Animals that frequently damage trees include birds, deer, small mammals, and livestock.
Woodpeckers cause the most noticeable tree damage as they probe beneath loose bark or peck holes into sapwood in search of insects. Such feeding activity is concentrated on dead, dying, or damaged trees so the bird's feeding is a sign of poor tree health, but not its cause.
One exception to this is the yellow-bellied sapsucker which feeds not only on insects, but also on sweet sap. Sapsuckers bore 1/4-inch diameter holes in closely spaced, parallel rows that may completely encircle a tree. These birds are known to feed on more than 250 species of woody plants. Birch, maple, and hemlock are their preferred food sources in the Lake States.
Sapsucker holes lead to wood stain and may become points of entry for wood decay. If you leave their favorite feeding trees untreated, sapsuckers will concentrate their feeding activities on those trees, which helps protect nearby trees from serious injury. Sapsuckers are especially attracted to aspen with heartwood decay, which they can excavate for nesting cavities. To protect a valuable aspen timber stand, eliminate trees that show signs of decay when you are thinning the stand. This may help discourage sapsuckers from using the area.
Some bird species, including pine grosbeaks and ruffed grouse, eat buds, causing minor damage.
Bird damage usually is limited, so no bird control measures are needed in woodlands. Most bird species (except English sparrows, European starlings, and pigeons) are protected by federal law. A federal permit is needed to destroy protected birds, even if they are pests. Check with the U.S. Fish and Wildlife Service before attempting any control method that may harm birds.
Deer browse on branch tips, especially on young trees and stump sprouts. Browsing stunts tree growth and disfigures trees by causing them to develop crooked stems. Browsing may seriously damage regeneration where there is a high deer density and relatively little natural browse or few agricultural crops available. Browsing damage occurs mainly in winter. Bucks also rub small tree stems and branches with their antlers to remove velvet. Antler rubbing may kill small trees (usually those that are less than 3 inches DBH), but few trees are damaged in this manner so control is not warranted.
In most cases the deer population can be controlled by hunting following state regulations. High fences are effective deterrents, but are prohibitively expensive for forestry purposes. Electrical fences with high voltage and low impedance are more economical and in some cases may be justified to protect young, high-value plantations. Contact a forester or wildlife damage control expert for advice on fencing. Commercial chemical repellents sometimes are effective, but may need to be reapplied after a rain or wet snow. Bud caps are sometimes placed on white pine seedlings to protectthem from deer browsing (see pg. 71 in Chapter 6: Managing Important Forest Types).
You also can minimize forest openings and brushy habitat, making your forest less attractive to deer, or make cutting blocks and regeneration areas as large as possible, thus providing more browse than the deer can consume.
Rabbits, snowshoe hares, mice and other small rodents can girdle or cut off young trees near the ground. Reduce damage by eliminating tall grass and brush piles that provide cover for these animals, especially in or near new tree plantations. Do not place organic mulch (such as straw or wood chips) within 4 inches of a seedling tree stem, because the mulch may provide cover for small mammals.
Pocket gophers feed on roots and bark around the base of young trees and other plants, especially in sandy soils. They are pests in agricultural fields that are being converted to woodland. The best control is to reduce their food sources by eliminating as much vegetation as possible in a tree plantation. In small areas gophers can be trapped. Where the population is high and the plantation is large, control them using a device that creates an artificial tunnel and drops poisoned grain into it. When using poisoned grain, take great care to prevent spills and accidental poisoning of nontarget animals.
Beavers commonly dam small streams, which can flood woodlands and kill trees in the area. They also fell trees (especially aspen and willow) near streams and lakes and either feed on the bark and small branches or use the wood for building dams and huts. The best way to solve a beaver problem is to trap and remove the animals. Contact a wildlife conservation officer for information on trappers in your area.
Figure 7-2. Rabbits and hares eat tree bark in the winter.
Porcupines eat bark and may girdle and kill some trees, especially white and red pines. If damage is serious, they can be live-trapped or killed.
High concentrations of cattle, horses, sheep, goats, or other livestock pastured in a woodland compact the soil, trample young seedlings and sprouts, damage roots, rub bark from stems, and eat or defoliate small trees. Heavy grazing and forest management are not compatible on the same site. In general you should fence livestock out of woodlands if you expect to grow high-quality trees in it.
Figure 7-3. Fence livestock out of woodlands to protect small trees.
Grazing may be acceptable for a short period (a few months to a couple of years) when you want to suppress understory vegetation in preparation for a shelterwood harvest that will be followed by natural regeneration or planting trees. Grazing also may be appropriate in a silvo-pasture where trees and pasture are intentionally managed together. You must give appropriate attention to tree selection, spacing, pruning and other cultural practices to develop widely spaced, high quality trees. Likewise the pasture grass must be intensively managed with fertilizer, rotational grazing, and other practices as needed.
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