Climate benefits of wetland restoration are constrained by slow vegetation recovery
Ilona Tamm, Dennis Baldocchi, Evelyn Uuemaa, Kyle Delwiche, Kadir Yildiz, Mihkel Pindus, Ain Kull, Daphne Szutu, Joseph Verfaillie, Kuno KasakAbstract
Introduction
Wetland restoration is widely used to enhance ecosystem resilience, biodiversity, and climate mitigation. However, restoring hydrology may not lead to rapid vegetation establishment or reduced greenhouse gas (GHG) emissions in severely degraded wetlands.
Objectives
We evaluated six site‐years of vegetation development and carbon dynamics in two wetlands restored in 2021: a reclaimed estuarine tidal marsh in California, U.S.A. (Hill Slough), and an abandoned peat extraction area in Estonia (Ess‐soo).
Methods
Eddy covariance measurements of carbon dioxide (CO 2 ) and methane (CH 4 ) exchange were combined with vegetation surveys, hydrological monitoring, elevation data, and soil and water measurements. Environmental controls on GHG fluxes were assessed using random forest models.
Results
Vegetation development remained limited at both sites. After four growing seasons, Hill Slough was almost entirely unvegetated, while vegetation at Ess‐soo remained confined mainly to drier areas and did not expand. Spatially unsuitable hydrology, from prolonged inundation to low water tables, likely constrained plant establishment in both sites. Both wetlands remained net carbon sources. For example, 4 years after restoration in 2025, annual net ecosystem CO 2 emissions were 269.7 ± 99.4 g C m −2 yr −1 at Hill Slough and 41.6 ± 29.9 g C m −2 yr −1 at Ess‐soo, while CH 4 emissions reached 17.2 ± 13.4 and 8.9 ± 6.4 g C m −2 yr −1 , respectively. Fluxes were primarily controlled by temperature, water level, radiation, and wind.
Conclusion
Hydrological restoration alone may be insufficient to promote vegetation recovery in heavily disturbed wetlands, substantially delaying climate mitigation and other restoration goals.