Mulching Wetlands after Pipeline Construction: Effects on Plant Diversity and Density

Timothy L. Andersen and Gayle M. Konik

Wetland vegetation recovery following ground disturbance associated with construction along a corridor is generally not well understood. Land management agencies and project sponsors share the objective to quickly and effectively reestablish stable vegetation to control erosion. Mulch is commonly used to promote rapid plant growth by retaining soil moisture and reducing erosion in upland areas. The benefits of mulch application are less clear in wetlands. Land management agencies overseeing a pipeline construction project in southeastern Michigan wished to determine the benefits or disadvantages of mulching wetlands. This report compares post-construction vegetative recovery of wetlands mulched with straw with wetlands not receiving mulch, as measured by plant diversity (number of plant species per test plot) and density (number of specimens per test plot). Measurements were taken two, nine and eleven months after the completion of construction restoration. Factors influencing recovery rate were location of study wetlands, local conditions and susceptibility of study wetlands to invasion by exotic or opportunistic species. Study results yielded conflicting trends. Wetlands receiving mulch treatment did not overall appear significantly different from reference wetlands. Location of wetlands (i.e., proximity to drains, forests, etc.), seasonal factors (including precipitation and temperature) and topographic features seem to greatly overshadow any effect of mulch application to wetlands on plant density and diversity as measured in this study. Longer term examinations (multiple growing seasons) are needed to establish the effectiveness of mulch application to wetlands following pipeline construction.

Keywords: Wetlands, pipeline construction impacts, mulch, plant diversity and density, variability, local conditions, revegetation