Buckthorn is most easily identified by its glossy egg-shaped leaves, which are pointed at the tip and contain 3-5 well-defined veins. The bark is brown with elongate silvery corky projections, and when cut reveals orange heartwood and yellow sapwood. Buckthorn commonly grows 20-25 feet in height, but at several locations in Cowling Arboretum entire stands are well over this height, notably to the east of Kettlehole Marsh.
Caution: the bark of buckthorn is similar to that of native cherry trees. Among other small differences, the branches of buckthorn tend to grow far more cockeyed and angled that that of cherry trees.
Negative effects of Buckthorn on ecosystems:
- Out-competes native plants for nutrients, light, and moisture
- Degrades wildlife habitat
- Wide tolerance level and aggressive growth shades out the woodland understory and prairies.
- By shading out ground cover buckthorn contributes to erosion and a decrease in soil moisture.
- Serves as host to other pests, such as crown rust fungus and soybean aphids.
- Forms an impenetrable layer of vegetation.
- Is potentially mutually beneficial with invasive earthworm species.
Of Eurasian origin, buckthorn was introduced to the Upper Midwest in the mid 1800’s as a hedge plant. Those who planted it in the region soon found it to be uncontrollable. Buckthorn is currently one of the most problematic invasive species in Minnesota and the surrounding states, and clearing buckthorn to make way for the restoration of prairie and oak savanna ecosystems has been one of the major goals of the Carleton Arboretum over the past 15 years. Current removal projects are centered around the north and west shores of Kettlehole Marsh, and in the oak savanna restoration on the western end of the 1996 prairie planting. The remaining areas of worst infestation are the eastern shore of Kettlehole marsh, localities of the northern flood plain, and the hillside that runs from east of Goodhue to Bell Field.
Cowling Arboretum Procedures for Removal:
Medium buckthorns may be removed with brush cutters but the larger specimens (the Arb record trunk is a foot in diameter) must be chain sawed. Once all the standing buckthorn is removed from an area the increase in sunlight will lead to a blanket cover of new seedlings and the resprouting of each stump. A skid loader is then used to rip the entire root system out of the ground before significant regrowth can occur. Roots are manually removed, stacked, and burned with the original brush. After removal a burnable vegetation type (often prairie) is be planted to allow for the suppression of future seedlings with fire management. On ground that is too uneven for the use of a skid-loader, or in areas where massive ground disturbance is not desired, herbicide is applied to the cut stumps, but the success rate of this technique is not as high as that of complete root removal.