Fish Habitat: Essential Fish Habitat and Rehabilitation

Remote Sensing of Forest-Clearing Effects on Essential Fish Habitat of Pacific Salmon

Nina M. Kelly, Don Field, Ford A. Cross, and Robert Emmett

doi: https://doi.org/10.47886/9781888569124.ch19

Abstract. —The rivers and streams that drain into the lower Columbia River estuary in Oregon contain essential fish habitat (EFH) for several species of Pacific salmon. Seven subwatershed basins in the Columbia River drainage basin, each containing salmon spawning and nursery habitat, were examined using remote sensing and geographic information system techniques to measure the amount and pattern of upland forest clearing. Landsat Thematic Mapper imagery from 1989 and 1992 was used to determine the cleared forest patches produced by clear-cutting. Digital Elevation Models were used to determine slope underlying cleared patches. A digital coverage (or map layer) of streams containing EFH was used to measure proximity of cleared patches to streams. The size and slope of cleared forest patches and the proximity of cleared forest patches to streams can greatly exacerbate the deposition of sediment in streams, altering stream environments and the quality of EFH. Size, slope, and proximity of cleared forest patches to streams containing EFH were calculated for the seven subwatershed basins. This analysis was performed at a landscape scale and utilized readily available broadscale data to (1) compare forest-clearing patterns across basins and (2) locate critical areas for further analysis using finer-scale data. Once critical areas had been located, a second analysis was performed using finer-scale data. The landscape-scale results indicated major differences in the spatial pattern of forest-clearing change across the lower Columbia River estuary drainage basin, with some subwatershed basins significantly altered in the three-year period. Three subwatershed basins showed a pattern of large cleared patches close to streams containing EFH. Some of these cleared forest patches were situated at least partially on steep slopes. In the three basins, Milton Creek, Young’s River, and the Claskanie River run directly through large areas of cleared forest. The pattern evidenced in these critical areas is consistent with increased sedimentation and decreased stream shading characteristics, both of which can have a detrimental effect on fish habitat. Milton Creek was examined with finer-scale data, and these results showed an increased number of cleared forest patches and increased total area of cleared forest draining into streams. More cleared forest patches on steep slopes were also shown with the finer-scale data. These results provide an initial justification for performing searches for critical areas at a synoptic or landscape scale, with further research performed at a finer scale. These techniques provide a practical method to evaluate upland land-use activities and essential fish habitat.