Timing of cattle grazing alters impacts on stream banks in an Oregon mountain watershed

Abstract

How does season of use by cattle grazing riparian areas influence stream banks?Riparian areas are critical components of western rangelands. Although comprising less than 8% of the land area of the western United States (USDI 1995;Ehrhart and Hansen 1997), riparian ecosystems function to store water, recharge aquifers, moderate flood intensity, maintain water quality by filtering chemical and organic wastes, trap sediments, and provide primary biotic proAbstract: Timing of grazing by cattle may be a critical consideration to minimize impacts on stream banks. Damage to stream banks may be less when cattle preferentially graze uplands. We tested the hypothesis that early summer grazing (28 days; mid-June to mid-July) would have less impact on stream bank cover and stability compared to late summer grazing (28 days; mid-August to mid-September). The two-year study was conducted at the Eastern Oregon Agriculture Research Center in northeastern Oregon. Three replications each of three grazing treatments were examined: (1) nongrazed, (2) early summer grazing, and (3) late summer grazing. Each grazed pasture (approximately 11.5 ha [28.4 ac]) was stocked with cow-calf pairs for a mean stocking rate of 0.7 ha per animal unit month (AUM -1 ) (1.7 ac AUM -1 ) (range 0.5 to 9.0 ha AUM -1 [1.2 to 22.2 ac AUM -1 ]) to achieve moderate grazing intensity of 35% to 50% utilization. Estimates of stream bank cover ("covered" or "uncovered") and stability ("stable" or "unstable") were taken before and after each grazing period by examining plots approximately 0.5 × 0.3 m (19.7 × 11.8 in) placed on the greenline (the first vegetation at water's edge). Additionally, frequency of cattle hoof prints (plots with hoof prints ÷ total number of plots within the treatment pasture) was measured as an indicator of cattle presence. Treatments were compared using multifactor analysis of variance (ANOVA). Stream bank effects were consistent with observations of cattle distribution, with 53% (standard error [SE] ± 11%) of the greenline in early summer pastures showing cattle presence (hoof prints), versus 90% (SE ± 1%) for late summer pastures. In early summer, cattle spent more time in the uplands, resulting in the development of just 3% (SE ± 2%) uncovered stream banks, compared to 8% (SE ± 2%) late season. Similarly, early summer grazing resulted in 13% (SE ± 2%) unstable stream banks compared to 31% (SE ± 2%) in late summer. The primary cause of instability was sloughing of the bank into the stream channel. An "erosion index" indicated potential erosion was 1.62 times greater during late summer compared to early summer grazing. Our study suggests that grazing riparian areas when adjacent uplands are attractive to cattle may help reduce deleterious impacts on stream banks. Land managers should consider impacts of timing of grazing on individual streams when developing best management practices to meet grazing objectives in riparian areas.

Riparian vegetation communities change rapidly following passive restoration at a northern Utah stream

“…Beever et al, 2003) or acute (e.g. Walker, 1993) ecosystem impairment, depending on the intensity, timing and duration of grazing (McInnis and McIver, 2009;Sternberg et al, 2001). In small streams and rivers, grazing can destroy natural bank structure and deplete riparian vegetation (Beschta et al, 2012;Chambers et al, 2004), increasing instream turbidity, reducing stream shade and increasing stream temperatures, altering patterns of substrate deposition and erosion and exerting a strong influence on stream channel forms (Myers and Swanson, 1996a).…”

Prediction of Annual Streambank Erosion for Sequoia National Forest, California

“…Significantly greater streambank erosion and disturbance may occur in grazed areas than in livestock‐excluded areas (Kauffman et al ., ; Trimble, ). Timing of grazing practices (McInnis and McIver, ) and other actions that affect riparian functioning condition (Prichard et al . ) can also affect rates of streambank erosion.…”

Cattle grazing and fish recovery on US federal lands: can social–ecological systems science help?

“…Cattle that graze on Blue Mountains national forest lands typically use accessible riparian areas for water, thermoregulation, and nutritious forage, the last of which becomes especially important as summer progresses and upland forage senesces (Parsons et al . ; McInnis and McIver ). However, unmanaged grazing can have deleterious effects on riparian and aquatic ecosystems.…”