Landscape Influences on Stream Habitats and Biological Assemblages

Comparing Riparian and Catchment Influences on Stream Habitat in a Forested, Montane Landscape

Kelly M. Burnett, Gordon H. Reeves, Sharon E. Clarke, and Kelly R. Christiansen

doi: https://doi.org/10.47886/9781888569766.ch9

Abstract.—Multiscale analysis of relationships with landscape characteristics can help identify areas and physical processes that affect stream habitats, and thus suggest where and how land management is likely to influence these habitats. Such analysis is rare for mountainous areas where forestry is the primary land use. Consequently, we examined relationships in a forested, montane basin between stream habitat features and landscape characteristics that were summarized at five spatial scales (three riparian and two catchment scales). Spatial scales varied in the area encompassed upstream and upslope of surveyed stream segments and, presumably, in physical processes. For many landscape characteristics, riparian spatial scales, approximated by fixed-width buffers, could be differentiated from catchment spatial scales using forest cover from 30-m satellite imagery and 30-m digital elevation data. In regression with landscape characteristics, more variation in the mean maximum depth and volume of pools was explained by catchment area than by any other landscape characteristic summarized at any spatial scale. In contrast, at each spatial scale except the catchment, variation in the mean density of large wood in pools was positively related to percent area in older forests and negatively related to percent area in sedimentary rock types. The regression model containing these two variables had the greatest explanatory power at an intermediate spatial scale. Finer spatial scales may have omitted important source areas and processes for wood delivery, but coarser spatial scales likely incorporated source areas and processes less tightly coupled to large wood dynamics in surveyed stream segments. Our findings indicate that multiscale assessments can identify areas and suggest processes most closely linked to stream habitat and, thus, can aid in designing land management to protect and restore stream ecosystems in forested landscapes.