Chapter 2 Geo-Ecology of the North-Western Negev Sand Field A. Yair(* ü ), M. Veste, and S.-W. Breckle 2.1 Introduction The north-western Negev sand field represents the eastern extension of the extensive Sinai continental erg. It can be subdivided into several distinct units. The dry riverbed of the Nizzana channel separates the Haluza-Agur sand field north of the channel from the Hallamish-Shunra sand fields south of the channel (Fig. 2.1). The Nizzana research site is located in the proximity of the Egyptian-Israeli borderline in the southern Hallamish sandy area. The sand ridges in the area trend W–E and are con- sidered by Tsoar et al. (see Chap. 3, this volume) as vegetated stabilized linear dunes (Fig. 2.2). The dunes are up to 18 m high, with an average of around 8.5 m (Allgaier 1993). The relative height of the dune increases from north to south. The area is characterized by a sharp rainfall gradient. Average annual rainfall varies from approx. 170 mm in the north to approx. 90 mm in the south along a distance of 35 km. The rainy season is limited to the winter months, extending from October to May. Mean monthly temperatures vary from 9 °C in January to 27 °C in August (see Chap. 4, this volume). The northern sandy area is classified as arid, the southern area as hyper-arid. The whole sandy area is characterized by a low wind energy (see Chaps. 3 and 4, this volume). The prevalence of weak winds explains many of the special and important properties of this sandy ecosystem, such as the high stability of very large areas caused by the extensive development of biological topsoil crusts, the relatively high content of fine-grained particles in the topsoil crust, as well as the high vegetation cover (∼30% over the crusted areas) indicative of a relatively good water regime despite the arid and hyper-arid climatic conditions. The description and analysis of the various geo-ecological units will focus on the units identified in the southern Hallamish sand field where the Nizzana Arid Ecosystems Research Site is located. Numerous studies on various physical and biological aspects have been conducted at this site during the period 1989–2004, enabling an advanced understanding of the structure and functioning of this sandy ecosystem under wet and dry rainfall years. S.-W. Breckle et al. (eds.), Arid Dune Ecosystems. Ecological Studies 200. 17 © Springer-Verlag Berlin Heidelberg 2008 Breckle_Ch02.indd 17 Breckle_Ch02.indd 17 11/29/2007 9:51:26 AM 11/29/2007 9:51:26 AM