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ARS Home » Pacific West Area » Burns, Oregon » Range and Meadow Forage Management Research » Research » Publications at this Location » Publication #401883

Research Project: Restoration and Conservation of Great Basin Ecosystems

Location: Range and Meadow Forage Management Research

Title: Cross-scale analysis reveals interacting determinants of annual and perennial vegetation patterns across Northern Great Basin rangelands

Author
item CASE, MADELON - Us Geological Survey (USGS)
item Davies, Kirk
item Boyd, Chad
item AOYAMA, LINA - University Of Oregon
item MERSON, JOANNA - University Of Oregon
item PENKAUSKAS, CALVIN - University Of Oregon
item HALLETT, LAUREN - University Of Oregon

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Exotic annual grass invasion is a widespread threat to sagebrush ecosystems in the western United States. There is substantial uncertainty of how regional-scale and local-scale drivers of annual grass abundance interact. We conducted an extensive field survey across burned and unburned public grazing lands in Oregon and Idaho, with plots stratified by aspect and distance to water within pastures to capture variation in environmental context and grazing intensity. Annual grasses were widespread at burned and unburned sites alike, contrary to assumptions of annual grasses depending on fire, and more common at lower elevations and higher temperatures regionally as well as warmer slopes locally. Pasture-level grazing pressure interacted with temperature such that annual grass cover increased with grazing pressure at higher temperatures but decreased with grazing pressure at lower temperatures. However, at the local scale, annual grass cover did not vary with grazing metrics. This information is of interest to other scientists, natural resource managers, and the general public.

Technical Abstract: Western North America. Although many predictors of annual grass prevalence and native perennial vegetation have been identified, there remains substantial uncertainty about how regional-scale and local-scale drivers interact to determine vegetation heterogeneity, and how the environmental context shapes vegetation response to cattle grazing. Here, we conducted an extensive field survey across burned and unburned public grazing lands in Oregon and Idaho, with plots stratified by aspect and distance to water within pastures to capture variation in environmental context and grazing intensity. We analyzed regional and local-scale determinants of annual grass, perennial grass, and shrub cover, and examined to what extent local-scale variation was contingent on regional predictions of site potential. Annual grasses were widespread at burned and unburned sites alike, contrary to assumptions of annual grasses depending on fire, and more common at lower elevations and higher temperatures regionally as well as warmer slopes locally. Pasture-level grazing pressure interacted with temperature such that annual grass cover increased with grazing pressure at higher temperatures but decreased with grazing pressure at lower temperatures. This suggests that temperature and grazing effects on annual grass abundance are complex and context-dependent, though the causality of this relationship deserves further examination. At a local scale, annual grass cover did not vary with grazing metrics, but perennial cover did; perennial grasses, for example, had lower cover closer to water sources, but higher cover at higher dung counts within a pasture, suggesting contrasting interpretations of these two grazing proxies. Importantly for predictions of how ecosystems will respond to temperature change, we found that regional and local scale favorability interacted: perennial grasses had higher cover on cooler slopes, but this difference across topography was starkest at sites that were less favorable for perennial grasses regionally. Understanding the mechanisms behind cross-scale interactions and contingent responses of vegetation to grazing in these ecosystems will be critical to land management in a changing world.