Originally published Saturday, September 17, 2011 at 7:01 PM

Revegetation involves hundreds of thousands of plantings

Replanting the landscape left behind after the dams come out is in some ways harder than restoring fish populations — and just as important to the long-term restoration of the Elwha ecosystem.

Seattle Times staff reporter

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The aftermath of Mount St. Helens' eruption in some ways was nothing compared with the challenge of revegetating some 800 acres drowned by the reservoirs behind two dams.

While St. Helens was a much bigger disturbance, at least the soils left behind after the mighty volcano blew May 18, 1980, contained some biological legacy: roots and seeds from which new life could spring.

Revegetation of the land that will be exposed when the reservoirs behind the dams drop is in this respect more challenging: "There's no living plant material, no viable seed bank," said Joshua Chenoweth, who is helping lead the revegetation effort for the National Park Service.

Not like regeneration after a fire or blowdown, it's more like starting over after the retreat of a glacier.

Just how the landscape grows in — whether by invasive weeds or desirable native plants — will be the single most visible piece of the Elwha restoration effort.

"It gets overlooked, but it is what everyone is going to see," Chenoweth said. Beyond appearance, replanting is necessary in some areas too far from natural seed sources for nature to do the work. Because for fish restoration to work, the landscape must be restored to a healthy, functioning native forest. Acres of weeds won't cut it.

Upland forests are intimately linked to the health of the rivers that run through them. Forests provide the rain of nutritious litter that falls into the river, feeding bugs and invertebrates that are the base of the aquatic food chain. Upland trees, shrubs and plants also hold the soil and prevent erosion, and shade and cool the water. And when it falls into the river, woody debris provides the complexity in the river channel that lets the river create scours, pools, and side channels and refugia for fish.

It's a lot harder to fix the landscape than to just get the dams out of the way and let the fish saunter back. So inhospitable are the fine sediments to plant growth that even Himalayan blackberry would not grow in test plots. "It's not often you see one to five feet of fines," Chenoweth said. "We know things will grow, native grasses for sure." But what they really want are shrubs that hold the ground, and the team will plant those abundantly.

The soils aren't that bad everywhere, and within 160 feet of the forest growing along the former reservoir banks, nature is expected to revegetate the land unassisted. But elsewhere, the project lands will be actively replanted.

One of the most important parts of the revegetation plan started years ago. The Lower Elwha Klallam Tribe back in 2002 began deploying a crew to cut, pull and spray weeds that would be the seed source for an invasion of exotics. And since 2001, the forest that scientists hope will one day grow on this land has been quietly in the works, in seeds gathered by hand from the Elwha watershed to broadcast on the project lands.

David Allen, park-service botanist, has overseen the growth of tens of thousands of plants that will be established in the project lands, in a seven-year revegetation plan. More than 400,000 plants and more than 5,000 pounds of seed will be planted to revegetate the landscape. Unprecedented in its scale, most of what's being attempted here is all new, and will require adaptation as the plan unfolds, Allen said.

"We can't go into this with the idea that we know everything," Allen said. "We will have to adapt, find what works."

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