Habitat snags – what are they and why do they matter?
To the untrained eye, standing dead trees look sad, like a blight on the landscape. But give them a second glance and you’ll see they are teeming with life.
These trees are called habitat snags. When they decay, birds, bats, bugs, mammals and small reptiles co-create or compete for living quarters in the crown or cavities.
Some stay one night, and some stay for the season. Some make nests and have babies there. Cavity nesters use snags to help them survive.
In recent years, the State Parks Arbor Crew, a team of six professional arborists who care for the trees in our parks, have helped make these snags more hospitable to wildlife.
A helping hand, or chainsaw cut
What makes a good candidate for a habitat snag? Our Arbor Crew identifies and cuts dangerous trees that are at risk of falling – particularly if they pose a hazard for our visitors.
Then, they carve the top to look like a tree that broke naturally. Clean cut flat tops don’t exist in nature.
“Trees and the organisms that rely on them didn’t evolve for millions of years waiting on folks with chainsaws to come along,” Parks Arborist Beowulf Brower said.
As you can imagine, birds prefer to land and perch on broken, jutting snags because their feet can’t grab onto flat stumps.
When time allows, the Arbor Crew also drills holes into dead tree trunks to create slits for bats to roost or cavities for birds and mammals.
Fungi and decomposers like slime molds also move in and slowly turn the dead wood to soil, where lichen and plants begin to grow.
Bug life
As birds build nests and slime molds ooze, insects take up residence in tree snags. Solitary bees like mason and leafcutter bees claim cavities left by woodpeckers, which bore holes but leave after one season.
You can see these busy bees at work at Squilchuck State Park. Sit near the day lodge and watch as shiny (and gentle) mason bees zip in and out of holes in the giant outdoor wood beams.
Parasitic wasps also use tree snags – and bees – as places to lay their eggs. If they find a bee’s nest, they lay eggs inside the bee and emerge as adults. Other parasitic wasps use fungi in snags, and not bees, to feed their larvae.
East and West
Though people associate snags with densely forested Western Washington, you can see them in Central and Eastern Washington too.
While dead Ponderosa pine, larch and aspen provide options for critters, there aren’t as many trees on the east side, so there aren’t as many snags.
This ups the ante for wildlife.
“From a survival perspective, if you’re a bird that finds a primo cavity, you’re ensuring the survival of your offspring,” said Brower.
It may sound counterintuitive, but the dry east side climate does not help the snag’s longevity. Eastern Washington has more beetle activity, whereas the west side has more non-insect decomposers. And, in a race to the finish, beetles beat out wood-eating fungi.
Where to see them
State parks may have thousands of habitat snags, but the Arbor Crew recently used improved GIS mapping to mark 500 snags with small signs.
From pine trees at Riverside to forests around Beacon Rock’s upper campground, you can see signed habitat snags in more than 20 state parks, including Millersylvania, Jarrell Cove, Moran, Rockport, Squilchuck and Twenty-Five-Mile Creek.
To observe them, bring binoculars and field guides, or download the iNaturalist app.
Safety first
Keep a safe distance when observing habitat snags.
“Don’t climb on, kick or shake them,” said Brower. “You don’t want to be dive-bombed by a raptor, stung by wasps or confronted by a bear,”
Keep in mind, branches might break, or the snag may fall over altogether. It is, after all, a decomposing tree.
Snags are also not a good choice when you’re looking for firewood.
“These trees may look dead,” Waxwing said, “but they sustain a lot of life.”
Originally published March 11, 2025
