Assessing trees damaged or killed by drought can be tricky, but grouping trees into one of three categories – definitely dead, likely to live and questionable – can help with the task.
Definitely Dead – It is easier to make this call for pines, Ashe junipers (cedars) and other needle-bearing, coniferous trees. The determination can be more difficult for hardwoods, which are more commonly thought of as shade trees. In most cases, a red pine is a dead pine, and the same can be said for cedars with red needles. Once all or most of the foliage of a pine or cedar tree turns red or brown, the tree is incapable of recovering.
Pine trees in this stage probably are already infested with tree-killing bark beetles and will eventually harbor wood-boring insects, termites and other critters. These trees should be cut down and removed, particularly if they are likely to fall on homes, buildings or power lines.
Shade trees, such as oaks, that have lost all their foliage and are beginning to drop limbs or lose large patches of bark are most likely already dead and should be removed. Hypoxylon canker, a fungus that appears as gray or brown patches on the trunk of the tree, is another sign of a dead shade tree.
Likely to live - This category includes shade trees with at least some green or yellow leaves still attached to the limbs. In fact, even those that have dropped all their leaves may still be alive. Some native shade trees, such as post oaks and live oaks, are more drought resistant than others like water oaks or elms.
You can use a scratch test to determine if the tree is dead or just dormant. If you scrape the bark off a small branch or limb and find green, moist tissue underneath, the tree is still hanging on, waiting for the next rain. That means you may need to wait until the following spring to see if the tree makes a recovery — unless the tree starts to show other signs of being definitely dead. If the scratch test doesn’t reveal any green, moist tissue, the tree is likely dead.
An exception is the baldcypress. This tree is a conifer, but unlike pines and cedars, its foliage generally turns red and drops in the fall or during periods of drought stress. Baldypress trees usually will re-sprout in the spring. If in doubt, apply the scratch test or wait until spring to be sure.
Pines with a few yellow or red needles scattered throughout an otherwise green canopy have a good chance at survival. Pine trees typically shed a large portion of their older needles every year as winter approaches, and then put on new needles in the spring.
Though it’s not as feasible to water your forest, any yard trees that show signs of life (green inner tissues or green foliage) should be watered deeply to reduce lingering drought stress.
Questionable - Questionable trees are those that appear to fit somewhere between the Definitely Dead and Likely to Live categories.
A pine that is topped with brown or red needles but still has green foliage in its lower branches is alive, but likely will eventually die. That’s because bark beetles will eventually invade the lower trunk, killing the tree in stages.
When inspecting a questionable pine tree, look for popcorn-sized masses of resin (pitch tubes) or brown dust in the bark fissures. These are early signs of attacks by pine bark beetles. The foliage of the infested pine may still be green, but the tree is ultimately doomed. This is particularly true if you find bark beetle galleries or trails beneath the bark. Pines with these signs of bark beetle attack should be removed as soon as possible.
In the case of shade trees, those that have many dead or dying limbs or mostly bare branches may or may not survive. A few green, yellow or red leaves may remain for a while as the tree slowly dies, or it may partially recover when rains return, although likely with quite a few dead branches scattered through the canopy that will need to be addressed through proper pruning.
Deciding whether to remove a questionable tree can be a tough decision for both property owners and professional tree care experts. Removal should be considered if a severely drought-stressed or fire-damaged tree is close to a house or other structure on which it might fall. If it is away from such areas, it may be more feasible to wait and see if the tree makes a comeback.