The use of stem dissection to sample trees of different ages for determining pulping properties of tropical pines

Abstract

A study was undertaken to determine the effects of rotation age and site altitude on the quality of unbleached kraft pulp made from Pinus elliottii and P. patula grown in the Usutu Forest, Swaziland. Stands well beyond the current rotation age of 18 years were selected at site altitudes of 850, 1200 and 1450 metres. From each tree felled, sample discs were removed to represent the tree as it was at 11, 18 and 25 years of age. This was done by counting back the appropriate number of growth rings for the required age at each sampling point up the stem and paring them off the disc. Wood density, alpha-cellulose, lignin and ethanol-benzene-soluble extractives were measured in the wood and tear and tensile indices on the pulp. The patterns of variation with age were as expected from previous work where whole trees were sampled for each age class except for the ethanol-benzene solubles which showed a decrease with age for the dissected tree. It is concluded that the technique reduces the logistical problems of sampling separate trees to represent different ages from different sites; it controls within-site genetic and environmental variation and it is suitable to determine variation of pulping properties with age and site.