Tierra del Fuego — the windswept hook of rugged land stretching towards Antarctica at the southernmost point of South America — is not known for its hospitable climate. When visiting the area in the southern summer of 1832, Charles Darwin wrote “the atmosphere, likewise, in this climate, where gale succeeds gale, with rain, hail, and sleet, seems blacker than anywhere else (C. Darwin, The Voyage of the Beagle; 1839). The presence at the timberline of gnarled and dwarfed trees, as seen in this image, seems testament to the harsh weather of the region. But Hector D'Antoni at NASA and colleagues have found that it's not the weather that makes the environment extreme: the area is subject to high levels of ultraviolet radiation (Geophys. Res. Lett. 34, L22704; 2007).

The researchers measured a number of environmental parameters on vertical transects of the steep slopes forming the northern shore of the Beagle Channel near Ushuaia, Tierra del Fuego. They found that although the temperature, moisture, acidity and nutrient content of the soils were not unusual for the region, levels of ultraviolet solar radiation were sufficiently high to classify the upper timberline environment as extreme. As ultraviolet radiation is dangerous to life — it damages important biological molecules like proteins and DNA — trees growing under these conditions must have evolved strategies for coping with such high levels in order to survive.

Credit: LEE CHAI LAU

Previous work showed that leaves from the dominant tree genus in the area — the beech Nothofagus — contain glycoside compounds, which protect the leaf by absorbing the ultraviolet radiation. The local evergreen N. betuloides contains higher concentrations of these protector compounds than the two deciduous species, N. antarctica and N. pumilio. DAntoni and colleagues suggest that the leaf shape of these trees, with a rippled profile and glossy surface, may have evolved to maximize the reflection of ultraviolet radiation.

Studies of extreme environments may help understand the conditions in which the early stages of life have evolved, for example high temperature, pressure or salinity. The high elevation forests on Tierra del Fuego broaden the repertoire by adding high ultraviolet solar radiation.