Professor Iain Stewart – from salt flats to savannah:
It’s one of the most truly extraordinary landscapes on Earth. The Salar De Uyni. The biggest salt flat on the planet, stretching out across the Bolivian altiplano plateau, 3700 metres up in the Andes mountains of South America.
In winter, especially during the snowmelt of late March, water ponds on the Salar’s flat surface, turning the land into a vast natural mirror. But at this altitude, any runoff from the mountain is subject to the cyclical and seasonal evaporation, laying down layer after layer of salt brine.
A stunning white vista made all the more remarkable because this vast expanse of high plateau was originally part of a complex of great lakes at low altitudes, which gradually became uplifted over millions of years as the Andean mountains themselves began to rise.
The upheaval of the Andes has shaped South America’s natural history, not least by creating some of the world’s most rich, unique and biodiverse natural habitats. The continent is a true patchwork of ecological zones: from deserts, flooded plains and savannah, to lofty salt flats, cloud forest and mountain peaks. And at the continent’s heart, a vast rainforest that overflows with life: the Amazon.
That Amazon basin is itself a creation of the towering Andes. Before the Andes, the main rivers on the continent flowed in the opposite direction to today, westward into the Pacific ocean. When the mountain barrier started to rise it diverted rivers to the north, where they flowed out into the Caribbean, creating a huge expanse of wetlands close to the growing mountains.
Later, further uplift blocked the route north and forced the rivers to converge towards the Atlantic. From around 20 million years ago, the resulting wall of high mountains disrupted rain-bearing air masses. With the increased rainfall on its eastern flank, more and more sediment flowed off the Andes in new rivers that drained down into the Amazon basin. And with that flow came nutrients that enriched the Amazon forest and its flora.
With the growing Andes on one hand and the flourishing Amazon on the other, South America saw the development of an astonishing diversity of life.
Many species are still only found on this continent. Species like the xenathrans – armadillos, anteaters, and sloths – found in diverse habitats across South America, not only in the rainforest but also in the savannah-like regions of southern Brazil and Argentina. Or the iconic llama, restricted to the steep Andean peaks and high salty plateau.