By: Audrey Rader, Watershed & Habitat Restoration Program Manager
Due to drought conditions, habitat fragmentation, historic unsustainable grazing and timber harvests, and flooding events, watersheds within the Madrean Archipelago have been severely degraded. Smith Canyon is one such degraded site, located in the Sonoita Creek Watershed and part of the Nogales Ranger District of the Coronado National Forest.
In collaboration with entities such as the Arizona Department of Environmental Quality, Arizona Game and Fish Department, United States Fish and Wildlife Service, United States Forest Service, United States Geological Survey, and the University of Arizona Cooperative Extension, Borderlands Restoration Network staff has implemented various watershed restoration techniques across Smith Canyon in an effort to address the aforementioned habitat degradation concerns. Restoration treatments within Smith Canyon were designed to reduce erosion impacts and nonpoint source pollution downstream, with the overarching goal of improving the overall ecological function of the watershed.
Smith Canyon consists of mixed mesquite shrubland and oak grassland across roughly 90 structurally similar sub-basins. The unique, repeated pattern of these ~90 sub-basins presents an exciting opportunity for rigorous, large-scale experimentation when considering each sub-basin as a replicate unit.
In 2018, Roy Petrakis (USGS) developed a model to cluster sub-sets of these sub-basins based on their structural and biophysical traits. BRN staff then assessed each of these clustered sub-basins by level of restoration need (high/medium/low), allowing BRN staff to standardize best management practices across the adjacent Stevens and Little Casa Blanca Canyons for future projects.
Between June 2019 and November 2019, BRN staff installed erosion control structures per the restoration prescription in all of the clustered sub-basins. As an effective and low-cost technique employed around the world for thousands of years, erosion control structures are potent restoration tools in arid regions suffering from ecosystem degradation and the destructive effects of drought, fire and flooding. These structures consist of several parallel rows of self-reinforcing rocks or wood incorporated into the bed of the eroding channel. Often only one-rock high in profile but several rows wide, these structures rest at right angles to the direction of flow but remain passive to overtop flows. This arrangement allows these structures to trap organic-rich sediment upstream, while slowing flows and increasing water infiltration into the channel bottom and banks.
Erosion control structures temporarily detaining water in Smith Canyon after a rain event.
These structures extend the hydro-period for plant establishment without retaining water long term. When placed in a coordinated series according to landforms and observed water flows, each individual erosion control structure is part of a system that decreases erosive forces, increases surface water availability, and aids ecological recovery. Each of the 90 sub-basins received at least five erosion control structures constructed of rock and five erosion control structures constructed of dead and down woody material, depending on local resource ability. After installing the erosion control structures, BRN staff monitored each erosion control structure within the sub-basins for theoretical sediment yield by measuring their basin length, width, and height.
Finally, in collaboration with the Gornish Lab of the University of Arizona Cooperative Extension, BRN tested the effectiveness of various planting methods on reducing erosion in Smith Canyon. Planting methods included seedling out-planting (plugs), pelletized seed addition, and bare seed addition. The target species used for this study included Giant Sacaton (Sporobolus wrightii), Blue Grama (Bouteloua gracilis), Parry’s Penstemon (Penstemon parryi), and Soaptree Yucca (Yucca elata), chosen in order to tease out details on the influence life-form may have on treatment success and habitat value.
Planting treatments included forb seeds, forb pelletized seed, forb plugs, forb and grass seeds, forb and grass pelletized seed, and forb and grass plugs. These treatments were randomly assigned across six plots, with each treatment type replicated ten times. Five of the planting treatment replicates were installed in control sub-basins with no erosion control structures and five of the planting treatment replicates were installed in sub-basins with erosion control structures. Plots were 2m x 2m in size to cover the width of the sub-basin flow-lines. BRN and University of Arizona staff will monitor survival and recruitment of each planting method in addition to the relative cost of each. We hope this data will help improve the efficacy and cost effectiveness of planting efforts for practitioners across the borderlands region.
In the face of ever-increasing anthropogenic and natural stressors, it is critical to restore our degraded watersheds. Restoring watershed conditions to a trajectory of recovery improves water quality and quantity with additional benefits to surrounding habitats and downstream populations. We hope these projects will validate the effectiveness of various watershed restoration techniques and inform future management of the Madrean Sky Islands.
Special thanks to the Frances V. Seebe Charitable Trust for support of this project.
Contact Audrey Rader with any questions.
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