Tundra

Alpine tundra occurs in climatically stressed environments at high mountainous altitudes. Alpine tundra can even occur on mountaintops at tropical latitudes, although this vegetation type is much more common in temperate regions. Compared with the arctic tundra, alpine environments have much larger daily variations of temperature and solar radiation during the growing season. Because of the thinness of the atmosphere at high altitude, alpine tundra is also subject to large inputs of ultraviolet radiation, which can be an important biological stressor. Because the skies are often clear at high altitude, the surface cools very quickly at night, so that frost can be a daily occurrence during the growing season.

In general, alpine tundra is considerably richer in plant species than arctic tundra. At temperate latitudes, this occurs because alpine environments were not regionally obliterated by glacial ice during the most recent glaciations, so the component species were able to endure this period of intense climatic stress. This survival was made possible by the occurrence of non-glaciated refugia where plants could survive on some mountaintops (these are called nunataks). In addition, as the climate deteriorated, alpine tundra could migrate to lower-altitude, non-glaciated parts of mountainous regions, as the tree-line moved downwards. In contrast, almost all of the arctic tundra was destroyed by the extensive continental glaciers that covered northern regions during the most recent ice ages. It is believed that after deglaciation the arctic tundra was re-established by a northward migration of some of the plant species of alpine tundra. However, because only some species were capable of undertaking the extensive migrations that were necessary, the arctic tundra is relatively poor in species, compared with temperate alpine tundras.

There are relatively few animals that only occur in alpine tundra and not in other types of ecosystems. In North America some of the characteristic mammals of alpine tundra include a small relative of rabbits called the pika (Ochotona princeps), and the hoary marmot (Marmota caligata). The gray-crowned rosy finch (Leucostichte tephrocotis), horned lark (Eremophila alpestris), and water pipit (Anthus spinoletta) all breed in alpine tundra of North America, but also in arctic tundra (the lark also breeds in other open habitats, such as prairie and fields).