Deforestation

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.

Fig. 3 - Local subsistence farmers selling their produce. Subsistence farming is responsible for 48% of deforestation, making it the main cause of deforestation.

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.

Fig. 4 - Illegal logging of rosewood in Madagascar. The vast majority of this wood was exported to China.

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.

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.

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 number 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.

Fig. 5 - Infographic showing how deforestation has an impact on climate change.

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 mean 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 the interception, the 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 increase, 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.

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.

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.