Wildfire Protection in the Wildland-Urban Interface

Wildfire Protection in
the Wildland-Urban Interface
Ross W. Gorte
Specialist in Natural Resources Policy
Resources, Science, and Industry Division
Summary
Congress is giving increased attention and funding to wildfire threats. Much of the
concern focuses on protecting homes and other structures in and near forests, an area
known as the wildland-urban interface. However, not all agree on what can and should
be done during wildfires, in their aftermath, and especially beforehand to protect the
interface. This report describes the growth of the wildland-urban interface, wildfire
suppression efforts, post-fire responses, and especially the programs and options for
protecting the interface before the next wildfire strikes.
Wildfires have made national headlines in recent years, with major fires in the West
and South killing firefighters, burning homes, and threatening communities. Federal
funding for fire protection has more than doubled in the past decade, and administration
and congressional leaders have urged additional wildfire protection. (See CRS Report
RL33990, Wildfire Funding, by Ross W. Gorte.) Attention has focused on protecting
people, homes, and communities in the wildland-urban interface (WUI), but opinions
vary over how to protect the interface.
What Is the Wildland-Urban Interface?
The term wildland-urban interface (WUI) has been used for more than two decades
to suggest an area where homes are in or near wildlands (forests or rangelands). The
report from a 1986 conference on fire protection defined the WUI as “where combustible
homes meet combustible vegetation.”¹ In January 2001, the Forest Service (FS) and the
Department of the Interior (DOI) identified types of interface communities.² Based on

¹ USDA Forest Service, National Fire Protection Association, and U.S. Fire Administration,
Wildfire Strikes Home! (Jan. 1987), p. 2.
² U.S. Dept. of Agriculture and Dept. of the Interior, “Urban Wildland Interface Communities
Within the Vicinity of Federal Lands That Are at High Risk From Wildfire,” 66 Fed. Reg. 753
(continued...)

state data, they listed nearly 4,500 interface communities (with 11 states not providing
data). In particular, the agencies defined an interface community as where wildlands abut
structures with a clear line of demarcation between houses and wildland fuels, while an
intermix community is where houses are scattered and intermingled with wildlands and
fuels.
Recent research has found that the area of intermix communities is large and is
growing faster than the area of interface communities.³ In 2000, intermix communities
in the three Pacific Coast states totaled 9.8 million acres, almost three times the 3.3
million acres in interface communities in those states. The 10-year growth in area of
intermix communities was 14.1%, compared to only 2.5% for interface communities.
However, the study acknowledged that determining the area of WUI communities was
imprecise: “Mapping [the Federal Register] definition of the WUI using data and
operational definitions we developed, we arrived at one possible representation of the
WUI.”⁴ The intermingled nature of intermix communities poses significant challenges
for fire protection efforts.
Fire Suppression
In most of the Unites States, wildfires are inevitable. Biomass plus dry conditions
equals fuel to burn. Add an ignition source (e.g., lightning or a thrown cigarette) and a
wildfire happens. Fire is a self-sustaining chemical reaction that perpetuates itself as long
as all three elements of the fire triangle — fuel, heat, and oxygen — remain available.
Fire control focuses on removing one of those elements.
There are two principal kinds of wildfire, although an individual wildfire may
contain areas of both kinds.⁵ A surface fire burns the needles or leaves, grass, and other
small biomass within a foot or so of the ground and quickly moves on. Such fires are
relatively easy to control by removing fuel with a fireline, essentially a dirt path wide
enough to eliminate the continuous fuels needed to sustain the fire, or by cooling or
smothering the flames with water or dirt.
A crown fire burns biomass at all levels, from the surface through the tops of the
trees. Crown fires do not consume all the biomass; rather, a crown fire quickly burns the
needles or leaves and small twigs and limbs on the surface and throughout the crown of
the trees. Because the needles and leaves in the crown are green, they require more
energy to burn than dry fuels on the surface. Furthermore, because of the green fuels and
the often discontinuous biomass of the canopy, wind is usually needed to sustain a crown
fire. Once burning vigorously, a crown fire can create its own wind — the strong upward

² (...continued)
(Jan. 4, 2001).
³ Roger B. Hammer, Volker C. Radeloff, Jeremy S. Fried, and Susan L. Stewart, “Wildland-
Urban Interface Housing Growth During the 1990s in California, Oregon, and Washington,”
International Journal of Wildland Fire, v. 16 (2007): pp. 255-265.
⁴ Hammer et al., “Wildland-Urban Interface Housing Growth,” p. 256.
⁵ See Stephen F. Arno and Steven Allison-Bunnell, Flames in Our Forest: Disaster or Renewal?
(Washington, DC: Island Press, 2002), pp. 45-46.

convection of the heated air can draw in cooler air from surrounding areas, thus creating
a wind that feeds the fire. The strong upward convection can also lift burning biomass
(firebrands) and send it soaring ahead of the fire, creating spot fires and accelerating the
spread of the wildfire. Thus, crown fires are difficult, if not impossible, to control.
Firelines are often ineffective, especially if winds are causing spot fires. Water or fire
retardant (slurry) dropped from helicopters or airplanes can sometimes knock a crown fire
down (back to a surface fire) if the area burning and the winds are not too great. Often,
however, crown fires burn until they run out of fuel or the weather changes (the wind dies
or it rains or snows).
Fires burn structures in one of three ways: through direct contact with fire (the fire
burning right up to the structure); through radiation (heating from exposure to flames);
and through firebrands landing on a flammable roof.⁶ Surface fires generally only burn
houses through direct contact, and protection is a relatively simple matter of a break in the
continuous burnable material. In observing houses that burned in Los Alamos in 2000,
one researcher stated “in several cases, a scratch line that removed [pine] needles from
the base of a wood wall kept the house from igniting.”⁷ Crown fires, however, can burn
houses in any of the three ways. The opportunity and ability to prevent structures from
burning during a crown fire is small. Occasionally, water or some other wetting agent
sprayed on walls or roofs can prevent ignition or extinguish firebrands from an advancing
wildfire, but the firefighters could die of heat exposure or smoke inhalation from the
approaching fire.
In the Aftermath
Recovery and efforts to support recovery after a severe wildfire vary, depending on
the nature of the damages. For burned structures, insurance payment is the standard
means for homeowners to pay for recovery — repair, if that is possible, or replacement,
depending on the insurance policy. In a severe event, a presidential declaration of an
emergency (in response to a request from a governor) initiates a process for federal
assistance to state and local governments and to families and individuals to help with
recovery. The nature and extent of the assistance depends on several factors, such as the
nature and severity of damages and the insurance coverage of the affected parties.
For burned areas, site rehabilitation is sometimes warranted. In many temperate
ecosystems, wildfires (including crown fires) are natural events, and the ecosystems are
adapted to recover from the fire. Often, in severely burned areas, grass seed is spread to
try to accelerate growth of ground cover and slow erosion, but grass often inhibits tree
seed germination and growth, and thus may slow forest recovery. Rehabilitation efforts
commonly focus on the firelines created to try to control the fire, since firelines are
exposed bare earth that often run uphill, and thus can readily erode into gullies if left
untreated. Some severely burned areas, particularly in coastal southern California, are
susceptible to landslides during the subsequent rainy season. Monitoring can provide a

⁶ National Wildland/Urban Interface, Fire Protection Program, Wildland/Urban Interface Fire
Hazard Assessment Methodology, p. 5, at [http://www.firewise.org/resources/files/wham.pdf].
⁷ Jack Cohen, “The Cerro Grande Fire: Why Houses Burned,” Forest Trust Quarterly Report, no.

13 (Dec. 2000): p. 11.

warning to homeowners to evacuate an area prior to a landslide, but little can be done to
prevent landslides in such situations.
Minimizing Wildfire Damages
Various efforts can protect structures and wildlands from some of the damages of
wildfires. (See CRS Report RL34517, Wildfire Damages to Homes and Resources:
Understanding Causes and Reducing Losses, by Ross W. Gorte.)
Protecting Structures. A structure’s characteristics and landscaping significantly
affect its chance of surviving a wildfire. Evidence from models, experiments, and case
studies demonstrates that structural characteristics, especially the roofing materials,
largely determine whether a home burns in a wildfire. Homes of brick or adobe with non-
flammable roofs (e.g., tile, slate, metal) are far less likely to burn than homes with wood
siding and flammable roofs (e.g., wood shingles).⁸ Burnable materials (such as trees,
shrubs, grass, pine needles, woodpiles, wood decks, and wooden deck furniture) within

40 meters (131 feet) of the structure also strongly influence whether the structure burns⁹

in a wildfire.
Furthermore, the structure and landscape characteristics are more important than the
intensity of the fire in determining whether a house burns. The Hayman Fire, in Colorado
in June 2002, burned 132 houses — 70 houses (53%) were surrounded by crown fire,
while 62 houses (47%) were surrounded by surface fire.¹⁰ In addition, 662 homes (83%
of all homes within the fire perimeter) survived the fire, even though 35% of the area was
severely burned and 16% was moderately burned.¹¹ This suggests that at least some of
the structures survived despite a crown fire around them; why these structures survived
was not reported.
Protecting Wildlands. The impact of wildfires on wildlands depends largely on
the nature of the ecosystem. Some ecosystems are adapted to and recover from periodic
crown fires — perennial grasslands, chaparral, lodgepole and jack pines, and more. In
these ecosystems, the plants have evolved to resprout or reseed the burned areas, and thus
recover from crown fires by outcompeting other plant species. Eliminating crown fires
could eventually eliminate these ecosystems. However, eliminating crown fires in these
ecosystems is probably impossible, since the plants contribute to the development and
spread of crown fires — grasses burn quickly; chaparral has a high volatile-oils content;
and lodgepole and jack pines grow in dense, even-aged stands.

⁸ Jack D. Cohen, “Preventing Disaster: Home Ignitability in the Wildland-Urban Interface,”
Journal of Forestry, v. 98, no. 3 (Mar. 2000): 15-21.
⁹ Cohen, “Preventing Disaster.”
¹⁰ Jack Cohen and Rick Stratton, “Home Destruction Within the Hayman Fire Perimeter,”
Hayman Fire Case Study, Gen. Tech. Rept. RMRS-GTR-114 (Ft. Collins, CO: USDA Forest
Service, Sept. 2003), p. 264.
¹¹ Peter Robichaud, Lee MacDonald, Jeff Freeouf, Dan Neary, Deborah Martin, and Louise
Ashman, “Postfire Rehabilitation of the Hayman Fire,” Hayman Fire Case Study, Gen. Tech.
Rept. RMRS-GTR-114 (Ft. Collins, CO: USDA Forest Service, Sept. 2003), p. 294.

Other ecosystems are adapted to relatively frequent (5- to 35-year intervals) surface
fires. Fire suppression has been moderately successful in controlling surface fires, and
thus the needles, twigs, and other fine and small fuels have been accumulating for three
or more fire cycles. This abnormal fuel accumulation, combined with fuel ladders of
brush, small trees, and low limbs (many of which would have burned in a surface fire),
have led to crown fires where such fires were historically rare. Fuel reduction treatments
can restore conditions in frequent-surface-fire ecosystems to again make crown fires rare
occurrences, reducing damages to resources.
Protecting the WUI. Reducing fuels in the WUI has been a controversial aspect
of congressional debates over fire protection legislation. The evidence discussed above
indicates that fuel reduction provides little protection for structures. However, some¹²
observers have noted that the WUI is more than just a collection of houses:
A town is not just the place where people have homes. Communities are in the forest
because they are emotionally, economically, and socially linked and dependent on the
forest. When we consider the areas that need immediate treatment we should consider
the human community “impact area” — the entire area that, if impacted by a
catastrophic fire, will undermine the health and livelihood of a community.
At a minimum, most would agree on the need for an area of defensible space around
homes that needs to be cleared of burnable materials — at least 10 meters (33 feet) and
possibly as much as 40 meters (131 feet). One observer recommended that protecting
communities should include intensive treatment to reduce fuels and burnable materials
in the home ignition zone, up to 200 meters (655 feet) around structures, with less
intensive fuel treatment in the community protection zone, generally up to 500 meters¹³
(1,640 feet, or about a third of a mile) from structures.
The Healthy Forests Restoration Act of 2003 (HFRA; P.L. 108-148; 16 U.S.C. §
6511) established a somewhat broader standard for fuel reduction activities under its
authorities. Section 101(16) of HFRA defined the WUI to include an area out to ½ mile
from the boundary of an at-risk community or 1½ miles from the boundary if a sustained
steep slope could cause dangerous fire behavior or to an effective fire break, such as a
road or ridge top. HFRA included no guidance on how to apply these standards in
intermix communities, with no definitive boundary.
Issues for Congress
As more acres and homes have burned in recent years, and more people are at risk
from wildfires, Congress is facing increasing pressures for wildfire protection. Congress

¹² W. Wallace Covington, Director, The Ecological Restoration Institute, Northern Arizona
University, “Prepared Statement,” National Fire Plan, hearing before the Senate Committee on
Energy and Natural Resources, July 16, 2002, S.Hrg. 107-834 (Washington, DC: GPO, 2003),
p. 61.
¹³ Brian Nowicki, Effectively Treating the Wildland-Urban Interface to Protect Houses and
Communities from the Threat of Forest Fire (Tucson, AZ: Center for Biological Diversity, Aug.

2002).

decides what programs to authorize and fund. Many programs exist, and other options
are possible.
Firefighting uses the majority of wildfire management funding, accounting for $1.1
to $1.9 billion annually (including emergency supplemental funds) since FY2003.
Appropriations for fire suppression have risen in nearly every year for a decade, going
from $277 million in FY1999 to the requested $1.33 billion for FY2009. Given the
difficulty in suppressing crown fires, one might question the effectiveness of continued
increases in suppression funding, although the agencies also clearly need to show the
public that they are doing all they can to stop the threatening and damaging fires.
Federal programs to protect homes are currently limited to information, primarily
through FIREWISE, for homeowners on how to protect their homes. Programs could be
expanded to educate homeowners, state and local governments, and the insurance industry
about the ways to protect homes through actions, planning, and zoning and building
regulations. Congress could create and fund new programs to assist homeowners in
renovations to make their homes fire-safe and to create defensible space around their
structures, through direct federal assistance or through the states.
Congress could also consider expanding protection for defensible space beyond the
home ignition zone to a community protection zone. HFRA authorizes an expedited
review process for activities on federal lands in the WUI. Perhaps other changes could
further accelerate action. Funding for fuel reduction in the WUI could also be expanded.
Appropriations for fuel reduction have averaged$500 million annually since FY2006, but
only a portion is used in the WUI, and funding is far below the estimated amount needed
to treat the lands at risk. (See the discussion in CRS Report RL33990, Wildfire Funding,
by Ross W. Gorte). State fire assistance funding through the Forest Service could be used
for fuel reduction in the WUI, at the discretion of the states, but funding has averaged $88
million annually and the states have many wildfire priorities. Additional funding through
the states for fuel reduction on private lands in the WUI is a possibility that Congress
could contemplate.
In addition, Congress might debate choices for compensating homeowners for
property losses due to wildfires. One option might be to restrict compensation to those
who had acted to protect their homes, but got burned anyway. Another option might be
to require that compensation for rebuilding be used only for fire-safe building designs and
materials. Alternatively, Congress could establish a national wildfire insurance program,
with premiums based on fire threats, the fire-safety of the structures, and the defensible
space being maintained.
Finally, Congress could consider compensation for landowners that suffer resource
losses from wildfires. An emergency reforestation assistance program has existed for
many years, although it has not been funded since FY1993. (See CRS Report RL31065,
Forestry Assistance Programs, by Ross W. Gorte.) In the 2008 farm bill, Congress
included forest restoration assistance in an existing emergency conservation program.
(See CRS Report RL33917, Forestry in the 2008 Farm Bill, by Ross W. Gorte.) These
programs can provide assistance in recovery from a wildfire disaster, but do not
compensate landowners for losses in the way that homeowners are compensated for the
loss of their homes. Congress might consider such additional compensation.