Biodiversity loss due to climate change is predicted at high latitudes and altitudes, but losses are likely to occur more broadly, whenever range shifts result in a low diversity replacing a high diversity assemblage. Here, we report the predicted decline of a diverse assemblage of mid-latitude salt marsh plants, based on the results of an ecosystem warming experiment. In New England salt marshes, a diverse guild of salt marsh forbs occupy edaphically stressful, waterlogged high marsh pannes. We examined the sensitivity of this guild to warming using open top warming chambers.

Results/Conclusions

At three New England sites, forb panne habitat was sensitive to warming, which induced biodiversity decline and rapid takeover by surrounding Spartina patens. In Rhode Island, the southernmost site and the southern range limit of forb panne habitat, pannes were more sensitive to warming than farther north in Maine, and forb panne area also declined in control plots over the three-year experiment. Biodiversity decline was detectable after only a single summer of warming. After three years of experimental warming, panne areas were reduced to less than 10% of cover in warmed plots, and warming reduced Shannon-Wiener biodiversity by up to 74%. These results suggest that warming will rapidly reduce forb panne area and plant species diversity in New England salt marshes.