Why Woody Debris on the Forest Floor is Important

A young hemlock rises from the decaying materials of a nurse log at Trillium Community Forest. Photo by Dave Schoen.

Combating climate change is just one benefit

Joe Sheldon understands why it makes perfectly good sense to leave fallen trees resting on the forest floor.

When dozens of trees came down at our Trillium Community Forest during last December’s powerful windstorm, efforts were made to remove them from the trails without taking them out of the forest. And there was a sound reason for that.

“Once those Douglas fir logs break down enough—20, 30, 40 years from now—that’s  going to be the site where the next generation of hemlock trees is going to take root,” said Sheldon, a retired college professor with a Ph.D. in entomology (the study of insects) who lives on Whidbey Island.

“In a hundred years, every one of those Douglas fir logs is going to be a nursery for ferns and hemlocks. A whole ecosystem will be growing on top of those logs.”

A rough-skinned newt migrates from the forest to a wetland on Central Whidbey in the spring. Newts also use downed woody debris as shelter in the forest.

Downed woody debris decomposes to help make up a high percentage of material in soils. But that’s only part of its benefit to the forest floor, according to Dan Matlock, a retired biology professor and current Land Trust board member.

“Woody plants represent a huge amount of energy, mostly in the form of cellulose, but also contain a lot of protein and some fat, like resins and waxes,” he said. “They also contain a great amount of minerals. When they die and decompose, all of these are available to other organisms, starting with the decomposers and detritivores (such as earthworms and snails), which in turn are eaten by other organisms, sending all the nutrients back up the food chain.”

Amphibians, such as frogs, toads and salamanders, and reptiles, such as lizards, benefit from this in multiple ways. Woody debris left on the ground provides bugs to eat and habitat to live in or under. Some amphibians and reptiles hide beneath logs or burrow under the duff in the forest floor to stay moist and protected during winters.

The benefits extend to the entire planet, according to Matlock. Woody debris left to decompose releases carbon dioxide back into the atmosphere at a much slower rate than if it were burned. Allowing woody debris to accumulate naturally has a modulating effect on carbon dioxide levels in the atmosphere.

“The forests of the Pacific Northwest are considered to be among the largest, if not the largest, carbon reservoirs of any forests in the world,” Sheldon said. “From a habitat perspective, the importance of downed woody debris and allowing forests to grow to old growth is one of the most effective methods we have to combat climate change.”

So leave the wood on the ground.