A characterization of unmanaged riparian areas in the central Coast Range of western Oregon

Abstract

As an approach to providing baseline information about riparian ecosystems, this study characterized the dominant riparian vegetation along unmanaged streams in central Oregon Coast Range forests. We systematically sampled along various reaches of nine first- to fourth-order streams, all of which were subject to stand-replacing fires ca. 145 year ago. The near-stream communities were divided into different vegetative and/or topographic units called landscape units (LUs); LU1s were closest to the stream, and LU2s were farther from the stream. Fifty-two percent of LU1s had no trees, and among all LUs, red alder was the most frequently found tree species. Although in some cases sample plots simply fell between widely spaced trees, we hypothesize that red alder originally dominated many of the current treeless patches and has since senesced to release understory shrubs. With increased distance from the stream, hardwoods decreased in compositional importance relative to conifers, not because hardwood frequency changed, but because conifer frequency increased. Our results suggest that the competitive advantage of hardwoods and shrubs is the biggest limiting factor of conifer growth in the near-stream micro-environment and that without vigorous competition, conifers have the potential to grow over more of the riparian area than that on which they occurred in unmanaged areas. Calculations of disturbance frequency, based on ages of shade-intolerant stand dominants, indicate that along the stream reaches we sampled, a minimum of 2.6 disturbances per stream km per century occurred since the last stand-resetting fire. Riparian areas are spatially and temporally diverse, and any riparian management model should incorporate this variability.