How the hydraulic and mechanical properties of wood influence branch form in Norway maple (Acer platanoides L.)

An in-depth understanding of the functions of branches (hydraulics and mechanics) and how they influence canopy form is needed in order to assess the impacts of cultural practices such as pruning in the future. This dissertation is comprised of three studies that investigate how anatomical and material properties of wood vary along Acer platanoides L. (Aceraceae) branches and whether the variation influences branch form. The hydraulic study found that vessel radii size decreased and density increased in the distal direction, consistent with the hydraulic flow found in previous studies. Vessel density was highest 5 cm proximal to the most recent terminal bud scale scar, suggesting that the increase in vessels may be due to hydraulic constrictions and partitioning through the branch attachment zones for the paired lateral branches. The mechanics study observed that modulus of elasticity (E) was 75% lower at the branch tips than in the proximal (structural) locations. Density-specific stiffness (E/ρ) was not found to vary between the three structural locations, suggesting that the elastic similarity modeled cannot be rejected due to variation in E/ρ. Variation in E was negatively correlated with the percent area of vessels and positively correlated with mean fiber cell wall size, suggesting a balance between hydraulics and mechanics. The allometric study found branches transitioned from a log-log curvilinear relationship converging to a linear relationship after 3 m in length. The linear relationship was best modeled with the elastic similarity model. The shift in allometry corresponds to a shift from increasing slenderness ratio (length / radius) with increasing branch length to a decreasing ratio as flexible sun branches transition to stiffer structural branches. The number of subordinate branches was found to increase after the primary branch length passed 3 m, suggesting that branches transition to a structural role as size increases. The differences in anatomical and material properties, the increase in the number of lateral branches and the shift in allometry are probably related to wood development type. Torsional balance of bending moments were found to be relatively evenly distributed along the left and right side of the branches.Ph.D.Includes bibliographical referencesby Gregory Ames Dahl