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Non-Native, Invasive Plants: Why Worry?

Non-Native, Invasive Plants Disrupt Native and Agricultural Ecosystems

Non-Native, Invasive Plants Cause a Wide Variety of Unwanted Changes in Native Ecosystems

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 Recent studies indicate that in New England, the native strain of Phragmites has been replaced by a non-native strain that is an aggressive invader.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 agriculturally-important grasslands.

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 human activities.