Workday wilderness.

Portlanders love their urban forest, but it takes some real pull to meet the management challenge.

On a good day in Portland, Oregon, when the traffic lights let you drive without stopping, you can make it from downtown to the woods in less than six minutes.

Forest Park, a thin green expanse of 5,000 acres that stretches along the face of the Tualatin Mountains, begins just 20 blocks outside the business district. It is the nation's largest self-contained urban forest - nothing else even comes close - and is home to a sprawling pastiche of second-growth conifers and maple dotted with a few small, diverse stands of old-growth. Sword ferns are ubiquitous in the moist soil here, and there is wildlife - deer, coyotes, great blue herons, and even reports of black bears - and also a 27-mile-long path, the Wildwood Trail, that takes you past a rose garden, an old mansion, and a creek with cutthroat trout.

A New York Times travel writer, James Sturz, hiked the Wildwood and gushed about the "untamed foliage" and the "bounty of life which sets the trees teeming," but I don't share all Sturz's wonderment. Forest Park is, for me, a workaday wilderness. This is the place I go, once or twice a week, for a quick hike after work. It is a tranquil place, yes, but it is also part of the city.

Forest Park, created by Portland's City Council in 1948, is the well-loved playground of a booming metropolis. The Portland area is now home to 1.5 million people. Its population is expected to grow by 14 percent over the next 10 years, and many of the newcomers will no doubt be affluent outdoorsy types lured by the Northwest's fabled cafes and mist-shrouded forests.

Forest Park will be used (see photo above), as it already is. Small armies of mountain bikers descend on its trails every evening. Scores of horses and hikers come too, inevitably compacting the soil and causing erosion. Transients camp by the streams.

Neighbors also pose challenges. Homeowners plant non-native flora, which can creep into the woods and slowly take over, and developers carve lavish subdivisions into the park's fringes.

The city is knocking at Forest Park's door, and it is the charge of Portland Parks and Recreation to keep the place wild as it caters to thousands. The department, walloped by budget cuts, has just four people on the job. There is a natural-resources expert, two groundskeepers, and Fred Nilsen, an arboriculturist, who for nine years now has overseen Forest Park's day-to-day maintenance from hit desk in the back of a shed.

Nilsen knows the park best of all, so one hot spring afternoon I phoned him and got him to show me around.

"Hey, you want some chocolate cake?" Nilsen asks as he shoots his white pickup along toward the park. I take it, and now I'm balancing cake on my lap as I try to scratch notes. It's all a bit awkward, but Nilsen, 44, is a casual guy with a sunburn and dirt under his fingernails, and we're on a pretty informal mission.

Our first stop is a weed patch - a hillside that's been choked by an invasion of English ivy. Nilsen hops out of the truck and lifts up the thick tangle of vines. There are no plants underneath.

"I call places like this ivy deserts," he says. "The ivy runs in from the houses. It displaces the native plants - the ferns, the duck's foot, the wild ginger - and it climbs up the trees; it tricks them."

Nilsen explains that often an ivy vine will wind round the top of an alder or maple, causing the tree to give up on growing - to "think" that a taller tree has shaded it, and defeated it in its quest for sunlight.

Ivy deserts are fairly common where Forest Park borders houses with gardens. About 10 percent of the park's entire 5,000 acres are covered with ivy, and the glossy weed could proliferate. Portland's temperate climate makes it the perfect greenhouse for ivy production.

Which is why Nilsen is glad that the "No Ivy League" sprang up last year. The League consists of myriad volunteers - Cub Scouts, church groups, and seniors - and a few paid summer workers, all of whom venture into Forest Park to fight back the ivy, either by yanking it from trees or clearing it from the ground. It is funded by two grants and has an enthusiastic coordinator, Sandy Diedrich, who jokes about "De vine intervention" and quips, "We've got some pull."

Diedrich has so far lured about 800 No Ivy Leaguers out to Forest Park. Her program is gaining momentum and eliciting local media attention. And she is making definite progress. Near the "desert," for instance, Nilsen and I pass a cluster of white trilliums on a slope that recently was home to nothing but ivy. The flowers are lovely and are also, I discover, well-earned: Nilsen tells me it took scores of workers to clear the vines off this two-acre hillside - and he knows that, even if the League keeps up its assault, ivy will always afflict Forest Park.

We walk on a bit more, and soon we are standing on a wood bridge looking down on six-foot-wide Balch Creek. "Portland's refrigerator," Nilsen says, "You come down here on a hot day, and it's cool. It's wonderful and refreshing."

I've never dipped my toes into Balch Creek, but I have watched this stream in a rainstorm in the middle of a wet Oregon winter. The water is frothy, almost exploding its banks. Now, in June, it is calm. It will be a thin trickle all summer long.

The steam was once far less erratic. The acute variations began, Nilsen says, about 10 years ago when people began building large houses upstream. Suddenly, Balch Creek's headwaters were surrounded by driveways and roofs - slick surfaces that, during rainstorms, provide a fast runway for water (and, of course, inhibit rainfall from seeping into the soil).

If Balch Creek flowed steadily again, Nilsen says, it could provide deep, cool spawning pools for its 2,000 or so resident trout. Since he can't remove the houses upstream, he's doing what he can for fish habitat: About five years ago, Nilsen changed Portland Parks' policy of removing floating debris from the stream. Now fir boughs and downed tree trunks straddle the creek. The debris slows the water, and lets it riffle back into pools.

There's no scientific data that show this strategy is helping Forest Park's trout. But, Nilsen says, "We like to think the fish are more vital now - that they're healthier and that they live longer."

A few blocks outside the park, in the pickup, we pass the Thurman Mart, then Napa Auto Parts, and the looming Montgomery Park office tower. It's hard to believe that amid all this sprawl is a forest that offers wildlife a wooded corridor that stretches to the city limits, and then to the Pacific, 60 miles away.

The wildlife corridor exists largely because Portland is the only big city in the nation to have an urban growth boundary - a law strictly regulating development outside the city. The corridor could continue to flourish thanks to a ballot measure, passed by voters, that authorizes the metropolitan government to spend $135 million to protect wild places (see "A Vote for Wild Places" on page 62).

But Forest Park's habitat is threatened in other ways. Within the park there are several small privately owned chunks of land. Private inholders could build homes - and even roads - that fragment the park. And there are more immediate problems. A quarry is expanding just north of Forest Park, and Lakota, an exclusive community, is going up on a hilltop that drains into Balch Creek. The houses, yet to be completed, will surely be mansions.

"I'm a sanctimonious hypocrite," Nilsen jokes as we drive along toward Lakota's security gate. "I don't want development, but I'm going to be real nice to these people because here's what's going to happen: They'll get in there, and then they'll work to preserve the park, to keep it pristine."

We get to the Lakota driveway, and Nilsen turns grim. There are just a few trees left standing here amid all the driveways. A bulldozer has severed the roots of some, and a scar remains where the dozer bumped against one tree.

An advocacy group, Friends of Forest Park, has tried to stave off such scars. Over the last seven years, the Friends have bought over 200 acres of once-private land and obtained conservation easements on an additional 1,000 acres near Forest Park. They've been aided by Portland's Bureau of Planning, which last spring enacted stringent standards for the land surrounding Forest Park and other sensitive areas.

New zoning laws help but won't change the fact that several parcels of land bordering Forest Park will inevitably be made into subdivisions over the ensuing decades.

As Nilsen and I stroll back to the truck, we stop to gaze at Mount Adams, which looms snowcapped and craggy in the blue distance. "People are going to see Adams from their kitchen windows, yeah," he says, "but you build houses and you're bringing in asphalt, non-native plants, dogs. The cats are going to chase voles. . . The park as we know it could be history."

Before we head home, Nilsen wants to check a trail in the northern part of the park. He's heard of a faint side path here, and wonders if it leads to a transient's camp.

He hopes not, because eight or 10 people already camp out illegally in the park every night. Some stay for a year at a time, and many cause problems by building campfires. One smoldering fire in the late '80s burned five or six acres of understory, and Nilsen worries that, on a dry night, hundreds of acres could go up in flames. He's also bothered by the bottles and odd scraps of plywood that litter most camps. "It's ugly," he says, "and part of my job is to pull the wool over people's eyes, to make them think they're in wilderness."

Nilsen parks, and we start hiking in. The side path, it turns out, is nothing, just a trail beat into the grass by some kids. But it's evening now, and getting cooler, and we decide to keep going toward a small creek Nilsen knows.

We hike into a tall stand of hemlock, and we go sort of hard. My muscles are working now and there is sweat on my skin. And it feels, at least for the moment, like Portland is a million miles away.

RELATED ARTICLE: A Vote for Wild Places

Though Forest Park is by far Portland's largest wild place, it is hardly its only one. Portland has about 5,000 additional acres of park land, including an extinct volcano and a wetland that is home to bald eagles. The metro area is likely to stay green over the coming decades:

Last May, metropolitan Portland voters decided to spend $135 million to buy about 6,000 acres to preserve wild spaces in the city and the suburbs and small towns surrounding it.

Most of the money will not go to Forest Park, says Nancy Chase, a senior planner with Portland's regional government, Metro. The "open spaces" program will focus instead on saving wild areas that are now unprotected and threatened by development. For instance, Metro will buy about 370 acres of forest land in suburban Newell Creek Canyon, 800 acres in the more rural Sandy River Gorge, and 500 acres among the volcanic buttes and lava domes in the region.

In and around Forest Park, Metro will spend $4.7 million to buy several small chunks of land that together cover about 300 acres. The purchases will probably begin sometime this fall.

"We want to secure the wildlife corridor," says Chase, "and we'd like to purchase some of the privately owned land inside the park and create a buffer zone, so there isn't development around all the edges. But, really, Forest Park is just part of the larger plan. All over the metro area, we'd like to keep wildlife close to urban users. If we plan ahead, I think, we can have both growth and a quality environment." - BILL DONAHUE

BILL DONAHUE - a contributor to People and other magazines, writes and hikes from his home in Portland.