Fencing isn’t enough to protect streams from livestock

Posted on March 28, 2013

The damaging effects of livestock trampling and grazing on streamside habitats have been well documented, but there’s been much less research on the impacts of livestock disturbance on aquatic ecosystems.  The Golden Trout Wilderness area of California has had protected wilderness status since 1978, but was subjected to extensive sheep grazing in the nineteenth century 1800s and has been grazed by cattle since the early 1900s.  At the turn of the present century, grazing was halted in parts of the area in order to collect information on ecological recovery for land management purposes.  At a range of sites data were collected on the condition of the physical habitat and the composition of aquatic macroinvertebrate communities.   In each case a 250 m length of stream was surveyed.  Analyses were made at two spatial scales.  First, the condition of sites in catchments where grazing had been completely discontinued for four years were compared with sites where grazing had continued.  Second, sites where cattle-exclusion fences had been in place for at least ten years were compared with grazed sites immediately upstream.  In the catchment-level analysis, the recently-protected sites scored significantly higher in terms of aquatic invertebrate richness, mean substrate particle size, bank stability, bank steepness, the channel depth : width ratio and riparian plant cover.  In contrast, the local- scale analysis revealed that exclusion fencing had a positive significant effect only on the cover of riparian and bank vegetation, and was largely ineffective at improving aquatic habitat conditions due to the persistent influences of cattle grazing upstream.  These findings suggest that stream habitats can recover quickly – in a few years – once livestock are removed from the catchment, and that this approach is a lot more effective than the small-scale exclusion of livestock using riparian area fencing, even when such exclusion extends over a long period.

Reference:  Herbst, D.B., Bogan, M.T., Roll, S.K. & Safford, H.D.  2012.  Effects of livestock exclusion on in-stream habitat and benthic invertebrate assemblages in montane streams.  Freshwater Biology 57, 204–217.  http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2427.2011.02706.x/abstract