Three factors determine whether sand dunes are bare of vegetation and active or are vegetated and fixed: wind power, precipitation, and human impact. Sand dunes in the world's deserts were formed during the Pleistocene, when climate changed considerably. Models of nonlinear phenomenon that show hysteresis behavior can explain the present status of desert and coastal sand dunes. Biocrust formed on vegetated desert sand dunes and human impacts add to the nonlinearity of these complex phenomena. Vegetated linear dunes, the most prevalent dune type in the world deserts, were formed in Late Pleistocene, which had a climate characterized by higher wind power. Keywords: Biocrust, Climate change, Drought, Dune mobility, Dune stability, Inverse texture effect, Linear dunes, Negev desert, Sand seas, Vegetated linear dunes (VLDs), Wind power.