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Volumetric yields in small-scale plantations of Guadalcanal Island

Authors: David L. Cornelio
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2021, Issue N.Z.J.For. 66(2) 2021, pp 34-42, Aug 2021
Publisher: New Zealand Institute of Forestry

Abstract: This paper aims to quantify the growth performance of four exotic timber species commonly planted in Guadalcanal Island, which is in line with a new strategy of the Solomon Islands Government to restructure and further develop the forestry sector. The inventories were carried out in three woodlots on Guadalcanal Island of 5.0, 11.25 and 11.5 years of age. A total of 726 trees were measured and the results of mean annual increments (MAIs) were statistically compared. Tree heights were estimated by trigonometry and their merchantable volumes by considering the main stem as a frustum of paraboloid. It was found that the tree dimensions and the MAIs for the tree species at the Tetere site in Guadalcanal Island were similar, with larger basal areas (BAs) being achieved by trees in the borders of the plantation due to less competition for light and soil nutrients. The performance of the first species Eucalyptus deglupta (eucalyptus) compared to the other species at two of the sites was exceptional, even in areas where the other species did not perform well. The lack of pruning and thinning slows down potential volume gains and lowers the quality of the main stem of the second species Tectona grandis (teak). The third species of Acacia mangium (acacia) trees were sensitive to diseases in the woodlots, but further results from other provinces are needed, including soil and canopy cover assessments. The fourth species Swietenia macrophylla (mahogany) grows well if placed in humid areas or areas without risk of drying and it does not need regular pruning. The potential gains that can be obtained by intercropping the species studied remain unexplored in the islands. However, local farmers are familiar with native fastgrowing hardwoods such as Flueggea sp., inter-planting them with teak for early returns. It also facilitates the thinning of the teak trees and is highly valued in the building of traditional houses. This paper aims to contribute to the optimisation of tree plantations by enhancing the prediction of their productivity and therefore their potential economic returns.
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