Alpine Tundra and the Treeline

Alpine tundra occupies the zone above the treeline and below permanent snow, and despite being assembled from entirely unrelated plant lineages on different continents, it converges on a strikingly similar physiognomy worldwide: cushion plants, rosette-forming herbs, dwarf shrubs pressed close to the ground, and a general absence of trees. These convergent forms reduce exposure to desiccating wind, intense solar radiation, and freezing temperatures that can occur even during the growing season. The treeline itself, the elevational limit beyond which trees cannot maintain an upright growth form, is one of the most conspicuous and abrupt vegetation boundaries on Earth.