Delicate Ecosystem : Owl a Major Link in Forest Web of Life

It’s night, deep in an old-growth forest, and a ruffle-feathered spotted owl sits high in an 800-year-old Douglas fir tree, waiting.

In a nearby tree a hungry flying squirrel catches the scent of truffles growing in the moldering duff on the forest floor and launches itself into a spraddle-legged dive, aiming to land at the base of the tree and dig up the fungi that constitutes the rodent’s primary diet.

The spotted owl--one of the most specialized of the raptors--leaps to wing, silently plummeting down on the squirrel, talons extended. Thump! The owl grabs off its favorite prey and, with powerful wings flapping, rises to its nest high in the broken top of the fir.

Delicate Balanced

The owl, the squirrel, the fungi and the ancient trees are linked one to another and to hundreds of other animals and plants in the delicately balanced ecosystem unique to old-growth forests, according to Chris Maser, a wildlife biologist at the U.S. Forest Service’s Forestry Sciences Laboratory in Corvalis, Ore.

Life in these forests in the Pacific Northwest and Northern California has evolved over thousands of years. Douglas firs, the giants of the forest, live for 1,000 years or more, standing tall over a rich and complex biological mix of plants and animals, some of them found only in these ancient forests, Maser said.

There are nearly 7 million acres of old-growth forests left, most of it in public ownership managed by the Forest Service in Washington, Oregon and Northern California. Each year more than 100,000 acres are lost, mostly to commercial logging, officials report.

These timberlands are at the heart of the growing controversy between environmentalists who want to preserve the virgin forests and the lumber industry that needs the premium, clear-grained wood to keep the saws running in mills that were designed to cut only big logs.

Scientists agree that the old-growth ecosystem is one of the most complex known to man, an intricate and fragile web of life that still contains mysteries that puzzle research ecologists like Maser who spend their lives trying to unlock the forest’s genetic and environmental secrets.

Each Needs the Other

To illustrate the complex, symbiotic relationships within the old-growth ecosystem, Maser uses the example of how the owl, flying squirrel, certain fungi and the fir tree need one another. He starts with the squirrel and the recent discovery of how this rodent helps sustain the life of the tree and the fungi.

For decades scientists could not explain how pine and fir trees managed to obtain and utilize more life-sustaining nitrogen than appeared to be readily available within their environment. The trees were getting the added nitrogen, but no one knew from where, Maser explained. Recently he and other researchers from the Forestry Sciences Lab discovered one source by studying forest rodents.

“Flying squirrels (the primary item on the owl’s menu) live and nest in the tree tops and, at night, glide to earth to dig for truffles that grow on the tiny feeder roots of conifers,” Maser explained. As it eats, the squirrel ingests not only the nutrients it needs, but also fungal spores, nitrogen-fixing bacteria and a yeast that it cannot digest.

These undigested elements are carried around the forest in the squirrel’s digestive tract and finally excreted.

If these undigested elements are excreted while the squirrel is digging for truffles, the fungal spores from the fecal pellets penetrate a tree’s root tips, producing more truffles that begin to grow and feed on the roots. In the process the truffles, a parasitic fungi, create a sponge-like growth that helps the tree take up water, phosphorous and nitrogen.

Source of Nitrogen

“What we discovered is that inside that tiny root tip, the yeast and the fungus give off an extract that nitrogen-fixing bacteria need for food, the bacteria in turn takes nitrogen out of the air, transforms it into a form usable by both the tree and the fungus,” Maser explained. This, he said, is where the tree gets its added nitrogen.

Thus, the tree, the fungi and the squirrel are dependent on one another, but the system of relationships can work only if it is kept in proper balance, he said. The owl’s ecological role is to prey on the squirrels, keeping their populations in balance.

These highly specialized birds are about 18 inches tall, weigh a pound and a half on the average and are dark brown, with white spots around the head. Once a pair of owls establish a nesting site, they remain in the area and become territorial, fighting off other owls. They require up to 2,200 acres of old-growth forest per pair, according to ornithologist Eric Forsman, a spotted owl expert.

While owls can find food outside these old forests, both Forsman and Maser said they prefer the old growth and their reproductive patterns require nesting in the broken tops of ancient trees. Without the old-growth habitat, their survival would be questionable, they said.