Roots need water and air for survival. If excess moisture is present for a prolonged period of time, trees may suffer lack of oxygen and start to decline. Roots may try to form near the surface reaching for an oxygen source, causing the plant to weaken.
New sprouts may also start to form near the trunk of the tree, chlorosis may become a visual symptom and leaf dieback in the crown of the plant as well as early leaf defoliation are also common visual signals of stress sue to too much water. If repeated or prolonged periods of flooding occur, the tree will suffer severe injury and decline, the tree may also suffer root decay and possibly death. Also, since the tree is weakened, the tree is prone to insects and disease activity which will further damage the plants.