Take care to protect vulnerable tree trunks from damage

Tree bark is amazing stuff. Take a moment to look closely at the bark of any tree when out in the garden. Each species has a unique skin. Sumacs and acacias develop deep furrows and ridges that resemble the hide of an alligator. Others, like sycamore and crape myrtle, have peeling bark that easily flakes off to reveal a variety of pastel colors.

More importantly, bark is the first line of defense to protect the woody tissues within the trunk. Without this external layer the tree would be vulnerable to dehydration by the wind and sun. Bark also provides some protection from a variety of diseases and insects that are constantly trying to gain entry to the succulent cells located beneath. Once inside, both will attempt to consume as much of the conductive tissue as possible, often to the tree’s ruin.

Tree bark is constantly being replaced by a thin layer of tissue just beneath it known as the cambium. The new cells combine to produce fresh layers of bark, which is pulled and stretched during normal growth processes. Some bark is sloughed off and lost, which creates a continual need for bark tissue production.

Tree bark can be very thick. The ancient redwoods develop layers of bark many inches thick that allows them to withstand damage from fire. They have evolved to cope with an occasional blaze that helps maintain the health of the forest through the elimination of pests and competing plants.

On the other hand, some trees have paper-thin bark. This is common on young saplings or trees that bear fruit. Check any plum or apple tree and you will find fairly thin layers except on the oldest of specimens. Most trees available at the nursery have fairly thin bark. If you nick the trunk with your thumbnail you will find it easily turns up the bark to expose the green cambium layer below.

For this reason, it is very important to protect young trees and those with thin bark. Weed whips and mowers can create considerable damage to tree bark often referred to as human blight or lawn mower disease. A careless gardener can deform or even kill a prize tree. If your teenager likes to plow around the back yard, protect tender trunks with a guard. Commercial tree protectors are available, but you can also use a 6-inch length of 4-inch diameter drain pipe slit lengthways. Just pull open the slit side and place the guard around the trunk until the tree develops a thicker bark layer, or your teen goes to college.

The intense desert sunlight also can wreack havoc on thin bark. Sun scald, especially on the south and west sides of tree trunks, is a common entry point for borers. These beetles lay their eggs in the wounds created by the scald and the larvae hatch to feed upon the juicy tissue beneath the bark. You can protect the trunk by wrapping it with commercial wraps or by simply painting the trunk with white latex paint. The latter method is rather institutional looking, but it is a deterrent to scald and borers, especially on fruit trees. After some time, most trees will develop thick, corky tissue to insulate the trunk from the severe solar radiation.

Dennis Swartzell is the marketing director for Mountain States Wholesale Nursery. As an ISA board-certified master arborist and a member of the Southern Nevada Arborist Group, Swartzell has been helping Southern Nevadans with their gardening questions for over 25 years. If you have a question about a particular plant, or a general gardening issue, send them to Swartzell at treemender@cox.net.