Radiata pine wood anatomy structure and biophysical properties

Abstract

Several important characteristics such as density, acoustic velocity, modulus of elasticity and tracheid dimensions are examined in stemwood, branchwood and rootwood in young (age 3 and 7) Pinus radiata. Stemwood air-dry density decreases little from ground level to the top of the tree falling gradually from 415 kg/m³ to 405 kg/m³. Branchwood air-dry density is higher than stemwood density. The branchwood density is approximately 480 kg/m³ close to the stem and then decreases sharply to ca. 410 kg/m³ near the branch tips. Rootwood density at 12% moisture content is similar to stemwood density ranging between 420 and 405 kg/m³. Density varies from stemroot junction to root tip in lateral roots (420 to 405 kg/m³) but changes little along tap roots (405 kg/m³) In stemwood, the air-dry modulus of elasticity increases from ground level (ca. 2.5-3.5 GPa) to approximately 4 metres (ca. 5.5-6.5 GPa) and then decreases thereafter to 7 metres (ca. 2.5-3.5 GPa). The air-dry MOE of branchwood decreases linearly with tree height up the stem from approximately 4.5 GPa at 1 metre to 3 GPa at 6 metres. Roots are the least stiff part of the tree. The air-dry MOE value decreases along roots from the stem-root junction (ca. 1.9 GPa) to the root tip area (0.5 GPa) in lateral roots, and from 1.4 GPa to 0.4 GPa in tap roots. In stemwood and rootwood the tracheid dimensions change with distance from ground level in both directions with significant different patterns. For stemwood, the tracheid length decreases with height up the stem. The mean tracheid length is approximately 1.70 mm at breast height whereas it is 1.55 mm and 1.40 mm at 2.4 metres and 4.6 metres respectively. Rootwood tracheids are much longer (nearly double) than stemwood tracheids. The tracheid length increases with increasing distances from the stem-root junction. The mean tracheid length adjacent to the stemroot junction area is approximately 2.2 mm whereas for the middle and root tip areas it is 2.6 mm and 3.3 mm respectively. Compression wood is a common feature of stem and branchwood. However, this atypical tissue is absent in roots except in some restricted instances where compression wood extends a short distance from the stem down into the root. Branchwood in green condition can be used to predict volume-weighted stemwood qualities at 12% moisture content when specific conditions are applied (select a straight portion of first branch segment from the largest diameter branch at breast height, R2 = 0.64). However, this approach has little practical appeal as equally good or better correlations can be obtained using Fakopp on standing trees (R2 = 0.75). Therefore future work should focus solely on the use of time of flight instruments such as Fakopp on stemwood.