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Where the Andes created a Lost World
From a botanic point of view Chile is one of the most interesting places on earth because its flora, despite having a relatively small number of species (about 5000) has the largest percentage of endemic plants, i.e. plants which can be found only in Chile, bordering the 50 % mark. According to one study, out of 5082 different Chilean species, 2561 are endemic (C. Marticorena, "Composición de la flora vascular de Chile," Flora silvestre de Chile (Jürke Grau & Georg Zizka (eds.)), Sonderheft 19, Palmengarten, 1992), p. 74).
The high percentage of endemic plants in Chile is relatively simple to explain: it is due to the presence of habitats with distinctively different conditions where the plant species may adapt to these special conditions and where there is a discontinuity between these habitats, so that the species can not migrate from one location to another and are forced to evolve independently within their particular habitat.
In this sense Chile is an ideal example for this type of discontinuous habitats with very special conditions: on the level of the whole country it is very easy to find the characteristics which effectively cut off Chile from the rest of the world: in the north, close to the Peruvian border, the dry deserts block very effectively the possibility of migration - with the exception of very few cosmopolitan and South American species the vegetation is confined to small coastal areas with very special fog conditions, and these areas are often separated by hundreds of kilometres, so that a jump from one area to another is virtually impossible and the plants are forced to follow through independent development paths.
The eastern border with Bolivia and Argentina all the way down to about 38º latitude has extremely high mountains which rise up to 5000-6000 meters in the central and northern Chile and go a little down to about 2500-3000 meters in central-southern Chile and disappear almost completely in Patagonia, where only occasional peaks, like Mount Fitzroy or Torres del Paine break the monotony of the flat landscape. These mountains were always a formidable barrier for species dispersal and they are the main reason why Chile has such a high percentage of endemic plants: the Chilean species simply could not escape across the frontier, nor could new species come in: the lowest passes in the north are well above 4000 m. and around 38º latitude go down to about 2500 m, but this descent is compensated by the colder climate conditions towards the south, so that in practical terms, the barrier conditions are the same throughout the whole border extension) which also preclude migration. The southern limit of the Endemic Island of Chile, as one might call it, is not Patagonia, but the Campos de Hielo Sur, Southern Ice Fields, around 48º latitude, which are absolutely impenetrable for plant dispersal. More to the south (around the area of Torres del Paine, Punta Arenas, etc.), there are no effective geophysical blocking features, and the plants have a relatively continuous habitat and the possibility to migrate, so that many species of extreme south are not endemic. Now, the area between 38º and 48º latitude presents some problems as a barrier because there are many low-altitude passes which are below 1000 m and which do not present effective cut-offs for the plant species continuity today. However, if one considers the fact that during the last ice age the conditions were much harsher and these passes were either under permanent glacier ice or at least had heavy winters and snow for most of the year, one can clearly see the secluded status of the continental Chile all the way from extreme north down to latitude 48º.
These conditions began to arise about 65 million years ago with the rising of the Andean mountains, and became much more accentuated during the last 5 million years when the Andes reached their actual height.
In addition to this countrywide seclusion, the peculiar geophysical landscape created areas with very special conditions within the country. As was already mentioned, the northern habitat consists mainly of the coastal areas with heavy fog influence which brings the humidity necessary for life. These coastal areas are often separated by dry areas where the conditions change and where the plants find an effective barrier. This limitation is especially notable with cactaceae which do not depend on wind for their dispersal: in Chile are dozens of species which are confined to small areas of distribution of about 20 - 100 km long along the coast. Such is the case for instance with Copiapoa longistaminea (around Esmeralda - about 20 km), Copiapoa marginata (between Caldera and Chañaral - about 80 km.), Copiapoa echinoides (between Carrizal bajo and Totoralillo, about 40 km.), Copiapoa fiedleriana (80 km.), Copiapoa dealbata (from Llanos de Challe to about 20 km. north from Carrizal bajo - a total extension of about 35 - 40 km.), Copiapoa cinerea ssp. columna-alba (from Chañaral to Cifuncho - about 80 km.). The list is long, and the habitat extension are almost always small. In some cases one has to talk about.
Another type of habitat where there is considerable endemism within a certain area are the medium-altitude mountains in the central and central-southern Chile. The plants which grow at these medium altitudes are adapted to these conditions and can not cross over the high mountain ranges, where the conditions are much harsher; they are confined to small niche areas on the western slopes of Chile and have very high endemic percentage. In fact, very often their altitude limitation confines them to very small areas within Chile, because they cannot cross deep transversal valleys and they cannot expand along the higher reaches. That means that often a species is confined to an area as small as a few dozens of square kilometers, as is for instance the case with Alstroemeria pseudospatulata, Austrocactus philippii, Austrocactus spiniflorus; in some cases, this habitat is reduced to a few square kilometers, as is the case of Alstroemeria achirae: it is known to be growing on one mountain from 1500 m. up to the peak at 1850 m, equivalent to an area of about 3 km long x 1 km wide! Since the mechanism for seed dispersal for Alstroemeria precludes the seeds from being borne by either birds, animals, or wind, it is obvious that it never had a chance of crossing a valley more than 2 km wide and running at 650 m above sea level, i.e. about 1 km. below the plant habitat!
Finally, one should consider that there is a considerable number of plants which are endemic of the Andean mountains, but which are not exclusive either of Chile or Argentina. However, since in the scientific community of Chile, and to a lesser extent, in Argentina, there is a very clear-cut differentiation between Chile and Argentina as entities, a situation which may be due in large part to the political rivalry, this type of Andean endemism is largely ignored or delegated to a secondary level. If a plant grows in Chile and Argentina, even if its distribution area is small and limited to the high Andes, it is not of much interest as an endemic plant to be claimed as "unique" of either country. However, these high Andean plants may really be the most interesting ones because often they cannot escape from their high-altitude bastions. It is the strong opinion of the author that despite the fact that these plants cross the border, they should be regarded as endemic (provided that they grow only at these extreme elevations and do not descend on the other side of the border). In the end, one should not pay too much attention to the arbitrary border division which existed for such a short period of time. If one were to revise in this sense the high Andean species, it is very probable that the percentage of endemic plants of Chile would increase to about 55 - 60 %.