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.
The sentiments of the residents of Ghardaia, which led to the
establishment and protection of the cemeteries, made a close
botanical study of them injudicious. Enough was seen, however,
to establish several points, the most important being, at least
for the areas considered, that there is growing in them, without
irrigation, a somewhat rich flora composed of relatively large
perennials. And from this fact it seems probable, if also protected
against the predatory attacks of animals, that other areas under
the present rainfall and other physical environmental conditions
now obtaining would support a much heavier vegetation than is
generally the case. How far the presence of man and of his flocks has
otherwise modified the flora, especially as regards its composition,
is another question, but it certainly has not been without its
effect. In the portions of the M’Zab region, except certain
areas rather remote from the towns, where there is no protection,
the only forms which are at all abundant, or at least conspicuous,
are such as are armed, poisonous or distasteful, or too small for
use as fuel. Among these are _Peganum harmala_, _Zilla macroptera_,
_Tamarix_, and others seen later. However, _Haloxylon articulatum_,
although eaten by all animals so as never to develop in a normal
manner, is surprisingly abundant, although by no means conspicuous.