Study finds post-restoration wetland succession highly variable

A new study from researchers at the University of Illinois has looked at wetland restoration projects across the state and found that successional trends vary substantially from one site to another. The study findings have implications for the Clean Water Act and its ability to meet its mandate of enforcing no net-loss of wetland area or function in the United States.

All the wetlands in the study were restored to meet permit requirements under Section 404 of the Clean Water Act. The permits allow wetlands to be degraded or destroyed but only under the condition that the permittee restore an equal or greater area of equivalent wetlands.

The Clean Water Act assumes that restoration of degraded wetlands can consistently reach a target vegetative community. However, the study findings show that that successional pace and trajectory is highly unpredictable without a thorough understanding of the influence of site specific characteristics.

Jeffrey Mathews and Anton Endress examined 24 restored wetlands’ vegetative communities throughout Illinois to determine whether or not consistent successional trends existed that in turn could help inform restoration implementation and management. The team found that some common trends existed: wetlands initially contained annual species which were later replaced by clonal, perennials over time.

However the pace of succession and species composition was highly variable. Restoration of wetlands on former agricultural lands had faster rates of succession probably due to nutrient additions, but biodiversity was lower. There was no evidence for larger sites catering to more rapid succession, but species turn-over rates tended to be higher at smaller sites. There was no evident correlation between succession and site isolation, site age, or degree of urbanization.The researchers advise,

“Although a consistent trend in life-history group composition [annuals replaced by perennials] was apparent and largely predictable in the present study, the composition of individual species was stochastic and site-dependent. Even when direction of succession is convergent among sites, the pace of succession likely depends on site context.”

--Reviewed by Evyan Borgnis

Matthews, J., & Endress, A. (2010). Rate of succession in restored wetlands and the role of site context Applied Vegetation Science DOI: 10.1111/j.1654-109X.2010.01076.xMatthews, J., & Endress, A. (2010). Rate of succession in restored wetlands and the role of site context Applied Vegetation Science DOI: 10.1111/j.1654-109X.2010.01076.x