Clearfelling
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Clearcutting or clearfelling is a method of timber harvest in which all trees in a selected area are cut. There is no agreement upon the minimum area that constitutes a clear cut, but typically, areas smaller than 5 acres would be considered "patch cuts".
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[edit] Silvicultural issues
The reasons for clearcutting can range from optimizing the regeneration of a forest to clearing land for other uses to taking every tree worth any money. Reasons for clearcutting rather than selection cut include:
- regeneration
- Some tree species do not grow well, or at all, in the shade that is cast by larger trees.
- logging costs
- It is easier and therefore more cost effective to move logs and logging equipment in an open clearcut than among standing trees.
- ownership
- Loggers and land owners just have to agree on the boundaries of the clearcut, rather than agreeing on which trees are cut and which are left.
- stand damage
- In a selection cut residual trees can be damaged (often fatally) in the removal of the other trees.
- wind firmness
- Plantation forests that have been established in areas of high winds will suffer catastrophic wind damage once terminal height is achieved, (Quine and Miller 1990).
The most common and most criticized method of timber harvest in industrial operations is clearcutting, a practice that removes essentially all the trees in a selected area. In the case of a pure-age stand, such as a plantation, or in certain even-aged mature forests, such as some of the virgin Douglas-fir stands of the West, virtually all trees are cut. Clearcutting is often the most economically-efficient way to remove timber. Most forest managers do not consider large clearcuts to be appropriate in a forest managed for multiple uses.
[edit] Clearcuts and natural disturbances
The effects of sustainable clearcutting can mimic the effects of a forest fire or other natural disturbance in a number of important ways. In fact, some tree species, referred to as "shade intolerant" species, only regenerate well in bright sunlight, as in after a clearcut. Many trees species (e.g. aspen, pines, birch) are shade-intolerant. In other words, they don't grow well or perhaps not at all in the shade of other trees. In nature these trees typically establish themselves only after all the other trees in an area have died or been blown down (for example, in a fire or windstorm). Aspen, for example, will actually sucker (resprout from the roots) after being cut. There is no way to regenerate aspen in the shade of other trees, therefore clearcutting is the best tool foresters use to regenerate this species. Ecologically this would simulate a massive windstorm, a large fire, or perhaps a large insect or disease outbreak.
In an area where abundant seedlings and saplings are already established, clearcutting all designated trees 2 inches or greater in diameter at breast height would provide more sunlight to the smaller trees beneath. If this is the case the term "release cut" or "overstory removal" would be more appropriate. This done to maximize dollars and to maximize the amount of sunlight that reaches the ground.
[edit] Afforestation
In clearcuts where natural regeneration is insufficient, sound forestry legislation will demand that a logging company plant seedlings to aid the natural regeneration of the forest. Some argue that treeplanting leads to a "monoculture" forest which destroys the biodiversity of the area. Most seedlings used in reforestation come from the seeds found in the recently cut forest as these trees are naturally adapted to the area. In many areas multiple species will be planted according to the smaller ecoregions of the cutblock ie) lodgepole pine, white or black spruce, cedar, etc. However, clearcutting exposes previously shaded forest soils to direct sun and rainstorms which damage the microbiol diversities required for healthy forest growth.
[edit] Environmental impacts
In many instances commercial clearcutting can be justified as sound forestry. In some cases an area of forest may be in such poor condition that it is nessary to "start over". High-grading and poorly planned partials cuts have done more damage to the forest, in some areas, then clearcutting[1]. Abuses of clearcutting are often easily seen while a poorly managed select cut may be hidden from the public's view. 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, eroison and residual stand damage. On the other hand clearcutting is often used to maximize income regardless of silvicultural issues. Only trees worth money are removed and whatever regereration remains may be left in damaged conditon. 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. Riparian strips on watercourses should be preserved. Commonly clearcuts leave blocks of "reserve" trees that won't be cut. These can be left to mimimize 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 utilise unmerchantable tree tops and branches to construct routes upon which they travel [1].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.
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
- ^ The Northeast's Changing Forest, Lloyd Irland.
- Quine, C. P. and Miller, K. F. (1990). Windthrow - a factor influencing the choice of silvicultural system. Silvicultural Systems, pp. 71 - 81. Institute of Chartered Foresters, Edinburgh.
