Recent, large fires in the western United States have rekindled debates about fire management and the role of natural fire regimes in the resilience of terrestrial ecosystems. This real-world ...experience parallels debates involving abstract models of forest fires, a central metaphor in complex systems theory. Both real and modeled fire-prone landscapes exhibit roughly power law statistics in fire size versus frequency. Here, we examine historical fire catalogs and a detailed fire simulation model; both are in agreement with a highly optimized tolerance model. Highly optimized tolerance suggests robustness tradeoffs underlie resilience in different fire-prone ecosystems. Understanding these mechanisms may provide new insights into the structure of ecological systems and be key in evaluating fire management strategies and sensitivities to climate change.
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In seasonally dry environments, the amount of water held in living plant tissue—live fuel moisture (LFM)—is central to vegetation flammability. LFM-driven changes in wildfire size and frequency are ...particularly important throughout southern California shrublands, which typically produce intense, rapidly spreading wildfires. However, the relationship between spatiotemporal variation in LFM and resulting long-term regional patterns in wildfire size and frequency within these shrublands is less understood. In this study, we demonstrated a novel method for forecasting the LFM of a critical fuel component throughout southern California chaparral, Adenostema fasciculatum (chamise) using gridded climate data. We then leveraged these forecasts to evaluate the historical relationships of LFM to wildfire size and frequency across chamise-dominant California shrublands. We determined that chamise LFM is strongly associated with fire extent, size, and frequency throughout southern California shrublands, and that LFM–wildfire relationships exhibit different thresholds across three distinct LFM domains. Additionally, the cumulative burned area and number of fires increased dramatically when LFM fell below 62%. These results demonstrate that LFM mediates multiple aspects of regional wildfire dynamics, and can be predicted with sufficient accuracy to capture these dynamics. Furthermore, we identified three distinct LFM ‘domains’ that were characterized by different frequencies of ignition and spread. These domains are broadly consistent with the management thresholds currently used in identifying periods of fire danger.
Cloud shading limits surface radiation, thus reducing vegetation water stress and, presumably, flammability. Since the early 1970s, cloud observations from airfields in coastal Southern California ...(CSCA) indicate reductions of ~25–50% in warm‐season frequency of daytime stratus clouds at many sites, including fire‐prone wildland‐urban interface zones. We use 10 years of meteorological, surface radiation, and cloud observations to statistically model the effects of clouds on warm‐season surface energy fluxes in CSCA. Forcing our model with cloud observations, we estimate that reduced warm‐season cloud shading since the 1970s significantly enhanced daytime solar radiation and evaporative demand throughout much of CSCA, particularly in greater Los Angeles and northern San Diego. Correlation with burned area and live fuel moisture implicates stratus cloud shading as an important driver of warm‐season wildfire activity in CSCA. Large reductions in cloud shading have likely enhanced warm‐season wildfire potential in many CSCA areas when and where fuels are not limiting.
Plain Language Summary
In much of coastal Southern California, the frequency of summer clouds has declined rapidly in recent decades due to warming from urbanization and greenhouse gases. These reductions have significantly reduced cloud shading and increased evaporative demand, particularly in greater Los Angeles and northern San Diego, such that a relatively cloudy summer today is similar to a relatively clear summer in the 1970s. Clouds appear to be important regulators of summer wildfire activity in this region, as the shade they provide slows loss of moisture from vegetation. On the vegetated mountainsides that ring coastal Southern California's large cities, increases in summer sunlight and evaporative demand have likely enhanced summer wildfire potential over the past several decades. This effect is expected to continue due to continued urban expansion and positive feedbacks, where warming due to cloud loss promotes further warming and cloud loss.
Key Points
Warm‐season daytime cloud frequency significantly declined in much of coastal Southern California over the past half century
Based on a statistical model, observed reductions in coastal cloud frequency significantly increased net radiation and evaporative demand
Correlation analysis suggests that summer cloud frequency significantly affects fuel moisture and burned area in coastal Southern California
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34.
The Science of Firescapes SMITH, ALISTAIR M.S.; KOLDEN, CRYSTAL A.; PAVEGLIO, TRAVIS B. ...
BioScience/Bioscience,
02/2016, Volume:
66, Issue:
2
Journal Article
Peer reviewed
Open access
Wildland fire management has reached a crossroads. Current perspectives are not capable of answering interdisciplinary adaptation and mitigation challenges posed by increases in wildfire risk to ...human populations and the need to reintegrate fire as a vital landscape process. Fire science has been, and continues to be, performed in isolated “silos,” including institutions (e.g., agencies versus universities), organizational structures (e.g., federal agency mandates versus local and state procedures for responding to fire), and research foci (e.g., physical science, natural science, and social science). These silos tend to promote research, management, and policy that focus only on targeted aspects of the “wicked” wildfire problem. In this article, we provide guiding principles to bridge diverse fire science efforts to advance an integrated agenda of wildfire research that can help overcome disciplinary silos and provide insight on how to build fire-resilient communities.
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Fire is a naturally occurring process of most terrestrial ecosystems as well as a tool for changing land use. Since the beginning of history humans have used fire as a mechanism for creating areas ...suitable for agriculture and settlement. As fires threaten human dominated landscapes, fire risk itself has become a driver of landscape change, impacting landscapes through land use regulations and fire management. Land use changes also influence fire ignition frequency and fuel loads and hence alters fire regimes. The impact of these changes is often exacerbated as new land users demand alternative fire management strategies, which can impact land cover and management far from where land use change has actually occurred. This creates nuanced land use teleconnections between source areas for fires and economic cores, which demand and fund fire protection. Here we will review the role of fire and fire risk as a driver of land use change, the ways land use changes impact drivers of fire, and suggest that the integration of land use teleconnections into the fire/land use discussion can help us better understand and manage the complex interactions between fire and land use.
Large fires in chaparral-dominated shrublands of southern and central California are widely attributed to decades of fire suppression. Prehistoric shrubland landscapes are hypothesized to have ...exhibited fine-grained age-patch mosaics in which fire spread was limited by the age and spatial pattern of fuels. In contrast, I hypothesize that fires during extreme weather conditions have been capable of burning through all age classes of the vegetation mosaic. Using the mapped fire history (1911-1995) of Los Padres National Forest, I analyzed burning patterns for hundreds of fires using a geographic information system (GIS). To estimate the degree of age dependency exhibited by the fire regime at different spatial scales, I employed methods of fire frequency analysis (i.e., fitting a generalized Weibull function to fire interval distributions). Statistics were also calculated using a temporal breakpoint of 1950 to assess possible effects of suppression. Results indicated that shrubland fires have frequently burned through young age classes of vegetation, exhibiting a minimal degree of age dependency. Findings were not scale dependent and were consistent for all but one region of the study area. The anomalous region exhibited a more rapid increase in the hazard of burning with fuel age, reflecting a moderately age-dependent fire regime; this difference probably resulted from the fact that the region is somewhat sheltered from extreme fire weather that commonly affects other shrublands. Exposure to extreme fire weather therefore appears to override the sensitivity of a fire regime to fuels characteristics at the landscape scale. Fire suppression has affected characteristics of smaller fires much more than those of larger fires. Since 1950, there has been a decrease in size and an increase in the number of smaller fires. Findings support the claim that fire suppression could offset ecological risks posed by increasingly frequent human-caused fires in specific areas, but with a net decrease in annual burning rate of ∼14% across the landscape. Findings contradict the assertion that, in the absence of fire suppression, large fires would be constrained by more complex age-patch mosaics on the landscape.
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Increased wildfire frequency and size has led to a surge in flammability research, most of which investigates landscape-level patterns and wildfire dynamics. There has been a recent shift towards ...organism-scale mechanisms that may drive these patterns, as more studies focus on flammability of plants themselves. Here, we examine methods developed to study tissue-level flammability, comparing a novel hot-plate-based method to existing methods identified in a literature review. Based on a survey of the literature, we find that the hot plate method has advantages over alternatives when looking at the specific niche of small-to-intermediate live fuel samples—a size range not addressed in most studies. In addition, we directly compare the hot plate method to the commonly used epiradiator design by simultaneously conducting flammability tests along a moisture gradient, established with a laboratory benchtop drydown. Our design comparison addresses two basic issues: (1) the relationship between hydration and flammability and (2) relationships between flammability metrics. We conclude that the hot plate method compares well to the epiradiator method, while allowing for testing of bigger samples.
Wildfires are becoming larger and more frequent across much of the United States due to anthropogenic climate change. No studies, however, have assessed fire prevalence in lake watersheds at broad ...spatial and temporal scales, and thus it is unknown whether wildfires threaten lakes and reservoirs (hereafter, lakes) of the United States. We show that fire activity has increased in lake watersheds across the continental United States from 1984 to 2015, particularly since 2005. Lakes have experienced the greatest fire activity in the western United States, Southern Great Plains, and Florida. Despite over 30 years of increasing fire exposure, fire effects on fresh waters have not been well studied; previous research has generally focused on streams, and most of the limited lake‐fire research has been conducted in boreal landscapes. We therefore propose a conceptual model of how fire may influence the physical, chemical, and biological properties of lake ecosystems by synthesizing the best available science from terrestrial, aquatic, fire, and landscape ecology. This model also highlights emerging research priorities and provides a starting point to help land and lake managers anticipate potential effects of fire on ecosystem services provided by fresh waters and their watersheds.
Wildfires are becoming larger and more frequent across much of the United States. We show that fire activity has increased in lake watersheds across the continental United States from 1984 to 2015, particularly since 2005. Despite over 30 years of increasing exposure, fire effects on lakes have not been well studied. We propose a conceptual model of how fire may influence the physical, chemical, and biological properties of lakes. This model highlights emerging research priorities and provides a starting point to help land and lake managers anticipate potential effects of fire on ecosystem services provided by lakes and their watersheds.
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As temperatures soar, forests blaze and houses burn, the media and public may be forced to face up to the reality of a changing climate, says Max A. Moritz.
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Altered disturbance regimes in the context of global change are likely to have profound consequences for ecosystems. Interactions between fire and vegetation are of particular interest, as fire is a ...major driver of vegetation change, and vegetation properties (e.g., amount, flammability) alter fire regimes. Mediterranean-type ecosystems (MTEs) constitute a paradigmatic example of temperate fire-prone vegetation. Although these ecosystems may be heavily impacted by global change, disturbance regime shifts and the implications of fire-vegetation feedbacks in the dynamics of such biomes are still poorly characterized. We developed a minimal modeling framework incorporating key aspects of fire ecology and successional processes to evaluate the relative influence of extrinsic and intrinsic factors on disturbance and vegetation dynamics in systems composed of grassland, shrubland, and woodland mosaics, which characterize many MTEs. In this theoretical investigation, we performed extensive simulations representing different background rates of vegetation succession and disturbance regime (fire frequency and severity) processes that reflect a broad range of MTE environmental conditions. Varying fire-vegetation feedbacks can lead to different critical points in underlying processes of disturbance and sudden shifts in the vegetation state of grassland-shrubland-woodland systems, despite gradual changes in ecosystem drivers as defined by the environment. Vegetation flammability and disturbance stochasticity effectively modify system behavior, determining its heterogeneity and the existence of alternative stable states in MTEs. Small variations in system flammability and fire recurrence induced by climate or vegetation changes may trigger sudden shifts in the state of such ecosystems. The existence of threshold dynamics, alternative stable states, and contrasting system responses to environmental change has broad implications for MTE management.
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