Botanical features of the Algerian Sahara

by William Austin Cannon

THE VALLEY OF THE M’ZAB.

The bottom lands, as already has been shown, are relatively favorable for plant life; here the soil is the deepest and the water relations are the best. Accordingly we should expect to find in the valley of the M’Zab more plants than we have seen on the plain, and we will not be disappointed in these expectations; but it is almost certain that in primitive times the vegetation of the valley was even richer than at present. In fact we now find in the unprotected places only such plants as are too small for fuel or are not good for food, and the useful sorts are largely wanting. In other and similar valleys, which have not been so much disturbed by man as the M’Zab and where primitive conditions still largely obtain, there is a surprising wealth of vegetation. Such conditions were seen between Ghardaia and Ouargla and will be specially noted on another page.

At present no trees occur naturally in the valley in the vicinity of Ghardaia or any of the sister cities. The French portion of Ghardaia contains ornamental or shade trees, such as the ash, sycamore, and betoum. The largest native shrubs are a species of Tamarix, growing by the oued, and a few specimens of Zizyphus lotus, the latter confined to the side gulches and numbering half a dozen specimens. Among the most generally distributed plants in the valley are Peganum harmala (figs. [27] and [28]) and Haloxylon articulatum; the former is a half-shrub of wide distribution in southern Algeria, occurring from Biskra on the north, and although not strictly confined to the flood-plains of the oued is most abundant where the soil is relatively deep. The leaves are rather large and do not appear to have unusual protection against drought.[23] Like its relative in the southwestern portion of the United States, the creosote bush (Covillea tridentata), it is not eaten by any animals, although not armed and not poisonous. This species, therefore, is one of the few which to-day probably retains essentially the same distribution and appearance it had before the country was inhabited. It is interesting to note that Peganum is generally distributed through the M’Zab Valley, being especially abundant between Ben Isguen and Melika. Here in November Peganum, except where trodden under foot by the flocks and caravans, retained much of its foliage, although rain was said not to have fallen for twelve months. In the protected areas also, as will be mentioned below, this species was found to be fresh green, showing little or no indication of the long drought. Of other species found in unprotected places in the valley, Haloxylon articulatum and Henophyton deserti, although eaten by animals so as to be recognized only with difficulty, were also fairly abundant. There were found also Euphorbia guyoniana, called “le bain” by our French-speaking Arab helper, because it is used by the natives as a soap, and Nolletia chrysocomoides, Æluropus sp., and others.

PROTECTED AREAS NEAR GHARDAIA.

Of the plant habitats whose leading characteristics have been briefly given above, only the oasis and its gardens are secure against the inroads of animals. However, owing to the long settlement of the region, rather large tracts of land are at present in what must nearly approach their primitive condition. The areas referred to are the cemeteries, which, for the reason suggested, possess special interest to the botanist, showing briefly what plants might be expected to occur in the region naturally. The typical M’Zab cemetery is of varying size and surrounded by a stone wall. No plants are introduced to decorate it and no irrigation is practised within its walls. The only disturbance of the natural condition of the land is in the use for which it is set aside. The interments are so conducted that the ground appears to be always used progressively, that is, there is always an older portion and always a newer portion, and the part once used is never afterwards made use of again. From this fact, as well as others which need not be entered into, the more ancient portion of the cemeteries, after a lapse of several centuries, or even several decades, without disturbance, must be in essentially the same condition as regards the soil and water relations, which would be most affected by the fact of interment, that they were in pre-M’Zabite times.

Several cemeteries near Ghardaia and the other M’Zab towns vary greatly in their position as well as exposure; some are on the valley floor below the town of Ghardaia, and others are in side cañons; one is on the south wall of the valley with a northern exposure, and another is on the opposite wall and hence with a southern facing; one cemetery is on the edge of the plain itself. So far, therefore, as the flora of the older portions of these areas represent the ancient vegetation of the same areas, we have in them at present a means of learning something of the kinds as well as the abundance and the habits of the plants which formerly occurred here, and (by inference) of the plants which were in the region in primitive times.

Below and not far from Ghardaia, in the valley floor, is a very ancient cemetery, or rather a cemetery with a very ancient part. In the old portion the drifting sand has obliterated all traces of graves, which have long since been forgotten by the citizens of the town. In the newer portion, farther from the edge of the oued and on higher ground, the sand gives place to clay. In the older portion of the cemetery may be found a fairly rich flora and rather large plants—a striking contrast to the vegetation of the unprotected area immediately without the wall. Here one finds Haloxylon articulatum and Henophyton deserti, both species eagerly eaten by animals, as well as Deverra scoparia, Lithospermum callosum, Zilla macroptera, and Helianthemum sessiliflorum; also grasses and other plants which I did not know. Something of the abundance and the large size of the plants is indicated in figs. [29,] [31,] and [32.]

In one of the cemeteries situated against the south wall of the valley, but not including the wall, the conditions are somewhat different from those just sketched; the soil is a sandy loam, with rocks of various sizes in abundance, and here may be found a fairly rich flora. In the ancient portion of this cemetery the most numerous species is perhaps Haloxylon articulatum, also Fagonia glutinosa, Fagonia bruguieri, Cleome arabica, Echinopsilon muricatus, Helianthemum sessiliflorum, Zollikoferia resediflora, Salsola sp., and others. The plants are relatively abundant and of fairly large size.

In a cemetery on the north wall of the valley, reaching from the floor to the plain above, the wall is less precipitous than at other places and there is a small amount of earth. The number of species here is very limited, being confined almost wholly to Haloxylon articulatum, which is fairly abundant; but in the upper portion of the cemetery are also found Peganum harmala and Capparis spinosa.

The cemetery situated wholly on the edge of the plain has an unexpectedly large number of plants, almost all of them Haloxylon articulatum, which is of good size. Outside this protected area the species is neither large nor abundant, since it is eagerly sought after by camels, sheep, and goats, and a shoot no sooner appears than it is eaten to the base.