Monday, January 6, 2014

Wildlife Trees


At one time wildlife trees were called snags, and considered an unhealthy component of the forest, useful only as firewood or felled because of safety concerns. Over the years, our knowledge of forest ecology has increased and wildlife trees have undergone a transformation from the perception of them as sick and decadent, to the realization that they are an integral and important component of forest health. Over eighty wildlife species native to British Columbia depend on these trees for some portion of their lives.
What is a Wildlife Tree?
A wildlife tree is any standing, dead or live tree, with characteristics that provide habitat for wildlife.

Why Are Wildlife Trees Important?
Wildlife trees are essential contributors to ecological diversity. They provide food, shelter, nesting, roosting or denning sites, or hunting perches. When dead, they continue to play a critical role in providing habitat as they begin the long, slow process of nurturing a new cycle of plant and animal growth, providing nutrients to the forest floor.

What makes a Good Wildlife Tree?
A good wildlife tree has at least two of the following characteristics present:
§  Internal decay
§  Large crevices in bark
§  Large witches’ brooms,
§  Active or recent wildlife use such as woodpecker nest holes and fresh wood chips at the base of the tree,
§  Insect infestation,
§  Solid structure suitable for wildlife uses such as a bear den, hunting perch, large nest,
§  Tall, large diameter trees (>70 cm)
A broken branch, stem scar, frost crack, or other damage, which allows the decay process to begin, creates cavities. Heart rot softens the interior of the wood and primary cavity excavators, such as woodpeckers are then able to excavate and create holes.
Squirrels, salamanders, small owls and some ducks are secondary cavity users, they cannot excavate their own nest holes and must rely on natural cavities or those created and abandoned by woodpeckers, nuthatches, chickadees and sapsuckers.
The bark of old trees can be deeply furrowed, providing habitat for insects, and food for woodpeckers and other bark gleaners. When a tree dies, and as the bark begins to loosen and peel away, the protected spaces under the bark provide roosting and nesting space for bats and brown creepers.
Trees with hollow trunks and sturdy shells are uncommon and provide shelter and safety for many species. They are even used as denning sites by black bears. Hollow trunks are formed by interior decay and can be unstable; they benefit by retaining a surrounding treed buffer zone that supplies some wind fastness, as well as enhancing the habitat value of the hollow tree.
Witches’ Brooms
Large, dense clusters of branches provide nesting and security areas for mammals such as squirrels and marten, and some birds.
Which Tree Species are the Best Wildlife Trees?
In the coastal forests of BC, large, long-lived species such as Douglas-fir, Grand Fir, Western Redcedar and Western Hemlock are preferred by wildlife for cavity construction, and nesting or denning. Larger diameter deciduous trees, particularly Cottonwood, Red Alder and Bigleaf Maple, can also become excellent wildlife trees.

Dead Wood and Firewood
After a tree has fallen, it can retain habitat values for centuries by providing moist breeding and egg laying sites for amphibians, drumming sites for grouse, habitat for myriad insect species, which in turn feed many creatures, nurse logs for plants, and by enriching and stabilizing soil. It is beneficial to leave the dead and rotting trees for wildlife habitat and ecological functions, rather than use as firewood.
A better firewood alternative is to use small to medium diameter trees such as red alder and Douglas-fir that are cut green and allowed to adequately cure for a season.

Check BEFORE You Cut
Look for obvious signs of wildlife use: nests, feeding or denning holes, wood chips around base of tree, claw marks or fur on bark, food caches, or bat or bird guano around or beneath the tree.

Wildlife trees are critically important to the biodiversity of our forests, please consider leaving them alone, unless they pose a threat to life and property.

With thanks to, and for further information, see:
Mike Fenger, Todd Manning, John Cooper, Stewart Guy and Peter Bradford, “Wildlife & Trees in British Columbia,” Lone Pine Publishing, 2006.
BC Ministry of Forests brochure: Stand Level Biodiversity

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