Carex stricta is considered an ecosystem engineer for its ability to structure sedge meadow vegetation via tussocks. To harness the structuring capacity of this ecosystem engineer for carbon sequestration during restoration, we investigated the composition of field-collected C. stricta tussocks and initiated a mesocosm experiment to determine how hydroperiod and nutrient addition influence tussock formation. 

Results/Conclusions

Our finding that field-collected tussocks of C. stricta were only 8% inorganic rejected the hypothesis that sediment accumulation is necessarily the dominant mechanism of tussock formation.  The organic components (duff 42%, shoot bases 25%, roots 24% and rhizomes 1%) comprised 92% of tussock dry weight.  Our mesocosm experiment with six hydroperiod treatments ± nutrients rejected a related hypothesis that tussocks necessarily grow slowly.  Constant high water levels (18 cm above the soil) produced tall structures (mean = 12.6 cm ± 1.35; maximum = 19 cm) during the second growing season.  These young tussocks had compact culms, adventitious roots, and long leaves (~1 m).  Growth decreased with reduced inundation (time or depth).  With a summer drawdown, young-tussock height averaged 10.5 cm ± 0.83, while constant low water (18 cm below the soil) reduced mean height to 2.21 cm ± 0.28 and increased lateral spread of tillers.  Nutrient addition (15 g N m^-2) increased total plant biomass as well as the circumference and volume of young tussocks, but did not affect their height.  Together, the high organic content and rapid growth of young tussocks suggest that C. stricta has high potential for sequestering carbon during sedge meadow restoration.