Yan-San Huang

Biomechanical modeling of gravitropic response of branches: roles of asymmetric periphery growth strain versus self-weight bending effect

Bending movement of a branch depends on the mutual interaction of gravitational disturbance, phototropic response, and gravitropic correction. Four factors are involved in gravitropic correction: asymmetric growth strain, eccentric growth increment, heterogeneous longitudinal elasticity (MOE), and initial radius which are associated with reaction wood production. In this context, we have developed a simplified model to calculate the rate of curvature change by combination of these factors. Experimental data from Taiwan red cypress were used to test the validity of the model. Our results show clearly that asymmetric growth strain is the main factor involved in correction. Eccentric growth increment has positive efficiency and increases correction in addition to growth strain, while the total effect of longitudinal MOE variation has negative efficiency and decreases correction. Spring-back strain measurement is found to be useful for the measurement of self-weight bending moment of branch. The branches studied are essentially close to a biomechanical equilibrium which maintains branches in horizontal positions. In the case of a deciduous dicotyledonous tree, flamegold, the effect of defoliating behavior on measured growth strain and curvature change was formulated by a modified model. Growth strain is the sum of measured growth strain after defoliation and spring-back strain during defoliation. The curvature change can be calculated by using measured growth strain and spring-back strain after defoliation. These results show that full-leaf branches of flamegold have a tendency to bend downward, but defoliated branches have a tendency for upward bending. The efficiency of correction increased after defoliation due to weight loss.

Effects of chemical modification reagents on acoustic properties of wood.

Summary The acoustic properties of several chemically modified Sitka spruce samples (Picea sitchensis Carr.) were evaluated in the longitudinal direction of wood specimens. Sitka spruce treated with glyoxal and carboxymethyl cellulose (CMC) displayed superior acoustic properties to those obtained by the other treatments. The acoustic converting efficiency (ACE) of the glyoxal-CMC treated Sitka spruce was 1.84 times of that of the untreated specimen and the specific dynamic Youngs modulus (E′/r) was retained without decrement after such treatment. Changes in the tanδ of Sitka spruce treated with glyoxal and different concentrations of 1,4-butanediol were opposite. With a low concentration of 1,4-butanediol (10%), the tanδ of the treated specimen decreased as a result of the formation of crosslinked cyclic structures. The potential presence of more alkyl hydroxyl groups in the Sitka spruce, after being treated with glyoxal and a high concentration of 1,4-butanediol (20%), resulted in the increment of tanδ and the decrement of ACE. The impairment of the acoustic properties of Sitka spruce was caused by the introduction of free chains with endwise carboxylic acid groups into cell walls after the succinic anhydride treatment. Slight improvement on the ACE of Sitka spruce was achieved by the reaction with acetic anhydride and the decrease in the tanδ was about 15%, which was attributed to the partial formation of crosslinked matrix. These results revealed the improvement of the acoustic properties of chemically modified wood that was probably achieved only by the formation of network structures between wood components and reagents.

Growth stresses and related anatomical characteristics in coconut palm trees

The surface growth strains and the distribution of internal stresses in woody palms, coconut (Cocos nucifera L.), were determined by measuring the strains released by the kerf method using strain gauges. Measurements of the surface strains showed that longitudinal tensile stresses existed at the cortex, while longitudinal compressive stresses existed at the periphery of the central cylinder. These stresses may be generated from the fibers located in the scattered fiber and vascular bundles. In the central cylinder of narrow and wide trunks, both positive and negative stresses were observed, indicating the existence of some tensile and compressive stresses in the trunks. The amount of stress varied from base to top and from periphery to core because of the variation in proportion of the vascular bundles and the fibers, and the cell wall layers of fibers along these points. Furthermore, changes in the angle of vascular bundles and of the fiber microfibrils were correlated with the various tensile and compressive stresses located in the central cylinder of the trunks.

GROWTH STRAINS AND RELATED WOOD STRUCTURES IN THE LEANING TRUNKS AND BRANCHES OF TROCHODENDRON ARALIOIDES - A VESSEL-LESS DICOTYLEDON

Leaning trunks and branches of Trochodendron aralioides Sieb. & Zucc., a primitive vessel-less dicotyledon, show increased radial growth and gelatinous fibers on the upper side similar to the features found in dicotyledons with vessels. The patterns of peripheral longitudinal growth strain are variable among trees but similar at different heights within the same leaning trunk. Growth strains on the lower side of the trunks are very small but they are relatively large on the lower side of the branches. Growth stress in the branches is partly affected by the gravitational bending stress, which would be exerted mostly on the lower side. Large spring back strains of branches are associated with large surface strains. Both the microfibril angle (MFA) and the percentage area of gelatinous fiber show positive relationships with the measured strains. The MFA of the S2 wall layer in tracheids in the opposite wood is 24.6 ± 2.2°, whereas the MFA of gelatinous layer in the tension wood is only 14.2 ± 2.7°. The difference of MFA between the gelatinous fibers and the opposite wood is one of the factors accounting for the large contracting force for reorientation.

Biomechanical features of eccentric cambial growth and reaction wood formation in broadleaf tree branches

Tree branches and stems have different physiological functions that work collaboratively to maximize light interception. Light penetration in tree crowns is controlled by the orientation of the branches. However, mechanisms of branch bending have not received the attention they deserve. This study approached the problem by investigating the growth strain distribution in the upper and lower sides of branches of broadleaf trees, estimating the bending tendency of branches, and observing the branch eccentricity and the distribution of gelatinous fibers. The strain distribution was compared between the branches of 11 species (including 8 examined species and 3 referenced species) and tilted stems of 37 species from both our data and previous reports. Compressive strain was generally observed on the lower side of branches, but little was measured in tilted stems. The pith eccentricity of branches was in a reverse pattern to the corresponding strain distribution of stems. The radial growth of branches was hypotropic in contrast to the epitropic eccentric growth in inclined trunks. Furthermore, on the upper side of branches, G-fibers within the fiber arcs formed in an intermittent manner rather than in the continual manner found in artificially inclined stems. The resultant upward bending moment might not suffice to counteract the branch’s own weight; therefore, most of the measured branches, differing from tilted stems, tended to bend downward. In conclusion, by comparing the biological and mechanical aspects of the strain distribution, bending tendency, and eccentricity, our experiments could discriminate the bending dynamics and role of G-fibers in tree branches from that of main stems.

Strain distribution, growth eccentricity, and tension wood distribution in the plagiotropic and orthotropic branches of Koelreuteria henryi Dummer

Key messageWith the diversified distribution of growth strain and tension wood,Koelreuteria henryibranches function in a different way from the trunk in maintaining the tree architecture.AbstractThe tree branches, as well as trunks, function in keeping tree biomechanical equilibrium; however, researches regarding the reorientation of branches have received less attention than those of trunks. The presented paper aims to discriminate the biomechanical behavior of branches from leaning trunks. We thus investigated the development of growth strains, distribution of tension wood, and eccentricity on the branchwood of Koelreuteria henryi. The results revealed the unusual distribution of released growth strain and tension wood as well as growth eccentricity. The growth strain parameter showed seasonal changes, possibly due to the maturation of the secondary cell wall. Both the upper and the lower sides of the plagiotropic branches exhibited either contractive or extensive growth strains, whereas the orthotropic branches exhibited mostly contractive strains on the both sides, which implied different physiological functions of the two branch types. The tension wood arcs may occur in any direction of the branchwood which is different from the inclined trunk with tension wood on the upper side, suggesting dynamic adjustment in branch reorientation. In contrast to trunks, the hypotrophic eccentric growth in branches functioned in obstructing upward movement and even facilitates downward movement, probably because of the dissociation between tension wood and eccentric growth. Diversified growth strain and tension wood distribution on the branches may reflect the individual biomechanical requirements for each branch depending on the environmental factors, possibly gravitropic and phototropic stimuli.

Applicability of Plantation Wood for Blockboard and Fancy Plywood Making

This study focused on the use of plantation wood grown in Taiwan for making wood blockboard and fancy plywood and their actual practice tests. The ultimate goal of the study is to enhance the value of the wood for these uses, thereby stimulating more effective use of forest resources. In the experiment, the wood of plantation China fir (Cunninghamia lanceolata) was used as central block or ply. The veneers of radiata pine (an imported wood species) were placed near the central layer and also served as the face plies. Then the wood blockboard and the plywood were made. The resulting wood blockboard and plywood were further processed to form the fancy plywood by way of overlaying. Certain property tests were chosen to examine the test panels in an attempt to learn their application potentials. The test results obtained from the static bending of the wood blockboard showed no difference as to whether the glue was applied or if it was not applied to the edge of the wood blocks that formed the core of the panel. As noted, the bending strength was stronger in the parallel grain direction than in perpendicular direction. The use of glue on the edge of the wood blocks caused an adverse effect on the panel stability with a severer warpage result as compared to those blocks without glue on edge. The shear test results indicated that the plywood with China fir veneer as central ply had a comparable glue shear strength to that with radiata pine veneer and that both panels were superior to commercial lauan plywood. The shear through-the-thickness tests of plywood were conducted using the test specimens prepared with the grain of face veneers in the parallel or 45 direction. In both cases, the plywood with radiata pine as the core showed higher shear strengths than those of China fir. The use of China fir veneer core showed a better shear strength than that of commercial lauan plywood when tested in the parallel grain direction of face veneer. The reverse was true in the 45° direction. The study used an ultrasonic wave test to examine the starved joint of plywood defect. The results were promising, indicating the nondestructive test potential. Furthermore, it was found that after applying NC lacquer, the degree of gloss, surface hardness, and wetting angle of the fancy plywood all increased. It is concluded that the plantation wood of China fir may be used as core materials in making blockboard and plywood.