Seed ecology of wetland Carex spp.: Implications for restoration

In the prairie pothole region of the mid-continental U.S., plant recolonization in most hydrologically restored wetlands occurs through natural recolonization. Little emphasis has been placed on accelerating succession through seeding or planting of native species. While some plants return quickly, others do not, especially the Carex spp., the dominant vegetation of seasonally flooded wetlands. The slow establishment of Carex spp. is problematic because potential sites for recolonization are preempted by the invasive species reed canary grass (Phalaris arundinacea), resulting in a wetland with low plant diversity and little wildlife habitat value.; I evaluated why Carex are not returning to restorations through studies of (1) seed availability using seeds traps placed in restored and natural wetlands in northwest Iowa to quantify the seed rain and (2) seed germination where seeds of 5 Carex spp. were sown into restorations and neighboring natural wetlands. At restored sites, all Carex were limited by seed availability but germinated well when sown into plots, indicating that practitioners should sow Carex seeds into restorations to achieve the diversity characteristic of natural wetlands.; I conducted dormancy and germination growth chamber studies with 14 Carex spp. to determine whether stratification is required to break dormancy and the best season to sow seeds for optimal germination in the field. First, seeds were stratified (i.e., moist, cold conditions) for 0 to 6 months and then incubated under one of five temperatures for seed germination. Widely varying dormancy and germination patterns were found but after stratification, seeds of all species germinated faster to higher percentages across a wider range of temperatures than unstratified controls. Second, white light requirements for germination of nondormant seeds and response of seeds to far red light, the predominant kind of light under plant canopies, were determined. All but two species required light for germination and germination in all species was inhibited by far red light. To accelerate succession of native Carex spp., practitioners should stratify seeds and then sow them early in the spring before the establishment of plant canopies to ensure optimal light and temperature conditions for Carex germination.