Three years after construction, alternative planting and management strategies in experimental marshes induce differences in biodiversity and heterogeneity, but not in function

There is considerable variability in the intensity of plant species management undertaken in wetland restoration projects during the first few years of development. Practices range from no seeding of any kind to extensive and repeated seeding, planting and invasive species management. Our study is designed to assess the effects of management on patterns of biodiversity and ecological function. In the fall of ’03 we completed construction of six hydrologically isolated experimental wetland “cells” (each ¼ ha) in marginal farmland in NE Ohio. Wetlands were subjected to three alternate seeding/management practices: 1) natural recruitment (“self-design”), 2) one-time seeding and planting with a native species mix, 3) seeding and multiple plantings to replace lost species. Invasive species were selectively removed from all three treatments. Three years into the restoration project, the four planted cells are significantly more species rich, diverse, and spatially heterogeneous than the self-designing wetlands. However, patterns observed in the levels of dissolved inorganic phosphorus and nitrogen (DIP and DIN) are similar across treatments. Other water quality parameters, including turbidity and dissolved oxygen likewise show no differentiation based on treatment. This suggests that environmental factors common to all of the cells are currently a stronger determinant of water quality than management practices. Other studies suggest that plant effects on DIP, DIN and other water quality parameters may not be evident for several years after initial restoration. Subsequent planned perturbation of these experimental systems with nutrients will elucidate whether functional differences eventually follow the significant structural differences that are already evident.