Land clearance

DEFINITION: Removal of plant life, stones, and other obstacles from a land surface to increase the area available for farming or for construction of buildings

Although humans have modified land surfaces for food production and habitation since prehistoric times, the process of land clearance escalated tremendously from the mid-twentieth century onward, causing dramatic changes in ecosystems around the world. These changes have raised environmental concerns regarding soil, water, and air pollution and the loss of animal habitats.

Land clearance increased significantly when human beings transitioned from hunter-gatherer to agricultural societies. As agriculture developed, extensive land areas were cleared for crop growth. With the advancement of technology, the process of land clearance escalated as humans using heavy equipment became capable of not only rapidly clearing but also reshaping the landscape. Often, areas of cleared land that have become less productive than they were previously are abandoned in favor of newly cleared land that is more supportive of agricultural endeavors. These deserted areas often become barren wastelands devoid of human and animal habitation.

The Amazon Rain Forest

An example of land clearance of epic proportions is the Amazon rain forest. The Amazon River basin is the largest rain forest on the planet; it covers about 40 percent of the South American continent and is roughly the size of the contiguous forty-eight US states. The of the rain forest is unequaled: It is home to some 40,000 plant species, 2.5 million insect species, and more than 5,000 bird, fish, and other animal species.

Deforestation began in the Amazon basin during the 1960s, when access to the forest’s interior was first allowed. Large areas were cleared for the planting of crops, and when the soil became depleted, the farmers moved to adjacent areas. These practices resulted in extensive damage to the forest. However, the rate of deforestation in the Amazon and throughout the world has been steadily decreasing. In the Amazon rain forest, 5,153 square kilometers (1,990 square miles) were cleared in 2023, down from 10,278 square kilometers (3,968 square miles) in 2022. According to the UN Food and Agriculture Organization, from 1990 to 2010, 15.5 million hectares (38 million acres) of land throughout the world was cleared each year. This number dropped to 12 million hectares (29.7 million acres) per year from 2010 to 2016. While still high, between 2015 and 2020, the amount of land cleared dropped to 10 million hectares (24.7 million acres) of land was cleared each year.

Negative Consequences

Land clearance and the agricultural activities that follow have major impacts on climate through the of greenhouse gases into the atmosphere. (Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbons.) Soil disturbance results in the release of carbon dioxide, and methane is also produced by soil disturbance, wetland drainage, rice paddies, and cattle flatus. Nitrous oxide is produced by nitrogen fertilizers, irrigation, the cultivation of nitrogen-fixing plants, and the burning of plant materials, or combustion. Sulfur dioxide and are also produced by biomass combustion.

Another effect of land clearance is related to the alteration of the reflection of sunlight from land surfaces, known as the albedo effect (albedo is a measure of the amount of incident radiation, such as sunlight, that a surface reflects). Altered vegetation (such as crops replacing rain forest) and the construction of structures change the land’s heat balance by changing albedo, affecting the amount of moisture evaporated from plants (transpiration) and altering air circulation by changing the surface roughness (for example, planted areas interspersed with structures versus a smooth rain-forest canopy). An example of this alteration is the fact that urban areas have generally warmer temperatures than do rural areas in a given region.

When a forest is cleared for agriculture, animal and plant life within that forest is immediately lost. When plants eaten by the herbivores (plant eaters) native to an area no longer exist, the dies out or migrates; the carnivores, which feed on the herbivores, thus lose their food source as well. Forested areas adjacent to cleared areas are also affected. When contiguous areas of forest are replaced by “islands” of forest interspersed with cultivated areas, the movements of forest animals are restricted, and some may not be able to reach food sources or mating grounds. Land clearance can thus markedly reduce the populations of species or even result in species extinction.

Cleared land becomes vulnerable to soil erosion by wind and water. As topsoil erodes, the land’s fertility decreases and particulate matter is released into the air and into surface water, such as streams and rivers. When land is cleared by burning, pollutants are immediately discharged into the atmosphere. Plants and animals are negatively affected by the contamination of air and water with particulate matter, and runoff from agricultural irrigation, containing nitrogen and from fertilizers as well as toxins from pesticides, further pollutes the water supply.

Some areas that have been cleared for agriculture become nonproductive over time owing to overgrazing or soil depletion. These areas may have been simply abandoned or may have been taken over by commercial and residential structures, particularly in regions where populations are increasing. The urbanization of former agricultural lands often adds to pollution, as the numbers of motor vehicles in these areas increase.

Countering the Negative Consequences

The negative environmental impacts of land clearance can be reduced through the implementation of sustainable agriculture practices. Such practices include crop rotation to avoid depletion of soils and contour farming (in which crops are planted in furrows that follow natural land contours rather than in straight rows) to reduce erosion. The management of agricultural lands must allow for a constant or growing supply of food and other resources to human populations. It also must incorporate the use of less toxic pesticides and the control of runoff into the water supply. Sustainable agriculture practices do not solve the problem of the contribution of land clearance to climate change, however.

To counter the impacts of land clearance on biodiversity, some nations have developed conservation reserves where animals and plant species are protected within their natural habitats. In some areas previously subjected to land clearance, native plants have been reintroduced and their growth supported by both government and volunteer efforts. Another strategy used to promote biodiversity is the establishment of corridors connecting areas where these have been separated by cleared land; this greatly expands the area available to animal species and preserves the migratory habits of many animals.

Bibliography

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