Thirsty trees Recent drought can have long-term effects BY LAURA C. MARTIN The 12-month period ending in July marked the most severe drought in Georgia's history. Coupled with the prolonged high temperatures during the summer, the lack of rain severely stressed the trees of our state.
Learning how to recognize a drought-stressed tree and determining the degree of damage may help gardeners better know how to care for them. Our state is blessed with an abundance of beautiful trees. If we take our responsibility of earth stewardship seriously, then let's do what we can to help keep our trees healthy.
Several signs indicate that a tree is suffering the effects of drought. On deciduous trees, the leaves look curled or rolled. You might notice mottling on the leaves or brown on the leaf edges (called scorching). The leaves may turn autumn colors early and may begin to drop. Conifers show drought damage when needle tips turn yellow or brown.
The most obvious visible effect of the onset of drought stress is wilting leaves. The turgor pressure in the leaf cells drops, making the leaves go limp. Some tree leaves wilt during the day but recover at night. If this continues over time, the tree won't recover during the night and leaves will still look wilted in the morning. Wilting varies from one tree species to another -- trees such as dogwood and birch wilt readily, while others, such as pines and hollies are more resilient.
If a tree continues under stress due to drought, it will next begin to shed leaves. Again, the amount of leaf drop depends on the species. Yellow poplars almost always shed during the summer, even when rainfall is abundant. Dogwood leaves usually wilt and then drop but will sometimes put out a second set of leaves if rainfall occurs. Extreme drought also results in the dieback of twigs and branches in the crown.
Drought also affects the roots. As the water table drops, young trees or trees with shallow root systems simply cannot reach the water. Even for large, established trees, reduced concentration of water in the soil causes roots to shrivel. As roots contract, there is less soil-to-root contact, making the tree less stable and less capable of withstanding high winds.
Trees stressed by drought are also susceptible to pest damage. Like a person whose immune system has been damaged, a drought-stressed tree cannot withstand the onslaught of pests or diseases as well as a healthy tree can. The weaker the tree is, the more damage insects and other pests will do.
Irrigating trees, of course, helps them weather a drought, but how you water makes a tremendous difference. Trees that are watered daily actually have a more difficult time withstanding the effects of drought than those watered less often. Water no more than two times a week and water deeply. The best place to put the water is in a radius starting two feet from the trunk out to the drip line. Use a drip irrigation method, not a sprinkler, and water early in the day. In addition, make generous use of mulch to retain every bit of water.
Thinning tree limbs helps reduce damage from drought stress. Begin by cutting back any dead, diseased or obviously weakened branches. But beware -- tree limbs are often much larger than they appear, and trimming large tree limbs, especially dead ones can be dangerous; a tree surgeon knows best how to get down larger limbs.
If you are planting new trees in a landscape, choose species that can withstand long periods of drought. Try native trees such as sassafras, Eastern redbud or pines, or thick, waxy-leafed trees such as Eastern red cedar, or deciduous trees with small leaves such as willow oak, pin oak or elm.
Though we love the attractiveness and sweet scents of the flowers in our gardens, it's the trees that form the backbone of our landscapes, offering shade, beauty and a deep connection to the earth. Let's do what we can to protect this living legacy.
Laura Martin, of Atlanta, is the author of 26 books on gardening and nature crafts. |
