Pearson, C.W. and L.N. Gillette. 2001. Monitoring various Common Buckthorn Control Methods in Maple-Basswood and Oak Woods within the historic range of the Big Woods. Final report submitted to the Natural Heritage and Nongame Research Program, Minnesota Dept. of Natural Resources. 8 pp.
Common buckthorn (Rhamnus cathartica) is an exotic species that is becoming a major problem in woodlands in the southern half of Minnesota. Numerous reports have dealt with treatment of buckthorn using chemicals and/or fire. To date, however, there has been little research into the long-term control of buckthorn using these, or a combination of these techniques. An economically practical method of treating large areas needs to be identified. The study described herein spanned a six-year period from 1993 to 1999. The DNR Nongame Research Program provided funding support for the project from 1996 through 1998.
The objectives of the study were 1) to measure the success of 3 chemical and 2 mechanical control treatments on buckthorn; 2) to sample the recruitment and survival of buckthorn after initial control treatment; 3) to sample the recruitment and survival of native trees and forbs after initial buckthorn control; and 4) to analyze the cost effectiveness of the various techniques.
The study areas were located in woodlots at Carver Park Reserve (Carver County), and at Crow-Hassan and Hyland Lake Park Reserves (Hennepin County). Mature seed-bearing buckthorn trees were chemically killed or were cut and stump-treated in each study area. Chemical and mechanical follow-up treatments were then applied in various combinations at the different study sites.
Chemical treatment followed by annual controlled burns at Carver Park Reserve reduced the number of buckthorn seedlings from 27 per plot in 1996 to 3 per plot in 1998. Repeated annual spraying of buckthorn saplings > ? inch diameter at Crow-Hassan Park Reserve reduced the number of saplings from 65 per acre in 1996 to 3 per acre in 1999. At Hyland Lake Park Reserve, results were inconclusive due to difficulties encountered in completing the proposed treatment regime.
One-time removal of mature seed-bearing trees is ineffective in controlling buckthorn. Periodic follow-up treatment is required to control the buckthorn saplings and seedlings that are ?released? by removal of the overstory trees. If treatment can be continued until the seed bank is exhausted, buckthorn control is theoretically possible. Fire is an effective method for eliminating buckthorn seedlings, but also eliminates some desirable woody species, and is ineffective in controlling buckthorn saplings. Without follow-up treatment, the density (stems/acre) of buckthorn seedlings and saplings becomes greater than it was before the initial removal of mature seed-bearing trees.