Notes of a naturalist in South America

by John Ball

The middle, or temperate, zone, extending from about eight thousand to about thirteen thousand feet above the sea, possesses a very varied flora which includes many groups characteristic of the Andes, and entirely or mainly confined to that range, with representatives of numerous genera that are widely diffused through the temperate regions of the northern hemisphere, and a smaller number of representative species of groups belonging to the tropical American flora. The climate of this region is marked by the absence of all extremes of temperature. Cool nights, in which frosts are infrequent and of short duration, alternate with days wherein the shade temperature rarely surpasses 70°. The division between the temperate and subtropical zones is marked rather by the more frequent, though moderate, rainfall, which in the former recurs at intervals throughout the year, than by any marked change of temperature. Hence there may be distinguished a rather broad intermediate zone in which many of the characteristic forms of each meet and are intermingled; but this does not appear to be defined by any genera, or even by more than a few species peculiar to it, and does not deserve to be treated apart in a general survey of the flora.

DIVISIONS OF THE ANDEAN FLORA.

The upper, or Alpine, zone of the Cordillera, extending from about thirteen thousand feet to the utmost limit of vegetation, is well defined by the circumstance that night frosts here recur throughout the year, and snow lies at least occasionally on the surface, while a somewhat greater amount of aqueous precipitation, in the form of rain or snow, combined with diminished evaporation, maintains a moderate degree of moisture in the soil. The proportion borne by some groups of the characteristic Andean flora as compared with the entire vegetable population is here larger than in the temperate zone, but other types better adapted to the climate of the latter zone are here nearly or altogether wanting. The forms common to the north temperate zone are present in about an equal proportion, while the representatives of the tropical flora are but very few.

With reference to the opinion expressed by writers of authority, and especially by Engler,[13] that the Andean flora is exceptionally rich in endemic genera and species, and to the explanation which would account for the facts, first, by the greater facility afforded for the extension of new varieties in dry climates, where the soil is not continuously covered by the existing vegetation; and, secondly, by the isolation of the summits, favouring the development of special local forms, I may venture on some sceptical remarks.

When we are struck by the large number of genera and species that are exclusively confined to the Andean flora, we are apt to forget the vast extent of the region which we are contemplating. Even if we exclude the mountains of Central America, and also those of Southern Chili, from Araucania to the Straits of Magellan, we have in the Andes a mountain region considerably more than three thousand miles in length, and from two hundred to over five hundred miles in breadth. This vast region is as yet far from being sufficiently explored to enable us to fix the geographical limits of its genera and species with any precision; but it appears to me that, while a very large number of genera are limited to the Andes as a whole region, the range of most of them within the limits of that region is very wide. I am further disposed to form a similar opinion as to the distribution of the species if compared to what is found in some other mountain districts. If we were to find in South America anything like the variety of species limited to very small areas that is encountered in Southern Spain, Greece, Asia Minor, and Southern Persia, where on each mountain that we ascend we find several well-marked local species, differing from those in similar stations a few miles distant, the catalogue of the Andean flora would have to be extended to three or four times its actual length.

PHYSICAL GEOGRAPHY OF THE ANDES.

Fully agreeing, as I do, with Engler in his general conclusion that dry climates are more favourable than moist ones to the development of new varieties, which are the ancestors of future new species, I must remark that in the Andes, so far as we know, the species with very restricted area abound more in the upper zone, where the soil is relatively moist, than in the drier middle or lower zones. Nor does it appear that isolation of the summits can be with reason invoked as an explanation. The most marked feature in the range, and one that geologists have perhaps not taken enough to heart, is the extremely continuous character of the crest of the range, especially on the western side, as is evidenced by the fact that from Colombia to Southern Chili there are so very few passes below the limit at which snow frequently lies on the surface. For a rational explanation of the facts as to the distribution of mountain floras, we are forced to assume that the various agencies which are in daily operation—birds and land animals, winds, etc.—are competent to effect the transference of the great majority of species from one mountain to another not very far removed; and if that be true in districts where peaks are separated by arms of the sea or by intervals of low country having a very different climate, the process must be still easier in a chain so continuous as that of the Andes.

On the evening of the 24th I had the advantage of meeting the representatives of nearly all the European powers then present at Lima at the table of Don R. C——, a native gentleman of large fortune and influential position. The entertainment might properly be described as sumptuous, and, excepting in some royal palaces, could not easily be matched in Europe. One feature, indeed, was unique, and appealed to the susceptibility of a botanist. The vases heaped with choice specimens of tropical fruits could scarcely have been seen out of Peru. The occasion was not one on which political questions could with propriety be discussed, but I was struck by the complete agreement amongst men of various nationalities, whose duty it was to know the real state of things, as to the formidable prospect of anarchy and disorder that must ensue whenever the Chilian forces should be withdrawn from Lima and the adjoining provinces—a prospect, I need scarcely add, that has been since fully realized.

Soon after sunrise on the 25th Mr. Nation was good enough to call for me. We had agreed to make a short excursion along the bed of the Rimac, the best, if not the only, ground near the city where one can form some idea of the indigenous vegetation of the low country. As happens elsewhere, the river has carried down seeds or roots of many plants of the valley, which find a home on its broad gravelly bed, while the continual moisture has enabled many species of the plain, elsewhere dried up at this season, to maintain a vigorous growth. The little expedition was full of interest, and, with the aid of Mr. Nation’s extensive local knowledge, I was able to make acquaintance with many forms of vegetation not hitherto seen. It was necessary to return early to the town, as my Chicla collections required many hours of diligent work until nightfall, when I had the pleasure of joining an agreeable party at the house of Mr. Graham, the British chargé d’affaires.

M. LOMBARDI.