Contrasting grazing practices alter plant community trajectories across western Canada’s grasslands with implications for ecosystem function

Abstract

Livestock grazing influences grassland biodiversity and ecosystem function. We report on the effects of adaptive multi-paddock (AMP) grazing (characterized by extended recovery periods between pulsed high animal density grazing events) on plant community composition and diversity across western Canada, compared to neighboring properties managed with conventional grazing (n-AMP). We also evaluated the influence of grazing practices, specifically stocking rate, cattle density, and variations in rest-to-grazing ratio at the start of the grazing season on plant community composition and diversity. We further explored the relationship between soil organic carbon (SOC) and plant diversity. Overall, AMP grazing, and specifically the use of high rest-to-grazing ratios early in the growing season, increased the proportion of non-native species. Native grasslands without prior cultivation had greater plant species richness, with fewer non-native species and containing phylogenetically more divergent plant communities, independent of grazing practices. The n-AMP pastures had higher functional trait dispersion, a pattern especially pronounced for tame (previously cultivated and seeded) pastures, and those with lower cattle stock densities (animals per unit area). Greater SOC was associated with communities higher in non-native plants, of lower species richness, and greater phylogenetic divergence, while no trend was identified for functional dispersion. Overall, AMP grazing did not increase plant species richness, functional diversity, or phylogenetic diversity. Instead, pulsed rotational grazing, specifically using high stock densities and extended rest periods, facilitated non-native species prevalence and reduced functional diversity. However, non-native species and lower overall species richness may benefit SOC accumulation, illustrating the challenges associated with building biodiverse plant communities with a high capacity for climate change mitigation.