Ailanthus altissima (Tree-of-Heaven, TOH) is a widespread invasive common to disturbed habitats and an increasing component of near urban forests in eastern North America. An allelopathic compound (ailanthone) has been previously isolated from TOH, however, production is greatest in seedlings. We investigated the effects of above-ground injury on the ability of reproductively mature TOH to effect neighbors via soil properties. Five small TOH trees at the edge of each of three populations received the following injury treatments: 0% (control) 10%, 20% 40%, and 100% removal of above-ground biomass, based on height. Moderate injury treatments were designed to simulate those that may occur naturally, whereas more severe injury simulated frequently used roadside management. Soil from the top 20 cm was collected each week, 0.5 meters from each TOH, dried, and an extract made by pouring 5.0 L water through the soil suspended in a cheesecloth. The extract was used to water seeds of Fagopyrum esculentum (buckwheat) for germination and radicle growth studies and to water seedlings for studies of growth and reproduction. Seed germination rates were reduced in the 40% and 100% injury treatments, relative to control, only during the second of three weeks. Patterns of radicle growth across treatments were complex and changed in sign (increased vs. decreased growth) between weeks, however, most treatments were associated with increases in radicle growth. In the seedling experiment, no differences in total dry weight biomass (DWB) were detected. In contrast, root: shoot DWB ratio was reduced, whereas height and reproductive effort (reproductive DWB total DWB) were elevated in the more severe (30%, 40% and 100%) injury treatments. In general, a trend of increasing release from TOH effects with increasing injury was observed. Loss of leaf tissue, which has been previously associated with ailanthone production, may be responsible for these trends.

Key words: allelopathy, injury-induced response, Invasive species