History of the montane forests of the northern Andes

Abstract

From the vascular plant genera of the tropical Andean montane forests about 65% have a tropical-neotropical, 15% tropical-Andean, 5% amphi-pacific (Malayo-American), 5% Austral-antarctic and 10% Holarctic distribution. The explosive evolution of Andean centred taxa probably started in the lower Tertiary from tropical Gondwana stock, when in the area of the present day Andes, locally there may have been hills up to 1 000 m. With the final upheaval between the Late Miocene and Late Pliocene, extensive areas with a montane climate were created and populated from the low mountain flora by evolutionary radiation. Taxa of Austral-antarctic origin migrated along the Andean chain to the tropics. At the same time the formation of the Panama isthmus connected N. and S. America, and enabled many plants to enter the tropical Andes from the north. First to cross were tropical to subtropical and warm-temperate species from the Tertiary Laurasian flora that had migrated southward during the period of Miocene cooling, taking refuge in the montane tropics. Because the same happened in SE. Asia there is a good number of amphi-pacific taxa known as fossils from Tertiary Laurasia but largely extinct in the present-day Holarctic (e.g., Trigonobalanus). Later to cross were cool-temperate to cold elements that still exist in the Holarctic (e.g., Alnus and Quercus).To understand the history of the montane forests of the northern (tropical) Andes, it is necessary to know the general historical background of the South American continent, and of the flora and vegetation of tropical S. America, in relation to temperate S. America and temperate N. America. For that reason we will first give some background information on the earlier history, then treat shortly the vegetation and phytogeography of the Andes, followed by an overview of the Late Tertiary and Quaternary history of the area, and finally general conclusions.