Sudanian Trees at Dead Sea Valley; References
7. Sudanian trees at the Dead Sea Valley
The Dead Sea Valley has an exceptional temperature regime in our area. In all the temperature maps of our area the Dead Sea Valley looks like a long narrow tongue of tropical regime that penetrates northwards (Fig. 8.1.3, right). Trees and shrubs of tropical origin grow in habitats that have a sufficient quantity of water. En Gedi spring (Fig. 8.1.45) represents a good example of the special situation having a combination of sufficient water with a suitable hot temperature regime. A partial list of the trees includes: Ziziphus spina-christi, Acacia raddiana, Acacia tortilis, Maerua crassifolia, Cordia sinensis, and Salvadora persica. The trees grow also in large wadis. A. tortilis (Figs. 8.1.46, 8.1.47) reaches not far from En Gedi, its northernmost location in the world. Most A. tortilis trees grow in Israel in the hottest places. A. raddiana (Figs. 8.1.48, 8.1.49) is resistant to colder weather than A. tortilis and is therefore more common throughout the country.
Most A. raddiana trees have one or two trunks (Fig. 8.1.48) whereas A. tortilis has several trunks (Fig. 8.1.46). The inflorescences of the two acacias may develop in their blooming season (the end of our summer) even without leaves. The leaves and young stems of A. raddiana are glabrous (Fig. 8.1.50) whereas in A. tortilis these organs are hairy. The three projections on the leaf axis (Fig. 8.1.50) are extra-floral nectaries. In unique species of Acacia living in symbiosis with ants in Central America and in East Africa, the nectar is provided as a reward to the ants. The thorns on the Acacia stems are stipular thorns and appear in pairs. I do not know of a proper explanation for the function of straight thorns (as in the center of Fig. 8.1.51) versus the short hooked one (ends of the stem in Fig. 8.1.51). In some places straight thorns occur and in others there are no such thorns.
The Acacia trees are accompanied by desert shrubs and rare Sudanian vines such as Pergularia tomentosa (Fig. 8.1.52) and Cocculus pendulus. Capparis aegyptia is the bluish shrub (Fig. 8.1.53) that accompanies the A. raddiana in the Dead Sea Valley. It grows on cliffs and in large pebbly wadis. C. aegyptia is an evergreen shrub; in summer its leaves become thick and are covered with wax. The whitish-bluish color rejects solar radiation better than the green color. The difference between summer- and winter leaves is clear in February when the new sprouting and blooming starts (Fig. 8.1.54). In the afternoon hours the flowers of this caper are completely opened (Fig. 8.1.55).
Danin, A. 1976. Plant species diversity under desert conditions. I. Annual species diversity in the Dead Sea Valley. Oecologia (Berl.) 22: 251 259.
Danin, A. and Barbour, M.G. 1982. Microsuccession of cryptogams and phanerogams in the Dead Sea area, Israel. Flora 172: 173 179.
Danin, A. and Ganor, E. 1997. Trapping of airborne dust by Eig's meadowgrass (Poa eigii) in the Judean Desert, Israel. J. Arid Env. 35: 77-86.