Spatial patterns and controls on burned area for two contrasting fire regimes in Southern California

Abstract

An improved understanding of the mechanisms that regulate wildfire risk at local to regional scales is needed for the design of effective fire and ecosystem management. We investigated the spatial distribution of burned area in Southern California during 1960–2009 using five different data‐driven methods: multiple linear regression, generalized additive models (GAMs), GAMs with spatial autocorrelation, non‐linear multiplicative models, and random forest models. We used each method to separately develop burned area risk maps for Southern California's two distinct wildfire regimes: Santa Ana (SA fires), which occur during high wind events mostly in autumn, and non‐Santa Ana fires (non‐SA fires), which occur mostly during the hot and dry Mediterranean‐climate summer. The different methods explained 38–63% of the spatial variance in burned area for SA fires and 21–48% for non‐SA fires. The two fire regimes had contrasting drivers, with Fosberg fire weather index, relative humidity, minimum temperature, and distance to housing most important for SA fires, and shrub cover, road density, and distance to minor and major roads most important for non‐SA fires. Our modeling framework carries implications for the strategic placement of fire suppression resources, and for prevention planning in areas facing increasing human and climate pressures.

Seed Origin and Protection Are Important Factors Affecting Post-Fire Initial Recruitment in Pine Forest Areas

“…Thus, post-dispersal seed predation does not predict good expectations for pine species in non-masting years. Contrary to previous studies developed in this area (see [34,38,50]), the high emergence levels of unprotected seeds indicated that seed predation was not significant in our experiment, but post-emergence seedling herbivory was a key factor.…”

“…Under ongoing global change, models fitted to simulate forest occupancy under a climate change scenario project a reduction in the P. sylvestris Spanish range and a decline in P. nigra forests, whereas P. pinaster would maintain or increase the area it occupies [35,37]. Forest fires, which are natural components of Mediterranean forest ecosystems [38] might change pine species distribution through altering post-fire initial recruitment. Fire significantly reduces seedling emergence and survival rates in the short term and seed availability is a crucial variable for post-fire natural regeneration.…”

Detecting Drought-Induced Tree Mortality in Sierra Nevada Forests with Time Series of Satellite Data

“…In ecological applications, such as land cover classification or burned area mapping, RFs often produce more accurate and interpretable results than linear or additive models [18,36,77].…”

Spatial Distribution of Wildfires Ignited under Katabatic versus Non-Katabatic Winds in Mediterranean Southern California USA

“…Globally, most fire-prone regions are characterized by a singular type of fire regime that is prescribed by dominant vegetation, climatology, and ignitions [8][9][10]. Southwestern California, by contrast, has two distinct types of wildfires that are delineated seasonally through atmospheric circulation patterns [7,11]. One fire regime is associated with Santa Ana winds that occur when a strong regional pressure gradient produces downslope offshore katabatic wind events across the southward and westward facing slopes of the peninsular and transverse ranges.…”

“…By contrast, non-Santa Ana fires predominately occur during the summer months when synoptic-scale winds are generally weak. Several recent studies have begun to demonstrate the distinctions between these two regimes, including modeling their dominant drivers and socioeconomic impacts [7,[11][12][13], but they have not yet delineated spatial extents to determine if well-defined boundaries exist between regimes.…”