We describe a biocultural restoration project to remove mangrove that has limited stream connectivity at the mouth of a windward stream in the He‘eia watershed on the island of O‘ahu, Hawai‘i. Three native-Hawaiian-led community partners have led the charge to clear over 10 acres of mangrove in the last three years, and in 2017, the 200-acre wetland and 88-acre fishpond were designated as the He‘eia National Estuarine Research Reserve, 29th in the system. Restoration of coastal wetlands in Hawai‘i involves removing invasive species not typical for tropical wetlands in other parts of the world, including the red and black mangrove. The mangrove was intentionally introduced in 1923 to mitigate erosion from poor farming practices upland. While beneficial for multiple ecosystem services in other parts of the world, mangrove in He‘eia stream prevents native diadromous fish from moving upstream, and does not provide habitat for native wetland bird species such as the Hawaiian moorhen, or ‘alae ‘ula. In the last two years, we have documented the effect of clearing on sediment loss, nutrient export, changes in soil carbon, fish connectivity, and native bird population recovery. Soil cores have revealed that over three feet of leaf litter and organic matter has built up over formerly predominantly clay soils. Immediately after removal, native bird species (Gallinula chloropus, ‘alae ‘ula; and Himantopus mexicanus, ae‘o) have been observed utilizing the restored wetland. We continue to monitor changes in fish species utilizing the newly opened estuarine area and cleared freshwater stream. Lastly, the installation of six long-term relative surface elevation tables (R-SETs) has shown where the surface of the restored area is lowering or accumulating. The project has pioneered new methods for wetland restoration, including the use of equipment in sensitive areas to minimize sediment loss. This talk will describe both the successes and challenges of the restoration process and the results of the monitoring that document the effects of the restoration process.
Presented by: Kim A. Falinski (Nature Conservancy)