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Deforestation

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Deforestation

Deforestation is a major factor reshaping global geography. We may hear on the news or read online that the Amazon rainforest is in danger of over-deforestation--but what does this actually mean? When forests are cleared, we call this process deforestation. If we are to fully understand deforestation, it is best to study the causes of deforestation and their effects.

First, let's define the term deforestation.

Meaning and Definition of Deforestation

At its simplest level, deforestation is:

The large-scale removal of trees from an established forest.

Deforestation can occur naturally or deliberately with human involvement. Natural deforestation is usually not permanent, whereas when humans are involved, deforestation is usually permanent. The forest is removed so that a change in land use can occur.

Most deforestation is occurring in tropical rainforests. Rainforest Foundation Norway estimates that the Earth has lost approximately 34% of these forests since 2002. In 2019 alone, 121,000 km2 of established forested land was lost. On a global scale, over the last 120 years, The World Bank estimates that deforestation has resulted in a loss of 1.3 million km 2- this equates to roughly the size of South Africa.1

The opposite of deforestation is afforestation or reforestation. Afforestation occurs when a new forest is planted on land that has not had a forest established on it for a long time. Reforestation occurs when trees are replanted soon after they have been removed.

Deforestation, Key Contributors, StudySmarterA map showing the key contributors to deforestation abroad. Wikimedia Commons.

Causes of Deforestation

The natural causes of deforestation are hurricanes, floods, parasites, diseases, and wildfires. Over time, however, afforestation will gradually occur.

Human activities also cause deforestation. This will usually be a permanent land-use change (except when the natural forest is removed and a tree plantation is established in its place). As the world's population grows, the forested land that surrounds expanding settlements is cleared to make way for buildings and infrastructure.

By far the biggest cause of deforestation is the growing demand for food and fuel. In the Amazon, deforestation occurs to make room for agriculture such as soy plantations. Cattle ranching farms are another cause of deforestation in the Amazon. In countries like Indonesia and Malaysia, deforestation is occurring to make way for palm oil plantations. Palm oil is used as a biofuel, as an ingredient in a wide variety of foodstuffs and household consumables (shampoo, cleaning products, cosmetics), and in animal feed.

Logging operations are carried out to provide wood for construction and paper. Generally, this deforestation will be accompanied by reforestation. Illegal logging activities will generally lead to deforestation. This kind of activity also results in the felling of trees to create roads to access more remote forests.

Increasing demands for energy cause deforestation when dams are constructed to produce hydroelectric power. Examples of this include the Jirau and the Santo Antônio dams on the Madeira River, Brazil.

The Madeira River is a tributary to the Amazon. The Jirau and Santo Antônio dams are just two of hundreds of mega-dams that have been built in Brazil. Many more are planned and are part of the country's Growth Acceleration Program (Programa de Aceleração do Crescimento) or PAC.

The construction and flooding caused by the Jirau and Santo Antônio dams are shown on the map below. The reservoirs and upstream flooding (including flooding in the neighbouring country of Bolivia) spread across approximately 898 km2. The vast majority of this area was forested.

Mining activities are responsible for a large proportion of deforestation. The World Bank estimates that around 44% of operational mines are in forests and more than 60% of all nickel, titanium, and aluminium mines occur in forested areas.

Climate change is resulting in a shift in the location of climate belts due to the enhanced greenhouse effect. This shift is causing droughts and an increase in temperatures resulting in a reduction in tropical rainforests. Forested areas are then replaced by brush and savannah-type grasslands. Overgrazing and wildfires caused by human activities also cause deforestation.

A 'once in a centenary' drought occurred in the Amazon area in 2005. However, this drought occurred again in 2010 and 2015. These droughts (potentially triggered by a combination of the El Niño Southern Oscillation and climate change) have had a devastating effect on these forests resulting in damage to many trees (defoliation), dieback of branches, tree falls (particularly the older, taller trees), and wildfires. The wildfires during the 2015 drought resulted in the loss of some 2.5 billion trees.

Deforestation, 2010 drought in the Amazon rainforest Western Brazil, StudySmarterDamage to trees from a surface fire, 2010, Western Brazil,NASA/JPL-Caltech

Effects of Deforestation

When deforestation occurs, an important ecosystem is disrupted, triggering a chain of events, the effects of which reach far and wide. Several direct effects occur as a result of deforestation.

Effects of Deforestation - reduction in the amount of carbon that can be stored

In their natural state, forested areas worldwide act as a carbon sink. Forests absorb CO2 from the atmosphere and, through the process of photosynthesis, this carbon is then changed into biomass and stored. Decomposition gradually releases CO2 back into the atmosphere, but new growth (reforestation and afforestation) will absorb this CO2. Unlike other sources of carbon dioxide, there is a carbon flux at play with forests. They absorb the CO2 when they are growing and release it when they die or are cleared. Current estimates suggest that worldwide forests emit 8.1 billion metric tons of CO2 and absorb 16 billion metric tons of CO2.

During periods of drought, defoliation occurs, as outlined above. Some trees die and others take several years to recover. A forest's ability to absorb CO2 is reduced during this period.

If deforestation is permanent (due to human activities listed above), then this carbon sink is removed: less CO2 can be absorbed and global warming continues. Huge amounts of stored CO2 are released into the atmosphere when the forest is cleared.

There is also a concern that as climate bands shift due to rising temperatures, a positive feedback loop will be created which will accelerate the loss of tropical forests as they are replaced by savanna /semi-arid vegetation. The Amazon River basin is almost at a tipping point where it may well begin to produce more CO2 than it absorbs.

Effects of Deforestation - climate change and global warming

According to figures collated in 2013 by the Intergovernmental Panel on Climate Change, deforestation accounted for 10% of CO2 emissions from human activities. The Food and Agriculture Organisation of the United Nations (FAO) states that deforestation is the second-leading culprit of climate change, the first culprit being the burning of fossil fuels. Estimates today put the total contribution of deforestation to the amount of greenhouse gases in our environment up at around 20%.

When the forest is cleared (either by being burnt or left to decompose), carbon dioxide is released into the atmosphere. This contributes to the enhanced greenhouse effect which leads to an overall increase in global temperatures.

Often, the change in land use results in even more greenhouse gas emissions. For example, if rainforests are cleared to make way for livestock and crops, then methane and nitrous oxide (both greenhouse gases) will be added to the environment.

However, deforestation actually increases the reflectivity of the Earth's surface (forests are darker than grassland or the crops that replace them). An increased albedo effect (that is, the Earth's ability to reflect incoming solar energy) would lead to a cooling effect. This cooling effect needs to be balanced against the warming effect of the CO2 released when deforestation occurs.

Deforestation, climate change due to disturbance of forests, StudySmarterDeforestation and climate change, Wikimedia Commons, CC-BY-4.0

Effects of Deforestation - changes in the hydrological cycle

Deforestation changes the water cycle in several ways.

As soon as the trees are cleared, there is an immediate change because fewer plants and trees means less evapotranspiration (the movement of water from the Earth's surface to the atmosphere).This results in a decrease in rainfall, making drought conditions more likely to occur.

With no trees, the interception of rainfall stops. Forests are multilayered, meaning that large amounts of rainfall are intercepted by forest canopies before it reaches the ground. After interception, rain gradually reaches the forest floor as it drips from leaves and through steam flow. Deforestation means that the rain falls directly onto the cleared ground.

Without interception, an increase in run-off occurs. Forests allow for a slower infiltration of rainwater which in turn regulates how quickly the rain drains off the land. With no trees, the infiltration and percolation of rainfall increases but the water table is closer to the surface and overland flow is more likely to occur.

Without the regulating effect of the trees, more severe droughts and flooding are likely to occur. Deforestation also means that less water can be stored in the biosphere.

Effects of Deforestation - reduction in biodiversity

It is estimated that around 80% of the Earth's land-based species can be found in forests. Deforestation destroys and breaks up the habitat of these species and is largely responsible for driving extinction.

A recent study (2017) of over 19,000 species (including mammals, amphibians, and birds) showed that deforestation was a major factor in determining the likelihood of a species being included on the International Union for Conservation of Nature's (IUCN) red list. The IUCN red list documents all the species that have declining numbers and are therefore potentially at risk of extinction. Species on this 'Red List' are officially classed as 'threatened' and 'endangered'.

Deforestation removes the food sources, shelter, and breeding grounds of these species. Deforestation fragments these habitats and also introduces human activity into these previously undisturbed landscapes.

An example of where this is happening is in Malaysia and Indonesia. Deforestation has occurred to make way for palm oil plantations. As a result, many species including rhinos, orangutans, elephants, and tigers have become isolated in the fragmented forests that have been left behind. Their shrinking habitats have brought them into closer contact with humans, resulting in many of them being killed or captured.

Deforestation also affects the microclimate of the surrounding area. The forest canopy regulates the temperature of the forest by shading large areas during the day and retaining heat during the night. Without this regulation, more extreme temperature swings are experienced which harms the animals left in the fragmented pieces of forest that are left behind.

Effects of Deforestation - Soil Erosion

Deforestation is one of the main causes of soil erosion. The removal of trees removes the tree roots that stabilise the soil. Not only do the roots help bind the soil together and give it much-needed structure, but the trees themselves, above ground, shelter and protect the soil from wind and rain.

When this protection is removed through deforestation, the soil can be washed away by the rain (consider the increased runoff explored above) and blown away by the wind. The removal of the trees also removes the source of leaf litter which protects the soil and contributes to the soil's quality. Deforestation therefore also degrades the quality of the topsoil.

Impacts of Deforestation

The impacts of deforestation are widespread and will ultimately be felt well beyond any area that has been cleared of trees. The increase in CO2 emissions from destroyed forests is contributing to global warming and climate change. Rising sea levels, coastal flooding, changes in ocean currents, and weather systems are just some of the impacts.

These changes in the hydrological cycle impact communities that rely on the regularised flow of rivers to drain deforested areas. Irregular flooding and droughts reduce the viability of crops sustaining and supporting these settlements.

A reduction in biodiversity will impact the overall 'health' of the planet because it decreases the stability of the ecosystem. A reduction in biodiversity will ultimately potentially lead to an impact on our food supply as plants become more vulnerable to disease and attack from pests.

Soil erosion and soil degradation impact local populations by clogging up streams and rivers, leading to flooding. The increased sediments in the waterways can also cause a decline in fish and other species.

Deforestation - Key takeaways

  • Deforestation is the large-scale removal of trees from an established forest.
  • Most deforestation is occurring in tropical rainforests.
  • The natural causes of deforestation are hurricanes, floods, parasites, diseases, and wildfires.
  • Human activities that cause deforestation are urbanisation, demand for food and fuel, logging operations, mining activities, and shifting climatic belts.
  • The effects of deforestation are a reduction in the size of the Earth's carbon sink, climate change, global warming, changes to the hydrological cycle, reduction in biodiversity, and soil erosion.
  • The impacts of deforestation linked to climate change and global warming are rising sea levels, coastal flooding, and changes in ocean currents and weather systems.
  • The impacts of deforestation linked to changes in the hydrological cycle are floods and droughts in areas that were served by the drainage from the deforested area.

References

  1. Tariq Khokar & Mahyar Eshragh Tabary (2016). Five forest figures for the International Day of Forests. World Bank Blog. https://blogs.worldbank.org/opendata/five-forest-figures-international-day-forests
  2. Spring, J. (2021, March 8). Two-thirds of tropical rainforest destroyed or degraded globally, NGO says. Reuters. https://www.reuters.com/article/us-climate-change-forests/two-thirds-of-tropical-rainforest-destroyed-or-degraded-globally-ngo-says-idUSKBN2B00U2

Frequently Asked Questions about Deforestation

Deforestation is the large-scale removal of trees from an established forest.

The natural causes of deforestation are hurricanes, floods, parasites, diseases and wildfires. Human activities also cause deforestation, for example, urbanization, agriculture, logging operations and mining activities.

Deforestation is happening because the world's population is growing and there are increasing demands for food and resources.

Deforestation is bad because it reduces the size of the Earth's carbon sink, contributes to climate change and global warming, changes the hydrological cycle and leads to a reduction in biodiversity and soil erosion. 

Final Deforestation Quiz

Question

What is the definition of deforestation?

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Answer

Deforestation is the large-scale removal of trees from an established forest.

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Question

What is the opposite of deforestation?

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Answer

Afforestation/reforestation

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Question

What is the difference between afforestation and reforestation? 

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Answer

Reforestation is the replanting of trees shortly after they have been removed from a forested area. Afforestation is the planting of trees in an area where trees have not grown for a long time.

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Question

Which of the following is NOT a natural cause of deforestation? 

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Answer

Hurricanes

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Question

Which of the following is NOT a man-made cause of deforestation? 

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Answer

Urbanization

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Question

How do forested areas act as "carbon sinks"?

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Answer

They absorb carbon dioxide and use it for photosynthesis. 

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Question

True or false: deforestation is the third-highest cause of man-made climate change.

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Answer

False. Deforestation is the second-highest cause of climate change.

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Question

Approximately what percent of Earth's land-based species can be found in forests?

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Answer

80%.

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Question

True or false: tree roots add stability and structure to soil. 

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Answer

True. The lack of trees in previously forested areas can lead to soil erosion.

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Question

What is the biggest cause of deforestation?

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Answer

The growing human need for food and fuel. 

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Question

True or false: climate change is causing a shift in climate belts. 

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Answer

True. A shift in the general climate of different areas is contributing to the death of trees. Formerly forested areas are then supplanted by grasslands. 

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