Livestock exclusion influences on riparian vegetation, channel morphology, and benthic macroinvertebrate assemblages

Abstract

Measurements in paired stream reaches with and without livestock access in southwestern Virginia suggest that livestock exclusion practices installed on short, isolated stream reaches result in improved geomorphic and riparian vegetation conditions, but do not significantly improve benthic macroinvertebrate assemblages. Numerous state and federal programs encourage agricultural producers to protect environmentally sensitive lands (such as streams and wetlands) through the elimination of livestock access to these sensitive areas. In addition to achieving soil conservation goals, it is widely believed that livestock exclusion from streams will result in improvements in riparian vegetation, channel morphology, as well as instream habitat and aquatic insect assemblages. This research assessed the changes in channel morphology, riparian vegetation, and benthic macroinvertebrate assemblages as affected by livestock exclusion over time. Study sites consisted of paired, nearly contiguous stream reaches (five pairs), with and without active livestock access, across a range of time since livestock exclusion was implemented. Four of the livestock exclusion reaches ranged in time since best management practice implementation from 1 to 14 years, while one site consisted of a grazed reach paired with a reach that has been forested and without cattle access for at least 50 years. Livestock exclusion reaches were significantly deeper, had larger median riffle substrate, and scored higher on the Reach Condition Index (a qualitative geomorphic assessment methodology). The livestock exclusion reaches also had significantly higher riparian groundcover vegetation biomass; however, the benthic macroinvertebrate assemblages were not significantly different. The only parameter that showed correlation with time since livestock exclusion was the Reach Condition Index, which increased (indicating improved bank stability) with time since livestock exclusion. Our observations suggest that, while livestock exclusion from streams has positive impacts on streams, best management practice implementation along short stream stretches does not have the desired instream benefits. In particular, benthic macroinvertebrate response depends more on upstream watershed-scale conditions and impacts than localized, reach-scale livestock-access issues. Therefore, a more targeted approach addressing entire stream lengths and the associated watersheds may be required to restore the integrity of aquatic ecosystems.