May 16 - 22, 2011

Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a non-forest use. Examples of deforestation include conversion of forestland to agriculture or urban use. The term deforestation is often misused to describe any activity where all trees in an area are removed.

In temperate mesic climates, natural regeneration of forest stands often will not occur in the absence of disturbance, whether natural or anthropogenic. Deforestation occurs for many reasons: trees or derived charcoal are used as, or sold, for fuel or as lumber, while cleared land is used as pasture for livestock, plantations of commodities, and settlements. The removal of trees without sufficient reforestation has resulted in damage to habitat, biodiversity, loss and aridity. It has adverse impacts on biosequestration of atmospheric carbon dioxide. Deforested regions typically incur significant adverse soil erosion and frequently degrade into wastelands.

Deforestation is a contributor to global warming, and is often cited as one of the major causes of the enhanced greenhouse effect. Tropical deforestation is responsible for approximately 20 per cent of world greenhouse gas emissions. According to the Intergovernmental Panel on Climate Change, deforestation, mainly in tropical areas, could account for up to one-third of total carbon dioxide emissions. But recent calculations suggest that carbon dioxide emissions from deforestation and forest degradation contribute about 12 per cent of total anthropogenic carbon dioxide emissions with a range from six to 17 per cent.

Trees and other plants remove carbon dioxide from the atmosphere during the process of photosynthesis and release oxygen back into the atmosphere during normal respiration. Both the decay and burning of wood release much of this stored carbon back to the atmosphere. The water cycle is also affected by deforestation. Trees extract groundwater through their roots and release it into the atmosphere. When part of a forest is removed, the trees no longer evaporate away this water, resulting in a much drier climate. Deforestation reduces the content of water in the soil and groundwater as well as atmospheric moisture.

Deforestation reduces soil cohesion and erosion, flooding, and landslides ensue. Shrinking forest cover lessens the landscape's capacity to intercept, retain and transpire precipitation. Instead of trapping precipitation, which then percolates to groundwater systems, deforested areas become sources of surface water runoff, which moves much faster than subsurface flows. That quicker transport of surface water can translate into flash flooding and more localized floods than would occur with the forest cover.

A 99 per cent of the water absorbed by the roots moves up to the leaves and is transpired. As a result, the presence or absence of trees can change the quantity of water on the surface, in the soil or groundwater, or in the atmosphere. This in turn changes erosion rates and the availability of water for either ecosystem functions or human services.

The forest may have little impact on flooding in the case of large rainfall events, which overwhelm the storage capacity of forest soil if the soils are at or close to saturation. Tropical rainforests produce about 30 per cent of our planet's fresh water.

Deforestation generally increases rates of soil erosion by increasing the amount of runoff and reducing the protection of the soil from tree litter. This can be an advantage in excessively leached tropical rain forest soils.

Forestry operations also increase erosion through the development of roads and the use of mechanized equipment. Tree roots bind soil together, and if the soil is sufficiently shallow, they act to keep the soil in place by also binding with underlying bedrock. Tree removal on steep slopes with shallow soil thus increases the risk of landslides, which can threaten people living nearby.

Deforestation results in declines in biodiversity. The removal or destruction of areas of forest cover has resulted in a degraded environment with reduced biodiversity. Since the tropical rainforests are the most diverse ecosystems on Earth and about 80 per cent of the world's known biodiversity could be found in tropical rainforests, removal or destruction of significant areas of forest cover has resulted in a degraded environment with reduced biodiversity.

Historically utilization of forest products, including timber and fuel wood, have played a key role in human societies, comparable to the roles of water and cultivable land. Today, developed countries continue to utilize timber for building houses, and wood pulp for paper. In developing countries, almost three billion people rely on wood for heating and cooking.


The trees are used for building materials, furniture, and paper products. Forests are also cleared in order to accommodate expanding urban areas. Forests are also cut down in order to clear land for growing crops. Forests are cut down in order to create land for grazing cattle. Trees are cut down in developing countries to be used as firewood or turned into charcoal, which are used for cooking and heating purposes. When forest areas are cleared, it results in exposing the soil to the sun, making it very dry and eventually infertile due to volatile nutrients such as nitrogen being lost.

In addition, when there is rainfall, it washes away the rest of the nutrients, which flow with the rainwater into waterways. Because of this, merely replanting trees may not help in solving the problems caused by deforestation, for by the time the trees mature, the soil will be totally devoid of essential nutrients. Ultimately, cultivation in this land will also become impossible, resulting in the land becoming useless. Large tracts of land will be rendered permanently impoverished due to soil erosion.

Trees contribute in a large way in maintaining the water cycle. They draw up water via their roots which are then released into the atmosphere. A large part of the water that circulates in the ecosystem of rainforests, for instance, remains inside the plants. When these trees are cut down, it results in the climate getting drier in that area.


The unique biodiversity of various geographical areas is being lost on a scale that is quite unprecedented. Even though tropical rainforests make up just six percent of the surface area of the Earth, about 80-90 per cent of the entire species of the world exist here.

Due to massive deforestation, about 50 to 100 species of animals are lost each day. The outcome of which is the extinction of animals and plants on a massive scale.

One of the vital functions of forests is to absorb and store great amounts of water quickly when there are heavy rains. When forests are cut down, this regulation of the flow of water is disrupted, which leads to alternating periods of flood and then drought in the affected area. It is well known that global warming is caused largely due to emissions of greenhouse gases like carbon dioxide into the atmosphere. However, what is not known quite as well is that deforestation has a direction association with carbon dioxide emissions into the atmosphere. Trees act as a major storage depot for carbon, since they absorb carbon dioxide from the atmosphere, which is then used to produce carbohydrates, fats, and proteins that make up trees. When deforestation occurs, many of the trees are burnt or they are allowed to rot, which results in releasing the carbon that is stored in them as carbon dioxide. This, in turn, leads to greater concentrations of carbon dioxide in the atmosphere.

Deforestation and desertification lead to landslides and drought. Trees help attract clouds for rain, help to reduce the amount of carbon monoxide in the air, and slow the rate of desertification. Trees help recharge ground water and sustain stream flow. Trees have a positive impact on the incidence of asthma, skin cancer, and stress-related illness by filtering polluted air, reducing smog formation, shading out solar radiation and by providing an attractive, calming setting for recreation.

Trees strengthen neighborhood communities by providing people with an opportunity to work together for the benefit of the local environment. Trees play a vital role in the urban ecosystem, by helping to support a great variety of wildlife, which people can enjoy close to home.

With the advent of agriculture, forest became the prime tool to clear land for crops. Cities are built in a woody area providing the wood for some industry, which starts consuming so fast that it becomes impossible to obtain it close enough to remain competitive. Above all the massive use of wood in paper making has led to a new onslaught on forest. According to a recent UN report, paper production is responsible for 50 per cent of the total wood harvested worldwide. The report further states that an area of forest equal to 20 football fields is lost every minute. Currently, about 29.6 million acres of forests are cleared annually and more than 13 million acres of forests are cut annually to produce paper products. This resulted in the major loss in biodiversity.

(The writer is in the Botany Department, Jinnah University for Women, Karachi)