There's plenty happening in those "trunk wells".

Consider the intricate topographic landscape of tree trunks. On a single tree, the number and diversity of insects differs immensely.

Older trees provide deep furrows and thick plates of craggy bark with more surface area and hiding places for over-wintering adult insects or tasty caterpillars tucked inside a chrysalis hidden beneath bark. Common winter resident birds include chickadees, nuthatches and titmice specialize in foraging beneath bark. These crenulated, fluted columns of the forest are a vertical dinner table.

Tree also provide “melt wells” that form beneath a bare deciduous canopy in late winter. At the base of south-facing trees, particularly dark-barked species like oak, trunks absorb strengthening sunlight and radiate heat that melts the snowpack . Pines, hemlocks and spruces have dark bark, but these evergreens typically shade the forest floor preventing the "trunk well" phenomenon.

Trunk wells catch wind-blown crumbs of fallen food including insects, seeds and lichens. The warm, sheltered, mossy micro-climate is a good place to find tracks of rodents including mice and squirrels. Frequently, their snow tunnels emerge in a tree well for safety from predators including owls, foxes or bobcats. Small carnivorous shrews are particularly "subnivian" - meaning “living under snow.” Meandering tracks of foraging coyotes reveal how predators routinely check tree wells for small mammal prey.

Foraging birds on tree bark confirms the presence of insects. There they must remain concealed while inactive or actively foraging for food. Tree bark and trunk wells provide both food and shelter!