Big Sagebrush Plant Communities Research Articles

A comparison and development of methods for estimating shrub volume using drone‐imagery‐derived point clouds

AbstractShrub volume is used to calculate numerous, essential ecological indicators in rangeland ecosystems such as biomass, fuel loading, wildlife habitat, site productivity, and ecosystem structure. Field techniques for biomass estimation, including destructive sampling, ocular estimates, and allometric techniques, use shrub height and canopy widths to estimate volume and translate it to biomass with species‐specific allometric equations. These techniques are time‐consuming and pose challenges, including removal of plant material and training of observers. We compared canopy volume estimates from field‐based measurements with drone‐collected canopy volume estimates for seven dominant shrub species within mountain big sagebrush (Artemisia tridentata subsp. vaseyana) plant communities in southern Idaho, USA. Canopy height and two perpendicular width measurements were taken from 103 shrubs of varying sizes, and volume was estimated using a traditional allometric equation. Overlapping aerial images captured with a DJI Mavic 2 Professional drone were used to create a 3D representation of the study area using structure‐from‐motion photogrammetry. Each shrub was extracted from the point cloud, and volume was estimated using allometric and volumetric methods. The volumetric method, which involved converting point clouds to raster canopy height models with 2.5‐ and 5‐cm grid cells, outperformed the allometric method (R2 > 0.7) and was more reproducible and robust to user‐related variability. Drone‐estimated volume best‐matched field‐estimated volume (R2 > 0.9) for three larger species: A. tridentata subsp. tridentata, A. tridentata subsp. vaseyana, and Purshia tridentata. The volume of smaller shrubs (canopy widths <1 m) was slightly overestimated from drone‐based models. We argue that drone‐based models provide a suitable alternative to field methods, while having the added benefit of being less time‐consuming, with fewer limitations, and more easily scaled to larger study areas than traditional field techniques. Finally, we demonstrate a proof of concept for automating canopy volume estimates using point‐cloud‐based automatic shrub detection algorithms. These findings demonstrate that drone‐collected images can be used to assess shrub canopy volume for at least five upland sagebrush steppe shrub species and support the integration of drone data collection into rangeland vegetation monitoring.

Effect of burn season and grazing deferment on mountain big sagebrush plant communities

Effect of burn season and grazing deferment on mountain big sagebrush plant communities

Effects of a decade of grazing exclusion on three Wyoming big sagebrush community types

Livestock grazing is the most extensive land use in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) steppe and its effects on plant community characteristics have been greatly debated. However, most of the studies used to support grazing removal evaluated the impacts of excluding historic grazing, rather than the impacts of excluding moderate contemporary grazing (40–50% utilization, altering season of use) which has vastly different effects on plant communities. Thus, to understand the effects of removing contemporary grazing, we compared contemporary grazed areas to long-term (+10 yrs.) grazing exclusion areas in three common Wyoming big sagebrush community types: intact, degraded, and exotic annual grass-dominated types. Plant community characteristics (cover, density, diversity, richness, dissimilarity) were measured in 2020 and 2021 in five grazed and grazing excluded areas within each community type. Most plant community characteristics were not influenced by grazing exclusion, suggesting that the removal of contemporary grazing has little effect on Wyoming big sagebrush plant communities. The effect of grazing exclusion on Sandberg bluegrass (Poa secunda J. Presl) abundance and litter cover varied among community types, suggesting that grazing exclusion effects slightly varied among community types. In contrast, most plant community characteristics varied among community types and between years, suggesting that grazing management plans need to account for the spatial and temporal variability among Wyoming big sagebrush communities. Furthermore, our results suggest that contemporary grazing exclusion has negligible effects compared to contemporary grazing on plant communities, and that exclusion of contemporary grazing (passive restoration) does not promote the recovery of degraded and annual grass invaded plant communities.

Small effects of livestock grazing intensification on diversity, abundance, and composition in a dryland plant community.

Livestock grazing is a globally important land use and has the potential to significantly influence plant community structure and ecosystem function, yet several critical knowledge gaps remain on the direction and magnitude of grazing impacts. Furthermore, much of our understanding of the long-term effects on plant community composition and structure are based on grazer exclusion experiments, which explicitly avoid characterizing effects along grazing intensity gradients. We sampled big sagebrush plant communities using 68 plots located along grazing intensity gradients to determine how grazing intensity influences multiple aspects of plant community structure over time. This was accomplished by sampling plant communities at different distances from 17 artificial watering sources, using distance from water and cow dung density as proxies for grazing intensity at individual plots. Total vegetation cover and total grass cover were negatively related to grazing intensity, and cover of annual forbs, exotic cover, and exotic richness were positively related to grazing intensity. In contrast, species richness and composition, bunchgrass biomass, shrub density and size, percentage cover of bare ground, litter, and biological soil crusts did not vary along our grazing intensity gradients, in spite of our expectations to the contrary. Our results suggest that the effects of livestock grazing over multiple decades (mean=46 years) in our sites are relatively small, especially for native perennial species, and that the big sagebrush plant communities we sampled are somewhat resistant to livestock grazing. Collectively, our findings are consistent with existing evidence that indicates the stability of the big sagebrush plant functional type composition under current grazing management regimes.

Virtual Fencing Effectively Excludes Cattle from Burned Sagebrush Steppe

On public lands grazing allotments in the western US sagebrush steppe, cattle are generally excluded from burned pastures for 2 yr post fire. If only a portion of a pasture burns, the burned area may be fenced, allowing for cattle grazing to resume in the unburned portion. However, traditional wire-based fencing is often not an option due to expense, conflicts with wildlife management objectives, and extensive procedural logistics. We evaluated the use of a “virtual fence” (VF) for excluding cattle from burned areas within small pastures in the sagebrush steppe of southeast Oregon. VF technology (Vence Corporation, San Francisco, CA) uses satellite-controlled collars that direct animal movement within user-defined polygons using auditory and electrical cues. We fall-burned a 0.6-ha area in each of six adjacent 2.1-ha pastures in a Wyoming big sagebrush plant community in 2019. In June 2020, each pasture was stocked with 3 mature dry cows for 14 d. All cows were fitted with VF collars; collars were programed to create a virtual fence around the burned area within three of the pastures (VF treatment), and remaining pastures had electrical and auditory cues turned off (control treatment). Collars recorded animal location every 5 min. Cows in the control treatment initially spent up to 40% of their time within the burned area, and forage utilization of the burned area was nearly 70%. Cows in the VF treatment spent approximately 4% of their time in the burned area on day 1 and were recorded in the burn only incidentally thereafter; forage utilization in the burn was < 3%. Our trial suggests VF technology is effective in controlling rangeland cattle movements and can severely curtail use of burned areas. Additional work is needed to evaluate VF technology in larger rangeland settings.

Allometric Modeling of Bunchgrasses in Big Sagebrush Plant Communities

Estimating plant biomass in rangeland ecosystems is essential to understanding carbon cycling, impacts on natural resources, and ecological functioning or structure—all of which inform sustainable land management. However, biomass estimation has been relatively understudied for the sagebrush steppe of North America, one of the continent's most widespread ecosystems. As a nondestructive alternative to direct biomass measurements, allometric models may be used to estimate aboveground plant biomass using predictor variables once models are developed. With this as our aim, we developed species-specific and multispecies models for eight common bunchgrass species in Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) plant communities. As codominant perennials, these bunchgrass species provide much of the forage for large herbivores while contributing to soil stability and carbon storage. To develop allometric models for these bunchgrass species, we used individual height, basal diameter, and tiller count as predictor variables. On average, multiple-predictor models (RMSE CV = 61%) were more effective (i.e., exhibited more agreement between predicted and actual biomass) than single-predictor models (RMSE CV = 79%). Power models (RMSE CV = 66%) were slightly more effective than exponential models (RMSE CV = 72%). Applying models to each species demonstrated that the effectiveness of multispecies (RMSE CV = 65%) versus species-specific (RMSE CV = 67%) models largely depended on the species being modeled. Combining our models with plant density resulted in an area-based biomass estimate range (2.3–26.7 g/m2) that generally agreed with previous studies (0.2–19 g/m2). It is our hope that the allometric models developed in this study will be tested on various locations and ultimately inform rangeland management throughout the big sagebrush region.

Seedling Emergence Patterns of Six Restoration Species in Soils from Two Big Sagebrush Plant Communities

Despite the critical need to improve degraded herbaceous understory conditions in many semiarid ecosystems, the influence of soil properties on seedling emergence of species seeded in shrubland plant communities is largely unexplored. We evaluated emergence patterns of 6 restoration species in soils from wyomingensis (i.e., Wyoming big sagebrush, Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) and vaseyana (i.e., mountain big sagebrush, A. t. ssp. vaseyana [Rydb.] Beetle) plant communities that differed in soil texture, soil organic matter content, and soil water-holding capacity. We conducted 2 separate experiments that regularly wetted soils to standardized soil water potentials (i.e., field capacity; −0.03 MPa) and allowed differences in evaporation to create distinct wet-dry watering pattern cycles over a 26–29 d period. Our objectives were to compare soil attributes of wyomingensis and vaseyana soils, evaluate whether emergence patterns of restoration species vary within these soils, and determine how these patterns are altered by soil water-content levels. We found differences in soil texture and organic matter between soils and thus soil water-holding capacity: finer-textured vaseyana soils held roughly twofold more water than coarse-textured wyomingensis soils. Seeds in vaseyana soils were exposed to fewer wet-dry cycles compared to wyomingensis soils because of the greater capacity of vaseyana soils to retain water. Restoration species also collectively exhibited greater emergence in vaseyana soils than in wyomingensis soils, yet emergence patterns were vastly different among species, and differences between soils became more pronounced under low soil water for only 2 species. We conclude that the manner in which soils and water uniquely influenced emergence patterns provides new insights into species suitability for restoration sites and how inherent soil differences may constrain seeding success.

Patterns of Big Sagebrush Plant Community Composition and Stand Structure in the Western United States

Big sagebrush (Artemisia tridentata Nutt.) plant communities are found in western North America and comprise a mix of shrubs, forbs, and grasses. Climate, topography, and soil water availability are important factors that shape big sagebrush stand structure and plant community composition; however, most studies have focused on understanding these relationships at sites in a small portion of the big sagebrush region. Our goal was to characterize detailed stand structure and plant composition patterns and identify environmental variables related to those patterns by sampling 15 sites distributed across the western United States. In each site, we characterized stand structure at the individual shrub level and at the site level. We quantified size distributions and assessed relationships among canopy volume, age, and height. We also characterized functional type cover and species composition and related those to climatic, topographic, and edaphic variables. Mean big sagebrush age ranged from 21 (±8) to 57 (±22) yr at individual sites, mean height ranged from 0.23 (±0.12) to 0.67 (±0.23) m, and mean canopy volume ranged from 0.03 (±0.04) to 0.62 (±0.51) m3. Bare ground and litter contributed the most cover (mean = 64%), followed by big sagebrush (mean = 39% of vascular plant cover). There was a negative relationship between big sagebrush cover and grass and forb cover. Species composition was related to both climate and elevation, likely because these variables influence water availability. Although our study was limited to 15 field sites, our detailed descriptions of widely distributed sites provide insight into the magnitude of variability in big sagebrush plant community structure.

Characteristics of Intact Wyoming Big Sagebrush Associations in Southeastern Oregon

The Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) alliance is the most extensive of the big sagebrush complex in the Intermountain West. There is a lack of information describing vegetation characteristics, diversity, and heterogeneity of the Wyoming big sagebrush alliance. We annually sampled 48 Wyoming big sagebrush plant communities over 10 yr to delineate major vegetation associations and describe their major vegetation characteristics including canopy cover, density, species richness, and yield. Six associations were identified on the basis of dominant or codominant perennial bunchgrass species, using MRPP analysis, and they included ARTRW8 (Wyoming big sagebrush)/PSSP6 (Pseudoroegneria spicata [Pursh] A. Löve, bluebunch wheatgrass), ARTRW8/ACTH7 (Achnatherum thurberianum [Piper] Barkworth, Thurber’s needlegrass), ARTRW8/FEID (Festuca idahoensis Elmer, Idaho fescue), ARTRW8/HECO26 (Hesperostipa comata [Trin. & Rupr.] Barkworth, needle-and-thread), ARTRW8/PSSP6-ACTH7, and ARTRW8/PSSP6-FEID-ACTH7. On average, PSSP6 and FEID associations had the highest total herbaceous cover and annual yields and the HECO26 and ACTH7 associations had the lowest. Perennial forb cover averaged over 5% in PSSP6 and FEID associations and ranged from 0.3% to 3.5% in the other associations. Sagebrush cover was greatest in ACTH7 and PSSP6-ACTH7 and lowest in FEID and HECO26 associations. Habitat suitability criteria for sage-grouse indicated that Wyoming big sagebrush associations at the stand/site level will generally not meet breeding habitat requirements and only attain suitable habitat requirements for other life stages about 50% of the time.

STEPWAT2: an individual‐based model for exploring the impact of climate and disturbance on dryland plant communities

AbstractThe combination of climate change and altered disturbance regimes is directly and indirectly affecting plant communities by mediating competitive interactions, resulting in shifts in species composition and abundance. Dryland plant communities, defined by low soil water availability and highly variable climatic regimes, are particularly vulnerable to climatic changes that exceed their historical range of variability. Individual‐based simulation models can be important tools to quantify the impacts of climate change, altered disturbance regimes, and their interaction on demographic and community‐level responses because they represent competitive interactions between individuals and individual responses to fluctuating environmental conditions. Here, we introduce STEPWAT2, an individual plant‐based simulation model for exploring the joint influence of climate change and disturbance regimes on dryland ecohydrology and plant community composition. STEPWAT2 utilizes a process‐based soil water model (SOILWAT2) to simulate available soil water in multiple soil layers, which plant individuals compete for based on the temporal matching of water and active root distributions with depth. This representation of resource utilization makes STEPWAT2 particularly useful for understanding how changes in soil moisture and altered disturbance regimes will concurrently impact demographic and community‐level responses in drylands. Our goals are threefold: (1) to describe the core modules and functions within STEPWAT2 (model description), (2) to validate STEPWAT2 model output using field data from big sagebrush plant communities (model validation), and (3) to highlight the usefulness of STEPWAT2 as a modeling framework for examining the impacts of climate change and disturbance regimes on dryland plant communities under future conditions (model application). To address goals 2 and 3, we focus on 15 sites that span the spatial extent of big sagebrush plant communities in the western United States. For goal 3, we quantify how climate change, fire, and grazing can interact to influence plant functional type biomass and composition. We use big sagebrush‐dominated plant communities to demonstrate the functionality of STEPWAT2, as these communities are among the most widespread dryland ecosystems in North America.

Resource quantity and resource heterogeneity shape species richness and beta-diversity patterns in big sagebrush plant communities

Resource quantity and resource heterogeneity shape species richness and beta-diversity patterns in big sagebrush plant communities

Current reclamation practices after oil and gas development do not speed up succession or plant community recovery in big sagebrush ecosystems in Wyoming

AbstractReclamation is an application of treatment(s) following disturbance to promote succession and accelerate the return of target conditions. Previous studies have framed reclamation in the context of succession by studying its effectiveness in reestablishing late‐successional plant communities. Reestablishment of plant communities is especially important and challenging in drylands such as shrub steppe ecosystems where succession proceeds slowly. These ecosystems face threats from climate change, invasive species, altered fire regimes, and land‐use change, as well as fossil‐fuel extraction and associated disturbance. As such, the need for effective reclamation after this type of energy development is great. However, past research regarding this type of reclamation has focused on mining rather than oil and gas development. To better understand the effect of reclamation on rates of succession in dryland shrub steppe ecosystems, we sampled oil and gas wellpads and adjacent undisturbed big sagebrush plant communities in Wyoming, U.S.A., and quantified the extent of recovery for forbs, grasses, and shrubs on reclaimed and unreclaimed wellpads relative to undisturbed plant communities. Reclamation increased the recovery rate for early‐successional types, including combined forbs and grasses and perennial grasses, but did not affect recovery rate of late‐successional types, particularly big sagebrush and perennial forbs. Rather, subsequent analyses showed that recovery of late‐successional types was affected by soil texture and time since wellpad abandonment. This is consistent with studies in other ecosystems where reclamation has been implemented, suggesting that reclamation may not help reestablish late‐successional plant communities more quickly than they would reestablish naturally.

Assessing growth response to climate in a Great Basin big sagebrush (Artemisia tridentata) plant community

The response of dominant plant species to climate is vital to our understanding of ecosystem function and viability. We compared annual growth ring indices of a dominant Great Basin shrub (Artemisia tridentata) growing in the semiarid desert of northern Nevada, USA to historical climate records to identify and determine the extent specific climatic variables have on wood growth. Growth ring indices had a strong, positive correlation with total hydrologic-year precipitation (Oct–Sep; r=0.82, p<0.001) measured at the nearest meteorological station with the months of January, March, April, and June being the most highly correlated to ring growth (r=0.48, 0.36, 0.47, and 0.41, respectively; p<0.05). Mean maximum growing season temperatures were found to be negatively correlated to growth during the months of April, May, June, and October of the previous year (r=−0.40, −0.37, −0.50, and −0.30, respectively; p<0.001). Multiple regression analysis determined hydrologic year precipitation and maximum growing season temperature to be the best predictors of ring growth (adj. r2=0.72, p<0.001). May NDVI (Normalized Difference Vegetation Index) values were adequate predictors of annual ring growth (r2=0.48, p<0.01), and ring growth patterns of big sagebrush were consistent with those of other species in the greater region demonstrating the utility of the shrub for climate studies.

Climate and soil texture influence patterns of forb species richness and composition in big sagebrush plant communities across their spatial extent in the western U.S.

Big sagebrush (Artemisia tridentata Nutt.) plant communities are widespread in western North America and, similar to all shrub steppe ecosystems worldwide, are composed of a shrub overstory layer and a forb and graminoid understory layer. Forbs account for the majority of plant species diversity in big sagebrush plant communities and are important for ecosystem function. Few studies have explored geographic patterns of forb species richness and composition and their relationships with environmental variables in these communities. Our objectives were to examine the fine and broad-scale spatial patterns in forb species richness and composition and the influence of environmental variables. We sampled forb species richness and composition along transects at 15 field sites in Colorado, Idaho, Montana, Nevada, Oregon, Utah, and Wyoming, built species-area relationships to quantify differences in forb species richness at sites, and used Principal Components Analysis, non-metric multidimensional scaling, and redundancy analysis to identify relationships among environmental variables and forb species richness and composition. We found that species richness was most strongly correlated with soil texture, while species composition was most related to climate. The combination of climate and soil texture influences water availability, which our results indicate has important consequences for forb species richness and composition, and suggests that climate change-induced modification of soil water availability may have important implications for plant species diversity in the future.

Ecosystem resilience is evident 17 years after fire in Wyoming big sagebrush ecosystems

AbstractRecent policy has focused on prevention of wildfire in the sagebrush steppe in an effort to protect habitat for the greater sage grouse (Centrocercus urophasianus). Historically, fire return intervals in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) ecosystems were 50–100 yr or more, but invasive species, climate change, and a legacy of intensive grazing practices have led to degraded rangeland condition, altered fire regimes and fire effects, and declines in sagebrush cover. Little is known about the long‐term impacts of fire in this ecosystem in areas where grazing pressure has been removed, few invasive species exist, and fire return intervals are maintained. In this study, we quantified vegetation composition prior to prescribed burning, 1 year following fire, and 17 years after fire in a native‐dominated Wyoming big sagebrush ecosystem at Hart Mountain National Antelope Refuge, Oregon, United States. Seventeen years following fire, the ecosystem was dominated by native herbaceous vegetation, with 8.3% cover of broad‐leaved forbs and bunchgrasses in the understory, compared to just 3.8% cover of native herbaceous vegetation in unburned controls. Invasive annual grass cover ranged from 0.2% to 8.4% across all treatments and years (P = 0.56). One year following fire, the distance from a randomly located point and the nearest mature sagebrush was 16.6 m, but by 17 years after the fire, that distance had decreased to 2.5 m. Seventeen years after fires, shrub cover was 0.4–4% in burned plots compared to 13–24% in unburned controls. Collectively, these data demonstrate that good condition ungrazed Wyoming big sagebrush plant communities exhibited resilience following fire and maintained a native‐dominated mosaic of shrubs, bunchgrasses, and forbs. Further, unburned control plots were dominated by woody vegetation and exhibited losses in herbaceous understory, possibly indicating that they are outside of their natural fire return interval. Our results illustrate that management of all habitat components, including natural disturbance and a mosaic of successional stages, is important for persistent resilience and that suppression of all fires in the sagebrush steppe may create long‐term losses of heterogeneity in good condition Wyoming big sagebrush ecosystems.

Sagebrush, Greater Sage-Grouse, and the Occurrence and Importance of Forbs

Big sagebrush (Artemisia tridentata Nutt.) ecosystems provide habitat for sagebrush-obligate wildlife species such as the Greater Sage-Grouse (Centrocercus urophasianus). The understory of big sagebrush plant communities is composed of grasses and forbs that are important sources of cover and food for wildlife. The grass component is well described in the literature, but the composition, abundance, and habitat role of forbs in these communities is largely unknown. Our objective was to synthesize information about forbs and their importance to Greater Sage-Grouse diets and habitats, how rangeland management practices affect forbs, and how forbs respond to changes in temperature and precipitation. We also sought to identify research gaps and needs concerning forbs in big sagebrush plant communities. We searched for relevant literature including journal articles and state and federal agency reports. Our results indicated that in the spring and summer, Greater Sage-Grouse diets consist of forbs (particularly species in the Asteraceae family), arthropods, and lesser amounts of sagebrush. The diets transition to sagebrush in fall and winter. Forbs provide cover for Greater Sage-Grouse individuals at their lekking, nesting, and brood-rearing sites, and the species has a positive relationship with arthropod presence. The effect of grazing on native forbs may be compounded by invasion of nonnative species and differs depending on grazing intensity. The effect of fire on forbs varies greatly and may depend on time elapsed since burning. In addition, chemical and mechanical treatments affect annual and perennial forbs differently. Temperature and precipitation influence forb phenology, biomass, and abundance differently among species. Our review identified several uncertainties and research needs about forbs in big sagebrush ecosystems. First, in many cases the literature about forbs is reported only at the genus or functional type level. Second, information about forb composition and abundance near lekking sites is limited, despite the fact that lekking sites are an important center of Greater Sage-Grouse activity. Third, there is little published literature on the relationship between forbs and precipitation and between forbs and temperature, thereby limiting our ability to understand potential responses of forbs to climate change. While there is wide agreement among Greater Sage-Grouse biologists that forbs are an important habitat component, our knowledge about the distribution and environmental responses of forb species in big sagebrush plant communities is limited. Our work for the first time synthesizes the current knowledge regarding forbs in sagebrush ecosystems and their importance for Greater Sage-Grouse and identifies additional research needs for effective conservation and management.

Seed bank and big sagebrush plant community composition in a range margin for big sagebrush

AbstractThe potential influence of seed bank composition on range shifts of species due to climate change is unclear. Seed banks can provide a means of both species persistence in an area and local range expansion in the case of increasing habitat suitability, as may occur under future climate change. However, a mismatch between the seed bank and the established plant community may represent an obstacle to persistence and expansion. In big sagebrush (Artemisia tridentata) plant communities in Montana, USA, we compared the seed bank to the established plant community. There was less than a 20% similarity in the relative abundance of species between the established plant community and the seed bank. This difference was primarily driven by an overrepresentation of native annual forbs and an underrepresentation of big sagebrush in the seed bank compared to the established plant community. Even though we expect an increase in habitat suitability for big sagebrush under future climate conditions at our sites, the current mismatch between the plant community and the seed bank could impede big sagebrush range expansion into increasingly suitable habitat in the future.

Mid-latitude shrub steppe plant communities: climate change consequences for soil water resources.

In the coming century, climate change is projected to impact precipitation and temperature regimes worldwide, with especially large effects in drylands. We use big sagebrush ecosystems as a model dryland ecosystem to explore the impacts of altered climate on ecohydrology and the implications of those changes for big sagebrush plant communities using output from 10 Global Circulation Models (GCMs) for two representative concentration pathways (RCPs). We ask: (1) What is the magnitude of variability in future temperature and precipitation regimes among GCMs and RCPs for big sagebrush ecosystems, and (2) How will altered climate and uncertainty in climate forecasts influence key aspects of big sagebrush water balance? We explored these questions across 1980-2010, 2030-2060, and 2070-2100 to determine how changes in water balance might develop through the 21st century. We assessed ecohydrological variables at 898 sagebrush sites across the western US using a process-based soil water model, SOILWAT, to model all components of daily water balance using site-specific vegetation parameters and site-specific soil properties for multiple soil layers. Our modeling approach allowed for changes in vegetation based on climate. Temperature increased across all GCMs and RCPs, whereas changes in precipitation were more variable across GCMs. Winter and spring precipitation was predicted to increase in the future (7% by 2030-2060, 12% by 2070-2100), resulting in slight increases in soil water potential (SWP) in winter. Despite wetter winter soil conditions, SWP decreased in late spring and summer due to increased evapotranspiration (6% by 2030-2060, 10% by 2070-2100) and groundwater recharge (26% and 30% increase by 2030-2060 and 2070-2100). Thus, despite increased precipitation in the cold season, soils may dry out earlier in the year, resulting in potentially longer, drier summer conditions. If winter precipitation cannot offset drier summer conditions in the future, we expect big sagebrush regeneration and survival will be negatively impacted, potentially resulting in shifts in the relative abundance of big sagebrush plant functional groups. Our results also highlight the importance of assessing multiple GCMs to understand the range of climate change outcomes on ecohydrology, which was contingent on the GCM chosen.

Effects of Using Winter Grazing as a Fuel Treatment on Wyoming Big Sagebrush Plant Communities

More frequent wildfires and incidences of mega-fires have increased the pressure for fuel treatments in sagebrush (Artemisia) communities. Winter grazing has been one of many fuel treatments proposed for Wyoming big sagebrush (A. tridentata Nutt. subsp. wyomingensis Beetle and A. Young) communities. Though fire risk and severity can be reduced with winter grazing, its impact on vegetation characteristics of Wyoming big sagebrush plant communities is largely unknown. We evaluate the effect of winter grazing at utilization levels between 40% and 60% at five sites in southeastern Oregon. Winter grazing was applied for 5−6 yr before measurements. The winter-grazed and ungrazed treatments generally had similar vegetation characteristics; however, a few characteristics differed. The consumption of prior years’ growth resulted in less large perennial bunchgrass, perennial forb, and total herbaceous cover and standing crop and litter biomass. Large perennial bunchgrass and perennial forb density and biomass and exotic annual grass and annual forb cover, density, and biomass did not differ between treatments, suggesting that winter grazing is not negatively impacting resilience and resistance of these communities. Shrub cover was also similar between treatments. These results imply that winter grazing can be applied to reduce fine fuels in Wyoming big sagebrush communities without adversely affecting the native plant community. Winter grazing should, however, be strategically applied because the reduction in perennial grass and perennial forb cover with the consumption of prior years’ growth may negatively impact the habitat value for wildlife species that use herbaceous vegetation for concealment.

Sagebrush steppe recovery on 30–90‐year‐old abandoned oil and gas wells

Oil and natural gas extraction is rapidly expanding in semiarid intermountain big sagebrush ecosystems of the western USA. Formerly covering over 60 million ha, this ecosystem has lost almost half its area due to land use changes. In this study, we measured the natural recovery of the big sagebrush plant community across a chronosequence of 29 oil and gas well sites that were abandoned without reclamation between 1923 and 1980. We measured big sagebrush cover and density with strip transects inside and outside of the well sites, and we estimated big sagebrush biomass using both canopy measurements and allometric equations. Cover of other shrubs, grasses, and forbs was estimated with line transects inside and outside of well sites. We estimated that it takes at least 87 years for Wyoming big sagebrush cover to recover naturally, although big sagebrush density recovered in fewer than 70 years. Grasses and non‐sagebrush shrubs recovered rapidly, shown by the high cover of those groups in the youngest sites. We found none of the invasive plants that are common in disturbed big sagebrush communities in other parts of the big sagebrush range. The forbs that account for the largest portion of plant species richness in semiarid ecosystems and promote consumer diversity showed very little indication of recovery after 87 years. Our results suggest that reclamation efforts in disturbed big sagebrush plant communities in southwestern Wyoming should target big sagebrush and forbs.