Changes in species composition and channel geomorphology following passive restoration in the Middle Fork John Day River, Oregon

Authors: Matthew Goslin*, University of Oregon
Topics: Geomorphology, Biogeography, Applied Geography
Keywords: Oregon, river restoration, species shifts, biogeomorphology
Session Type: Virtual Paper
Day: 4/8/2021
Start / End Time: 4:40 PM / 5:55 PM
Room: Virtual 3
Presentation File: No File Uploaded

The Middle Fork of the John Day River (MFJDR), Oregon, has been the focus of both active and passive restoration efforts since the late 1990s following the establishment of private conservation areas and reforms in U.S. Forest Service cattle grazing management. In the mid-1990s, a multidisciplinary, multi-institutional effort gathered data on geomorphology, vegetation, and aquatic fauna throughout the MFJDR prior to these management changes. In 2018-2019, a renewed collaborative effort resurveyed these data in order to assess long term changes relative to differing restoration strategies. These remeasurements were paired with analysis of historic air photo sequences. Here we present results focused on changes in greenline vegetation and channel planform. Greenline surveys show a shift in species composition in towards perennial, deep-rooted sedge communities. In particular, the native riparian sedge, Carex nudata, became a dominant species whereas it had previously been suppressed by cattle grazing. Aerial imagery analysis showed narrower greenline-to-greenline channel widths and increases in channel complexity metrics. These results will be discussed in the context of complimentary research focused on C. nudata specifically in which we have employed multiple methods to investigate changes in channel morphology in association with C. nudata. C. nudata appears to stabilize patches where it becomes established, but cut banks continue to retreat and channel boundaries continue to move often leading to compound or multi-threaded channels around C. nudata islands. We propose a conceptual model in which alternative pathways of river lead to complex patterns of river morphology and planform consistent with key restoration goals.

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