Land Use and its Effect on the Mobilization and Stabilization of the North-Western Negev Sand Dunes

Sand dunes are known to be (1) free of vegetation and active, (2) partly vegetated and active or (3) fully vegetated and fixed. All stabilized sand dunes of the world indicate mobility in the past, under different climate regimes. The sand dunes of the north-western Negev Desert are fully vegetated and fixed, in spite of the climate that is between semi-arid and hyper-arid with low amounts of annual average precipitation – from 170 mm in the north to 90 mm in the south (Tsoar and Møller 1986). The relatively dense plant cover and the microphytic crust cover of the dunes (Chap. 10, this volume) make the Negev sand dunes less arid than would appear at first glance. This phenomenon has puzzled many scientists because many models have shown that, under such arid climate, sand dunes should be active with no vegetation (Sarnthein 1978; Talbot 1984; Lancaster 1988). The perennial vegetation covers about 0–17% of the dune area, with higher cover in the interdune area and with decreasing numbers of shrubs towards the linear dunes' crests. The microphytic crust covers the areas between the shrubs, except for some of the linear dune crests. The crust is resistant to water stress (Chap. 10, this volume) during the hot and dry summer, when it is in a dormant stage (Danin et al. 1989). Annual plants grow during a short period between the beginning of winter and early spring. The number and density of annuals depend on the rain amount and distribution, which determine the moisture in the upper 10 cm of the soil necessary for germination (Chaps. 27 and 28, this volume). Such continuous, shallow moistening of the sand occurs mostly during years with frequent, above-average rainfall, largely during the months of December, January and February, the coldest months of the year (Tsoar and Karnieli 1996).