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Global warming is expected to affect competitive interactions of grassland species. Early season grazing can allow warm season grasses to predominate in mixed prairie, speeding plant community adaptation to climate change. From 2010 to 2013, a southwest Manitoba prairie dominated by big bluestem (12% cover) and Kentucky bluegrass (4% cover) was subjected to warming using open top chambers (OTC) combined with three clipping treatments including; early July clip, early August clip, and no clip. Cover estimation was done twice each year, in early July and August, to take into account phenological differences among species. Species covers after two years of the treatments were compared using Proc Mixed of SAS. OTC's did not affect species composition or diversity components. Also there were no significant interactions between OTC's and clipping time.  The clipping treatments, however had significant effects on species composition and diversity components. Compared to the non- clipped controls, August clipping approximately halved the cover of big bluestem and doubled the cover of Kentucky bluegrass.  August clipping also increased the cover of thistles and smooth aster.  August clipped plots had greater species number, evenness and Shannon diversity than the two other treatments. With July clipping species covers were similar to no clip. With these two treatments big bluestem cover was greater than August clip but covers of the subordinate species were less.  In the short term we found warming with OTC's had no effect on big bluestem cover, but over the long term climate change could favour warm season grasses. Earlier grazing could enhance this trend.