Part 8

The temperature conditions for the year 1908 will serve very well to further illustrate this phase of the climate of Algeria. No freezing temperatures were reported from the coast stations, although at the northern base of the Atlas of the Tell several degrees of frost were recorded. At Blida, for example, the thermometer registered -4.0° C. as the minimum. Away from the littoral at every station whose records were seen the lowest temperatures were zero centigrade, or below. The coldest weather was felt at Aflou, at the north base of the Dj. Amours, of the Saharan Atlas, where -11.0° C. was reported. The summer was warm along the coast and hot in the interior. The records of temperature of 23 stations of the Tell were seen, and of this number, at only 8 was a temperature of 40° C. reached or exceeded. On the other hand, at 44 out of 56 stations on the High Plateau and the desert, the temperatures reported are as great or greater than 40° C. Where temperatures below this figure were recorded the stations were situated in the mountains.

The western portion of the Sahara is apparently not so hot as the eastern portion. The mean annual temperature for Biskra is 20.3° C.; for Ghardaia it is 21° C.; for El Golea it is 22.2° C.; and for Touggourt it is 23.4° C. The mean temperature at Cairo is 21.3° C.; for Suez it is 21.5° C.; and for Djedda, on the Red Sea, it is 27.3° C. The absolute maximum temperatures in southern Algeria for as many years and for two of the most southern army posts, El Golea and In Salah, are as follows: El Golea, 47°, 46.5°, 48°, and 49.2° C.; In Salah, 50.0°, 49.2°, 50.2°, and 48° C.; at Ouargla the maxima are 50.2°, 51°, 52°, 49°, and 48.4° C. On account of the fact that in the western Sahara at these stations in winter there are usually freezing temperatures, the yearly range of temperature is 50.0° C., or over. The greatest range reported for the western Sahara is that for Ghardaia as given by Engler, namely, 57°, from -7° to 50° C. At Timmimoun, 1904, the range was from -3.0° to 53.1° C., or one of 56.1° C. The extreme absolute daily range in temperature on the desert appears not to exceed that of certain stations on the High Plateau, although, as shown below, the temperature variations on the desert may be much larger than the records indicate. At Laghouat and at Ghardaia the thermometers which I exposed showed a daily range of from 10.5° to 12.5° C. only. The instruments were placed on the outside of buildings, and usually on the second story. As a contrast to this observed diurnal variation, an opportunity was given to take temperatures on the open desert at a time when the days were fairly warm and the nights were rather cold. The place was between Touggourt and Ouargla. At 3 o’clock on the afternoon of November 26, 1910, the shade temperature at the place in question was 23° C. During the night the thermometer registered -1.7° C. as the minimum, thus showing a drop of 24.7° C. in something over 12 hours. Table 9 gives the extreme daily range in temperature for three years observed at the stations named.

TABLE 9.—Absolute daily range in temperature.

+----------+-------+-------+-------+-------+-------+-------+ | Station. | Jan. | Feb. | Mar. | Apr. | May. | June. | +----------+-------+-------+-------+-------+-------+-------+ | | °C. | °C. | °C. | °C. | °C. | °C. | | In Salah | 21.6 | 23.0 | 24.4 | 24.6 | 22.0 | 23.2 | | Ouargla | 20.8 | 25.4 | 24.0 | 25.0 | 27.0 | 26.0 | +----------+-------+-------+-------+-------+-------+-------+ [**Continued]

+----------+-------+-------+-------+-------+-------+-------+ | Station. | July. | Aug. | Sept. | Oct. | Nov. | Dec. | +----------+-------+-------+-------+-------+-------+-------+ | | °C. | °C. | °C. | °C. | °C. | °C. | | In Salah | 23.4 | 22.0 | 29.0 | 20.0 | 23.4 | 22.6 | | Ouargla | 26.0 | 27.8 | 24.6 | 23.0 | 20.0 | 23.8 | +----------+-------+-------+-------+-------+-------+-------+

A further examination of the maximum temperatures shows certain climatic features of interest and of great importance as factors in the environment of the desert plants, especially the high average maxima and the large amount of heat received in the desert, as indicated by a summation of the maximal temperatures. That the greatest daily temperatures must be high is indicated by table 10, which gives the average maxima for three to five years at three typical desert stations.

TABLE 10.—Average maximum temperatures.

+----------+-------+-------+-------+-------+-------+-------+ | Station. | Jan. | Feb. | Mar. | Apr. | May. | June. | +----------+-------+-------+-------+-------+-------+-------+ | | °C. | °C. | °C. | °C. | °C. | °C. | | Ouargla | 21.9 | 18.3 | 30.9 | 37.8 | 41.1 | 47.1 | | El Golea | 23.0 | 25.8 | 35.6 | 27.5 | 40.9 | 44.4 | | In Salah | 27.4 | 30.1 | 37.2 | 41.0 | 43.4 | 47.6 | +----------+-------+-------+-------+-------+-------+-------+ [**Continued]

+----------+-------+-------+-------+-------+-------+-------+ | Station. | July. | Aug. | Sept. | Oct. | Nov. | Dec. | +----------+-------+-------+-------+-------+-------+-------+ | | °C. | °C. | °C. | °C. | °C. | °C. | | Ouargla | 49.4 | 47.7 | 44.3 | 40.0 | 31.0 | 25.0 | | El Golea | 47.5 | 46.0 | 43.8 | 36.7 | 29.9 | 22.4 | | In Salah | 44.3 | 47.1 | 45.9 | 41.3 | 37.0 | 27.1 | +----------+-------+-------+-------+-------+-------+-------+

The maximum temperatures show that the total amount of heat received on the desert, as compared to that received in the climatic provinces nearer the sea, is not only great, but also that the amount is variable on the desert itself, one station receiving much more heat at certain times of the year than another station. The total heat for each station is arrived at by adding up the daily maxima for the midseasonal months, January, April, July, and October, and dividing by the number of years whose records were consulted. The amounts given in table 11 are the averages for three to four years, for three desert stations and for one station in the Tell.

TABLE 11.—Sums of the daily maximum temperatures.

+--------------+----------+--------+-------+----------+ | Station. | January. | April. | July. | October. | +--------------+----------+--------+-------+----------+ | | °C. | °C. | °C. | °C. | | Laghouat | 439 | 476 | 1,135 | 668 | | In Salah | 641 | 1,027 | 1,455 | 1,121 | | Ouargla | 570 | 909 | 1,444 | 923 | | Ft. National | 230 | 470 | 697 | 564 | +--------------+----------+--------+-------+----------+

The variation in total heat received at the three desert stations may probably be explained partly at least by their differences in latitude and in elevation above the sea, as well as the different relations they hold to the highlands of the northern portion of the colony. Laghouat lies immediately south of the Saharan Atlas, latitude 33°48′, and at an elevation of 780 meters. Ouargla is approximately 200 miles south of the mountains, latitude 31°55′, and altitude 150 meters. In Salah is in the midst of the western Sahara, latitude 27°17′, and about 300 meters above the sea. Fort National lies in the Tell about 30 miles from the sea, and at an altitude of 916.3 meters. The latitude of Fort National is 36°38′.

There are no published records of the soil temperatures of southern Algeria. In the following table is given soil-temperature data taken at Ghardaia by M. Buret. Maximum and minimum standard chemical thermometers were used. They were placed in a horizontal position in fixed tubes which were about 30 cm. in length. Precautions were taken to properly insolate the instruments. The depth was 15 cm.

TABLE 12.—Soil and air temperatures, Ghardaia, July 2-11, 1911.

+---------+---------------------+---------------------+ | | Soil. | Air. | | Date. +----------+----------+----------+----------+ | | Maximum. | Minimum. | Maximum. | Minimum. | +---------+----------+----------+----------+----------+ | | °C. | °C. | °C. | °C. | | July 2 | 36.0 | 31.0 | 41.0 | 21.0 | | July 3 | 36.0 | 31.0 | 41.0 | 22.0 | | July 4 | 36.0 | 31.0 | 41.0 | 23.0 | | July 5 | 36.5 | 31.5 | 41.0 | 23.5 | | July 6 | 33.7 | 32.0 | 41.0 | 25.0 | | July 7 | 36.0 | 32.5 | 40.0 | 26.0 | | July 8 | 36.0 | 32.5 | 38.0 | 26.5 | | July 9 | 37.0 | | | 25.0 | | July 10 | 37.0 | 32.5 | 40.0 | 24.0 | | July 11 | | 33.0 | | 23.0 | +---------+----------+----------+----------+----------+

An examination of the meteorological reports for Algeria shows that the direction of the prevailing winds varies considerably, although the variation is possibly greater near the coast than in the interior. The winds undoubtedly play an important rôle in the environment of the vegetation of the country. At Algiers, in 1907, winds were reported from the north 288 times, from the east 203 times, from the west 224 times, and from the south 51 times. At Barika, on the High Plateau, the number of times and the directions of the winds for the same year are as follows: northeast, 203 times; east 242; south 21, west 89, and southwest 93. At El Golea, on the desert, the winds were as follows: north 192, northeast 614, southeast 107. The winds from the north, or northerly winds, are cool and laden with moisture, but they are most effective in regions near the coast or in the mountains. Winds from the south are dry winds, and are probably of great importance in limiting the distribution of plants through the increased aridity caused by them.

The most important of these desert winds is the sirocco, a wind that is most likely to blow in spring and summer, although occurring in autumn also, and to a very limited degree in the winter season. The sirocco crosses the Mediterranean and is felt in the southern portions of France, on the Italian Riviera, and in other parts of southern Europe. It is especially common on the High Plateau; for example, during five years it was reported on an average of 28.4 days each year. It does not generally last more than three days, but at Batna, in July, 1902, it was recorded on eight consecutive days. The sirocco operates to lower the relative humidity and to raise the temperature. For instance, on the first day of the eight-day sirocco above alluded to, the average relative humidity was 16 per cent, while the average on the preceding day was 25.6 per cent. It has already been remarked that on the days of the greatest temperature variation the sirocco was usually blowing. In the desert the winds often bring with them much dust and sometimes last during several days; for example, one is reported at In Salah, in May, 1904, for six consecutive days. Such winds on the desert may come from the north, or at least may be northerly, and when storms of this character are in progress, although possibly destructive of animal life or at least comfort, the effects as regards decreasing the relative humidity and raising the air temperature are not so marked as is the case when the sirocco is blowing.

=SOME CHARACTERISTICS OF THE VEGETATION OF THE TELL.=

Because of the similarity in the flora of Algeria and southern Europe, a very good introduction to Algeria is by the way of southern Spain, France, or Italy. As one approaches southern France, for instance, he begins to see evidences of increasing aridity. Upon passing Lyons grassy fields and heavy forests are left behind, the hills become bare or covered with a chaparral-like growth, and the practice of irrigation is observed on the plains. The vegetation, especially of the region between Avignon and Nimes, recalls that of portions of California, and one sees the mulberry, the olive, and the pomegranate in abundance, and occasionally the orange. Very much the same conditions greet one when he arrives in Algiers, except that along the littoral, at and in the vicinity of Algiers, there is a wealth of native and especially of introduced plants, which give little hint of the arid regions close at hand. The hills which make a part of the beautiful city of Algiers contain fine plantations of foreign trees, such as eucalyptus, conifers of various species, acacias, figs, and a variety of fruit trees like the apricot, peach, plum, apple, almond, orange, and others. In the fine public squares one sees large palms also, and in the botanical garden are bamboos, palms, bananas, India-rubber trees, and a large number of forms from the subtropics. The great variety of introduced plants which appear to thrive on the littoral again recalls portions of California, where the kinds and numbers of introduced plants which grow well are likewise large, and where the floral strangers are gathered from the antipodes. But among the species there are also many natives to the colony and which one will see when he begins to travel away from the coast; for example, the cedar from the higher mountains (Cedrus atlantica) and the fine pine (Pinus halepensis) from lower altitudes; there are junipers and oaks, among the latter the cork oak (Quercus suber), and fine specimens of Pistacia atlantica and its protector the jujube (Zizyphus lotus), the relationship of which will be given later in this paper. Both of the last-named species are native to the Sahara and are of rather frequent occurrence in the regions visited.

Upon leaving Algiers one soon encounters a striking change in the character of the vegetation, evidences of a rather small rainfall and a low humidity, and one appreciates the fact that even near the coast the climate of the colony is fairly arid. A fine general view of the region about Algiers, giving at a glance its setting and these features, is to be had from the heights behind the city. In the words of Tristram (The Great Sahara):

Here we turned to observe the magnificent panorama of the city and the harbour below, with the bay stretching far beyond, the slopes of Mustapha on the right studded with villas, the Sahel range terminating beyond the massive tower of the seminary of Kouba, the conspicuous Maison Carée . . . planted where the plain of the Metidjeh opens to the sea, the range of the lesser Atlas in the distance beyond, and the peaks of the Djudjura, the last stronghold of the Kabyles, behind them, capped with snow.

Crossing the plain of the Mitidja (Metidjeh), the route runs through a country devoted largely to the raising of wine grapes, with bare hillsides, or hills covered with low shrubs and small trees, and, following a custom derived from France, with either side of the highway lined with trees, mulberry and ash. At the base of the Atlas we see large orange-groves and numerous fig trees. The lower slopes of the mountains are covered with a chaparral-like growth, and as one penetrates the mountains, ascending gradually alongside the Oued Chiffa, he sees, among other forms, extensive areas of dwarf palm, doum (Chamærops humilis), which resembles remotely the familiar saw-palmetto of the southern portion of the United States. The leaves of the doum are gathered by the Arabs for making into baskets, rope and other useful articles, and several donkeys laden with doum bales were observed being vigorously driven marketward by their small bournoused masters. On the sides of the gorge one sees species of delicate ferns, bunch-grass in tumbling masses (very luxuriant where there is moisture), chestnut, arbutus, and masses of evergreen ivy overhanging the way in places. At one place, fairly high in the mountains, a colony of native monkeys has found a safe retreat and may be frequently seen gamboling among the rocks and the shrubs near the stream. They were seen and described by Tristram about 50 years ago, who states that they “are of the same species as those of the rock of Gibraltar.” Here are a few oaks, myrtles, some “dherou” (Pistacia sp.), and a few and scattering specimens of Pinus halepensis. The upper portion of the mountain, at least of the part seen, is nearly treeless, and is under some cultivation. After leaving the pass a drive of a few minutes brought us to the old Roman town of Medea, which appears from the character of the vegetation, both native and introduced, to have a cooler as well as drier climate than Algiers. Conspicuous among the ornamentals are the Judas tree and the plane, both planted much about the town; among the fruits the apple is cultivated extensively.

From Medea to Berrouaghia the mountain range is broken up into large rounded hills, in part cultivated, but almost wholly open, scantily covered with shrubs or trees and mainly grazed over by large flocks of sheep and goats. About midway between the two places we pass through an open forest of oaks, from whose boles the bark has been removed. A chance acquaintance told us that the cork was removed about once in four years, but this is probably not the true cork oak (Quercus suber), which grows under more moist conditions, as between Tunis and Constantine, or between the latter place and Algiers, along the littoral. The altitude of this region is somewhat under 4,000 feet.

From Berrouaghia to Boghari, which is on the northern edge of the High Plateau, the route runs through an open grazing country, with scattering oaks (Quercus ballota), juniper (Juniperus oxycedrus), and “dherou” (Pistacia lentiscus), and, among other herbaceous plants, not a little bunch-grass, whose species I did not learn. On the northern slopes of Mount Gorno, 3,500 feet, is an open forest of oak of the species named, the formation recalling the chaparral of California. Upon reaching the crest of the mountain one is suddenly brought to a forest of pine (Pinus halepensis) which covers the entire southern slope to the exclusion of other species of trees. Spreading over the slope on the upper levels, it avoids the gulches near the base and reaches out on the crests of the ridges for a considerable distance. The width of forest where crossed is about 50 kilometers. In its habitat, which comprises the lower Atlas Mountains, Pinus halepensis forms a rather small tree, shapely, with rounded summit. When growing somewhat apart from its fellows it is of a more squat appearance than when in the forest, although the forest of the species is by no means a dense one.

=THE FORESTS OF ALGERIA.=

There are estimated to be between 5,000,000 and 8,000,000 acres of forested land in Algeria. Although the forests lie mainly in the Tell, certain species, notably Pinus halepensis, occur in the Saharan Atlas as well. Trees also grow along the oueds, especially on the High Plateau, but not in sufficient abundance to constitute forests proper. The leading species are, among the conifers, Cedrus atlantica and Pinus halepensis. The junipers are of importance mainly as a fuel, but do not form forests. Three oaks, namely, Quercus ballota, Q. suber, and Q. lusitanica, are forest-making species, but several other common forms, such as the olive, the plane, the ash, and the betoum (Pistacia), may share in the making of a mixed forest, but do not occur in sufficiently large numbers each to constitute a forest. In 1908 in the civil domain the acreage of the leading kinds of forest trees was as follows: oak, 1,853,520; pine (Pinus halepensis), 1,398,470; juniper (about one-half being Juniperus communis), 444,780; and Cedrus atlantica, 85,000.

The species of trees are distributed in well-defined zones, because of which they may to a large degree be segregated, or at least the specific composition of the forest, if a mixed one, may be determined. In altitudinal range, the oaks are found from sea-level to 6,000 feet, within which each species may have its characteristic range. For example, Quercus suber reaches from sea-level to 2,500 feet; Q. ballota from 2,500 to 4,000 feet; and Q. lusitanica from 3,500 to 6,000 feet. Pinus halepensis grows from the sea-level to 3,600 feet, and probably much higher in the Saharan Atlas, while Cedrus atlantica is to be found from 4,000 to 6,000 feet. Abies barborensis is said to attain a higher altitude than the cedar.