Recovery of Pinus radiata saplings from tilting and bending

Summary

A study was made of how radiata pine saplings tilted to about 45 degrees by wind or by hand, when 1 to 4 m tall, recovered their upright posture, first by curving and then by tending to straighten their stems. Trees up to 1.5 or 2 m tall grew upright within a year and usually straightened their stems satisfactorily, except for a remnant of buttsweep near the ground. Larger trees took longer and tended to retain more substantial stem curvatures, such as buttsweep, top kink and S-curves.

The elongating zone at the tip of the stem responded by differential growth of its immature cells, and righted itself within a week. Curving in the rest of the stem was slower, because it depended on the prior formation of sufficient compression wood, and because bending resistance increases with stem diameter. These progressive time delays, combined with the fact that each displaced stem segment tended to right itself irrespective of the orientation of all other stem segments, resulted in complex sinuosities, which were further complicated by the twisting of leaning stems where compression wood developed within sloping grain. Most larger sinuosities were eventually straightened. Even the correction of buttsweep, the most obvious and persistent sinuosity, was substantial. In small trees this correction continued for 2 or 3 years after the tree had grown upright. Persistent local sinuosities tended to be hidden very effectively over the years by redirected (cavity filling) radial growth. When wind dislocates roots within the soil and thus causes the tree to tilt, the stem not only assumes a lean, but also bends under its own weight. This bending is due to immediate elastic deformation followed by indefinitely continuing creep. Both of these deformations were found to be reversible to a degree that depended on how long the trees had remained bent. Height growth was reduced while the trees were righting themselves, but diameter growth at the butt was not. Survival after tilting was often close to 100%, but it was much reduced in some boggy situations.

Key Words:

• wind damage
• sinuosity
• righting
• bending
• creep
• compression wood