Forest conversion and soil erosion

Soil erosion commonly appears after conversion of forests to agricultural land, sweeping away fertile soil, pesticides and the sources of liveliood for humans and wildlife.

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Soil erosion in Madagascar
© WWF-Canon / Olivier Langrand

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More calamities after the forests are gone

Damage to areas that are cleared of forests and replaced with plantations continues long after the trees are gone.
Erosion is also accentuated by planting trees in rows up and down hillsides rather than on contours around them, and by poorly planned infrastructure such as roads.

What is erosion?

When forests are cleared, the exposed topsoil often begins to erode, increasing sedimentation into watercourses (e.g. rivers). The situation worsens if there are no forests left along the banks of rivers to hold soil carried by rain. Coffee, cassava, cotton, corn, palm oil, rice, sorghum, soybean, tea, tobacco, and wheat are some of the crops whose cultivation cause soil erosion

During soy production, lack of soil cover and exposure to the wind causes erosion and infertile soils. As a result, every year, Brazil loses 55 million tonnes of topsoil.
 

What is the scale of the erosion problem?

It is estimated that since 1960, one-third of the world’s arable land has been lost through erosion and other degradations. The problem persists, with a reported loss rate of about 10 million hectares per year.

In reality, the situation may be much more worrying. Over the last 5 decades, increases in agricultural productivity have made it possible to produce more crops on the same amount of land.

But the problem is that because agricultural land is often degraded and almost useless, producers keep moving to more productive land. Globally, the land used and abandoned in the last 50 years may be equal to the amount of land used today.

 

 / ©: Olivier van Bogaert
Erosion is a result of deforestation. Ivohibe, Madagascar
© Olivier van Bogaert

From savanna to desert: a ‘how-to’ guide

 Urbanisation and erosion in the Cerrado, Brazil. / ©: WWF-Canon / Mauri RAUTKARI
Urbanisation and erosion in the Cerrado, Brazil.
© WWF-Canon / Mauri RAUTKARI
In the Brazilian Cerrado, the combined effects of deforestation and increased soil temperatures have made it difficult for rainwater to sink into the soil.

When plantation areas of up to 10,000 hectares are exposed following deforestation, the soil becomes extremely vulnerable to wind and water erosion. As a result, desertification has become a serious threat to these areas, which experience a long dry season.

In the Santarem region, intensive rainfall causes erosion, especially near streams and rivers. The sediment is transported downstream, where it makes the rivers and coves turbid.

Priority Places

Impacts of erosion

    • Impact on wildlife: Rainwater runoff carries pesticides, which are then found in the soil, water and sediment affecting fish and other wildlife. For example, Indians living in Xingu Indigenous Park in Brazil report a decline in fish numbers. This trend is attributed to changes in the courses of waterways resulting from farming-related erosion and the silt deposition this causes.
    • Impact on ecosystems: As a result from erosion, pesticides are carried away by the rain to the coast. In Central America, plantation soil run-off ends up in the sea, where it affects the Meso American Reef.
    • Flooding: In banana plantations, flooding occurs partly because of deforestation (soil is no longer there to absorb the water) and partly because of poorly constructed plantation drainage systems.
  • Blue and yellow macaw, Amazonas, Brazil. / ©: WWF / Zig KOCH

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