Spruce trees, recognized by their evergreen needles and conical shapes, are common conifers found across many landscapes. They contribute significantly to ecosystems, providing shelter and sustenance for various forms of wildlife. While these trees are generally resilient, they also serve as a food source for a wide array of animals, ranging from microscopic insects to larger mammals. Understanding these interactions is important for maintaining the health and longevity of spruce trees in gardens and natural settings.
Mammals That Feed on Spruce Trees
Deer, elk, and moose commonly browse on the tender new shoots and foliage of young spruce trees, often causing defoliation on lower branches. Rabbits and hares frequently gnaw on the bark, particularly on younger trees, which can lead to girdling if the bark is removed entirely around the trunk. Porcupines also consume spruce bark, often climbing higher into the canopy to strip bark from branches and trunks.
Squirrels eat the seeds found within spruce cones, often leaving piles of cone scales, known as middens, at the base of trees. They may also consume buds and occasionally strip bark from young trees. Voles and mice can cause damage by gnawing on the bark at the base of spruce trees, especially when protected by snow cover during winter. Beavers, in some regions, may fell entire spruce trees to access bark for food or to use the wood for dam and lodge construction.
Insects Affecting Spruce Trees
The spruce budworm primarily defoliates new growth, consuming buds and current-year needles, which can turn a reddish-brown color. Prolonged infestations can lead to reduced tree growth and, in severe cases, tree mortality. Various bark beetles, such as the European spruce bark beetle, bore tunnels under the bark to lay eggs, and their larvae feed on the inner woody layers. This feeding disrupts the tree’s vascular system, potentially causing girdling and tree death.
Spruce aphids are tiny, sap-sucking insects that feed on needles, causing them to yellow, mottle, or turn brown before prematurely dropping. Damage often appears first on older, inner needles and can lead to sparse foliage. Spruce spider mites also feed on needle cell contents, resulting in a stippled or mottled appearance, which can progress to yellowing or bronzing. Fine webbing may be visible on infested needles during heavier outbreaks. Gall-forming insects, like the Cooley spruce gall adelgid, cause abnormal, cone-shaped growths on new shoots as they feed, which can distort twig growth.
Birds and Other Occasional Feeders
Birds typically interact with spruce trees by consuming their seeds, rather than causing extensive damage to the tree structure. Crossbills, with their uniquely adapted beaks, are specialized in extracting seeds from spruce cones. Both Red Crossbills and White-winged Crossbills grasp cones with one foot and use their bills to pry open scales, allowing them to access the small seeds. Pine siskins are another finch species that frequently feed on spruce seeds.
Identifying Signs of Animal Damage on Spruce Trees
Chewed or missing needles, particularly on new growth or lower branches, suggest browsing by deer or elk. Stripped bark, especially in patches or around the circumference of the trunk (girdling), often indicates activity from rabbits, voles, or porcupines. Small holes or sawdust-like material (frass) on the bark, sometimes accompanied by resin flow, point to bark beetle infestations.
Discolored or prematurely dropping needles, appearing yellow, brown, or stippled, can signal sap-sucking insects like aphids or spider mites. Abnormally shaped growths or swellings on twigs are characteristic galls caused by adelgids. The location of damage, such as feeding high in the canopy or concentrated at the base, provides further clues about the responsible animal.
Protecting Spruce Trees from Animal Activity
Protecting spruce trees from animal activity often involves a combination of physical barriers, repellents, and maintaining tree health. For browsing mammals like deer and rabbits, installing physical barriers such as fencing around young trees can deter access. Tree wraps or guards around the base of trunks offer protection against gnawing rodents and porcupines. Applying animal repellent sprays can also discourage browsing, though these often require reapplication.
Maintaining the overall health and vigor of spruce trees is important for resisting insect infestations. Ensuring adequate water, proper nutrition, and avoiding soil compaction can improve a tree’s natural defenses. For insect pests, specific treatments might include horticultural oils or insecticidal soaps applied at appropriate times, or in severe cases, targeted insecticides. Removing heavily infested branches or fallen wood can also help limit pest populations.