Elevated sensitivity: riparian vegetation in upper mountain zones is especially vulnerable to livestock grazing

Abstract

Abbreviations AUM = animal unit month; DBH = tree diameter at breast height; TSR = transformed species richness Abstract 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 o 0.05; 1 P o 0.1). Fifteen differed with grazing (12 P o 0.05; 3 P o 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 o 0.05; 2 P o 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.

Hydrologic linkages between a climate oscillation, river flows, growth, and wood Δ13C of male and female cottonwood trees

“…Three increment cores were extracted from each tree with a 5.15‐mm‐diameter Haglöf borer, with a core from the N‐, SE‐ and SW‐facing sectors. The different sectors were exposed to different environmental conditions, especially solar radiation and wind, and this provides a progressively increasing sequence of drying index of N, SE and SW (Samuelson & Rood ). The different environmental conditions might be reflected in differences in growth among the radial sectors, because in poplars there is partial vertical vascular alignment (Kozlowski & Winget ).…”

Increasing River Flow Expands Riparian Habitat: Influences of Flow Augmentation on Channel Form, Riparian Vegetation and Birds Along the Little Bow River, Alberta

“…To investigate the responses of channel form, riparian vegetation, and riparian birds to flow augmentation, this study was undertaken along the Little Bow River in Southern Alberta. Longitudinal patterns were investigated to consider possible transitions in channel characteristics, vegetation, and avian communities along this corridor that links sequential elevational ecoregions (Samuelson and Rood, ). Our study extended over a decade, allowing the identification of initial responses to the most recent flow augmentation.…”

Ecohydrology and stewardship of Alberta springs ecosystems

“…In southwestern Alberta, Samuelson and Rood (2011) found that grazing was associated with coarsening substrata, lower soil pH, reduced diversity and density of shrubs and trees, reduced vegetation cover overall, and increased percent cover and dominance of weedy species. In southwestern Alberta, Samuelson and Rood (2011) found that grazing was associated with coarsening substrata, lower soil pH, reduced diversity and density of shrubs and trees, reduced vegetation cover overall, and increased percent cover and dominance of weedy species.…”

“…Grazing differentially affects higher elevation riparian zones and may similarly affect springs. In southwestern Alberta, Samuelson and Rood (2011) found that grazing was associated with coarsening substrata, lower soil pH, reduced diversity and density of shrubs and trees, reduced vegetation cover overall, and increased percent cover and dominance of weedy species.…”