An 8,000-year fire and vegetation history of an oak savanna in East Central Minnesota
Oak savanna, a transitional ecosystem between open prairie and dense oak forest, was once widespread in central and southeastern Minnesota. As Europeans settled the area during the mid-1800s AD, much of the oak savanna ecosystem was destroyed through clearing for homesteads and agriculture, or converted into forest as a result of fire suppression practices. Since the middle of the 20th century, efforts to restore and preserve this now greatly reduced ecosystem have increased, and often include the reintroduction of fire. Though fire is known to serve an important role within oak savannas, there are currently few paleoecological studies which address issues of fire frequency, ecology, or natural range of variability on timescales longer than the last century. This research presents a fire and vegetation history spanning the last ~ 8000 years, using lake sediments collected on the Sherburne National Wildlife Refuge (SNWR) in east central Minnesota. The pollen record indicates a transition from woodland to prairie vegetation ca. 7500 cal yr BP as the climate became warmer and drier, followed by a gradual transition to oak savanna as conditions became wetter beginning ca. 6500 cal yr BP. The destruction of the oak savanna upon Euro-American arrival to the region is evident in the later part of the record, followed by restoration upon the establishment of the refuge. Fire activity appears to be driven by vegetation fuel loads, and ultimately climate, and is highest at periods in the record with greater tree and fewer herb taxa. These data provide insight into the natural fire regime, development, destruction, and recovery of the oak savanna and information on the specific disturbance history of SNWR, and will be used to inform land management considerations when prescribing fire and developing restoration objectives for the refuge.
University of Utah;
Charcoal; Fire; Minnesota; Oak savanna; Pollen; Sherburne