Transpiration is primarily a physical process driven by atmospheric relative humidity with biological control valves. There are several places along the transpiration stream that indirect energy input by the tree is required. Energy for maintaining cell functions, stomates, and pressure adjustments are quickly compromised under flooded conditions. The ironic sounding result is the drying of tree parts above water while the tree is surrounded with water. Water loss continues during flooded conditions while uptake declines greatly in the roots.
Flooding initiates many growth regulator problems.
Growth regulators are how one part of a tree communicates with other parts. The messages are carried by different types of chemicals. Auxin, ethylene and abscisic acid concentrations increase in flooded trees while gibberellic acids and cytokinins decrease. Flooding changes the ecology of the soil, causing anaerobic organisms to replace aerobic organisms. Leaf drop can take from two weeks in upland species to eight weeks in wetland species after flooding.