Understanding Wildland Urban Interface and Its Connection to Wildfires

The wildland urban interface (WUI) is an area where human-made structures and infrastructure are located in or near areas of undeveloped wildland or vegetation.

The communities and ecosystems are often at greater risk of catastrophic wildfire. This is because of the amount of fuel that accumulates within the WUI. This fuel can include wildland vegetation, buildings, infrastructure, and any number of other items and materials (think gasoline stored under the porch or woodpiles in the front yard). The wildfires that occur within the WUI are usually more difficult to fight, while an abundance of structures can make natural or controlled fire burns nearly impossible.

People who live or work in these areas are encouraged to understand their risks and reduce activities that make their properties more susceptible to fires. In California, researchers have found that significantly more fires occur in WUI areas. It is also a common (and dangerous) misconception that those who don’t live in the western states of the U.S. won’t have to worry about wildfires; in reality, the states with the most number of homes within the WUI after California are actually Texas, Florida, North Carolina, and Pennsylvania.

What happens inside the WUI can influence the places outside of it, too. New development and road construction can introduce or spread invasive plants and animals to natural areas, and wildfires that begin in the WUI can grow to threaten nearby cities or produce smoke that causes visibility and health problems for people who live many miles away.

The Growth of Wildland Urban Interface

The number of houses within and adjacent to wildland vegetation is growing quickly. In fact, the most recent study of WUI growth by the U.S. Forest Service found that the WUI in the United States saw a 41% growth in new homes and 33% in land area from 1990 to 2010, making it the fastest-growing land use type in the country. New WUI areas during this period totaled nearly 73,000 square miles, an area larger than the entire state of Washington.

If the WUI proves anything, it's that policymakers, forest managers, and people who choose to move into these beautiful, wild places have an added responsibility to reduce the threat of wildfire and prepare for increased fire activity in their area.

The Relationship Between Wildlands and Fire

As one of the Earth's oldest and most natural agents of change, fire plays an essential role in many landscapes (if you don't trust us, take Smokey the Bear's word for it). Periodic low-intensity fires can speed up forest decomposition, improve habitat and food sources for certain animals, create open areas for new plants to grow, and even help deliver nutrients to those plants. It's also been shown that fire can improve groundwater and increase water flow to aquatic habitats, and some trees, like the lodgepole pine, have actually adapted to require heat to open up their cones and disperse new seeds.

Smaller, natural fires can also build an environment’s resistance to larger intensity fires by reducing immature trees, dry brush, and dead branches. This creates pockets of burned or partially burned areas, making it less likely for future fires to burn the entire landscape all at once. The U.S. Department of the Interior manages fuels by deliberately starting controlled fires under favorable conditions to remove excess vegetation, thinning forests and removing brush by hand.

Before the arrival of European colonists in the Americas, various ecosystems showed patterns of frequent small-scale fires caused by a combination of lightning strikes and Indigenous land management, while patterns of severe fires were mostly caused by things like climate, topography, and vegetation dynamics. These patterns changed with the arrival of the colonists. European colonists brought smallpox and other infectious diseases to the Americas, decimating Indigenous populations. They also dismissed the value of controlled burns for land management and in some places sought to outlaw the practice entirely. All of these changes meant the number of small-scale fires dropped, causing the landscape to slowly thicken with dry vegetation and creating the perfect kind of kindling for massive-scale wildfires.

Connections to the Climate Crisis

Warming temperatures can cause earlier spring melting, resulting in less water availability during hot, dry summer conditions, thus allowing fire to move easier and burn hotter. A study in 2017 found that recent wildfires across the western United States, which have increased in both size and numbers over the past decade, will continue to rise as the Earth's climate changes. These researchers believe that contemporary approaches to wildfire that focus on resisting large natural fires through suppression techniques aren’t enough to address the continually increasing fire activity in the country.

Even though wildfires occur naturally and play an important role in the health of the Earth’s ecosystems, climate-related complications such as drought and rising temperatures threaten to significantly increase the frequency and severity of wildfires in the future. If you cross-reference the National Interagency Fire Center data with the U.S. and Global Temperatures indicator, the latest period of 10 years when the largest acreage burned coincides with the warmest years on record. All of these years have occurred since 2004, including 2015, when the numbers hit their highest peak.

Wildfires also contribute to the larger climate feedback loop, as large-scale, unnatural wildfires can affect the Earth’s climate. As forests burn, they release massive amounts of carbon dioxide into the atmosphere, and in turn, those trees no longer function as essential carbon-catchers.

Steps to Reduce Risk

The National Parks Service offers resources and suggestions for reducing wildfire risk within the WUI, including:

• Removing combustible vegetation from around structures
• Thinning out tree or brush cover and vegetation fuel (fallen trees, dead limbs, leaves, twigs, pinecones, etc.) within 30 feet of buildings
• Keeping gutters clear from leaves and branches
• Keeping grass mowed to a maximum of two to four inches
• Pruning trees to 10 feet above the ground
• Stacking firewood at least 15-30 feet away from the home

Those who live in or around the WUI should be aware of their home’s roof and wall materials, such as wood shingles, that can easily ignite from wind carried embers. FEMA has valuable resources and printable flyers for teaching your local community to create defensible space with instructions for making and executing wildfire evacuation plans.