Interannual variability in ephemeral pond and permanent wetland plant community structure: Sensitivity to climate fluctuations
The plant communities of ephemeral ponds in the Eastern United States are understudied, and ephemeral pond hydrology is highly dependent upon precipitation patterns. Given climate change, there is a strong need to understand the sensitivity of these systems to precipitation fluctuations. We collected two growing seasons of data (2013 and 2014) in forty ephemeral pond and seventeen associated permanent wetland plant communities in the forested moraine region of Northwestern Wisconsin using both permanent plots and whole-wetland transects. The 2013 growing season had average precipitation, and most ephemeral ponds dried by late August. 2014 had substantially above average precipitation, to the extent that many ephemeral ponds remained flooded throughout the growing season. Permanent plots were established at within each wetland at edge, transition, and bottom elevation zones within each ephemeral pond. Our objectives were two-fold: 1) determine whether important factors influencing ephemeral pond and permanent wetland plant community organization, including functional group structure, differed between 2013 and 2014, and 2) determine whether zonation patterns within ephemeral ponds shifted in response to increased hydroperiod.
Species richness and total vegetative cover declined in both permanent wetlands and ephemeral ponds in response to elevated water levels, but declines were more significant in ephemeral ponds. This result indicates that ephemeral pond plant communities are more sensitive to changes in precipitation than those of permanent wetlands. Both annual and woody plant functional groups declined in ephemeral ponds. There was no significant difference in ephemeral pond edge plot communities between the two years. Bottom plot communities were significantly different, with the absence of annual species and an increase in Lemna minor. The communities of 2014 transition plots were more similar to the bottom plots of 2013, indicating a capacity of ephemeral pond plants to shift zonation. With the uncertainty surrounding a possible increase in large precipitation events in the future, it remains to be seen whether ephemeral ponds dry less frequently, resulting in permanent losses in species richness.