sentences:  From the early 1900s to the early 2000s the area of sand dunes has declined by about 70% from 129,000 ha to 39,000 ha.This decline has been mainly due to erosion caused by the depletion of vegetation cover in order to convert sand dunes to land for forestry, farming and urban areas.Loss in vegetation cover exposes sand to the action of wind and leaves sand dunes vulnerable to increased erosion as it is vegetation that binds sand together.