Background/Question/Methods Climate change is a growing threat to the diversity and functioning of grassland ecosystems, as it is expected to increase average temperatures and exacerbate drought conditions in the Midwestern United States over the next century. Midwestern tallgrass prairies are especially important for conservation purposes, as they support a high diversity of flowering plant species which provide essential habitat for native pollinators. However, there is evidence that the warmer and drier conditions under climate change will favor non-flowering C4 grass species, causing them to outcompete native wildflowers and potentially decreasing the ability of prairies to support pollinators in the future. Despite this threat, little research to date has established a link between climate change and the abundance and diversity of flowering plant species. Here, we use a fully factorial warming and drought experiment to examine the effects of elevated temperature and reduced rainfall treatments on biodiversity and flower abundance in a tallgrass prairie ecosystem at Cedar Creek Ecosystem Science Reserve in East Bethel, MN. We measured flower resources by counting flower head abundance in the plots every two weeks over the growing season and quantified plant diversity by harvesting, identifying, and weighing individual species biomass. Results/Conclusions Experimental elevated warming had the strongest effect on the ability of prairies to provide flower resources, although both warming and drought determined the relationship between Andropogon gerardii (a C4 grass species) biomass and plant diversity. A. gerardii biomass increased significantly (nearly 2-fold) with both elevated warming (P < 0.05) and drought (P < 0.05). A. gerardii also contributed to a 3-fold increase in grass/forb biomass ratios under warming. Plant diversity declined significantly with increasing A. gerardii biomass (P < 0.0001) under warming, although not under drought (P = 0.395). There was also a strong positive correlation between plant diversity and the total flower count throughout the growing season under the combined effects of warming and drought treatments (P < 0.05). Overall, these results indicate that future climate change will likely favor warm-adapted grasses, which outcompete other native plants, thereby reducing the overall diversity of tallgrass prairies in the future. This research is highly relevant to conservation, as it indicates that highly diverse prairies may be better able to maintain larger numbers of blooming flowers under extreme hot and dry conditions, allowing for more effective conservation of prairies for pollinators in the future.
