This page focuses on why homes burn and why the almost exclusive focus on the "clearance" of native vegetation is counterproductive to our efforts to reduce fire risk.
After becoming familiar with the details presented here, please see our Fire Safe Techniques page for products and methods available to homeowners and communities.
Also see a summary of California's new defensible space law near the bottom of this page.
It's not the Wildland Vegetation, it's the Location
In a new research paper concerning why homes burn in wildfires, Alexandra Syphard, a research scientist with the Conservation Biology Institute concluded, "We're finding that geography is most important—where is the house located and where are houses placed on the landscape."
Syphard and her coauthors gathered data on 700,000 addresses in the Santa Monica Mountains and part of San Diego County. They then mapped the structures that had burned in those areas between 2001 and 2010, a time of devastating wildfires in the region.
Buildings on steep slopes, in Santa Ana wind corridors and in low-density developments intermingled with wild lands were the most likely to have burned. Nearby vegetation was not a big factor in home destruction.
Looking at vegetation growing within roughly half a mile of structures, the authors concluded that the exotic grasses that often sprout in areas cleared of native habitat like chaparral could be more of a fire hazard than the shrubs. "We ironically found that homes that were surrounded mostly by grass actually ended up burning more than homes with higher fuel volumes like shrubs," Syphard said.
Needless to say, we hope local planning agencies, fire agencies, and politicians finally come around to using the science to protect both human communities and the beautiful wildlands that often surround them.
You must address the entire fire risk equation which involves location, building design, and fuel management. It is not just about managing vegetation.
In the short video below, Dr. Jack Cohen, a fire scientist with the USFS, explains what causes most homes to burn down.
Why we are concerned about over exuberant "clearance" regulations...
There have been efforts by some politicians to change California state law and local ordinances to require homeowners to unnecessarily "clear" vegetation up to 300 feet around their homes (nearly the length of a football field). Such excessive "clearance" distances have zero scientific validity.
There is no question that vegetation around homes can pose a risk to both communities and the firefighters asked to protect them. However, by demanding that citizens unilaterally clear their properties over such extreme distances, destroying garden landscapes and valuable habitat, policy makers and insurance companies are failing to recognize the true nature of fire. In addition, such unreasonable demands unfairly infringe upon private property rights.
Most homes do not burn from an imagined "wall of flame," but rather from embers that can travel up to three miles ahead of the flame front. How to reduce fire risk is not a one answer question. Excessive clearance zones will not protect poorly designed homes from embers during a typical Santa Ana wind driven firestorm. In fact, excessive clearance zones can actually increase fire risk by causing the growth of flammable weeds and creating a clear pathway for embers to impact structures.
We can create fire-safe communities without destroying the natural landscapes we enjoy.
Unfortunately, there are examples of private contractors who have been hired by fire districts to inspect, issue "abatement" notices, and do the "clearance" work. This is an obvious conflict of interest. The consequences of such a conflict are clearly described on our Help Joseph Diliberti page.
Is this the environment in which we want to live? 300 feet of dirt soon to be covered in flammable weeds and scarred by erosion gullies.
Video: Bare dirt clearing creates a "bowling alley" for embers to shoot directly at the house See the video above by Darian Spencer, a young scientist who has demonstrated how vegetation can protect a home from flying embers, the main cause of home ignition.
For details on the influence of flying embers in igniting homes, please read the 2009 report linked below. One of the report's main conclusions: During the 2007 Witch Creek Fire, houses in Rancho Bernardo started burning by ember contact when the fire front was 3 MILES away. 2/3rds of the burning homes were set on fire by embers.
Creating a "Defensible Space" Around Your Home: The Difference Between Rational Action and Overreaction
Dense and flammable vegetation needs to be removed from the area immediately around a home in order to reduce the risk of structural ignition during a wildfire. The question is how to properly do so without causing additional problems. The basic rule is to eliminate flammable materials (fire-prone vegetation, wood stacks, wood decking, patio furniture, umbrellas, etc.) from within 30 feet of the home. Then for structures near wildland open space, an additional 70 feet should be modified in such a way as to remove dead wood from shrubbery, thin and trim trees and shrubs (lower limbs removed), and prevent the growth of weedy grasses. Maintaining a modified canopy of vegetation to shade the ground is important to reduce weed growth.
The basic rule of thumb is to reduce the level of vegetation within 70 foot zone so that 50% of the ground remains covered by a vegetative canopy.
Unfortunately the term "clearance" is frequently used when referring to this 100 foot zone, leading people to think all vegetation must be removed down to bare soil. This is why the city of San Diego Fire and Rescue Department has replaced the word "clearance" to "thinning" when referring to vegetation management around homes and the new California defensible space law has changed the way vegetation management should be viewed (see below). Officials in the California Department of Forestry and Fire Protection (CalFire) are continually trying to help citizens understand that clearance doesn't mean the removal of all native plants. Bare soil clearance not only unnecessarily compromises large amounts of native wildlands and increases erosion, but will lead to the growth of weeds in the now disturbed soil. These weeds are considered "flashy fuels" which actually increase fire risk because they ignite so easily.
If fire risk and natural resource value had been properly considered, this house would never have been permitted. This shows why proper land planning is so important.
San Diego Mission in the late 1880's looking south. This type of "clearance" to mineral soil will certainly reduce fire risk, but at what cost? The conditions here were the the result of excessive grazing, repeated burning, and wood collecting.
A classic example of massive over-clearing in San Marcos, San Diego County. When do the total costs of such action exceed the assumed benefits? Although the total fuel load has been reduced, the amount of highly flammable fine, flashy fuel has been increased dramatically and a huge amount of native habitat has been destroyed.
WHAT'S WRONG WITH THE ABOVE PHOTO?
This often-used photo leaves the impression that clearing alone will save your house from a wildfire. It ignores other important variables. While some may think the "best" way to reduce fire risk is by striping down to bare ground wide areas around your house and replacing part of it with lawn or ice plant as shown above, the important question to ask is "considering the total costs, is this the most effective way to protect my house?"
The answer is No. It may be the easiest approach politically, but by no means does it guarantee your safety.
1. The primary mechanism for homes igniting during a wildfire is glowing embers. Embers can travel up to miles from the fire front. This is why wildfires jump ten-lane interstate highways and over large lakes. In a detailed report from the Institute for Business and Home Safety (2008), it was explained that “Wind-blown embers, which can travel one mile or more, were the biggest threat to homes in the Witch Creek Wildfire. There were few, if any, reports of homes burned as a result of direct contact with flames.” The Witch Creek Fire occurred in north San Diego County in 2007.
The reason the home above did not burn down could have been due to the presence of firefighters, shift in the direction or speed of the wind, fire resistant construction, time of day the fire reached the property (evening weather typically moderates fires), or just simple probability. We do not know from just looking at this photo.
2. The concept of "defensible space" by itself is not an adequate solution for Southern California. It presumes wildfires are small and firefighting resources will always be available. This is not realistic. The most damaging wildfires are typically large events that tax firefighting agencies. Chances are there may not be a firefighter available to use the defensible space. It is best to create a "survivable space" in which the home can survive on its own. This means fire-safety needs to focus on fire-resistant construction as well as proper fuel management.
3. Striping the land of native vegetation as the owner did above leads to erosion and the growth of invasive weeds. Weeds demand continual maintenance to control. Once dried, they pose an extended fire risk since they are much more flammable than properly thinned native vegetation. See the impact of such type-conversion on our Threats to Chaparral page.
4. Lightly irrigated, properly thinned and spaced shrubs can act as a "green" fire barrier, absorbing heat and deflecting oncoming embers. Bare, open space can not do this.
5. There are a number of reasons one decides to live next to a natural environment; peacefulness, enjoyment of wildlife, uncluttered vistas, native wildflowers, a chance to take an evening stroll through nature. While surrounding one's self with ice plant and other non-native additions may appeal to some, it is generally not supportive of these types of values. Although an easy target, native vegetation is not the enemy. We are next to it because of it. Therefore, it makes sense to build a home that is adapted to the environment in which it exists. Consequently, the first place to start when trying to protect your home from wildfire is from the structure out, not from the wildland in which includes: a. Proper attic vent construction (to keep out embers), non-combustible roofing (to resist embers), enclosed eaves (to defend against embers), and the removal of flammable objects such as wood fences, patio furniture, wood decking, etc. (to prevent ignition by embers). b. Making sure the first 30 feet around the home is free of flammable materials and is landscaped with fire resistant vegetation. c. The next 70 feet should not be stripped to bare ground as the photo above suggests. Selectively thin the native vegetation, remove the dead wood, maintain a loose canopy, without disturbing the soil. Make sure to avoid ornamentals such as Mexican fan palms and low growing acacia. Burning material from these species are well known by firefighters for being responsible in igniting homes. Once these three basic steps are accomplished, only minimal yearly maintenance needs be done, preserving the reason you live next to nature in the first place. The use of goats in some areas to create hundreds of feet of bare dirt clearance is more of a political response than one based on science. Not only will such action unnecessarily damage native plant communities, but it fails to address the main reason homes ignite - flying embers. See our Human Habitat page for a few more details on goat use.
During the July 2006 Sawtooth Fire, more than 50 homes burned in and near Pioneertown, a small community west of Yucca Valley and northwest of Palm Springs. Numerous homes with 100 feet+ of bare dirt clearance were destroyed by the fire. One interesting post-fire observation relates to the vegetation surrounding burned homes that didn't have adequate defensible space. In many cases, the only portion of the shrubs and trees that showed fire damage were the sides facing the home. It was the burning structure that ignited the vegetation, not the other way around.
During the 2007 Grass Valley fire near Lake Arrowhead, approximately 199 homes were destroyed or damaged. This was despite the fact that the US Forest Service had done an excellent job thinning the surrounding forest and removing fuels. The main cause of the losses was that individual homeowners failed to understand that vegetation management is only one part of the fire risk reduction equation. Fire will exploit the weakest link, and did so in Grass Valley. In the detailed report on the fire, the USFS (2008) wrote,
“Post-fire visual examination indicated a lack of substantial fire effects on the vegetation and surface fuels between burned homes. Lack of surface fire evidence in surrounding vegetation provides strong evidence that house-to-house ignitions by airborne firebrands were responsible for many of the destroyed homes.”
No Turning Back...
Once native vegetation is cleared and the soil is disturbed the homeowner is permanently shackled with a number of negative consequences:
1. Unnecessary destruction of the natural habitat 2. Continual maintenance costs 3. The introduction and growth of invasive weeds 4. Increased soil erosion and the formation of gullies 5. Surrounding aesthetics seriously damaged 6. Reduction of native animal life 7. Potential legal costs if “clearance” is done improperly or on public/private land without proper authorization 8. Failure to account for future changes in vegetation management laws 9. Failure to account for changes in personal tastes. Will you always want your home surrounded by dirt and weeds? 10. False sense of security that “clearance” will prevent your home from burning
The important point to understand is that there are multiple variables involved in trying to create a fire safe environment. "How do I prevent my home from burning?" is NOT a one answer question. While vegetation management will reduce the risk of home ignition, depending on it alone to protect your home in a firestorm is wishful thinking at best.
To read a full analysis of the negative impacts of excessive clearance distances, read our letter to the California State Senate commenting on a bill that would have required 300 feet of clearance around homes. The bill was defeated in committee.
For addtional information concerning the personal experiences of others regarding the uneven and confusing enforcement of fire clearance regulations see the Save the Chaparral blog.
The 1st pdf. file to the right is an excellent study done in Australia about why homes burn in wildland fires.
How to Properly Manage Vegetation
The 2nd pdf. file to the right provides one reasonable plan to reduce fire risk around your home WITHOUT unnecessary, excessive clearing. It shows an excellent diagram of what an area looks like after proper thinning.
Depending on clearance? Study this photo for a moment. This is a post-fire scene after the July, 2006 Sawtooth Fire near Yucca Valley. You can see the termination of the fire front on the blackened ground in the background. The distance between the fire front and the little burned shrub in the left foreground is approximately 250 feet. Why did this shrub burn? Invasive weeds directly under the shrub caught fire from flying embers. Weeds and embers are a dangerous combination that current "clearance" regulations fail to address. Details about this particular fire and the role invasive weeds play in spreading fire can be found in issue #20 of The Chaparralian. To request a copy, please go to our membership page.
This map shows a development that was heavily damaged by the 2003 Cedar Fire in San Diego County. Houses marked in orange burned down.
The movement of the fire front is indicated by the red arrow. Based on the concept of defensible space, houses 1 and 2 should not have burned down because they were hundreds of feet away from the actual fire. They burned because embers ignited the roof of one which in turn ignited its neighbor.
California's requirements for defensible space around structures according to Public Resources Code 4291
The latest defensible space law was signed by the Governor on September 27, 2008 (SB 1595 by Senator Kehoe) makes it very clear that reducing fire risk around a home needs to be a multi-faceted effort. The new defensible space law makes it clear that fire risk reduction is not just about native vegetation. The new law will took effect January 1, 2009.
Here are the key definitions in the law
1. Embers. "The wildfire front is not the only source of risk since embers, or firebrands, travel far beyond the area impacted by the front and pose a risk of ignition to a structure or fuel on a site for a longer time."
2. Fuel. "Fuel means any combustible material."
3. Vegetation. "Vegetation means all plants, including trees, shrubs, grass, and perennial or annual plants." This is an important definition because previous language focused on native plants, ignoring highly flammable ornamental species such as Mexican fan palms, acacia, etc.
4. Statewide.It is the intent of the Legislature that this law "apply to all local agencies." However, the law does not limit "the authority of a local agency to impose more restrictive fire and public safety requirements..."
5. More than just vegetation. "The Legislature finds and declares that site and structure defensibility is essential to reduce the risk of structure ignition as well as for effective fire suppression by firefighters. This need to establish defensibility extends beyond the site fuel management practices required by this chapter, and includes, but is not limited to, measures that increase the likelihood of a structure to withstand ignition, such as building design and construction requirements that use fire resistant building materials, and provide standards for reducing fire risks on structure projections, including, but not limited to, porches, decks, balconies and eaves, and structure openings, including, but not limited to, attic, foundation, and eave vents, doors, and windows."
Here are the law's key provisions
If you live within a designated "very high fire hazard severity zone" as identified by the director of the California Department of Forestry and Fire Protection, the following will apply:
1. 100 feet. Maintain a defensible space zone "no greater than 100 feet" from each side of an occupied structure, but not beyond the property line unless allowed by state law. A greater distance may be required by local ordinance if no other feasible mitigation measure is possible to reduce the risk of ignition of a structure.
2. How much management. "The amount of fuel modification necessary shall take into account the flammability of the structure as affected by building material, building standards, location, and type of vegetation. Fuels shall be maintained in a condition so that a wildfire burning under average weather conditions would be unlikely to ignite the structure. This paragraph does not apply to single specimens of trees or other vegetation that are well-pruned and maintained so as to effectively manage fuels and not form a means of rapidly transmitting fire from other nearby vegetation to a structure or from a structure to other nearby vegetation. The intensity of fuels management may vary within the 100-foot perimeter of the structure, the most intense being within the first 30 feet around the structure. Consistent with fuels management objectives, steps should be taken to minimize erosion."
3. Insurance companies. "An insurance company that insures an occupied dwelling or occupied structure may require a greater distance than" 100 feet "if a fire expert, designated by the fire chief or fire official from the authority having jurisdiction, provides findings that such a clearing is necessary to significantly reduce the risk of transmission of flame or heat sufficient to ignite the structure, and there is no other feasible mitigation measure possible to reduce the risk of ignition or spread of wildfire to the structure."
4. Other people's property. "A person is not required under this section to manage fuels on land if that person does not have the legal right to manage fuels, nor is a person required to enter upon or to alter property that is owned by any other person without the consent of the owner of the property."
5. Exemption.The local agency may exempt from the standards set forth in this law "structures with exteriors constructed entirely of nonflammable materials, or conditioned upon the contents and composition of the structure, and may vary the requirements respecting the management of fuels surrounding the structures in those cases."
6. Consequences of noncompliance. "The director may authorize the removal of vegetation that is not consistent with the standards of this section. The director may prescribe a procedure for the removal of that vegetation and make the expense a lien upon the building..."
7. Protection of habitat and homes. "The Department of Forestry and Fire Protection shall develop, periodically update, and post on its Internet Web site a guidance document on fuels management pursuant to this chapter. Guidance shall include, but not be limited to, regionally appropriate vegetation management suggestions that preserve and restore native species, minimize erosion, minimize water consumption, and permit trees near homes for shade, aesthetics, and habitat; and suggestions to minimize or eliminate the risk of flammability of nonvegetative sources of combustion such as woodpiles, propane tanks, wood decks, and outdoor lawn furniture."
Know the difference between the law and an interpretation of the law
It is important to remember that this is a state law. Local jusistictions are allowed to require additional vegetation management procedures. Unfortuantely, many of these are based on misconceptions and political inertia rather than science. While most fire departments are very helpful in working with residents to develop reasonable vegetation management practices, there are exceptions. Every law is open to intrepretation. Become familiar with your own local ordinances in order to help inspectors enforce them properly. Do not allow contractors to take the easy way out and unnecessarily destroy native landscapes.
DISCOVER YOUR HOME'S or COMMUNITY'S WILDFIRE RISKS
To see the latest research on how to prepare for wildfire from the community outward instead of from the wildland inward, see the ONLINE WILDFIRE RISK ASSESMENT TOOL from UC Berkeley.