Secrets for Nurturing Sturdy Trees

By Alan J. Heavens
The Philadelphia Inquirer
Saturday, October 4, 2008

A thunderstorm with strong wind is enough to send tree limbs crashing down onto property.

Why not do some preventive tree maintenance? Here are tips from a variety of sources.

· Need to know: University of Georgia professor Kim Coder says trees are formed to adjust to wind loading -- that is, a breeze from one direction applied evenly over the stem, branches and tree leaves. In any wind, gusts and calms alternately load and release the tree; under normal weather conditions, trees sway. Movements in the wind initiate changes in the woody material developing the tree's stem.

· Strong, silent types: Say the wind comes from the east all the time. The side of an oak tree facing the wind is stronger than the opposite side. With pines, however, the stronger part of the tree is on the side opposite the wind's direction. Such "wind firmness" increases over the seasons, with most open-growth trees developing strength in all directions.

· Damaged goods: Trees are generally damaged in one or more of six ways: blow-over (the tree falls over); stem failure (injured points become weaker, even if new growth covers the spot); crown twist (the crown is a tree's leaves and supporting twigs and branches; twisting weakens old injuries); root failure; branch failure; and lightning.

· Pruning advisory: Doug Caldwell of the University of Florida recommends starting when trees are young. Look for branch "unions," or spots where they meet. Branches that unite in a V are weaker than those joined in U-shapes. Each time you prune, remove one-third of the length. This gradual cutback funnels nutrients into the larger branch. This is called subordination pruning and will result in less damage when storms strike.

· Support system: Strong metal cables and rods can be used to relieve the strain that causes structurally weak trees to split and break in high winds and ice. But they also can help reduce the potential for fork splitting and branch damage. If you start when the tree is young, you spread wind loading evenly.

· Bolt from the blue: When lightning strikes, a tree may be severely blown apart -- or it may suffer only a spiraling dead area on the trunk. A lightning-protection system will conduct the electrical charge to the ground and bypass the tree itself. Such systems, which protect individual trees, are best installed by arborists. With proper maintenance, they can last 30 years, experts say.

· Look, cavities! An open cavity in the trunk means a weak point in the structural-support system. Some arborists recommend filling cavities with cement. Others argue that filling can damage a tree. Bob Rouse, of the National Arborist Association, says the rubbing against the cement further damages the tree.

· No vining: Vines compete with trees for water and sunlight. At a tree's top, they can cause shade and may suppress photosynthesis, weakening the tree; their weight can cause crown twist. Vine-covered branches can snap off.

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