Clearcutting
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Clearcutting or clearfelling is a forestry/logging practice in which most or all of all trees in a harvest area are cut down.[1] Clearcutting is a practice that has been shown to have many positive benefits including the renewal of the topsoil layer in areas exposed to the practice.[2] However, clearcutting can also cause erosion on a large scale, causing landslides and de-nutrification of the soil.
Clearcutting includes both:
- silvicultural clearcut, which removes every stem so the forest will be regenerated with no overstory.
- commercial clearcut (or high grading), which removes only commercially valuable trees, leaving the other trees standing.
Before the advent of modern forestry, high grading was the chief method of logging, with no regeneration for the areas cut, which were converted to other uses or left to regenerate naturally. In areas of the world where replanting is not undertaken, this continues to be the case. In the past and present, this kind of clearcutting without any replanting is practiced in forests where virtually every tree is valuable, as in an old growth forest.
In forestry, clearcutting is practiced to regenerate species that require large disturbed high light intensity environments. In a silvicultural planned clearcut virtually all trees are removed, even trees that are not commercially valuable, in order to achieve the outcome environment desired by commercial foresters, including light and soil factors. Clearcuts that are improperly planned have some of the same negative effects of clearcuts with no plan for regeneration. Clearcutting on steep slopes can result in very high erosion rates, for instance.
In Developing countries and Least developed countries the practice of slash-and-burn is a common form of clearcutting, and in modern times is especially prevalent in tropical and subtropical forests, as a way for overpopulated regions strive to eke out a subsistence.
Wildlife
In many parts of the world monocultures are common and clearcutting is a widespread practice for such plantation timber stands.[3] Conversion from a diverse stand to a monoculture reduces tree diversity by definition, but it also reduces total biotic diversity because many animals, people, and understory vegetation have complex needs fulfilled only by a forest of diverse composition.
Immediately following a clearcut, there may be a superficial surge of shrub growth along with seedling growth in that high light, elevated resource availability setting. This condition provides ephemeral forage and some habitat for wildlife. The timing of a silvicultural clearcut is often planned with this in mind, sometimes to provide forage for a desirable species and sometimes to prevent an undesirable or overpopulated species from having that area available.
Silvicultural issues
As a silvicultural practice, the removal of stems or nearly all stems provides an ideal situation for the regeneration of pioneer species, that prefer or require high light, high resource availability and disturbed sites. A clearcut is also the means of regenerating a coppice forest.
Clearcutting is one of many silvicultural treatments that alter the environment for regeneration to optimize harvest. The type of regeneration method used, (clearcutting, selection cutting, etcetera) depends on the land type and the species desired.
Managing for a large area of even aged trees has benefits over multi aged management. Damage to residuals, or trees not cut is minimal in a professional logging operation, but in the developing world, residual trees can be damaged (often fatally) in the removal of the other trees. In a situation where a vast majority of trees are valuable to harvest, it is easier for loggers and economically sound to remove trees in an open clearcut, as opposed to moving equipment around standing trees.
Clearcutting commonly leaves residuals, either trees of value are left standing to stabilize the area or trees of no value or less value are left standing because it was not economically worthwhile to harvest them. The latter practice leads to a kind of high grading. The stunted trees and the undesirable species will grow and re-seed the area, especially where no seed bank or root stock of desirables are present. The less desirable stunted individuals from a valuable tree species will generate less viable individuals, often passing on their less vigorous genes. In the field of forestry planting is often prohibitively expensive and a clearcut often leaves seedlings vulnerable to herbivory. Foresters can combat these costs by planning for natural regeneration through use of species that root sprout, like aspen, or burning of residuals where a fire-dependent seedbank is present, as in jack pine stands.
Public criticism
Clearcutting is commonly criticized since bare soils may be broadly exposed, often leading to unacceptably high erosion rates and loss of biodiversity. Adverse aesthetic impacts typically ensue, broadening the public concern in many natural areas. These impacts diminish the enjoyment of scenic areas for motorists and hikers alike.
Clearcutting has not only a strongly negative visual impact, but often a strongly negative environmental impact. The impact of periodic clearcutting on a viewshed can reduce their value for housing or nearby recreation. This has led to the creation of the "beauty strip", which is a narrow band of trees left as a buffer to conceal clearcut areas from public view. An unspecified number of silviculturalists are recommending variable retention as an alternative to clearcutting.
Mitigating measures
Depending on when, where, and the scale of the clearcut takes place effect on the environment can be massive, especially in erosion-prone country if countermeasures are not taken. Commonly clearcuts leave blocks of "reserve" trees that won't be cut. These can be left to minimize the aesthetic impact of a clearcut, to maintain cavity or den trees for wildlife, to maintain biodiversity, or other similar reasons. Conscientious logging will leave standing snags and a mosaic of small "residual patches" for wildlife, and organic matter such as "slash piles" of unusable material are left on-site as ash to fertilize the soil or as partly-burnt wood that will decay into the soil. If logged on frozen ground with low ground pressure machinery, or even horses, the ground can be left generally undisturbed and unbroken which can sometimes let ground cover regenerate quickly. Ground damage can be reduced, on conifer clearcuts, if harvesting machines utilize unmerchantable tree tops and branches to construct routes upon which they travel.[4]
References
- ^ "a method of regenerating an even-aged stand in which a new age class develops in a fully-exposed microclimate after removal, in a single cutting, of all trees in the previous stand." Adams, D.L., J.D. Hodges, D.L. Loftis, J.N. Long, R.S. Seymour, J.A. Helms. (1994). Silvicultural Terminology. Silviculture Working Group (D2). Society of American Foresters. Bethesda, MD. pp 5.
- ^ >"a method of regenerating an even-aged stand in which a new age class develops in a fully-exposed microclimate after removal, in a single cutting, of all trees in the previous stand." Adams, D.L., J.D. Hodges, D.L. Loftis, J.N. Long, R.S. Seymour, J.A. Helms. (1994). Silvicultural Terminology. Silviculture Working Group (D2). Society of American Foresters. Bethesda, MD. pp 5.
- ^ Savill, P. Evans, J. Auclair, D. Falck, J. (1997) Plantation Silviculture in Europe, Oxford University Press. Oxford. ISBN 0-19-854909-1
- ^ Moffat, A. Jones, B. Mason, B. (2006) Managing Brash on Conifer Clearfell Sites. Forestry Commission Practice Note. Edinburgh
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