clear-cutting

clear-cutting, the practice of cutting down most or all of the trees in a forest or a section of forest at the same time, usually in a uniform way. Clear-cutting is done to clear land for agriculture or ranching or simply to provide timber and other wood products. In some cases, clear-cutting may be carried out as a forest management tool in degraded forests prior to reforestation. Deforestation occurs when clear-cutting is done without any intent to reforest an area and causes severe damage to the environment and accelerates anthropogenic climate change.

Effects of clear-cutting

As a form of deforestation, clear-cutting has important global consequences. Forests sequester carbon in the form of wood and other biomass as the trees grow, taking up carbon dioxide—a potent greenhouse gas—from the atmosphere (see carbon cycle). Because large amounts of carbon are “locked up” in trees, cutting them down destroys the carbon sink provided by the forest. In addition, understory plants and other plant matter are often burned when a forest is clear-cut, a practice that releases enormous amounts of carbon dioxide and other air pollutants into the atmosphere and further contributes to global warming. Even when a clear-cut area is allowed to regenerate, it takes decades before it can absorb comparable levels of carbon.

In North America and other parts of the world, logging companies that clear-cut forests for timber often replant the area with tree seedlings. Such plantings may create mixed stands of useful timber species or may form a monoculture tree plantation. Given that land managers may seek to maximize profit and may not prioritize ecosystem health, the subsequent generations of mixed or monoculture timber forests generally do not have the same resiliency to disease, climate change, and natural disasters as forests with a diverse assortment of tree and understory species. These replanted commercial forests also lack biodiversity and do not serve as quality habitats for native plants and animals, some of which may be endangered species.

In other cases, a clear-cut forest is simply left to regenerate naturally. Although such abandoned forests may regrow, this is not always the case, especially if the remaining forests are highly fragmented. For example, logging companies often build roads in forests in order to move the heavy equipment needed for clear-cutting, including road graders, log splitters, and bulldozers. Such habitat fragmentation isolates populations of plant and animal species from one another, making it difficult for them to reproduce without genetic bottlenecks, and the fragments may be too small to support large animals or animals with large territories. Naturally regenerated forests might not form the same types of habitats for plants, animals, and other organisms, and the food webs and other relationships among organisms may be altered compared with those in the original forest. In addition, the new forest likely will not provide the same types of ecosystem services as the original forest, or it will not be able to provide them in the same quantities or qualities.

The heavy machinery used for clear-cutting can cause soil compaction, which leads to reduced water-holding capacity. Clear-cutting can also cause severe soil erosion, a situation worsened by the lack of tree roots and understory plants to hold the soil in place and that may result in landslides and mudslides, particularly on steep mountain slopes. In addition, avalanches are more likely to occur in snowy areas devoid of trees. In some cases, mountain clear-cutting causes such extensive soil erosion and nutrient leaching that it results in a complete loss of soil. Without healthy soil and the organisms that live in it, it is impossible for a forest to regenerate. Compacted soils are also more difficult for seeds to penetrate, slowing natural regrowth from the soil seed bank.

Clear-cutting also often negatively affects water quality, especially since water filtration is one of the major ecosystem services provided by forests. With no trees to take up the water in the soil, the herbicides and other chemicals often used in clear-cutting become part of precipitation runoff that enters streams and other bodies of water. Decreased water quality affects many species, including humans, that use the water for drinking and other purposes. Increased runoff also exacerbates erosion along the banks of streams and rivers.

Arguments in favor of clear-cutting

Timber harvesting companies say that clear-cutting is the most efficient, economical, and profitable method of tree harvesting. Acknowledging that humans will continue to use timber products, some scientists argue that clear-cutting can have certain environmental benefits compared with other harvesting methods. For example, although soil compaction occurs with clear-cutting, there can actually be less disturbance to the forest soil by heavy machinery if a section of forest is cut down all at once than if the forest is repeatedly visited by logging equipment. Careful, controlled clear-cutting can create what scientists describe as “early successional” habitat for plants and animals that thrive in such environments. For example, clear-cutting creates wide-open spaces that benefit seedlings of species that need full sun to grow, such as Douglas firs. In these situations, clear-cutting can imitate the type of habitat created by natural disturbances such as storms, floods, insect invasions, and beavers damming streams (see also secondary succession). However, there is a fierce debate over whether artificially creating early successional habitat is necessary or desirable.

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Many places have laws that seek to reduce the environmental harm of clear-cutting. Such laws include limits on the size of clear-cuts, requirements to leave some trees to provide habitat and protect water quality, requirements for replanting trees within certain time frames, and specifications on when trees on land adjacent to a clear-cut may be harvested. However, not all states or countries have such laws, and laws that are in place may not always be enforced or may have ineffectual penalties that do little to deter illegal logging activity.