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.

Plant community response to prescribed fire varies by pre-fire condition and season of burn in mountain big sagebrush ecosystems

Artemisia tridentata ssp. vaseyana ecosystems evolved with periodic fire, but invasive grasses, conifer encroachment, fire suppression, and climate change have resulted in altered fire regimes and plant communities. Post-fire increases in invasive annual grasses such as Bromus tectorum and reductions in native vegetation are common across the sagebrush steppe. Where fire has been excluded though, there are increases in the native tree Juniperus occidentalis, which outcompetes the native understory. We applied prescribed fire in spring and fall at three sites (native-dominated, B. tectorum-dominated, and J. occidentalis-dominated). We documented 65% survival of A. tridentata following fall burns and 33% survival following spring burns in native-dominated plots, with evidence of post-fire sprouting in Purshia tridentata and Tetradymia canescens. At the B. tectorum-dominated site, shrub cover was reduced to <1%. Fires at the J. occidentalis site were discontinuous, resulting in ∼50% mortality of trees and shrubs, with little resprouting. Native herbaceous vegetation persisted following fires, with no increases in B. tectorum. There were higher plant survival rates following fall fires and native-dominated sites than in spring burns or where exotics dominated. These results show that burn season and prefire condition are important considerations when evaluating management alternatives in A. tridentata ssp. vaseyana ecosystems.

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.

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.

Effects of climate change on snowpack and fire potential in the western USA

We evaluate the implications of ten twenty-first century climate scenarios for snow, soil moisture, and fuel moisture across the conterminous western USA using the Variable Infiltration Capacity (VIC) hydrology model. A decline in mountain snowpack, an advance in the timing of spring melt, and a reduction in snow season are projected for five mountain ranges in the region. For the southernmost range (the White Mountains), spring snow at most elevations will disappear by the end of the twenty-first century. We investigate soil and fuel moisture changes for the five mountain ranges and for six lowland regions. The accelerated depletion of mountain snowpack due to warming leads to reduced summer soil moisture across mountain environments. Similarly, warmer and drier summers lead to decreases of up to 25% in dead fuel moisture across all mountain ranges. Collective declines in spring mountain snowpack, summer soil moisture, and fuel moisture across western mountain ranges will increase fire potential in flammability-limited forested systems where fuels are not limiting. Projected changes in fire potential in predominately fuel-limited systems at lower elevations are more uncertain given the confounding signals between projected changes in soil moisture and fuel moisture.

Community Vulnerability to Health Impacts of Wildland Fire Smoke Exposure

Identifying communities vulnerable to adverse health effects from exposure to wildfire smoke may help prepare responses, increase the resilience to smoke and improve public health outcomes during smoke days. We developed a Community Health-Vulnerability Index (CHVI) based on factors known to increase the risks of health effects from air pollution and wildfire smoke exposures. These factors included county prevalence rates for asthma in children and adults, chronic obstructive pulmonary disease, hypertension, diabetes, obesity, percent of population 65 years of age and older, and indicators of socioeconomic status including poverty, education, income and unemployment. Using air quality simulated for the period between 2008 and 2012 over the continental U.S. we also characterized the population size at risk with respect to the level and duration of exposure to fire-originated fine particulate matter (fire-PM_2.5) and CHVI. We estimate that 10% of the population (30.5 million) lived in the areas where the contribution of fire-PM_2.5 to annual average ambient PM_2.5 was high (>1.5 μg/m³) and that 10.3 million individuals experienced unhealthy air quality levels for more than 10 days due to smoke. Using CHVI we identified the most vulnerable counties and determined that these communities experience more smoke exposures in comparison to less vulnerable communities.