Question: Riparian zones provide ecologically rich interfaces between land and flowing water, and are favoured areas for grazing by native ungulates and livestock. Overgrazing can degrade riparian vegetation. Will sensitivity and vulnerability to grazing increase in upper mountain zones because of the harsh physical environment?
Location: We compared the impact of cattle grazing along natural elevational corridors provided by two first-order creeks in the Rocky Mountains of Alberta, Canada.
Methods: Substrate and vegetation characteristics were assessed in quadrats within transects positioned in ungrazed or lightly grazed, versus moderately to heavily grazed sites extending from the alpine down through the subalpine, montane, parkland and prairie zones.
Results: Analyses revealed that 18 of 19 substrate and vegetation characteristics varied along the elevational profile (17 P<0.05; 1 P<0.1). Fifteen differed with grazing (12 P<0.05; 3 P<0.1), which was associated with coarser substrate with lower pH, reduced diversity and density of shrubs and trees, reduced vegetation cover, increased percent cover and species of weeds and changes in proportions of particular plants such as increasing yarrow (Achillea millefolium) and decreasing mountain valerian (Valeriana sitchensis). Significant grazing × elevation interactions for seven characteristics (5 P<0.05; 2 P<0.1) indicated greater impacts at higher elevations.
Conclusions: This study revealed that the upper elevations were heavily affected, despite their shorter, seasonally restricted grazing history. This indicates that riparian zones in upper mountain environments are particularly vulnerable to livestock grazing.