Just off a winding, narrow road in Wisconsin’s Baraboo Range, a gravel driveway cuts into the forested margins of Devil’s Lake State Park and leads to a new log cabin sitting in a small clearing. If you closed your eyes and imagined the perfect house in the woods, it might look like this. The sun-speckled roof, half shaded by a rustling green canopy. Bird feeders swaying from tree branches that nearly brush the front porch. Flower beds cradling clumps of color, resplendent against the brown leaf litter of the forest floor. Thoreau would’ve happily stretched out his legs here, not far from where an inspired Leopold took up his pen. It seems an ideal human complement to untrammeled nature – a soft, blurred line between domesticity and wilderness. Yet to the trained eye, all is not well in this Eden. Which is why Gregorio Gavier Pizarro is tromping into the nearby woods where there are no trails.

People want to live closer to nature, which is a good thing. But by building houses there, they are destroying the very thing they sought out in the first place.

Sweat drips from Pizarro’s nose and onto the screen of a handheld GPS device as he winds his way through the forest with a familiarity bred from repeated visits over the last two years. Waving away the persistent swarms of mosquitoes, he pauses every few yards to point at a plant and call out its name. They sound pleasant enough-Japanese barberry, honeysuckle, European buckthorn, Rosa multiflora. But these plants don’t belong here. They just act like they do, proliferating across the forest understory, shoving native plants aside and changing the dynamics of entire ecosystems. They hint at a harder edge to the bucolic boundaries of house and wood.

And they’re everywhere. Pizarro, a graduate student in forest and wildlife ecology, began his research with a hypothesis that invasive species were linked to human land use and housing development. But when he started sampling random plots around Devil’s Lake, he found so many invaders that he thought he would never make sense of his data. “Everything was just totally invaded,” he says.

Eventually, he found a pattern in his maps. A ring of invasive plants forms around houses in the Baraboo Range as the species establish themselves on the fringe between yard and forest. Then they emanate outward, pushing deeper into the woods. The invasion slows as you look further into the woods-the largest intact swath of upland forest in southern Wisconsin. In places such as Baxter’s Hollow, 5,000 acres of woodland protected from development by the Nature Conservancy, native plants and animals still hold dominion. But in most of the Baraboo Range, each new gravel drive cutting into the woods brings human influence with it.

Pizarro’s work is just one chapter of a story playing out on the fringe of civilization, a shifting boundary that ecologists refer to as the wildland-urban interface. At this edge, some of the most pressing conflicts between humans and nature occur, from the property damage caused by raging wildfires to the eroding habitat for forest-dwelling species to run-ins with predatory animals. And to see what is truly going on with the wildland-urban interface-to really separate the forest from the trees-you can’t just focus on a single house in the woods. You need to plot out that edge at its widest scale, finding where it lies, what moves it forward and what stands in its path. And that is where Pizarro’s advisor, Volker Radeloff PhD’98, enters the picture. He has his eye on the Baraboo Range-and a thousand other places like it-to tell the story of what’s happening to the edge of the wilderness, where people and nature meet in often inharmonious ways.

Radeloff, an associate professor of forest and wildlife ecology, runs a UW-Madison lab called SILVIS, which roughly derives its name from its mission to provide “spatial analysis for conservation and sustainability.” With his wife, associate scientist Anna Pidgeon PhD’00, and a team of staff, graduate students and postdocs, Radeloff examines pastoral settings like the Baraboo Range in excruciating detail and then stitches them together into a larger picture of what’s happening on the nation’s landscape. It’s a modern kind of mapmaking, which dispenses drafting tables for powerful computers and topographical sketches for information-laden pixels. The SILVIS lab amasses mountains of information-from small-scale field studies like Pizarro’s to census reports on the spread of houses and the growth of towns-and feeds them into a mammoth database that carves the entire country into pieces as small as 30 square meters. The end result is a geographic information system, or GIS-a map that reveals startling detail about every last parcel of American soil, from how many houses sit on it, to what plants grow there, to what percentage of its area is covered by woods or crops or development.

“Even 10 years ago it was simply not possible to analyze such a large data set,” Radeloff says, sitting at his desk in a first-floor office of the Russell Labs building. He turns to one of the two wide-screen monitors that dominate his desktop and pulls up a series of maps of the United States, all alight in various pixels of reds, yellows and greens. “The computers (that) process this,” he says, patting his desktop machine, “well, this wouldn’t do it. We have servers down in the basement where the processing happens.” In fact, in terms of memory and speed, the computers that generate the SILVIS maps rival those used to run complex experiments for the UW’s physics department.

Why so much power? Consider the census data alone. Every decade, the U.S. Census Bureau compiles surveys on each household in the country. In 2000, there were 105.5 million of them. In the 1990s, those millions of paper documents were transferred into digital files, awaiting a computer with the power to crunch the data. Now, with today’s processing power, scientists and policymakers can analyze demographic patterns on a national scale.

And when they started looking at these data, researchers saw something interesting. Until the 1970s, population growth in metropolitan areas far exceeded that of rural areas. But then, the trend reversed. The outskirts became the choice destination. Americans moved out.

It’s impossible to pinpoint what, exactly, led to this “back-to-the-land” movement, but it’s clear several forces were at work. For one, the expanding interstate highway system let both people and workplaces move away from cities. But another powerful draw was our notion of cities. Urban areas have long suffered an image problem in the country’s environmental literature, which has often blamed them for their fabricated landscapes and detachment from nature. In his 1932 book The Vanishing City, Frank Lloyd Wright called urban areas a threat to our very future, “like some tumor grown malignant.” Wright’s own flight from the Chicago suburbs to the Wisconsin hills followed a long line of philosophers-from Thoreau to Emerson to Muir to Leopold-who sought the perfect balm of nature as a place where a man could live a proper, wholesome life. Their sentiments fueled a growing environmental movement, punctuated by Gaylord Nelson’s first Earth Day on April 22, 1970, which primed a nation to search for undeveloped plots of land to call their own.

“People want to be closer to nature, which is a good thing,” Radeloff says of our spread to the exurbs. “It shows where their heart is. But by building houses there, they are destroying the very thing that they sought out in the first place.”

Radeloff began seeing the effects of this movement in the late 1990s, when much like Pizarro, he was a CALS Ph.D. student canvassing the woods. He was interested in how human suppression of wildfire in northwest Wisconsin’s pine barrens was affecting wildlife, and it soon dawned on him that while he knew tons about the local flora and fauna, he knew far less about the human half of the equation. “I just got more and more curious about who was living there,” he says. “What was the population trend? What’s the area going to look like in 20 or 30 years?”

He enlisted Roger Hammer, then a UW professor of rural sociology, to help him answer these questions. They set out to map northern Wisconsin with a view toward wildfire, plotting where houses stood closest to forests, what access roads could aid fire trucks, how much rain fell and even what species of trees surrounded homesteads. Officials with the U.S. Forest Service, coming off a particularly bad year of wildfires in 2000, took note. Under pressure to develop a national wildfire plan, they asked Hammer and Radeloff for help.

“With a gulp,” Radeloff remembers, “we said, ‘We can do that.”

Today, their maps have been downloaded by thousands of federal agents, civic planners and academic researchers. They provide a century’s worth of information, showing changing national conditions and predicting trends through the year 2030. Through the clever combination of data and visual display, they identify literal hot spots- the places most vulnerable to damage from wildfires, where extra precautions are most advised.

But risks from wildfire aren’t the only thing Radeloff’s maps can tell us. There is another, perhaps more troubling trend visible when you map the wildland-urban interface: Green is disappearing.

Beginning with the earliest data from 1940, Radeloff’s decade-by-decade maps of the United States reveal a remarkable shift in color. Red blobs, indicating urban areas like Chicago and the Twin Cities, expand as they move through the decades. But these consolidated areas are outpaced by a faint yellow pall spreading across the land. This is the color of low-density housing. A rural exurb. A cabin in the woods. Each new yellow pixel means another small chunk of green-the uninhabited wild land of our country-is being zoned and developed right out of existence. All because so many Americans want to live near the green.

This is a conundrum that Michael Slavney knows all too well. Slavney is a principal planner for Vandewalle & Associates, a Madison-based consultant group that helps officials with regional planning and economic development. He often uses GIS maps to show civic planners how their farmed and forested land has been shaped over the decades. While the vast majority of those towns initially welcomed development, he says most eventually put the brakes on growth in order to preserve their “rural character.”

“What everybody thinks of is the first house in the subdivision or that first little isolated lot,” Slavney says. “And what you need to think about is, what will be the character when the last one goes in?”

There are profound economic and environmental tolls of decentralized development, he says. A typical town may average around five dwellings per acre, but out beyond the suburbs, at the fringe of natural lands, it’s not uncommon for a homeowner to live on five or more acres. That’s 25 times more land supporting a single household. “When I hear the term urban sprawl,” Slavney says,” “to me, it’s an oxymoron. The sprawl that we really get is exurban.”

But while such developments raise questions about resources and energy use, there’s another reason to worry about houses pushing out on the fringes of wildlands. It turns out that nature loves the fringe, as well. Anna Pidgeon, who studies the effect of development on ecosystems, worries that we are “perforating forest(s) with holes for houses.” And where the sun can shine unhindered by a forest canopy, a riot of growth occurs. Birds settle into these over-producing habitats because they provide bugs and berries for food and cover for nests. But the birds bring in seeds of invasive plants and, as those plants grow and flower, they help move them deeper into the forest. A bird feeder hung in an open lawn can also be a magnet for aggressive species such as house finches and cowbirds, which swoop in and force native birds out. This avian population explosion is soon tempered by predators such as raccoons, skunks, and domestic cats and dogs that roam these man-made avenues, sampling the bounty of the edge.

Pidgeon says she’s not advocating that people stop moving. Her hope is that people will realize it’s a question of scale. “The old hunting cabin probably didn’t have too much of an effect,” she says, “but McMansions with big lawns and forest all around them, that’s something else.”

This is the kind of development visible all over the town of Middleton, just west of Madison. Two-lane rural routes are growing to four-lane arteries, from which a sprawling network of subdivisions sprout like weeds. On each sit three-story houses, ringed by acres of lush grass and exotic flowering trees. It is here that Wright’s remarks about cancer seem most apt. While a city may indeed sit like a giant tumor on a landscape, belching greenhouse gases and paving over green space, it is at least operable. Contained. The truly dangerous cancers, oncologists will tell you, are the ones that spread throughout the body. Now, three decades after the American Dream adopted the American ideology of wide-open spaces, the yellowing dots on Volker Radeloff’s maps seem like blips on an MRI readout. They are diagnostic tools, and they’re signaling big problems.

Back in the boundaries on Devil’s Lake State Park, Pizarro stops at a thick cluster of garlic mustard, another invasive plant flooding into Wisconsin. Most people strolling through these woods might not even notice the weeds, entranced instead by the whispering leaves overhead. But Pizarro frowns at the ground. Already this crop has gone to seed, spreading future invaders deeper into the forest. “We call this the loneliness of the ecologist,” he says. Other people enjoy their walks in the woods, envisioning a pristine habitat. But ecologists see the reality-the closer we move towards our cherished wildlands, the further we push them away.