Extirpating an Exotic Invasive from the Ecosystem Preserve

Experimental Removal of Buckthorn by students in Biology 243 (Plant Biology)

Poster prepared by Adam Derrickson, Alan Kalf, and

Dr. David Warners

Exotic Invasive Species

• 22% of plant species in North America today are non-native, having originated on a different continent.

• 400 of these non-native species are considered invasive because they pose serious threats to native habitats.

• This ‘biological pollution’ has already reduced the populations of 42% of our nation’s endangered plants.

• In 1998 an inventory of Calvin’s natural area turned up 307 plant species, 100 of which are non-native.

• The most threatening non-native plants at Calvin are garlic mustard (Alliaria petiolata), purple loosestrife (Lythrum salicaria), and two species of buckthorn (Rhamnus cathartica and R. frangula).

Buckthorn (Rhamnus cathartica and R. frangula)

• Buckthorn is native to Eurasia and first arrived in North America in the late 1800s.

• Its rapid growth and wide tolerance range make it highly valued by landscapers and homeowners.

• Both species of buckthorn are sold as ornamental shrubs in Grand Rapids and throughout Michigan..

• Buckthorn is rapidly spread by birds (starlings, robins, waxwings) who eat the fruit and disperse the seeds in their feces.

• In natural areas, buckthorn outcompetes and replaces native vegetation.

Experimental Design

• Four removal treatments were performed: digging, cutting, cutting and applying herbicide, and injecting with herbicide.

• Each treatment was repeated by 4 groups (16 groups total) during the week of September 20-24, 1999.

• Each group (of 4-6 students) worked for one hour and recorded the number and diameter of every buckthorn they treated.

• Data were pooled and summarized to compare the efficiency of the different treatments.

• Next years’ class will evaluate the regrowth from treated shrubs and assess long-term effectiveness of each treatment

Four Treatments

• Digging - shovels were used to remove entire shrubs; flags indicate where shrubs had been

• Cutting - loppers were used to cut shrubs approximately 10 cm above soil surface; cut shrubs were removed.

• Cutting and Painting - shrubs were cut and Round-up herbicide was painted on the exposed stumps; cut shrubs were removed.

• Injecting - an E-Z-Ject herbicide injector was used to ‘shoot’ small shells of herbicide into the base of shrubs.

Results and Conclusions

• 615 shrubs were treated by 80 students in three days.

• The number of shrubs treated showed little variation between treatments, partially due to high variation among the groups who were performing the same treatment.

• The injection treatment appears to have treated the largest buckthorns, possibly because workers in the other treatments avoided the largest shrubs.

• Digging was the most disruptive treatment to the soil and nearby plants, and the least efficient, although long term success with digging is expected to be high.

Management Suggestions

• It will be important to monitor the test plots from this study to evaluate the regrowth success of the various treatments. After next years’ class evaluates regrowth, management guidelines can be developed.

• Based upon this years’ data, many students recommend a combination of the injection treatment for large buckthorns and either a cut and paint or digging treatment for the smaller buckthorns.

• 80 students each working one hour made a dent in the buckthorn population of the Ecosystem Preserve, but only a very small dent. More removal projects are needed. Buckthorn is everywhere!