Clearcutting
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Clearcutting or clearfelling is defined by the Society of American Foresters as "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."[1] There is no agreement upon the minimum area that constitutes a clearcut, but typically, areas smaller than 5 acres would be considered "patch clearcuts". Clearcutting to convert land for other uses is not the same as clearcutting for forestry. That is called land conversion - converting the use of land from forest to another type of use.
Clearcuts will sometimes leave residuals, or not cut every tree. In what is sometimes called a silvicultural clearcut, every stem is removed, so the forest will be regenerated with no overstory. In what is sometimes called a commercial clearcut, only the valuable trees are cut, and other trees are left standing. This practice can constitute high grading.
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[edit] History
Before the advent of modern forestry, clearcutting was practiced as the major method of logging, with no planned regeneration for the areas cut, which were converted to other uses or left fallow. In areas of the world where long term planning is not undertaken, this continues to be the case. In the past and present, this kind of clearcutting without any planning is practiced in forests where virtually every tree is valuable, as in an old growth forest.
In modern 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 valuable, in order to achieve the desired environment, 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 higher erosion rates, for instance.
[edit] Wildlife
In many parts of the world monocultures are common and clearcutting is a standard practice for these types of plantation timber stands[2]. Conversion from a diverse stand to a monoculture reduces tree diversity by definition, but it also reduces wildlife diversity because creatures have complex needs fulfilled by different trees. Clearcutting is a type of even aged management.
Immediately following a clearcut, there is a surge of shrub growth along with seedling growth in that high light, high resource availability setting. This provides forage and some habitat for wildlife. The timing of a silvicultural clearcut is 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 forage available.
[edit] Silvicultural issues
As a silvicultural practice, removal of all 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.
[edit] Public criticism
The most common and most criticized method of timber harvest in industrial operations is clearcutting. Clearcutting is criticized because, like any logging operation, it can expose bare mineral soils. However clearcutting differs because when managers attempt to mimic a pioneer species ideal setting they create a disturbed site with scarified exposed bare mineral soil. In areas with high slope or other local considerations, clearcutting could cause unacceptably high erosion rates
Perhaps it is because clearcutting is a cheaper way to harvest trees that the public associates it with destructive practices and a lack of long term management. Images taken directly after a clear cut are often used politically because they can be used to imply that the area is not managed for regeneration. But it is undeniably true that clearcutting has a strongly negative visual impact. The impact of periodic clearcutting on a view shed can reduce their value for housing or nearby recreation.
[edit] Natural disturbances
Clearcutting facilitates regeneration of early succession stage species, which are reliant on disturbance for regeneration. Many trees species (e.g. aspen, pines, birch) are shade-intolerant. In nature these trees typically establish themselves only after some disturbance, like a blow down, fire or disease outbreak. Aspen, for example, will actually sucker (re sprout from the roots) after a harvest. Clear cutting provides conditions optimal for species like aspen, many of which are very important to the timber market.
[edit] Management
High-grading and poorly planned partial cuts have done more damage to the forest, in some areas, than clearcutting[3]. Abuses of clearcutting are often easily seen while a poorly managed selection cut may be poorly recognized by the public. Selection cut for the same volume of wood requires more total area of the forest must be harvested, with more roads and skid trail with more potential for soil compaction, erosion and residual stand damage.
What is sometimes called commercial clearcutting is used to maximize income regardless of silvicultural issues. Only trees worth money are removed and whatever regeneration remains may be left in damaged condition. In the case of a poorly planned larger (over 1 km²) clearcut, there are few or no residual patches or wildlife snags left behind and the ground will be highly disturbed and compacted; erosion and poor forest regeneration will result. Some forest types are especially intolerant of clearcutting exposing soils to direct sun and winter rains, which damages soil nutrients and fungi required for healthy forests. Because silvicultural issues involved are complex with many factors to be considered, regulation of the over-use of clearcutting is very difficult. Clearcuts are also used to clear land prior to real estate development projects. Large poorly planned clearcuts are far more destructive than cuts that take into consideration natural topography, and bioregions.
[edit] Mitigating impacts
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 quickly 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 let ground cover regenerate quickly. Ground damage can be significantly reduced, on conifer clearcuts, if harvesting machines utilize unmerchantable tree tops and branches to construct routes upon which they travel [4].
The long term effect of clearcuts on water-flow, erosion and soil nutriments has been studied at Hubbard Brook Experimental Forest
[edit] See also
[edit] Notes and references
- ^ 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
- ^ The Northeast's Changing Forest, Lloyd Irland.
- ^ Moffat, A. Jones, B. Mason, B. (2006) Managing Brash on Conifer Clearfell Sites. Forestry Commission Practice Note. Edinburgh
