Lyndsey Tanabe

The study of the impact of the invasive tree of heaven, Ailanthus altissima, has focused largely on its effect on species convenient for greenhouse and agricultural experiments, with the application of its allelopathic chemicals in a highly concentrated form. Few studies have addressed the degree of Ailanthus impact on the germination of the native plant species that share its temperate forest habitat, and thus the degree to which Ailanthus may decrease species diversity. We hypothesized that the presence of allelopathic chemicals from Ailanthus in the soil would inhibit germination. We tested this by planting the seeds of four species native to central Pennsylvania, as well as an experimental control species, in soils collected at three different distances from the roots of Ailanthus trees. These soils differed slightly in pH, phosphorus, and potassium content. We predicted that percent germination would be lowest in seeds planted in soil that was in direct contact with the roots of Ailanthus, higher in seeds planted in soil ten centimeters from the roots, and highest in seeds planted in native soil. We found no significant difference in percent germination among different soils for any seed type. This is inconsistent with similar studies that have indicated that the chemicals released by Ailanthus have a negative impact on the growth and survival of other plant species. Thus, we conclude that allelopathic chemicals are not naturally released into the soil by Ailanthus in high enough concentrations to adversely affect the germination of the native species that we used.