Botanical features of the Algerian Sahara

by William Austin Cannon

LAGHOUAT.

The ancient Arab town of Laghouat, which is also an important military post, is a very favorable place from which to begin a study of the plants and the environment of the plants of the northern Sahara. Its altitude (780 meters) is greater than that of Ghardaia (520 meters), as also that of the latter place is greater than the altitude of Ouargla (150 meters). The annual rainfall of Laghouat is more than that at either of the places mentioned and more dependable. The surface of the desert at Laghouat is, for example, not of one type only, but characteristic of much of the Sahara; that is, it is mainly stony, a hamada, but there are also sand areas, a oued and its flood-plain. Finally, the plants growing in the vicinity of Laghouat are largely typical of those found farther to the south, as at Ghardaia and Ouargla, or even deeper in the desert. It is of great interest to observe the change in the habits of the plants, in their number, distribution, and other features, when one leaves a less arid region and goes toward a region of gradually increasing aridity, as when passing southward from Laghouat.

The leading plant habitats are the oasis, the arid plain, and the dunes. It is not likely that any of these habitats have been greatly changed because of the settlement by Arabs. The arid plain and the dunes surely have per se not suffered marked alteration, and the oasis itself is probably not so different from what it was formerly, as the great difference in plants growing in it might at first lead one to suspect. More water is brought to the surface at present than in primitive times, but if it were possible to remove all introduced plants, and restore all native plants peculiar to the oasis, there is no apparent reason why they should not live there quite as successfully as in earlier times. It does not follow that there has been no modification of the flora itself, a result of the founding of a town at the oasis, and it will be pointed out later that such has surely been the case, but to what extent or in what way does not appear.

THE OASIS OF LAGHOUAT.

The oasis of Laghouat is situated on the Oued Mzi, the upper portion of the Oued Djedi, one of the most important oueds of Algeria. The Oued Djedi runs in an easterly direction from Laghouat, receiving many tributary oueds en route, by a rather long course to the great Chott Melrirh, which is southeast of Biskra. Like other desert rivers, the Oued Djedi is dry most of the year, but is occasionally filled to overflowing with a rushing flood, which is of great erosive power and may be very dangerous to the traveler. Above the town of Laghouat, where the Oued breaks through the last pass of the Atlas, the flood-plain is narrow, but upon leaving the pass the plain widens until in the immediate proximity of the town it is about 1.5 kilometers in width. On either side of the flood-plain stretches the arid plain (hamada), usually stony, but near the mountains covered with low, slowly moving sand ridges. To the south of the oasis, the arid plain merges into the topography characteristic of the region of the dayas.

The portion of the oasis devoted to the cultivation of date and other trees, and to gardens, is about 3 square kilometers in size, but arable land extends above and below the town, so that outside of the oasis, as delimited above, there are about 6 square kilometers, all of which have at times been under cultivation. The last referred to is the flood-plain of the oued and is used mainly for growing barley. By the edge of the oued, or along the irrigating ditches, are several characteristic species of plants, which may point to the character of the primitive flora; for example, willows, oleander, and Tamarix, with a few palms. The betoum (Pistacia atlantica), which must surely have been an inhabitant of the oasis formerly, is now apparently wholly absent. The species just mentioned are to be found between the town and the pass above; but below the oasis, owing to an apparently poorer water-supply, there are fewer large species. Among those found are a few specimens of Rhus oxyacantha and Zizyphus vulgaris, and it was probably below the town that the betoum was to be found in earlier times.

The oasis is under intensive cultivation (see fig. [1]). There are about 300 gardens, each bounded by mud walls, and often separated by picturesque, meandering lanes. The plant life, almost wholly introduced, is luxuriant. In some gardens the effect is tropical, where vines reach from tree to tree, making a canopy nearly sun-proof and separating the spreading tops of the palms from the wealth of shrubbery and herbaceous plants beneath. First among the trees of the gardens, in numbers as well as in economic importance, is the date palm, of which there are said to be about 30,000. Although this is small in comparison to the number of date palms at Ouargla, Touggourt, or the Oued Rirh, the dates are of great importance to the dwellers at Laghouat, where the products of the gardens are almost all consumed. The living tree provides shelter against the intense heat and light of the desert, and the dead leaves constitute an important source of fuel in a land where fuel is extremely hard to obtain. The flesh of the date fruit is eaten by the Arab and the cracked seeds are given to the camels. Without the date a continuous occupancy of a remote oasis by the Arab is clearly impossible. Besides the date palm fruit trees of other kinds are abundant, among them the apricot, fig, mulberry, peach, pear, and orange. The pomegranate and the table grape are also very generally grown. The lowest story of the vegetation of the gardens is composed of garden vegetables, such as artichoke, bean, carrot, melon, pea, potato, squash, and radish. Among the ornamentals one sees roses, asters, and chrysanthemums, and occasionally very luxuriant cannas. One or two parks contain interesting introduced trees and shrubs. We recognized among the trees Ailanthus, Eucalyptus, umbrella, plane, poplar, pine, cypress, ash, locust, willow, and St. John’s tree. The Barbary fig (Opuntia ficus indica) is also common, but does not stray away from the best-watered situations.

THE PLAIN.

The part of the plain (hamada) studied lies to the west of the oasis, between it and the adjacent hills, Mountains of the Nomads, which are to the west of the pass of the Oued Mzi. Emerging from the oasis, one finds himself on the arid plain, the transition from the one to the other being abrupt. The plain, at first view, with a covering of small stones and pebbles, gives the impression of total barrenness. Not a tree, shrub, or herb appears to hide the bare ground. The mountains are naked rock, while the harsh outline of desert ranges and the distant low sand ridges give no evidence of plant life. But a closer examination of plain, dune, and mountains reveals the presence either of living forms or of the dried remains of plants of a preceding moist season, in numbers and in kinds not at first suspected.

Close to the oasis the plain forms the highway for caravans as well as the drilling ground for army recruits, so that the herbage is either trodden under foot or eaten to the roots. Somewhat farther away, where the plain rises to meet the mountains, we first encounter perennials large enough and abundant enough for consideration, the most prominent being quedad (Acanthyllis tragacanthoides), adhidh (Zollikoferia spinosa), rempt (Haloxylon articulatum), and drinn (Aristida pungens); Acanthyllis is perhaps the most numerous.