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Snags are valuable part of healthy forest diversity

I recently spent time cross-country skiing through a beautiful stand of hardwood trees in a nearby forest. Large red oaks, bur oaks, American basswood and scattered sugar maple trees typified the portion of forest I found myself enjoying.

As I glided along on my skis over the hard-pack snow, weaving my way around deadfalls and brush, I also noticed several big aspen trees - some dead and some old relics that were near the ends of their lives.

Struck by not only the enormity of those aged aspen trees, I was also in awe of the contribution the trees provided to the forest, particularly to the resident wildlife that seeks such trees for food and shelter. Even in death, trees such as aspen, cottonwood, maple, elm and oak provide all kinds of wildlife many of the essential elements they need for their survival.

Most of the huge aspen trees that I encountered were riddled with the elongated and chiseled excavations of pileated woodpeckers. Many others also included neat and roundish cavities that were made by other woodpeckers such flickers or yellow-bellied sapsuckers. These and other cavities, whether naturally occurring or created, are important nest sites or homes for many creatures - birds and mammals alike.

It occurred to me once again just how important cavities are to the survival of forest wildlife. But even more importantly, is the tree itself. If not for the tree, where would the wildlife species that depend on them be? Perhaps, if not for trees, woodpeckers - and many other species of birds and mammals that rely on woodpecker holes and natural cavities for their own survival -would not exist.

In managing a forest or woodland, one has to consider the importance of dead trees to wildlife. Forest and wildlife managers have known for a long time about this vital component to forest wildlife's health and, in so doing, encourage that forestry best management practices are included when planning timber harvests.

Dead or dying trees are sometimes called snags. According to literature, snags are utilized by 43 species of birds and as many as 26 species of mammals throughout the Midwest. That's a lot of critters that rely on dead and dying trees. Therefore, removing dead trees from a forest, woodlot, or backyard could potentially have negative effects on local wildlife populations by depriving some species critical sources of food and shelter.

In the Minnesota DNR publication, "Landscaping for Wildlife," it is written that, "To many wildlife species, a snag is a bird's version of a fast food restaurant - a valuable habitat component filled with fast food."

Indeed, what often attracts, say, a pileated woodpecker to a tree is the smorgasbord sometimes found underneath the tree's bark, namely, carpenter ants, a favorite food. In this latter case a snag, or dying tree, may become infested with wood-eating ants, which, in turn, attract the ant-eating woodpecker.

Believe it or not, an indicator of a healthy forest is not only a measure of its living trees but, also, the number of its dead trees - both standing dead trees and trees on the ground. How can this be? Again, according to the literature, it is estimated that as many as 50-percent of forest wildlife species depend on dead wood for food, shelter, and survival. Furthermore, dead and decaying wood provides forest soils with valuable nutrients, as well as the benefits to the surrounding watershed through dead wood's water retention capacity.

Snags are definitely important to wildlife. For example, fishers and pine martens depend on the cavities of standing dead trees, hollow logs on the ground and brush piles for shelter and for den sites to raise their offspring inside of. Aside from their use as sites for cavities (nests and dens), and food (ants and other insects), they also provide birds with sites for perching. Have you ever noticed that raptors like hawks, eagles and owls often choose the stout limbs of dead trees to view their surroundings from? This is by no accident, for these birds seek out such trees and will sometimes defend them from other birds and animals.

Whether a snag is large, full of limbs and of relatively sound wood, or is but a stub of soft wood much smaller than its original grandeur once was, matters not to wildlife. Both types of snags are valuable. Woodpeckers excavate cavities that they themselves raise broods inside.

As well, raccoons, weasels, deer mice, squirrels, bats, chickadees, nuthatches, wood ducks, mergansers, common goldeneyes, buffleheads and some species of raptors such as saw-whet owls actively look for abandoned woodpecker holes and naturally occurring cavities for their own use. And many other species of wildlife, including insects, frogs, plants and fungi, need dead and decaying wood for food and shelter too.

Make no mistake, the fields of trees so neatly planted in rows across the landscape, void of ecological diversity, are not forests, though indeed important for forest products and to the forest industry. A genuine and healthy forest is one in which species diversity, age and size diversity, genetic diversity, and structural diversity - snags included - prevail.

Snags and logs in the woods are vital to the long term health of woodlands, water and wildlife for you to appreciate as you get out and enjoy the great outdoors.


Blane Klemek is the Bemidji area assistant wildlife manager, DNR Division of Fish & Wildlife. He can be reached at