Non-Native, Invasive Plants Disrupt Native and Agricultural Ecosystems
They out-compete desired plants (native or crop) for space.
Non-Native, Invasive Plants Cause a Wide Variety of Unwanted Changes in
Invasive plants replace a diversity of native plants with just one, or
only a few, non-native plants. Invasives may upset ecological relationships
among native species. For example, when Monarch Butterflies that have mistaken
Black Swallow-wort for native milkweeds lay eggs on the Swallow-wort, the
caterpillars that hatch soon die because Swallow-wort leaves are toxic.
The loss of plant diversity in an area affects wildlife and humans. The
replacement of native vegetation with one type of plant that will grow on a
wide variety of sites (for example, Japanese Barberry instead of multiple
species of shrubs and wildflowers) can reduce the unique sense of place valued
by the site's users. There also is a loss of food diversity for the diets of
native animals (birds, mammals, fish, insects, etc.).
Some non-native, invasive plants grow much more densely than the native
plants they replace. These invasives can replace multiple layers of vegetation
with a single layer. Their dense growth can make the plant cover less suitable
for wildlife shelter and movement. Some grow so densely they impede human
movement in forests and fields. In waterbodies, dense growth of invasive
plants can interfere with boating and swimming, or clog water pumps.
Plants That are Both Non-Native and Invasive Will Dominate Sites and Spread
to New Sites
Water plants may be spread by well-meaning people (for example, when the
contents of fish tanks are dumped into local ponds) or through natural
occurrences (such as windblown seeds or floods that carry plants out of
backyard ponds to other waterbodies).
Phragmites (Phragmites australis, also called Common Reed) is found
worldwide. Within the species, the genetic make-up varies. Recent studies
indicate that in New England, the native strain of Phragmites has been
replaced by a non-native strain that is an aggressive invader. The aggressive
strain was accidentally (and perhaps also intentionally) introduced to
Connecticut. Once introduced to a new site, it benefits in places where road
salt gets into freshwater wetlands because it is more tolerant of salt than
other freshwater plants.
In Connecticut, agricultural weeds tend not to spread into native forests
or wetlands. However, important weeds of the western United States rangelands
(such as Spotted Knapweed and Leafy Spurge [or the related Cypress Spurge])
that are increasingly beginning to be found on dry roadsides in Connecticut
should be watched carefully to make sure they do not move into native or
The Spread of Non-Native, Invasive Plants is Affected by Things That People
Do on the Sites Where the Plants are Found.
For example, transporting roadside soil to a new location may spread
invasive plant seeds or root fragments. The tires, undercarriages, and other
parts of machinery that is moved from site to site can spread seeds and root
fragments that will start new infestations. Ready-to-root wetland plant
fragments can be spread by boats, boots, and machinery parts that are not
rinsed off between wetlands. Hikers' shoes (soles and shoelaces) can bring
invasive plant seeds into natural areas well away from roads. Finally,
disturbing soil in sunny sites near the location of invasive plant
infestations can create conditions that favor the establishment of invasive
plants. Seeds may be carried to disturbed sites by wind, water, animals, or