Polylepis - Habitat and Distribution

Habitat and Distribution

Tree species in the genus Polylepis are confined to the high tropical South American Andes Mountains, with the most abundant concentrations of Polylepis ranging from northern Venezuela to northern Chile and adjacent Argentina. One known group of extra-tropical populations of Polylepis is distributed in the mountains of Northwestern Argentina. Most species of Polylepis grow best at high elevations between 3500 to 5000 meters. However, there are occurrences of species at altitudes as low as 1800 meters. These low altitude species are mixed with montane forest which indicates that components of the genus could have been present in western South America during the Miocene Period or even earlier. It is extremely rare for tree species to live at such altitudes, making Polylepis one of the highest naturally occurring trees along with the conifers of the Himalayan Mountains. Polylepis racemosa grows as shrubby trees on steep, rocky slopes above cloud forest. Polylepis tarapacana is one that reaches 4,800 m; the highest elevation of tree growth in the world.

There is much debate on whether Polylepis was forced to exhibit such extreme elevation habitats due to habitat destruction by human interference. Physiological tolerances for growth at these elevations are subject to considerable debate among scientists, but evidence indicates that even before severe decimation by man, high elevation trees were limited in their distribution by the presence of specialized microhabitats. Due to the harsh environment in which many species of Polylepis grow the growth of the tree's stems and branches are generally contorted. This abnormal growth is often associated with windy, cold or arid habitats. The climate of the South American Andes changes drastically throughout the region creating lots of microhabitats. Overall, the climate consists of short southern summers when temperatures are warm and rainfall is high and long winters when temperatures are low and rainfall is limited. The temperature and amount of rainfall also depend on which side of the mountain (eastern or western side), elevation and latitude.