From Laghouat to Ghardaia
Region of the Dayas
From Laghouat the way lay through a gently rolling country, ever dipping to the south and southeast. No mountains relieved the monotonous horizon. “A hard stony desert alternated with rolling sandhills,” followed by a “vast level plain dotted with dayas,” to quote again from Tristram’s narrative. Somewhat to the south of Laghouat depressions are met here and there, separated from each other by the low ridges of the plain, which receive the drainage each of a limited territory. (See figs. 10 and 11.) These are dayas, and are in fact oases with an uncertain water-supply but with favorable soil conditions, so that such rain as falls on them, or is conducted to them from higher ground, sinks deeply and creates relatively favorable conditions for plants. In that the daya is the center of a drainage system, and has no visible outlet, it is comparable to the chott or salt-spot, but it is to be distinguished from the chott by the absence of salts in excessive amounts. That salts are not present in the dayas in quantity is probably due to subterranean drainage, the daya being in fact similar to the bolsons of western America. On the plain in the northern portion of the daya region the following may be observed:14
| Echinops spinosus. | Citrullus colocynthis. | Teucrium polium. |
| Acanthyllis tragacanthoides. | Artemisia herba-alba. | Aristida obtusa. |
| Thymelæa microphylla. | Artemisia campestris. | Stipa gigantea. |
| Peganum harmala. | Haloxylon articulatum. | Noæa spinosissima. |
| Euphorbia guyoniana. | Anabasis articulata. | Asteriscus pygmæus. |
In the dayas one sees Zilla macroptera, Peganum harmala, but chiefly Zizyphus lotus and the betoum (Pistacia atlantica), which is perhaps the only species of tree outside of the oasis in this portion of the Sahara. Massart mentions not seeing any tree away from oases from the time he left Biskra until he reached the region north of Berrian, the northern portion of the Chebka. As the betoum is so conspicuous among the Saharan plants, and also from the very remarkable relationship existing between it and the jujube, the species is of very great interest. The relationship will be described under an account of one of the largest dayas of the region, that of Tilrempt.
Daya of Tilrempt
The daya of Tilrempt is one of the largest (about 103 hectares) and is the most southerly of all. It lies near the southern margin of the daya region, and is surrounded by a gently undulating plain (hamada), whose surface is strewn with stones and pebbles, with apparently an underlying stratum of impervious material, since such is to be seen wherever erosions have laid it bare. The floor of the daya is free from stones, being composed of soils of a fine texture which have been washed or blown by the wind from the surrounding higher country, and is apparently not underlaid by a hardpan. Judging from the depth of the two wells at the daya (which were dug, not bored), the deeper of which is said to be 95 meters, there is an abundance of earth for the roots of the plants. Besides the wells there is a cistern, sunk below the general level of the daya floor, which receives and stores up flood-water; it is rarely filled, but occasionally contains considerable water, possibly up to one-fourth of its capacity; its filling is very uncertain, depending on the rare and scant rains. According to Massart, no rain had fallen during the two years previous to his visit, and the cistern was empty when we were there. These observations are given to show under what intensely arid conditions such a tree as the betoum (mature specimens of which carry an immense evaporating area) can become of large size, giving but slight evidence of a severe struggle against such adverse conditions. The altitude of the daya is about 600 meters.
As one crosses the plains in the vicinity of Tilrempt he notes the scantiness of the vegetation. (See fig. 9.) Here and there in the depressions are a few betoums, often only one specimen, but usually more, and in the erosion channels leading to the dayas is a sparse population of low, gray shrubs. Over the higher portions of the plain, one is aware that small perennials, 20 to 30 cm. high, are widely scattered, but it is the bare ground which gives the character to the landscape. Among other forms are species of Aristida and Stipa, Anabasis and Haloxylon, with dwarfed specimens of Zizyphus lotus in the washes near the dayas. The leading species, Haloxylon articulatum, is much eaten by the flocks of sheep and goats (over 7,000 sheep are said to obtain water at the daya), but occasionally it is present in surprising numbers. For example, on a slope to the northeast of the daya, and but a few meters distant, 227 living specimens of Haloxylon were counted on an area of 16 meters square; in another place, near the crest of a low hill to the west of Tilrempt, where the conditions were probably as unfavorable as any in the region, 118 specimens were found on an area of the same size. In both squares there appeared to be no other species present. Tilrempt is said to contain 2,400 betoum trees, although the visitor would not be likely to estimate the number at nearly so high a figure.15 Numerous specimens of jujube are also scattered through the daya, with some Peganum harmala and Francœuria crispa.
As a person visits the floor of the daya he is struck by the great beauty of the betoums. They are of a compact habit of growth, shapely, and cast a dense shade, an unusual feature in a desert tree. Attaining a height of 15 meters or more, the tree may have a spread equaling or exceeding this amount. The bole of the largest specimens is of large size; one was found 4.56 meters in circumference, another 4 meters, while a third measured 3.36 meters. All measurements were made 1 meter from the surface of the ground. No betoums, however, were seen to have developed in a perfectly normal way, and this observation applies not only to Tilrempt but to all other dayas seen, but they were disfigured in a peculiar manner, the lower branches giving the appearance of having been cut and removed at a height of 2.85 meters. In fact, this had been done, and the lowest existing branches marked the highest point to which a browsing camel can reach.
The leaves of the betoum are compound, consisting of 7 to 9 large leaflets. The branches are unarmed and the twigs, younger branches, and leaves are eagerly eaten by whatever herbivorous animals can reach them. (Fig. 12.) So much is the betoum sought after as a food that it would be exterminated if it were not protected by another plant, namely, the jujube.16 The character of the leaves and young shoots of the betoum may be seen in fig. 15.
In considering the main characteristics of the jujube we find that it is a spreading shrub, frequently attaining a height of 3 to 4 meters, with branches well armed with stout spines. The leaves are small, simple, and leathery. (Compare fig. 14.) The spines are so efficient as a means of protection that the shrub shows no signs of being eaten by animals, although, as quoted above, Massart remarks that after his camels had gone five days without food they ate the jujube branches in spite of the spines.
The unarmed betoum and the armed jujube have a very interesting relationship, which is as follows: When the seeds of the betoum germinate the seedling is eagerly eaten by animals if it chances, as is usually the case, that the germination occurs on the open daya floor; but if the seeds are carried to a Zizyphus and germinate in its midst, the young plants may attain to a considerable height before being seen by animals, and, being protected by the encircling jujube, will continue growing until they are too large to be easily killed through grazing. It usually happens that once the betoum plant appears above the top of the protecting shrub the camels attempt to reach the attractive shoots and the jujube is trodden under foot. The jujube is thus ultimately destroyed and a mound around the base of the young betoum is all of it that remains. If the jujube is relatively small and the developing betoum is discovered while still small, it will be much eaten, and probably killed; but if it reaches a considerable height before the discovery is made, only the lower branches will be devoured and the specimen will survive. Massart was unable to find any young betoums, but when my visit to Tilrempt was made, November, 1910, there were several, although so well hidden as to cause much trouble in finding them. A view of one of these is shown in fig. 13.
The betoum is eaten by the gazelle as well as by domestic animals, which are abundant enough in this region, and this fact is probably of great influence in restricting its distribution. Fairly numerous on the desert at present, according to Tristram the gazelle was very abundant in earlier times; he speaks of their tracks marking the plain like sheep-walks.
From what we have already seen regarding the ill effect of grazing, it will appear that the relation between the betoum and the jujube is a very vital one to the former; and it probably is not too much to say that the distribution of the betoum in the daya region is entirely dependent on that of the jujube, since there is no other armed shrub in the region to afford the protection essential to its survival; with relatively favorable moisture conditions, considerable depth of soil, and a protecting jujube, the betoum will flourish and reproduce now quite as well as in former years.
The Chebka
No dayas were seen after leaving Tilrempt, and the aspect of the country changed markedly and suddenly as the drainage became better defined. The hills were more abrupt and in systems, and the valleys became broad and continuous. At first the valleys were wide and shallow, the hills being low and with flat summits, but as the distance from the daya region increased, the valleys became deeper, until at Ghardaia the effect was that of low, flat-topped mountains with broad valleys between, thus remotely suggesting the topography of southern Arizona. However, in southern Algeria the mountains are not so high nor is the “mesa” (hamada) so extensive as in Arizona. The general level of the daya region is prolonged as the summits of the mountains of this the chebka region, while the valleys are eroded to a new level, that of the plain of the M’Zab. A similar condition is seen as one goes from Ghardaia to Ouargla, so that in fact there are several immense terraces, reminders of that remote period when there was more rainfall in this portion of the Sahara than at present.
Although the drainage to the south of the daya region is well developed, the valleys and mountains run in a rather confused way, so as to give to the fancifully inclined Arab the idea of a net, from which the name “chebka” is said to be derived.
The country from Tilrempt to Ghardaia is characterized by a continuously decreasing amount of vegetation. In place of the country as a whole having a covering, however sparse, as in the daya region, one is apt to consider the chebka a barren desert, absolutely devoid of plant life; but closer inspection dispels this illusion and reveals the presence, in the more favorable situations, of not a little vegetation.
In the northern portion of the chebka region one sees here and there, on the bottoms, specimens of the jujube and the betoum, as well as Zilla macroptera, Retama sphærocarpa, and Coronilla juncea. On the rocks at Settafa, Massart reports finding lichens, the first he had seen after leaving Biskra. However, crustaceous lichens occur on the flat tops of the low mountains by Ghardaia. Massart suggests that the absence of lichens in the Sahara (possibly they are not to be found south of Ghardaia) is because of the intense dryness and the great heat, the temperature of the rocks becoming from 60 to 70° C.17
At Berriane, one of the M’Zab cities, there are over 30,000 palms of a superior sort, watered from over 400 wells. The surroundings of this oasis are extremely desertic and a casual survey of the route between this place and Ghardaia, 44 kilometers distant, reveals almost no vegetation. Here the calcareous plain of Cretaceous origin, the Chebka, is even more eroded than in the portion farther to the north, and the valleys are wider. The soil is a fine clay without an admixture of sand. It is only in the most favorable places, along the washes, that plants are to be found, and here are Deverra chlorantha, Anabasis articulata, Gymnocarpon fruticosum, Artemisia herba-alba, Ononis angustissima, Linaria fruticosa, Antirrhinum ramosissima, and Haloxylon articulatum (Massart, loc. cit.). Peganum harmala occurs very sparingly by the roadside. The habits and the habitats of certain of the above-mentioned species will be described in greater detail later in this paper.