Variation of heartwood and sapwood in 18-year-old Eucalyptus globulus trees grown with different spacings

摘要

Heartwood and sapwood development was studied in 18-year-old Eucalyptus globulus trees from pulpwood plantations with different spacings (3 x 2, 3 x 3, 4 x 3, 4 x 4 and 4 x 5 m), on cross-sectional discs taken at breast height. The trees possessed a large proportion of heartwood, on average 60% of the wood cross-sectional surface. Spacing was a statistically significant source of variation of heartwood area, which ranged between 99 and 206 cm(2) for the closer (3 x 2) and wider (4 x 5) spacings, respectively. There was a positive and high statistical significant correlation between heartwood diameter and tree diameter (heartwood diameter = -0.272 + 0.616 dbh; r (2) = 0.77; P < 0.001), and larger trees contained more heartwood regardless of spacing. Heartwood proportion in cross-section remained practically constant between spacings but increased with tree diameter class: 55.1, 62.2, 65.0 and 69.5% for diameter at breast height classes < 15, 15-20, 20-25 and > 25 cm, respectively. The sapwood width did not depend on tree diameter growth and remained practically constant at an average of 18 mm (range 15-21 mm), but sapwood area showed a good linear regression with tree diameter. Therefore, tree growth enhancement factors, such as wide spacings, will induce formation of larger heartwoods that can negatively impact raw-material quality for pulping. The increase in heartwood in relation with tree dimensions should therefore be taken into account when designing forest management guidelines.