Invasive Species
Invasive species are non-native organisms whose introduction to the ecosystem causes or are likely to cause harm. These species can negatively impact native habitat, displace native species, lower property values, and disrupt recreational activities. Invasive species are primarily spread through human activities such as vehicle and watercraft movement, air travel, and the release of unwanted pets. Once introduced to a new environment, invasive species can reproduce rapidly. Without natural predators, they quickly take over an area and disrupt the natural ecosystem.
St. Croix County and Invasive Species
There are several known invasive species in St. Croix County. County staff are working with the St. Croix – Red Cedar Cooperative Weed Management Area (CWMA) to raise awareness about invasive species. Some species of concern include Zebra Mussels, Eurasian Water Milfoil, Purple Loosestrife, and Buckthorn.
Zebra Mussel Monitoring
Zebra Mussels are invasive mollusks native to Eurasia. They are about the size of a fingernail and have dark zig-zagged stripes against a cream background on each shell. These mussels negatively impact the ecosystem through their rapid reproduction and population growth. They filter out algae that native species rely on for food and attach to native species, effectively incapacitating them. Zebra Mussels can also accumulate in great numbers over time on docks, boats, and intake pipes causing clogging and damage.
In 2024, St. Croix County began working with members of the Bass Lake association to distribute several settlement samplers in Bass Lake to monitor the population of Zebra Mussels. Bass Lake is the only lake in St. Croix County with a confirmed population of Zebra Mussels. Through continued monitoring and community involvement, we hope to prevent the spread and increase our understanding of zebra mussel distribution within the County.
Aquatic Plant Monitoring
Starting in 2023, St. Croix County Land and Water staff began monitoring several waterbodies within the County to document the aquatic plant species present in our lakes and rivers. This includes documenting any invasive species found during sampling.
Washdown Stations
Installing wader and boat washdown stations is a practical measure to prevent the unintentional transfer of aquatic invasive species between waterbodies. These stations help users to clean their equipment, reducing the risk of spreading invasive species.
Buckthorn Control
County staff have worked to educate landowners about buckthorn control methods and have helped provide cost-sharing assistance along riparian areas when funding was available. Buckthorn can invade many types of habitats, including oak forests, riparian woods, savannas, prairies, old fields, and roadsides. It thrives in well-drained soils. Common buckthorn has a broad environmental tolerance. It leafs out very early in the spring and retains its leaves late into the fall, giving it a longer growing season than native plants. This allows buckthorn to create dense shade that prevents tree seedlings and understory species from regenerating. Additionally, buckthorn is allelopathic, meaning it produces chemical compounds that inhibit the growth of other plants and vegetation.