On a gray November morning, a dead oak can look like a silhouette from a ghost story—ragged crown, hollowed limbs, charcoal-dark openings where bark has split. In Barrington and Barrington Hills, where wooded lots meet pasture edges, it’s easy to see such a snag and wonder if it’s time for the chainsaw. But linger a moment. That “spooky” tree is likely doing essential work.

An apartment for wildlife

Bats, screech owls, woodpeckers, bluebirds, squirrels, and a rotation of other tenants make homes in the cavities that form in living and dead trees. “It’s almost like an apartment building for wildlife,” said Spencer Campbell, Plant Clinic manager at The Morton Arboretum in Lisle.

Those holes start where a trunk or limb has cracked, or where decay has softened wood enough for a woodpecker to excavate and enlarge a nest. After the first residents move out, a squirrel or bat may take over. “The mammals are opportunists,” said Lyn Myers, lead education program guide in the Arboretum’s school field trip program. “They take advantage of a cavity that’s already there.”

Not every animal needs a full room. Some tuck themselves into the bark. Butterflies such as the mourning cloak overwinter in the deep furrows of bur oak or the peeling ridges of shagbark hickory; bats sometimes wedge beneath sun-warmed bark on the south side of a trunk, folded into tight packets of wing and fur.

Safety first, then stewardship

A holey or dead tree near a home, sidewalk, or road deserves attention. “If you see cavities in a tree in your yard, you should have it inspected by a certified arborist to determine whether it poses any risk,” Campbell said. “Sometimes, a decayed branch or tree may need to be removed.” But when a snag is not threatening people or property, leaving it upright pays ecological dividends. “A dead tree that isn’t at risk of falling on people or property can actually be more valuable left standing,” Campbell said.

For practical help, local residents can contact the Plant Clinic at The Morton Arboretum (630-719-2424, plantclinic@mortonarb.org) for guidance.

What the science shows

Scientists have a term for standing dead trees—snags—and for the logs and big limbs that eventually topple: downed woody debris. Together, they are workhorses of a healthy forest. Researchers estimate that at least 30% of birds, mammals, reptiles, and amphibians rely on dead or dying trees for part of their life cycles, according to US Forest Service Research and Development. Lose the dead wood, and habitat for many species disappears with it.

Decomposition is a team sport. Fungi are the specialist starters. “Wood-decay basidiomycetes are unusual in that they can break down a major compound of the wood called lignin,” said Gregory Gilbert, Professor of Environmental Studies, University of California, Santa Cruz, in National Geographic. As decomposers unlock wood’s tough compounds, they open the pantry for insects, microbes, and the rest of the food web—an ecological engine that, as reported by National Geographic, ultimately feeds the forest.

As coarse woody debris breaks down, it returns key nutrients to the soil—among them:

  • carbon
  • nitrogen
  • potassium
  • phosphorus

Those nutrients, cycled through successive stages of decay, enrich soil organic matter and help retain water, which benefits seedlings and understory plants, according to Wikipedia.

Large dead trees, in particular, carry weight beyond their imposing silhouettes. They act as slow-release carbon reservoirs for decades to centuries, while their crags and hollows sustain a rich array of microhabitats, research in Ecological Processes shows. And the point isn’t just abstract carbon accounting. “Large dead trees have a very, very important role for storing carbon, providing habitat, [and] nutrient recycling,” said David Lindenmayer, Forest Ecologist and Professor of Ecology and Conservation Biology, Australian National University, in National Geographic.

Why some dead trees stay standing

In the Arboretum’s East Woods—and in many local forest preserves—dead trees that don’t endanger visitors are often left in place. As they remain, they continue to “give back” in the form of nest sites, perches, and food, before ultimately becoming soil. The long arc matters. Many cavity-bearing trees take a century or more to develop the large hollows that birds and mammals need, and without steady recruitment of new cavity trees, shortages can develop within a few decades, according to a Mountain Ash study in PLoS ONE. The lesson for any woodland is clear: today’s middle-aged trees are tomorrow’s critical habitat.

That imperative is sharpened by a sobering global trend. Big, old trees are declining across ecosystems—from rainforests to urban parks—due to drought, climate stress, logging, altered fire regimes, and failures to replace dying giants, as reported by LiveScience. When the elders go, so do the specialized homes and services they provide.

What this means close to home

In a neighborhood or along a Barrington Hills fenceline, a dead limb over a driveway is a hazard; call a certified arborist. But if a snag leans safely away from people and property, consider what it shelters. Many holes in a living tree don’t undermine its structure and can even help, Myers noted: “If woodpeckers and other animals have a cavity to live in, they may be helping it by eating the insect larvae that would be eating the wood,” she said.

And remember that wildlife apartments don’t always have doors. The coarse, furrowed bark that defines our venerable oaks and hickories doubles as winter housing for insects and butterflies, and as a snug day roost for bats. Each of those tenants plays its part in the wider landscape of fields, wetlands, and woodlots that make this corner of the region special.

So the next time a broken-top burr silhouette catches your eye against a November sky, look past the “spooky.” Think of the owls and bats, the fungi and beetles, and the carbon banked in that timber. Then decide what’s prudent—and what’s possible to keep. If you have questions, the Plant Clinic at The Morton Arboretum can help (630-719-2424, plantclinic@mortonarb.org). What looks lifeless may be holding the neighborhood’s liveliest real estate—and quietly growing tomorrow’s soil.