See the paper: Biomass and Burn Cycles in a Tallgrass Prairie of Southern Minnesota

Background

Approximately 90% of Minnesota’s prairies have disappeared due to conversion of land to agriculture. Much of the remaining prairie is used for cattle grazing, which completely changes the landscape and species composition. Prairie restoration is therefore a key focus of many conservationists in Minnesota. The St. Olaf Natural Lands currently have converted over 150 acres of agricultural land into restored prairie. 

Prescribed burning is a method of managing and supporting prairie growth. It involves applying fire to an area of land in a controlled manner in order to increase the resilience and diversity of native plant species. When restoring a prairie, it’s necessary to understand the effects of burning and the frequency at which it is most beneficial. In 2014, a St. Olaf student decided to assess how time since a prescribed burn impacts the composition of a prairie. 

The Study

Emily Patterson (Class of 2015, B.A. Biology) chose four sites to study in the Natural Lands that had each been burned at different times. Each site was either burned that year, one year prior, two years prior, or four years prior to the study. Patterson then took plant and soil samples within a small plot from two places at each site to be dried, weighed, and tested. 

The Findings

Patterson compared the biomass (dry weight) of grasses and forbs (non-woody flowering plants). It was found that as the time since a burn increased, the biomass of grasses decreased and the biomass forbs increased. 

Relevance

The Natural Lands actively practices prescribed burning as a prairie management technique. When choosing when to burn certain plots, managers consider the goals they have for that plot and the current species composition. Knowing how to best time these burns is crucial, and research like Patterson’s is beneficial in growing this knowledge.  

Citation

Patterson, E. 2014.Biomass and Burn Cycles in a Tallgrass Prairie of Southern Minnesota. St. Olaf College Local Ecology Papers.