Response of thicket swamp species to soil moisture levels: Implications for restoration

Abstract

Wetlands dominated by shrubs are ubiquitous features in the Great Lakes Region of North America, yet little is known about the interactions between plants and the environmental conditions of these ecosystems. We measured the response of seven common wetland shrub species and two forbs to soil moisture treatments over a growing season. Average soil moisture content across three treatments ranged from <30% to >75%. These soil moisture differences produced a measurable effect on plant growth for six of the nine species tested. While Rosa palustris and Spiraea alba preferred the highest soil moisture treatments, Salix interior, Sambucus nigra, and Solidago uliginosa had higher biomass from moderate soil moisture, with no effect observed for Cornus sericea, Salix discolor, and Viburnum lentago. Most of the growth differences were from aboveground portions of the plants. A significant difference in root-to-shoot ratio (R:S) was found for eight of the species, with contrasting directions of change between the soil moisture treatments. New growth was compared to mean stomatal conductivity to determine an estimated water use efficiency (WUEe), which demonstrated a montonal relationship for six of the species across the measured soil moisture regime. Only the upland goldenrod, Solidago altissima, demonstrated the expected increase in WUEe with decreasing soil moisture, which suggests wetland shrubs are inefficient at low soil moisture. The results of this study provide quantitative data on the range of responses to soil moisture of common species of shrub wetlands, which can be used by wetland managers to improve restoration success.