(9/23) Dead trees. These words bring up multiple negative images. A lone leafless one standing in a field, harboring evil spirits or a gateway to the underworld. Branches scratching the glass of a house window when the wind blows, frightening the lone sleeping inhabitant. Falling on a house during a storm, destroying part of the roof, or onto the road, pulling down electrical wires.

Finally, it is just an ugly site in a yard.

In fact, dead or dying trees that remain standing have a specific name: snags. Furthermore, they provide much needed food and habitat for a wide variety of creatures.

The decline of a tree can be caused by damage due to animals or humans, drought, fire,

lightning, not enough shade, not enough sun, old age, or root competition. Early signs of problems include large dead limbs, fungus on the bark, the appearance of sap, splits in the trunk, and woodpecker holes.

Usually, the earliest lifeform to move into the snag as a weakened tree would be microbial, particularly fungus, which would begin to decay the bark or the heartwood (center of the tree). When the decomposition has reached the proper state, insects will move into the tree to consume it, to hide or to lay eggs. Birds arrive, particularly insect eating birds with pointed bills, such as the woodpecker. It possesses an extraordinary ability to find insects for food, using its bill to hammer the wood and a long tongue with sticky saliva to locate and grab insects. Therefore, this bird is called a primary excavator. If a hole large enough in which to build a nest is created, it is referred to a primary cavity nester.

When a woodpecker hole is abandoned, it can become the home for secondary cavity nesters, such as bluebirds, chickadees, nuthatches, swallows, and wrens. If the space is large enough, owls and wood ducks may become residents. Finally, non-avian creatures may move in, such as bats, raccoons and squirrels.

Trees do not have to be completely dead for wildlife to begin using them as snags. Bald eagles, hawks, kingfishers, ospreys, and owls will perch on bare limbs at the tops of trees to scan the surrounding area for prey. Flycatchers will sit and wait on branches for insects to pass and jump up to catch them out of the air. Multiple species of birds search for insects and their larvae near the surface in dead wood or under bark. Bats use the areas under peeling bark to roost and raise young. Insects hide under slightly raised bark during the winter, providing a critical food source for birds.

The best snags are living trees that are large in diameter and tall in height with some dead main branches. Also it should have decaying heartwood and solid sapwood (the outer layer just under the bark) of the trunk. Usually, this wood retains its shape and forms a "shell" around the disintegrating middle. Also, they should have wounds or scars from fire or lightning, woodpecker holes or cavities, and fungus in the form of mushrooms.

If a tree with these characteristics exits in a yard, it will provide the wildlife value as described above. However, safety is important and the tree should be away from buildings and areas frequently utilized by domestic animals and people, driveways, electrical lines, and roads. If it is not a threat, it may be left in place to decay. If it threatens property, it does not need to be completely removed; it can become a snag by cutting it to approximately six feet tall, depending on its distance from structures, and allowed to decompose.

Nature is not the only one to create a snag. Humans can also, either by allowing a dying tree to remain standing or by making one from a living tree. The best candidates for snags made by landowners are "hazard trees," such as ones with disease or a forked top; in an area where sun is desired; in a grove that needs to be thinned; in an area where no snags exist; or a tree with roots invading drainage or septic systems.

To create a snag, it may be best to consider consulting or hiring an arborist who is certified by the International Society of Arboriculture and specializes in creating trees for wildlife. To locate a professional, visit the website www.treesaregood.org.

The best time of year to complete this project occurs after the nesting season; September-December are the best months in North America to avoid disrupting nesting birds and wildlife.

Several methods exists to create a snag. Topping a tree involves removing its top third, along with half of the side branches. This cut encourages decay to begin in the heartwood and to grow outward into the sapwood, creating areas suitable for cavity-nesting birds. Also, some branches (living and dead) should be left to serve as perches and to create a more natural appearance. Rough or jagged areas from topping the tree encourage the growth of fungi and other organisms. Water will collect in small indentations; then, insects will be attracted, speeding the decay.

Another technique is to remove most of the side branches and leave the top in place. This strategy creates a wind-resistant and long-lasting snag and is usually done to softwoods, such as pine. Jagged branch ends from cutting are more prone to rot and have a natural look.

Finally, the tree may be girdled, which involves removing a four-inch strip of bark completely around the trunk, thereby stopping the flow of water and nutrients. This type of cut should be done as high as possible to avoid the part above cut decaying quickly and falling, leaving a short snag. However, girdling can cause a tree to rot from the outside in, rather than the opposite, which causes weak nesting cavities. Also, the bark around some of the branches can be cut and removed.

Overall, the best snag should be pruned to resemble one in the wild. It should have some living branches to slow decay. Cavities for birds can be drilled in various sizes in the trunk. Long slits can be cut in the top of the tree, since higher ones are more attractive to wildlife, particularly in winter, since they have more sun exposure for warmth. The slits should be at least eight inches deep, at least one inch wide, and angled sharply upward to enable bats to enter, as they need to fly upward to enter them. The bark can be peeled back to create areas for bats and insects.

Whether created by nature or humans, snags can be adjusted by pruning for safety and to promote its longevity. With the loss of forests and the concepts that dead trees are not aesthetically pleasing and have no environmental value, this type of habitat has disappearing rapidly and is probably rarer but is just as important as edge rows and meadows. Any species of tree at any age and size can be a snag. Therefore, consider leaving dead or dying trees in a yard or field and monitor its progress. The reward will be a bounty of wildlife.

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