U.S. Fish and Wildlife Service

Alaska Peninsula/Becharof National Wildlife Refuge Landscape Change Study

Within the Alaska Peninsula-Becharof National Wildlife Refuge (APBNWR) region there exists a strong confluence of environmental change processes, natural hazards, important wildlife habitats, and a subsistence-based human population. Time-series analysis of data from earth-observing satellites provides a powerful tool to assess vegetation and landscape changes at regional and landscape scales. Trends and changes in the satellite-observed Normalized Difference Vegetation Index (NDVI)—a spectral metric of vegetation productivity or “greenness”—provide spatially explicit information on gradual and abrupt changes on the landscape, such as shrub expansion, wetland drying, landslides, and shoreline erosion. We conducted NDVI analyses to provide refuge-wide spatial data products that depict recent changes in vegetation greenness for APBNWR, and provide historical context for assessing and monitoring future ecological change.

Subsequently, The U.S. Fish and Wildlife Service (USFWS) identified knowledge gaps in wetland status and habitat conditions over the past 50+ years in the Ugashik Unit of the Alaska Peninsula/Becharof National Wildlife Refuges (APBNWR). A variety of studies have shown that climate warming is driving changes in surface wetness, open water extent, and shrub abundance in palustrine wetlands of southern Alaska, but information needed to manage and conserve wildlife habitat, subsistence, and recreational resources are lacking for APBNWR. To address these gaps, ABR undertook field and remote sensing studies to provide information on possible drying trends and other environmental changes in palustrine wetlands. The target wetlands and waters within the Ugashik unit of the APBNWR occur in a broad lowland area north of the Aleutian Range, and consist of numerous small ponds with adjacent saturated or flooded tundra wetlands. The area is undeveloped and wetland habitats are intact, thus providing an excellent basis from which to examine the potential effects of climate change on wetlands. ABR undertook the project in two phases. First, ABR quantified change in palustrine wetlands and waters below 100 m in elevation in the Ugashik Bay hydrologic unit using georectified, high-resolution imagery for three time-steps (circa 1950, 1980, and 2015). Attributes were assigned to wetland change-detection points within a stratified-random grid system that characterized wetland hydrology and vegetation indicators useful for ranking the stability of wetlands and waters through time. Second, ABR field-verified a subset of the wetland change-detection points. The points were selected within low elevation (<100 m) palustrine wetlands (excluding riverine, lacustrine [large lakes], marine, or inter-tidal wetlands) and spanned the range of conditions present along hydrologic and successional gradients. The field effort was used to confirm the relationship between current wetland condition and the selected wetland-stability indicators assessed in Phase 1. This information is useful to help predict future outcomes and provide a detailed framework to develop wetland monitoring programs for APBNWR.