Woody browse is an ecological term describing the consumption of twigs, buds, and bark from woody plants by herbivorous animals. This natural and widespread feeding activity strongly influences the structure and health of forested ecosystems globally. This fundamental interaction shapes plant communities and forest regeneration patterns. Understanding this process provides insight into ecosystem dynamics and is central to effective land management.
Defining Woody Browse and Its Components
Woody browse consists of the most nutrient-rich parts of woody vegetation, specifically the terminal buds, tender new shoots, and the bark of small branches. These plant parts are sought out by animals primarily during the dormant season when lush, herbaceous forage is unavailable. The consumption of twigs and buds represents a concentrated source of energy that helps animals survive winter.
Browsing is distinct from grazing, which involves consuming low-growing grasses and other non-woody herbaceous plants. Browsers, such as deer and moose, focus on the leaves, stems, and shoots of shrubs and trees. Grazers like cattle and bison primarily consume ground-level vegetation. Although woody browse is generally not as high in protein as summer forage, its consistent availability provides a survival diet during nutritionally stressful periods.
Key Herbivores Involved in Browsing
Many different animals engage in woody browsing, but the most significant ecological impact comes from ungulates and certain small mammals. Large ungulates, such as moose, elk, and white-tailed deer, are the primary browsers in many temperate forests. Their size dictates their browsing height, creating distinct feeding zones.
Moose are classified as high browsers, often reaching woody material up to three meters above the ground. White-tailed deer are lower browsers, typically feeding on vegetation below 1.5 meters. This difference influences which plant species successfully grow past the animals’ feeding height. Smaller mammals, including rabbits, hares, and voles, also contribute to damage on young saplings. Rabbits clip small branches, while voles often girdle the base of a tree trunk by chewing the bark, especially beneath the cover of snow.
Ecological Impact on Plant Communities
The persistent removal of buds and shoots by herbivores creates significant “browse pressure” that fundamentally alters the composition and structure of a plant community. When browsing intensity is high, it can suppress the height growth of preferred tree and shrub species, preventing them from growing into the forest canopy. This selective feeding can lead to a phenomenon known as a “browse line,” where all vegetation below a certain height is completely removed.
Over time, this pressure results in a shift in species dominance, favoring plants that are less palatable to the animals. Highly preferred species, such as maples or aspens, may be replaced by species with natural defenses, like spruces or shrubs containing chemical deterrents. This process can stall forest succession and reduce overall plant diversity by eliminating vulnerable young seedlings and saplings.
In response to herbivory, woody plants have evolved various physical and chemical defenses. Physical defenses include the development of thorns, spines, and hard shells that deter animals from feeding. Chemical defenses involve the production of specialized secondary metabolites, such as tannins or alkaloids, which can be toxic or make the plant material less digestible and bitter-tasting.
Assessing and Managing Browse Damage
Quantifying the extent of woody browse damage is important for foresters and wildlife managers. Assessment methods involve systematically measuring the percentage of terminal shoots browsed on specific indicator species within a defined area. Techniques like the Assessing Vegetation Impacts from Deer (AVID) method use metrics such as the height of the tallest unbrowsed stem to determine the severity of browsing pressure.
Management strategies focus on protecting valuable plants and regulating the herbivore population. Physical barriers are highly effective, including tall fencing around regeneration areas or plastic tree tubes that protect individual seedlings until they grow above the browse zone. Chemical deterrents, such as contact repellents that make the plant taste bitter, can provide short-term protection but require frequent reapplication. For long-term ecological balance, the most effective management tool is population control, involving the consistent harvest of antlerless deer to reduce herd density and lower browse pressure.