To most people, the term “dead wood” means “useless.”
But there’s a lot of life in dead trees. In the world of ecology, dead wood provides immense value in healthy habitats.
“Besides growing trees and other plants, if you had to pick one other thing that was key in the forest, it would be dead wood,” said Lori Hennings, a senior natural resources scientist at Metro.
Snags – standing dead trees – downed logs and woody debris in forests and streams provide food, shelter and habitat for mammals, birds, fish, insects, plants, fungi and lichens. Lightning, fire and old age create dead wood in healthy habitats, but younger forests and land cleared for farming, logging and development often lack a healthy supply. Sometimes land managers and scientists create snags and downed logs to kick-start habitat restoration.
Elaine Stewart, natural resources scientist at Metro, recalls placing downed Douglas fir logs from a project in rural West Linn onto an adjoining piece of cleared land. Crews placed one trunk upright to create a snag.
“We were using Douglas fir stems to jumpstart the wood cycle,” Stewart said. “There was a red-tailed hawk circling above. The instant the snag was in place, it came and perched on it.”
Snags make great perches. Owls and raptors survey the terrain from their bare branches. Flycatcher birds use them as a base to survey insects before jumping out and catching them, Hennings said.
Woodpeckers excavate nest cavities in snags. Once they’re done using them as nests, a whole host of other birds that can’t excavate their own nests move in. These secondary cavity nesters include native western bluebirds and white-breasted nuthatches. Raccoons, northern flying squirrels and bats also sometimes shelter in abandoned woodpecker nests.
“No snags, no nesting,” Hennings said.
Dead wood on the ground also serves as shelter. Small rodents such as mice and voles use downed logs to hide from predators. Salamanders and other amphibians, which don’t have waterproof skin, shelter under logs so that they don’t dry out.
And dead wood is a source of food. Birds feed on the beetles, ants and other bugs that eat dead wood.
“Birds undress the log,” drilling or pulling the bark off, looking for insects, Hennings said. This allows in water and fungus and speeds decay. Other bugs eat the fungus. The nutrients in the decaying wood then feed the soil.
Dead wood is important for rivers and streams, too. Historically, rivers were cleared of wood to make navigation easier, but this resulted in wide, shallow stretches of warm water that was deadly for fish.
To restore natural areas along the Clackamas River last summer, Metro placed logs in the floodplain and created log jams, said Peter Guillozet, a senior natural resources scientist at Metro.
“Wood is important in creating channel diversity,” Guillozet said.
The wood adds complexity to the flow of water and improves fish habitat. Water that cascades over the logs forms fast-moving, oxygen-rich riffles that attract invertebrates that many fish feed on. Behind the logs, water collects in cool, deep pools where fish like to rest. The sediment at the bottom of these pools is important for salmon spawning.
From dead wood, it seems, springs new life in rivers and forests.