Longitudinal residual strains of maturation and kraft pulp yield in the genus Eucalyptus, first results

The present study was within the framework of AFOCEL¿s research on selection of Eucalyptus clones for pulp and paper properties. In a stand located in Pyrénées-Atlantique (French department), four 7 year old trees of the same clone (E. gunnii x dalrympleana hybrid) were chosen. Every metre from 0.5 to 7.5 m, four longitudinaI residual strains of maturation (LRSM) were measured with an even distribution around the circumference. The measurement of LRSM is directly linked with growth stresses. At the same places, increment cores or little pieces of wood were sampled to a depth not exceeding 2 or 3 cm. These samples were measured for wood basic density, and by using micropulping methods, pulp yield (unbleached Kraft pulp) and pulp colour (strongly correlated with permanganate index) were determined. Two series of Kraft micropulping tests were undertaken. firstly with 22% alkali and 22% suIfidity. then with 24% alkali and 30% sulfidity. Results indicate that wood basic density and colour of unbleached Kraft pulps are not significantly correlated with LRSM¿s values, but on the other hand, unbleached Kraft pulp yield is always highly correlated with LRSM¿s measurements. LRSM is indeed a predominant explanatory factor of the high intra-tree and intra-clonal variability (coefficient of variation around 15%). The covariance analysis (pulp yield, cov. LRSM) indicated that neither individual tree nor sampling height significantly influenced the relationship between pulp yield and LRSM. (Texte intégral