Investigations into allelopathic characteristics and autecological development of successional Rhus glabra stands in East Tennessee

In a series of laboratory bio-assays, three standard species of the families of, Cucurbitaceae (cucumber), Compositae (lettuce), and Crucifera (radish) and three forest species, Acer rubrum (red maple), A. Saccharinum (silver maple), and Robina pseudoacacia (black locust) were treated with leachates from leaves of Rhus glabra L., smooth sumac, to determine if, a) the leaves of smooth sumac are a source of allelochemicals, b) the allelopathants can be deposited in the soil by the action of rain water, c) whether the allelopathants increase in potency during the growing season. The autecology of smooth sumac was investigated by observations in the field during the development of the species. The investigations included plant association surveys, determining the phenological development of R. glabra, and by investigating the reproductive strategies of several clones in successional stands in east Tennessee.

The laboratory bioassays revealed that leachates from the leaves of smooth sumac did not inhibit the germination of any of the test species with the exception of black locust. The leachates however, did inhibit radicle development in all of the test species with the exception of silver maple. The bioassays further showed that it is possible for allelochemicals to be washed from the surface of the leaves and deposited into the surrounding soil, but that the potency of the allelochemicals within the leaves did not vary over the growing season, nor did it vary between green and senescent leaves.

The autecological studies showed that R. glabra clones have two types of ramets, reproductive and vegetative. The studies produced a calendar of the various phenophases of R. glabra for successional stands in east Tennessee and that the reproductive ramets have different event time responses than those of the vegetative ramets for the phenophases of stem growth cessation, leaf turn, senescence and drop. Reproduction within a clone is maximized by asexual root sprout following the germination of a single seed which develops into the genet of the clone. The studies into the reproductive strategies showed that radiate clonal patterns have many rhizome crossovers, meanderings, and possible graftings. The studies also revealed that competition among smooth sumac clones and the clones and individuals of other woody competitors along with micro-habitat resource distribution appear to be factors that influence the location of the ramets with respect to the genet within the clone. Individual clones attain a maximum age of from 8-10 years and the mortality of the ramets and the genet within a clone are in unison, although individual ramets may die due to other factors such as lack of solar energy, disturbance, etc.