Useful in Certain Ecosystems
There is ample evidence that fire has been excluded in dry Jeffrey/ponderosa pine and mixed-conifer forests found at high elevations in California, as well as in some types of oak woodlands and savannas at lower elevations, over the past century or more. Allowing fire to do its important ecological work in these ecosystems is a goal shared by most agencies and organizations engaged in conservation work across the state.
Implementing prescribed fire—specifically understory or broadcast burning—where ecologically appropriate can reduce fire severity in a subsequent wildfire, though extreme weather conditions may reduce this effect. Prescribed fire can also provide benefits to many fire-adapted plants and wildlife.
Importantly, the use of prescribed fire in conifer forests does not necessarily need to be preceded by intensive mechanical thinning and vegetation removal. Prescribed fire has been used with great success in dense, unthinned mixed-conifer forests in the Sierra Nevada for decades. This is in contrast to the use of slash pile burning, which does not fully mimic low- to moderate-severity fire and which may follow ecologically damaging commercial thinning or logging activities involving the use of heavy machinery.
Like any vegetation management activity, prescribed fire must be used thoughtfully and carefully on landscapes where it makes sense ecologically. This tool is not without risk, which is why we advocate that projects undergo proper environmental review to ensure that ecosystems will benefit and that non-target adjacent landscapes will not be negatively affected.
Check out our detailed comment letter on a large U.S. Forest Service proposal to see an example of how we have supported the use of ecologically appropriate prescribed fire in Los Padres National Forest.
The Wrong Approach for Chaparral
While prescribed fire can be beneficial in some ecosystems in our area, there is broad agreement that its use in chaparral in southern California can be ecologically harmful and ineffective at mitigating subsequent wildfires. About 72% of Los Padres National Forest is dominated by chaparral, making this an important issue to highlight. To understand why prescribed fire can be problematic in this ecosystem, it is important to first understand the issue of type conversion. Simply put, type conversion is the replacement of one vegetation type with another. In this case, native chaparral is typically replaced with non-native grasses and weeds (e.g. wild oats and black mustard). A major cause of type conversion in our region is overly-frequent fire or fire return intervals that are too short.
Chaparral Loss to Frequent Fire
Before European colonization, chaparral across the central and south coasts of what is now California generally burn every 30 – 100+ years depending on the frequency of lightning—the primary natural source of wildfire ignition—and human-caused fires. Chaparral wildfires are naturally intense crown fires, meaning they burn most or all above-ground vegetation. Between fires, chaparral species need ample time to grow to maturity and produce enough seed to recolonize an area after the next fire. The pre-colonization fire regime allowed for fire to occur on the landscape at intervals that allowed native shrub species to persist over the long term.
With European colonization and the spread of ranching and other activities, more fires were started both intentionally and unintentionally, while non-native plant species were being introduced simultaneously. In the 20th century, these effects became even more pronounced with a rapidly growing network of roads, suburban areas, and human activity. Fire frequency has generally increased, with less time between fires for plants to grow to maturity and produce seed. As fires burn the same area more frequently than every 30 years (and especially when we see chaparral burn more than once every decade or two), that area becomes more susceptible to non-native species dominating as the native chaparral seed bank is depleted and resprouting species experienced reduced carbohydrate stores.
The Ineffectiveness of Prescribed Fire in Chaparral
The use of prescribed fire in areas already experiencing overly frequent fire only exacerbates the type conversion process while not necessarily reducing an area’s risk of burning later. In short, it is not a cost-effective method in chaparral. This can be easily seen by overlapping wildfire burn areas in and around the Los Padres National Forest. For example, the 2017 Thomas Fire burned most of the areas burned by 1985’s Wheeler and Ferndale Fires, areas burned by the 2003 Piru Fire and 2006 Day Fire, and canyons that burned in the 2008 Tea Fire and 2009 Jesusita Fire. The 2016 Soberanes Fire burned over half of the area burned by the 2008 Basin Complex Fire in the Monterey Ranger District. The recent Thomas Fire also burned through several coastal sage scrub and grassland areas near Ventura where prescribed fire had been conducted in prior years. To be effective, chaparral prescribed fires would probably have to be conducted very frequently (every five years or less) in a specific area. But the paradox here is that such frequent fire occurrence can and will lead to the loss of the native shrub species that make chaparral such a unique and important ecosystem.
The timing of prescribed fire is also of concern to fire scientists. Prescribed fires must be conducted during a narrow window in order to be successful due to vegetation moisture levels and weather conditions, meaning they are often done in winter or spring when many wildlife species are breeding and birds are nesting in the area. Prescribed fire during this time may heat up the moist soil to the point that seeds are damaged by the resulting steam. Conversely, these fires may not burn hot enough to stimulate native seed germination. For example, many native Ceanothus species require high heat to modify their seed coat and allow germination. Lower temperature fires—which may intuitively seem like a good thing—have actually been shown to reduce the post-fire regeneration of these and other similar species with fire-cued dormant seed banks.
Indigenous Use of Prescribed Fire in Chaparral
There is evidence that Native Americans used prescribed fire along the central coast before Europeans settled in our region. However, researchers have determined prescribed fire was being used to purposefully convert chaparral to grasslands, primarily along coastal plains and inland valleys, to allow for movement across the landscape, the creation of open hunting areas, the selection of edible herbaceous plants, and the reduction of habitat for potentially dangerous predators such as grizzlies—not necessarily to reduce the incidence of large wildfires. In fact, large landscape-scale fires still occurred prior to European colonization and subsequent American expansion.
Where Native Americans burned chaparral prior to colonization tended to be localized, indicating thoughtful use of fire rather than the indiscriminate burning of the landscape. Many of the areas that were converted from chaparral to native grassland or savannas were then claimed by European colonizers to be used for non-native cattle grazing. American ranchers later expanded these areas through use of frequent fire, which likely led to large losses of chaparral in the 19th and early 20th centuries. Unlike the native grasses and herbs that grew in the chaparral’s place when Native Americans purposefully type converted areas, today’s type conversion results in the spread of highly flammable non-native species. These species actually pose a greater wildfire risk as they dry out earlier in the year, ignite more easily, and spread wildfire more quickly than chaparral.
Approaches That Work for Chaparral Areas
So, with the concerns and challenges surrounding prescribed burning in chaparral, is there a more effective way to protect our communities from wildfire in wildland-urban interface areas adjacent to this ecosystem? Scientists and fire ecologists agree that the most effective ways to protect communities involve hardening structures against wind-blown embers, creating smart defensible space around homes, and rethinking where and how we build in fire-prone areas.
