Clearcutting

From Wikipedia, the free encyclopedia
  (Redirected from Clearcut)
Jump to: navigation, search
For other uses, see Clearcut (disambiguation).
After a century of clearcutting, this forest, near the source of the Lewis and Clark River in Clatsop County, Oregon, is a patchwork with each patch composed of trees that are mostly the same age

Clearcutting, or clearfelling, is a forestry/logging practice in which most or all trees in an area are uniformly cut down. Clearcutting, along with shelterwood and seed tree harvests, is used by foresters to create certain types of forest ecosystems and to promote select species that require an abundance of sunlight or grow in large, even-age stands.[1] Logging companies and forest-worker unions in some countries support the practice for scientific, safety, and economic reasons. Detractors see clearcutting as synonymous with deforestation, destroying natural habitats[2] and contributing to climate change.[3]

Clearcutting is the most popular and economically profitable method of logging. However, clearcutting also imposes other externalities in the form of detrimental side effects such as loss of topsoil; the value of these costs is intensely debated by economic, environmental, and other interests. Aside from the purpose of harvesting wood, clearcutting is also used to create land for farming.[4] The "insatiable human demand for wood and arable land" through clear cutting has led to the loss of over half of the world's rainforests.[5]

While deforestation of both temperate and tropical rainforests through clearcutting has received considerable media attention in recent years, the other large forests of the world, such as the taiga, or boreal forests, are also under threat of rapid development. The same reasons for preserving the world’s tropical rainforests also apply to the taiga, as do the reasons for destroying them. In Russia, as in North America and Scandinavia, creating protected areas and granting long-term leases to tend and regenerate trees—thus maximizing future harvests—are ways of limiting the harmful effects of clearcutting.[6] Long-term studies of clearcut forests, such as studies of the Pasoh Rainforest in Malaysia, are also important in providing insights into the preservation of forest resources worldwide.[7]

Types[edit]

Many variations of clearcutting exist; the most common professional practices are:[8]

  • Standard (uniform) clearcut – removal of every stem (whether commercially viable or not), so no canopy remains.
  • Patch clearcut – removal of all the stems in a limited, predetermined area (patch).
  • Strip clearcut – removal of all the stems in a row (strip), usually placed perpendicular to the prevailing winds in order to minimize the possibility of windthrow.[9]
  • Clearcutting-with-reserves – removal of the majority of standing stems save a few reserved for other purposes (for example as snags for wildlife habitat), (often confused with the seed tree method).
  • Slash-and-burn – the permanent conversion of tropical and subtropicals forests for agricultural purposes. This is most prevalent in tropical and subtropical forests in overpopulated regions in developing and least developed countries. Slash-and-burn entails the removal of all stems in a particular area. This is a form of deforestation, because the land is converted to other uses. Slash and burn techniques are typically used by civilians in search of land for living and agricultural purposes. The forest is first clear cut, and the remaining material is burned. One of the driving forces behind this process is a result of overpopulation and subsequent sprawl. These methods also occur as a result of commercial farming. The lumber is sold for profit, and the land, cleared of all remaining brush and suitable for agricultural development, is sold to farmers.[4]
  • Selective Harvesting – Selective harvesting is perhaps the most environmentally friendly method of logging. Unlike the aforementioned techniques, this method is used solely for harvesting wood. Logs are selectively harvested around old-growth trees, whose durability and long interconnectedness with the ecosystem provide unique habitats for plants and animals. This method of deforestation is intended to preserve the ecosystem while still reaping the benefits of timber harvesting. However, selective harvesting can still cause habitat destruction, fragmentation, and microclimate alteration that can harm the remaining trees and ecosystem.[4]

Clearcutting contrasts with selective cutting, such as high grading, in which only commercially valuable trees are harvested, leaving all others. This practice can reduce the genetic viability of the forest over time, resulting in poorer or less vigorous offspring in the stand.[citation needed] Clearcutting also differs from a coppicing system, by allowing revegetation by seedlings. Additionally, destructive forms of forest management are commonly referred to as 'clearcutting'.

Clearcutting in Southern Finland
Clearcutting near Eugene, Oregon

Negative impacts[edit]

Clearcutting can have major negative impacts, both for humans and local flora and fauna.[10] A study from the University of Oregon found that in certain zones, areas that were clear cut had nearly three times the amount of erosion due to slides. When the roads required by the clearcutting were factored in, the increase in slide activity appeared to be about 5 times greater compared to nearby forested areas. The roads built for clearcutting interrupt normal surface drainage because the roads are not as permeable as the normal ground cover. The roads also change subsurface water movement due to the redistribution of soil and rock.[11] Clearcutting can also lead to an increased possibility of rapid runoff, loss of economic sustainability in that no timber products are available for a long time after clearcutting, loss of habitat for some wildlife species, unattractive visual effect, greater possibility of unwanted shrub and grasses becoming established,[12] as well as a decrease in property values; diminished recreation, hunting, and fishing opportunities.[13] Clearcutting decreases the occurrence of natural disturbances like forest fires and natural uprooting. Over time, this can deplete the local seed bank.[14] An example of what clearcutting did in Ontario before 1900 can be found in Edmund Zavitz.

The world's rain forests could completely vanish in a hundred years at the current rate of deforestation. Between June 2000 and June 2008 more than 150 000 square kilometers of rain forest were cleared in the Brazilian Amazon. Huge areas of forest have already been lost. For example, only around eight percent of the Atlantic forest in South America now remains.[15] While deforestation rates have slowed since 2004, forest loss is expected to continue for the foreseeable future.[16] Farmers slash and burn large parcels of forest every year to create grazing and crop lands, but the forest's nutrient-poor soil often renders the land ill-suited for agriculture, and within a year or two, the farmers move on.[17]

Positive perspectives[edit]

Clearcutting can be practiced to encourage the growth and proliferation of tree species that require high light intensity.[18] Generally, a harvest area wider than double the height of the adjacent trees will no longer be subject to the moderating influence of the woodland on the microclimate.[1] The width of the harvest area can thus determine which species will come to dominate. Those with high tolerance to extremes in temperature, soil moisture, and resistance to browsing may be established, in particular secondary successional pioneer species.

Clearcutting can be used by foresters as a method of mimicking a natural disturbance and increasing primary successional species, such as poplar (aspen), willow and black cherry in North America. Clearcutting has also proved to be effective in creating animal habitat and browsing areas, which otherwise would not exist without natural stand-replacing disturbances such as wildfires, large scale windthrow, or avalanches.

In temperate and boreal climates, clearcutting can have an effect on the depth of snow, which is usually greater in a clearcut area than in the forest, due to a lack of interception and evapotranspiration. This results in less soil frost, which in combination with higher levels of direct sunlight results in snowmelt occurring earlier in the spring.[19]

Clearcuts are used to help regenerate species that cannot compete in mature forests. A number of them are aspen, jack pine and, in areas with poor soils, oaks—are important species for both game and nongame wildlife species. Clearcutting can also lead to increased vascular-plant diversity in the area. This is most pronounced after a couple years of clearcutting and in herb-rich forests where scarification took place.[14]

No significant changes in water temperature were observed when patch clearcutting was done 100 feet away from a river. This suggests that patch clearcutting is a possible solution to concerns about changes in water temperautre due to clearcutting. The effects of clearcutting on soil nutrient content were not examined in this study.[20]

More recently, forest managers have found that clearcutting oak stands helps regenerate oak forests in areas of poor soil. The tree canopies in oak forests often shade out the ground, making it impossible for newly sprouted oaks to grow. When the mature trees are removed, the saplings stand a chance of recruiting into the forest.[21]

Effects on wildlife[edit]

Clearcutting's main destruction is towards habitats, where it makes the habitats more vulnerable in the future to damage by insects, diseases, acid rain, and wind. Removal of all trees from an area destroys the physical habitats of many species in wildlife. Also clearcutting can contribute to problems for ecosystems that depend on forests, like the streams and rivers which run through them.[22]

In Canada, the black-tailed deer population is at further risk after clearcutting. The deer are a food source for wolves and cougars, as well as First Nations and other hunters. While deer may not be at risk in cities and rural countryside, where they can be seen running through neighbourhoods and feeding on farms, in higher altitude areas they require forest shelter.[23]

Effects on the environment[edit]

Environmental groups criticize clear-cutting as destructive to the water, soil, wildlife, and atmosphere, and recommend the use of sustainable alternatives.[24] Clear-cutting has a very big impact on the water cycle. Trees hold water and topsoil. Clear-cutting in forests removes the trees which would otherwise have been transpiring large volumes of water and also physically damages the grasses, mosses, lichens, and ferns populating the understorey. All this bio-mass normally retains water during rainfall. Removal or damage of the biota reduces the local capacity to retain water, which can exacerbate flooding and lead to increased leaching of nutrients from the soil. The maximum nutrient loss occurs around year two, and returns to pre-clearcutting levels by year four.[25]

Clear-cutting also prevents trees from shading riverbanks, which raises the temperature of riverbanks and rivers, contributing to the extinction of some fish and amphibian species.[where?] Because the trees no longer hold down the soil, riverbanks increasingly erode as sediment into the water, creating excess nutrients which exacerbate the changes in the river and create problems miles away, in the sea.[24] All of the extra sediment and nutrients that leach into the streams cause the acidity of the stream to increase, which can kill marine life if the increase is great enough.[25] The nutrient content of the soil was found to return to five percent of pre-clearcutting levels after 64 years, which demonstrates how clearcutting affects the environment for many years.[26]

Clearcutting can destroy an area's ecological integrity in a number of ways, including: the destruction of buffer zones which reduce the severity of flooding by absorbing and holding water; the immediate removal of forest canopy, which destroys the habitat for many rainforest-dependent insects and bacteria; the removal of forest carbon sinks, leading to global warming through the increased human-induced and natural carbon dioxide build-up in the atmosphere; the elimination of fish and wildlife species due to soil erosion and habitat loss; the removal of underground worms, fungi and bacteria that condition soil and protect plants growing in it from disease; the loss of small-scale economic opportunities, such as fruit-picking, sap extraction, and rubber tapping; and the destruction of aesthetic values and recreational opportunities.[27]

See also[edit]

Main article: Outline of forestry

References[edit]

  1. ^ a b Dr. J. Bowyer; K. Fernholz; A. Lindburg; Dr. J. Howe; Dr. S. Bratkovich (2009-05-28). The Power of Silviculture: Employing Thinning, Partial Cutting Systems and Other Intermediate Treatments to Increase Productivity, Forest Health and Public Support for Forestry (pdf). Dovetail Partners Inc. Retrieved 2009-06-06. 
  2. ^ U.S. Environmental Protection Agency, Washington, DC (1992). "Clear cut." Terms of Environment: Glossary, Abbreviations and Acronyms. p. 6. Document no. EPA-175-B-92-001. Accessed 2011-10-12.
  3. ^ Center for Biological Diversity, Tucson, AZ. "Clearcutting and Climate Change." Accessed 2011-10-12.
  4. ^ a b c Global Environmental Governance Project: Forests
  5. ^ National Geographic. Rain Forest Threats. Retrieved: 2013-08-05.
  6. ^ Kunganavolok (June 25, 1998). "Taiga! taiga! burning bright." The Economist. Retrieved: 2013-08-06.
  7. ^ Khan, Madeline (February 9, 2004). "Clear cut forests in Malaysia offer lessons for logging worldwide." The Varsity, University of Toronto. Retrieved: 2013-08-06.
  8. ^ Helms, John A. (1998-09-01). The Dictionary of Forestry. Society of American Foresters. ISBN 978-0-939970-73-5. 
  9. ^ British Columbia Ministry of Forests, Victoria, BC. "Clearcut System Variations." Introduction to Silvicultural Systems. Based on the published workbook: "Introduction to Silvicultural Systems, second edition (July 1999)." Forest Practices Branch.
  10. ^ Forest Encyclopedia Network Advantages and disadvantages of clearcutting
  11. ^ Swanson, F.J.; Dyrness, C.T. (1975). "Impact of clear-cutting and road construction on soil erosion by landslides in the western Cascade Range, Oregon". Geology (Geological Society of America) 3 (7): 393–396. doi:10.1130/0091-7613(1975)3<393:IOCARC>2.0.CO;2. 
  12. ^ Toso Bozic (September 14, 2009). "Woodlot Harvest". Government of Alberta: Agriculture and Rural Development. Retrieved 2011-03-07. 
  13. ^ Foothill Conservancy, Pine Grove, CA (2001). "Clearcutting in local forests." Foothill Focus. Spring 2001. Accessed 2011-10-12.
  14. ^ a b Pykälä, J. (2004). Immediate increase in plant species richness after clear‐cutting of boreal herb‐rich forests. Applied vegetation science, 7(1), 29-34.
  15. ^ "Reforestation". Arkive. Retrieved 2013-01-10. 
  16. ^ Future threats to the Amazon rainforest
  17. ^ National Geographic:rain forest threats
  18. ^ Belt, Kevin and Campbell, Robert (1999). "The Clearcutting Controversy - Myths and Facts." West Virginia University Extension Service. Accessed 2011-12-12.
  19. ^ Ottosson Löfvenius, M.; Kluge, M., Lundmark, T.. (2003). "Snow and Soil Frost Depth in Two Types of Shelterwood and a Clear cut Area". Scandinavian Journal of Forest Research (Taylor & Francis) 18: 54–63. doi:10.1080/0891060310002345. ISSN 0282-7581. 
  20. ^ Brown, G. W., & Krygier, J. T. (1970). Effects of clear‐cutting on stream temperature. Water resources research, 6(4), 1133–1139.
  21. ^ Clearcuts Provide Multiple Benefits to Forests and Wildlife
  22. ^ Responses of Wildlife to Clearcutting and Associated Treatments in the Eastern United States. [1]
  23. ^ Ancient Forest News - Clearcutting threatens black-tailed deer
  24. ^ a b Clear-cutting land Greeniacs Articles
  25. ^ a b Martin, C. W., Pierce, R. S., Likens, G. E., & Bormann, F. H. (1986). Clearcutting affects stream chemistry in the White Mountains of New Hampshire. Broomall, PA: US Department of Agriculture, Forest Service, Northeastern Forest Experiment Station.
  26. ^ Covington, W. W. (1981). Changes in forest floor organic matter and nutrient content following clear cutting in northern hardwoods. Ecology, 41-48.
  27. ^ What Is Clearcutting? This method of logging can destroy an area's ecological integrity. [2]

External links[edit]