Print PageMost of the North American tallgrass prairie ecosystem was lost to farming and development during European settlement of the Midwest. Restoration of previously agricultural fields to native prairies is a current method implemented to increase nutrient retention, create habitat for native species, and re-establish ecosystem functions. Although some studies suggest that soil organic carbon and total nitrogen may take several hundred years to reach remnant prairie levels, more research is needed to determine the time frame to reestablish prairie ecosystem diversity and function. Twenty-one years ago St. Olaf College joined a national effort to restore tallgrass prairie and seeded eight prairies from 1989 to 2004. We sampled from seven of the St. Olaf prairies to assess the effects of restoration on soil and plant communities. Our goals were to (1) determine if soil characteristics or biomass production change as prairies age, (2) compare the restored prairies to a remnant prairie and (3) investigate the relationship between soil and plant characteristics in the restored prairies. We measured soil characteristics - including organic matter, bulk density, nitrates, ammonium, and phosphates - in the St. Olaf prairies and a nearby remnant prairie. Aboveground biomass and species richness were also measured.
Results/Conclusions
Within the restored prairies, organic matter and the soil nutrients of PO4-3-P, NO3-1-N, and NH4+decreased with prairie age. The remnant prairie had significantly higher organic matter content than six of the restored prairies. Aboveground biomass also decreased with age in the restored prairies. Species composition was similar across prairies despite being planted at different times. The species richness may be increasing over the chronosequence, but the differences observed were not significant. We also found no significant trends in the grass to forbs ratio. Overall the variables studied decreased with age in the restored prairies. Fertilizers remaining from farming are likely the cause of the increased phosphate levels in the more recently restored prairies. As competition for nitrates and water intensifies with prairie age, plant communities are expected to shift the allocation of biomass belowground. We expect that the accrual of more native species as these prairies age will aid in recovery of ecosystem functions. Future studies on burn regimes, fertilization and species richness in this restored chronosequence will provide more insight into observed trends.
