Non-native plant species are often more successful within introduced areas when compared to their natural ranges. Allelopathy is a process that occurs in select species of plants which disseminate deleterious allelochemicals that are integrated into the soil and decrease plant growth. Allelopathy, the chemical inhibition of co-occurring plants via leachates of leaf or rhizome tissues has been suggested as a mechanism for the success of non-native plants. Invading species frequently establish monocultures and may introduce evolutionarily novel allelochemicals into the invaded community. Several species have been tested for allelopathy, but comparisons among studies are difficult because of variation in methodology. Our goal was to conduct a survey of a suite of non-native forest invaders and determine whether they have allelopathic potential. We conducted laboratory bioassays for eight woody non-native species: Trees - Acer platanoides, Ailanthus altissima; lianas - Celastrus orbiculatus, Lonicera japonica and shrubs - Elaeagnus angustifolia, Ligustrum vulgare, Rosa multiflora, and Rubus phoenocolasius. We determined the germination responses of a target species to a gradient of leaf extract concentrations to assess the allelopathic potential of each species.                                                                                         

Results/Conclusions

Laboratory bioassays showed that at low leaf extract concentrations, all species were similar, with minimal reduction in seedling germination. As concentration increased, germination proportions differentiated among all species. Ailanthus altissima exhibited the most allelopathic potential out of all eight species. Celastrus orbiculatus was also moderately phytotoxic, whereas A. platanoides, L. vulgare, L. japonica, and E. angustifolia had much smaller effects on seed germination even in the higher concentrations. This study provides an assessment of the allelopathic potential of these non-native species which can be compared directly. Though all species decreased germination to some degree, Ailanthus altissima and Celastrus orbiculatus were the strongest of all eight species. Allelopathy appears to be potentially important in the invasion of some, but not all woody invasive species in this system.