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Conversion of native grassland to cropland and tame pasture is decreasing the area of rangeland in the northern Great Plains, and currently only ~ 40% of Alberta's native grasslands remain. Furthermore, some climate change models predict that crop growing conditions will improve in northern temperate zones, placing remaining native grassland under a greater threat of conversion. Rangelands provide numerous ecological goods and services, such as carbon storage, which can be reduced by cultivation. However, current carbon offset policy in Alberta only supports demonstrable increases in soil carbon from cropland practices such as reduced-tillage, but not the maintenance or increase of soil carbon on native grasslands. This policy may have the inadvertent effect of bringing additional native grasslands into crop production. In order to quantify the benefit of native grasslands for carbon storage, we compared soil carbon content and stability in grazed native grasslands with adjacent (< 1 km) cropland and/or tame pasture (n=30). Sites were typically “broken” prior to 1935, allowing us to quantify long-term effects of cultivation. Sites were distributed along a large agro-climatic gradient (P:E ratio from 0.3 to >1) in Alberta, Canada, encompassing a variety of crop and tame pasture systems. We sampled soils and vegetation, determined soil carbon content, and assessed soil carbon stability using particle size fractionation. Results of this study will serve to better understand the long-term effects of cultivation and native grassland conversion on carbon storage.