Wayne K. Clatterbuck Associate Professor Forestry, Wildlife & Fisheries University of Tennessee
Trees have varying tolerances to flooding. However, flooding during the growing season, especially during and after leaf out, can be harmful to trees. The roots need oxygen to survive and grow. Flooding results in poor aeration, because the oxygen supply in flooded soil is severely limited. Oxygen deficiency is likely the most important environmental factor inhibiting growth and causing injury in flooded trees. Most trees will tolerate flowing water for a few days during the growing season. Flowing water retains dissolved oxygen (aerobic conditions) such that the oxygen to the roots is not depleted. However, oxygen is exhausted (anaerobic conditions) in water that is standing or puddled. Few trees can tolerate standing or puddled water during either the dormant or growing season.
Once trees are stressed by floods (symptoms are leaf yellowing, defoliation, reduced leaf size, sprouting and crown dieback), secondary organisms, particularly opportunistic fungi, insects and disease, invade the hosts and further weaken the tree. These symptoms may progress and eventually lead to tree death, especially with repeated, annual flooding. Generally, though, flooding does not occur each year and stress symptoms may subside, indicating the tree is recovering.
Knowledge of the varying tolerances of different tree species to flooding is critical in selecting the right tree for the right place for planting and for managing growth and development of trees in the landscape. Trees that are not well suited to certain moisture conditions will perform poorly. Matching the tree’s physiological requirements to its most conducive environment will increase the probability of success in managing your landscape with minimum maintenance costs.
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