Article

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

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Abstract

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.

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... Shrub steppe ecosystems are a common type of dryland ecosystem that occupy the western United States, southeastern South America, and a large portion of central Asia. Winter is the wet season in these shrub steppe plant communities, which results in spring recharge of soil water deep in the soil (Lauenroth et al. 2014;Palmquist et al. 2016a). As a result of their ability to take advantage of these deeply stored water sources, shrubs are the dominant growth form in these ecosystems. ...
... Shrub steppe ecosystems are frequently associated with regions rich in energy resources (oil, gas, coal, wind, solar, geothermal;Pocewicz et al. 2011), such that up to 25% of western North American shrub steppe is projected to be affected by energy development in the future (Pocewicz et al. 2011). In addition to oil and gas development, big sagebrush shrub steppe is increasingly threatened by climate change, invasion by exotic species, altered fire regimes, and other changes in land use (Knick et al. 2003;Bradley 2010;Manier et al. 2013;Palmquist et al. 2016aPalmquist et al. , 2016bSchlaepfer et al. 2017). As such, the need for reclamation and restoration of dryland plant communities after oil and gas development and other disturbances is growing and will continue into the future. ...
... Our work suggests that current reclamation practices in big sagebrush ecosystems in the South Baxter Basin, Wyoming, are not currently effective at speeding up recovery of the plant community overall, but that they do result in increased rates of recovery for C. viscidiflorus and perennial grass. This has implications for other mid-latitude shrub steppe ecosystems, where future conditions may limit both regeneration and survival of shrubs and the plant community as a whole (Palmquist et al. 2016a) and further decrease the likelihood of reclamation success. Furthermore, the limited response of disturbed ecosystems to human intervention during recovery is not unique to big sagebrush ecosystems or, in fact, shrubland ecosystems, suggesting that this challenge is potentially inherent in a portion of most reclamation efforts worldwide, regardless of ecosystem (Ratzlaff & Anderson 1995;Fernández-Abascal et al. 2004;Kruse et al. 2004;Dodson & Peterson 2009). ...
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Dryland soils store approximately 10-15% of the world's soil organic matter (SOM) to 1 m. Threats to carbon stocks in global dryland soils include cultivation, overgrazing, urbanization, and energy development. To limit loss of carbon from these soils, it is important to understand, first, how disturbances affect SOM and second, how SOM recovers after disturbance. In this study, we address current gaps in our understanding of the effects of oil and gas development and reclamation on SOM in the sagebrush steppe of Wyoming, a cold temperate shrub-dominated dryland. Most studies have found that soil disturbance, including from the respreading of topsoil during wellpad reclamation, is damaging to SOM stores; however, research on ~80 year old unreclaimed oil and gas wellpads found no difference in SOM between wellpads and undisturbed sites. Using a chronosequence approach and paired study design, we evaluated the effects of reclamation on SOM by comparing undisturbed sites to wellpads where reclamation activities either had or had not occurred. Our results suggest that the most important factor in recovery of SOM after disturbance in this area was not the presence or absence of reclamation, but time since wellpad abandonment and spatial heterogeneity of plants. Further study on the effectiveness of different reclamation techniques is warranted if the goal of reclamation is to aid SOM recovery and prevent further C loss from these systems.
... In North America, temperate drylands are projected to experience increases in temperature and modest increases in cool-season precipitation on average with the largest increases in temperature and precipitation in the northernmost parts of the region (Bradford et al., 2020;Palmquist et al., 2016aPalmquist et al., , 2016b. Warming and increases in potential evapotranspiration are projected to increase the fraction of precipitation lost to evaporation during times of the year that currently have low evaporative demand (i.e., early spring and late fall), regardless of changes in precipitation. ...
... Warming and increases in potential evapotranspiration are projected to increase the fraction of precipitation lost to evaporation during times of the year that currently have low evaporative demand (i.e., early spring and late fall), regardless of changes in precipitation. This shift from low to high evaporative demand at transitions between the current cold season and warm season is expected to result in longer dry growing seasons, especially in surface soil layers (Palmquist et al., 2016a), and reduced plant productivity (Tietjen et al., 2010). These reductions in soil moisture, especially when combined with hot temperatures, will have potentially larger negative consequences for plant growth in warm dry sites (Munson et al., 2011;Renwick et al., 2018;Winkler et al., 2019). ...
... Studies examining the effects of climate change in the big sagebrush region have primarily focused on changes in the distribution of or suitability for big sagebrush itself (Bradley, 2010;Palmquist et al., 2016aPalmquist et al., , 2016bSchlaepfer et al., 2012;Shafer et al., 2001;Still & Richardson, 2015;Tredennick et al., 2016; but see Renwick et al., 2018 where one of four models represented multiple plant functional types). While these studies are useful for understanding the potential future distribution and abundance of big sagebrush, they do not include competitive interactions between big sagebrush and co-existing species, which are likely to influence future community composition. ...
Article
Plant community response to climate change will be influenced by individual plant responses that emerge from competition for limiting resources that fluctuate through time and vary across space. Projecting these responses requires an approach that integrates environmental conditions and species interactions that result from future climatic variability. Dryland plant communities are being substantially affected by climate change because their structure and function are closely tied to precipitation and temperature, yet impacts vary substantially due to environmental heterogeneity, especially in topographically complex regions. Here, we quantified the effects of climate change on big sagebrush (Artemisia tridentata Nutt.) plant communities that span 76 million ha in the western United States. We used an individual‐based plant simulation model that represents intra‐ and inter‐specific competition for water availability, which is represented by a process‐based soil water balance model. For dominant plant functional types, we quantified changes in biomass and characterized agreement among 52 future climate scenarios. We then used a multivariate matching algorithm to generate fine‐scale interpolated surfaces of functional type biomass for our study area. Results suggest geographically divergent responses of big sagebrush to climate change (changes in biomass of ‐20% to +27%), declines in perennial C3 grass and perennial forb biomass in most sites, and widespread, consistent, and sometimes large increases in perennial C4 grasses. The largest declines in big sagebrush, perennial C3 grass and perennial forb biomass were simulated in warm, dry sites. In contrast, we simulated no change or increases in functional type biomass in cold, moist sites. There was high agreement among climate scenarios on climate change impacts to functional type biomass, except for big sagebrush. Collectively, these results suggest divergent responses to warming in moisture‐limited vs. temperature‐limited sites and potential shifts in the relative importance of some of the dominant functional types that result from competition for limiting resources.
... Shrub steppe ecosystems are a common type of dryland ecosystem that occupy the western United States, southeastern South America, and a large portion of central Asia. Winter is the wet season in these shrub steppe plant communities, which results in spring recharge of soil water deep in the soil (Lauenroth et al. 2014;Palmquist et al. 2016a). As a result of their ability to take advantage of these deeply stored water sources, shrubs are the dominant growth form in these ecosystems. ...
... Shrub steppe ecosystems are frequently associated with regions rich in energy resources (oil, gas, coal, wind, solar, geothermal;Pocewicz et al. 2011), such that up to 25% of western North American shrub steppe is projected to be affected by energy development in the future (Pocewicz et al. 2011). In addition to oil and gas development, big sagebrush shrub steppe is increasingly threatened by climate change, invasion by exotic species, altered fire regimes, and other changes in land use (Knick et al. 2003;Bradley 2010;Manier et al. 2013;Palmquist et al. 2016aPalmquist et al. , 2016bSchlaepfer et al. 2017). As such, the need for reclamation and restoration of dryland plant communities after oil and gas development and other disturbances is growing and will continue into the future. ...
... Our work suggests that current reclamation practices in big sagebrush ecosystems in the South Baxter Basin, Wyoming, are not currently effective at speeding up recovery of the plant community overall, but that they do result in increased rates of recovery for C. viscidiflorus and perennial grass. This has implications for other mid-latitude shrub steppe ecosystems, where future conditions may limit both regeneration and survival of shrubs and the plant community as a whole (Palmquist et al. 2016a) and further decrease the likelihood of reclamation success. Furthermore, the limited response of disturbed ecosystems to human intervention during recovery is not unique to big sagebrush ecosystems or, in fact, shrubland ecosystems, suggesting that this challenge is potentially inherent in a portion of most reclamation efforts worldwide, regardless of ecosystem (Ratzlaff & Anderson 1995;Fernández-Abascal et al. 2004;Kruse et al. 2004;Dodson & Peterson 2009). ...
Article
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Reclamation 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.
... Their results suggested increases in GWR by approximately 100 mm/ year due to a greater fraction of precipitation received as rain than as snow and increasing temperatures that will reduce ground frost and increase recharge ( Jyrkama and Sykes 2007). Palmquist et al. (2016aPalmquist et al. ( , 2016b used SOILWAT2, a soil-water balance model, to project mean increases of 30% in GWR and shifts in peak GWR to earlier in the year by mid-and end-of-century for 898 randomly selected big sagebrush ecosystems in the western United States. ...
... We calculated changes in diffuse groundwater recharge for each of our 51 sites using SOILWAT2, a daily time-step, multiple soil layer, process-based soil water balance simulation model (Lauenroth and Bradford 2006, Schlaepfer et al. 2012a, 2012b, Bradford et al. 2014a). SOILWAT2 has been successfully applied to multiple dryland ecosystems, such (Lauenroth and Bradford 2006), big sagebrush ecosystems (Schlaepfer et al. 2012a, 2012b, Palmquist et al. 2016a, 2016b, lodgepole pine-sagebrush ecotones (Bradford et al. 2014b), and other drylands globally (Schlaepfer et al. 2017). The version for big sagebrush ecosystems incorporates a validated snow module, hydraulic redistribution, and site-specific vegetation parameters (Schlaepfer et al. 2012b). ...
... Our simulation results indicated that climate change will likely affect the water balance of big sagebrush ecosystems in Wyoming through increasing total precipitation and temperature and shifting precipitation type and seasonality, similar to other dryland studies ( Jyrkama et al. 2007, Ajami et al. 2012, Schlaepfer et al. 2012a, 2012b, Klove et al. 2014, Palmquist et al. 2016a). Similar to our work, several studies have reported shifts in the mean seasonal and annual groundwater levels (Schlaepfer et al. 2012b, Lauenroth et al. 2014, Palmquist et al. 2016a, 2016b, which were correlated with the amount of precipitation and snowmelt (Schlaepfer et al. 2012a, Klove et al. 2014). ...
Article
Water is the most limiting and important natural resource in drylands where low precipitation, high evaporative demand, and drought events are common. Groundwater is the critical resource making it possible for human livelihoods to persist through the intra-annual dry periods in dryland ecosystems. Overexploitation of groundwater resources and the externalities associated with depleted aquifers makes understanding the ecohydrology of drylands an essential issue. We focus on the water balance and climatic drivers of big sagebrush ecosystems, an important dryland ecosystem type in Wyoming that covers a large spatial extent. The goal of this project was to understand how groundwater recharge (GWR) may change in magnitude and seasonality across multiple sites in Wyoming in the future. We used a combination of fieldwork and simulation modeling to explore key climatic and ecohydrological drivers of GWR. We simulated soil water balance using SOILWAT2, a process-based ecosystem-scale soil water model and future climate data to estimate change in GWR through 2100. We found that mean annual temperature and precipitation explained 65% of the variation in future change in GWR. High elevation, wet sites (>2200 m) had larger increases in GWR in the future compared to low elevation, dry sites. The among-site variability in GWR was also higher for sites >2200 m, which indicates that mean annual precipitation and perhaps snowpack are important explanatory variables for GWR. Our research suggests that GWR for high elevation big sagebrush sites may increase in magnitude from current values and occur earlier in the year, with important implications for the timing and availability of water resources.
... Moreover, many climate models indicate increased variability in weather (Debinski et al. 2010, Collins et al. 2013, which is already quite variable in western U.S. rangelands (Reeves et al. 2020). The nature of precipitation events is expected to change, often to a lower number of more intense events (Collins et al. 2013), which is problematic in dryland environments where plants are vulnerable to increased aridity (Munson 2013, Palmquist et al. 2016b. ...
... Although sagebrush individuals may survive extremely dry soil conditions in the short term, leaf area and canopy cover are greatly reduced (Kolb and Sperry 1999). In many cases, these hydrological changes will decrease the likelihood of seedling survival, key to maintaining a healthy population, in the future (Lysne 2005, Bradford et al. 2014, Palmquist et al. 2016b), especially in drier sites (Renwick et al. 2017, Kleinhesselink and. At the same time, recruitment and growth may increase in the cooler (Renwick et al. 2017, Kleinhesselink and and wetter (Flerchinger et al. 2019) portions of the current sagebrush range. ...
... NGSTMAX (Shi et al. 2018). In much of the sagebrush biome, precipitation is concentrated in the winter, making snowpack and overall winter moisture, a major crux for sagebrush propagation (Palmquist et al. 2016b) and limitation to the primary growing season of March-June. In the north and east portions of the biome, precipitation tends to less winter-dominated, where precipitation patterns in April-July are strongly related to net primary production (NPP, e.g., Chen et al. 2019). ...
Article
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Climate change over the past century has altered vegetation community composition and species distributions across rangelands in the western United States. The scale and magnitude of climatic influences are unknown. While many studies have projected the effects of climate change using several modeling approaches, none has evaluated the impacts to fractional component cover at a 30‐m resolution across the full sagebrush (Artemisia spp.) biome. We used fractional component cover data for rangeland functional groups and weather data from the 1985 to 2018 reference period in conjunction with soils and topography data to develop empirical models describing the spatiotemporal variation in component cover. To investigate the ramifications of future change across the western United States, we extended models based on historical relationships over the reference period to model landscape effects based on future weather conditions from two emission scenarios and three time periods (2020s, 2050s, and 2080s). We tested both generalized additive models (GAMs) and regression tree models, finding that the former led to superior spatial and statistical results. Our results indicate more xeric vegetation across most of the study area, with an increasing dominance of non‐sagebrush shrubs, annual herbaceous cover, and bare ground over herbaceous and sagebrush cover in both the representative concentration pathway (RCP) 4.5 and 8.5 scenarios. In general, both scenarios yielded similar results, but RCP 8.5 tended to be more extreme, with greater change relative to the reference period. Results demonstrate that in cool sites some degree of warming to growing season maximum temperature or nongrowing season minimum temperature could be beneficial to sagebrush and shrub growth. However, warming nongrowing season maximum temperature was beneficial to shrub, but not to sagebrush growth. Our results inform rangeland managers of potential future vegetation composition, cover, and species distributions, which could improve prioritization of conservation and restoration efforts.
... In this region, temperature is projected to increase on average by 5.5°C by the end of the 21st century under representative concentration pathway RCP8.5, while predictions for precipitation are more uncertain, with potential increases or decreases of 10% possible (IPCC 2013, Anderegg andDiffenbaugh 2015). Palmquist et al. (2016) explored climate change impacts on water balance for big sagebrush ecosystems using a process-based soil water simulation model and found that on average soils may be wetter in the future during the late fall to early spring due to projected increases in cold-season precipitation, but will likely dry out more rapidly and remain drier for a longer portion of the growing season, due to shifts in transpiration, evaporation, and groundwater recharge to earlier in the year. These results reflect region-wide expectations for big sagebrush ecosystems, but do not capture the important spatial variability in ecohydrological responses to climate change that may emerge in response to gradients of precipitation, temperature, elevation, topography, and soil properties across the western United States (Miller et al. 2011, Chambers et al. 2014a. ...
... In addition, future climatic regimes will likely be contingent on elevation, with anticipated increases in precipitation at higher elevations and decreases at lower elevations (IPCC 2013). The ratio of precipitation falling as snow and the duration of snowpack is predicted to decrease across much of the western United States, but particularly for lower elevations in the southwestern United States (Brown and Mote 2009, Klos et al. 2014, Palmquist et al. 2016. Collectively, these changes may result in considerably drier conditions in the southwest United States (Diffenbaugh et al. 2008, Abatzoglou and Kolden 2011, Anderegg and Diffenbaugh 2015, which are already being realized (Seager et al. 2007) and potentially wetter conditions in the northeastern portion of the western United States (Maloney et al. 2014, Melillo et al. 2014. ...
... We used 898 sites described in Schlaepfer et al. (2012a) and Palmquist et al. (2016), which are located within a 3.1 9 10 6 km 2 region of the western United States (Fig. 1). We chose these sites randomly from land cover data from regional gap analysis programs (GAP, grid cells of ❖ www.esajournals.org ...
Article
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Ecohydrological responses to climate change will exhibit spatial variability and understanding the spatial pattern of ecological impacts is critical from a land management perspective. To quantify climate change impacts on spatial patterns of ecohydrology across shrub steppe ecosystems in North America, we asked the following question: How will climate change impacts on ecohydrology differ in magnitude and variability across climatic gradients, among three big sagebrush ecosystems (SB-Shrubland, SB-Steppe, SB-Montane), and among Sage-grouse Management Zones? We explored these potential changes for mid-century for RCP8.5 using a process-based water balance model (SOILWAT) for 898 big sagebrush sites using site-and scenario-specific inputs. We summarize changes in available soil water (ASW) and dry days, as these ecohydrological variables may be helpful in guiding land management decisions about where to geographically concentrate climate change mitigation and adaptation resources. Our results suggest that during spring, soils will be wetter in the future across the western United States, while soils will be drier in the summer. The magnitude of those predictions differed depending on geographic position and the ecosystem in question: Larger increases in mean daily spring ASW were expected for high-elevation SB-Montane sites and the eastern and central portions of our study area. The largest decreases in mean daily summer ASW were projected for warm, dry, mid-elevation SB-Montane sites in the central and west-central portions of our study area (decreases of up to 50%). Consistent with declining summer ASW, the number of dry days was projected to increase rangewide, but particularly for SB-Mon-tane and SB-Steppe sites in the eastern and northern regions. Collectively, these results suggest that most sites will be drier in the future during the summer, but changes were especially large for mid-to high-elevation sites in the northern half of our study area. Drier summer conditions in high-elevation, SB-Montane sites may result in increased habitat suitability for big sagebrush, while those same changes will likely reduce habitat suitability for drier ecosystems. Our work has important implications for where land managers should prioritize resources for the conservation of North American shrub steppe plant communities and the species that depend on them.
... In the coming century, climate change is projected to impact precipitation and temperature regimes worldwide (IPCC 2022), with especially large effects on arid and semiarid landscapes (Palmquist et al. 2016). Predictions for the Intermountain West include increased winter temperatures that will reduce snowpacks and result in earlier spring snowmelt (Barnett et al. 2005;Klos et al. 2014), with important consequences for the amount and timing of soil water recharge (Schlaepfer et al. 2012). ...
... Predictions for the Intermountain West include increased winter temperatures that will reduce snowpacks and result in earlier spring snowmelt (Barnett et al. 2005;Klos et al. 2014), with important consequences for the amount and timing of soil water recharge (Schlaepfer et al. 2012). In addition, higher temperatures are expected to increase evaporative demand, causing soils to dry out earlier in the year and contributing to longer and drier summer conditions (Palmquist et al. 2016). Shifting patterns of precipitation, increasing temperatures, and rising CO 2 levels are likely to impact western public lands through alteration of fire regimes and an increased spread of exotic annual grasses (Creutzburg et al. 2015; Mote et al. 2019). ...
... By removing livestock before most spring and summer precipitation occurs, it was assumed plants would be able to store carbohydrates, set seed, and maintain their vigor (USDI BLM 2003b). But climate change is projected to result in drier summer conditions (Palmquist et al. 2016) where soil moisture will not be available for regrowth. This will affect native plants to a much greater extent than exotic annuals. ...
Article
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Public lands of the USA can play an important role in addressing the climate crisis. About 85% of public lands in the western USA are grazed by domestic livestock, and they influence climate change in three profound ways: (1) they are significant sources of greenhouse gases through enteric fermentation and manure deposition; (2) they defoliate native plants, trample vegetation and soils, and accelerate the spread of exotic species resulting in a shift in landscape function from carbon sinks to sources of greenhouse gases; and (3) they exacerbate the effects of climate change on ecosystems by creating warmer and drier conditions. On public lands one cow-calf pair grazing for one month (an “animal unit month” or “AUM”) produces 875 kg CO 2 e through enteric fermentation and manure deposition with a social carbon cost of nearly $36 per AUM. Over 14 million AUMs of cattle graze public lands of the western USA each year resulting in greenhouse gas emissions of 12.4 Tg CO 2 e year ⁻¹ . The social costs of carbon are > $500 million year ⁻¹ or approximately 26 times greater than annual grazing fees collected by managing federal agencies. These emissions and social costs do not include the likely greater ecosystems costs from grazing impacts and associated livestock management activities that reduce biodiversity, carbon stocks and rates of carbon sequestration. Cessation of grazing would decrease greenhouse gas emissions, improve soil and water resources, and would enhance/sustain native species biodiversity thus representing an important and cost-effective adaptive approach to climate change.
... Additionally, recent warming associated with climate change has been impacting the big sagebrush region by reducing snowpack and snow season (Mote et al. 2018, Zeng et al. 2018, increasing burned area and fire season length (Dennison et al. 2014, Abatzoglou andWilliams 2016), and exacerbating regional droughts, particularly in the Southwestern U.S. (Williams et al. 2020). Projected 21st century climate change (U.S. Global Change Research Program 2017) is expected to intensify these trends (Coates et al. 2016) and increase drought risk (Cook et al. 2015), particularly in warm and southern areas of the big sagebrush region, whereas projected increases in growing season duration and cold-season precipitation may promote big sagebrush in cool and northern regions (Schlaepfer et al. 2012a, Palmquist et al. 2016a, Renwick et al. 2018, Flerchinger et al. 2020. ...
... v www.esajournals.org 5 August 2021 v Volume 12(8) v Article e03695 Tietjen et al. 2017) and North American dry grasslands (e.g., Bradford et al. 2014b, Lauenroth et al. 2014, dry forests , and shrublands (e.g., Schlaepfer et al. 2012b, Palmquist et al. 2016b, Renne et al. 2019 including simulations under climate change projections (Schlaepfer et al. 2012a, c, 2015, Palmquist et al. 2016a). ...
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Regeneration is an essential demographic step that affects plant population persistence, recovery after disturbances, and potential migration to track suitable climate conditions. Challenges of restoring big sagebrush (Artemisia tridentata) after disturbances including fire‐invasive annual grass interactions exemplify the need to understand the complex regeneration processes of this long‐lived, woody species that is widespread across the semiarid western U.S. Projected 21st century climate change is expected to increase drought risks and intensify restoration challenges. A detailed understanding of regeneration will be crucial for developing management frameworks for the big sagebrush region in the 21st century. Here, we used two complementary models to explore spatial and temporal relationships in the potential of big sagebrush regeneration representing (1) range‐wide big sagebrush regeneration responses in natural vegetation (process‐based model) and (2) big sagebrush restoration seeding outcomes following fire in the Great Basin and the Snake River Plains (regression‐based model). The process‐based model suggested substantial geographic variation in long‐term regeneration trajectories with central and northern areas of the big sagebrush region remaining climatically suitable, whereas marginal and southern areas are becoming less suitable. The regression‐based model suggested, however, that restoration seeding may become increasingly more difficult, illustrating the particularly difficult challenge of promoting sagebrush establishment after wildfire in invaded landscapes. These results suggest that sustaining big sagebrush on the landscape throughout the 21st century may climatically be feasible for many areas and that uncertainty about the long‐term sustainability of big sagebrush may be driven more by dynamics of biological invasions and wildfire than by uncertainty in climate change projections. Divergent projections of the two models under 21st century climate conditions encourage further study to evaluate potential benefits of re‐creating conditions of uninvaded, unburned natural big sagebrush vegetation for post‐fire restoration seeding, such as seeding in multiple years and, for at least much of the northern Great Basin and Snake River Plains, the control of the fire‐invasive annual grass cycle.
... Long-term deficits in available water associated with prolonged droughts and a changing climate threaten production systems and ecosystem resilience in many arid and semiarid regions worldwide. Reduced snowpack [1], shifts from snow to rain-dominated precipitation [2], and reduced groundwater recharge [3][4][5] can severely impact water availability for human and environmental use. Seasonal timing of precipitation is a key factor influencing the water balance, and therefore water availability, in sagebrush steppe ecosystems [6], particularly in regions with already variable precipitation patterns [7]. ...
... In particular, the encroachment of juniper (Juniperus spp.) in sagebrush steppe ecosystems has been associated with altered flow regimes [9], earlier snowmelt and increased evapotranspiration [10], and increased overland flow and erosion [11]. In the sagebrush steppe ecosystems of the Great Basin, the combined effects of woody plant encroachment [10,12] and increased temperatures and precipitation variability associated with climate change [2,13] can alter the seasonal water balance. ...
Article
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The combined impacts of woody plant encroachment and climate variability have the potential to alter the water balance in many sagebrush steppe ecosystems in the Western USA, leading to reduced water availability in these already water-scarce regions. This study compared the water-balance characteristics of two adjacent semiarid watersheds in central Oregon, USA: one dominated by big sagebrush and one dominated by western juniper. Precipitation, springflow, streamflow, shallow groundwater levels, and soil moisture were measured. The potential evapotranspiration was calculated using the Hargreaves–Samani method. Potential evapotranspiration and a water-balance approach were used to calculate seasonal actual evapotranspiration. The shallow aquifer recharge was calculated using the Water-Table-Fluctuation-Method. Evapotranspiration, followed by deep percolation, accounted for the largest portion (83% to 86% of annual precipitation) of water output for both watersheds. Springflow and streamflow rates were generally greater at the sagebrush-dominated watershed. Snow-dominated years showed greater amounts of groundwater recharge and deep percolation than years where a larger portion of precipitation fell as rain, even when total annual precipitation amounts were similar. This study’s results highlight the role of vegetation dynamics, such as juniper encroachment, and seasonal precipitation characteristics, on water availability in semiarid rangeland ecosystems.
... The supply is driven by meteorological patterns that determine the spatial availability of soil water and timing of plantavailable soil water (Loik et al., 2004). Soil water availability for plants is also affected by soil texture, rooting patterns, and plant community composition (Palmquist et al., 2016a). The atmospheric demand is a consequence of water vapor pressure and temperature; as air temperature warms, the atmosphere can hold more water. ...
... This loss of SWE exceeds the water storage capacity of Lake Mead, the West's largest reservoir (32 km 3 of water). The change from snow to rain in conjunction with higher temperatures is likely to accelerate current trends and decrease the depth of soil water recharge, produce earlier starts of the growing season, and shorten the duration of soil water availability, resulting in hotter summers with longer periods of drysoil conditions (Palmquist et al., 2016a(Palmquist et al., , 2016bGergel et al., 2017). ...
Article
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Climate change is already resulting in changes in cold desert ecosystems, lending urgency to the need to understand climate change effects and develop effective adaptation strategies. In this review, we synthesize information on changes in climate and hydrologic processes during the past century for the Great Basin and Columbia Plateau and discuss future projections for the 21st century. We develop midcentury projections of temperature and climate for the Great Basin and Columbia Plateau at timescales relevant to managers (2020 − 2050) and discuss concepts and strategies for adapting to the projected changes. For the instrumented record in the Great Basin and Columbia Plateau (1985 − 2011), a temperature increase of 0.7 − 1.4°C has been documented, but changes in precipitation have been relatively minor with no clear trends. Climate projections for 2020 − 2050 indicate that temperatures will continue to increase, especially in winter and during the night. Precipitation is more difficult to project, and estimates range from an 11% decrease to 25% increase depending on location. Recent records indicate that the Great Basin and Columbia Plateau are becoming more arid, a trend that is projected to continue. Droughts are likely to become more frequent and last longer, invasive annual grasses are likely to continue to expand, and the duration and severity of wildfire seasons are likely to increase. Climate projections can help in developing adaptive management strategies for actual or expected changes in climate. Strategies include reducing the risks of nonnative invasive plant spread and wildfires that result in undesirable transitions, planning for drought, and where necessary, facilitating the transition of populations, communities, and ecosystems to new climatic conditions. A proactive approach to planning for and adapting to climate change is needed, and publicly available Internet-based resources on climate data and planning strategies are available to help meet that need.
... These issues are particularly pertinent for dryland ecosystems, as soil water availability and temperature are often key limiting factors for plant growth, influence plant species composition and richness (Butterfield andMunson 2016, Pennington et al. 2017), and are expected to change in the coming century (Palmquist et al. 2016a, b, Schlaepfer et al. 2017. Several lines of evidence suggest dryland ecosystems are already being exposed to increasingly extreme climate conditions, including increases in the frequency of extreme events (Trenberth et al. 2014, Wu et al. 2015, large-scale drought (Seager et al. 2007, Cook et al. 2015, and drought-related mortality (Fensham et al. 2015, Meddens et al. 2015. ...
... Climate change and altered disturbance regimes are expected to impact drylands in the future (Palmquist et al. 2016a, b, Schlaepfer et al. 2017) and alter competitive hierarchies. Thus, quantifying the direct and indirect effects of climate change will be critical for understanding future plant community responses. ...
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2018. STEPWAT2: an individual-based model for exploring the impact of climate and disturbance on dryland plant communities. Ecosphere 9(8): Abstract. The 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 sage-brush 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 sage-brush-dominated plant communities to demonstrate the functionality of STEPWAT2, as these communities are among the most widespread dryland ecosystems in North America.
... Analyses of recent climate change in the Great Basin indicate that seasonal soil water availability and soil temperature variables related to plant growth are already changing (Snyder et al. 2019). Climate change projections indicate that higher temperatures combined with decreases in snow-to-rain ratios are likely to accelerate current trends, resulting in decreases in depth of soil water recharge, earlier starts of the growing season, shorter duration of soil water, and ultimately longer periods of dry soil conditions (Palmquist et al. 2016a,b, Gergel et al. 2017. ...
... Lines above bars are 1 SE. evapotranspiration (Palmquist et al. 2016a). Drier late spring and summer conditions at mid and upper elevation in the northern distribution of sagebrush may maintain or increase suitability for big sagebrush, but those conditions may decrease suitability at lower elevations (Palmquist et al. 2016b). ...
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Changing climatic conditions prompt concerns about vegetation response to disturbance under future compared to past conditions. In this long‐term study, we examined soil climate and vegetation differences at lower, mid, and upper elevations in two separate locations in the Great Basin, USA. We hypothesized that soil climate and vegetation associations across the elevational gradient could help predict responses under future warming and drying. We measured soil water availability, soil temperatures, and vegetation cover in relation to fire and perennial herb removal at each elevation for 13–17 yr after treatment. Seasonal soil water availability increased, while soil temperature‐related variables decreased with increasing elevation. Soil water availability in spring was positively correlated with October through June precipitation (r2 = 0.53), while water availability in spring through fall was positively correlated with perennial plant cover (r2 = 0.65). Partition models separated low, mid, and high elevations by spring soil water availability and growing degree days when soil water was available (R2 = 0.93). Current soil climate and vegetation conditions at lower elevations could indicate future conditions at higher elevations under a warmer and drier climate. During the first years after removal of perennial grasses and forbs, there was an increase in soil water availability in spring at 13–30 cm soil depth that was associated with sagebrush establishment, particularly at upper elevations. In subsequent years, sagebrush continued to dominate even though little difference in soil water availability existed between disturbed and undisturbed plots. This indicates that quickly establishing sagebrush preempted resources and reduced perennial herb recovery. Resource preemption after disturbance will likely be a major driver of plant succession in the future as in the past. Species that establish best under future warmer and drier conditions are most likely to dominate after disturbance. A negative correlation (r2 = 0.34) between the standard deviation of annual spring soil water availability and perennial vegetation cover, which helps resist annual grass invasion, supports the hypothesis that greater resource fluctuation is associated with greater plant community invasibility. Current responses to fire and loss of native plant cover across elevational gradients can indicate future responses under a warmer and drier climate.
... Additionally, climate change is an emerging threat to big sagebrush communities. Global Climate Models (GCMs) suggest that temperatures in western North America will likely be warmer (IPCC 2013) and soils will likely be drier for longer time periods during the summer (Bradford et al. 2014, Klos et al. 2014, Palmquist et al. 2016. Climate change will likely affect the timing of snowmelt (Bradford et al. 2014), which may affect forb reproduction, phenology, and mortality (Inouye 2008). ...
... TEMPERATURE.-Adler and Hille Ris Lambers (2008) hypothesized that shrub and grass functional groups may fare better under future climate change than forbs because shrubs and grasses occur in higher densities than forbs. Increased temperatures will likely cause snowmelt to occur sooner (Harte and Shaw 1995, Price and Waser 1998, Palmquist et al. 2016, with important implications for forb species because timing of snowmelt and winter precipitation influences forb phenology (Price andWaser 1998, Inouye 2008). Warmer temperatures can cause forb species to emerge sooner and die later (e.g., Munro's globemallow, Sphaeralcea munroana Douglas Spach, and Lewis flax, Linum lewisii Pursh), emerge sooner and die sooner (e.g., Palmer's penstemon, Penstemon palmeri A. Gray), or have lower emergence and higher mortality rates (e.g., tapertip hawksbeard, Crepis acuminata Nutt.; Whitcomb 2011). ...
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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.
... Climate.-An understanding of how climate influences the distribution of pygmy rabbits is not well-developed; however, they live in strongly seasonal environments. Additionally, increased precipitation seasonality coupled with longer dryer summers is predicted by current climate modeling which can negatively impact sagebrush communities (Schlaepfer et al. 2012, Palmquist et al. 2016). Using monthly temperature and precipitation normals from 1981 to 2010 (PRISM Climate Group 2012, Daly et al. 2015), we calculated 19 bioclimatic variables patterned after Hijmans et al. (2005). ...
... Finally, pygmy rabbits are predicted to experience range contractions, regional extirpations, and possibly extinction by 2080 according to current climate change modeling (Leach et al. 2015). Climate modeling predicts that longer drier summers of increased evapotranspiration may negatively impact sagebrush communities because these ecosystems have a tight relationship with precipitation seasonality and will be limited in soil water during particularly dry summers (Schlaepfer et al. 2012, Palmquist et al. 2016. Range contractions for pygmy rabbits under climate change are predicted to be driven, in part, by rising temperatures, and one estimate of the possible spatial distribution of future habitat for this species given expected climate change (Leach et al. 2015) is relatively similar to the distribution of the four core areas in our SDM (Fig. 2). ...
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Sagebrush ecosystems are affected by a variety of factors, and loss and degradation of sagebrush habitat threatens many wildlife species. Federal land management and wildlife agencies have invoked the umbrella species concept to protect this ecosystem, designating >580,000 km2 as Habitat Management Areas (HMAs) for greater sage‐grouse (Centrocercus urophasianus; hereafter “sage‐grouse”) putatively benefiting multiple wildlife species. The pygmy rabbit (Brachylagus idahoensis) also is a species of conservation concern due to its obligate relationship with the sagebrush ecosystem, and our goal was to evaluate the degree to which grouse‐focused HMAs might serve as a conservation umbrella for pygmy rabbit habitat. We acquired 18,598 records of pygmy rabbit occurrence from all eight range states (excluding Washington because that population is undergoing reintroduction); after screening for reliability, we retained 10,420 records, which we used to estimate minimum occupied area (MOA) and to create an inductive species distribution model (SDM) for pygmy rabbits across their full geographic range. We used the program Maxent to build models of varying complexity, incorporating topographic, vegetation, fire, climate, and soil information. The pygmy rabbit MOA is estimated at 28,367 km2, and ~92% of this area is included within sage‐grouse HMAs. We identified 224,820 km2 of suitable habitat for pygmy rabbits (maximum test sensitivity plus specificity threshold of 0.3167) and 145,725 km2 of primary habitat (equal test sensitivity and specificity threshold 0.4661), with concentrations in four distinct core areas. Overlap with sage‐grouse HMAs was high (87% of suitable habitat and 91% of primary habitat), suggesting that the sage‐grouse umbrella has the potential to conserve habitat for pygmy rabbits. Two of the largest HMAs are Priority Habitat Management Areas (PHMAs; which have the most habitat protection) and General Habitat Management Areas (GHMAs; which have less protection). Our results suggest that PHMAs encompass 59% and GHMAs encompass of 34% of primary habitat for pygmy rabbits. The SDM of habitat for pygmy rabbits can be used by land managers and biologists to prioritize survey locations for pygmy rabbits and to identify areas for habitat management, conservation, or restoration.
... Results from these fixed soil simulations are presented in Appendix 3. For each cell, we estimated the relative composition of C 3 and C 4 grasses and woody plants as well as monthly biomass, litter, and root depth distributions from climate conditions (e.g., relatively more C4 grasses in warm areas with high summer precipitation, more C3 grasses in cooler areas with winter precipitation, and more shrubs in cool-dry areas with winter precipitation; Paruelo and Lauenroth, 1996) using methods described in Bradford et al. (2014b) and Palmquist et al. (2016a). ...
... In recent years, big sagebrush ecosystems have become an important focus for policy makers and natural resource managers because of the widespread changes in vegetation structure and plant species composition (Knick et al., 2011) that impact the value of these systems as crucial wildlife habitat (Connelly et al., 2000;Crawford et al., 2004). Many of the moisture variables indicate increases in soil moisture availability in the future across areas with plant communities dominated by big sagebrush, implying that they may be able to persist under a changing climate if the plant communities can adapt their phenology in response to hotter, drier summer conditions accompanied by wetter, warmer spring and fall seasons (Palmquist et al., 2016a;Renwick et al., 2017). In particular, within regions established to guide the management of the big sagebrush-dependent greater sage grouse (Centrocercus urophasianus), the abundance of aridic soil moisture regimes are expected to decline while the abundance of xeric regimes increase. ...
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Assessing landscape patterns in climate vulnerability, as well as resilience and resistance to drought, disturbance, and invasive species, requires appropriate metrics of relevant environmental conditions. In dryland systems of western North America, soil temperature and moisture regimes have been widely utilized as an indicator of resilience to disturbance and resistance to invasive plant species by providing integrative indicators of long-term site aridity, which relates to ecosystem recovery potential and climatic suitability to invaders. However, the impact of climate change on these regimes, and the suitability of the indicator for estimating resistance and resilience in the context of climate change have not been assessed. Here we utilized a daily time-step, process-based, ecosystem water balance model to characterize current and future patterns in soil temperature and moisture conditions in dryland areas of western North America, and evaluate the impact of these changes on estimation of resilience and resistance. Soil temperature increases in the twenty-first century are substantial, relatively uniform geographically, and robust across climate models. Higher temperatures will expand the areas of mesic and thermic soil temperature regimes while decreasing the area of cryic and frigid temperature conditions. Projections for future precipitation are more variable both geographically and among climate models. Nevertheless, future soil moisture conditions are relatively consistent across climate models for much of the region. Projections of drier soils are expected in most of Arizona and New Mexico, as well as the central and southern U.S. Great Plains. By contrast, areas with projections of increasing soil moisture include northeastern Montana, southern Alberta and Saskatchewan, and many areas dominated by big sagebrush, particularly the Central and Northern Basin and Range and the Wyoming Basin ecoregions. In addition, many areas dominated by big sagebrush are expected to experience pronounced shifts toward cool season moisture, which will create more area with xeric moisture conditions and less area with ustic conditions. In addition to indicating widespread geographic shifts in the distribution of soil temperature and moisture regimes, our results suggest opportunities for enhancing the integration of these conditions into a quantitative framework for assessing climate change impacts on dryland ecosystem resilience and resistance that is responsive to long-term projections.
... Here, we examine the impact of annual environmental conditions, including temperature, precipitation, snowpack, and soil moisture, on the success of sagebrush restoration after fire in the Great Basin of western North America. Big sagebrush plant communities in the Great Basin are expected to experience increased warming, declines in snowpack, and increased inter-annual variability in weather, including precipitation amount in the next century (Collins et al., 2013;Palmquist et al., 2016aPalmquist et al., , 2016b. Using field data and process-based soil water modeling at 771 plots across the Great Basin, we examine whether environmental conditions at the time of seeding can help explain the likelihood of sagebrush occurrence at plots that were seeded after fire. ...
... In Press;Hardegree et al., 2018). One of the most robust and consistent climate projections in the Great Basin is increasing temperatures which will lead to declines in snowpack, regardless of the effect on total precipitation (Collins et al., 2013;Palmquist et al., 2016a). ...
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Restoration and rehabilitation of native vegetation in dryland ecosystems, which encompass over 40% of terrestrial ecosystems, is a common challenge that continues to grow as wildfire and biological invasions transform dryland plant communities. The difficulty in part stems from low and variable precipitation, combined with limited understanding about how weather conditions influence restoration outcomes, and increasing recognition that one‐time seeding approaches can fail if they do not occur during appropriate plant establishment conditions. The sagebrush biome, which once covered over 620,000 km² of western North America, is a prime example of a pressing dryland restoration challenge for which restoration success has been variable. We analyzed field data on Artemisia tridentata (big sagebrush) restoration collected at 771 plots in 177 wildfire sites across its western range, and used process‐based ecohydrological modeling to identify factors leading to its establishment. Our results indicate big sagebrush occurrence is most strongly associated with relatively cool temperatures and wet soils in the first spring after seeding. In particular, the amount of winter snowpack, but not total precipitation, helped explain the availability of spring soil moisture and restoration success. We also find considerable inter‐annual variability in the probability of sagebrush establishment. Adaptive management strategies that target seeding during cool, wet years or mitigate effects of variability through repeated seeding may improve the likelihood of successful restoration in dryland ecosystems. Given consistent projections of increasing temperatures, declining snowpack, and increasing weather variability throughout mid‐latitude drylands, weather‐centric adaptive management approaches to restoration will be increasingly important for dryland restoration success. This article is protected by copyright. All rights reserved.
... Sagebrush is considered to have strong and tractable responses to climate (Palmquist et al. 2016), although Schlaepfer et al. (2014a) found that accounting for plot-level factors was important for modeled predictions of sagebrush regeneration. ...
... Our results are most applicable to areas that contain a big sagebrush overstory, a relatively intact perennial understory of forbs and grasses, and low abundance of exotic species. Our work contributes to knowledge about the effects of livestock grazing intensity in big sagebrush ecosystems, which are likely to experience increasing conservation challenges over the coming decades (Knick et al. 2003, Palmquist et al. 2016, Schlaepfer et al. 2017 ...
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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 otherwise. 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 stability of big sagebrush plant functional type composition under current grazing management regimes.
... Sagebrush is considered to have strong and tractable responses to climate (Palmquist et al. 2016), although Schlaepfer et al. (2014a) found that accounting for plot-level factors was important for modeled predictions of sagebrush regeneration. ...
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Context Reestablishing foundational plant species through aerial seeding is an essential yet challenging step for restoring the vast semiarid landscapes impacted by plant invasions and wildfire-regime shifts. A key component of the challenge stems from landscape variability and its effects on plant recovery. Objectives We assessed landscape correlates, thresholds, and tipping points for sagebrush presence from fine-scale sampling across a large, heterogeneous area burned the previous year, where we were able to quantify soil surface features that are typically occluded yet can strongly affect recovery patterns. Methods Hypothesis testing and binary-decision trees were used to evaluate factors affecting initial sagebrush establishment, using 2171 field plots (totaling ~ 2,000,000 m² sampled) over a 113,000-ha region. Results Sagebrush established in 50% of plots where it was seeded, a > 12-fold greater establishment frequency than in unseeded areas. Sagebrush establishment was enhanced in threshold-like ways by elevation (> 1200 m ASL), topographic features that alter heatload and soil water, and by soil-surface features such as “fertile islands” that bore the imprint of pre-fire sagebrush. Sagebrush occupancy had a negative, linear relationship with exotic-annual grass cover and parabolic relationship with perennial bunchgrasses (optimal at 40% cover). Conclusions Our approach revealed interactive, ecological relationships such as novel soil-surface effects on first year establishment of sagebrush across the burned landscape, and identified “hot spots” for recovery. The approach could be expanded across sites and years to provide the information needed to explain past seeding successes or failures, and in designing treatments at the landscape scale.
... It is possible that the current dominance gained by G. sarothrae is lost over time in the absence of fire (Morris and Leger, 2016), but such predictability is also challenged by climate change and the expected increase of late-fall to early-spring precipitation in sagebrush areas (Palmquist et al., 2016). It is well established that G. sarothrae populations are highly responsive to increased fall and spring precipitation (Ralphs and Sanders, 2002;Ralphs and McDaniel, 2011). ...
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The role of fire in restoration of sagebrush plant communities remains controversial mainly because of paucity of information from long-term studies. Here, we examine 15-year post-fire responses of big sagebrush (Artemisia tridentata ssp wyomingensis) and broom snakeweed (Gutierrezia sarothrae), the two most abundant native shrubs at the John Day Fossil Beds National Monument, a protected area in north-central Oregon, USA. Fire effects were studied along gradients of topography and community type through time post-burn. Community types were distinguished as brush, plots dominated by big sagebrush and woodland, plots with a significant presence of Western juniper (Juniperus occidentalis) trees. Fire reduced big sagebrush cover in brush plots up to 100% and in woodland plots up to 86%. Broom snakeweed cover declined by 92% and 73% in brush plots and woodland plots, respectively. Big sagebrush did not show signs of recovery 15 years after burning regardless of topography and community type while broom snakeweed populations were clearly rebounding and prospering beyond pre-burn levels. Our results showed that an area initially dominated by big sagebrush (cover of big sagebrush 10-20%, cover of broom snakeweed 2-4%) dramatically shifted to an area dominated by broom snakeweed (cover of big sagebrush < 1%, cover of broom snakeweed 5%) in brush-dominated plots. Our results indicated that brush-dominated plots at lower elevation and southern exposures are the least post-fire resilient. We also observed a declining population of big sagebrush on unburned areas, suggesting the lack of post-fire recovery on burned areas was perhaps a result of low seeding potential by extant populations. Although more years of observation are required, these data indicate that recovery time, the encroachment of opportunistic competing shrubs, and the initial condition of vegetation are essential considerations by land managers when prescribing fire in big sagebrush communities.
... Model tests suggest a 60% overall accuracy for yearly regeneration success/failure . The model obtains daily air and top-soil temperature, water potential in soil layers, and snow cover from SOILWAT2, a daily-time step, multiple soil layer, ecosystem water balance simulation model (Schlaepfer et al., 2012a;Bradford et al., 2014;Palmquist et al., 2016). The model determines favorable periods for germination, time to germination, and daily germination success and seedling emergence. ...
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A number of modeling approaches have been developed to predict the impacts of climate change on species distributions, performance and abundance. The stronger the agreement from models that represent different processes and are based on distinct and independent sources of information, the greater the confidence we can have in their predictions. Evaluating the level of confidence is particularly important when predictions are used to guide conservation or restoration decisions. We used a multi-model approach to predict climate change impacts on big sagebrush (Artemisia tridentata), the dominant plant species on roughly 43 million hectares in the western United States and a key resource for many endemic wildlife species. To evaluate the climate sensitivity of A. tridentata, we developed four predictive models, two based on empirically-derived spatial and temporal relationships, and two that applied mechanistic approaches to simulate sagebrush recruitment and growth. This approach enabled us to produce an aggregate index of climate change vulnerability and uncertainty based on the level of agreement between models. Despite large differences in model structure, predictions of sagebrush response to climate change were largely consistent. Performance, as measured by change in cover, growth, or recruitment, was predicted to decrease at the warmest sites, but increase throughout the cooler portions of sagebrush's range. A sensitivity analysis indicated that sagebrush performance responds more strongly to changes in temperature than precipitation. Most of the uncertainty in model predictions reflected variation among the ecological models, raising questions about the reliability of forecasts based on a single modeling approach. Our results highlight the value of a multi-model approach in forecasting climate change impacts and uncertainties, and should help land managers to maximize the value of conservation investments.
... These changes in temperature, even if precipitation does not change, can influence water cycling and alter the timing and depth of soil water available to plants. If slightly wetter winters promote greater moisture availability during winter and early spring, higher winter and spring temperatures coupled with longer and drier warm seasons indicate that soils are likely to dry out earlier in the year, further stressing these ecosystems (Palmquist et al. 2016a). ...
Technical Report
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The Science Framework is intended to link the Department of the Interior’s Integrated Rangeland Fire Management Strategy with long-term strategic conservation actions in the sagebrush biome. The Science Framework provides a multiscale approach for prioritizing areas for management and determining effective management strategies within the sagebrush biome. The emphasis is on sagebrush (Artemisia spp.) ecosystems and Greater sage-grouse (Centrocercus urophasianus). The approach provided in the Science Framework links sagebrush ecosystem resilience to disturbance and resistance to nonnative, invasive plant species to species habitat information based on the distribution and abundance of focal species. A geospatial process is presented that overlays information on ecosystem resilience and resistance, species habitats, and predominant threats and that can be used at the mid-scale to prioritize areas for management. A resilience and resistance habitat matrix is provided that can help decision makers evaluate risks and determine appropriate management strategies. Prioritized areas and management strategies can be refined by managers and stakeholders at the local scale based on higher resolution data and local knowledge. Decision tools are discussed for determining appropriate management actions for areas that are prioritized for management. Geospatial data, maps, and models are provided through the U.S. Geological Survey (USGS) ScienceBase and Bureau of Land Management (BLM) Landscape Approach Data Portal. The Science Framework is intended to be adaptive and will be updated as additional data become available on other values and species at risk. It is anticipated that the Science Framework will be widely used to: (1) inform emerging strategies to conserve sagebrush ecosystems, sagebrush dependent species, and human uses of the sagebrush system, and (2) assist managers in prioritizing and planning on-the-ground restoration and mitigation actions across the sagebrush biome.
... Soil water availability is considered to be a key limiting resource for sagebrush (Schlaepfer et al. 2014) and for many other plants that grow in arid and semi-arid environments (Noy-Meir 1973). Soil water is likely to become even less available for sagebrush in the future (Palmquist et al. 2016). Sagebrush is considered to be well adapted to withstand arid conditions and droughts (Schlaepfer et al. 2014). ...
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Models of climate change predict more variable precipitation for much of western North America, including more severe multi-year droughts. Droughts are known to increase mortality to trees although less is known about effects on shrubs from arid environments and about effects on reproduction. In this study, we followed a cohort of young sagebrush plants from 2010 to 2016, a period that included a severe drought from 2012 to 2015. Plants experienced little mortality preceding and during the drought. However, in the year following the drought, 14% of individuals died and 33% of branches on living plants died. There was little flowering in the years preceding the drought and flowering increased in each successive year from 2014 to 2016. Plants that produced more flowers in 2015 had more dead branches in 2016. Larger plants had fewer branches that died. Contrary to expectations, afternoon shade was not associated with greater survival or flowering, perhaps because shaded plants were in proximity to large trees which likely competed for water. Plants of the two common chemotypes had similar rates of survival and flowering. Experimental watering during the summer of 2015 did not affect survival and may have increased flowering in 2016. If multi-year droughts become more common in the future, even drought-adapted shrubs may be expected to suffer high rates of mortality.
... SOILWAT provides more proximate estimates of water ecosystem water balance than climate data alone by incorporating soil characteristics obtained from the STATSGO database (NRCS 1998) into estimates of long-term water availability. SOILWAT has been applied and validated in a number of semi-arid grasslands similar to those in this study (Schlaepfer et al. 2012;Bradford et al. 2014;Palmquist et al. 2016). Weather inputs to SOILWAT include mean daily temperature and precipitation, mean monthly relative humidity, wind speed, cloud cover, and latitude. ...
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Aridity is an important environmental filter in the assembly of plant communities worldwide. The extent to which root traits mediate responses to aridity, and how they are coordinated with leaf traits, remains unclear. Here, we measured variation in root tissue density (RTD), specific root length (SRL), specific leaf area (SLA), and seed size within and among thirty perennial grass communities distributed along an aridity gradient spanning 190–540 mm of climatic water deficit (potential minus actual evapotranspiration). We tested the hypotheses that traits exhibited coordinated variation (1) among species, as well as (2) among communities varying in aridity, and (3) functional diversity within communities declines with increasing aridity, consistent with the “stress-dominance” hypothesis. Across communities, SLA and RTD exhibited a coordinated response to aridity, shifting toward more conservative (lower SLA, higher RTD) functional strategies with increasing aridity. The response of SRL to aridity was more idiosyncratic and was independent of variation in SLA and RTD. Contrary to the stress-dominance hypothesis, the diversity of SRL values within communities increased with aridity, while none of the other traits exhibited significant diversity responses. These results are consistent with other studies that have found SRL to be independent of an SLA–RTD axis of functional variation and suggest that the dynamic nature of soil moisture in arid environments may facilitate a wider array of resource capture strategies associated with variation in SRL.
... These changes in temperature, even if precipitation does not change, can influence water cycling and alter the timing and depth of soil water available to plants. If slightly wetter winters promote greater moisture availability during winter and early spring, higher winter and spring temperatures coupled with longer and drier warm seasons indicate that soils are likely to dry out earlier in the year, further stressing these ecosystems (Palmquist et al. 2016a). ...
Technical Report
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The Science Framework is intended to link the Department of the Interior’s Integrated Rangeland Fire Management Strategy with long-term strategic conservation actions in the sagebrush biome. The Science Framework provides a multiscale approach for prioritizing areas for management and determining effective management strategies within the sagebrush biome. The emphasis is on sagebrush (Artemisia spp.) ecosystems and Greater sage-grouse (Centrocercus urophasianus). The approach provided in the Science Framework links sagebrush ecosystem resilience to disturbance and resistance to nonnative, invasive plant species to species habitat information based on the distribution and abundance of focal species. A geospatial process is presented that overlays information on ecosystem resilience and resistance, species habitats, and predominant threats and that can be used at the mid-scale to prioritize areas for management. A resilience and resistance habitat matrix is provided that can help decisionmakers evaluate risks and determine appropriate management strategies. Prioritized areas and management strategies can be refined by managers and stakeholders at the local scale based on higher resolution data and local knowledge. Decision tools are discussed for determining appropriate management actions for areas that are prioritized for management. Geospatial data, maps, and models are provided through the U.S. Geological Survey (USGS) ScienceBase and Bureau of Land Management (BLM) Landscape Approach Data Portal. The Science Framework is intended to be adaptive and will be updated as additional data become available on other values and species at risk. It is anticipated that the Science Framework will be widely used to: (1) inform emerging strategies to conserve sagebrush ecosystems, sagebrush dependent species, and human uses of the sagebrush system, and (2) assist managers in prioritizing and planning on-the-ground restoration and mitigation actions across the sagebrush biome.
... Our findings indicate that areas similar to JODA, which have been converted to broom snakeweed dominance, have potentially lowered resistance and should be considered areas of concern and at risk of additional invasive species establishment. The dominance of broom snakeweed is also of concern because of the expected patterns of climate change involving augmented late fall to early spring precipitation for the region (Palmquist et al., 2016). Such patterns would favor the dominance of the opportunistic broom snakeweed and medusahead over foundational species such as Wyoming big sagebrush (Bates et al., 2006). ...
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Protected-area sagebrush steppe ecosystems are few in number and increasingly important to the North American conservation network as sagebrush steppe faces growing threats from land-use, climate change, and invasive species. We analyzed the distribution and abundance of native perennial and invasive annual plants to better understand patterns of plant invasion within two protected areas: John Day Fossil Beds National Monument (JODA), located in central Oregon, and Craters of the Moon National Monument and Preserve (CRMO), located in southeast Idaho, USA. We used multivariate analysis to examine vegetation monitoring datasets and illuminate geographic variation in plant cover along gradients of well-known aspects of resistance to plant invasion (elevation, exposure [slope and aspect], precipitation and proximity to disturbance). Topographically mediated resistance to invasion appeared to manifest in the park with greater topographic variability (JODA), while increased elevation was more strongly associated with resistant sites in the park which spanned a greater elevational gradient (CRMO). Factors which may mitigate moisture mediated resistance also differed between sites. Slope and aspect were factors of apparent resistance for bunchgrass communities in JODA, while high crop year precipitation appeared to benefit medusahead (Taeniatherum caput-medusae [L.] Nevski) and the weedy native subshrub broom snakeweed (Gutierrezia sarothrae [Pursh] Britton & Rusby) over bunchgrasses and Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young). Increased elevation and distance to disturbed areas were the most important factors of resistance in forb rich communities at CRMO, with the invasive annuals cheatgrass (Bromus tectorum L.), tumblemustard (Sisymbrium altissimum L.), and Descurainia spp. Webb & Bethel. invading in low elevations and in close proximity to roads or agricultural fields. Such complexity underscores the idiosyncratic nature of the manifestation of resistance and the need for place-based empirical studies to provide information for guiding protected-area management.
... In the western US, big sagebrush (Artemisia tridentata spp.) ecosystems are the dominant dryland system [15,16], covering 48 million hectares (ha) and 13 states [17]. Despite its current extent in the US, up to 60% of the historic, pre-settlement big sagebrush range has been partially or completely converted to exotic annual grasslands because of increased disturbance to these systems and conversion to grazing and agricultural lands [18]. ...
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Nitrogen additions are known to elicit variable responses in semi-arid ecosystems, with responses increasing with precipitation. The response of semi-arid ecosystems to nitrogen are important to understand due to their large spatial extent worldwide and the global trend of increasingly available nitrogen. In this study, we evaluated the impact of a single nitrogen addition pulse on a semi-arid big sagebrush (Artemisia tridentata) ecosystem in western Wyoming. This is important given that sagebrush ecosystems are poorly understood, despite their prevalence in the western US. In addition, large-scale nitrogen additions have begun on sagebrush landscapes in Wyoming in order to mitigate population declines in mule deer (Odocoileus hemionus). The study objectives were (1) to evaluate the effectiveness of a nitrogen fertilization pulse in increasing sagebrush biomass and forage quality, and (2) to assess effects of nitrogen addition on soil biogeochemistry and vegetation community structure. We fertilized 15 plots across 5 locations in western Wyoming using a single pulse of urea (5.5g N m⁻²). In addition, we immobilized available nitrogen through surface hay treatments (250g hay/m²). Nitrogen additions failed to increase growth of sagebrush, alter nitrogen content of sagebrush leaders, or alter greenhouse gas efflux from soils. The plant community also remained unchanged; total cover, species richness, and community composition were all unaffected by our treatment application. Over the two years of this study, we did not find indications of nitrogen limitation of ecosystem processes, despite a wet growing season in 2014. Thus, we have found a general lack of response to nitrogen in sagebrush ecosystems and no treatment effect of a single pulse of N to sagebrush biomass or forage quality.
... Notably, the BLM also manages land in eastern Nevada, which has cooled slightly during this timeframe, further highlighting the challenges faced in planning for changes in this large and diverse region. Overall, however, climate models are in close agreement that the IMW will experience additional warming under all foreseeable future scenarios ( Fig. 2; IPCC 2014, Fr€ olicher et al. 2014, Palmquist et al. 2016, USGCRP 2017, Gonzalez et al. 2018. ...
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Although natural resource managers are concerned about climate change, many are unable to adequately incorporate climate change science into their adaptation strategies or management plans, and are not always aware of or do not always employ the most current scientific knowledge. One of the most prominent natural resource management agencies in the United States is the Bureau of Land Management (BLM), which is tasked with managing over 248 million acres (>1million km2) of public lands for multiple, often conflicting, uses. Climate change will affect the sustainability of many of these land uses and could further increase conflicts between them. As such, the purpose of our study was to determine the extent to which climate change will affect public land uses, and whether the BLM is managing for such predicted effects. To do so, we first conducted a systematic review of peer-reviewed literature that discussed potential impacts of climate change on the multiple land uses the BLM manages in the IntermountainWest, USA, and then expanded these results with a synthesis of projected vegetation changes. Finally, we conducted a content analysis of BLM Resource Management Plans in order to determine how climate change is explicitly addressed by BLM managers, and whether such plans reflect changes predicted by the scientific literature. We found that active resource use generally threatens intrinsic values such as conservation and ecosystem services on BLM land, and climate change is expected to exacerbate these threats in numerous ways. Additionally, our synthesis of vegetation modeling suggests substantial changes in vegetation due to climate change. However, BLM plans rarely referred to climate change explicitly and did not reflect the results of the literature review or vegetation model synthesis. Our results suggest there is a disconnect between management of BLM lands and the best available science on climate change. We recommend that the BLM actively integrates such research into on-the-ground management plans and activities, and that researchers studying the effects of climate change make a more robust effort to understand the practices and policies of public land management in order to effectively communicate the management significance of their findings.
... However, big sagebrush occupies vast landscapes, and management of sagebrush ecosystems occurs at large spatial extents. Existing research concerning the ecohydrology of big sagebrush ecosystems has been completed at scales that correspond to those at which these ecosystems are managed and monitored: watershed (Kormos et al., 2017), experimental range (Lauenroth & Bradford, 2006), and species distribution scales (Palmquist et al., 2016;Schlaepfer et al., 2012a). Therefore, quantifying interception at the plot-or stand-scale instead of the individual plant is warranted. ...
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Canopy interception loss is an important component of the water budget for many ecosystems, and may be particularly influential in semi-arid shrublands where water is limiting. In this experiment, we quantified interception loss by mountain big sagebrush (Artemisia tridentata spp. vaseyana) using simulated rainfall events in the field. Various levels of canopy cover and rainfall intensities were tested to measure their effects on net precipitation and interception loss. Additionally, the comparisons were made between three methods of measuring shrub cover to enhance scalability of results. Stands of sagebrush from 20 to 50% canopy cover intercepted 18.5 ± 12.5% of incoming precipitation. Percent interception loss differed by 13.7% between the high and low cover classes, indicating that net precipitation may be significantly reduced under mature, dense stands of sagebrush. Hemispherical photography was a viable method for estimating canopy cover in this vegetation type. Interception loss by sagebrush was 14% lower on average than pinyon and juniper measured in the same watershed. Results from this study quantified the effects of sagebrush canopy on rainfall interception and improved understanding of vegetation dynamics in the sagebrush steppe. This article is protected by copyright. All rights reserved.
... Interannual variability may strongly influence ecosystem responses to climate change (Werner et al., 2020). Climate projections indicate declining snowpack, warming temperatures and increased variability in soil water availability in cold deserts of the western U.S. (Klos et al., 2014;Palmquist et al., 2016;Schlaepfer et al., 2012). ...
Article
Key to the long‐term resilience of dryland ecosystems is the recovery of foundation plant species following disturbance. In ecosystems with high interannual weather variability, understanding the influence of short‐term environmental conditions on establishment of foundation species is essential for identifying vulnerable landscapes and developing restoration strategies. We asked how annual environmental conditions affect post‐fire establishment of Artemisia tridentata, a shrub species that dominates landscapes across much of the western United States, and evaluated the influence of episodic establishment on population recovery. We collected A. tridentata stem samples from 33 plots in 12 prescribed fire sites that burned 8‐11 years before sampling. We determined individual establishment years using annual growth rings. We measured seasonal soil environmental conditions at the study sites and asked if these conditions predicted annual establishment density. We then evaluated whether establishment patterns could be predicted by site‐level climate or dominant subspecies. Finally, we tested the effect of the magnitude and frequency of post‐fire establishment episodes on long‐term population recovery. Annual post‐fire recruitment of A. tridentata was driven by the episodic availability of spring soil moisture. Annual establishment was highest with wetter spring soils (relative influence [RI] = 19.4%) and later seasonal dry‐down (RI = 11.8%) in the year of establishment. Establishment density declined greatly four to five years after fire (RI = 17.1%). Post‐fire establishment patterns were poorly predicted by site‐level mean climate (marginal R2 ≤ 0.18) and dominant subspecies (marginal R2 ≤ 0.43). Population recovery reflected the magnitude, but not the frequency, of early post‐fire establishment pulses. Post‐fire A. tridentata density and cover (8‐11 years after fire) were more strongly related to the magnitude of the largest establishment pulse than to establishment frequency, suggesting that population recovery may occur with a single favorable establishment year. Synthesis and applications. This study demonstrates the importance of episodic periods of favorable weather for long‐term plant population recovery following disturbance. Management strategies that increase opportunities for seed availability to coincide with favorable weather conditions, such as retaining unburned patches or repeated seeding treatments, can improve restoration outcomes in high‐priority areas.
... Simultaneously, disturbance and extreme events, such as severe wildfires, droughts or heat waves, can also catalyze rapid shifts in forest structure and composition by killing established, large trees. Increases in storm intensity (Polade et al. 2017) may promote greater water loss to deep drainage in spring months and longer and hotter periods of dry soils in summer (Palmquist et al. 2016. Indeed, forest transitions have already been observed and are expected to continue across western North America and other dry areas (Breshears et al. 2009, Allen et al. 2010, Williams et al. 2013, Stevens-Rumann et al. 2017. ...
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Increasing aridity is a challenge for forest managers and reducing stand density to minimize competition is a recognized strategy to mitigate drought impacts on growth. In many dry forests, the most widespread and common forest management programs currently being implemented focus on restoration of historical stand structures, primarily to minimize fire risk and enhance watershed function. The implications of these restoration projects for drought vulnerability are not well understood. Here, we examined how planned restoration treatments in the Four Forests Restoration Initiative, the largest forest restoration project in the United States, would alter landscape‐scale patterns of forest growth and drought vulnerability throughout the 21st century. Using drought–growth relationships developed within the landscape, we considered a suite of climate and treatment scenarios and estimated average forest growth and the proportion of years with extremely low growth as a measure of vulnerability to long‐term decline. Climatic shifts projected for this landscape include higher temperatures and shifting seasonal precipitation that promotes lower soil moisture availability in the early growing season and greater hot‐dry stress, conditions negatively associated with tree growth. However, drought severity and the magnitude of future growth declines were moderated by the thinning treatments. Compared to historical conditions, proportional growth in mid‐century declines by ~40% if thinning ceases or continues at the status quo pace. By comparison, proportional growth declines by only 20% if the Four Forest Restoration Initiative treatments are fully implemented, and <10% if stands are thinned even more intensively than currently planned. Furthermore, restoration treatments resulted in dramatically fewer years with extremely low growth in the future, a recognized precursor to forest decline and eventual tree mortality. Benefits from density reduction for mitigating drought‐induced growth declines are more apparent in mid‐century and under RCP4.5 than under RCP8.5 at the end of the century. Future climate is inherently uncertain, and our results only reflect the climate projections from the representative suite of models examined. Nevertheless, these results indicate that forest restoration projects designed for other objectives also have substantial benefits for minimizing future drought vulnerability in dry forests and provide additional incentive to accelerate the pace of restoration.
... Future conditions in the Great Basin are predicted to be warmer with more variable precipitation (Palmquist et al., 2016), invasive annual grasses continue to spread across western North America, and associated fire frequencies are expected to increase (Fusco et al., 2019). Therefore, "favorable" restoration years and suitable mean site conditions (Schlaepfer et al., 2014a) may become rarer regionally, as the total area requiring restoration intervention expands, possibly without a comparable increase in resources for restoration. ...
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Interannual variation, especially weather, is an often‐cited reason for restoration “failures”; yet its importance is difficult to experimentally isolate across broad spatiotemporal extents, due to correlations between weather and site characteristics. We examined post‐fire treatments within sagebrush‐steppe ecosystems to ask: (1) Is weather following seeding efforts a primary reason why restoration outcomes depart from predictions? and (2) Does the management‐relevance of weather differ across space and with time since treatment? Our analysis quantified range‐wide patterns of sagebrush (Artemisia spp.) recovery, by integrating long‐term records of restoration and annual vegetation cover estimates from satellite imagery following thousands of post‐fire seeding treatments from 1984 to 2005. Across the Great Basin, sagebrush growth increased in wetter, cooler springs; however, the importance of spring weather varied with sites' long‐term climates, suggesting differing ecophysiological limitations across sagebrush's range. Incorporation of spring weather, including from the “planting year,” improved predictions of sagebrush recovery, but these advances were small compared to contributions of time‐invariant site characteristics. Given extreme weather conditions threatening this ecosystem, explicit consideration of weather could improve the allocation of management resources, such as by identifying areas requiring repeated treatments; but improved forecasts of shifting mean conditions with climate change may more significantly aid the prediction of sagebrush recovery.
... Studies using climatic niche models and mechanistic ecohydrology models suggest declining opportunities for sagebrush suitability and seedling establishment. These different models show that the trailing (southern) edge of sagebrush taxa is contracting due to increasing aridity (Still & Richardson, 2015) and decreasing soil water (Schlaepfer et al., 2015;Palmquist et al., 2016). It is possible that delayed flowering and subsequent seed development could have a negative feedback by limiting the opportunities sagebrush seed can imbibe and establish under favorable conditions. ...
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Rising temperatures have begun to shift flowering time, but it is unclear whether phenotypic plasticity can accommodate projected temperature change for this century. Evaluating clines in phenological traits and the extent and variation in plasticity can provide key information on assessing risk of maladaptation and developing strategies to mitigate climate change. In this study, flower phenology was examined in 52 populations of big sagebrush (Artemisia tridentata) growing in three common gardens. Flowering date (anthesis) varied 91 days from late July to late November among gardens. Mixed-effects modeling explained 79% of variation in flowering date, of which 46% could be assigned to plasticity and genetic variation in plasticity and 33% to genetics (conditional R2 = 0.79, marginal R2 = 0.33). Two environmental variables that explained the genetic variation were photoperiod and the onset of spring, the Julian date of accumulating degree days > 5°C reaching 100. The genetic variation was mapped for contemporary and future climates (decades 2060 and 2090), showing flower date change varies considerably across the landscape. Plasticity was estimated to accommodate, on average, a +/- 13-day change in flowering date. However, the examination of genetic variation in plasticity suggests that the magnitude of plasticity could be affected by variation in the sensitivity to photoperiod and temperature. In a warmer common garden, lower latitude populations have greater plasticity (+16 days) compared to higher latitude populations (+10 days). Mapped climatypes of flowering date for contemporary and future climates illustrate the wide breadth of plasticity and large geographic overlap. Our research highlights the importance of integrating information on genetic variation, phenotypic plasticity and climatic niche modeling to evaluate plant responses and elucidate vulnerabilities to climate change. This article is protected by copyright. All rights reserved.
... To compare effectiveness of the GLMM an R 2 value is listed. Model variable significance is represented through bolded values (α=0.05).predicted to include increases in daytime minimum temperatures by 2°C as well as increases in winter precipitation in the form of rain(Palmquist et al 2016, Brabec et al 2017, Snyder et al 2019. Our results suggest that a 2°C increase in daytime minimum temperatures would cause a ∼13% reduction in sagebrush establishment probability (figure 3). ...
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Ecological droughts are deficits in soil-water availability that induce threshold-like ecosystem responses, such as causing altered or degraded plant-community conditions, which can be exceedingly difficult to reverse. However, 'ecological drought' can be difficult to define, let alone to quantify, especially at spatial and temporal scales relevant to land managers. This is despite a growing need to integrate drought-related factors into management decisions as climate changes result in precipitation instability in many semi-arid ecosystems. We asked whether success in restoration seedings of the foundational species big sagebrush (Artemisia tridentata) was related to estimated water deficit, using the SoilWat2 model and data from >600 plots located in previously burned areas in the western United States. Water deficit was characterized by: 1) the standardized precipitation-evapotranspiration index (SPEI), a coarse-scale drought index, and 2) the number of days with wet and warm conditions in the near-surface soil, where seeds and seedlings germinate and emerge (i.e. days with 0-5 cm deep soil water potential > -2.5 MPa and temperature above 0 °C). 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.
... Factors defining these contexts include weather (Booth et al., 1999;Huber-Sannwald and Pyke, 2005;Maier et al., 2001;Schlaepfer et al., 2012a), soil conditions (Nelson et al., 2014;Smith et al., 1988), reclamation and site preparation (Allen-Diaz and Bartolome, 1998;Booth et al., 1999;Pyke, 2011;Ziegenhagen and Miller, 2009), and interspecific competition (Booth et al., 1999;Rinella et al., 2015). Interactions between temperature and precipitation are particularly important in semi-arid ecosystems because temperature is a fundamental driver of evaporative losses and transpiration by plants (evapotranspiration; Dhungel et al., 2014;Malek et al., 1997;Palmquist et al., 2016a), and characterizing the ecohydrological niche of these ecosystems is necessary for understanding resilience (Chambers et al., 2014a). Sagebrush ecosystems primarily recharge their water during winter and spring and the top soil layers dry out first while deeper soil layers remain moist for extended periods (Schlaepfer et al., 2012a(Schlaepfer et al., , 2012b. ...
Article
Using localized studies to understand how ecosystems recover can create uncertainty in recovery predictions across landscapes. Large archives of remote sensing data offer opportunities for quantifying the spatial and temporal factors influencing recovery at broad scales and predicting recovery. For example, energy production is a widespread and expanding land use among many semi-arid ecosystems of the Western United States dominated by sagebrush (Artemisia spp.), a keystone species providing a variety of ecological services. With remotely-sensed (Landsat) estimates of vegetation cover collected every 2-5 years from southwestern Wyoming, USA, over nearly three decades (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. We found the rate of change in sage-brush 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. These predictions and maps could inform future restoration efforts as they reflect resilience. This approach also is applicable to other disturbance types (e.g., fires and vegetation removal treatments) across landscapes, which can further improve conservation efforts by characterizing past conditions and monitoring trends in subsequent years.
... Yet, the comparison among oil and gas development and climate impacts were not equal as climate responses were driven only by changes in vegetation and indirect responses to climate were not available or implemented as they were for development. Climate can affect many sagebrush system processes and states (Palmquist et al. 2016b), and could have lagged effects on sage-grouse demography as a result of changes in temperature and precipitation, interspecific interactions, physiological intolerances, catastrophes, and challenges associated with increasingly severe weather (Foden et al. 2008, Gibson et al. 2017. As our future climate analyses focused only on precipitation change, future research at broader spatial extents would benefit from the development of vegetation forecasts that incorporate both temperature and precipitation to refine expected habitat outcomes. ...
Article
Multiple environmental stressors impact wildlife populations, but we often know little about their cumulative and combined influences on population outcomes. We generally know more about past effects than potential future impacts, and direct influences such as changes of habitat footprints than indirect, long-term responses in behavior, distribution, or abundance. Yet, an understanding of all these components is needed to plan for future landscapes that include human activities and wildlife. We developed a case study to assess how spatially explicit individual-based modeling could be used to evaluate future population outcomes of gradual landscape change from multiple stressors. For Greater Sage-grouse in southwest Wyoming, USA, we projected oil and gas development footprints and climate-induced vegetation changes 50 years into the future. Using a time-series of planned oil and gas development and predicted climate-induced changes in vegetation, we recalculated habitat selection maps to dynamically modify future habitat quantity, quality, and configuration. We simulated long-term Sage-grouse responses to habitat change by allowing individuals to adjust to shifts in habitat availability and quality. The use of spatially explicit individual-based modeling offered a useful means of evaluating delayed indirect impacts of landscape change on wildlife population outcomes. The inclusion of movement and demographic responses to oil and gas infrastructure resulted in substantive changes in distribution and abundance when cumulated over several decades and throughout the regional population. When combined, additive development and climate-induced vegetation changes reduced abundance by up to half of the original size. In our example, the consideration of only a single population stressor the final possible population size by as much as 50%. Multiple stressors and their cumulative impacts need to be broadly considered through space and time to avoid underestimating the impacts of multiple gradual changes and overestimating the ability of populations to withstand change.
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Dryland ecosystems may be especially vulnerable to expected 21st century increases in temperature and aridity because they are tightly controlled by moisture availability. However, climate impact assessments in drylands are difficult because ecological dynamics are dictated by drought conditions that are difficult to define and complex to estimate from climate conditions alone. In addition, precipitation projections vary substantially among climate models, enhancing variation in overall trajectories for aridity. Here, we constrain this uncertainty by utilizing an ecosystem water balance model to quantify drought conditions with recognized ecological importance, and by identifying changes in ecological drought conditions that are robust among climate models, defined here as when >90% of models agree in the direction of change. Despite limited evidence for robust changes in precipitation, changes in ecological drought are robust over large portions of drylands in the United States and Canada. Our results suggest strong regional differences in long‐term drought trajectories, epitomized by chronic drought increases in southern areas, notably the Upper Gila Mountains and South‐Central Semi‐arid Prairies, and decreases in the north, particularly portions of the Temperate and West‐Central Semi‐arid Prairies. However, we also found that exposure to hot‐dry stress is increasing faster than mean annual temperature over most of these drylands, and those increases are greatest in northern areas. Robust shifts in seasonal drought are most apparent during the cool season; when soil water availability is projected to increase in northern regions and decrease in southern regions. The implications of these robust drought trajectories for ecosystems will vary geographically, and these results provide useful insights about the impact of climate change on these dryland ecosystems. More broadly, this approach of identifying robust changes in ecological drought may be useful for other assessments of climate impacts in drylands and provide a more rigorous foundation for making long‐term strategic resource management decisions.
Technical Report
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The greater sage-grouse (Centrocercus urophasianus; hereafter called “sage-grouse”), a species that requires sagebrush (Artemisia spp.), has experienced range-wide declines in its distribution and abundance. These declines have prompted substantial research and management investments to improve the understanding of sage-grouse and its habitats and reverse declines in distribution and population numbers. Over the past two decades, the U.S. Fish and Wildlife Service (USFWS) has responded to eight petitions to list the sage-grouse under the Endangered Species Act of 1973, with the completion of the most recent listing determination in September 2015. At that time, the USFWS determined that the sage-grouse did not warrant a listing, primarily because of the large scale science-based conservation and planning efforts completed or started by Federal, State, local agencies, private landowners, and other entities across the range. The planning efforts culminated in the development of the 2015 Bureau of Land Management (BLM) and U.S. Forest Service Land Use Plan Amendments, which provided regulatory certainty and commitment from Federal land-management agencies to limit, mitigate, and track anthropogenic disturbance and implement other sage-grouse conservation measures. After these policy decisions, the scientific community has continued to refine and expand the knowledge available to inform implementation of management actions, increase the efficiency and effectiveness of those actions, and continue developing an overall understanding of sage-grouse populations, habitat requirements, and their response to human activity and other habitat changes. The development of science has been driven by multiple prioritization documents including the “Greater Sage-Grouse National Research Strategy” (Hanser and Manier, 2013) and, most recently, the “Integrated Rangeland Fire Management Strategy Actionable Science Plan” (Integrated Rangeland Fire Management Strategy Actionable Science Plan Team, 2016). In October 2017, after a review of the 2015 Federal plans relative to State sage-grouse plans, in accordance with Secretarial Order 3353, the BLM issued a notice of intent to consider whether to amend some, all, or none of the 2015 land use plans. At that time, the BLM requested the U.S. Geological Survey (USGS) to inform this effort through the development of an annotated bibliography of sage-grouse science published since January 2015 and a report that synthesized and outlined the potential management implications of this new science. Development of the annotated bibliography resulted in the identification and summarization of 169 peer-reviewed scientific publications and reports. The USGS then convened an interagency team (hereafter referred to as the “team”) to develop this report that focuses on the primary topics of importance to the ongoing management of sage-grouse and their habitats. The team developed this report in a three-step process. First, the team identified six primary topic areas for discussion based on the members’ collective knowledge regarding sage-grouse, their habitats, and threats to either or both. Second, the team reviewed all the material in the “Annotated Bibliography of Scientific Research on Greater Sage-Grouse Published since January 2015” to identify the science that addressed the topics. Third, team members discussed the science related to each topic, evaluated the consistency of the science with existing knowledge before 2015, and summarized the potential management implications of this science. The six primary topics identified by the team were: Multiscale habitat suitability and mapping tools Discrete anthropogenic activities Diffuse activities Fire and invasive species Restoration effectiveness Population estimation and genetics
Technical Report
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The sagebrush (Artemisia spp.) ecosystem extends across a large portion of the Western United States, and the greater sage-grouse (Centrocercus urophasianus) is one of the iconic species of this ecosystem. Greater sage-grouse populations occur in 11 States and are dependent on relatively large expanses of sagebrush-dominated habitat. Sage-grouse populations have been experiencing long-term declines owing to multiple stressors, including interactions among fire, exotic plant invasions, and human land uses, which have resulted in significant loss, fragmentation, and degradation of landscapes once dominated by sagebrush. In addition to the sage-grouse, over 350 species of plants and animals are dependent on the sagebrush ecosystem. Increasing knowledge about how these species and the sagebrush ecosystem respond to these stressors and to management actions can inform and improve strategies to maintain existing areas of intact sagebrush and restore degraded landscapes. The U.S. Geological Survey (USGS) has a broad research program focused on providing the science needed to inform these strate-gies and to help land and resource managers at the Federal, State, Tribal, and local levels as they work towards sustainable sage-grouse populations and restored landscapes for the broad range of uses critical to stakeholders in the Western United States. USGS science has provided a foundation for major land and resource management decisions including those that precluded the need to list the greater sage-grouse under the Endangered Species Act. The USGS is continuing to build on that foundation to inform science-based decisions to help support local economies and the continued conservation, management, and restoration of the sagebrush ecosystem. This report contains descriptions of USGS sage-grouse and sagebrush ecosystem research projects that are ongoing or were active during 2017 and is organized into five thematic areas: Fire, Invasive Species, Restoration, Sagebrush and Sage-Grouse, and Climate and Weather.
Chapter
A longer growing season with climate change is expected to increase net primary productivity of many rangeland types, especially those dominated by grasses, although responses will depend on local climate and soil conditions. Elevated atmospheric carbon dioxide may increase water use efficiency and productivity of some species. In many cases, increasing wildfire frequency and extent will be damaging for big sagebrush and other shrub species that are readily killed by fire. The widespread occurrence of cheatgrass and other nonnatives facilitates frequent fire through annual fuel accumulation. Shrub species that sprout following fire may be quite resilient to increased disturbance, but may be outcompeted by more drought tolerant species over time.
Chapter
Few data exist on the direct effects of climatic variability and change on animal species. Therefore, projected climate change effects must be inferred from what is known about habitat characteristics and the autecology of each species. Habitat for mammals, including predators (Canada lynx, fisher, wolverine) and prey (snowshoe hare) that depend on high-elevation, snowy environments, is expected to deteriorate relatively soon if snowpack continues to decrease. Species that are highly dependent on a narrow range of habitat (pygmy rabbit, Brewer’s sparrow, greater sage-grouse) will be especially vulnerable if that habitat decreases from increased disturbance (e.g., sagebrush mortality from wildfire). Species that are mobile or respond well to increased disturbance and habitat patchiness (deer, elk) will probably be resilient to a warmer climate in most locations. Some amphibian species (Columbia spotted frog, western toad) may be affected by pathogens (e.g., amphibian chytrid fungus) that are favored by a warmer climate.
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USGS sage-grouse and sagebrush ecosystem research is aligned with priority needs outlined in the “Integrated Rangeland Fire Management Strategy Actionable Science Plan” (Integrated Rangeland Fire Management Strategy Actionable Science Plan Team, 2016). The list of 116 research projects is organized into five thematic areas: fire (16 projects); invasive species (7 projects); restoration (23 projects); sagebrush, sage-grouse, and other sagebrush-associated species (60 projects); and weather and climate (10 projects). Individual projects often overlap multiple themes (for example, effects of wildfire and invasive annual grasses on greater sage-grouse habitat); therefore, project descriptions are organized according to the main focal theme.
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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. [Springer Nature SharedIt Initiative Full-Text Article Available : http://rdcu.be/tFJu].
Article
Aim Drought stress has focused on water availability during the growing season, thus primarily on summer. However, variation in rainfall continentality can produce striking vegetation differences. We aim to disentangle summer water balance from winter rainfall continentality, to better understand how climate regulates the distributions of woody plants in the western USA. Location Western USA. Time period Actual. Major taxa studied Angiosperms and conifers. Methods We used redundancy analysis (RDA) to investigate correlations between rainfall continentality, summer water balance, minimum winter temperature and length of growing season on the distributions of 130 tree and shrub species in 467 plots. Rainfall continentality was calculated using the Gams index, modified for winter precipitation, and summer water balance with the ratio of summer precipitation to temperature. We estimated actual evapotranspiration (AET), deficit (DEF), mean annual temperature and rainfall from global gridded data sets and correlated them with RDA axes. Results Rainfall continentality measured with the Gams index and minimum temperatures best explained the contrast between oceanic vegetation in the Pacific Coast Ranges and continental vegetation in the Intermountain Region and Rocky Mountains. Growing season length (GSL) was the second strongest factor correlated with vegetation distributions. Summer water balance, despite being the most widely used climatic factor to assess drought stress in biogeography, was the third strongest factor correlating with vegetation classes of the western US. AET was equally correlated with RDA axes 1 and 3, and, thus, could not discriminate between the contrasts in the RDA. Main conclusions Rainfall continentality measured with the winter Gams index provides a more precise metric than summer water balance for understanding the biogeography of woody plants in the western USA. Broadly integrating the Gams index of continentality into plant distributions may improve our understanding of biogeographical distributions and predictions of responses to climate change.
Technical Report
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The sagebrush (Artemisia spp.) ecosystem extends across a large portion of the Western United States, and the greater sage-grouse (Centrocercus urophasianus) is one of the iconic species of this ecosystem. Greater sage-grouse populations occur in 11 States and are dependent on relatively large expanses of sagebrush-dominated habitat. Sage-grouse populations have been experiencing long-term declines owing to multiple stressors, including interactions among fire, exotic plant invasions, and human land uses, which have resulted in significant loss, fragmentation, and degradation of landscapes once dominated by sagebrush. In addition to the sage-grouse, over 350 species of plants and animals are dependent on the sagebrush ecosystem. Increasing knowledge about how these species and the sagebrush ecosystem respond to these stressors and to management actions can inform and improve strategies to maintain existing areas of intact sagebrush and restore degraded landscapes. The U.S. Geological Survey (USGS) has a broad research program focused on providing the science needed to inform these strategies and to help land and resource managers at the Federal, State, Tribal, and local levels as they work towards sustainable sage-grouse populations and restored landscapes for the broad range of uses critical to stakeholders in the Western United States. USGS science has provided a foundation for major land and resource management decisions including those that precluded the need to list the greater sage-grouse under the Endangered Species Act. The USGS is continuing to build on that foundation to inform science-based decisions to help support local economies and the continued conservation, management, and restoration of the sagebrush ecosystem. This report contains descriptions of USGS sage-grouse and sagebrush ecosystem research projects that are ongoing or were active during 2018 and is organized into five thematic areas: Fire, Invasive Species, Restoration, Sagebrush, Sage-Grouse, and Other Sagebrush-Associated Species; and Climate and Weather.
Chapter
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Adaptive management and monitoring efforts focused on vegetation, habitat, and wildlife in the sagebrush (Artemisia spp.) biome help inform management of species and habitats, predict ecological responses to conservation practices, and adapt management to improve conservation outcomes. This chapter emphasizes the adaptive resource management framework with its four stages: (1) problem definition, (2) outcomes, (3) decision analysis, and (4) implementation and monitoring. Adaptive resource management is an evolving process involving a sequential cycle of learning (the accumulation of understanding over time) and adaptation (the adjustment of management over time). This framework operationalizes monitoring a necessary component of decision making in the sagebrush biome. Several national and regional monitoring efforts are underway across the sagebrush biome for both vegetation and wildlife. Sustaining these efforts and using the information effectively is an important step towards realizing the full potential of the adaptive management framework in sagebrush ecosystems. Furthermore, coordinating monitoring efforts and information across stakeholders (for example, Federal, State, nongovernmental organizations) will be necessary given the limited resources, diverse ownership/management, and sagebrush biome size.
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Amphibians and reptiles are vertebrates that are often overlooked in assessments of the importance of sagebrush (Artemisia spp.) ecosystems for wildlife. Given their dependence on water, few amphibians are strongly associated with sagebrush habitats, although several use these uplands for foraging, shelter, or dispersal. Of the 60 amphibian species that are predicted to occur within the sagebrush biome, the Great Basin spadefoot (Spea intermontana) is probably the only species that occupies enough of the biome and lives predominantly in terrestrial habitats (mostly in burrows) to be considered sagebrush associated. Of the 116 reptiles that are predicted to occur within the sagebrush biome, about 5 lizards and 5 snakes were identified as both strongly associated with sagebrush habitats and occupied areas likely to be managed for sage-grouse (Centrocercus spp). However, this list could be lower or higher depending on the specific location within the biome, and there remains considerable uncertainty regarding potential threats to reptiles, as well as basic information on distribution and abundance of most reptile species.
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Nitrogen additions are known to elicit variable responses in semi-arid ecosystems, with responses increasing with precipitation. The response of semi-arid ecosystems to nitrogen are important to understand due to their large spatial extent worldwide and the global trend of increasingly available nitrogen. In this study, we evaluated the impact of nitrogen additions on semi-arid big sagebrush (Artemisia tridentata) ecosystems. This is important given that sagebrush ecosystems are poorly understood, despite their prevalence in the western US. In addition, large-scale nitrogen additions have begun on sagebrush landscapes in Wyoming in order to mitigate population declines in mule deer (Odocoileus hemionus). The study objectives were (1) to evaluate the effectiveness of nitrogen fertilization in increasing sagebrush biomass and forage quality, and (2) to assess effects of nitrogen addition on soil biogeochemistry and vegetation community structure. We fertilized 15 plots across 5 locations in western Wyoming using nitrogen (5.47g N m-2), in the form of urea. In addition, we immobilized available nitrogen through surface hay treatments (254g hay/m2). Nitrogen additions failed to increase growth of sagebrush, alter nitrogen content of sagebrush leaders, or alter greenhouse gas efflux from soils. However, the vegetation community shifted; nitrogen-fertilized plots were only 72% similar to the controls (Bray-Curtis). Over the two years of this study, we did not find indications of nitrogen limitation of ecosystem processes, despite a wet growing season in 2014. Thus, we have found a general lack of response to nitrogen in sagebrush ecosystems, with some shifts in the plant community composition.
Technical Report
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USGS sage-grouse and sagebrush ecosystem research is aligned with priority needs outlined in the “Integrated Rangeland Fire Management Strategy Actionable Science Plan” (Integrated Rangeland Fire Management Strategy Actionable Science Plan Team, 2016). The list of 116 research projects is organized into five thematic areas: fire (16 projects); invasive species (7 projects); restoration (23 projects); sagebrush, sage-grouse, and other sagebrush-associated species (60 projects); and weather and climate (10 projects). Individual projects often overlap multiple themes (for example, effects of wildfire and invasive annual grasses on greater sage-grouse habitat); therefore, project descriptions are organized according to the main focal theme.
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Degradation, fragmentation, and loss of native sagebrush (Artemisia spp.) landscapes have imperiled these habitats and their associated avifauna. Historically, this vast piece of the Western landscape has been undervalued: even though more than 70% of all remaining sagebrush habitat in the United States is publicly owned, <3% of it is protected as federal reserves or national parks. We review the threats facing birds in sagebrush habitats to emphasize the urgency for conservation and research actions, and synthesize existing information that forms the foundation for recommended research directions. Management and conservation of birds in sagebrush habitats will require more research into four major topics: (1) identification of primary land-use practices and their influence on sagebrush habitats and birds, (2) better understanding of bird responses to habitat components and disturbance processes of sagebrush ecosystems, (3) improved hierarchical designs for surveying and monitoring programs, and (4) linking bird movements and population changes during migration and wintering periods to dynamics on the sagebrush breeding grounds. This research is essential because we already have seen that sagebrush habitats can be altered by land use, spread of invasive plants, and disrupted disturbance regimes beyond a threshold at which natural recovery is unlikely. Research on these issues should be instituted on lands managed by state or federal agencies because most lands still dominated by sagebrush are owned publicly. In addition to the challenge of understanding shrubsteppe bird-habitat dynamics, conservation of sagebrush landscapes depends on our ability to recognize and communicate their intrinsic value and on our resolve to conserve them. ¿Tambaleando en el Borde o Demasiado Tarde? Asuntos de Conservación e Investigación para la Avifauna de Ambientes de Matorral de Artemisia spp Resumen. La degradación, fragmentación y pérdida de paisajes nativos de matorrales de Artemisia spp. han puesto en peligro a estos ambientes y su avifauna asociada. Históricamente, esta vasta porción del paisaje occidental ha sido subvalorada: aunque más del 70% de todo el hábitat de matorral de Artemisia de los Estados Unidos es de propiedad pública, <3% de éste es protegido por reservas federales o parques nacionales. En este artículo revisamos las amenazas a las que se enfrentan las aves de los matorrales de Artemisia para enfatizar la urgencia de emprender acciones de conservación e investigación, y sintetizamos la información existente que constituye la base para una serie de directrices de investigación recomendadas. El manejo y conservación de las aves de los matorrales de Artemisia necesitará más investigación en cuatro tópicos principales: (1) la identificación de prácticas primarias de uso del suelo y su influencia sobre los ambientes y las aves de Artemisia, (2) un mejor entendimiento de las respuestas de las aves a componentes del hábitat y a procesos de disturbio de los ecosistemas de Artemisia, (3) el mejoramiento de diseños jerárquicos para programas de censos y monitoreos y (4) la conexión de los movimientos de las aves y los cambios poblacionales durante la migración y en los períodos de invernada con la dinámica en las áreas reproductivas de matorrales de Artemisia. Estas investigaciones son esenciales porque ya hemos visto que los ambientes de Artemisia pueden ser alterados por el uso del suelo, la diseminación de plantas invasoras y la disrupción de los regímenes de disturbio más allá de un umbral en el que la recuperación natural es poco probable. La investigación en estos asuntos debe instituirse en tierras manejadas por agencias estatales o federales porque la mayoría de las tierras aún dominadas por Artemisia son de propiedad pública. Además del desafío de entender la dinámica aves-hábitat en las estepas arbustivas, la conservación de los paisajes de matorral de Artemisia depende de nuestra habilidad de reconocer y comunicar su valor intrínseco y de nuestra decisión para conservarlos.
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Drylands cover 40% of the global terrestrial surface and provide important ecosystem services. While drylands as a whole are expected to increase in extent and aridity in coming decades, temperature and precipitation forecasts vary by latitude and geographic region suggesting different trajectories for tropical, subtropical, and temperate drylands. Uncertainty in the future of tropical and subtropical drylands is well constrained, whereas soil moisture and ecological droughts, which drive vegetation productivity and composition, remain poorly understood in temperate drylands. Here we show that, over the twenty first century, temperate drylands may contract by a third, primarily converting to subtropical drylands, and that deep soil layers could be increasingly dry during the growing season. These changes imply major shifts in vegetation and ecosystem service delivery. Our results illustrate the importance of appropriate drought measures and, as a global study that focuses on temperate drylands, highlight a distinct fate for these highly populated areas.
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Anthropogenic climate change is hypothesized to modify the spread of invasive annual grasses across the deserts of the western United States. The influence of climate change on future invasions depends on both climate suitability that defines a potential species range and the mechanisms that facilitate invasions and contractions. A suite of downscaled climate projections for the mid–21st century was used to examine changes in physically based mechanisms, including critical physiological temperature thresholds, the timing and availability of moisture, and the potential for large wildfires. Results suggest widespread changes in 1) the length of the freeze-free season that may favor cold-intolerant annual grasses, 2) changes in the frequency of wet winters that may alter the potential for establishment of invasive annual grasses, and 3) an earlier onset of fire season and a lengthening of the window during which conditions are conducive to fire ignition and growth furthering the fire-invasive feedback loop. We propose that a coupled approach combining bioclimatic envelope modeling with mechanistic modeling targeted to a given species can help land managers identify locations and species that pose the highest level of overall risk of conversion associated with the multiple stressors of climate change.
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In the Southwest and Central Plains of Western North America, climate change is expected to increase drought severity in the coming decades. These regions nevertheless experienced extended Medieval-era droughts that were more persistent than any historical event, providing crucial targets in the paleoclimate record for benchmarking the severity of future drought risks. We use an empirical drought reconstruction and three soil moisture metrics from 17 state-of-the-art general circulation models to show that these models project significantly drier conditions in the later half of the 21st century compared to the 20th century and earlier paleoclimatic intervals. This desiccation is consistent across most of the models and moisture balance variables, indicating a coherent and robust drying response to warming despite the diversity of models and metrics analyzed. Notably, future drought risk will likely exceed even the driest centuries of the Medieval Climate Anomaly (1100-1300 CE) in both moderate (RCP 4.5) and high (RCP 8.5) future emissions scenarios, leading to unprecedented drought conditions during the last millennium.
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Sagebrush (Artemisia spp.) ecosystems constitute the largest single North American shrub ecosystem and provide vital ecological, hydrological, biological, agricultural, and recreational ecosystem services. Disturbances have altered and reduced this ecosystem historically, but climate change may ultimately represent the greatest future risk. Improved ways to quantify, monitor, and predict climate-driven gradual change in this ecosystem is vital to its future management. We examined the annual change of Daymet precipitation (daily gridded climate data) and five remote sensing ecosystem sagebrush vegetation and soil components (bare ground, herbaceous, litter, sagebrush, and shrub) from 1984 to 2011 in southwestern Wyoming. Bare ground displayed an increasing trend in abundance over time, and herbaceous, litter, shrub, and sagebrush showed a decreasing trend. Total precipitation amounts show a downward trend during the same period. We established statistically significant correlations between each sagebrush component and historical precipitation records using a simple least squares linear regression. Using the historical relationship between sagebrush component abundance and precipitation in a linear model, we forecasted the abundance of the sagebrush components in 2050 using Intergovernmental Panel on Climate Change (IPCC) precipitation scenarios A1B and A2. Bare ground was the only component that increased under both future scenarios, with a net increase of 48.98 km2 (1.1%) across the study area under the A1B scenario and 41.15 km2 (0.9%) under the A2 scenario. The remaining components decreased under both future scenarios: litter had the highest net reductions with 49.82 km2 (4.1%) under A1B and 50.8 km2 (4.2%) under A2, and herbaceous had the smallest net reductions with 39.95 km2 (3.8%) under A1B and 40.59 km2 (3.3%) under A2. We applied the 2050 forecast sagebrush component values to contemporary (circa 2006) greater sage-grouse (Centrocercus urophasianus) habitat models to evaluate the effects of potential climate-induced habitat change. Under the 2050 IPCC A1B scenario, 11.6% of currently identified nesting habitat was lost, and 0.002% of new potential habitat was gained, with 4% of summer habitat lost and 0.039% gained. Our results demonstrate the successful ability of remote sensing based sagebrush components, when coupled with precipitation, to forecast future component response using IPCC precipitation scenarios. Our approach also enables future quantification of greater sage-grouse habitat under different precipitation scenarios, and provides additional capability to identify regional precipitation influence on sagebrush component response.
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Although arid and semiarid regions are defined by low precipitation, the seasonal timing of temperature and precipitation can influence net primary production and plant functional type composition. The importance of precipitation seasonality is evident in semiarid areas of the western U.S., which comprise the Intermountain (IM) zone, a region that receives important winter precipitation and is dominated by woody plants and the Great Plains (GP), a region that receives primarily summer precipitation and is dominated by perennial grasses. Although these general relationships are well recognized, specific differences in water cycling between these regions have not been well characterized. We used a daily time step soil water simulation model and twenty sites from each region to analyze differences in soil water dynamics and ecosystem water balance. IM soil water patterns are characterized by storage of water during fall, winter, and spring resulting in relatively reliable available water during spring and early summer, particularly in deep soil layers. By contrast, GP soil water patterns are driven by pulse precipitation events during the warm season, resulting in fluctuating water availability in all soil layers. These contrasting patterns of soil water—storage versus pulse dynamics—explain important differences between the two regions. Notably, the storage dynamics of the IN sites increases water availability in deep soil layers, favoring the deeper rooted woody plants in that region, whereas the pulse dynamics of the Great Plains sites provide water primarily in surface layers, favoring the shallow-rooted grasses in that region. In addition, because water received when plants are either not active or only partially so is more vulnerable to evaporation and sublimation than water delivered during the growing season, IM ecosystems use a smaller fraction of precipitation for transpiration (47%) than GP ecosystems (49%). Recognizing the pulse-storage dichotomy in soil water regimes between the IM and GP regions may be useful for understanding the potential influence of climate changes on soil water patterns and resulting dominant plant functional groups in both regions.
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To assess the temporal and spatial dynamics of soil water at a shortgrass steppe site in northcentral Colorado, we evaluated the precipitation regime for a 33-yr period and ran a simulation model for this period. Small precipitation events accounted for a large fraction of the total number of events and represented a source of water with small interannual variability. The difference between wet and dry years was related to the occurrence of a few large events. Average daily precipitation was concentrated during the warmest months of the year with a maximum in late spring. Water in the surface soil layers had a short residence time and no seasonal pattern. Intermediate layers reflected the seasonal pattern of precipitation. Maximum soil water availability occurred in the late spring, but this was also the period with the highest interannual variability. The wettest layer was at 4-15 cm of depth. The frequency of wet conditions decreased above this layer because of the strong influence of evaporation and below because recharge was infrequent. No deep percolation events were recorded. During dry years distribution of soil water was very shallow and during wet years wet conditions reached to depths of 120-135 cm. This shallow distribution of soil water matches the distribution of processes and structural elements in the steppe suggesting that there is a cause-effect relationship between them. We speculate that the pattern of water availability interacts with biotic constraints and determines the rate of ecosystem processes. The depth distribution of water in dry and wet years is compared to the root distribution of grasses, shrubs, herbs, and succulents to suggest the response of each group to modal and extreme conditions. Comparison of long-term soil water patterns and traits of the major species allows us to suggest why Bouteloua gracilis is the dominant species in the shortgrass steppe.
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Many semi-arid plant communities in western North America are dominated by big sagebrush. These ecosystems are being reduced in extent and quality due to economic development, invasive species, and climate change. These pervasive modifications have generated concern about the long-term viability of sagebrush habitat and sagebrush-obligate wildlife species (notably Greater Sage-Grouse), highlighting the need for better understanding of the future big sagebrush distribution, particularly at the species' range margins. The leading and trailing edges of potential climate-driven distribution shifts are likely to be areasmost sensitive to climate change. Although several processes contribute to distribution shifts, regeneration is a fundamental requirement, especially for specieswith episodic regeneration patterns, such as big sagebrush. We used a process-based regeneration model for big sagebrush to simulate potential germination and seedling survival in response to climatic and edaphic conditions. We estimated current and future regeneration under 2070-2099 CMIP5 climate conditions at trailing and leading edges that were previously identified using traditional species distribution models. Our results supported expectations of increased probability of regeneration at the leading edge and decreased probability at the trailing edge compared to current levels. Our simulations indicated that soil water dynamics at the leading edge will become more similar to the typical seasonal ecohydrological conditions observed within the current range of big sagebrush. At the trailing edge, increased winter and spring dryness represented a departure from conditions typically supportive of big sagebrush. Our results highlighted that minimum and maximum daily temperatures as well as soil water recharge and summer dry periods are important constraints for big sagebrush regeneration. We observed reliable changes in areas identified as trailing and leading edges, consistent with previous predictions. However, we also identified potential local refugia within the trailing edge, mostly at higher elevation sites. Decreasing regeneration probability at the trailing edge suggests that it will be difficult to preserve and/or restore big sagebrush in these areas. Conversely, increasing regeneration probability at the leading edge suggests a growing potential for conflicts in management goals between maintaining existing grasslands and croplands by preventing sagebrush expansion versus accepting a shift in plant community composition to sagebrush dominance.
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Big sagebrush (Artemisia tridentata) is one of the most widespread and abundant plant species in the intermountain regions of western North America. This species occupies an extremely wide ecological niche ranging from the semi-arid basins to the subalpine. Within this large niche, three widespread subspecies are recognized. Montane ecoregions are occupied by subspecies vaseyana, while subspecies wyomingensis and tridentata occupy basin ecoregions. In cases of wide-ranging species with multiple subspecies, it can be more practical from the scientific and management perspective to assess the climate profiles at the subspecies level. We focus bioclimatic model efforts on subspecies wyomingensis, which is the most widespread and abundant of the subspecies and critical habitat to wildlife including sage-grouse and pygmy rabbits. Using absence points from species with allopatric ranges to Wyoming big sagebrush (i.e.. targeted groups absences) and randomly sampled points from specific ecoregions, we modeled the climatic envelope for subspecies wyomingensis using Random Forests multiple-regression tree for contemporary and future climates (decade 2050). Overall model error was low, at 4.5%, with the vast majority accounted for by errors in commission (>99.9%). Comparison of the contemporary and decade 2050 models shows a predicted 39% loss of suitable climate. Much of this loss will occur in the Great Basin where impacts from increasing tire frequency and encroaching weeds have been eroding the A. tridentata landscape dominance and ecological functions. Our goal of the A. tridentata subsp. wyomingensis bioclimatic model is to provide a management tool to promote successful restoration by predicting the geographic areas where climate is suitable for this subspecies. This model can also be used as a restoration-planning tool to assess vulnerability of climatic extirpation over the next few decades.
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Climate change, along with exotic species, disturbances, and land use change, will likely have major impacts on sagebrush steppe ecosystems in the western U.S. over the next century. To effectively manage sagebrush steppe landscapes for long-term goals, managers need information about the interacting impacts of climate change, disturbances and land management on vegetation condition. Using a climate-informed state-and-transition model, we evaluated the potential impacts of climate change on rangeland condition in central Oregon and the effectiveness of multiple management strategies. Under three scenarios of climate change, we projected widespread shifts in potential vegetation types over the twenty-first century, with declining sagebrush steppe and expanding salt desert shrub likely by the end of the century. Many extreme fire years occurred under all climate change scenarios, triggering rapid vegetation shifts. Increasing wildfire under climate change resulted in expansion of exotic grasses but also decreased juniper encroachment relative to projections without climate change. Restoration treatments in warm-dry sagebrush steppe were ineffective in containing exotic grass, but juniper treatments in cool-moist sagebrush steppe substantially reduced the rate of juniper encroachment, particularly when prioritized early in the century. Overall, climate-related shifts dominated future vegetation patterns, making management for improved rangeland condition more difficult. Our approach allows researchers and managers to examine long-term trends and uncertainty in rangeland vegetation condition and test the effectiveness of alternative management actions under projected climate change.
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While modeling efforts suggest that invasive species will track climate changes, empirical studies are few. A relevant and largely unaddressed research question is: how will the presence of exotic species interact with precipitation change to alter ecosystem structure and function?We studied the effects of changes in seasonal timing of precipitation on species composition and resource availability in a grassland community in Colorado, USA. We examined how seasonal precipitation patterns affect the abundance of historically present (native) and recently-arrived (exotic) plant species, as well as soil moisture, nitrogen, and above-ground biomass. Over four years, we applied four precipitation treatments based on climate model predictions for the study area: winter-wet/summer-ambient, winter-wet/summer-dry, winter-wet/summer-wet and winter-dry/summer-wet.Cover of exotic winter-active grasses was greater in winter-wet treatments than in control or winter-dry treatments. Cover of native warm-season grasses and forbs was greatest in the winter-dry/summer-wet treatment, and lowest in the winter-wet/summer-dry treatment. These results support the expectation that increased winter precipitation benefits new arrivals, whereas increased summer precipitation benefits later-growing native plants.Structural equation models showed that interactive effects of increased winter precipitation and increased cover of winter-active grasses reduced growing season soil water content and species diversity. In addition, the dominant winter-active species, Bromus tectorum, flowered and senesced earlier in plots receiving increased winter precipitation and reduced summer precipitation, suggesting that earlier growth of winter-active grasses decreases available soil resources and impacts later-growing native plants. Peak above-ground biomass was lowest in the treatment receiving reduced summer precipitation, but only in years with dry springs. Plant-available nitrogen in spring was lower in plots receiving supplemental winter precipitation, and highest in plots with reduced winter precipitation.Synthesis. Our results indicate that altering the seasonality of precipitation can have large direct effects on plant community composition and phenology, as well as significant indirect effects, mediated through exotic species, on plant-available resources and plant interactions.This article is protected by copyright. All rights reserved.
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Abstract. In arid and semi-arid landscapes around the world, wildfire plays a key role in maintaining species diversity. Dominant plant associations may depend upon particular fire regime characteristics for their persistence. Mountain shrub communities in high-elevation landscapes of the Intermountain West, USA, are strongly influenced by the post-fire recovery dynamics of the obligate-seeding shrub, mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle). This species is a short-distance disperser with a short-lived seedbank, leading to highly variable post-fire recovery times (15–100 years). We investigated the relative importance of site productivity and seasonal climate in explaining the variance in recovery time for 36 fires, comprising a fire chrono-sequence (from 1971 to 2007) for the Great Basin and Colorado Plateau. A. t. vaseyana recovery was positively related to precipitation in the cool season immediately following fire, likely because deep soil-water recharge that persists throughout the growing season enhances first-year seedling survival. Percentage sand fraction positively correlated with recovery rate yet negatively correlated with live cover in unburnt stands. Our data support the hypothesis that post-fire recovery rate of A. t. vaseyana depends on the climatically controlled ephemerality of the regeneration niche, as is likely true for many arid-land shrub species.
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Previous research suggested that big sagebrush (Artemisia tridentata Nutt.) recruitment occurs in pulses consistent with favorable climatic conditions. In 1997, 75 stem sections were collected from 9 stands of each of the 3 subspecies of big sagebrush in Wyoming along elevation and climatic gradients. Annual growth rings were used to identify the year plants were established. Large cohorts of Wyoming big sagebrush (A. tridentata ssp. wyomingensis Beetle and Young) appeared in 1982, 1981, 1964, 1961, and 1955. Basin big sagebrush (A. tridentata ssp. tridentata Beetle and Johnson) cohorts flourished in 1991, 1986, 1985, 1982, and 1977. Mountain big sagebrush (A. tridentata ssp. vaseyana [Rydb.] Beetle) cohorts prospered in 1985, 1982, 1981, 1979, and 1974. Mean monthly precipitation and temperature records were compared to years with high and low recruitment using logistic regression models at 3 geographic scales (single-stand, regional, statewide). Wyoming big sagebrush recruitment was greatest in years with above-average December and January precipitation occurring after the first growing season (r(2) = 0.10, 0.04, P < 0.05). Basin big sagebrush recruitment was most successful in years with above-average March, May, and June precipitation during the first growing season (r(2) = 0.06, 0.09, 0.18, P < 0.05). Mountain big sagebrush recruitment was greatest in years with below-average February, April, and May precipitation after the first growing season (r(2) = 0.03, 0.04, 0.04, P < 0.05). While variable precipitation patterns appear to contribute significantly to recruitment of big sagebrush, responses among the 3 major subspecies were quite variable. More complex models need to be developed to foster our understanding of the mechanisms affecting big sagebrush establishment.
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Climate change threatens to exacerbate the impacts of invasive species. In temperate ecosystems, direct effects of warming may be compounded by dramatic reductions in winter snow cover. Cheatgrass (Bromus tectorum) is arguably the most destructive biological invader in basins of the North American Intermountain West, and warming could increase its performance through direct effects on demographic rates or through indirect effects mediated by loss of snow. We conducted a two-year experimental manipulation of temperature and snow pack to test whether 1) warming increases cheatgrass population growth rate and 2) reduced snow cover contributes to cheatgrass' positive response to warming. We used infrared heaters operating continuously to create the warming treatment, but turned heaters on only during snowfalls for the snowmelt treatment. We monitored cheatgrass population growth rate and the vital rates that determine it: emergence, survival and fecundity. Growth rate increased in both warming and snowmelt treatments. The largest increases occurred in warming plots during the wettest year, indicating that the magnitude of response to warming depends on moisture availability. Warming increased both fecundity and survival, especially in the wet year, while snowmelt contributed to the positive effects of warming by increasing survival. Our results indicate that increasing temperature will exacerbate cheatgrass impacts, especially where warming causes large reductions in the depth and duration of snow cover.
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Reduction of greenhouse gas (GHG) emissions to minimize climate change requires very significant societal effort. To motivate this effort, it is important to clarify the benefits of avoided emissions. To this end, we analysed the impact of four emissions scenarios on future renewable groundwater resources, which range from 1600 GtCO2 during the 21st century (RCP2.6) to 7300 GtCO2 (RCP8.5). Climate modelling uncertainty was taken into account by applying the bias-corrected output of a small ensemble of five CMIP5 global climate models (GCM) as provided by the ISI-MIP effort to the global hydrological model WaterGAP. Despite significant climate model uncertainty, the benefits of avoided emissions with respect to renewable groundwater resources (i.e. groundwater recharge (GWR)) are obvious. The percentage of projected global population (SSP2 population scenario) suffering from a significant decrease of GWR of more than 10% by the 2080s as compared to 1971–2000 decreases from 38% (GCM range 27–50%) for RCP8.5 to 24% (11–39%) for RCP2.6. The population fraction that is spared from any significant GWR change would increase from 29% to 47% if emissions were restricted to RCP2.6. Increases of GWR are more likely to occur in areas with below average population density, while GWR decreases of more than 30% affect especially (semi)arid regions, across all GCMs. Considering change of renewable groundwater resources as a function of mean global temperature (GMT) rise, the land area that is affected by GWR decreases of more than 30% and 70% increases linearly with global warming from 0 to 3 ° C. For each degree of GMT rise, an additional 4% of the global land area (except Greenland and Antarctica) is affected by a GWR decrease of more than 30%, and an additional 1% is affected by a decrease of more than 70%.
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Global change is likely to affect invasive species distribution, especially at range margins. In the eastern Sierra Nevada, California, USA, the invasive annual grass, Bromus tectorum, is patchily distributed and its impacts have been minimal compared with other areas of the Intermountain West. We used a series of in situ field manipulations to determine how B. tectorum might respond to changing climatic conditions and increased nitrogen deposition at the high-elevation edge of its invaded range. Over 3 years, we used snow fences to simulate changes in snowpack, irrigation to simulate increased frequency and magnitude of springtime precipitation, and added nitrogen (N) at three levels (0, 5, and 10 g m(-2) ) to natural patches of B. tectorum growing under the two dominant shrubs, Artemisia tridentata and Purshia tridentata, and in intershrub spaces (INTR). We found that B. tectorum seedling density in April was lower following deeper snowpack possibly due to delayed emergence, yet there was no change in spikelet production or biomass accumulation at the time of harvest. Additional spring rain events increased B. tectorum biomass and spikelet production in INTR plots only. Plants were primarily limited by water in 2009, but colimited by N and water in 2011, possibly due to differences in antecedent moisture conditions at the time of treatments. The threshold at which N had an effect varied with magnitude of water additions. Frequency of rain events was more influential than magnitude in driving B. tectorum growth and fecundity responses. Our results suggest that predicted shifts from snow to rain could facilitate expansion of B. tectorum at high elevation depending on timing of rain events and level of N deposition. We found evidence for P-limitation at this site and an increase in P-availability with N additions, suggesting that stoichiometric relationships may also influence B. tectorum spread.