By Jason Smith
MANY SPECIES of woodland wildlife benefit from the presence of “den trees.” Den trees, or snags, are those standing trees that are used by animals for nesting, roosting, cover, food supply and other critical functions of basic survival.
These trees are often over-mature with many defects and no financial value from a forestry standpoint. However, from a wildlife standpoint, their value is life itself.
Wildlife that inhabit these den trees, such as woodpeckers, nuthatches, bluebirds, squirrels, and raccoons, are called cavity nesters. The type of wildlife that utilize these den trees will also depend on the kind, size, and location of the den tree.
There are two basic kinds of den trees: hard or soft. Hard den trees have rotten centers with a solid exterior and a few limbs. These usually make the best den trees because the center can be easily excavated to form a home. Trees that usually form good cavities are large hardwoods that decay slowly; such as sugar maple, beech, white oak, hickory and sycamore. These trees are normally quite old and may look totally healthy, but with close inspection, in and around the base of the tree a cavity, will indicate its hollow nature.
Soft den trees have softer exterior wood, and usually have no limbs. These den trees usually make good foraging sites for insect-eating birds, as well as nesting sites for woodpeckers, chickadees and nuthatches. These trees often have short life spans and rot quickly. Aspen would be a perfect example of this type of tree.
Evergreen den trees do not usually last as long as hardwoods, and are usually not utilized for a den tree. However, eastern white pine makes an excellent nest and perch site for Bald Eagles and Osprey when located next to water.
In general, regardless of the kind of den tree, the larger it is the more wildlife it can support. The best den trees, live or dead, are over 20-inches diameter at breast height (DBH) with a den opening of four inches or more.
Keep an eye out for trees that appear to be potential den trees and you may get a chance to view an owl looking out at you or Flying Squirrels running around. Often times, these trees have large, sprawling branches, and often are fruit and nut producers. Missing or bare branches, fungal growth, wounds, and discolored bark are all signs of a dying tree. Also, look for woodpecker holes, which usually indicate a rotting core.
Fallen logs in the forest are snags that have toppled over or healthy trees that fell, usually by a great windstorm like we had last week around here. Once these trees fall to the ground, they do not lose their value to wildlife. Fallen logs in or near water provide cover for various species of fish. Male Ruffed Grouse use fallen logs in their attempts to attract females with their springtime courtship drumming.
Hollow logs will be used by a number of species for dens, especially in winter. If the log is big enough, foxes and even Black Bears will use it for this purpose. As the log becomes more decayed it becomes home to salamanders, moles, shrews, and many kinds of insects. Eventually, these fallen logs will regenerate the forest as they return to the soil, providing rich nutrients for new plants to grow.
Many times, den trees may be difficult to locate during your hike through the forest, but once you start learning what to look for, your chance of viewing wildlife greatly increases. Of course, you never have your camera when you need it! –Williamsport Sun-Gazette