Recovery of the herbaceous component of degraded sagebrush steppe is unimpeded by 75 years of moderate cattle grazing

Authors: Copeland, Stella; Davies, Kirk; Boyd, Chad; Bates, Jonathan - Jon

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2020
Publication Date: 3/26/2021
Citation: Copeland, S.M., Davies, K.W., Boyd, C.S., Bates, J.D. 2021. Recovery of the herbaceous component of degraded sagebrush steppe is unimpeded by 75 years of moderate cattle grazing. Ecosphere. 12(3). Article e03445. https://doi.org/10.1002/ecs2.3445.
DOI: https://doi.org/10.1002/ecs2.3445

Interpretive Summary: Documenting how livestock grazing affects vegetation over the long-term is an important aspect of managing for habitat and productivity. We analyzed records from a 75 year old livestock grazing exclusion experiment to look at the effects of cattle grazing on vegetation, as well as responses to a shift from higher intensity sheep grazing to cattle grazing at the beginning of the experiment. We found that both grazed and ungrazed sites largely recovered over several decades after sheep grazing, but that there was little difference in composition or density of plants within and outside of the cattle grazing exclosures with current, moderate levels of grazing. We conclude that the weak effects of moderate cattle grazing differ strongly from the intense effects of historic high levels of sheep grazing, and moderate cattle grazing did not impede recovery from the previously heavily grazed state.

Technical Abstract: Understanding the effects of contemporary cattle grazing on herbaceous perennial communities in big sagebrush steppe is important for managing for wildlife habitat, plant diversity, and productivity, yet potentially complicated by legacy impacts of historic, often higher intensity, livestock grazing. Here, we evaluate whether recovery of herbaceous communities in eastern Oregon, USA, after the cessation of intense spring sheep grazing (1935) was affected by moderate cattle grazing in paired plots with or without grazing over the past 75 yr (1936–2011). We tested for the effects of cattle grazing on herbaceous community recovery, as indicated by changes over time in plant density, and composition, as measured by Bray–Curtis dissimilarity. We also included current and prior to sampling year precipitation anomalies, to account for the weather effects, and a random term for pasture location of plot pairs to include potential subtle differences in abiotic environment and grazing management. We further tested whether time since cessation of intense sheep grazing and moderate cattle grazing were associated with convergence or divergence in community composition indicated by changes in evenness, richness, species relative abundance (rank order), and turnover or species appearance or disappearance. Total perennial herbaceous, forb, and grass density increased over time in sites grazed and ungrazed by cattle, though species varied in the direction of their response to contemporary cattle grazing. Community composition metrics indicated convergence over time including increasing evenness, decreasing Bray–Curtis dissimilarity, decreasing shifts in species relative abundance (rank order), and lower rates of species turnover (and gain and loss). Contemporary cattle grazing was not associated with convergence or divergence in composition. Precipitation anomalies for the current or prior water year were only occasionally significant in herbaceous density and community composition change models. Our results indicate similar long-term recovery trajectories occurred in sites with moderate cattle grazing or removal of all livestock following cessation of intense sheep grazing. Management planning and resource assessment focused on herbaceous perennial communities in sagebrush steppe should seek to separate the impacts of historic from contemporary livestock grazing practices.