Early successional vegetation assembly in a spatially variable hydrologic regime

Abstract

Mitigation wetlands are intended to replace the ecological conditions of wetlands lost to development or drainage, resulting in a theoretical expectation that the replacement wetland will support a species composition and diversity comparable to a reference standard. I analyze a freshwater mitigation wetland in central Ohio, USA to evaluate factors that influence spatial patterns of plant community assembly in terms of floristic quality and diversity. Soil seed bank, bulk density, organic content, and pH are evaluated, along with average depth, exposure time, depth variance, and spatial location within the wetland basins, for their relationship with plant community characteristics in the first three years after wetland creation. The plant community was highly variable during the study period, with general trends toward greater diversity and more hydrophilic vegetation. The spatial distribution of nonnative cover, planted cover, mean coefficient of conservatism, and diversity in the third-year plant community were unrelated to soil and seed bank metrics; however, all were strongly related to hydrologic metrics. Shallow depth (<0.2 m) and moderate depth variance were found to facilitate plant community diversity, while floristic quality is more likely in deep (>0.2 m) and relatively stable water levels (<60% exposure time). Nonnative vegetation cover was particularly high at shallow locations with high depth variance and long exposure times. Geographic analysis of floristic quality and diversity indicates a weak spatial correlation between the two, suggesting that these two measures of the plant community are unlikely to coincide in early succession. The implications are that site design and hydrologic manipulation can drive the early successional vegetation characteristics, and that site design, compliance criteria, and monitoring regimes should seek to concertedly facilitate species composition, community diversity, or both.

Keywords:

• mitigation wetland
• vegetation
• floristic quality
• diversity
• hydrology

Acknowledgements

The access and assistance provided by Dawes Arboretum is gratefully acknowledged. Thanks to Simonne Benoit, Miranda Carter, Melissa Kennedy, Xije Lv, Jackson Means, Jordan Mora, Kyle Plummer, and the Denison University Departments of Biology and Geosciences for field and lab assistance.

Additional information

Funding

This work was funded in part by the Denison University Anderson Endowment.