Only isolated specimens in inaccessible spots of rocky affluents succeed in flowering and fruit setting in such years. Other grasses remain small in size, even in favorable years, and it seems as if these grasses are present at the fringe of their distribution area. A good example is the presence of dwarf specimens installations, only one could be assigned to this variety. Several specimens were found between stones in a small affluent, which are relatively large in comparison with the variety typicum. The variety ehrenbergii Henr. is characterized by its scabrous lemmas, which are covered by thick hyaline-curved hairs. This variety is not mentioned for Egypt. According to Henrard , its distribution area stretches from Ethiopia and Eritrea to Arabia and Iran. In the more southerly Gebel Elba area, which is characterized by the presence of the Sudanese flora, in addition to the variety typicum, only two other varieties have been recorded, viz. pumila and aethiopica . Thus the presence of the variety ehrenbergii in Shenshef clearly points to a connection with more-southerly-located areas. One may wonder if the presence of this plant in the vicinity of Berenike can be related to the former trade contacts with Arabia, Ethiopia, and Eritrea.
The investigated localities in the Eastern Desert have many species in common, especially when they are connected by the same wadi system. In Khesm Umm Kabu and Qariya Mustafa ‘Amr Gama,plastic seedling pots which are located about 115 km apart, mutual species are rare, namely, Tamarix aphylla, Salvadora persica, and Trichodesma africanum. The number of unique species for a particular site is relatively small. Examples are Ifl oga spicata and Rumex simpliciflorus near Khesm Umm Kabu in the upstream part of Wadi Gimal. Obviously, both species were also found in the delta of this wadi and this shows that the dispersal within a specific wadi is not problematic.The high percentage of species that is present in more than one locality seems to indicate that seed dispersal, which is mainly dependent on wind and animals, is quite effective. Additionally, strong water currents after heavy rainfall transport a lot of sediment including the existing seed bank. Dispersal by the agency of water is, however, always restricted to the specific catchment area of a wadi system. Moreover, seeds are transported in either the direction of the Nile Valley or the Red Sea coast. The effectiveness of this kind of dispersal can be observed, for example, in drift litter along the Red Sea coast. Fruits of Zilla spinosa, Balanites aegyptiaca, and Neurada procumbens, for example, were frequently found in such concentrated organic debris.
Due to wind and animals, seeds succeed in reaching new wadi systems. Probably, the fl at coastal plain plays an important role in this respect as seeds that arrive on this coastal strip can easily be transported in a northerly or southerly direction, depending on the prevailing wind direction. Wadi branches in the coastal plain proper constitute no serious obstacles in this respect. I once witnessed a huge Zilla spinosa of almost 1.5 m in diameter rolling over the coastal plain. The wind was strong enough to lift this plant over a steep slope of a wadi branch of about 3 m high. The mountain slopes, however, constitute insurmountable barriers, resulting in large concentrations of tumbleweeds on specific spots . Dispersal of seeds by means of tumbleweeds, which lose their seeds during rolling, is an effective method in arid and semi-arid environments. Due to the scarcity of water, no closed vegetation is developed, and most plants can reach their optimal shape. This enables plants such as Zilla spinosa to develop into a spherical shape. The root of this species is twisted alternately to the left and right and weakens at the ground level after seeds are ripe. As a result, the plant is easily uprooted and becomes a tumbleweed. Not only spherical-shaped plants behave as tumbleweeds. For example, the procumbent Aizoon canariense also is uprooted and becomes a tumbleweed, even with part of the root still attached. The small seeds can easily escape from the cracks in the capsules. Finally, the whole plant becomes disintegrated. A special case in this respect seems to be Aristida funiculata, which might be described as “tumbleseeds.” Unlike the other two Egyptian species of this genus, namely, A. adscensionis and A. mutabilis, both column and awns of A. funiculata are long and stiff.
The total length of a spikelet is almost 8 cm. It has been observed several times that seeds form a cluster in such a way that the awns are interwoven and the seeds are projected on the outside of the clump. Another advantage of this species in this respect is that the articulation point is just below the base of the column. Due to this position, the shape of the clump of seeds is not affected when seeds break off during tumbling. Two such seed tumbles were found entangled in Convolvulus hystrix, showing that only part of the seeds were lost during their probably short trip. Dispersal by animals is possible by external carriage and by secretion via the guts. Spiny fruits, such as those of Arnebia hispidissima, or sticky ones, such as those of Boerhavia repens, are primarily transported via the outside of animals. The seeds of Acacia tortilis may serve as an example of the second mode of dispersal. Both unripe and ripe fruits of A. tortilis are partly found beneath the foliage, partly covered by sand. Such seeds need a secondary dispersal agent to find a safe site to germinate. More effective is the dispersal by camels internally. Camels have no problems with the long, stiff spines and are able to browse from the branches . Whereas twigs, leaves, and fruits are digested, the extremely hard seeds are excreted with the dung. Frequently, seedlings can be observed that germinate from inside camel dung . Owing to the wind, dung particles are quickly covered with sand, which in turn improves the growing conditions for the young tree. The number of seedlings that develop in a dung particle may vary considerably and will depend on the number of fruits excreted in a dung particle, as well as the number of mature, unaffected seeds in those fruits. Failed fertilization, abortion of seeds, and the attack of insects all contribute in reducing the number of viable seeds in a fruit . A concentration of 17 seedlings of A. tortilis proved to have originated from camel dung containing 18 seeds and covered by 10 cm of sand. Only when such camel dung is dropped at the edge of a wadi can one of the seedlings become a full-grown tree because strong water currents periodically destroy the vegetation in the central part of a wadi. For the same reason, these trees have a better chance of surviving along convex banks. One of the few shrubs that has frequently been observed in the central part of the wadi and is capable of surviving flooding is Chrozophora tinctoria, though its appearance is little more than that of a heavily damaged dwarf specimen.A variety of trees and shrubs were found in the vicinity of the Roman installations: Lycium shawii, Tamarix nilotica, T. aphylla, Suaeda monoica, Acacia tortilis, Salvadora persica, Balanites aegyptiaca, Calotropis procera, and Leptadenia pyrotechnica. The most common tree proved to be A. tortilis, found along the edges of many wadis, both in the mountains and in the coastal plain. Also around Berenike, this tree is frequently present in the small wadi branches. More substantial populations of acacias have been observed in the coastal plain south of Berenike. Despite its predominance, Acacia tortilis may be absent locally, such as in Wadi Gimal near Khesm Umm Kabu. Here, Balanites aegyptiaca and Calotropis procera are the predominating trees. Ababda nomads confirmed that Wadi Gimal, in particular, was characterized by B. aegyptiaca. In wadi branches dissecting the coastal plain,container size for raspberries this tree is a rather strange phenomenon. This is not the case with C. procera, which can frequently be observed in the coastal plain, especially south of Berenike. Tamarix nilotica and Suaeda monoica are halophytes and occur in the near vicinity of Berenike. On the higher levels of the salt marsh north of Berenike, several large hillocks of T. nilotica are currently present.
When several rows of such hillocks are present, the population functions as a natural barrier against penetrating windblown sand. In the salt marsh south of Berenike, T. nilotica is intermixed with S. monoica. Here, T. nilotica does not form hillocks and is present on the moreelevated levels, whereas S. monoica is concentrated in the lower levels of the salt marsh, together with the halophytic Halopeplis perfoliata. On both sides of the Red Sea coast, S. monoica gradually replaces the halophyte Nitraria retusa in a southerly direction. Halfway between Wadi Gimal and Ras Banas there is a transitional zone, whereas south of Ras Banas only populations of S. monoica are present . The Suaeda population south of Berenike dropped most of its leaves after the heavy showers in November 1996. The distribution of the salt-requiring S. monoica is confined to locations with a specific chloride content and the water table . Laboratory experiments with artificial solutions containing only traces of sodium resulted in the yellowing of leaves of S. monoica, as well as curling and wilting, whereas field observations revealed that seasonal fl uctuations have apparent effects on the distribution of this species . Other salt-tolerant species present in the salt marsh around Berenike are Cyperus conglomeratus, Zygophyllum album, and Z. simplex and an herbaceous Suaeda sp. Zygophyllum album has a wide ecological range with respect to the salt content of the soil, and Z. simplex is even less demanding as it also grows in the mountains, far away from the influence of the sea. The ecological preference of Z. coccineum, which is also rather common in the surroundings of Berenike, is less clear. The species has a large tolerance with respect to salinity and it is said to be indicative of limestone . In fact, both environmental conditions are present around Berenike, and each condition could explain its presence in itself. With respect to the salt content, possibly two ecotypes exist: a salt-tolerant and a nonsalt-tolerant one. It could be that the specimens growing in the vicinity of Berenike concern the salt-tolerant ecotype. Obviously, these specimens are full sized, whereas those found in the vicinity of the Roman settlements in the Red Sea mountains were less frequent and also of a reduced size. The population of Z. coccineum near Hitan Rayan might be of the nonsalttolerant type as this inland area does not witness the maritime influence of the Red Sea. Furthermore, the area is of Precambrian crystalline rocks and no limestone is present in Hitan Rayan or any of the surrounding hills . Salt-tolerant plant species are present near the shoreline on the supratidal flat , which consists of sandy, silty, and clay-like sediments and on a broad strip of the coastal plain adjacent to the sabkha. The latter is characterized by a salty horizon near the surface, which is quite difficult to penetrate. Mangrove vegetation is absent in the near vicinity of Berenike; its nearest population is located several kilometers north of Ras Banas. In Egypt this kind of vegetation mainly consists of Avicennia marina. South of lat 23° N it is also mixed with Rhizophora mucronata . Mangrove is present in calm, shallow water and on a fl at, muddy soil, permanently flooded or during high tides. Both protected lagoons and bays are suitable habitats. The northeast boundary of the present distribution is marked by some scattered specimens about 20 km north of Hurghada and becomes quite dense south of lat 25° N. At some localities this species also grows on sandy hills along the coast.Living in a desert environment essentially leads to its exploitation. Due to the limited carrying capacity of the environment, which is basically determined by the availability of water, people mostly live in relatively small groups that have adopted a nomadic life style. As a consequence, the material culture is strongly related to the bare essentials of life. The current arid climate of Egypt was established during the early second part of the Holocene and has had an intrinsic influence on the desert culture.