Bureau of Land Management

Considering potential cumulative effects of proposed actions is fundamental to environmental impact analysis. However, cumulative effects analyses historically are not robust, especially for site-specific decisions. We sought to identify opportunities to strengthen cumulative effects analysis in a large United States public land management agency, the Bureau of Land Management (BLM). We asked 1) how cumulative effects analyses were legally challenged, 2) how site-specific cumulative effects analyses aligned with policy and compared to the broader-scale analyses to which they tiered, and 3) whether characteristics of cumulative effects analyses varied with category of proposed action, type of resource, or agency office. We used thematic analysis to assess litigation and appeals case documents finalized from 2010 to 2020 and a set of document analysis questions to assess National Environmental Policy Act (NEPA) analyses for BLM decisions completed prior to 2020 in Alaska and Colorado. We found that legal challenges related to cumulative effects focused on absence of cumulative effects analysis. In NEPA analyses, cumulative effects were frequently considered, but elements recommended in policy, such as citations, methods, and scope, were rarely included. These elements were present more often in the broader analyses to which site-specific analyses tiered. Many elements of cumulative effects analyses varied by proposed action and BLM office, and analyses of potential cumulative effects on air quality were consistently more detailed than for other resources. Our results suggest that many problems that historically plagued cumulative effects analysis persist. Advances in methods, training, and guidance could strengthen the defensibility of NEPA analyses. • Mention of cumulative effects was common in environmental assessments. • Cumulative effects analyses seldom aligned with all policy recommendations. • Legal challenges usually focused on absence of cumulative effects analysis. • Tiering to planning-level analyses added detail but was inconsistent. • Characteristics of cumulative effects analyses varied across actions and offices.

Utah parks are attracting an increasing number of visitors due to the quality dark sky viewing opportunities. Despite increasing engagement in nighttime recreation, limited research exists on visitor interest in interpretation for dark skies in state and national parks. Nighttime visitors at nine Utah state and national park units certified as dark sky parks were surveyed to evaluate their preferences for dark sky-related interpretive topics and communication methods. Visitors expressed the strongest interest in astronomy and improving dark sky viewing, with ranger-led programs emerging as the most favored delivery method. National park visitors showed greater interest than state park visitors in self-guided learning formats such as interpretive displays and mobile apps for topics such as dark sky viewing/astronomy and viewing wildlife at night. These findings highlight the benefits of diverse, yet targeted communication strategies to improve visitor experiences of dark skies and foster stewardship of natural darkness in parks.

Thermal runaway from chemical reactions is the result of competition between heat generation and heat dissipation in industrial chemical vessels. However, the worldwide used TD24 (the temperature at which time to maximum rate under adiabatic conditions equals 24 h) focuses solely on heat generation for abnormal conditions of cooling failure, which account for only an insignificant portion of thermal runaway incidents. In contrast, the temperature of no return (TNR), defined by the balance of heat generation and heat dissipation, provides a more relevant threshold for process upsets in industrial chemical vessels. As the operating temperature approaches the TNR, minor thermal disturbances can precipitate thermal runaway. To estimate this threshold, calorimetry is coupled with reactor-scale energy-balance modeling. Kinetic parameters are determined using accelerating rate calorimetry (ARC), with corroborating measurements from differential scanning calorimetry (DSC), vent sizing package (VSP) calorimetry, and micro reaction calorimetry (μRC). In this work, the downside of TD24 for runaway hazard assessment is first analyzed. Guided by the Semenov diagram, a heat-balance model for stirred-tank reactors (STRs) is established, and based on ARC tests on a 20 wt % solution of di-tert-butyl peroxide (DTBP) in toluene under adiabatic conditions, a heat-generation-rate expression and a coolant heat-dissipation-rate expression are derived. A computational procedure is then proposed to determine TNR. Relative to adiabatic TD24, TNR supports optimization of reactor-cooling design, enhancing alarms and interventions under abnormal conditions, and quantitative assessment of reaction hazards.

Rangelands are extensive ecosystems, providing important ecosystem services while undergoing continuous change. As a result, improved monitoring technologies can help better characterize vegetation change. Satellite remote sensing has proven effective in this regard, tracking vegetation dynamics at broad and fine scales. We leveraged the spatial, spectral, and temporal resolution of Sentinel-2 satellites to estimate fractional cover and canopy gap across rangelands of the western United States. We produced annual, 10 m spatial resolution estimates of fractional cover and canopy gap size class for years 2018 to 2024. Fractional cover estimates include that of common plant functional types (annual forb and grass, bareground, littler, perennial forb and grass, shrub, tree) and select genera (including invasive annual grass species, pinyon-juniper species, and sagebrush species); canopy gap size classes include gap sizes 25 to 50, 51 to 100, 101 to 200, and greater than 200 cm. We make these data available as Cloud Optimized GeoTIFFs, organized as 75 × 75 km tiles covering the 17 western states of the United States.

Abstract. An improved mechanistic model of mercury redox chemistry has recently been implemented in the GEOS-Chem model. In this study, GEOS-Chem simulations were compared to ambient measurements made during a high-oxidized mercury episode that originated in the free troposphere at a mountaintop site in Colorado, USA (40.455° N, −106.744° W, 3220 m above sea level). Measurements were collected with a dual channel atmospheric oxidized mercury measurement system that has been shown to accurately quantify oxidized mercury compounds in ambient air. The model and observations showed similar temporal trends for elemental and oxidized mercury (R2 of 0.54 to 0.79) and similar elemental mercury concentrations (normalized mean square error of 0.04 in the base model). However, the base model only produced 17 % of the maximum oxidized mercury observed in the dual channel system. In sensitivity tests with increased oxidation rates, the model still only produced, at most, 23 % of maximum observed oxidized mercury. In addition to underestimating net mercury oxidation, an analysis of elemental to oxidized mercury slopes indicated the model overestimated oxidized mercury deposition. An analysis of GEOS-Chem results from a separate study confirmed that while GEOS-Chem is able to simulate the range of measured oxidized mercury in low-oxidized mercury episodes and locations it consistently underestimates measured values during high-oxidized mercury periods at surface locations in western USA.

The basal friction coefficient, defined as the ratio of basal shear to normal stress, is fundamental to understanding granular avalanche dynamics. Normalized stress fluctuations, quantifying deviations from the mean stress, capture grain-scale interactions, yet their link to bulk friction remains unclear. Through inclined-chute experiments using uniform glass beads under varying slopes and flow thicknesses, we show that the fluctuation intensity systematically decreases as the flow becomes thicker and increases with slope. When both basal friction and stress fluctuations are rescaled by geometric parameters, the data collapse onto a unified curve, revealing a robust power-law trend. This scaling demonstrates that frictional resistance strengthens with enhanced stress variability but weakens with flow depth, offering a quantitative framework for modeling the mobility of landslides and debris flows.

Abstract Background Large, severe fires are increasing throughout frequent-fire forests of the western United States due to warming climatic conditions, as well as legacies of early twentieth century land-use practices and anthropogenic fire exclusion. Resource objective (RO) wildfires—where naturally ignited wildfires are allowed to burn to accomplish management objectives—are increasingly accepted due to relatively low cost and flexibility on lands where mechanical treatments are not allowed (e.g., designated wilderness) or economically feasible. We previously implemented a field study across a portion of the Mount Trumbull Wilderness to identify differences between historical (ca. 1870) and contemporary (1999) forest structural conditions following 100 + years of fire exclusion. The study area subsequently experienced two RO wildfires (2012 and 2019), which presented an opportunity to (1) assess how closely post-wildfire (2023) conditions approximated historical forest conditions and (2) evaluate how RO fires influenced patterns of tree mortality and regeneration. Results Reconstructed forest structure was made up of open stand conditions (density: 62 trees ha −1 ; basal area: 9 m 2 ha −1 ) with large ponderosa pines (quadratic mean diameter: 42 cm). By 1999, the site was dominated by closed-canopy stands with many small-diameter trees. In 2023, following the two RO wildfires, tree density, basal area, and canopy cover were significantly reduced (20–50%), and tree size significantly increased. Ponderosa pine regeneration density declined relative to pre-fire levels, whereas regeneration of sprouting hardwood species increased. About half of the old trees (i.e., pre-dating ca. 1870) that were alive in 1999 died by the end of the study period, likely due to effects of fire-caused injury and drought. High-severity patch sizes in each fire were relatively small (6.2–46.6 ha) and within the historical range of variability for southwestern ponderosa pine ecosystems. The 2012 fire reduced remotely sensed fire severity in 2019. Conclusions Overall, RO fires shifted forest structure in a remote wilderness area toward open conditions that were historically present at the site, and likely reduced vulnerability to severe fire in the future. However, tree density remained six times higher than historical levels, and managers should consider allowing future RO wildfires to burn within the wilderness to further reduce tree density and accomplish ecological restoration goals.