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!