Measuring How Hard ‘Old Growth’ Takes it on the Chin

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Two hours north of Seattle, a quick exit off I-5 brings you within striking distance of some of this country’s last remaining old-growth forests.

Here, in season, a wide swath of farmland is normally rife with raspberries, tulips and potatoes, but with summer now only a vague notion, in the distance, the massive North Cascades mountain range shows signs of fresh snow.

There, for miles along the bottom of a meandering glacial stream, lies a healthy stand of old-growth Douglas fir, Western hemlock and Western red cedar.

Such hauntingly majestic stands of old growth were commonplace when Lewis and Clark first set foot in the Northwest. But in the last century, roughly half of old-growth forests in Washington and Oregon have been whacked by logging and wildfire. Now, it’s feared climate change looms as their nemesis.

“In Washington and Oregon, we’re down to less than a quarter of what we might have had historically,” said Tom Spies, a forest ecologist at the U.S. Forest Service’s Pacific Northwest Research station in Corvallis, Ore. “There’s between 3-to-8 million acres of Pacific Northwest old growth left. And most of that reduction has been due to land-use change on non-federal land.”

In Washington and Oregon, 350- to 750-year-old Douglas fir and Western hemlock forests make up the bulk of old growth on the western, wetter side of the Cascade mountains.

To take a firsthand look, I set out in a steady rain with Mignonne Bivin, an energetic plant ecologist from the North Cascades National Park. Our first stop was about a tenth of a mile from the Thunder Creek trailhead, technically part of the Ross Lake National Recreation area.

There, Bivin verified a bona fide specimen of old-growth Douglas fir, its trunk roughly 60 inches in diameter. It can take 60 to 80 years to grow a tree 20 inches in diameter. However, North Cascades old growth tends to run between 50 to 60 inches in diameter, roughly 5 feet — a lot of tree to hug. But despite their characteristic old-growth resiliency to fire and seasonal changes, these old trees are still not immune to gravity.

A couple of hundred yards further down the trail, a whole cedar has been upended; its roots on full display, taking dirt and boulders the size of small coffee tables along with it.

Thus, it’s clear that even without logging or climate extremes, old-growth longevity can be cut short by a potent combination of rain-sodden soil and a few strong gusts of wind.

And 40 years after the North Cascades National Park was first established, there remain a few trees along this trail that still show signs of mutilation by timbermen.

Today, however, the combination of the Mount Baker-Snoqualmie National Forest to the west and the Okanogan and Wenatchee national forests to the east, makes this region the United States’ largest federally protected wilderness area outside of Alaska.

In Washington and Oregon, at least 75 percent to 85 percent are on federal lands. The Northwest Forest Plan of 1994, an initiative of the Clinton administration, continues to monitor some 24 million acres of federally managed land.

While there has been significant progress in preserving old growth since that plan was first enacted, Spies said, it’s hard to guess what climate change is going to do over the next century.

In another decade, however, such predictive old growth models are expected to be aided by NASA’s planned Desdyni (Deformation, Ecosystem Structure and Dynamics of Ice) satellite, a five-year Earth-observing mission, scheduled for launch in 2019.

Desdyni will probe Northwest forests with light detection and ranging (or LIDAR) sensors that use laser pulses to reflect the forests’ structure, foliage, canopy and biomass. Old-growth forest structure should cause lots of reflectance in the laser pulse signal, but differentiating between specific tree species would be more difficult.

Still, the ultimate goal for such technology is to give an up-to-date, unbiased estimate of just how much Northwest old growth is still out there. Some environmentalists put that figure at only 10 percent.

“There is no consistent definition of old growth and there never will be,” Spies said. “If you define it by age, in the Pacific Northwest, it usually starts around 150 to 200 and goes up from there.”

The logging industry would like old-growth age classifications to be skewed older, while environmentalists want them lowered. But Bivin says if an ecosystem functions like an old-growth forest, it doesn’t really matter if it’s 200, 300 or 1,000 years old. Most of the old-growth trees in the North Cascades National Park, she notes, average between 350 to 800 years old.

For the past 15 years, much of the old forests have been preserved and managed under the Northwest Forest Plan. The plan was initiated in large part to try and preserve wildlife species that depend on Northwest old growth. As a result, the northern spotted owl quickly became an environmental poster child.

Even so, northern spotted owl populations are going to continue to decline, since old forests on non-federal lands are still being lost, said Eric Forsman, a research scientist with the U.S. Forest service, also at the Pacific Northwest Research Station. As a result, he remains pessimistic about the spotted owl’s long-term prospects.

While the northern spotted owl has not been plentiful in the North Cascades in recent years, even casual hikers can detect hints of abundant wildlife. We come upon a large hollowed-out cedar snag that looks like a soundstage prop from The Lord of the Rings. Such snags (essentially vertically standing dead trees) play host to a variety of insects and thus make good food sources for wildlife. The same goes for the forest floor’s old-growth logs, which can take 600 years or more to completely decompose.

The trail snakes around the creek bottom until reaching the Thunder Creek bridge. Although the bridge marks the end of the line for most day hikers, it’s the gateway to a 15-mile stretch of mountainous backcountry.

Bivin said it’s no coincidence that this old growth lies along a creek bed fed by nutrient-rich glacial silt and a steady supply of moisture. She also notes that this river corridor is a lot more stable than much of the area’s steep slopes where the risk of avalanche, rock fall and fire is much more prevalent.

But it’s debatable just how much of such remaining Northwest old growth will actually be preserved in these types of thriving ecosystems.

Forsman said that, in theory, it’s possible to grow old forests, but it will require “long-term vision and willpower.”

“We’ll always have some old growth in the Pacific Northwest,” Spies said, “but the longer we go into the latter part of this century, it’s not clear how much. We do know that there are elevated rates of mortality in old-growth trees due to drought stress and fire,” both hallmarks of climate change.

In many parts of the country, Spies said conservationists see logging as less of a threat than real estate development. But now, he notes the biggest threat of all is climate change.

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