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Boulder City, NV, United States

Harrington M.G.,Rocky Research
International Journal of Wildland Fire | Year: 2013

Western larch is one of the most fire-adapted conifers in western North America. Its historical perpetuation depended upon regular fire disturbances, which creates open stand conditions and mineral seedbeds. A stand of 200-to 500-year-old larch in western Montana with deep duff mounds resulting from an unusually long 150-year fire-free period was mechanically thinned and prescribed burned to reduce the probability of high intensity wildfire near a community and increase opportunities for larch regeneration. Little documentation is available regarding basal damage to larch from lengthy duff mound burning; therefore this study was established to assess: duff consumption from prescribed burning and resulting cambial damage and tree vitality. Ninety trees averaging 91-cm diameter at breast height were selected, half with duff mounds measured and burned in autumn and half with mounds removed. Duff depths nearest the bole averaged 20cm and mound consumption approached 100% including large amounts of the basal bark with smouldering combustion lasting 18-24h. Cambial mortality ranged from 0 to 36% of the basal circumference but no trees had died after 7 years. The cambium mortality was likely due to the spatially infrequent coincident of deep duff and thinner bark. Under similar site and environmental conditions removal of the potential duff consumption injury hazard appears unwarranted. © 2013 IAWF. Source

In the US, wildfires and prescribed burning present significant challenges to air regulatory agencies attempting to achieve and maintain compliance with air quality regulations. Fire emission factors (EF) are essential input for the emission models used to develop wildland fire emission inventories. Most previous studies quantifying wildland fire EF of temperate ecosystems have focused on emissions from prescribed burning conducted outside of the wildfire season. Little information is available on EF for wildfires in temperate forests of the conterminous US. The goal of this work is to provide information on emissions from wildfire-season forest fires in the northern Rocky Mountains, US. In August 2011, we deployed airborne chemistry instruments and sampled emissions over eight days from three wildfires and a prescribed fire that occurred in mixed conifer forests of the northern Rocky Mountains. We measured the combustion efficiency, quantified as the modified combustion efficiency (MCE), and EF for CO2, CO, and CH4. Our study average values for MCE, EFCO2, EFCO, and EFCH4 were 0.883, 1596 g kg-1, 135 g kg-1, 7.30 g kg-1, respectively. Compared with previous field studies of prescribed fires in temperate forests, the fires sampled in our study had significantly lower MCE and EFCO2 and significantly higher EFCO and EFCH4. The fires sampled in this study burned in areas reported to have moderate to heavy components of standing dead trees and down dead wood due to insect activity and previous fire, but fuel consumption data was not available. However, an analysis of MCE and fuel consumption data from 18 prescribed fires reported in the literature indicates that the availability of coarse fuels and conditions favorable for the combustion of these fuels favors low MCE fires. This analysis suggests that fuel composition was an important factor contributing to the low MCE of the fires measured in this study. This study only measured EF for CO2, CO, and CH4; however, we used our study average MCE to provide rough estimates of wildfire-season EF for PM2.5 and four non-methane organic compounds (NMOC) using MCE and EF data reported in the literature. This analysis suggests the EFPM2.5 for wildfires that occur in forests of the northern Rocky Mountains may be significantly larger than those reported for temperate forests in the literature and that used in a recent national emission inventory. If the MCE of the fires sampled in this work are representative of the combustion characteristics of wildfire-season fires in similar forest types across the western US then the use of EF based on prescribed fires may result in an underestimate of wildfire PM2.5 and NMOC emissions. Given the magnitude of biomass consumed by western US wildfires, this may have important implications for the forecasting and management of regional air quality. ©Author(s) 2013. Source

Butler B.W.,Rocky Research
International Journal of Wildland Fire | Year: 2014

Current wildland firefighter safety zone guidelines are based on studies that assume flat terrain, radiant heating, finite flame width, constant flame temperature and high flame emissivity. Firefighter entrapments and injuries occur across a broad range of vegetation, terrain and atmospheric conditions generally when they are within two flame heights of the fire. Injury is not confined to radiant heating or flat terrain; consequently, convective heating should be considered as a potential heating mode. Current understanding of energy transport in wildland fires is briefly summarised, followed by an analysis of burn injury mechanisms within the context of wildland fire safety zones. Safety zone theoretical and experimental studies are reviewed and a selection of wildland fire entrapments are examined within the context of safe separation distances from fires. Recommendations are made for future studies needed to more fully understand and define wildland firefighter safety zones. © IAWF 2014. Source

Maron J.L.,University of Montana | Pearson D.E.,Rocky Research
Ecology Letters | Year: 2011

The strength of trophic cascades in terrestrial habitats has been the subject of considerable interest and debate. We conducted an 8-year experiment to determine how exclusion of vertebrate predators, ungulates alone (to control for ungulate exclusion from predator exclusion plots) or none of these animals influenced how strongly a three-species assemblage of rodent consumers affected plant productivity. We also examined whether predator exclusion influenced the magnitude of post-dispersal seed predation by mice. Both ungulates and rodents had strong direct effects on graminoid biomass. However, rodent impacts on plant biomass did not differ across plots with or without predators and/or ungulates. Deer mice removed more seeds from seed depots on predator exclusion plots, suggesting trait-mediated indirect effects of predators, but this short-term behavioural response did not translate into longer-term impacts on seed survival. These results suggest that vertebrate predators do not fundamentally influence primary production or seed survival in our system. © 2011 Blackwell Publishing Ltd/CNRS. Source

Urbanski S.,Rocky Research
Forest Ecology and Management | Year: 2014

While the vast majority of carbon emitted by wildland fires is released as CO2, CO, and CH4, wildland fire smoke is nonetheless a rich and complex mixture of gases and aerosols. Primary emissions include significant amounts of CH4 and aerosol (organic aerosol and black carbon), which are short-lived climate forcers. In addition to CO2 and short-lived climate forcers, wildland fires release CO, non-methane organic compounds (NMOC), nitrogen oxides (NOx=NO+NO2), NH3, and SO2. These species play a role in radiative forcing through their photochemical processing, which impacts atmospheric levels of CO2, CH4, tropospheric O3, and aerosol. This paper reviews the current state of knowledge regarding the chemical composition of emissions and emission factors for fires in United States vegetation types as pertinent to radiative forcing and climate. Emission factors are critical input for the models used to estimate wildland fire greenhouse gas and aerosol emission inventories. © 2013. Source

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