiation transmitancy are suitable for crown dynamic evaluation, with the LAI data being more consistent. The method using digital photograph is inexpensive and easy to use, although it still requires improvement.