Dominant wetland plants as drivers of productivity and diversity, and as restoration targets

Restoration projects in urban wetlands are often confronted with hydrologic disturbance, high nutrient inputs, and invasive species, all of which can favor highly productive but nearly monotypic vegetation. The potential trade-off between wetland plant diversity and productivity has implications for practice because both are common restoration targets. We investigated that trade-off and its dependence on dominant species, the association of diversity and productivity with hydrologic and water-quality-based ecosystem services, and restoration planting practices that could promote the establishment Carex stricta, a native wetland dominant that supports diversity and ecosystem services.;We investigated the relationship between wetland plant diversity and productivity in three contrasting systems with similar vegetation: 1) a mature restored wetland, 2) created wetland swales, and 3) a mesocosm experiment. We found negative correlations between plant diversity and productivity in systems 1-2 and no correlation in system 3; we reasoned that tall, highly productive graminoids in unweeded systems became frequent and excluded other species. In a collaborative project, we quantified six ecosystem services in the aforementioned wetland swales. Due to differences in hydrologic regime, the swales offered divergent suites of ecosystems services: fast drainage favored relatively high plant diversity and levels of hydrologic and water-quality-based services, whereas ponding led to high productivity and low levels of all other services.;Having observed that dominant native sedges in systems 1-2 were associated with higher plant diversity and, more generally, that dominant species identity was paramount in determining the provision of ecosystem functions and services, we undertook restoration experiments with the aim of establishing C. stricta, or tussock sedge. In one experiment, we artificially enhanced microtopography by building soil mounds and applying other manipulations to increase variation in soil moisture. In some cases, manipulations supported growth and survival of C. stricta even when conditions were unfavorable due to spatial variation in soil moisture or extreme weather. In a separate experiment, we found evidence suggesting that seed provenance affected C. stricta growth and survival. Hence, restoration of diverse microhabitats and seed provenances could help ensure establishment of a desirable wetland dominant.