Wood density of Eucalyptus saligna grown in Hawaiian plantations: effects of silvicultural practices and relation to growth rate.

摘要

We evaluated the effects of chemical fertilizer, spacing, and interplanted nitrogen fixing trees on wood density and diameter growth of 15-year-old Eucalyptus saligna trees. The trees were grown in silvicultural trials established in 1982 on formersugarcane land on the island of Hawaii, USA. Elevation was 480 m, slopes were gentle, and annual rainfall averaged 4600 mm at the trial locations. Breast-high increment core samples were obtained by boring more than 100 dominant and codominant trees. Diameters of individual trees ranged from 16.4 to 45.9 cm, and cross-sectional wood densities from 349 to 496 kg m-3. Silvicultural treatment means for 15-year diameter ranged from 24.2 to 35.6 cm, and means for cross-sectional wood density from 400 to 424kg m-3. Wider spacing (4 m by 4 m vs. 2 m by 2 m) increased mean diameter by 34% without decreasing, and may have increased, wood density. Level of chemical fertilizer application did not affect wood density, and mean diameter of trees sampled in the twofertilizer treatments was identical. When compared to chemical fertilizer application, interplanting of N-fixing Albizia falcataria (Paraserianthes falcataria) trees increased mean diameter by 37% but did not alter wood density. Regression and covariance analyses indicated that growth rate per se (as evidenced by 15-year diameter) had negligible influence on wood density. Pith-to-bark profiles of wood density revealed that trees with rapid growth had more uniform wood density patterns across the radii.We conclude that diameter growth (hence, productivity) can be increased substantially through supplemental nitrogen and increased growing space without decreasing wood density; moreover, wood density may be slightly increased with additional growing space. Moreover, rapid growth - whether associated with improved nutrition or increased growing space - will result in wood with a more uniform density from pith to bark.