Figure 11. (click here)

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Generally, both intermediate cuttings (thinning, weeding, etc.) or regeneration cuttings (clearcuts, shelterwood, etc.) eliminate larger cavity trees and snags; these should be clearly marked for retention before any cutting is done.  Where broken topped trees occur or result from logging, they should also be saved for wildlife if they do not present a safety hazard.

Natural processes and disturbances such as logging usually produce a sufficient number of cav ity trees.  However, some stands have few apparent cavity trees or snags.  The usual procedure for the direct creation of snags has been to girdle large trees with a chainsaw, or to cut away a 3- to 4-inch band of bark and cambium around the entire circumference of the trunks with an axe or hatchet, or to inject them with herbicide.

Where no trees exhibit signs of decay, as in a young stand, nest boxes can be used to attract secondary cavity nesters.  Boxes should be constructed so that they can be opened for autumn cleaning.  Nest box dimensions are given in Table 4.  In the Northeast, nest boxes need not be stained or painted.  They should be erected in autumn so that they weather before spring.  Boxes can be erected on posts or fastened (aluminum nails) directly to the undersides of slightly leaning trees.

Den trees are living hollow trees that are used as homes by mammals (Fig. 12).  Species using den trees vary greatly, ranging from mice (Peromyscus spp.) and flying squirrels (Glaucomys spp.), to gray squirrels (Sciurus carolinensis), rac-

Table 4 (Click here)     

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Figure 12. (Click here)

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coons (Procyon lotor), and black bears (Ursus americanus) (Table 3).  In New England, such trees are usually old boundary or "leave" trees, or large lone trees in fence rows or along old roads.  Thus, they are not well distributed across the landscape.  There are generally fewer than could be used by wildlife.  For example, Southern New England contains 4,998,600 acres of commercial forest land (Kingsley 1974).  Among large sawtimber hardwoods (15.0 inches and larger), 3.1 percent are rough and rotten trees 21.0 to 28.9 inches d.b.h.  Less than 0.5 percent of such trees are greater than 29 inches d.b.h.  Together, these size classes contain the existing and potential den trees in Southern New England woodlands.

By area, then, southern New England contains 16.3 rough and rotten trees at least 21.0 inches d.b.h., per 100 acres of commercial forest land (Table 5).

Table 5 (Click here)

Gray squirrels, for example, can occupy up to 25 or more den trees per 100 acres because their home range is often less than 2 acres (Doebel and McGinnes, 1974).

Cavity trees generally have central columns of decay in the limbs or trunk; den trees are hollow or have large hollow limbs, but are otherwise vigorous.  Most den trees have rather conspicuous openings in sound wood-usually either a round hole on the trunk where a dead limb had dropped off or an opening at the base resulting from a fire scar or other wound.  But some much-used den trees are large hardwoods whose top was snapped off previously.  Even though the opening would seem to offer little protection from the elements, such trees are common den sites for raccoons.

Den trees that grow in open areas-at old homesites, along roads or fences-tend to have large wide crowns.  They are frequently very valuable for wildlife because they often produce more mast or fruit than trees with smaller, more erect crowns.

Den Tree Management

In most cases. den trees need only be marked for retention.  Probably all trees greater than 29 inches d.b.h. should be retained when possible. along with smaller living trees with major defects on the trunks-such as open or spiral seams, butt scars, or holes- retained as replacements.  An ideal den tree distribution for wildlife would be two or more very large (> 29 inches d.b.h.) den trees per 100 acres for raccoons. opossums (Didelphis virginiana). porcupines (Erethizon dorsatum) and the like, and 25 such trees 21 to 28.9 inches

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d.b.h. per 100 acres for squirrels and other small mammals that use tree dens.  Birds such as owls will use these trees also.  Den trees have low stumpage values and then only once.  The development of a very large den tree takes a century or more; some species such as red and white oaks and sugar maple can live for several centuries.  When it falls, the hollow log can last another quarter-century, and later, the rotted stem is used by terrestrial reptiles and amphibians-for example, the ring neck snake (Diadophis punctatus) and redback salamander (Plethodon cinereus)-as breeding habitat.  Finally, a barely discernible patch of dust, used by ruffed grouse (Bonasa umbellus) and other birds for dusting, is left.  The process of den tree development and sequential use by wildlife can last for more than 400 years.

Where no den trees exist, the process can be started by cutting off a 4- to 6-inch limb of a tree 20 inches or more in diameter, leaving a stub about 6 inches from the trunk.  Or chop out a section of bark and inner wood 6 x 6 inches at the base of a suitable wolf tree.  These open wounds allow fungal diseases to enter the tree and begin processes, which over several years will sometimes form a natural cavity surrounded by sound wood.  Ash, beech, hemlock, and basswood are especially good trees to select for a future den tree because they readily form natural cavities.

Wildlife Use of "Sound" Trees

Although the wildlife values of cavity trees and den trees are considerable, it is also necessary to consider wildlife use of sound or apparently sound trees.  Yellow- bellied sapsuckers nest in the firm decayed wood of soft hardwoods such as aspen.  Often, the column of firm decayed wood is difficult to detect.  Other woodpeckers also excavate cavities in trees, usually spruce or fir, that show no outward sign of decay.

Urban Hazard Trees - Wildlife Trees

It is possible to have wildlife trees in parks and other open spaces used by people.  Rotted wood that is about to fall is unlikely to be used for nesting or denning and should be cut to prevent injury to people or property damage.  However, proper pruning of large dead branches may help preserve a hazard tree for wildlife.  The small diameter ends should be removed to reduce strain on the lower, thicker portion of the branch.  Cavities will usually be in the thicker portions.  Weak branches, dead or alive, can be cabled and braced to prevent breakage.  In some situations, planted shrubs, or even a fence could be put around select wildlife trees to keep people away.

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A Look to the Future

Will we have enough large trees for wildlife in the future?  The trend on much managed forest land is toward smaller trees.  We do know that the degree of compartmentalization is under moderate to strong genetic control.  It is time to begin selecting trees for our forests and cities that are strong compartmentalizers.  A strong compartmentalizing tree will not only provide us with more and better quality products, but also will, if not cut down, stay alive long enough to grow to a large size.  Small, weak, unhealthy trees provide people and wildlife with few benefits.  Even if cavities form in small unhealthy trees, they will be small and short-lived.  The best type of tree for people and wildlife is the strong tree that will grow relatively quickly to a massive size and stand a long time.  And, strong compartmentalizing ability will result in strong-boundaried cavities that will last.  Tree species and their cavity values are shown in Table 6.

Table 6 (Click here)

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