How Flooding Affects Trees

These spring rains might make you wonder how flooding affects trees. The long and short answer is- it depends! It depends on when the flood happens; how long the flood water stays; how old or young the tree is; how healthy it is; and also what kind of tree it is.

These rains are happening at a bad time for trees since they are actively growing. They are less effected by flooding when they are dormant and are more negatively effected just after their first growth flush. Though these high waters may be happening when trees are most vulnerable, the timing of these rains is offset by the resilience of most trees.  Many tree species can withstand flooding over their roots for weeks, though very young trees and very old or unhealthy trees of even the most flood resistant trees won’t.

Here is a table showing the relative tolerance of cultivated species to short-term flooding during the growing season.

Trees growing in floodplains are adapted to rains such as these and long term negative consequences aren’t likely to happen to them. For the rest, we should adopt a wait and see approach and remember these rains if we see stress symptoms this or next year. Such symptoms include yellow leaves, small leaves and shoots, defoliation, excessive branch sprouting, or dead branches. Boring insects may invade trees in future years.

If trees show such symptoms, using good tree care will do much to help them cope with the stresses of the excess water. Hallmarks of good tree care include proper pruning, mulching, planting and choosing the appropriate replacement trees (if needed). Click here to request information on How to Help Trees Recover from Stress.

The USDA Forest Service has gained experience with trees and flooding, much of it as a result of the 1990’s flooding in the Midwest and this past year’s Katrina disaster. They have posted a concise and relevant description of Flood Tolerance of Trees.