Airborne measurements of western U.S. wildfire emissions: Comparison with prescribed burning and air quality implications

Wildfires emit significant amounts of pollutants that degrade air quality. Plumes from three wildfires in the western U.S. were measured from aircraft during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC⁴RS) and the Biomass Burning Observation Project (BBOP), both in summer 2013. This study reports an extensive set of emission factors (EFs) for over 80 gases and 5 components of submicron particulate matter (PM₁) from these temperate wildfires. These include rarely, or never before, measured oxygenated volatile organic compounds and multifunctional organic nitrates. The observed EFs are compared with previous measurements of temperate wildfires, boreal forest fires, and temperate prescribed fires. The wildfires emitted high amounts of PM₁ (with organic aerosol (OA) dominating the mass) with an average EF that is more than 2 times the EFs for prescribed fires. The measured EFs were used to estimate the annual wildfire emissions of carbon monoxide, nitrogen oxides, total nonmethane organic compounds, and PM₁ from 11 western U.S. states. The estimated gas emissions are generally comparable with the 2011 National Emissions Inventory (NEI). However, our PM₁ emission estimate (1530 ± 570 Gg yr⁻¹) is over 3 times that of the NEI PM_2.5 estimate and is also higher than the PM_2.5 emitted from all other sources in these states in the NEI. This study indicates that the source of OA from biomass burning in the western states is significantly underestimated. In addition, our results indicate that prescribed burning may be an effective method to reduce fine particle emissions.

After the Fire Workshop: Connecting People, Ideas and Organizations

Fire adaptation is about more than pre-fire work. It’s also about considering the needs of a community and the land post-fire. In Washington State, the last several fire seasons have given communities lots of opportunities to learn about post-fire recovery. Last month, members of organizations that work on community issues, landscape resilience and disaster-recovery gathered to share some of the things they’ve learned.

Alternative characterization of forest fire regimes: incorporating spatial patterns

The proportion of fire area that experienced stand-replacing fire effects is an important attribute of individual fires and fire regimes in forests, and this metric has been used to group forest types into characteristic fire regimes. However, relying on proportion alone ignores important spatial characteristics of stand-replacing patches, which can have a strong influence on post-fire vegetation dynamics. We propose a new more ecologically relevant approach for characterizing spatial patterns of stand-replacing patches to account for potential limitation of conifer seed dispersal. We applied a simple modified logistic function to describe the relationship between the proportion of total stand-replacing patch area and an interior buffer distance on stand-replacing patches. This approach robustly distinguishes among different spatial configurations of stand-replacing area in both theoretical and actual fires, and does so uniquely from commonly used descriptors of spatial configuration. Our function can be calculated for multiple fires over a given area, allowing for meaningful ecological comparisons of stand-replacing effects among different fires and regions.

Fall and spring grazing influence fire ignitability and initial spread in shrub steppe communities

The interaction between grazing and fire influences ecosystems around the world. However, little is known about the influence of grazing on fire, in particular ignition and initial spread and how it varies by grazing management differences. We investigated effects of fall (autumn) grazing, spring grazing and not grazing on fuel characteristics, fire ignition and initial spread during the wildfire season (July and August) at five shrub steppe sites in Oregon, USA. Both grazing treatments decreased fine fuel biomass, cover and height, and increased fuel moisture, and thereby decreased ignition and initial spread compared with the ungrazed treatment. However, effects differed between fall and spring grazing. The probability of initial spread was 6-fold greater in the fall-grazed compared with the spring-grazed treatment in August. This suggests that spring grazing may have a greater effect on fires than fall grazing, likely because fall grazing does not influence the current year’s plant growth. Results of this study also highlight that the grazing–fire interaction will vary by grazing management. Grazing either the fall or spring before the wildfire season reduces the probability of fire propagation and, thus, grazing is a potential fuel management tool.

Contrasting Spatial Patterns in Active-Fire and Fire- Suppressed Mediterranean Climate Old-Growth Mixed Conifer Forests

In Mediterranean environments in western North America, historic fire regimes in frequent-fire conifer forests are highly variable both temporally and spatially. This complexity influenced forest structure and spatial patterns, but some of this diversity has been lost due to anthropogenic disruption of ecosystem processes, including fire. Information from reference forest sites can help management efforts to restore forests conditions that may be more resilient to future changes in disturbance regimes and climate. In this study, we characterize tree spatial patterns using four-ha stem maps from four oldgrowth, Jeffrey pine-mixed conifer forests, two with active-fire regimes in northwestern Mexico and two that experienced fire exclusion in the southern Sierra Nevada. Most of the trees were in patches, averaging six to 11 trees per patch at 0.007 to 0.014 ha21, and occupied 27–46% of the study areas. Average canopy gap sizes (0.04 ha) covering 11–20% of the area were not significantly different among sites. The putative main effects of fire exclusion were higher densities of single trees in smaller size classes, larger proportion of trees ($56%) in large patches ($10 trees), and decreases in spatial complexity. While a homogenization of forest structure has been a typical result from fire exclusion, some similarities in patch, single
tree, and gap attributes were maintained at these sites. These within-stand descriptions provide spatially relevant
benchmarks from which to manage for structural heterogeneity in frequent-fire forest types.

A Compendium of Brief Summaries of Smoke Science Research In Support of the Joint Fire Science Program Smoke Science Plan

Introduction --- The Smoke Science Plan (SSP) and Brief Project Summaries
During the course of the Joint Fire Program Smoke Science Plan’s five-year duration, 41 research projects came under its umbrella. Each of these projects whether funded under the plan or funded before it began, were managed to further the four themes of the plan and each theme’s objectives. The SSP themes and their objectives are:
• The objective of the Smoke Emissions Inventory Research Theme is to develop science and knowledge needed to improve national wildland fire emissions inventories, paving the way for the design of a national consensus inventory system.
• The objective of the Fire and Smoke Model Validation Theme is to identify the scientific scope, techniques and partnerships needed to objectively validate smoke and fire models using field data.
• The objectives of the Populations and Smoke Theme are to quantify the impact of wildland fire smoke on population centers and on fire fighters, and to elucidate the mechanisms of public smoke acceptance in light of the needed balance between human smoke exposure risk and ecosystem health risk. Ultimately this is envisioned to help in the development of a national smoke hazard warning system/methodology based on best science.
• The objectives of the Smoke and Climate Change Theme are to better understand implications of climate change on wildland fire smoke and of wildland fire smoke on climate change using UN IPCC future climate scenarios for guidance (IPCC, 2013).

In this document readers will find concise summary statements for each of the projects under the SSP. These statements were prepared for the JFSP for use in guiding the program’s ‘smoke line of work’ or smoke research portfolio. They are not inclusive of everything that might be reported about each of the research projects, but they do provide the reader with a concise place to begin determining what research has been done and more importantly, what results may address their needs. This compendium of brief summaries is arranged by JFSP SSP theme. All are either summaries of project final reports (where available) or summaries of responses submitted (March 2017) by project principal investigators. All JFSP project final reports can be found at WWW.FIRESCIENCE.GOV.

Prescribed Burning in Ponderosa Pine: Fuel Reductions and Redistributing Fuels near Boles to Prevent Injury

Fire suppression and other factors have resulted in high wildfire risk in the western US, and prescribed burning can be an effective tool for thinning forests and reducing fuels to lessen wildfire risks. However, prescribed burning sometimes fails to substantially reduce fuels and sometimes damages and kills valuable, large trees. This study compared fuel reductions between spring and fall prescribed burns and tested whether removing (i.e., raking) fuels within 1 m of boles reduced fire damage to ponderosa pine (Pinus ponderosa Douglas ex Lawson & C. Lawson). In 2007 and 2008, raking was applied to alternating trees along 18 transects in central Oregon, USA. Fuels surrounding 292 trees were burned in fall 2010, and fuels surrounding 216 trees were burned in spring 2012. Both seasons of burn affected most fuel size classes similarly, with one exception being duff, which was more fully consumed in fall than in spring. Where fall burning occurred, raking reduced the percentage of dead cambium samples from 24.3 ±4.9 % to 6.4 ±3.0 % (point estimates ±95 % confidence intervals), in addition to reducing bole scorch. Conversely, where spring burning occurred, injury of not-raked trees was milder, so raking did not have the potential to greatly reduce damage. Redistributing fuels away from boles would be more beneficial under relatively dry conditions when duff is prone to extensive smoldering. Our study and most other studies suggest that duff is, on average, drier in fall than in spring, so raking would tend to afford more protection from fall burns than from spring burns. The little tree mortality that occurred was split nearly evenly between raked trees (25) and not-raked trees (30), so raking did not appreciably increase survival in this study. However, the finding that raking reduced injury suggests that it may reduce mortality from more intense burns.