The Effects of Flooding on the Transpiration and Survival of Some Southeastern Forest Tree Species.

Field observations indicate that the distribution of certain forest tree species is modified by periodic flooding of the soil. There appear to be distinct differences between species with respect to the amount of flooding which they will tolerate. Overcup oak, for example, often occurs on areas which are flooded for considerable periods of time during the year, but northern red oak usually occurs only on the better drained sites. Cypress commonly grows on flooded soil, but loblolly pine seldom occurs in such wet locations. Presumably the roots of some species are more susceptible to injury from the lack of oxygen and excess of carbon dioxide found in flooded soils, and injury to the roots usually results in decreased absorption of water and minerals and in damage to the shoots. Since very few measurements of the effect of flooding the soil on forest trees have been made, a study was planned on potted seedlings. It was assumed that injury to the roots by flooding would be indicated by a decrease in transpiration resulting from decreased water absorption. Measurement of transpiration should therefore indicate the extent of injury to the roots caused by flooding. The species used and their origin were as follows: Loblolly pine, Pinus taeda, L., North Carolina. Red cedar, Juniperus virginiana, L., North Carolina. Cypress, Taxodium distichum, (L.) Richard, South Carolina. White oak, Quercus alba, L., North Carolina. Swamp chestnut oak, Quercus prinus, L., Tennessee. Red oak, Q. borealis, var. maxima (Marsh.) Ashe, North Carolina. Overcup oak, Q. lyrata, Walt., Tennessee. Dogwood,Cornus florida , L., North Carolina. All of these seedlings except cypress had been grown out-of-doors in clay pots for two years and were about 16 inches tall. The cypress was brought from the Coastal Plain about four months before the experiments were started and kept out-of-doors in clay pots until used.