A stately, old tree in the landscape is a reminder that it is possible to endure whatever nature can hand us, but too often now, we're left wondering how to care for flood damaged trees. Trees are able to survive so long because they have adapted to their circumstances. Trees that have been grown and allowed to evolve in flood plains have developed the means to weather occasional flooding. For most trees, flooding is a shock to the system. When caring for flood damaged trees, how well the tree will survive depends on multiple factors:
- The species tolerance to flooding.
- The condition and health of the tree prior to the flood.
- The duration of the flooding. Roots submerged in water cannot access the oxygen they need to survive. Most landscape trees can withstand a week or two of standing water, but even then there may be damage that will cause some dieback or loss of vigor.
- How much soil is left covering the roots of the tree when the water recedes. A heavy buildup of soil can be just as damaging as standing water, blocking the tree root's access to oxygen. Lack of oxygen can also kill off the microorganism in the soil that are needed to maintain the soil's nutrients and composition. Additionally the type of sediment that settles around the tree can cause problems. If salty sea water was pulled in, it will burn the roots. Soil salinization is a major problem and will need to be addressed before anything will grow again in the area.
Symptoms of Flood Damage to Trees
It is often difficult to judge a trees reaction to flooding and the safety of retaining the tree. Trees in general are slow to show symptoms. Symptoms of flood stress can include:
- Leaf yellowing or chlorosis followed by leaf drop
- Early fall color and leaf drop
- Small leaf size when it does leaf out
- Excessive watersprouts
- Dieback at the crown or top of the tree
Any of these symptoms may occur quickly or progressively and none are guarantees that the tree won't survive. A more important signal of decline would be infestation by insects or disease. If a tree was stressed before the flood, it will be all the more susceptible to insect damage and disease. It is possible that the tree could survive the flooding, only to be done in by a secondary problem. Root rot in particular, can quickly take hold because the combination of standing water and the lack of oxygen getting to the roots provides ideal conditions. You probably won't be able to see the roots well enough to notice rot, but dieback from the top of the tree down could be a symptom.
Caring for Trees Recovering from Flood Damage
If your trees survive the flooding, they will need some therapeutic care to fully recover. Once the bark has dried out, remove any dead or damaged limbs. Be sure the limbs are actually dead and not just defoliated. The U.S. Forest Service recommends feeding with a low nitrogen fertilizer, to encourage new growth. You can also mulch the soil under the tree to stabilize conditions around the roots and, odd as it may seem, make sure the tree receives water should the weather become especially dry. What you don't want is for the tree to be exposed to one extreme after another. Only time will tell the actual damage done to your trees.