Allelopathic influences of the invasive Ailanthus altissima on a native and a non-native herb1,2

Abstract

As a highly aggressive non-native invasive and an allelopathic species, Ailanthus altissima (tree of heaven) has the capacity to negatively affect native plant communities by suppressing resident species and altering competitive interactions. We examined effects of A. altissima on the establishment and growth of two herbaceous species common in invaded natural areas. Soil samples were collected from six replicate A. altissima-dominated stands and six control stands (no A. altissima present) in the Appalachian Ridge and Valley province of southwestern Virginia. Two target species, Verbesina occidentalis, native to the southeastern US, and Dipsacus fullonum, non-native and invasive throughout North America, were selected for their high germination success and contrasting native vs. invasive status. Germination and growth of target species were monitored in greenhouse flats for six weeks. We found severe reductions in all measured aspects of V. occidentalis when grown in Ailanthus versus control soils, including seed germination (P = 0.002), seedling height (P = 0.001), leaf production (P < 0.001), and root∶shoot ratio (P = 0.008). In contrast, Dipsacus fullonum appeared resistant to allelopathic effects, with no significant differences in germination or growth relative to soil type (P > 0.25 for all measures). Our results support the role of allelopathy in the invasive success of A. altissima and further suggest that A. altissima may differentially affect resident native versus non-native species, potentially facilitating the spread of other non-natives in the invaded community.