An intact hydrologic regime and the presence of peat forming vegetation are critical for the persistence of fen wetlands. Fen restoration projects often focus on reestablishing water tables near the soil surface, with little effort directed toward identifying historic hydrologic regimes, hydrologic modifications, and the sources of degradation. We used inconsistencies in the modern hydrologic regime and historic hydrologic indicators present in the soil seedbank, vegetation, and organic soil composition to identify areas of Drakesbad Meadow, a mountain fen in Lassen Volcanic National Park, California, that had been degraded. A network of ground-water monitoring wells and piezometers were used to identify the hydrologic regime of the 4.7-ha site. The presence of thick organic soils in sites with deep late summer water tables, inconsistencies between species present in the seedbank and the existing vegetation, and the presence of dry meadow species such as Poa pratensis and Hordeum brachyantherum in areas with organic soils were used to determine that 2.4 ha of the site was degraded. A drainage ditch within the fen and diversions of the fen's water supply caused by a road outside of the fen were identified as the source of hydrologic modification and degradation. These were restored by blocking the flow of water in the main drainage ditch and by installing a series of channels to allow water to cross the road. Reconnecting flow beneath the road resulted in raising the summer water table from 80 cm below the soil surface to less than 10 cm in areas downslope of the road. The addition of five sheet-metal dams perpendicular to flow in the main drainage ditch resulted in raising the water table to within 10 to 20 cm of the soil surface in areas adjacent to and down gradient of the ditch. Before restoration, average late August water table levels across the entire site were 30 cm below the soil surface, while average post-restoration water table levels were 19 cm below the soil surface. One year following hydrologic restoration, the percent canopy cover of species indicative of uplands and wet meadows, but not fens including Deschampsia cespitosa, Hordeum brachyantherum, and Poa pratensis decreased compared with pre-restoration years, while the cover of the peat-forming species Carex utriculata, Scirpus microcarpus, and Carex simulata increased. It is clear from our study that fens in this region will not persist under drought-like conditions created by water diversions, yet well-designed restoration projects can be used to restore modified hydrologic regimes and peat-forming vegetation necessary for the persistence of fen wetlands.
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Vol. 27 • No. 2