Notes of a naturalist in South America

by John Ball

On the way from Valparaiso to Santiago I had already been much struck by the prevalence over wide areas of plants not indigenous to the country, most of them introduced from Southern Europe. The most conspicuous are plants of the thistle tribe, all strangers to South America, and especially the cardoon, or wild state of the common artichoke. This is now far more common in temperate South America than it anywhere is in its native home in the Mediterranean region. In Chili it is regarded with some favour, as mules, and even horses, eat the large spiny leaves freely at a season when other forage is scarce. The same cannot be said of our common coarse spear-thistle (Cnicus lanceolatus), which, though of much more recent introduction, has now invaded large tracts of country, especially in the rather moister southern provinces. I was informed that, with the strange expectation that it would be useful as fodder, an Englishman had imported a sack of the seed, which he had spread broadcast somewhere in the neighbourhood of Concepcion. Many other European plants have been introduced, either intentionally or by accident, and have in some districts to a great extent supplanted the indigenous vegetation. As to many of these, it appears to me probable that their diffusion is due more to the aid of animals than the direct intervention of man. This is especially true of the little immigrant which has gone farthest in colonizing this part of the earth—the common stork’s-bill (Erodium cicutarium), which has made itself equally at home in the upper zone of the Peruvian Andes, in the low country of Central Chili, and in the plains of Northern Patagonia. Its extension seems to keep pace with the spread of domestic animals, and, as far as I have been able to ascertain, it is nowhere common except in districts now or formerly pastured by horned cattle. It is singular that the same plant should have failed to extend itself in North America, being apparently confined to a few localities. It is now common in the northern island of New Zealand, but has not extended to South Africa, where two other European species of the same genus are established.

IMMIGRANT PLANTS.

In considering the facts relating to the rapid extension of certain plants when introduced into new regions, and the extent to which they have supplanted the indigenous species, I confess that I have always been a little sceptical as to the primary importance attributed by Darwin[25] to the fact that most of these invaders are northern continental species. In the course of a long existence extending over wide areas, he maintains that these have acquired an organization fitting them better to maintain the struggle for existence than the indigenous species of the regions over which they have spread. Of course, it is true in the case of territories very recently raised from the sea, and not in direct connection with a continental area inhabited by species well adapted to the conditions of soil and climate, that immigrant species well adapted to the conditions of their new home will spread very rapidly, and may easily supplant the less vigorous, because less well adapted, native species. The most remarkable case of this kind is perhaps presented by Northern Patagonia and a portion of the Argentine region, raised from the sea during the most recent geological period. The only quarters from which the flora could be recruited were the range of the Andes to the west, and the subtropical zone of South America to the north. Everything goes to prove that the forms of plants are far more slowly modified than those of animals—or, at least, of the higher vertebrate orders. The new settlers are unable quickly to adapt themselves to the new conditions of life, and as a result we find that the indigenous flora of the region in question is both numerically poor in species, and that these have been unable fully to occupy the ground. Among the species intentionally or accidentally introduced by the European conquerors, those well adapted to the new country have established a predominance over the native species; but I question whether, if the course of history had been different, and the conquerors of South America had come from South Africa or South Australia, bringing with them seeds of those regions, we should not have seen in Patagonia African or Australian plants in the place of the European thistles and other weeds now so widely spread.

CHECKS ON COLONIZATION.

If I am not much mistaken as to the history of the introduction of foreign plants into new regions, it very commonly happens that a species which spreads very widely at first becomes gradually restricted in its area, and finally loses the predominance which it seemed to have established. Attention has not, I think, been sufficiently directed to the fact that the chief limit to the spread of each species is fixed by the prevalence of the enemies to which it is exposed, and that plants carried to a distant region will, as a general rule, enjoy advantages which in the course of time they are likely to lose. Whether it be large animals that eat down the stem—as goats prevent the extension of pines—or birds that devour the fruit, or insects that attack some vital organ, or vegetable parasites that disorganize the tissues, the chances are great that in a new region the species will not find the enemies that have been adapted to check its extension in its native home. Of the marvellous complexity of the agencies that interact in the life-history of each species we first formed some estimate through the teachings of Darwin; but to follow out the details in each case will be the work of successive generations of naturalists. We cannot doubt that in a new region new enemies will arise for each species that has become common, or, in other words, that other organisms, whether animals or plants, will acquire the means of maintaining their own existence at the expense of the new-comer. The wild artichoke is doubtless perfectly adapted to the climate of the warmer and drier parts of the Mediterranean region, and is there rather widely spread; but it is nowhere very common, even in places where the ground is not much occupied by other species. We do not know all the agencies that prevent it from spreading farther, but we do not doubt that it is held in check by its appropriate enemies. In South America it would appear that these, or some of them, are absent, and the plant has spread far and wide. If some common bird should take to devouring the seeds, or some other effectual check should arise, the area would very speedily be reduced.

The train stopped for breakfast at the Rancagua station, a few miles from the town of that name. Along with very fair food at the restaurant, cheaper delicacies were offered by itinerant hawkers, including various sweet cakes of suspicious appearance and baskets of red berries of the peumo tree. At the next station, called Gualtro, about fifty miles from Santiago, we left the train, and, after the usual long delay, continued our journey in a lumbering coach set upon very high wheels. This seems to be the general fashion for carriages in South America, arising from the fact that the smaller streams, which swell fast after rain, are usually unprovided with bridges.

Incautious travellers in South America may easily be misled by the frequent use of the same name for quite different places. One bound for the Baths of Cauquenes must be careful not to confound these with the town of Cauquenes, the chief place of a department of the same name, more than a hundred miles farther to the south.

PHYSICAL GEOGRAPHY OF CHILI.

Before reaching Gualtro we had crossed the Cachapoal, a torrential stream which drains several valleys of the high Cordillera. Our course now lay eastward, towards the point where the river issues from the mountains into the plain, and where, as everywhere in Central Chili, its waters are largely used for irrigation. The road along the left bank lies on a slope at some height above the stream, and gives a wide view over the plain, backed by the great range of the Cordillera. Irrespective of the picturesque interest of the grand view, I added somewhat to the impressions respecting the physical geography of Central Chili which I had recently received from an examination of Petermann’s reduction from the large government map, and from the information given me at Santiago.

I had reached Chili with no other ideas respecting the configuration of the country than those derived from the twelfth chapter of Darwin’s “Journal of Researches,” which with little modification have been repeated by subsequent writers, even so lately as in the excellent article on “Chile,” in the American Cyclopædia.