Long-term changes in species & geomorphology following passive restoration in Middle Fork John Day

Year: 2023
Presenter/s: Matthew Goslin
Symposium Session: 2023 - 09 - An Open Toolbox: Tools and Assessments to Tackle Complex Questions
Topics covered: adaptive management and monitoring, lessons learned, passive restoration, and riparian


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 (Oregon State U. & U. Oregon) gathered data on geomorphology, vegetation, and aquatic fauna throughout the MFJDR prior to these management changes. In 2018-2019, a renewed collaborative effort (UO, OSU, Confederated Tribes of the Warm Springs) resurveyed these data across the watershed in order to assess long term changes relative to differing restoration strategies. Management classes included a) adaptive grazing (private ranches), b) partial passive restoration (U.S. Forest Service, reduced grazing), c) full passive restoration (conservation areas with grazing removed) and d) passive + active restoration. Survey 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 showed a dramatic shift in species composition towards perennial, deep-rooted, hydric sedge communities and away from mesic, grass-dominated communities. In particular, the native riparian sedge, Carex nudata, became the most common species. C. nudata’s dense root system allows it to colonize the edge of formerly bare channel bed and bars, facilitating the expansion of other previously absent riparian species behind it. Aerial imagery analysis showed narrower greenline-to-greenline channel widths and increases in channel complexity metrics, changes consistent with restoration goals. The direction of these changes was similar across management classes but were smallest for the adaptive grazing class and greatest for the full passive restoration and passive + active restoration classes with no difference among these two classes.
This study suggests two key messages. 1) While most monitoring efforts have focused on the effectiveness of active restoration projects, the role of passive restoration should be explicitly identified and monitored. In the case presented here, passive restoration was the critical driver of system-wide changes in vegetation as well as geomorphic responses linked to those changes. How particular suites of vegetation could respond to passive restoration should be incorporated within an overall restoration strategy. 2) Whole watershed strategies should not discount the potential contributions of private landowners, and it is critical to include them in the conversations around restoration. While private ranchers in the MFJDR did not have the same stated restoration goals as the conservation areas or public lands, similar changes (of smaller magnitude) were apparent, suggesting that practices may have been evolving in the context of watershed-wide conversations, collaboration, incentives and examples of restoration.