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A better understanding of the properties of Andean queñua woodlands has major implications for their conservation
In and out of mists and clouds of the high Andes of Bolivia appears an unexpected sight: patches of otherworldly trees and bushes surviving the harsh climate 4,000 meters above sea level. Called queñua by Andean natives, these members of the genus Polylepis are the highest growing trees in the world, and their distinctive appearance highlights the many adaptations necessary to survive at considerable altitude in the Cordilleras of South America. Species of Polylepis differ markedly from one another having specialized for very different habitats: Some grow on the cold and wet eastern flank of the Andes above the expansive Amazon Basin, whereas others eke out an existence in the high and arid western side, which slopes down into the Atacama desert. Because of the isolation of this amazing ecosystem, a wide range of animals, particularly birds and insects, has evolved close connections with the Polylepis trees, creating a fascinating and distinctive community.
Despite the uniqueness and fragility of the Polylepis ecosystem, it long remained poorly studied because early investigators believed that the patchy occurrence of Polylepis groves was a natural phenomenon, thus raising no alarms for its longevity. The German botanist Heinz Ellenberg challenged this notion in the 1950s. He claimed that much of the high Andes would naturally be covered with Polylepis and that the current restricted distribution of the Polylepis forests was the result of thousands of years of human activities. Other scientists refused to accept this view until the late 1980s, when Danish ornithologist Jon Fjeldså and one of us (Kessler) launched several wide-ranging expeditions to find areas of Polylepis and to catalogue the plant and bird species in each. These studies obtained conclusive evidence that in Ecuador, Peru, Bolivia and northern Argentina, Polylepis is the natural vegetation on mountain slopes at elevations up to 4,400 meters in humid regions and up to 5,000 meters in the arid volcanic soils of northwestern Bolivia. In Colombia and Venezuela, the situation may be different because these countries harbor only two Polylepis species specialized to live in humid cloud-forest conditions, as opposed to the 19 species farther south.
The finding that once-extensive natural Polylepis forest has been...