Invasive Plants in Wetlands

Invasive plants and their effect in degrading wetland habitats are receiving increased attention these days. Invasive plants can reduce the quality, functions, and values of both existing wetlands and those created for mitigation purposes.

An invasive plant is usually an introduced species that spreads quickly over an area, often out-competing other species and forming a monoculture. It is a species that provides little value to wildlife. Purple loosestrife (Lythrum salicaria) and common reed grass (Phragmites australis) are the two species most frequently considered invasive. Although invasive plants are usually non-native, there are many plants native to North America that may be considered invasive in wetlands. Reed canary grass (Phalaris arundinacea) and meadowsweet (Spiraea spp.) are examples of native invasive species.

Common reed grass Invasive plants are important in two areas of wetland permitting: 1) in determining baseline wetland conditions for function and value assessments, and 2) in wetland establishment (creation) for mitigation purposes.

The importance of assessing invasive plants during the baseline delineation for wetland permitting relates to the function and value assessment, in particular the habitat value of each wetland. Extensive stands of invasive plants reduce wildlife use by decreasing habitat interspersion and plant diversity for wildlife food and cover. If the functions and values of existing wetlands are low, it may affect permit issuance and the required mitigation ratio.

Mitigation plans that include wetland establishment are required to address the control of invasive plants. Often, the percent cover of invasive plants is not allowed to exceed the cover of nearby existing wetlands. Permit conditions usually require that control measures be implemented if invasive species exceed specified cover values during the monitoring period.

Control of invasive plants, particularly purple loosestrife and common reed grass, has received considerable attention over the years. Both species are difficult to control because they produce abundant seeds or spread so quickly in a vegetative manner. Another apparent problem in controlling these invasive plants is that we do not have the biological control agents (insects, herbivores, fungi, etc.) that exist in the plant’s native region. For that reason, biological controls are being carefully studied. Recent reports indicate good success in controlling purple loosestrife with introduced beetles (Galerucella spp.). Larval stages of the beetles feed on the plants and suppress flower and seed development. Such control may take some time, but shows promise for future loosestrife reduction. Biological controls for other invasive species are being studied. Control measures can be developed during wetland establishment by designing the wetland to have water depths and other conditions less suitable to invasive species.

TES, Inc. 23 County Route 6, Suite A, Phoenix, NY 13135. Tel: 315.695.7228 Fax: 315.695.3277

Web Design by: J. G. Bocsor, D. M. Matzke