The sight of torn tree bark often leads property owners to wonder why squirrels engage in such destructive behavior. This activity is not random mischief but a series of natural drives rooted in the squirrel’s biology and survival needs. Understanding these motivations, from seeking sustenance to managing dental health, helps explain why these woodland creatures cause damage to valuable trees.
The Biological Drive Behind Bark Stripping
The primary reason squirrels strip bark is to access the inner layer, known as the cambium and phloem. This tissue, found just beneath the outer bark, is rich in sugars, starches, and carbohydrates. It provides a readily available food source when their preferred diet of nuts and seeds is unavailable. This nutritional need is particularly acute during the lean months of late winter and early spring before new growth appears.
The need to gnaw is another significant biological driver for this behavior. Squirrels are rodents, meaning their incisor teeth grow continuously throughout their lives. If these teeth are not constantly worn down by chewing on hard materials, they can grow too long, leading to malocclusion and an inability to feed. Bark provides a suitable texture for this necessary dental maintenance.
Bark stripping can also be a quest for hydration. The inner bark and sap contain moisture, serving as a supplemental water source during periods of drought or when natural water sources are frozen in winter. Furthermore, squirrels may gather the stripped outer bark for use as nesting material. The soft, fibrous pieces help insulate and line their dreys.
Seasonal Timing and Preferred Tree Targets
Bark stripping activity is not a year-round phenomenon; it typically peaks from late winter through early summer. The timing is closely tied to the tree’s sap flow, which carries the desired sugars and moisture, making the inner bark most palatable. This period often coincides with when the squirrel’s stored food supply dwindles and new forage has not yet developed.
Squirrels are not indiscriminate in their choice of tree species, favoring those with smooth, thinner bark that is easier to penetrate. Commonly targeted species include various maples, beeches, sycamores, and pines, as well as young deciduous trees. Younger trees are especially vulnerable because their bark has not developed the thick, protective outer layer found on mature specimens.
Damage frequently occurs on the upper branches and main stems, not just the trunk base. The selection of a specific tree can be hyperspecific, with squirrels sometimes focusing on a single tree while ignoring others of the same species nearby. This suggests that certain individual trees may have a higher concentration of the specific nutrients or sap characteristics the animal is seeking.
Distinguishing Superficial vs. Harmful Damage
Not all bark stripping results in the death of the tree, and property owners should assess the extent of the damage. Minor scrapes or patches of bark removal that do not fully encircle the trunk or branch are considered superficial. The tree’s natural healing process will activate, forming callus tissue to cover the wound and prevent infection.
The truly harmful damage occurs when the squirrel performs what is known as girdling. Girdling is the complete removal of the bark layer around the entire perimeter of the trunk or a branch. This action severs the phloem, the vascular tissue just beneath the bark. The phloem is responsible for transporting sugars, produced during photosynthesis, down to the roots.
When the phloem is severed, the roots are starved of their energy supply, eventually leading to their death. Although the tree’s xylem, which transports water upward, remains intact initially, the roots’ inability to sustain themselves means the entire portion of the tree above the girdle will eventually die. Younger trees and branches are particularly susceptible to fatal girdling due to their smaller circumference and thinner bark.
Practical Methods for Deterrence and Prevention
To protect vulnerable trees, a combination of physical barriers and deterrents can be employed. One effective method is installing a physical guard around the trunk. Materials like wire mesh or metal flashing can be wrapped around the base, extending several feet up the trunk to prevent access to the bark.
These barriers must be installed loosely enough to allow for future tree growth without causing girdling themselves. Repellents, such as non-toxic, capsaicin-based sprays, can also be applied directly to the bark. These products create an unpleasant taste that discourages chewing. However, they require frequent reapplication, especially after rain, to maintain effectiveness.
Another approach focuses on reducing the squirrel’s motivation to strip bark. Providing alternative, easily accessible food sources, such as hard nuts or seeds, away from vulnerable trees can divert their attention. Ensuring a consistent, non-frozen water source during dry or cold periods may also lessen their need to seek moisture from the tree’s sap.