Effects of bioturbation on soil carbon and nutrient stocks: Insights from the American Prairie

Restoring functional ecosystems through rewilding has become a popular nature restoration strategy. The introduced keystone species are often large herbivores or carnivores due to their ability to shape ecosystem processes top-down. Much less focus has been given to restoring soil engineering, despite being a fundamental natural process in most ecosystems, not least in grasslands. I will present initial results from a field study of the role of bioturbation on soil carbon, nitrogen and phosphorous stocks in a large scale prairie restoration programme with bison reintroductions, the American Prairie in Central Montana, US. We show that, on average, the topsoil carbon stocks are almost doubled on prairie dog colonies in grazed prairie sites compared to grazed sites with no active prairie dog colonies. Further, we show that nearby sites without bovids for at least a century have substantially reduced carbon stocks, despite having higher clay content. This is driven by severely decreased soil bulk density, which we suspect may be partly due to high abundances of ground-dwelling spiders known to be sensitive to trampling. We show how important soil-dwelling animals can be for shaping the carbon and nutrient landscapes of the Great Plains. This belowground perspective deepens our understanding of what a fully functional prairie ecosystem looks like and should be considered in future restoration efforts.