When we walk in the forest, we are dazzled and soothed by the leaves and needles of the trees above and around us. These surfaces are the photosynthetic factory of the forest, gathering sunlight and pulling carbon from the air to build themselves, and all of the organisms dependent on trees. Animals that live in trees are known as “arboreal” species.
The surfaces of the branches and leaves, that is the canopy, can be considered a habitat niche with specialized functions for many species of wildlife. When trees reach into the sky to form a canopy layer in the forest, the interacting crowns create a remarkable maze of three-dimensional spaces between and on the branches. These branches will produce the cones and seeds intended for tree reproduction, but which are often taken by various wildlife as food. The surfaces of needles and branches are home for insects, and hunting grounds for their predators. This complex habitat contains varying opportunities for wildlife to make a living by hunting insects, eating lichens, gathering seeds, or other taking specialized actions.
Birds in the Canopy
Birds are the most obvious species to utilize this habitat niche, with rich varieties showing up at different times of the year. Some are resident, remaining in the same, or nearby, habitats year around, while others are migratory. Many of our migratory birds come back from the neo-tropics (that is, Central America and even South America) for breeding season, and return south in the fall.
Different birds can use different portions of canopy at different times. Dense canopies, for example, can provide thermal cover for overwintering chickadees or Stellar’s jays where they roost on a cold winter night. These same fronds can provide abundant insects for flycatchers, such as the Western wood pee wee, and Western tanagers to feed upon when they return from Central America for the summer. Golden-crowned kinglets nervously flit about these same branches throughout the year hunting tiny insects.
Our glorious migratory songbirds arrive between March and May to take advantage of the explosion of insect life in our temperate summer growing season. Research suggests that migratory birds, such as the Townsend’s warbler, Western tanager or various flycatchers, may key on deciduous trees for the insects living there, because it is most similar to the broad-leafed forests where they spend the winter (Sharpe 1996). Conifers have more consistent habitat features; with their needles present year-around, confers provide habitat for year-round residents such as chickadees and nuthatches.
These tiny avian powerhouses will glean insects from the surfaces of leaves (conifer needles are leaves too) throughout the canopy, often travelling in mixed species flocks and moving from tree to tree communicating with small chips and calls. Try “Phishing” when you hear one of these flocks nearby and see what happens. (That is, go “PSHHH, PSHHH, PSHHH” over and over until your mouth is tired and dry. It imitates a distress call among small birds and you will be amazed how close some of them will come!). Many eyes make it easier to spot predators, such as Cooper’s hawks, which make these travelling mixed flocks advantageous.
Truly arboreal mammals are not as numerous as bird species, but are important members of the forest wildlife ecosystem. Our native conifer squirrels are the Douglas and red squirrels, also locally known as chickarees. These two species are actually very similar, but occupy different habitat regions. Douglas squirrels are associated with wetter, westside type forests dominated by Douglas fir and hemlock. Red squirrels live on the drier and colder east side, as well as in Rocky Mountain forest types we have in Northeast Washington (Carey 1996). Both are common and important mammal species directly tied to the forest canopy as conifer specialists, actively harvesting and caching cones each year. Who among us woods walkers hasn’t been scolded by one of these little dervishes? ( I once caught one in a live trap on a small mammal study and was amazed at the sheer strength the squirrel used to bodily throw itself against the wire mesh in an attempt to bash out of the trap; it was released bruised, but unharmed.)
These species in the genus Tamiasciurus also eat mycorrhizal fungi (mushrooms), which work to help trees grow by adding root absorptive surface to trees. The squirrels spread spores throughout the forest through their feces. Flying squirrels occupy a similar niche, but work the night shift, often foraging on the ground for mushrooms to cache. For this reason, flying, Douglas and red squirrels can be considered keystone species in forest ecosystems, e.g., species whose presence has far-reaching impacts. These squirrels need canopy to provide hiding places and food, but also need down logs for cache sites, and woody cavities in snags for denning (that’s another article!). Habitat for these squirrels also includes low branches for resting and eating cones dropped to the ground.
Caring for the Canopy
In our forestry activities, we often thin and manipulate stands in order to grow trees as quickly as possible. This can provide much benefit for wildlife using canopy as the trees mature, but we often will harvest them just as the cone production and canopy reach good habitat status. Pruning can help reduce fire danger, but also remove habitat used by these animals. Retain some full crowned, seed bearing trees through this, and the next rotations. Keep some dense patches in your stand. Don’t prune every tree and keep some low branches for wildlife. Diversity is the key to good habitat.
We can maintain and create diverse canopy while managing our forest stands for diverse structure and multiple objectives through thoughtful management and structural retention.
Please feel free to contact me (and your WSU extension foresters) for a site visit or additional information on how to provide wildlife habitat while managing your small forest woodland.
Ken Bevis, DNR Stewardship Biologist
Carey, A. 1996. NW Science. “Interactions of Forest Canopies and Arboreal mammals.”
Sharpe, F. 1996. NW Science. “The Biologically Significant Attributes of Forest Canopies to Small Birds.”
Thomas, J.W. 1979. USDA Handbook No. 553. “Wildlife Habitats on Managed Forests: The Blue Mountains of Oregon and Washington.”