Abstract
The focal site of this restoration plan, Field 19W (3.24 ha), is a former agricultural field located within Alaksen National Wildlife Area (ANWA) in Delta, British Columbia. ANWA is a 349-ha protected area established in 1976 on historic deltaic islands in the Fraser River Estuary. ANWA is a Ramsar Wetland of International Importance and a key component of the Pacific Flyway that supports migratory, breeding, and overwintering bird populations. The land that comprises ANWA was extensively modified for agriculture following dike construction in the early 20th century. About 50 water control structures now regulate hydrology across the area to support agriculture. Field 19W, located along the western edge of ANWA near the shoreline, has proven difficult and costly to drain due to high groundwater levels and repeated flooding. Crop production attempts failed, and the field has since been abandoned from active cultivation. Environment and Climate Change Canada (ECCC) is seeking to transition Field 19W from a marginal agricultural site to functional overwintering bird habitat. This report integrates an avian habitat study with a restoration plan to guide this transition. The overarching goal is to restore Field 19W to a structurally diverse, groundwater-fed brackish wet meadow that enhances overwintering bird abundance and diversity while increasing resilience to climate change. Field 19W is influenced by multiple stressors. Historic diking and drainage infrastructure have disconnected the site from tidal processes and altered natural surface flows. Increasing precipitation variability and more intense storm events that result from climate change are projected to exacerbate flooding. Climate change also affects migration timing, food availability, and survival of overwintering birds. Additionally, invasive spread can commonly result from past agricultural activities. Two dominant invasive species - Himalayan blackberry and reed canary grass (RCG) - form monocultures across portions of the site. Vegetation surveys showed some strata with near 100% invasive cover. These monocultures reduce structural diversity, limit native plant regeneration, and simplify habitat complexity. Although birds were observed using invasive vegetation for cover and perching, invasive dominance threatens long-term ecosystem function and biodiversity. We conducted a field-based avian habitat study to inform restoration design. Vegetation was stratified into five community types and point count surveys were completed biweekly from late October through March. Song sparrows (Melospiza melodia), marsh wrens (Cistothorus palustris), and northern harriers (Circus hudsonius) were the most frequently observed species. We identified reference conditions to determine target bird communities for the restoration plan by conducting presence/not detected surveys in the Coast Guard Field adjacent to Field 19W. Point count data collected from Reifel Migratory Bird Sanctuary (RMBS), Westham Island, BC, supported these reference conditions in addition to a compilation of avian population ecology data in the Fraser River Estuary published by Campbell and Butler (1987). The findings informed our restoration treatment design in tandem with the restoration of hydrological processes in a wet meadow. This approach aimed to enhance structural and vegetation species diversity to increase avian species richness, particularly among songbirds, waterfowl, and wading birds. We recommend removing invasive plants and enhancing the cleared areas by implementing the following restoration treatments: creating wetlands, transplanting common rush, removing invasives, and planting clusters of native trees and shrubs. The planting plan includes wetland species, thicket-forming shrubs, and riparian trees in clusters to create a brackish marsh mosaic. We recommend transplanting common rush to retain low structure bird habitat, and broadcasting seeding of early seral native species to reduce reinvasion of invasive species. This approach maintains open areas for raptor foraging while increasing vertical and horizontal structural complexity that will enhance bird diversity and abundance. We recommend creating small wetlands to sequester carbon, mitigate flood risk during extreme rainfall events, and provide foraging and cover services for bird species such as American bitterns (Botaurus lentiginosus), Wilson's snipes (Gallinago delicata), marsh wrens, and Virginia rails (Railus limicola). These treatments will improve the structural and species diversity throughout the site, improving resilience to climate stressors and providing attractive habitat for overwintering birds. We suggest that post-restoration monitoring be carried out for five years to ensure the success of our priority objectives. We propose monitoring the success of native plantings, re-invasion of invasive species, species richness and abundance of the bird community, and water depths of the created wetlands. Our proposed public outreach includes communicating this restoration plan to the public and creating opportunities for them to be involved in the restoration and monitoring process. We recommend involving the Westham Island community by hosting an information sharing event and inviting them to participate in restoration. We recommend collaborating with the Ecological Restoration BSc and Fish, Wildlife and Recreation programs for wetland construction, invasive species removal, native planting, and post restoration monitoring to reduce costs and create learning opportunities for students. We estimate the total budget for the Field 19W restoration plan including a 10% contingency to be $51,459. This budget includes site preparation (invasive removal and on-site disposal), the excavation of three wetlands, native plantings, as well as five years of monitoring and the maintenance. Collaborating with BCIT programs could reduce costs by about $3,525.