Invasive, Non-Native Plants

     Invasive exotic plant species are prevalent in the Davis Creek Watershed.  These aggressive organisms negatively impact natural areas by crowding native plants out of existence.  Certain invasive species can increase soil erosion, disturb insect life cycles and alter natural processes such as soil nutrient levels and microbial activity.  Suprisingly, many plant nurseries still sell the seeds of these and other known invasive plants.  Knowledge is the best weapon against these nuisances.

Garlic Mustard (Alliaria petiolata), another aggressive non-native, affects natural areas by displacing native grasses, herbs and tree seedlings.  It is prevalent in upland areas, along stream banks, and in disturbed areas.  Due to its lack of natural predators and to prolific seed production, this plant has become a significant problem across the United States as well as in Canada.  It is common along the banks of Davis Creek.

Purple Loosestrife (Lythrum salicaria) is extremely prevalent in wetlands.  This invasive species was documented in 49 states as of 1996.  This very aggressive plant degrades the quality of wetlands by suppressing native plants.  As a result, sources of food and cover for native wetland animals are diminished.  Within the Davis Creek Watershed, this plant has been observed in numerous low-lying areas.

Spotted Knapweed (Centaurea maculosa) is very common in old fields.  In many cases, this species grows as a monoculture.

White Sweet Clover (Melilotus alba) and the very similar Yellow Sweet Clover (Melilotus officinale) both rapidly invade open areas and overtake native plants.  These plants provide excellent sources of pollen for bees, but do not provide the nutrients necessary for wildlife.

Canada Thistle (Cirsium arvense), a spiny herbaceous plant, is actually native to Europe, not Canada, as the name indicates.  Though it does not pose a great threat to natural areas, it is very competitive in cropped areas and at habitat restoration sites.  Because it forms clones, it rapidly covers large areas, choking out all other plant species.