Clear–cutting

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Clear–cutting

Introduction

Clear–cutting refers to the complete or nearly complete removal of trees from an area of land. The size of the area that is clear-cut varies, from about five acres to hundreds of acres. When the intent of clear-cutting is the commercial use of trees for lumber, a clear-cut can involve just the removal of one or a few target tree species, with a few species left standing. In contrast, when clear-cutting is done to prepare the land for conversion to grazing land for cattle or for crop-growing farmland (silvicultural clear-cutting), or to prepare the land for construction of residential or commercial buildings, all the trees are removed.

From a commercial or agricultural perspective, clear-cutting can be more economical and less time-intensive than scrutiny of the forest area tree by tree followed by a more selective cutting of trees. However, for many, these advantages are far outweighed by the adverse environmental consequences, which include erosion, loss of biological diversity, and loss of the climate-positive forest canopy.

Many forested regions in North America and Europe have been altered by clear-cutting. Elsewhere, clear-cutting of the rain forests in Borneo, the Amazonian rain forest, and the Great Bear rain forest in British Columbia is decimating these ancient ecosystems.

The Brazilian rain forest, which comprises about 30% of the global rain forests, is being logged at the rate of over five million acres each year. If this continues, the rain forests of Brazil, which have an important influence of moderating the global climate, could be eliminated by 2050.

Clear-cutting for agricultural purposes is only a short-term benefit because the removal of the forest stops the cycling of nutrients into the soil. In the Amazon, once fertile soils fail to support crop growth within several years, without the addition of fertilizers.

Historical Background and Scientific Foundations

A mature, natural forest is a complex ecosystem. Many different types of tree species and other vegetation are present. This supports the presence of many types of insect, bird, animal, and fish species (this is known as biodiversit).

Forests that are lumbered for a long time tend to be far less diverse, since only one or only a few species of tree are present. Driving past forest land owned by a lumber company reveals row upon row of the particular species of tree that has been deemed to be the most commercially valuable. This type of forest, which is termed a monoculture forest, can still thrive and support life, since the rate of tree-cutting and the harvesting locations are controlled. The intent is to make the forest sustainable as a source of lumber for centuries.

In a clear-cut where trees have been left standing, these remnants can supply seeds from which new trees grow. On commercial land, seedlings will also be planted to ensure that the desired species of trees are present.

Clear-cutting exposes the ground to more sunlight and reduces the competition for nutrients. Typically, fast-growing shrubs and grasses will appear. Grazing animals can find this habitat attractive. The growth, death, and decay of the ground cover supplies nutrients to the soil, allowing trees to reappear. Thus, the image of a clear-cut as a barren zone is really only the case for a short time. The following growing season will start the re-colonization of the area.

However, clear-cutting has adverse consequences for the lumbered area. Removal of trees near watercourses removes a “buffer”—the trees can impede the movement of sediment-laden water and pollutants into the water. In the absence of the trees, flow of undesirable materials into streams, rivers, and lakes occurs more easily. As a result, the water quality is lessened directly by

WORDS TO KNOW

EROSION: The wearing away of the soil or rock over time.

MONOCULTURE: Single species.

SILVICULTURE: Management of the development, composition, and long-term health of a forest ecosystem. The objective is often to allow logging of the forest over many years.

TRANSPIRATION: Loss of water taken in by roots from leaves through evaporation.

the sediment and indirectly by the surge in oxygen use when such a large amount of organic material is added.

As well, the chances of fire can be increased by the creation of a patchwork of clear-cuts, since it allows for air movement to occur.

In a tropical rain forest, the loss of the forest changes the surface from a dark, humid and cooler place to one that is brightly sunlit, drier, and warmer. This causes the soil to dry, and precipitation washes away soil fungi and dead vegetation that help sustain the soil. Within several years, the formerly rich soil becomes claylike and unable to support much growth. This limits the productive lifetime of a cattle farm or cropland that is created following the clear-cutting.

Re-planting in tropical areas is not necessarily a solution, since it will take a long time for the nutrients present in the plants to be transferred to the soil in appreciable amounts. Fertilization is not a solution either, since it only supplies a portion of the nutrients required for plant growth. Fertilizers are designed to supplement a balanced and productive soil, not to supply everything needed for growth.

A vital nutrient needed for forests and cropland is water. Typically, this comes in the form of rain. Unfortunately, in tropical regions, the great loss of trees due to large-scale clear-cutting reduces the amount of water vapor released from leaves into the atmosphere, which in turn reduces cloud formation. Ironically, clear-cutting in tropical regions, which are among the wettest areas on Earth, may ultimately create deserts.

Impacts and Issues

Clear-cutting is a divisive public issue. Those who support the practice argue that, done with care, clear-cutting allows the controlled harvesting of trees and then allows the land to regenerate another forest so that the cycle can repeat decades later. The use of tree varieties that have been selected for their fast growth can speed up the harvest-growth-harvest cycle. As well, clear-cutting is safer for the forestry worker than selective lumbering of trees within a forest. However, critics point to the well-documented consequences of clear-cutting to biodiversity and in promoting soil erosion. If, for example, a clear-cut is on a steep slope, the removal destabilization of the soil due to tree removal will increase the tendency of runoff during rains. The excess sediment flowing into a stream or river can deplete the oxygen from the water and smother bottom dwelling life.

The effects of clear-cutting can be enormous. For example, in the Canadian east coast province of Nova Scotia, more than 90% of lumbering is done via clear-cutting. Between 1975 and 1999, this amounted to nearly 40,000 sq mi (103,600 sq km) of land, an area about the size of the state of Maine. In about the same time period, over 210,000 sq mi (543,900 sq km) of forest in the Amazon has been clear-cut and lost, since the depleted soil cannot support the re-establishment of trees.

Since older tress are valued more as a commercial resource, the older forests in Nova Scotia and elsewhere

are the first to be clear-cut. In Nova Scotia, as one example, the percentage of forests more than 80 years old has fallen from 25% in the mid-1960s to only one percent in 2006.

In many jurisdictions, foresting occurs on both private and public lands. Private land can be subject to better stewardship than public land, since there is no long term interest in preserving public land as a commercial resource for those who clear-cut.

Furthermore, public lands are typically not monitored to the same degree as are private lands. In areas like the Amazon, the result can be the building of roads into the rain forest and subsequent clear-cutting. This strategy, which was conceived as a way to limit the environmental effects of clear-cutting, is called selective logging. Although in theory this permits more control over the extent of clear-cutting, the reality is proving to be much different. A 2006 study that combined satellite imagery with government-supplied maps of deforestation reported that, in the Amazon, selective logging leads to more extensive clear-cutting, because roads that are built provide access to pristine regions that have not been lumbered. In the Amazon, virtually all clear-cutting occurs within 15 mi (24 km) of roads. Selective logging is producing a loss of rain forest that is twice as fast as was previously thought.

The loss of biological diversity following a clear-cut can be considerable. Indeed, even though rain forests occupy only about 2% of Earth’s surface, they harbor an estimated 60%-70% of all life on the globe. The loss of this biodiversity could be tragic, since rain forests are thought to harbor thousands of insect species and types of microorganisms that have not yet been discovered, and could even be lethal to us, since some of these microbes could produce medically beneficial compounds such as antibiotics and anti-cancer agents.

In an era when the warming of the atmosphere is accelerating and the undesirable consequences of global warming are becoming more clear, the loss of forests takes away areas that can sequester carbon. These carbon sinks help keep carbon from escaping into the atmosphere and driving further warming.

Although some clear-cutting is done to create farmland, this boost to the local economy can be outweighed by the greater economic benefit of utilizing existing forests to harvest fruit and collect both sap and rubber. A farm can benefit the farm owner and a few employees, while the commercial use of forests in multiple ways benefits even more people.