Xerophytic Parameter - Drought Resistence
4. Preliminary Results
By the end of August 2012 I had completed the preparation of the data base with the factor “coefficient of drought resistance” or xerophytic parameter (“X” as follows) following the above key. I then obtained plant lists from 6 squares of 5 by 5 km. The plant lists produced from the data base are in alphabetical order. Therefore, if I study the first 20 species in the list there is no bias in any ecological direction. I marked the X parameter of the list and summed up the value for the first 20 species. The results are:
1. Square 10 = southern Arava, near Har Shkhoret, X=219.
2. Square 17 = southern Arava, near Beer Ora, X=232.
3. Square466 = western Negev near Kerem Shalom, X=174.
4. Square 1026 = Mt. Carmel, X=125.
5. Square 1090 = near Akko/Acre, X=102.
6. Square 1135= HaGolan, near Keshet, X=102.
My first conclusions were that the attempts to provide an effective parameter to obtain the xerophytic position of the site look well and agree with my expectations. To continue the investigations I prepared transects perpendicular to the isohyets (lines linking sites with the same amount of mean annual rainfall).
The transects were: 1. Between Ashdod near the Mediterranean coast, 2. Between Emek HaElah in the foothills of the Judean mountains and Mashabe Sade. Vegetation transects are drawn along these two lines (in Chapters 8 and 9 in the “Vegetation of Israel”…). The addition of lines showing the xerophytic position may assist in understanding the vegetation – environment relationships. An additional transect across the Upper Galilee and the Golan was done for comparison with the drier parts of the country.
5. Transects across Climatic Gradients
I prepared these transects in order to test if the method of analysis of the coefficient X along prominent climatic gradients agreed with the recorded mean annual rainfall. Proving sufficient agreement between coefficient X and the mean annual rainfall may enable accurate estimation of the degree of aridity when the measurement of mean annual rainfall and other meteorological variables is not available. The results for single squares are presented in Table 1.
The left part of the transect, from the Mediterranean coast to Jerusalem, displays a gradual rise from X=105 to X=120. East of Jerusalem there is a steep rise of the X values, in full agreement with the term “rain shadow” given to the Judean Desert in literature. There is a steep drop in the mean annual rainfall from west to east and a steep rise in the mean annual temperature. The X coefficient, based on the lists of species in the squares traversed displays these climatic gradients and reaches X=216 in the Dead Sea Valley.
In this transect, the squares selected are at almost the same altitude. Therefore there is no change in the temperature regime, which is important in transect 11.4.1. The distance between the isohyets in this moderate transect is rather long. The X coefficient displays here a significant rise from square 566, where mean annual rainfall is 300 mm; X= 125. In square 344 mean annual rainfall is 100 mm and X=194. The two transects terminate in a landscape of desert vegetation and X=200 in the area of the 100 mm isohyet.
The transect from Akko (Acre) eastwards to Rujum Hiri in the Golan passes through the most humid part of the country. The gradient of distance from the sea coast is known in many countries, however, it is not seen in the present transect. Here, all the transect dots are less than X=120.
The three transects presented here display the efficiency of the X coefficient in finding the drought level of a studied area. We may return now to the Gilboa and compare its level of X coefficient:
1. Square 979 including Gan Ner, X=126.
2. Square 967 including Fakua, X=128.
When comparing this data to Fig. 10.4.1, the Gilboa resembles the X value of Jerusalem (square 719) or in Fig. 10.4.2 that of the Mediterranean territory with a slight touch of the semi-steppe bathas.
I assume that in the future, with the upgrading of this website, the builders will enable the users to apply it to all plant names recorded in the study square. I hope that we shall be able to display the X coefficient in a map or a list of all squares with more than 40 species. When we analyzed the flora of Israel in 1985, I was assisted by Motti Schneider, a Ph.D. student in Florida State University (FSU). The parameter used then was the frequency of the chorotypes (phytogeographical elements) in squares with more than 40 species. The result was [http://flora.huji.ac.il/browse.asp?action=content&keyword=%D7%A6%D7%95%D7%9E%D7%97%D7%99%D7%A9%D7%A8%D7%90%D7%9C%D7%902 a new phytogeographical map of Israel and Sinai (Danin & Plitmann 1987)]
Table 2. Results of the study of X in three transects