THE EFFECTS OF FLOODING ON THE TRANSPIRATION AND SURVIVAL OF SOME SOUTHEASTERN FOREST TREE SPECIES

Abstract

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 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. Methods The soil masses containing the root systems of the experimental plants were transferred from clay pots in which they had been growing to metal cans painted with asphaltum on the inside and white enamel on the outside. Tops of all cans were covered with two layers of oilcloth which had been cut so that the cloth might be placed around the stems of the plants. Seedlings of each species were tested in groups of six, three individuals 453