How does overgrazing and planting in poor soil can cause desertification?

Overgrazing and deforestation encourages erosion of the soil and a decrease in biodiversity. Compaction may also be a problem, moreso with overgrazing than deforestation.

Desertification, though, is drying out and heating of the soil so that plant growth is limited. In "brittle" environments, desertification becomes a problem with too much rest and too much selective grazing by grazing animals. Plants die when they are severely overgrazed by selectivity, but are actually more likely to die out when the dead plant material isn't removed by grazing animals. Dead plant material that doesn't get broken down quickly builds up over time and eventually chokes out the new plants trying to come in.

Dead plant material is less likely to decompose as quickly in a arid environments as they would in warm, humid, tropical environments. A lack of ruminant animals in the former environment will lead to desertification problems: Alan Savory's work has proven this, though not on purely scientific grounds, but more by sequence of photographs before and after holistic management or managed-intensive grazing have been implemented to improve the landscape.