Overgrazing is excessive grazing, by exceeding the carrying capacity of the land (a number of animal units per acre).

Overcultivation is the cultivation of marginal lands, such as those with steep slopes, where accelerated erosion is more likely to take place.

All three, deforestation, overgrazing, and overcultivation, lead to desertification.

Desertification is the gradual change to a drier climate, with less rain and more intense storms.