FLORISTIC VARIATION IN ISRAEL - A GIS ANALYSIS

An extensive data base of vascular plant records (917 species, 71,062 records) was analyzed with the aid of a geographical information syste m (CIS) in an attempt to quantitatively characterize regional patterns of variation in the Israeli flora. The records were summarized in the form of a grid based site x species matrix, where each site represent s a grid cell of 10 x 10 km. A total of 231 grid cells representing th e entire area of Israel was included in the analysis. The 231 x 917 ma trix was subjected to PCA ordination, and the loadings of the grid cel ls on the first principal component were used to construct a contour m ap of floristic variation. The patterns obtained indicate that the flo ra of Israel consists of two major territories : a mesic one (mean ann ual rainfall greater than 400 mm), and an arid one (mean annual rainfa ll lower than 200 mm). These territories are separated by a narrow tra nsition zone characterized by steep floristic gradients. These results are consistent with the hypothesis that regional variation in rainfal l is important in structuring the flora of Israel. The clear patterns obtained and their consistency with previous studies on the distributi on of plants in Israel suggest that the analytical approach employed i n this study may serve as a powerful tool for the identification of la rge-scale patterns of floristic variation.