| |
'DANGEROUS GANG' THREATENING NATIVE PLANT COMMUNITIES
If you or I heard news that a dangerous gang had moved into our area and was threatening to destroy entire communities, we'd be justifiably alarmed.
The truth is, a dangerous gang has moved into our part of Minnesota and it is threatening some of our nicest communities...plant communities, that is.
The gang is made up of several species of non-native buckthorn, a single-trunk small tree that was introduced into North America from Europe and Asia in the 1700s. Many Minnesotans planted buckthorn as hedges in the 1930s until they discovered buckthorn was an alternative host of crown rust in oats.
Some of the plant communities that are being endangered include native cherry and gray dogwood.
Buckthorn is a threat because it is invasive and grows in large, spreading colonies that can quickly crowd out desirable shrubs and trees. Buckthorn can invade any yard because buckthorn berries containing four or five seeds are eaten by birds and the seeds are deposited wherever songbirds leave their droppings. Buckthorn seeds can remain viable in the ground without sprouting during dry years and sprout several years later when moist conditions return.
The two non-native buckthorn species of greatest concern are common buckthorn (Rhamnus cathartica) and Glossy, Alder or Fen buckthorn (Rhamnus frangula).
Buckthorn can mature to a height of 20 feet and has dark green elliptical to oval shaped leaves. The bark and leaves often resemble wild black cherry (Prunus serotina). Common buckthorn produces 1/4-inch black berries.
Buckthorn is often found invading woodlands near cherry trees. It is common for the green leaves of buckthorn to remain on the plant into early winter, which makes it easy to spot in late fall beneath the canopy of deciduous trees.
I recently discussed the buckthorn threat with Diana Bolander, a horticulturist with the Eagan forestry department. She explained that when buckthorn crowds out gray dogwood, it is a very real threat to robins.
"In the fall, robins like to eat large quantities of gray dogwood berries in preparation for their migration south," she said. "When dogwoods are crowded out by buckthorn, this important food supply of robins can be quickly eliminated."
Both Minneapolis and St. Paul have begun buckthorn eradication programs, Bolander said.
Common buckthorn's name comes from the terminal buds that resemble the hooves of deer and the small thorn found growing between the terminal buds on branches.
Glossy buckthorn has no thorns and its glossy leaves are narrower than common buckthorn. Some nurseries are now phasing out buckthorn because of its threat to native plant communities.
Bolander said buckthorn can be difficult to control once it has invaded native plant communities because its growth is always aggressive.
"Simply cutting it down results in vigorous resprouting if no other control measures are used," she said. "This is because the extra sunlight that reaches the ground after cutting a stand of buckthorn encourages many more buckthorn seeds in the ground to sprout."
Effective control requires an initial labor-intensive cutting and clearing process, followed by close monitoring. Both physical and chemical control is often necessary to eradicate buckthorn and the process can take up to five years, according to Bolander.
Physical control involves cutting all buckthorn stems or trunks as close to the ground as possible (since buds are located beneath the bark, and will sprout new growth from the left-behind stumps).
Chemical control involves using either Roundup or Rodeo herbicides, depending on whether the buckthorn is located near or away from a body of water (Roundup cannot be used near lakes, ponds or streams).
If you know you have buckthorn growing on your property, I suggest that you either write to me for more detailed instructions on controlling buckthorn or contact a tree inspector or forester in your community. Effective control requires following a detailed and rather specific five-year plan for eradicating buckthorn and restoring native plant communities.
|
|
|
 |
| |
|
 |
| |
PUTTING DOWN ROOTS:
A Delightful Blend of
Gardening Wisdom, Wit
and Whimsy
$10 + $2 for shipping
by Cliff Johnson |
 |
 |
| |
|
