Prescribed annual burns have long been used in remnant and restored prairies to boost nutrient cycling and control unwanted species. Moreover, prairie grazers tend to prefer recently-burned sites, which is often termed pyric herbivory. Plant and soil stoichiometry, specifically C:N, can be used to quantify the quality of the resource for grazers (plants) and microbes (soils). While the impacts of fires on soil and plant stoichiometery are known in old field prairies, little research has been done in more recently-restored ecosystems, especially those with newly-reintroduced grazers. This study examined how prescribed burns have affected plant community composition and plant and soil stoichiometry (C:N). We used matched pairs of burned and unburned sites with similar restoration ages. The first pair were restored in 2007 and 2008, and the second pair were restored in 2001 and 2002. Three soil samples and 55 plant samples were taken from each planting. Soil samples were sieved and analyzed for total carbon and nitrogen using a mass spectrometer. Three individuals of each plant species were collected, dried, homogenized, and also analyzed for total carbon and nitrogen. Data were analyzed using general linear mixed models.
Analysis of the composition of the four sites showed that they were each approximately 40% C4 grasses, 10% C3 grasses, 20% forbs and legumes, and 30% bare ground or thatch. Burned soil C:N had a modeled average of 14.22 and unburned soils had significantly lower C:N, averaging 13.1. When looking at previous years’ history of burns, we found that soil C:N increased by 0.86 in each successive year that a prairie is burned, with those not burned averaging 13.2, those burned recently averaging 14.22, and those burned two years in a row averaging 15.. This indicates that nitrogen is lost from soils as they are successively exposed to fire. The nitrogen loss may be from volatilization following fires, but it remains to be seen whether plant C:N follows a similar pattern and if it varies by nutrient uptake strategy (C3, C4, legumes). Plant C:N will be measured in summer 2017. This information will be useful to land managers so they can maintain healthier prairies, have more information about the impacts of fire on nutrient cycling, and give information about the quality of resources for both grazers and microbes, which drive prairie ecosystem functioning.