Vegetation trends in a restored coastal wetland at Prisoners Harbor, Santa Cruz Island, Channel Islands National Park

Prisoners Harbor on Santa Cruz Island, California, formerly supported a 5-ha wetland and riparian system, the largest on the California Channel Islands. During the late 1800s ranchers filled in about half of the wetland area in order to support ranching activities. They also rerouted the stream channel to the canyon edge and built an earthen berm along its west bank, which disconnected the stream from its floodplain. The National Park Service developed a wetland and riparian restoration design for Prisoners Harbor based on topographic and hydrologic analyses and on vegetation community depth-to-water-table relationships developed from neighboring reference wetlands. In 2011 Channel Islands National Park and The Nature Conservancy restored 1.25 ha of coastal wetlands by removing artificial fill and the earthen berm. Postproject vegetation monitoring during 2012 to 2016 showed increased abundance of 3 of the 8 herbaceous planted wetland species and declines in target invasive species. Severe drought conditions during this window likely influenced vegetation abundance. Postrestoration hydrologic monitoring showed that the restored marsh met the federal wetland hydrology standard only twice: once in late 2011 before the drought began and then again in January–September 2017. An exceptionally large swell and high tide during winter 2015/16 resulted in saltwater flooding of the site; salinity returned to more typical values only slowly after this event. Expansion of wetland species, even during a historic drought and atypical seawater intrusion, suggests that this evidence-based approach to restoration design will result in functional coastal wetland habitat as more typical precipitation levels return. However, we emphasize the need for aggressive control of nonnative plants until native plant cover is well established.