Forest Health Focus: An Even-aged Approach to Forest Regeneration and Biodiversity
Forestry expert explains why clearcutting can be an effective, environmentally sound harvesting tool if done right and you can't just the result by a single snapshot in time.
By John-Pascal Berrill
Date Posted: 5/1/2011
Even-aged management is one method foresters use to harvest and regenerate forests. It is generally applied in small openings where native species grow best in full sunlight conditions. While the initial harvest may be aesthetically unpleasing, the forest that will grow for the next 50 to 100 years will provide a wide range of values.
College textbooks on the subject define clearcutting as a regenerative technique, one of several even-aged forest management practices that include shelterwood and seed-tree methods. As with all science-based forest management, its focus is on sustaining and regenerating forests rather than on what trees or biomass may be removed.
In shelterwood and seed-tree methods, some mature trees are left on-site to provide seed for natural regeneration or to augment manual planting efforts. The result is a forest in which most trees are about the same age. In a clearcut, all trees are harvested and the site is replanted with native seedlings that are adapted to local growing conditions.
Performance Over Time
Clearcutting is a process that cannot be evaluated or fairly judged in a single moment. The freeze-frame image the public generally associates with clearcutting is not positive. The public often sees clearcuts as destructive and many equate clearcutting with deforestation. Deforestation occurs when forestland is converted to non-forest uses. When tropical rainforests become sugarcane fields, or condos replace trees, deforestation happens. When a site is replanted and managed to grow trees, the forest returns. Some of today’s most beautiful forests started as clearcuts many years ago.
Three factors generally determine how a forest will be managed: what the land can support biologically, the current forest condition, and ownership objectives. On government lands, the public essentially has said, “we value aesthetics very highly, clearcuts are ugly and we don’t want them.” Federal land managers have responded by shifting away from clearcutting toward thinning and uneven-aged regeneration methods.
Clearcutting is only one method practiced on private lands zoned for timber production. Private forestland owners may place greater emphasis on objectives such as improving growth rates of shade-intolerant trees, enhancing selected habitat characteristics or keeping productive forestland in the family. Desired future condition dictates which treatments are applied to the land, and even-aged forest management can achieve certain objectives effectively and sustainably.
In California, even-aged management is practiced differently than in other states. California clearcuts cannot exceed twenty acres in most areas and may not exceed 30 acres. By contrast, clearcuts in Oregon may exceed 100 acres. California clearcuts can mimic natural disturbances such as wind, fire or disease. Grasses and shrubs return quickly and attract wildlife such as deer and bear that forage in open forest conditions. Planted or naturally occurring seedlings soon rise above competing vegetation, resulting in a closed-canopy forest supporting wildlife that utilize the forest for shelter.
Concern over wildfire behavior, water quality and biodiversity failures stem from the tendency to view clearcutting in a single moment and forests as static. Even-aged forests present differing degrees of wildfire danger over the course of their development. Wildfire risk is relatively high when tree canopies start to grow close together, however thinning can substantially reduce wildfire risk and in the process provide biomass for energy production and small-diameter logs for lumber. Thinning may also help protect adjacent communities.
Protecting water quality is a primary concern during any timber harvest. Well designed and maintained roads are critical for protecting water quality, and foresters work closely with geologists to insure that soils and slopes are protected. Properly implemented even-aged harvesting results in minimal soil disturbance, and ‘buffers’ of trees retained along streams help protect fish habitat. In California, water quality impacts from even-aged management are likely within the range of natural disturbance and prolonged stewardship can conserve aquatic species habitat.
With even-aged management, biodiversity is maintained at the watershed or landscape level. Regulations require that even-aged harvests be separated by time and space, with specific re-entry periods and buffers between harvest areas. The result is a mosaic of different ages of forest across the watersheds with many mature trees along the streams. Certain species may be temporarily displaced at harvest, but can utilize habitat in the vicinity of the harvested area. Clearcuts create openings and highly-diverse edge zones in forests. Even-aged management in patches creates forests of diverse ages across the landscape with a varied forest structure that supports abundant biodiversity.
Even-aged management is a key tool for sustaining the growth and vigor of tree species that grow best in full sunlight. Arguably the least aesthetically pleasing forest management method, California regulations greatly limit the size and spacing of the openings created. The regenerated forest conserves habitat and water resources, promotes biodiversity and helps keep private forestlands resilient and productive.
Reprinted with permission from California Forests magazine.
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