ALLELOPATHIC EFFECTS OF HACKBERRY IN A BOTTOMLAND FOREST COMMUNITY

Hackberry was previously found to produce toxins that inhibit the growth of associated herbaceous species in a : grassland community. Nevertheless, it was hypothesized that bare areas under hackberry trees in a bottomland forest community may not be caused by allelopathy, since inhibitory compounds may be leached or metabolized faster than in a grassland community. Investigations indicated that the relatively bare areas under hackberry were not due to competition for minerals, light, or water, or to differences in texture or pH. The percent of soil moisture was always higher under hackberry trees than under bur oak trees where herbaceous species were prominent. Decaying hackberry leaves, leaf leachate, and soil collected from under hackberry trees significantly reduce seed germination and seedling growth of test species. Ferulic, caffeic, gentisic, and p-coumaric acids, and scopolin, and scopoletin were identified as phenolic phytotoxins produced in hackberry leaves. Thus it appears that the reduced growth of herbaceous vegetation associated with hackberry trees in both grassland and forest communities is due primarily to allelopathy, with the initial inhibition being accentuated by competition.