Chehalem Ridge Nature Park
Open to the public in December 2021, this is Oregon Metro’s largest nature park west of the Willamette River. The Chehalem Mountains are the tallest mountains in the Tualatin Valley. Metro is the Portland-area regional government; its jurisdiction encompasses several cities and counties.
This 2012 article describes how a government agency turns an industrial tree plantation into a natural area. I wrote it for Metro’s publication, GreenScene.
Chehalem Ridge Natural Area begins transition from an industrial forest
Close to half of Metro’s 1,200-acre Chehalem Ridge Natural Area [now Nature Park] was planted two decades ago for commercial timber production. This year [2012] Metro starts the work of tree thinning, to help the land begin the transition back to a more natural and diverse mosaic of habitats.
“I saw my first flying squirrel back in here,” said one longtime Chehalem Ridge farmer, leaning on a walking stick. He nodded to what was once an oak and fir woodland.
But on a rainy June Saturday, in what is now a timber plantation, the silence is chilling. No bird calls, no sudden scuttering of squirrels or snakes. Participants in a tour of Chehalem Ridge saw a forest floor unnaturally tidy and brown, littered only by fir needles. Trees are planted 8 to 10 feet apart in croplike rows. It’s an efficient landscape, profitable for the timber company that raised Douglas firs for pulp here. For wildlife, not so much.
Beginning this summer, and over the next several years, Metro’s holdings on the ridge will come back to noisy, dynamic life in a program of Douglas fir thinning, shrub and tree planting and removal of invasive species. Metro scientists and technicians are teaming with a Portland-based urban forestry firm, a father-son logging duo from Rainier, and students and researchers at nearby Pacific University to study the site, and plan and implement five to six years of restoration work.
Chehalem Ridge Natural Area occupies 1,200 acres of the Chehalem Mountains, the tallest mountains in the Tualatin Valley. Forming the valley’s southern boundary, the mountains were uplifted by tectonic forces and blanketed with rich soils during the last ice age. Since the 1850s, humans have planted orchard crops, wheat, wine grapes and timber on the mountains’ slopes. About 550 acres of Metro’s property are densely planted in fir — 500 trees to the acre . That’s roughly twice the density of a similar but more naturally-evolved forest.
Metro’s long-term objective is to transform this industrial forest into what it had been for millennia, a biodiverse, wildlife-rich mosaic of old growth upland forest, nectar- and fruit-producing shrub lands and shady, cool stream corridors.
“The goal is land that has a high value to wildlife,” said Metro natural resources scientist Kate Holleran, who is managing the restoration work at Chehalem Ridge. That means contiguous patches of forests with a variety of tree species, tall trees with large-diameter limbs and natural cavities, and snags and down wood. In the work to create such habitats, Metro has a powerful ally: nature.
“The nice thing about this property is that the forest will change fast,” said Scott Ferguson, lead forester with Portland’s Trout Mountain Forestry. His firm is working with Metro to thin and manage the land. “Only in Oregon and a few other places can you cut trees and in two years the land will look very different. “ Credit the rain and good soils.
Holleran explained how the thinning process will begin. “We’ll create irregularly-shaped micro-openings, about 30 feet wide, where just seven to eight trees are cut. In larger, 50 to 70 foot openings, we’ll cut 20 to 40 trees, and in other 50 foot openings, we will leave just one to three [future] legacy trees.” Legacy trees exhibit what Ferguson calls “wolfy growth” — big branches and full crowns — that makes excellent habitat for wildlife. The varying opening sizes allow Metro to adapt its management plan once soils and plants begins to respond to the newly available light, water and nutrients. From 2013 through 2016, more thinning will take place.
“We’re thinning at multiple densities because we’re not sure how the stand will respond,” Holleran said. “As time passes, we may realize, for example, that wide spacing is not going to work: that we’re having blow downs or too many weeds. We may find, also, that tight spacing doesn’t work, so everything else will be at “x” spacing.”
“We’re also looking at how well the understory responds to release (removal of competing vegetation),” she said. “In the natural world, gaps occur in all different sizes. Some are tiny: a big tree falls over, 20 feet of soil are exposed, and red alder comes in to colonize that.” Some natural gaps are larger, from blow downs or fires.
The 35 to 50 acres of timberland thinned this year were once farmed for wheat, before conversion to timber production. These acres offer an excellent laboratory for forest managers as they observe results of different thinning strategies.
“It’s a really good situation,” Ferguson said. “In fir plantations, timber companies manage the site and keep out invasives.” This relatively blank environmental slate offers Metro many options in its work to bring the land back to a more biodiverse state. In some of the newly formed gaps, shrubs, hardwoods and native perennials will be planted by Metro’s Native Plant Center. In others, the land will be left untouched, and scientists will watch what happens.
“In a natural forest, there is a native seed bank,” Holleran said. “Since these lands were agricultural fields we don’t know if there is a native seed bank left, or if it was sprayed — or if it will respond.”
Other thinning in the dense stands will create firebreaks. Some portions of Chehalem Ridge are upland oak habitat. There, firs and maples will be removed to provide the Oregon white oaks with the light they need to thrive. These areas historically would have remained oak woodlands as fires — both human-set and natural — swept through and eliminated the oaks’ faster-growing competitors.
Timber removed will be sold as pulp, to help defray costs to restore the land. After the first thinning, firs grow rapidly; as remaining trees mature, those thinned over the next five years will be sold either as pulp or for lumber.
By 2016, when the thinning regime ends, the land will have gotten a jumpstart in the forest succession that is naturally fostered by centuries of fire, wind throw and other forces. As a group of interested neighbors stood in the rain, learning about the changes coming to Chehalem Ridge, one neighbor asked Ferguson, “What will you do when you’re finished?”
The answer was succinct. “We’ll let it grow.”
Find out more at Metro’s Chehalem Ridge page, which also includes links to internal documents such as the area master plan.
