Before concluding this chapter, a few remarks on the botanical aspect of the Alpine problem might not be out of place. It will enable us to judge which of the views indicated is the more probable, and will add to the interest which may have been aroused by the perusal of this sketch of the fauna of the Alps. Very much the same train of argument was applied as to the course of events in the formation of the Alpine flora as in the case of the fauna. The plants were all supposed to have been killed or driven away by the arctic temperature of the Glacial period, and their place taken by new migrants from the north or east when the climate ameliorated.
Professor Engler, one of the highest living authorities on the geographical distribution of plants, is of opinion (p. 102) that a large number of the indigenous Alpine species did not originate till after the close of the Glacial period, because so many of them are absent from the Sierra Nevada in Spain, where the condition for their well-being exists, while many have evidently spread from the Alps to the Carpathian Mountains and to the Pyrenees. He does not believe that a glacial flora could have existed in the plain between the Sierra Nevada and the Pyrenees during the Glacial period (p. 109). In speaking of the Caucasus, Professor Engler informs us (p. 117) that a good many species which do not occur in the Alps reached these mountains from Siberia. Apart from the northern glacial plants, the Caucasus has only few species in common with the Alps, more with the Balkan mountains and Northern Persia. Turning to Afghanistan, our author mentions (p. 121) a few Alpine plants as occurring in that country, and likewise in the Caucasus and the Himalayas. He considers it probable that the route of migration of some glacial plants from the east to the west, and vice versâ, lay across the Afghan mountains. Many of our Alpine plants occur in the Siberian mountains, but in the Altaï and Eastern Siberia generally a considerable number of these are by no means confined to the mountains (p. 125). They are also met with in the lower regions, and the rare Alpine Edelweiss (Leontopodium alpinum) frequently covers wide tracts in the plain, and is passed by almost unnoticed by the Siberian botanist.
Special attention is drawn by Professor Engler to the fact (p. 130) that several of the Siberian plants inhabit the Alps and the Caucasus, but are not found in Scandinavia. And from this he deduces the conclusion that part of the Siberian flora migrated in a south-westerly direction towards the Caucasus and the mountains of the Mediterranean area, exactly in the manner indicated in respect to the fauna of the Alps. We learned that the migration to the Alps from Central and perhaps also parts of Northern Asia took a south-westerly course first, and was then followed by one in an easterly direction. I called the former the Oriental migration and the latter the Siberian. Later on Professor Engler states (p. 142) that the main mass of the Siberian forms of plants certainly wandered westward to the south of the Ural. This is proved by the numerous glacial plants found in the Caucasus, while the glacial flora of the Ural Mountains is poor. Finally, he expresses the opinion that the probability of most of the Alpine plants occurring in Arctic Siberia, having wandered from the Alps, by way of Scandinavia, Greenland, and North America, to North-eastern Siberia, is greater than the direct migration from Europe to Siberia (p. 143).
Another continental writer on the Alpine flora who deserves special mention is Dr. Christ. His observation that Alpine plants by no means suffer from a high temperature (p. 309), but solely from a drying up of the soil, seems to me to point to the correctness of the view I have expressed on several occasions, that these plants have originated long before the Glacial period at a time when the climate was warmer and moister than it is now. It seems quite natural to Dr. Christ that the Arcto-Alpine flora should have originated in Asia, but he excepts thirty species which are absent from Northern Asia, though occurring in America (p. 327). These he thinks have penetrated direct from America to the Alps by way of Scandinavia, since no less than twenty-three still occur in the latter country. In the human population of the Alps, he continues (p. 336), one can distinguish an indigenous Celtic race, a Germanic colder and more apathetic race, and a more lively Roman one. The flora is composed of quite a similar mixture. We find also an indigenous element—an Arctic and a Mediterranean one. The last element is a survival of the Tertiary flora of the Central European plateau (p. 532). The plants were driven down to the shores of the Mediterranean, and it is only after the retreat of the glaciers that a few of them have been able to regain their ancient territory. The incoming Asiatic and North American flora likewise retired at the end of the Glacial period to the Alps and the Arctic countries, and left isolated traces of its former abundance on the North European plain. The bulk of the Arctic or Alpine flora is held to be of Asiatic origin. Since Siberia shows little trace of having been glaciated, owing to the dryness of the climate, a rich flora was able to develop there, which spread into Europe as soon as the vanishing glaciers made room for it.
These are the views of Professor Engler and Dr. Christ. They agree in so far as both of them maintain that the bulk of the Alpine flora is post-glacial—that is to say, that it has developed quite recently, or migrated to the Alps after the glaciers had retreated from the plain to the mountain recesses. It is assumed by Dr. Christ that while Europe was practically uninhabitable, a rich flora survived in Northern Asia, because the climate there was too dry for the development of glaciers. Due consideration in this interesting speculation, however, is not given to the fact which he himself emphasised, that Alpine plants are particularly prone to suffer from a dry climate. Even a moderately dry cold kills most of them. How can we then reconcile this fact with the theory of their origin in a dry and intensely cold climate? I quite agree with the views as to the Asiatic origin of the bulk of the Alpine flora, while the dry state of the Siberian climate is certainly indicated by the extremely feeble development of the glaciers during a large part of the Glacial period. We know, however, that in Pliocene and even in early Glacial times the atmospheric conditions must have been very different in Siberia. A great slice of Central Asia was under water, and numerous freshwater lakes covered the lowlands in the north, so that the climate must have been damp though not cold enough for the formation of extensive glaciers. Everything, in fact, seems to indicate that the migration of the Asiatic Alpine flora took place at a very early date—probably long before the Glacial period—either by the Oriental or by the Arctic route viâ North America, Greenland, and Scandinavia. But would this not necessitate a survival of the Alpine plants in the Alps themselves? That is the view which has already been expressed with regard to the fauna, and the flora probably followed a very similar course. This is by no means a novel theory, however, and though unfortunately an untimely death has removed one of our very best authorities on the Alpine flora before he had completed his life's work, we have some indications in the earlier writings of John Ball that his opinions on the origin of that flora did not coincide with those held by the leading continental authors. To quote the words of this distinguished botanist (p. 576): "Is it credible that in the short interval since the close of the Glacial period hundreds of very distinct species and several genera have been developed in the Alps, and—what is no less hard to conceive—that several of these non-Arctic species and genera should still more recently have been distributed at wide intervals throughout a discontinuous chain some 1500 miles in length, from the Pyrenees to the Eastern Carpathians? Nor would the difficulties cease there. You would have left unexplained the fact that many of the non-Arctic types which are present in the Alps are represented in the mountains of distant regions, not by the same, but by allied species, which must have descended from a common ancestor; that one species of Wulfenia, for example, inhabits one small corner of the Alps, that another is found in Northern Syria, while a third allied species has its home in the Himalaya." Mr. Ball is of opinion (p. 584) that the effects of the Glacial period have been greatly overrated. "Even during the period of maximum cold the highest ridges of the Alps were not completely covered with snow and ice; for we still see by the appearance of the surface, the limit above which the ancient ice did not reach, and in the middle zone the slopes that rose above the ancient glaciers had a summer climate not very different from that which now prevails. In my opinion the effect of the Glacial period on the growth of plants in the Alps was to lower the vertical height of the zones of vegetation by from one to two thousand feet." He acknowledges that there was probably a moderate diminution of the mean temperature of Europe with an increased snowfall, so as to cause a great extension of glaciers on all the mountains of Northern Europe. "But that the climate of Middle Europe was such that the plants of the high Alps could spread across the plains seems to me an improbable supposition" (p. 584).
On the Continent, also, some botanists seem to feel that Forbes's theories of the origin of the Alpine flora, which were at first hailed with such delight, and accepted by almost every naturalist as the final verdict, must be modified in the light of recent researches. Professor Krasan believes that many plants which now live in the high Alps flourished in pliocene times at sea-level (p. 37). "Especially the evergreen species exhibit the impression of an originally mild climate—of a climate without winter frosts—for otherwise the plants would have developed into species with deciduous leaves." To the favourable conditions, consisting in periodic snowfalls and high summer temperature, must be attributed the fact that in the highlands so many more species from Tertiary times have survived than in the plains. The temperature was probably much higher during the Glacial period than is generally believed. The climate was more moist, thus contributing to an abundant snowfall, while the survivors of ancient Tertiary times were able to repeople the parts which were temporarily devastated by the advancing glaciers.
In so short a chapter it is impossible to deal with the Alpine fauna in a manner more deserving of this theme. I have merely sought to give a sketch of the general outlines of the subject and to suggest another possible mode of origin of Alpine animals than that currently believed in by naturalists. It is to be hoped these suggestions will be useful to those intending to reinvestigate the problems raised in this chapter. When our knowledge of the fauna of Asia is more complete, it will be possible to give a more thorough and in many respects a more satisfactory history of the European fauna than at present.
SUMMARY OF CHAPTER VIII.
In early Tertiary times the area now covered by the European Alps was covered by the sea. Islands slowly rose above the surface of the waters, which finally coalesced to form a peninsula connected with the mainland in the east. Animals now began to invade the new territory which continued to rise, while the sea retired farther and farther to the north and south. During the Pliocene Epoch the sea ceased to wash the northern shores of the Alps, and both emigration and immigration became possible in that direction, and also from and to the west.
The Alpine fauna and also the flora are made up of a number of elements, the eastern one being the oldest. The latter is represented in the Alps by the older and newer Oriental migration. The general range of the Alpine Steinbock, Chamois, Marmot, Vole, Shrew, and Hare are specially referred to. The Alpine birds are few in number, and all of them are readily traceable to an Asiatic ancestry. Among the Amphibia, the Salamanders are considered of Alpine origin.