The Vegetation of the Nizzana Research Site

The study of the vegetation of the Northern Negev has a long history (see Danin and Orshan 1999 and references cited therein). For example, previous phytosociological studies (Eig 1938; Zohary 1944; Eig 1946; Orshan and Zohary 1963; Danin 1978, Danin 1983; Zohary 1982) have characterized the vegetation of the large northern Sinai and northern Negev sandy areas as one association dominated by Stipagrostis scoparia and Artemisia monosperma. More recently, Danin and Solomeshch (1999) have presented a comprehensive work on the coastal and desert vegetation of Israel, which covers the Nizzana area. While the vegetation of the Nizzana research site has been previously mapped and described in detail (Tielbörger 1993, 1997), no attempt has yet been made to integrate the findings into a larger syntaxonomic system. One aim of this study was to fill that gap and search for ties to the more recent work of Danin and Solomeshch (1999).

Relatively little work has been done to classify the vegetation of desert areas, in contrast to the large amount of phytosociological studies in temperate regions. Therefore, there is still a lively discussion about the appropriate methodology to be used. For example, contrary to European tradition, the main criterion used for distinguishing between desert plant communities has been the dominance of perennial species (e.g. Zohary and Orshansky 1949; Danin 1978, 1983; Zohary 1982; Danin and Solomeshch 1999). The dominance criterion is based on the rationale that diagnostic species sensu Braun-Blanquet (1964) are missing in arid environments, and the ‘fitness’ of different species in various habitats is best reflected by their relative abundance (Zohary and Orshansky 1949; Danin et al. 1964). Annual species have mostly been neglected as ‘marker’ species (sensu Danin et al. 1964) for desert communities, since they show large year-to-year fluctuations in relative and absolute abundance (but see Danin and Solomeshch 1999). According to Zohary and Orshansky (1949), only perennial species form a permanent and characterizing framework of desert plant communities, whereas annual species simply mark a highly variable and seasonal aspect. However, Baierle (1993) and Sukopp (personal communication) pointed out that it may be worthwhile to distinguish between communities of different life forms, e.g. annual flora and shrub communities. Yet, in order to include annuals as a distinguishing criterion, they have to be recorded in separate and smaller sampling units, and over more than one growing season (Baierle 1993). In this study, we could utilize results of a 3-year study which investigated spatial patterns in annual plants at the Nizzana research site (see also Prasse 1999). In particular, we tested whether distribution patterns of annuals correlate with those of perennial plants, and whether the observed patterns are stable over more than a single growing season.

The explanation of patterns of distribution and abundance of organisms in space and time is the major goal of empirical ecological research. Using own measurements and results from parallel studies (Beyer et al. 1998), we attempted to investigate which are the factors in the physical environment which may determine the observed distribution patterns of the communities of higher plants. We focused on soil properties (Beyer et al. 1998), exposition, slope, and surface structure as determinants of plant community structure. Thus, the overall results may help in understanding the relationships between biotic and abiotic factors in determining the spatial distribution of certain habitat types within the Nizzana research site.