In the 1970s, Oaks Bottom was a garbage dump. The city wanted to fill in the wetland and build soccer and baseball fields. A motocross course was also envisioned.

But a group of activists -- including Houck, who was a graduate student at Portland State University -- fought the plan to develop the area. The dumping ceased.

The activists kept pushing for formal recognition of Oaks Bottom as an important natural resource and in 1988 the city made it Portland's first official urban wildlife refuge. Its two-mile trail is now one of the region's best known and most popular.

For Houck, it was just the beginning of a career in crusading for preserving wildlife habitat within the city limits. He became a full-time "urban naturalist" for the Audubon Society and played a key role in the development of metropolitan Portland's regional plan for natural areas.

"What we are attempting to do here is to redefine the definition of infrastructure," Houck says. "Infrastructure for metropolitan Portland now includes streams, wetlands, rivers and green spaces -- what I call 'greenfrastructure' -- that are considered as integral to the quality of life as sewers and roads."

Although conventional parks, with ball fields, playgrounds and tennis courts, are important, natural habitat where wildlife can thrive is also critical, Houck says. He sees it not just as a benefit to animals, but also to people.

The majority of voters in the region would appear to agree. In 1995 a bond measure passed calling for $135 million of tax money to go toward acquiring more than 6,000 acres of additional green space.

"One of the development criteria we've established in this region is everybody should have access to a natural area within a 15-minute walk of their home," Houck says. "They shouldn't have to get in a car to drive somewhere to see the wild. A sustainable city is not a city devoid of nature."