Perched 25 stories high in a construction crane - above the crowns of the Douglas firs - environmental writer Jon Luoma surveyed the forest canopy, searching for a humble lichen, Lobaria oregana. The lichen forges an intimate relationship with the trees, swapping nutrients for a home and helping the firs grow taller. These sorts of symbioses abound in The Hidden Forest, which charts the major advances in old-growth forest ecology through the eyes of the scientists who study them. Reissued with a new introduction by one such researcher, Jerry Franklin, the book offers a thorough introduction to old-growth ecology.

Nestled deep in Oregon's Cascade Mountains, between Eugene and Bend, H.J. Andrews Experimental Forest is the main character in Luoma's book. Since the Forest Service created Andrews in 1948, hundreds of ecologists have examined the 16,000-acre woods.

Foresters once called old-growth coniferous forests "decadent" - long past their harvestable prime, nothing more than a jumble of centuries-old firs, fallen trees, and a chaotic mat of moss, dirt and bugs. But where foresters saw inefficiency, scientists saw an ecosystem. At Andrews, they discovered that tree needles harmonize with fungi, exchanging natural insecticides for food and a home, and that microbes make up the bulk of soil and ensure the forest's recovery after fire or flood. "For all the appearance of stability," Luoma writes, "the ecosystem is always in flux."

The Hidden Forest is most compelling when Luoma tackles forestry policy. Emboldened by conservation biology, some foresters adopted an ecological view and pushed the Forest Service to do the same. Founded by Andrews researchers in the mid-1980s, "New Forestry" sought protection, not just management. Old-guard foresters and loggers fought the changes, and the debate came to a head during the spotted owl controversy, to which Luoma adds fresh perspective. He examines the dispute from the view of scientists who determined the habitat needs of the owls, rather than simply quoting politicians, activists and loggers.

Federal land policies show the debate over ecological forestry is still alive. Scientists have recently questioned the effectiveness of thinning forests to stave off fire, a provision of President Bush's Healthy Forests Initiative. Like old growth forests, the political landscape is ever shifting and evolving.

The Hidden Forest: The Biography of an Ecosystem

Jon R. Luoma

228 pages, softcover: $22.95.

Oregon State University Press, 2006.