Weather Effects
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The Great Basin of the western United States is experiencing dramatic increases in wildfire and Bromus species invasion that potentially accelerate wind erosion and plant community change. We used a wind erosion model parameterized for rangelands and standard ecological monitoring data sets collected at 10,779 locations from 2011 to 2019 to characterize potential wind erosion in the Great Basin, assess relationships between factors affecting wind erosion, and quantify effects of wildfire and invasive Bromus species on aeolian horizontal sediment flux, Q. There were 403 monitoring plots (∼3.7% of plots) with Q > 100 g m⁻¹ d⁻¹. Median values for the highest Q category (>100) ranged from 196.5 to 308.5 g m⁻¹ d⁻¹. Locations with Q > 100 g m⁻¹ d⁻¹ were associated with dry, low elevation areas of the Great Basin with low perennial grass and perennial forb cover, and with large bare gaps between plants. Areas with high perennial grass, perennial forb, and shrub cover had small Q (≤10 g m⁻¹ d⁻¹). Substantial wind erosion was predicted in areas that have experienced wildfires, but areas with multiple wildfires had a lower predicted probability of Q particularly as invasive Bromus species cover increased. Modeled Q was up to two orders of magnitude higher post‐wildfire (median 44.2 g m⁻¹ d⁻¹) than in intact or annual grass‐invaded regions of the Great Basin (median 0.4 g m⁻¹ d⁻¹). Our results reveal the complex interplay among plant community composition, wildfire, and the amount of bare ground controlling wind erosion on Great Basin rangelands.
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This paper provides a synthesis of the key laboratory- and field-based observational studies focused on wildland fire and atmospheric turbulence connections that have been conducted from the early 1900s through 2021. Included in the synthesis are reports of anecdotal turbulence observations, direct measurements of ambient and fire-induced turbulent flow in laboratory and wildland environments, and remote sensing measurements of fire-induced turbulent plume dynamics. Although considerable progress has been made in advancing our understanding of the connections between atmospheric turbulence and wildland fire behavior and smoke dispersion, gaps in that understanding still exist and are discussed to conclude the synthesis.
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Focus on wind changes and mid-tropospheric properties may be counterproductive or distracting when one is concerned about major growth events on very large fires.
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Here, we investigated the effects of seasonal weather and plant associations, related to abiotic characteristics, on herbaceous production dynamics across 44 intact, representative sagebrush steppe sites across eastern Oregon from 2003 to 2012. We tested for the effects of sampling year, lagged precipitation, and potential evapotranspiration predictors, as well as prior year biomass and plant association on production of major herbaceous functional groups. We also tested for synchrony across functional groups and plant associations. We found that spring precipitation was the most consistent predictor of production. However, several other variables including prior year weather significantly affected production. Production sensitivity to weather was combined with high synchrony across functional groups and associations, suggesting low potential for production stability associated with these factors in sagebrush steppe in the northern Great Basin.
Webinar recording.
The second webinar of the Forest Service’s Research and Development SCIENCEx FIRE week.
Fire Weather and Smoke
Fire Weather Forecasting | Brian Potter
New Technology for Monitoring Smoke Impacts | Shawn Urbanski
Smoke Plume Dynamics | Yong Liu
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We found the predicted positive relationship between mesic habitat availability and sage-grouse productivity, but annual precipitation explained additional variation in productivity even after accounting for mesic habitat availability. Hence, precipitation and drought may drive sage-grouse productivity via more than one mechanism acting on multiple demographic rates. Productivity was also limited by exotic annual grass invasion and conifer encroachment. Mesic habitat availability was a function of topographic relief, mean elevation, annual mean snow water equivalent, and winter temperatures, indicating that snowpack recharges the late summer mesic resources that support sage-grouse productivity. Management actions focused on maintaining and restoring mesic resources and drought resilient habitats, limiting the spread of exotic annual grasses, and reversing conifer encroachment should support future sage-grouse recruitment and help mitigate the effects of climate change.
Webinar recording.
Wotton, Canadian Forest Service, explains lightning fire ignition and the important processes that determine the day-to-day variation of this important source of summertime fire activity in Canada. This presentation is for both academic and operational audiences in Canada’s wildfire community.
Examples from models developed and used in Ontario’s fire occurrence prediction system were provided as well as some comparisons to similar model development in other regions of the country. Reviewing the history and operational use of these models in Ontario provides useful examples of the challenges and opportunities (and ultimately the long-term investment required) in getting research into operational use in wildland fire management.
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This study reports on preliminary investigations into recent and unexpected Great Basin bristlecone pine mortality at two sites, including the potential roles of weather-induced stress and bark beetles. At both sites climatic water deficit (CWD), a cumulative measure of moisture stress, and mean annual temperature increased during the 2010 decade and CWD was the highest in 2020 relative to any time during the past 40 years. Although Great Basin bristlecone pine mortality has not previously been attributed to bark beetles, we observed recent (i.e., 2013 to 2020) bark beetle-attacked trees at both sites, coincident with the timing of increasing temperature and CWD. Few adult beetles were produced, however, and our results support previous research that Great Basin bristlecone pine is a population sink for bark beetles. Because bark beetles are likely not self-sustaining in Great Basin bristlecone pine, bark beetle-caused mortality of this iconic species will most likely occur when it grows mixed with or near other pine species that support bark beetle population growth. We found Ips confusus and Dendroctonus ponderosae attacking Great Basin bristlecone pine in areas where their host trees, P. monophylla and P. flexilis, were also growing. These results suggest that the presence of these infested conifers likely contributed to Great Basin bristlecone pine mortality. We highlight several factors that may be used for prioritizing future research and monitoring to facilitate development of management strategies for protecting this iconic species.
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Forests in western North America are shaped by fire and — for the past century or more — by the absence of it. After more than a century of fire exclusion and under a rapidly changing climate, fire behavior has changed, and damage from wildfire is increasing. With more than a century of forest and fire science to build on, scientists, managers, and communities are refining management options for reducing risks to communities and ecosystems.
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In this study, we tested components of climatic water balance, including standardized precipitation-evapotranspiration index (SPEI) and SPEI computation lengths, to recreate multi-decadal and periodic soil-moisture patterns across soil profiles at 866 sites in the western United States. Modeling results show that SPEI calculated over the prior 12-months was the most predictive computation length and could recreate changes in moisture availability within the soil profile over longer periods of time and for annual recharge of deeper soil moisture stores. SPEI was slightly less successful with recreating spring surface-soil moisture availability, which is key to dryland ecosystems dominated by winter precipitation. Meteorological drought indices like SPEI are intended to be convenient and generalized indicators of meteorological water deficit. However, the inconsistent ability of SPEI to recreate ecologically relevant patterns of soil moisture at regional scales suggests that process-based models, and the larger data requirements they involve, remain an important tool for dryland ecohydrology.