Research and Publications
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Study results suggest that lateral root functioning in Artemisia tridentata is associated with intraspecific identity and ploidy level. Subspecies adapted to habitats with deep soils generally had a smaller horizontal reach, and polyploid cytotypes were associated with greater water uptake compared to their diploid variants. Plant crown volume was a weak predictor of water uptake, and that neighborhood crowding had no discernable effect on water uptake. Intraspecific variation in lateral root functioning can lead to differential patterns of resource acquisition, an essential process in arid ecosystems in the contexts of changing climate and seasonal patterns of precipitation. Altogether, we found that lateral root development and activity is more strongly related to genetic variability within A. tridentata than to plant size. This study highlights how intraspecific variation in life strategies is linked to mechanisms of resource acquisition.
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This study reports an automated method of mapping rangeland fractional component cover over a large portion of the northern Great Basin, from 1986 to 2016 using a dense Landsat imagery time series. Over the 30‐yr period, shrub cover declined and bare ground increased. While few pixels had >10% cover change, a large majority had at least some change. All fractional components had significant spatial relationships with water year precipitation (WYPRCP), maximum temperature (WYTMAX), and minimum temperature (WYTMIN) in all years. Shrub and sagebrush cover in particular respond positively to warming WYTMIN, resulting from the largest increases in WYTMIN being in the coolest and wettest areas, and respond negatively to warming WYTMAX because the largest increases in WYTMAX are in the warmest and driest areas. The trade‐off of lowering temporal density against removing cloud‐contaminated years is justified as temporal density appears to have only a modest impact on trends and climate relationships until n ≤ 6, but multi‐year gaps are proportionally more influential. Gradual change analysis is likely to be less sensitive to n than abrupt change. These data can be used to answer critical questions regarding the influence of climate change and the suitability of management practices.
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This study asked whether success in restoration seedings of the foundational species big sagebrush was related to estimated water deficit in previously burned areas in the western United States. Standardized precipitation-evapotranspiration index (SPEI), a widely used drought index, was not predictive of whether sagebrush had reestablished. In contrast, wet-warm days elicited a critical drought threshold response, with successfully reestablished sites having experienced 7 more wet-warm days than unsuccessful sites during the first March following summer wildfire and restoration. Thus, seemingly small-scale and short-term changes in water availability and temperature can contribute to major ecosystem shifts, as many of these sites remained shrubless two decades later. These findings help clarify the definition of ecological drought for a foundational species and its imperiled semi-arid ecosystem. Drought is well known to affect the occurrence of wildfires, but drought in the year(s) after fire can determine whether fire causes long-lasting, negative impacts on ecosystems.
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This study employed meta‐analyses of studies published from 1991 to 2019 to help resolve the role of fine‐scale vegetation structure in nest site selection and nest success across the geographic range of greater sage‐grouse and evaluate the validity of established habitat management objectives. Our approach tested habitat relationships at a range‐wide extent and a grain size closely matching scales at which agencies make management decisions. We found moderate, but context‐dependent, effects of shrub characteristics and weak effects of herbaceous vegetation on nest site selection. None of the tested vegetation characteristics were related to variation in nest success, suggesting nesting habitat–fitness relationships have been inappropriately extrapolated in developing range‐wide habitat management objectives. Our findings reveal surprising flexibility in habitat use for a species often depicted as having very particular fine‐scale habitat requirements, and cast doubt on the practice of adopting precise management objectives for vegetation structure based on findings of individual small‐scale field studies.
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Wildfires are increasingly common in the United States, the result of climate change, altered wildfire regimes, and expanding residential development in close proximity to wildland vegetation. Both suppression expenditures and damages are increasing as a result. Accelerating wildfire losses have been observed in other countries as well: Australia, Canada, Chile, Greece, and Portugal have all experienced record destruction due to wildfires in the past decade. Reducing wildfire losses is a daunting goal requiring a multi-part strategy across all levels of government. In the U.S., federal fire policy seeks to: create resilient landscapes and vegetation; use effective and efficient suppression; and promote fire-adapted communities where human populations and infrastructure can withstand wildfire, reducing loss of life and property.
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This plan represents the culmination of an unprecedented four-year collaboration among state and federal agencies investigating the threats of invasive plants to the sagebrush biome. The strategic plan identifies opportunities to overcome these threats through messaging, collaboration, prioritization, data sharing and increasing capacity to effectively implement cutting-edge, scientifically based management approaches across the Western landscape.
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This study analyzed changes in vegetation and bird abundance at a wildlife refuge in southeastern Oregon over 24 years, following cessation of 120 years of livestock grazing. We quantified long-term changes in overall avian abundance and species richness and, specifically, in the abundances of 20 focal species. We then compared the local responses of the focal species to population-scale trends of the same species at three different large spatial scales. Overall avian abundance increased 23% during the 12 years after removal and remained consistent from then through year 24. Three times as many species colonized the survey sites as dropped out. Of the focal species, most riparian woodland-tree or shrub dependent, sagebrush obligate, and grassland or meadow taxa increased in abundance or remained stable locally. As these species were generally of conservation concern, the population increases contradicted regionally declining or stable trends. In contrast, most riparian woodland-cavity nester species decreased in abundance locally, reflecting disruption of aspen stand dynamics by decades of grazing. Avian nest parasites and competitors of native species declined in abundance locally, matching regional trends. Restoring riparian ecosystems by removing livestock appeared to be beneficial to the conservation of many of these declining populations of migratory birds.
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This study found distinct evidence that within management group species composition was more similar than across groups for two of the three pairings. However, the other pairing, the most successfully protected area and the completely unprotected area, was not statistically distinct; likely a result a deteriorating overstorey in these two areas, whereas the third management type (2014 Fence) exhibited higher canopy cover. Indicator species analysis found that a small group of plant species had statistical allegiances to specific management groups, suggesting resource preference selection within Pando. Ordination analysis searching for causal factors reached two broad conclusions: (1) aspen regeneration, and therefore long-term resilience, is being negatively affected by chronic animal browsing and (2) current understorey species diversity is highest where forest canopy gaps are abundant.
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This study examined post-fire aspen stands across a regional climate gradient spanning from the north-central Great Basin to the northeastern portion of the Greater Yellowstone Ecosystem (USA). We investigated the influence of seasonal precipitation and temperature variables, snowpack, and site conditions (e.g. browsing levels, topography) on density of post-fire aspen regeneration (i.e. all small trees ha−1) and recruitment (i.e. small trees ≥2 m tall ha−1) across 15 fires that occurred between 2000 and 2009. The range of post-fire regeneration (2500–71,600 small trees ha−1) and recruitment (0–32,500 small trees ≥2 m ha−1) densities varied widely across plots. Linear mixed effects models demonstrated that both response variables increased primarily with early winter (Oct-Dec) precipitation during the ‘fire-regen period’ (i.e., fire year and five years after fire) relative to the 30-year mean. The 30-year mean of early winter precipitation and fire-regen period snowpack were also positively related to recruitment densities. Both response variables decreased with higher shrub cover, highlighting the importance of considering shrub competition in post-fire environments. Regeneration and recruitment densities were negatively related to proportion browsed aspen leaders and animal pellet densities (no./m2), respectively, indicating the influence of ungulate browsing even at the relatively low levels observed across sites. A post-hoc exploratory analysis suggests that deviation in early winter precipitation during the fire-regen period (relative to 30-year means) varied among sites along directional gradients, emphasizing the need to consider multiple spatiotemporal scales when investigating climate effects on post-fire successional dynamics.
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With remotely-sensed (Landsat) estimates of vegetation cover collected every 2–5 years from sw Wyoming (1985–2015), we modeled changes in sagebrush cover on 375 former oil and gas well pads in response to weather and site-level conditions. We then used modeled relationships to predict recovery time across the landscape as an indicator of resilience for vegetation after well pad disturbances, where faster recovery indicates a greater capacity to recover when similarly disturbed. Rate of change in sagebrush cover generally increased with moisture and temperature, particularly at higher elevations. Rate of change in sagebrush cover also increased and decreased with greater percent sand and larger well pads, respectively. We predicted 21% of the landscape would recover to pre-disturbance conditions within 60 years, whereas other areas may require >100 years for recovery.