They therefore deplete the soil of oxygen and create the need for anaerobic respiration.

Fungi can deplete the soil of readily available nutrients such as nitrogen, causing plants growing within the circle to be stressed which leads to plant discoloration.

It became clear, that food aid alone would not solve long-term problems caused by deforestation and desperate farming practices that depleted the soil.

This has deforested the area and depleted the soil leaving very little wildlife.

In addition, each year the plots are used for another type of crop (known as crop rotation) to prevent depleting the soil on specific trace elements.