Climate of the Alps
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The climate of the Alps is the climate, or average weather conditions over a long time, of the central Alpine region of Europe. As we rise from sea level into the upper regions of the atmosphere the temperature decreases. The effect of mountain chains on prevailing winds is to carry warm air belonging to the lower region into an upper zone, where it expands in volume at the cost of a proportionate loss of heat, often accompanied by the precipitation of moisture in the form of snow or rain.
The position of the Alps in the centre European continent has profoundly modified the climate of all the surrounding regions. The accumulation of vast masses of snow, which have gradually been converted into permanent glaciers, maintains a gradation of very different climates within the narrow space that intervenes between the foot of the mountains and their upper ridges; it cools the breezes that are wafted to the plains on either side, but its most important function is to regulate the water supply of the large region which is traversed by the streams of the Alps. Nearly all the moisture that is precipitated during six or seven months is stored in the form of snow, and is gradually diffused.
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Subalpine Region of the Alps
The Subalpine is the region which mainly determines the manner of life of the population of the Alps.
On a rough estimate we may reckon that, of the space lying between the summits of the Alps and the low country on either side, one-quarter is available for cultivation, of which about one-half may be vineyards and grain fields, while the remainder produces forage and grass. About another quarter is utterly barren, consisting of snow fields, glaciers, bare rock, lakes and the beds of streams.
There remains about one-half, which is divided between forest and pasture, and it is the produce of this half which mainly supports the relatively large population. For a quarter of the year the flocks and herds are fed on the upper pastures; but the true limit of the wealth of a district is the number of animals that can be supported during the long winter, and while one part of the population is engaged in tending the beasts and in making cheese and butter, the remainder is busy cutting hay and storing up winter food for the cattle.
The larger villages are mostly in the mountain region, but in many parts of the Alps the villages stand in the subalpine region at heights varying from 1200 m to 1700 m above the sea, more rarely extending to about 1800 m. The most characteristic feature of this region is the prevalence of coniferous trees, which, where they have not been artificially kept down, form vast forests that cover a large part of the surface. These play a most important part in the natural economy of the country. They protect the valleys from destructive avalanches, and, retaining the superficial soil by their roots, they mitigate the destructive effects of heavy rains. In valleys where they have been rashly cut away, and the waters pour down the slopes unchecked, every tiny rivulet becomes a raging torrent, that carries off the grassy slopes and devastates the floor of the valley, covering the soil with gravel and debris.
In the conifer forests of the Alps the prevailing species are the Norway Spruce and the Silver Fir; on siliceous soil the European Larch flourishes. The Scots Pine is chiefly found at a lower level and rarely forms forests. The Swiss Pine is found scattered at intervals throughout the Alps but is not common. The Mountain Pine is common at higher altitudes, often forming a distinct zone of Krummholz above the level of its congeners on the higher mountains. In the Northern Alps the pine forests rarely surpass the limit of 1800 m above the sea, but on the south side they commonly attain 2100 m, while European Larch, Swiss Pine and Mountain Pine often extend above that elevation.
Alpine Region of the Alps
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The alpine region of the Alps refers to the region in the Alps between the uppermost limit of trees (the tree-line) up to the permanent snow. This alpine region contains the full beauty and variety of characteristic vegetation of the Alps.
The region contains many shrubs:
- Three species of rhododendron have masses of red or pink flowers;
- The common junipers grow at elevations above the rhododendrons.
- Three species of bilberry are associated with the junipers.
- Several dwarf willows grow near the snow line.
Glacial Region of the Alps
On the higher parts of lofty mountains in the Alps more snow falls in each year than is melted on the spot. A portion of this is carried away by the wind before it is consolidated; a larger portion accumulates in hollows and depressions of the surface, and is gradually converted into glacier ice, which descends by a slow secular motion into the deeper valleys, where it goes to swell perennial streams.
As on a mountain the snow does not lie in beds of uniform thickness, and some parts are more exposed to the sun and warm winds than others, we commonly find beds of snow alternating with exposed slopes covered with brilliant vegetation; and to the observer near at hand there is no appearance in the least corresponding to the term limit of perpetual snow, though the case is otherwise when a high mountain-chain is viewed from a distance. Similar conditions are repeated at many different points, so that the level at which large snow-beds show themselves along its flanks as approximately horizontal. But this holds good only so far as the conditions are similar. On the opposite sides of the same chain the exposure to the sun or to warm winds may cause a wide difference in the level of permanent snow; but in some cases the increased fall of snow on the side exposed to moist winds may more than compensate the increased influence of the sun's rays.
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Still, even with these reservations, the so-called line of perpetual snow is not fixed. The occurrence of favourable meteorological conditions during several successive seasons may and does increase the extent of the snow-fields, and lower the limit of seemingly permanent snow; while an opposite state of things may cause the limit to rise higher on the flanks of the mountains. Hence all attempts to fix accurately the level of pernetual snow in the Alps are fallacious, and can at the best approach only to local accuracy for a particular district. In some parts of the Alps the limit may be set at about 2400 m above the sea, while in others it cannot be placed much below 2900 m. As very little snow can rest on rocks that lie at an angle exceeding 60°, and this is soon removed by the wind, some steep masses of rock remain bare even near the summits of the highest peaks, but as almost every spot offering the least hold for vegetation is covered with snow, few flowering plants are seen above 3350 m.
There is reason to think, however, that it is the lack of soil rather than climatic conditions that checks the upward extension of the alpine flora. Increased direct effect of solar radiation compensates for the cold of the nights, and in the few spots where plants have been found in flower up to a height of 3650 m, nothing has indicated that the processes of vegetation were arrested by the severe cold which they must sometimes endure. The climate of the glacial region has often been compared to that of the polar regions, but they are widely different. Here, intense solar radiation by day, which raises the surface when dry to a temperature approaching 27°C (80°F), alternates with severe frost by night. There, the Sun, which never sets sends feeble rays that maintain a low equable temperature, rarely rising more than a few degrees above the freezing-point. Hence the upper region of the Alps sustains a far more varied and brilliant vegetation.
Olive Region of the Alps
The great plain of Upper Italy has a winter climate colder than that of the British Islands. The olive and the characteristic shrubs of the northern coasts of the Mediterranean do not thrive in the open air, but the former valuable tree ripens its fruit in sheltered places at the foot of the mountains, and penetrates along the deeper valleys and the shores of the Italian lakes.
The evergreen oak is wild on the rocks about the Lake of Garda, and lemons are cultivated on a large scale, with partial protection in winter. The olive has been known to survive severe cold when of short duration, but it cannot be cultivated with success where frosts are prolonged, or where the mean winter temperature falls below 5.5°C (42°F); and to produce fruit it requires a heat of at least 24°C (75°F) during the day, continued through four or five months of the summer and autumn.
Vine Region of the Alps
The grape vine is far more tolerant of cold than the olive, but to produce tolerable wine it demands, at the season of ripening, a degree of heat not much less than that needed by the more delicate tree. These conditions are satisfied in the deeper valleys of the Alps, even in the interior of the chain, and up to a considerable height on slopes exposed to the Sun. The protection afforded by winter snow enables the plant to resist severe and prolonged frosts that would be fatal in more exposed situations. Many wild plants characteristic of the warmer parts of middle Europe are seen to flourish along with the vine. A mean summer temperature of at least 20°C (68°F) is considered necessary to produce tolerable wine, but in ordinary seasons this is much exceeded in many of the great valleys of the Alps.