Admired by experts, but otherwise still largely unnoticed, already damaged in places and very much in need of research: the largest lichen fields outside the arctic and subarctic regions of the northern hemisphere are found in the Namib Desert of Namibia, where lichens grow on almost every pebble in many places on the endless gravel plains. Some of them a striking orange-yellow, others dark green or the colour of sand. Certain areas are dotted with light green or with russet orange, bushy lichens, while crustose lichens thrive on loose alkaline soil. Dark, almost black plant material can be seen in depressions next to the gravel road in the northern parts of Namib-Naukluft Park. Living lichens make up this material, carried there by the wind. The Namib Desert is alive, though it may not look like it at first sight.
Lichens are often not easy to recognise at first glance. But if you leave the road and drive across these seemingly lifeless plains your vehicle will not only destroy countless lichens – the tyre tracks will also leave a very visible ugly scar in the desert landscape, which will remain visible for decades. Water could erase that scar, but then it hardly ever rains in the Namib. The average annual rainfall is 15 mm. Lichens and other organisms obtain their moisture from the fogs which rise from the Atlantic Ocean at night and move as far as 60 kilometres into the desert.
Lichens are a symbiosis between a fungus and green algae – two different organisms that mutually benefit from their relationship. Because of the low rainfall lichens may become dominant, even though numerous other plants have also adapted to the harsh conditions of the desert.
The most diverse types of lichens not only thrive on the gravel plains but also on numerous hills and rocks in the Namib. Usually they are found facing southwest because that is the direction from where the fogs roll in at night, pushed by the prevailing south-westerly winds. The precious fog moisture condenses on rocks and other surfaces facing windward.
Lichens are adapted to the harsh conditions of the desert in the best possible way. According to German lichenologist Prof. Volkmar Wirth they can absorb water with their entire surface directly from the atmosphere like a sponge and become physiologically active, but by remaining physiologically inactive they can also tolerate getting almost parched by the relentless heat. Lichens grow just a few millimetres per year. They do not occur in the dunes.
Prof. Wirth says that lichens are usually the first organisms to colonize a plain, a rock or a hill in the Namib. Since his first visit in 1986 he has been to Namibia nine times to study lichens. Prof. Wirth was a botanist at the State Museum of Natural History in Stuttgart from 1975 to 2001 and then became Director of the State Museum of Natural History in Karlsruhe, a post which he held until 2008. At the same time he was an Honorary Professor at the University of Hohenheim from 1994 to 2007. The enthusiastic lichenologist reckons that there are 200 to 250 species of lichen in the Namib Desert alone, scores of which have not been identified yet.
Author: Dirk Heinrich