On a recent day, driving out of the sun into a wooded community resulted in a temperature drop from 91 to 86 degrees. We all try to stay in the shade in hot weather, competing for the parking spaces under trees. What we may not realize is that tree-lined neighborhoods are cooler not just because of the shade but because the trees themselves act as air conditioners. The basic concept is that it takes energy to turn a liquid into a gas – we see that when boiling water. When a tree sucks up water through its roots and releases it as a gas through its leaves, a process known as transpiration, the energy that causes the water to evaporate is absorbed from the surroundings in the form of heat, and the result is a lower air temperature. This principle of physics also explains why sweating cools our bodies.
Newly planted trees are particularly vulnerable to high heat, so the most basic care needed from us is to provide enough water until they are well established. Seedlings establish quickly, but a landscaper-sized tree needs several years for its root to grow out of the planting hole into the surrounding soil. Our torrential summer storms can fool us into thinking we are getting enough rain, but many of them are brief and don’t even budge the rain gauge. A young tree with brown leaves is a very sad sight. At the same time, overwatering any plant can be worse than underwatering, by depriving the roots of oxygen, so we need to be careful to follow instructions in that regard and allow the soil to dry out between waterings.
Once a native tree gets established, though, little if any care may be required for the next twenty years or so. Our oaks and other native trees evolved here and are accustomed to the local soils and our variable temperatures and rainfall, although those 91 degree days are adding to the stress of living in an urban or suburban environment. Because older trees may start to develop issues, it is wise to have those that are near houses inspected every two years by an independent consulting arborist, meaning one who has no financial incentive to sell tree care services. They can recommend procedures that may prevent a tree from becoming hazardous. Even better, they may be able to provide reassurance, for instance, that a tree that is leaning a little may be quite stable, despite the dire warnings of a marketing rep from a tree company that is eager to keep its crew busy. Always use the services of arborists certified by the ISA (International Society of Arboriculture.)
When future residents are facing temperatures even higher than today’s, a five degree lower temperature may make a life or death difference. Consider what hundred degree weather does to the human body when a prolonged blackout shuts down everyone’s air conditioning. It pays to take good care of our trees. Find out how on the Plant NOVA Trees website.