Habitat change in the lower Columbia River estuary, 1870–2009

Abstract

We conducted a spatial analysis of long term land cover change for the lower Columbia River estuary and its floodplain by comparing GIS representations of late 1800’s maps (Office of Coast topographic sheets and General Land Office survey maps) with recent, high resolution land cover data from 2009. In terms of combined spatial and temporal extents, ours is the most comprehensive of similar studies that have been done for the region in recent decades. Losses of 68–70% were noted for vegetated tidal wetlands, which are critical habitats for juvenile salmonids that utilize the estuary. These values are consistent with those derived from previous studies. A loss of 55% of forested uplands was also noted. The majority of loss of these habitats was due to conversion of land for agriculture and urban development. Also significant was conversion of tidal wetlands to non-tidal wetlands. Tidal flats have changed more with respect to location than overall areal coverage, which could be expected for this high energy environment. Spatial patterns of change in these habitats were variable throughout the study area, which may have practical implications for guiding restoration and conservation practices. Uncertainties with our analysis are present as a result of differences in methodologies used to develop the historical and present day data sets as well as unknowns about, and difficulties interpreting, the historical data sources. Despite these uncertainties, the analysis provides useful insight into the extent of change which has occurred in the lower Columbia River Estuary and in particular the significant declines in vegetated tidal wetlands that have occurred.