Allelopathy of Frangula Alnus to Native New England Wetland Vegetation at Harvard Forest 2008

Glossy buckthorn (Frangula alnus), an invasive shrub from Eurasia, colonizes both upland and mesic sites in New England, USA, reducing the growth and survival of native tree saplings and lowering species richness. Although a generalist, buckthorn thrives particularly well along river, pond, and wetland margins, which are traditional habitat for speckled alder (Alnus incana ssp. rugosa), a native nitrogen-fixing shrub. As buckthorn’s dense, monospecific growth is typical of allelopaths, we wondered whether it chemically suppresses the growth of alder and other indigenous shrubs. We thus propagated three native shrub species: Alnus incana ssp. rugosa, Viburnum dentatum and Spiraea latifolia, in invasive buckthorn and native dogwood (Cornus amomum) root and leaf mulch. After seven weeks, alder grown in buckthorn root demonstrated significantly smaller basal diameter than alder grown in buckthorn leaf or other mulches. Therefore, putative buckthorn allelopathy to alder likely occurs through root exudation instead of leaf litter effects. Meadowsweet grown in buckthorn mulch, in contrast, was taller, thicker, and had more numerous leaves than meadowsweet grown in native mulch. These species-specific effects point to allelopathy as a mechanism by which buckthorn changes the structure of native plant communities.