Research and Publications
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Distributions of both native and invasive species are expected to shift under future climate. Species distribution models (SDMs) are often used to explore future habitats, but sources of uncertainty including novel climate conditions may reduce the reliability of future projections. We explore the potential spread of the invasive annual grass ventenata (Ventenata dubia) in the western United States under both current and future climate scenarios using boosted regression tree models and 30 global climate models (GCMs). We quantify novel climate conditions, prediction variability arising from both the SDMs and GCMs, and the agreement among GCMs. Results demonstrate that currently suitable habitat is concentrated inside the invaded range of the northwest, but substantial habitat exists outside the invaded range in the Southern Rockies and southwestern US mountains. Future suitability projections vary greatly among GCMs, but GCMs commonly projected decreased suitability in the invaded range and increased suitability along higher elevations of interior mountainous areas.
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Cloud-to-ground lightning with minimal rainfall (“dry” lightning) is a major wildfire ignition source in the western United States (WUS). Although dry lightning is commonly defined as occurring with <2.5 mm of daily-accumulated precipitation, a rigorous quantification of precipitation amounts concurrent with lightning-ignited wildfires (LIWs) is lacking. We combine wildfire, lightning and precipitation data sets to quantify these ignition precipitation amounts across ecoprovinces of the WUS. The median precipitation for all LIWs is 2.8 mm but varies with vegetation and fire characteristics. “Holdover” fires not detected until 2–5 days following ignition occur with significantly higher precipitation (5.1 mm) compared to fires detected promptly after ignition (2.5 mm), and with cooler and wetter environmental conditions. Further, there is substantial variation in precipitation associated with promptly-detected (1.7–4.6 mm) and holdover (3.0–7.7 mm) fires across ecoprovinces. Consequently, the widely-used 2.5 mm threshold does not fully capture lightning ignition risk and incorporating ecoprovince-specific precipitation amounts would better inform WUS wildfire prediction and management.
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The most destructive and deadly wildfires in US history were also fast. Using satellite data, we analyzed the daily growth rates of more than 60,000 fires from 2001 to 2020 across the contiguous US. Nearly half of the ecoregions experienced destructive fast fires that grew more than 1620 hectares in 1 day. These fires accounted for 78% of structures destroyed and 61% of suppression costs($18.9 billion). From 2001 to 2020, the average peak daily growth rate for these fires more than doubled (+249% relative to 2001) in the Western US. Nearly 3 million structures were within 4 kilometers of a fast fire during this period across the US. Given recent devastating wildfires, understanding fast fires is crucial for improving firefighting strategies and community preparedness
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Ecological disturbance can affect carbon storage and stability and is a key consideration for managing lands to preserve or increase ecosystem carbon to ameliorate the global greenhouse gas problem. Dryland soils are massive carbon reservoirs that are increasingly impacted by species invasions and altered fire regimes, including the exotic-grass-fire cycle in the extensive sagebrush steppe of North America. Direct measurement of total carbon in 1174 samples from landscapes of this region that differed in invasion and wildfire history revealed that their impacts depleted soil carbon by 42-49%, primarily in deep horizons, which could amount to 17.1-20.0 Tg carbon lost across the ~400,000 ha affected annually. Disturbance effects on soil carbon stocks were not synergistic, suggesting that soil carbon was lowered to a floor-i.e. a resistant base-level-beneath which further loss was unlikely. Restoration and maintenance of resilient dryland shrublands/rangelands could stabilize soil carbon at magnitudes relevant to the global carbon cycle.
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We seeded perennial grass (Elymus elymoides) at multiple depths to determine susceptibility and resistance. Herbicides were applied at full and reduced rates to mimic the effect of litter in natural systems. We observed reductions in most non-native species in all treatments, but also extensive reductions of native annual forbs, although these were offset at lower application rates, and some species (e.g. Amsinckia tessellata and Microsteris gracilis) were less susceptible than others. Herbicides, particularly indaziflam, reduced E. elymoides emergence, but planting seeds at 2–3 cm depths improved emergence, particularly for imazapic, with 15–68% greater emergence than seeds planted at 1 cm. We suggest surveys for native annual forbs and resistant invaders before applying herbicides and field testing to determine whether reduced rates could provide weed control while maintaining annual forbs. We suggest planting E. elymoides at 2–3 cm when applying herbicides, an approach that may be effective for other species. Herbicide use can be an effective tool, but our results indicate that mitigation of nontarget effects will be needed to maintain native plant diversity.
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Overall, indaziflam + imazapic had greater initial control of cheatgrass, but by 2023, both treatments led to similar ∼17 percentage-point reductions in cheatgrass cover. Cheatgrass individuals that “escaped” the herbicide treatment grew exceptionally large and fecund. There were no reductions in cover in any native vegetation type, including biocrusts, and nontarget increases in cover were observed for 1) deep-rooted perennial grasses treated with indaziflam + imazapic in the 2011 burn subregion and 2) the shallow-rooted Sandberg bluegrass (Poa secunda) treated with either herbicide in the 2011 or 2011 + 2019 burn subregions. Consideration of burn legacies, pretreatment landscape condition, and evenness of treatment application may improve restoration outcomes and help prioritize management allocation, timing, and treatment expectations.
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Our research shows that across deserts, grasslands, and forests, plant communities with higher abundance of naturalized species are more acquisitive above and belowground, shorter, more shallowly rooted, and less dependent on mycorrhizal symbionts for resource acquisition. These functional shifts likely drive observed changes in carbon storage, litter decomposition, and nutrient and water cycling in invaded ecosystems. This mechanistic understanding of functional community change is a crucial step toward predicting and mitigating impacts of naturalized and invasive species.
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Using the Gunnison sage-grouse as a case study, we leveraged existing resource selection function models to identify areas of high restoration potential across landscapes with variable habitat conditions and habitat-use responses. We also tested how this information could be used to improve restoration planning. We simulated change in model covariates across crucial habitats for a suite of restoration actions to generate heatmaps of relative habitat suitability improvement potential, then assessed the degree to which use of these heatmaps to guide placement of restoration actions could improve suitability outcomes. We also simulated new or worsening plant invasions and projected the resulting loss or degradation of habitats across space. We found substantial spatial variation in projected changes to habitat suitability and new habitat created, both across and among crucial habitats. Use of our heatmaps to target placement of restoration actions improved habitat suitability nearly fourfold and increased new habitat created more than 15-fold, compared to placements unguided by heatmaps. Our decision-support products identified areas of high restoration potential across landscapes with variable habitat conditions and habitat-use responses. We demonstrate their utility for strategic targeting of habitat restoration actions, facilitating optimal allocation of limited management resources to benefit species of conservation concern.
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The word “risk” is often used informally to talk about feelings of danger or chances of loss. When communicating about wildfire risk, both inside the Forest Service and with the public and others, careful and intentional use of the term “risk” is more likely to increase shared understanding of all involved. What does “risk” mean? How is risk measured? How can wildfire risk be reduced? Can wildfire risk be eliminated? Here, we share definitions of risk in a technical sense, consistent with how the insurance industry considers risk. We focus mainly on wildfire risk related to communities, and how that risk can be reduced.
This special issue of Rangeland Ecology and Management is dedicated to applying the Sagebrush Conservation Design (SCD) to improve conservation outcomes across the sagebrush biome in the face of pervasive ecosystem threats.
Articles included:
State of the sagebrush: Implementing the Sagebrush Conservation Design to save a biome
Closing the conservation gap: Spatial targeting and coordination are needed for to keep pace with sagebrush losses
Climate change amplifies declines in sagebrush ecological integrity
Well-connected core areas retain ecological integrity of sagebrush ecosystems amidst overall declines 2001–2021
Spatial prioritization of conifer management to defend and grow sagebrush cores
A strategic and science-based framework for management of invasive annual grasses in the sagebrush biome
Modeling cropland conversion risk to scale-up averted loss of core sagebrush rangelands
Characterizing wildfire risk for the Sagebrush Conservation Design
An assessment of conservation opportunities within sagebrush ecosystems of US National Parks and Wildlife Refuges
Tool to promote stepping down the Sagebrush Conservation Design to local conservation planning
Exploring the sage grouse initiative’s role in defending and growing sagebrush core areas
Satellite remote sensing to assess shrubland vegetation responses to large-scale juniper removal in the northern Great Basin
Cooperative conservation actions improve sage-grouse population performance within the bi-state distinct population segment
Evaluating the Sagebrush Conservation Design Strategy through the performance of a sagebrush indicator species
How a Sagebrush Conservation Strategy benefits rangeland birds
Carbon Security Index: Novel approach to assessing how secure carbon is in sagebrush ecosystems within the Great Basin
Using technical transfer to bridge science production and management action
Assessing conservation readiness: The where, who, and how of strategic conservation in the sagebrush biome
Where do we go from here with sagebrush conservation: A long-term perspective?
There is no hope without change: A perspective on how we conserve the sagebrush biome