EFFECT OF GROWTH-RATE AND WIND SWAY ON THE RELATION BETWEEN MECHANICAL AND WATER-FLOW PROPERTIES IN SLASH PINE-SEEDLINGS

The objective of this experiment was to measure the simultaneous response of mechanical and water-flow properties in slash pine (Pinus elliottii Engelm. var. elliottii) seedlings to changes in growth rate and wind sway. Seedlings from a single half-sib family were grown in field plots and subjected to (i) whole-plot treatments of weeding, fertilization, and irrigation (complete), or no weeding, fertilization, and irrigation (control) and (ii) subplot treatments of staking or free to sway. Mechanical properties were analyzed in relation to Euler buckling and cantilever beam theory, and water-flow properties were analyzed with the interrelationship of leaf area (A1), the height to the center of leaf area (l), sapwood cross-sectional area (A(s)), and sapwood permeability (k). Data showed that the complete treatment did not have a significant effect on either the stress required for Euler buckling or the bending stress generated by a lateral stem movement. Staking, however, significantly decreased critical buckling stress and significantly increased bending stress. Both treatments significantly reduced the ratio between A1l and A(s)k primarily through increases in k. The results suggest that k is determined more by the mechanical stresses experienced by the stem than by the water-flow properties of the stem. This linkage may allow the seedling to increase k quickly and, thus, set the stage for waterflow properties of the mature tree.