Grazing management systems involving relatively rapid rotations of dense herds are increasing in popularity across North-America. Though these “adaptive multi-paddock” (AMP) systems allow for relatively fine-scale adjustment of livestock pressure in response to environmental and economic pressures, large-scale controlled studies testing their effects are generally lacking. As part of a study examining the consequences of grazing management on a suite of soil and biodiversity measures, we describe the influence of grazing management on vascular plant species diversity at local and large scales between ranches and ecoregions. The spatial equalization of grazing pressure within AMP pastures is expected to reduce diversity of plant competitive strategies and thus plant diversity. However, potential differences in species assemblage between pastures and ecoregions make these impacts scale-dependent.
To test how grazing management strategies influence diversity across ecoregions, we compared the effect of grazing management systems on vascular plant species diversity on 22 pairs of ranches across environmental gradients in Western Canada. We examined plant diversity between adjacent ranches showing similar ecosites to compare between the two grazing strategies. Alpha and gamma species richness were defined as richness within plot and ranch, respectively. Beta diversity was calculated within individual ranches and between ranches in equivalent ecoregions.
Results/Conclusions
We failed to detect a significant response in any metric of biodiversity at any scale to alternative grazing practices. Nevertheless, there was a consistent trend towards reduced species richness and diversity under high grazing intensity grazing. No differences in community composition between systems were found using PERMANOVA and NMDS ordination. However, growing season precipitation and annual heat: moisture index of sites significantly drove beta diversity. No significant interactions between alpha, gamma or beta diversity with growing season precipitation or summer heat: moisture index was detected using general linear mixed models. Results suggest the ecological influence of grazing intensity systems on plant diversity and species assemblage are not meaningful. Such information contributes to our understanding of how land management extremes alter processes maintaining biodiversity.