A common group of companions of the Mediterranean maquis is the vines. In Edom several species of vines still survive. A very peculiar example is Hedera helix. A large specimen of this species grows on the cliff of Wadi Sik, the canyon leading into Petra (Fig. 3.1.69). The specimen closest to it is situated in the Upper Galilee, some 300 km away. H. helix functions as a vine in Central Europe as well (Fig. 3.1.70). Another vine is Rubia tenuifolia (Figs. 3.1.71, 3.1.72). This plant is assisted in climbing trees of the maquis by means of hooked teeth on the leaf margins and on the stem’s crests (Fig. 3.1.72). A single specimen of this species was collected in the anticlines of N Sinai. A species related to Rubia tenuifolia is endemic to the cliffs of Edom. It has no teeth on leaves or stems. One may look upon Rubia danaensis (Fig. 3.1.73) as a plant of common origin with Rubia tenuifolia, which is protected from competition by growing in limestone cliffs.
The islands as they appear on the regional vegetation maps
A comprehensive view of the rock vegetation in the Middle East displays islands morphology even when the area size increases. The impact of the two main factors responsible for the formation of smooth outcrops is seen in a vegetation map in part of the Negev Highlands (Fig. 3.1.74). These factors are: 1. Rock type (limestone and dolomite), 2. Humidity, through its impact on epilithic lichen development. The latter is responsible for the formation of most smooth rock outcrops. Due to the impact of drought, the number of smooth outcrops is reduced towards the east.
For our study of the flora and vegetation of Sinai, the peninsula was divided into ecological districts (Fig. 3.1.75). The total number of species in each such district was registered. The curve of log-species/log-area is drawn (Fig. 3.1.76). Most districts in this curve are seen near the correlation line. Those with a much higher number of species are district 4 = the N Sinai anticlines and district 11 – the S Sinai massif. Mountains in the Middle East, built up from hard rocks of limestone, dolomite, sandstone and granite, having large outcrops of smooth-faced rocks (Fig. 3.1.77), occur mostly at the precipitation range of 100-200 mm (Fig. 3.1.77). The highest numbers of representative plants of all the Mediterranean ecological groups are found in Edom; Sinai follows, and lastly in the Negev desert. It is suggested that these differences derive from rock-outcrop size.
Conclusions and summary
Conclusions and findings from islands of moist habitat in the desert “ocean” are similar to those of land islands in the ocean. We discussed here the increase in the number of habitats supporting different plants, when the study area is increased.
This increase can be shown from the single rock through rocky slopes and to large landscape units. The moist local conditions enable the growth of mesophytes in the desert and serve as refugia for Mediterranean species that penetrated into the desert at different periods in the past. They continue to live in these refugia even today, although the climate around them is arid, but their rhizosphere enjoys the Mediterranean moisture regime as in the past. The isolation by large desert areas has enabled parallel evolution with the survival of endemic species, since periods in which the final state of various genera was not yet determined.
- Begon, M., Harper, J.L. & Townsend, C.R. 1996. Ecology. Blackwell. 1068 pp.
- Myers, A.A. & Giller, P.S. 1988. Analytical biogeography. Chapman & Hall. 578 pp.
- MacArthur, R.H. & Wilson, E.O. 1967. The theory of island biogeography. Princeton University Press.
- Pagel, M. 2002. Encyclopedia of Evolution. Oxford University Press. vol. 1, 556 pp.