Instructor Oregon State University Eugene, Oregon, United States
Abstract: 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 I present results focused on changes in greenline species composition and channel planform. The watershed was classified into four different management “treatments”: 1) “adaptive management” (management primarily for economic objectives), 2) partial passive restoration (modifications in grazing timing, intensity or duration), 3) full passive restoration (removal of grazing from river banks) and 4) passive + active restoration (riparian/floodplain plantings, engineered log jams). An overarching aim of this study was to evaluate the relative contribution of passive restoration in the context of a basin with both active and passive restoration initiatives.
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. Community wetland and bank stability indices increased while plant species diversity decreased. Aerial imagery analysis showed narrower greenline-to-greenline channel widths and increases in channel complexity metrics. Complexity was driven primarily by the evolution of C. nudata islands leading to multi-threaded channel forms. Similar directional changes in species composition and greenline-width narrowing occurred throughout the watershed across management types but the magnitude of change was greater for areas with full passive restoration (with no difference between passive only and passive + active) followed by partial passive restoration. The findings suggest that while active restoration projects may instigate specific, localized changes, passive restoration can induce system-wide shifts in plant species composition and linked changes in channel morphology and planform. Potential changes induced by passive restoration should be explicitly recognized when developing restoration strategies that might otherwise be focused on active projects.
