Article Alert: Riparian vegetation communities change rapidly following passive restoration at a northern Utah stream
While working for the USDA Forest Service PACFISH/INFISH Biological Opinion, I was fortunate to assess the outcomes of an ongoing restoration project at Spawn Creek in northern Utah. Spawn Creek, a refugia for one of the state's most genetically pure meta-populations of Bonneville Cutthroat Trout (Oncorhynchus clarki Utah), was excluded from grazing in 2006, following intensive use for much of the 20th century. At various points, the Forest Service attempted to restore portions of Spawn Creek and Temple Fork using instream structures without removing the grazing disturbance. The restoration objective was usually to create better fish habitat, but a key component of the ecosystem was missing: riparian vegetation.
Over the course of the 1980s and 1990s, the Forest Service reduced the number of animals on the allotments within Logan Canyon, but grazing impacts remained concentrated in the stream. The primary impact was a denuded riparian zone that could not support riparian vegetation that shades the stream and contributes wood to the active channel. The absence of the shade that vegetation creates allows peak stream temperatures to increase, which perpetuate the whirling disease host parasite.
|A log structure used in fishery restoration at Temple Fork, UT in the 1970s. Note denuded banks.|
Based on degraded riparian vegetation and bank conditions, concerns about whirling disease decreasing cutthroat trout population size and health, and an obvious disturbance vector, a plan was hatched. In the early 2000s, a partnership between a number of organizations was born to address the grazing disturbance that led to Spawn Creek's impaired conditions:
- Cache Anglers- Trout Unlimited, local chapter
- US Forest Service (Logan office and Fish and Aquatic Ecology Unit)
- USGS Utah Cooperative Fish and Wildlife Unit
- Utah Division of Wildlife Resources (UDWR)
- Utah Division of Water Quality
- Intermountain Center for River Rehabilitation and Restoration
The partnership's plan was to get cows out of Spawn Creek and allow the riparian zone and stream banks to recover. The regenerating vegetation would shade the stream, cooling it, and making it less hospitable for the Tubifex tubifex whirling disease host parasite. Cooler temperatures would mitigate whirling disease establishment in trout, which might increase cutthroat trout spawning and survival success. Initially, fish, whirling disease host parasite, temperature, stream habitat, and vegetation were all measured. As funding for the project shifted following early assessments in 2004-06, vegetation and stream habitat were continuously monitored in the absence of fish, invertebrate and parasite data. We assessed vegetation changes at eight reaches over time to identify whether the riparian ecosystem was improving following grazing exclusion. Six reaches were impact reaches, excluded from grazing and two were controls where grazing continued outside the exclosure.
|Study reaches within the Spawn Creek exclosure (I reaches) and control reaches outside the exclosure (C reaches)|
The data showed that composition changed rapidly at six reaches, with indicator species shifting from disturbance-tolerant pasture grasses to hydrophytic graminoids and forbs. Willows, the woody species most likely to recolonize the banks, did not increase in abundance between 2004 or 2005 and 2009. This change in vegetation shows that hydrologic connectivity between the stream channel and banks improved following the exclusion of cattle, but the woody vegetation required to shade the stream did not regenerate in the same time period. This lack of willows and other woody vegetation may be due to recruitment limitations from native elk browse or a lack of propagules following prolonged grazing. This finding suggests that active restoration approaches like planting or seeding may expedite the meeting of instream objectives tied to riparian vegetation.
While Spawn Creek's restoration showed mixed results for vegetation between 2004 and 2009, the development of the stream corridor between 2010-2013 has taken new turns. Following the removal of grazing, beaver have increased their densities and built more and larger dams complexes than during the era of intense cattle grazing. These beaver dams have trapped sediment and caused channel widening, changing the habitat that trout can utilize within the stream. Trends in fish populations are presently monitored by the Utah State University Fish Ecology Lab using mobile and stationary PIT-tag scanning arrays. Vegetation and habitat monitoring is done sporadically by the USDA Forest Service PIBO EM.
The restoration of Spawn Creek was a cooperative effort, that brought together local grazing allotment holders, anglers, state and federal agencies. The foresight and flexibility of the Utah Division of Wildlife, Division of Water Quality and the USDA Forest Service were critical to the restoration of Spawn Creek. For more information, see the full USU ET-AL press release here.
Citation: Hough-Snee, N., B.B. Roper, J.M. Wheaton, P. Budy and R.L. Lokteff. 2013. Riparian vegetation communities change rapidly following passive restoration at a northern Utah stream. Ecological Engineering 58: 371-377. DOI: 10.1016/j.ecoleng.2013.07.042