Ecological Impacts

Common buckthorn typically forms dense patches along woods edges, moving into the woods after disturbance (EC 2002). Eventually it can form a shrubby near-monoculture in the forest understory, suppressing native shrubs and tree seedlings (Hoffman and Kearns 1997, EC 2002). It now dominates shelterbelts, parks, and natural areas around urban areas in southern Ontario (EC 2002) and other parts of eastern North America.

Like Eurasian bush honeysuckles (Lonicera tatarica L. and relatives), common buckthorn leafs out earlier in the spring and holds its leaves longer in the fall than native shrubs generally do (Harrington et al. 1989, Archibold et al. 1997). This allows the species to be accurately identified on color aerial photographs taken in the fall (Archibold et al. 1997). This early leaf-out has raised concern that Eurasian buckthorns (along with introduced Lonicera spp.) are a long-term threat to the eastern deciduous forest's spring ephemerals, which depend on the abundant early spring sunshine available before tree leaf-out for their survival.

The lack of seedlings of other species under dense buckthorn patches has led to the suggestion (e.g., Boudreau and Willson 1992) that common buckthorn produces allelopathic compounds. Archibold et al. (1997) found little evidence for this, though they did not test seeds of native species. They attributed common buckthorn's invasiveness to its prolific seed production, combined with its relatively high seed viability.

Moose (Alces alces) use the related glossy buckthorn as a winter food source in Eastern Europe (Borkowska and Konopko 1994). In North America white-tail deer (Odecoileus virginianus) tend to reject common buckthorn as a food source (City of Eagan 2003), though in areas such as central Wisconsin with high deer populations and lack of preferred browse, deer may browse common buckthorn to the point of suppressing it (Whitford and Whitford 1988). If ingested in more than very small amounts, the berries of common buckthorn cause potentially severe cramps and diarrhoea in humans (City of Eagan 2003).

Schmidt and Whelan (1999) found that American robin (Turdus migratorius) nests in common buckthorn and another invasive shrub, Amur honeysuckle [Lonicera maackii (Rupr.) Maxim.] experienced greater predation than nests built in comparable native shrubs and trees. They attributed this to these shrub's lower stature, a more open branch architecture, and a lack of sharp thorns, as native hawthorns (Crataegus spp.) have.

Common buckthorn is also a threat to agriculture, mainly because it is the principle alternate host for two serious introduced agricultural pests: the oat crown rust fungus, Puccinia coronata f. sp. avenae, and the soybean aphid, Aphis glycines Matsamura. The rust fungus causes stem rust, a serious disease of cultivated oats, and requires common buckthorn (or rarely, one of several other shrub species) to complete its life cycle (USDA-ARS 2003). The soybean aphid is (like the soybean) native to eastern Asia, and was first detected in North America in Michigan, southern Wisconsin, southeast Minnesota, and northwest Illinois in 2000 (Ostlie and Hutchison 2000). It has since spread throughout much of midwestern and northeastern US (Ostlie 2003). This aphid must overwinter on common buckthorn in order to survive the winter.

Status in Area

Common buckthorn is well-established in the upper Great Lakes region, especially around cities and towns (GLIFWC 2002). It is considered "ecologically invasive" in Wisconsin, "highly invasive" in Upper Michigan, and a "restricted noxious weeds" in Minnesota (WIS 2004, MIPC 2004, MDA 2001).