Tree care after a wildfire

Wednesday, March 30, 2016

Residents of Oklahoma have seen first-hand the damage caused by wildfires. The recent fire in the northwest part of the state and into the southern part of Kansas left tens of thousands of acres scorched.

Fortunately, not a large number of structures were burned, but pastureland, rangeland and some residential land suffered damage.

For many landowners, the trees on their property were in the direct line of the fire. However, trees can recover after a fire, depending on the intensity and duration of the burn and extent of dehydration, said David Hillock, Oklahoma State University Cooperative Extension consumer horticulturist.

“Following a fire, one of the first steps to take is to determine which trees may recuperate and which trees will need to be removed,” Hillock said. “Fire can damage trees in a number of ways, including leaf or needle scorch, root damage, trunk or branch damage, inner tissue injury and bud death. Other issues that can cause problems are soil desiccation or water-repellant soils.”

Trees vary in how readily they burn and whether they can survive a fire. A couple of important factors to consider are fire intensity and length of exposure to the flames. Trees starting to grow in the spring are more susceptible than dormant trees.

Hillock said if the bark has not been completely burned off the trunk, which exposes and damages the cambium, there is a chance the tree may survive. Cut a quarter-sized piece of bark off the trunk about half an inch through the bark.

“If there’s a green or white moist cambial layer immediately below the bark, there’s a good chance the tree will recuperate,” he said. “However, if the trunk is severely burned more than 50 percent around the circumference, it likely will not survive.”

Following a fire, it is crucial to water trees as soon as possible, but first you must determine if the soil will absorb water. Sometimes following a fire, soil can become water-repellent, or hydrophobic. Pour a cup of water on the soil to see if it soaks in. If the water beads on the surface, scrape off an inch or two of soil and try again. You may need to rake the ground to loosen the impermeable layer.

Hillocks suggests mulching the area with a thin layer of weed-free straw to help the soil absorb the water.

“In cases of severely burned soil, especially those high in organic matter, it may take up to a year to absorb water without corrective measures,” he said. “Once water does begin to absorb, soak the entire area under the dripline of the tree and a few feet beyond, to about 10 inches to 15 inches. The water-absorbing roots of a tree are at the top 12 inches to 15 inches of soil. A soaker hose slowly dripping water works well."

It is important to protect the trunks and large limbs of trees from sunburn until the canopy regrows. Wrap with a permeable substance such as light-colored cloth or tree wrap, or paint them with a water-based white paint. Loosen the wrap every few months to enable the tree to grow without being girdled.

Prune dead, broken or severely damaged limbs. If there are trees that did not survive, remove them from the property immediately to avoid beetle infestation.

“Fires can be devastating to your property, but with proper care and limiting stress factors, there’s a good chance some of your trees will survive,” Hillock said.