People and habitat intersect in the wildland-urban interface (WUI), a geography that now includes about one-third of homes in the U.S. within just 10% of the nation’s land area. Both numbers are growing, according to a new U.S. Department of Agriculture Forest Service map book summarizing the extent of the nation’s WUI nationally and by state.

The maps give land managers, policy makers, fire managers and homeowners a valuable new source of information on housing density, land ownership, land cover and wildland vegetation cover in WUI areas in the contiguous U.S.

The "2010 Wildland-Urban Interface of the Conterminous United States" was developed by lead author Sebastian Martinuzzi of the University of Wisconsin-Madison, Susan Stewart, formerly a research social scientist with the Forest Service's Northern Research Station who is now with the University of Wisconsin-Madison; Miranda Mockrin, a research scientist with the Forest Service's Rocky Mountain Research Station, and collaborators. The map and the data behind it are available online at www.nrs.fs.fed.us/pubs/48642.

"The wildland-urban interface map is a timely and important science product that shows us how deeply intermingled people are with natural areas, particularly in the Northeast," said Michael T. Rains, director of the Northern Research Station and the Forest Products Laboratory. "Scientists have generated data that can expand awareness of the wildland-urban interface and the risks associated with it for both people and natural resources."

To be considered wildland-urban interface, an area must have at least one structure per 40 acres. Scientists distinguish between "intermix" WUI, in which housing and vegetation intermingle, and "interface" WUI, where housing is near a large area of wildland vegetation.

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In all regions of the country, WUI is growing, and with it, the concern about wildfire. From Seattle, Wash., down the coast to San Diego, Cal., drought has created high fire potential in areas with medium to high housing density and very little water. In the Northeast, increased housing density is making any fire a riskier situation. In the Southeast, development is occurring quickly in areas that have been historically managed by fire, setting up potential conflicts between homeowners and land managers, the Forest Service explained.

"In some areas, building is occurring in fire-prone areas with little consideration of risks," Stewart said. "People tend to think about scenery when they build a home, not wildfire. Mapping the WUI is intended to raise awareness of where development is occurring so people and communities can be better prepared and reduce negative effects to homes as well as the environment."

"The expanding wildland urban interface is a critical issue for wildland firefighting and for the conservation of our forests," USDA undersecretary of natural resources and the environment Robert Bonnie said. "More people, homes and infrastructure are at risk than ever before. As the WUI grows, our fire fighters must commit greater resources to protect homes and property, which dramatically increases the cost of fire suppression."

In 2015, 52% of the Forest Service budget was set aside for fire suppression, up from 16% in 1995. By September 2015, the Forest Service had already exceeded the funding set aside for fire suppression and was forced to borrow funds meant for other Forest Service activities.

Wildfire is not the only concern when there is increased proximity of humans to habitat. Increased risk of invasive species and disruption of wildlife and ecosystem processes often accompany human habitation, making the WUI map a guide to potential ecosystem vulnerability.