Published on 06/30/97

Summertime Trees Need Water, Care to Thrive

The long days of summer are upon us. The bugs, humidity and heat can make a grown person seek the shelter of air conditioners. You may be miserable, but what about your trees? Should you bring them a cool drink?

Summertime trees have full, functional sets of leaves. Besides shading us from our ample sunlight, leaves take in carbon dioxide and churn out tree food.

They make food best just after they expand to their full size and before the pests start nibbling, sucking and invading. For trees, now is a great time to be alive.

Soon, fungi will take up housekeeping. Multiple generations of insects and other crawly things will move in. And all sorts of animals will hang around for the comfort, shade and food trees provide.

All too soon, the tree's bounty will go to feed many other mouths, processes and organisms.

Healthy, structurally sound trees have plenty to share. Trees that have been neglected, abused and damaged have little food for anything but survival.

As far as the bugs go, trees shelter the good and the bad under the same canopy of leaves and around the same roots. Under some conditions, the bad things reproduce fast. Only the good bugs and the environment can control the fast-growing populations of bad bugs.

A tree is a mini-ecological system with checks and controls for living things. Under stressful times, tree-damaging creatures can gain an upper hand.

For trees, it's not the humidity. It's the heat. High relative humidities mean a tree needs to spend less on water uptake and control. Leaves don't lose water as fast. With plenty of moisture in the air, nighttime dews and fogs reduce water loss.

Even on humid days, the humidity drops quickly with rising temperatures. If leaves lose water to the air faster than roots can absorb it from the soil, the leaves shut down. They take a noon siesta that ends when the roots catch up in supplying water.

Leaves begin work as the sun climbs 5 degrees above the horizon and closes down at day's end when the sun falls below 5 degrees from the horizon. It's always a long summer work day for a tree leaf.

Watering trees when they need it helps stressed trees make a living. During even short drought times, watering can greatly help young and old trees. Water is a tree's most valuable commodity in summer.

Water evaporating from soil and tree surfaces provide some cooling. Without water to make food or cool themselves, trees can overheat. Be neighborly. Provide a drink for your trees.

The summer heat forces a tree to use more of its food just to stay alive. For every 18-degree increase in temperature above 40 degrees Fahrenheit, a tree's respiration needs (or food use) doubles.

At the same time, the tree's food-making machinery breaks more often and becomes less efficient. In fact, at higher temperatures, one of the gas- capture systems in tree leaves mistakenly starts grabbing oxygen instead of carbon dioxide. This costs the tree more food to correct.

Next spring, you'll be able to see how well your tree survived this summer. That's when tree-food shortages, damaged tissues and health problems can be finally tallied.

Is your tree gaining growth to survive and thrive another season? Or will this summer be the year when your stressed tree finally evaporates into the environment from whence it came?

You can help save trees through timely and tree-literate care. A summertime dream under the spreading branches of a healthy tree can be well worth the effort.

Kim Coder is a forester with the University of Georgia Warnell School of Forestry and Natural Resources.