Attack of the Invasive Plants!
Matt Hyde and Maya Pisel
Macalester College – St. Paul, MN
Common Buckthorn (Rhamnus cathartica) Purple Loosestrife (Lythrum salicaria)
Buckthorn is a shrubby plant that arrived on the East Coast of the United States and in Minnesota in the mid-1800's. It was brought over as a
popular hedge plant from Europe. Buckthorn’s berries have a strong laxative effect on birds. This effective method of seed dispersal, combined
with the plant’s high tolerance of different soil types and freedom from natural enemies, led Buckthorn to quickly establish throughout the eastern
United States and Canada. Buckthorn tends to especially thrive in regions above limestone. This is one reason why today it dominates the
Mississippi River area of Minneapolis and Saint Paul.
Impacts
Purple Loosestrife is an invasive plant in all contiguous 48 states. It infests 68 of the 87 counties of Minnesota, including
many wetlands and freshwater areas in the watersheds of the Minnesota, St. Croix, and Mississippi Rivers. Purple Loosestrife is
native to Europe, and is found from Western Europe all the way to Russia. Purple Loosestrife seeds were probably accidentally
brought over in the ballast water of ships to the Eastern United States, and it was also brought over for ornamental purposes. Many
people used it to improve the look of wetland areas and gardens. It spread so extensively because of boats, animals, and also the
flooding of certain areas enabled more seed dispersal.
Controls
Because of its density and abundance, buckthorn creates too
much shade for many plants to survive, especially those on the
forest floor. Moreover, buckthorn generally outcompetes
natural vegetation for water and nutrients. There is particular
concern that buckthorn outcompetes young oak and maple
trees.
Impacts
Small plants less than 3/8 of an inch in diameter
can feasibly be removed manually. Plants between 3/8
of an inch and 2.5 inches diameter are more effectively
removed with a hand tool or machine.
Larger plants are best eradicated by sawing the plant
down to the stump and then applying an herbicide, either Triclopyr
amine or Glyphosate. There are several popular brands of
solutions with these chemicals. Merely sawing down to the
stump without applying herbicide does not kill the plant and
in fact will likely result in new shoots growing around the
base of the stump.
Buckthorn dramatically alters the chemistry of the soil in
which it resides, making it more difficult for native species to
survive. Soil under buckthorn plants has twice as much
nitrogen and 75% more carbon. It has also has a higher pH.
These changes are compounded by buckthorn’s symbiotic
relationship with the earthworm because the earthworm also
adds nitrogen to the soil.
These serious changes in forest in turn damage the health of the
watershed. Less species diversity, leaf litter and
native
vegetation can decrease both the rate of infiltration
and the
amount of infiltration. When less water is infiltrated
as
groundwater, more enters the river as run-off,
carrying with it many more impurities and
pollutants. Moreover, the extra nitrogen added to the soil by buckthorn
also enters the stream as run-off.
With more nutrients coming in, a river can
experience changes in productivity. Larger
algal blooms and/or a shift in which algae species is
dominant can in turn send shockwaves through the entire
food web. More impurities and pollutants can also alter food web
dynamics by restricting some species’ survival.
fire is
through chemicals. The herbicide
Glyphosyte can be used to impede the spread
of the plant. There are many popular
brand that contain Glyphosyte. However, this
can have detrimental effects to other
vegetation. It can also unintentionally harm
organisms and the ecosystem.
The other type of control is biological
This can create problems with the habitat of
control - the use of insects that are
some organisms that use the native
predators of purple loosestrife. The insects
that have been found to be effective
predators of purple loosestrife are four
different types of Beetles.
vegetation, thereby limiting the
Photo courtesy of: www.soilandwater.org
Photo courtesy of: http://www.nps.gov/
biodiversity of flora and fauna. Native
vegetation plays a critical role filtering
impurities out of the water.
Also, without the native plants for wildlife,
organisms’ source of food and shelter
Starting fires in early spring, when buckthorn has leafed
but other plants have not, often kills the emerging plants.
However, as re-sprouting will occurring, burning must be
repeated annually or used in conjunction with other controls.
However, controlled fires can cause significant damage to
the entire ecosystem. Moreover, starting a controlled
costly and often impractical in populated areas.
Many efforts are underway in St. Paul and Minneapolis to
remove buckthorn by the Friends of the Mississippi River, the Friends
of the Parks and Trails of St. Paul, and others.
One way to control purple loosestrife is
attributes allow it to outcompete
many native aquatic vegetation such as
cattails, sedges, and ferns, for nutrients.
Herbicides, however, percolate through the
topsoil and enter the groundwater. They also can
enter a river through run-off. The damage to water
quality and potential toll on amphibian, fish and
other organisms are especially severe if they are used in water, in
wetlands or close to a river. Moreover, once in the soil, herbicides may
unintentionally kill native vegetation.
Controls
Purple loosestrife’s has the ability to grow
in different soils as well as in different
water depths. Also, its rapid seed dispersal
and the enormous amount of seeds that it
creates (up to a million per a plant) allow
it to spread over a large distance. These
decrease, and they suffer. Ducks, wading
birds, and muskrats avoid the extensive
purple loosestrife.
Photo courtesy of: http://www.ci.golden-valley.mn.us/
However, great consideration must
when applying biological control
insects to an ecosystem. The insects
may have negative effects. They are
be used
an added element to the food
web and thus can alter the
dynamics
Some other
them to native
the control
of the entire ecosystem.
organisms may prefer
prey, which would alter
of the food web.
Photo courtesy of: http://www.forestry.ky.gov/
Photos courtesy of: http://ellerbruch.nmu.edu, http://rochesterenvironment.com, http://fohn.net
Photos courtesy of: http://www.dobbies.co.uk, http://www.invasive.org/, http://lakewhatcom.wsu.edu
CurlyLeaf Pondweed (Potamogeton crispus) Eurasian Milfoil (Myriophyllum spicatum)
Photos courtesy of: http://www.istockphoto.com, http://www.bu.edu/gk12, http://extension.oregonstate.edu, http://www.imageenvision.com/sm
Photos courtesy of: http://thisoldhouse.typepad.com, http://www.ecoshuttle.net, http://www.dobbies.co.uk, http://www.speedysigns.com, http://www1.istockphoto.com
Eurasian Milfoil is native to Europe, Asia, and Northern Africa. It was accidentally introduced to the United States in the early twentieth
century by boat, and it began spreading to the Midwest in the 1950s, primarily traveling from lake to lake attached to boats and water
bird. The first discovery of Eurasian Milfoil in Minnesota was made in 1987 in Lake Minnetanka. Today, there are 219 Minnesota water
bodies infested with Eurasian Milfoil, including the Mississippi River, the St. Croix River, five other rivers and four wetland areas.
Curly-Leaf Pondweed is an invasive aquatic plant that is very prevalent in the watersheds of the Minnesota, Mississippi, and St. Croix Rivers.
It was originally brought in as a popular aquarium plant, and many hobbyists used it as early as the 1800's. Today, it has spread through all of
the lower 48 states. This plant moves to new bodies of water from boats and trailers, and once it has made its way into a new body of water, it
can rapidly disperse.
Impacts
Curly leaf pondweed can provide
habitat and food for some organisms. This
is especially true in the winter when little other
vegetation is available. However, it has many
negative effects.
Tangled mats of Eurasian Milfoil block out light
for native macrophytes and other species.
These mats form early in spring before
native species have the chance to grow.
Therefore, at the critical growth period of
native species, hardly any lightis available
for photosynthesis.
Curly-Leaf Pondweed can be removed using
mechanical harvesters, hand cutting, and
raking.
more
In mid-summer, curly leaf pondweed begins to
decay. This takes much needed oxygen out of
the ecosystem. It also releases nutrients that cause
algal blooms. These changes to fundamental
Nutrient cycles can alter the entire food web.
An infestation of curly leaf pondweed damages
ecosystem services. Recreational use is
or
Impacts
Controls
especially impeded. It is very difficult to swim, boat,
waterski through dense thickets of curly leaf pondweed
and the algae that it creates during its mid-summer
decomposition.
When recreational activities can no longer occur on a
body of water, the surrounding property tends to
decrease in value. Moreover, it can be very expensive
to control the plant in order to regain that property
value.
This removal process occurs in the Spring. Plants
must be cut as close to the sediment as possible.
Removal is only effective if all parts of the plant are
removed from the water; otherwise the plants will
invertebrate biodiversity and density, and the
invertebrates that do survive are different from those
typical to native macrophytes. Damage to invertebrate communities,
most notably the benthos, can in turn send shock waves through the
entire food web.
Eurasian Milfoil also inhibits phytoplankton growth and reduces fish
Photo courtesy of: http://sevenhillslake.com/
by Eurasian Milfoil also seem to be less
appealing and less nutritious for many waterbirds.
Photo courtesy of: http://www.aqua-fish.net/
Eurasian Milfoil impedes cultural
ecosystem services and poses
public health risks. It is difficult if not
impossible to boat through or waterski on a
lake or river infested by Eurasian Milfoil, let
alone swim through the web of long stems.
The mats are convenient breeding grounds
for mosquitoes, and recently Eurasian Milfoil
related incidents caused the deaths of five
people in Washington.
Fluoridine is another herbicide. It is
sometimes used in whole water control, but
this causes severe harm to other vegetation
and organisms. Therefore, it is usually avoided.
no results. The watermilfoil moth also reduces
Eurasian Milfoil with its feeding and breeding patterns.
However, although the moth prefers Eurasian Milfoil, it
also attacks other species.
Eurasian Milfoil is removed
via machine harvesting,
hand cutting, hand pulling, or
diver-operated vacuuming.
The milfoil is likely to regrow quickly even after a
thorough harvest. Thus, the
labor intensive, expensive process is
often repeated several times within the summer. Machine harvesting
often removes native vegetation along with the targeted milfoil.
Moreover, when a milfoil plant is removed, the weevil and/or moth
populations go along with it, thus preventing those organisms from
reducing infestation for the long-term.
Photo courtesy of: http://www.co.stevens.wa.us/
Photos courtesy of: http://best.berkeley.edu, http://static.howstuffworks.com, http://www.utoledo.edu, http://i.ehow.com
Photos courtesy of: http://www.vandevertranch.org, http://www.canadianpond.ca, http://www.internationalwaterfromair.com, http://www.bigindianabass.com
The watermilfoil weevil has been an effective control
in some waterbodies in Minnesota, but others have seen
biodiversity. Waters dominated
Photo courtesy of: http://www.mainevlmp.org
Photos courtesy of: http://www.asiancarp.org, http://blog.pricegrabber.com, http://www.lochken.com, http://www.preventforeclosureinaz.com
Fluridone is an herbicide sometimes used
against Eurasian Milfoil. Flurodine can
conveniently be applied either to a specific
milfoil-infested area or distributed throughout a
water body. However, applying Flurodine to
lakes causes damage to native vegetation and
food webs thus it is is not used in Minnesota.
Ecosystems dominated by Eurasian Milfoil have less
quickly re-grow.
Herbicides can also be applied in the spring.
Diquat and Endothall are examples of popular
herbicides used to control curly leaf pondweed.
They can be used as a spot treatment and applied
specifically to the areas infested with curly leaf pondweed.
However, these herbicides should only be used when the water
temperature is between 50 and 55 degrees in order for it
to be effective. In addition, these herbicides may pose
risks to other organisms that use the water, including
humans. The EPA regulates Diquat in because of the
health damage it causes if it enters drinking water.
Controls
Photos courtesy of:http://1.bp.blogspot.com, http://www.ecy.wa.gov, http://www.lakehopatcong.org