Fire and climate change in the Sierra Nevada of California, USA have a complex interaction with human land management and forest ecology. Fire was an important agent of change for the fire prone forests of this landscape. Many species, such as the Giant Sequoia (Sequoiadendron giganteum) evolved to take advantage of frequent fire as this natural process sculpted the environment. Native Americans used fire widely for socioeconomic benefit and fuel reduction with moderate intensity fire encouraged to burn across the land. Euro-American settlement brought about an era of suppression that increased fuels and changed the forest composition and structure. But, suppression was and is the simple seeming solution. Even if suppression is not sustainable it will garner support. Historic suppression has currently brought an extreme fuel problem that has manifested into a greater and greater threat of destructive high intensity fire not typical of this ecosystem. Fire policy was and is slow to change due to risk aversion and lack of urgency. This is not in small part from increased smoke impacts as a result of heavy fuel loads and returning fire to the landscape. These emissions were essentially mortgaged to the current age from previous generations. Fire and land management policies collide with air regulatory policy in California because of already heavily anthropogenically polluted air with little to no capacity for an additional emission source. However, fire and the subsequent smoke are inevitable. Public smoke tolerance is low and a significant deterrent to bringing fire back to California wilderness.

AbstractSmoke from wildland fire is a significant concern to resource managers who need tools, knowledge, and training to analyze, address, and minimize potential impacts; follow relevant rules and regulations; and inform the public of possible effects. Successful navigation of competing pressures to appropriately use fire on the landscape to manage fire-adapted and fire-dependent ecosystems, while protecting public health and other air quality values, depends on credible science and tools conceived of and developed in partnership between managers and the research community. Fire and smoke management are made even more complex by the current condition of ecosystems as a result of fire exclusion and the future implications of a changing climate. This chapter describes the scope of smoke management, social and regulatory contexts, and pathways through which scientific information and tools can improve the accuracy and timeliness of management and communication with the public.

Wildland fire is a natural process integral to the formation and health of forest ecosystems globally. California, USA, is case study where large areas of wildland have a recent 100 plus year history of human suppression of fire that with extreme weather is combining to create large high intensity burns changing both species composition and increasing threats to life, health and property. The cool wet winters and hot dry summers in California produce a climate where fire is common and many environmental systems have evolved to rely on frequent fire for reproduction and health. Fire has been systemically removed creating a backlog of fuels as vegetation normally burned accumulates. Extreme weather enhanced by climate change is increasing the duration of the fire season and occurrence of extreme fire weather and events. The abundance of fuels and increase in probability of fire, primarily due to human-caused ignitions in the wildland-urban interface, are creating an increase of large catastrophic fires not typical of these ecosystems. These large high-intensity fires are an immediate threat to life and property, produce large amounts of smoke impacting human health far from the fire, and leave behind a burn area then susceptible to extreme rainfall events that create landslides and mudslides. Returning fire to the historic role it has played in sustaining these systems reduces the probability of catastrophic fire and the conditions where extreme rainfall can additionally cause further threats to life and property from debris flows. Exposure of the public to smoke from wildfire increases when high intensity burns occur. Wildland fire typical of this ecosystem which occurred before suppression limited the extent and amount of such exposure. There are current attempts to effect positive change to policy and give a voice to the role of fire in the ecosystem. Long-standing policy based on the unsustainable complete exclusion of fire and public pressure on air quality inhibits functional change to smoke and fire management. The collision of what current fire and smoke science advises as the appropriate action (inclusion of fire as a land management tool), and public opinion driving implementation of fire management decisions in California (the exclusion of fire) illustrates a global problem where climate change and policy driven by belief are synergistically worsening environmental and human health.

Wildland fire is an important component to ecological health in California forests. Wildland fire smoke is a risk factor to human health. Exposure to smoke from fire cannot be eliminated, but managed fire in a fire-prone ecosystem for forest health and resiliency allows exposure to be mitigated while promoting other ecosystem services that benefit people. The California Sierra Nevada is a paragon of land management policy in a fire-prone natural system. Past fire suppression has led to extreme fuel loading where extreme fire events are much more likely, particularly with climate change increasing the length of fire season and the probability of extreme weather. We use the California Sierra Nevada to showcase the clash of increased development and urbanization, past land management policy, future scenarios including climate change, and the intertwining of ecological health and human health. Fire suppression to avoid smoke impact has proven to be an unreliable way to decrease smoke-related health impacts. Instead ecological beneficial fires should be employed, and their management should be based on smoke impacts at monitors, making air monitoring the foundation of fire management actions giving greater flexibility for managing fires. Tolerance of smoke impacts from restoration fire that is best for forest health and resiliency, as well as for human health, is paramount and preferred over the political expediency of reducing smoke impacts today that ignores that we are mortgaging these impacts to future generations.

As the climate in California warms and wildfires become larger and more severe, satellite-based observational tools are frequently used for studying impact of those fires on air quality. However little objective work has been done to quantify the skill these satellite observations of smoke plumes have in predicting impacts to PM2.5 concentrations at ground level monitors, especially those monitors used to determine attainment values for air quality under the Clean Air Act. Using PM2.5 monitoring data from a suite of monitors throughout the Central California area, we found a significant, but weak relationship between satellite-observed smoke plumes and PM2.5 concentrations measured at the surface. However, when combined with an autoregressive statistical model that uses weather and seasonal factors to identify thresholds for flagging unusual events at these sites, we found that the presence of smoke plumes could reliably identify periods of wildfire influence with 95% accuracy.

Fuel treatments (prescribed fire and mechanical removal) on public lands in California are critical for reducing fuel accumulation and wildfire frequency and severity and protecting private property located in the wildland–urban interface. Treatments are especially needed in forests impacted by air pollution and subject to climate change. High ambient ozone (O3) concentration and elevated nitrogen (N) deposition weakens and predisposes trees to bark beetle attacks, increases foliar senescence and fuel build-up, and increases water stress during drought periods. Climate variability is expected to increase beyond historic ranges of variation, resulting in more severe droughts. Combinations of future climate variability and air pollution are likely to increase risk of episodic tree mortality, long-term ecosystem changes, and frequency and severity of wildland fires. Fuel treatments, however, are difficult to implement in these forests. Smoke from prescribed fires can adversely affect local and regional air quality leading to conflicts with local and regional air regulatory agencies. Over the past several years federal land air quality and fire managers have responded to these conflicting needs by expanding beyond the boundaries of their historical job responsibilities. For example, they are now actively forging cooperative relationships with local, state, and federal air regulators. The result has been fewer conflicts about smoke in populated or protected areas, with managers achieving an adequate level of prescribed fire treatments. Smoke monitoring by air managers has played a key role in this success. Social and regulatory acceptance of fire as a management tool in air polluted forests will depend on land managers developing a better understanding of air pollution and smoke interactions and interactions between air pollution, drought, and insects. Acceptance of fire as a management tool also requires better large-scale monitoring efforts (field collected and remotely sensed), development of models for predicting spatial and temporal distribution of air pollution and smoke resulting from forest fires, and incorporation of air pollution and climate effects into forest mensuration models used to predict stand development.

Air pollution impacts in the Sierra Nevada encompass a variety of social and scientific issues that require close coordination of land management agencies. Management approaches are largely opportunistic and include utilizing the legislated mandates and regulatory mechanisms to evaluate impacts and provide recommendations on permit issuance and mitigations to air regulatory agencies, and resource manipulation to slow or reduce effects, such as thinning, prescribed fire, soil treatment, water treatment, and visitor health warnings. The most effective mechanism of managing air resources on national forests in the Sierra is through the federal Clean Air Act and the Prevention of Significant Deterioration process to protect Class I areas. With compelling evidence, air regulatory agencies may have opportunities to strengthen standards and ozone reduction targets based on risk to forest ecosystems.

Over the next ten to twenty years, California's population is projected to increase, particularly in air basins upwind of the Sierra Nevada mountain range (i.e., San Francisco Bay Area, Sacramento and San Joaquin Valleys). Related trends in ozone (O 3 ) concentrations are a matter of special concern, due to a long history of O 3 injury to sensitive pines in national forests of the Sierra Nevada. While the USDA Forest Service has limited authority over polluted air masses crossing into forest boundaries, monitoring results can be used in a collaborative effort with state and federal environmental protection agencies to protect resources at risk. One such effort was initiated under the Sierra Nevada Framework for Conservation and Collaboration. An ambient O 3 concentrations and O 3 effects monitoring system is under development that will integrate previous and current monitoring efforts across agencies, and will track pollutant concentrations and effects over the entire bioregion.

Hourly ambient ozone exposure data and crown injury measurements were gathered in the Sierra Nevada and San Bernardino Mountains of California to develop relationships between the Ozone Injury Index (OII), the Forest Pest Management Index (FPM), chlorotic mottle, fascicle retention (OII index components) and cumulative ambient ozone indices for Pinus ponderosa Dougl. ex Laws and Pinus jeffreyi Grev. and Balf. Eleven sites located in the mixed conifer forest near ambient ozone monitoring sites were evaluated annually for 4 years. Four other sites in the San Bernardino Mountains were evaluated for 1 year. Analyses showed OII to be functionally equivalent (r2 = 0.96) to the FPM, and to depend only on fascicle retention and chlorotic mottle (R2 = 0.95) of the fourth whorl (or if four whorls are not present at the site, then the last whorl present for the majority of trees). Significant associations were found between OII and 4-year 24-h. summer SUM0, SUM06, W126 and HRS80 ozone indices. Three sites had higher levels of cumulative chlorotic mottle for individual whorls and larger numbers of trees with visible crown injury than other sites with similar cumulative ambient ozone levels. Including an indicator variable to discriminate between these two groups of sites increased R2 and decreased root mean square (RMSE) for all indices, especially SUM0 (R2 = 0.93, RMSE reduced by 46%).

An increasing need to treat hazardous fuel conditions in the Sierra Nevada combined with a geographic relationship to surrounding air basins with very serious air quality issues has resulted in challenges for land management and air regulatory agencies. A series of policies, plans and regulations at federal, state, and local levels addresses issues that require attention in order to increase treatment with prescribed fire while protecting public health. Monitoring fine particles (PM 10) produced by smoke provides land management and regulatory agencies with information necessary to avoid significant community impacts. Recently, new filter-based monitoring systems have been developed. Met One's BAM-1020 beta attenuation mass monitor is a federal reference method that meets the EPA requirements for monitoring PM10 compliance, but can be limited in use by land management agencies due to a lack of portability and reliance on line power. Met One's E-BAM is a portable real-time beta gauge. While not a federal reference method, the EBAM has shown strong correlation with BAM data and is highly portable. A pilot program has been developed to test the utility, accuracy, reliability, and data management requirements of these instruments in a comprehensive network. The test network will include three fixed-site BAMs in sensitive communities and approximately 10 portable EBAMs that will be deployed in communities as needed to characterize the impacts of smoke from prescribed fire and wildland fire.