Vortrag, Gesellschaft für Ökologie (GfÖ), 37. Jahrestreffen, Marburg: 12.09.2007 - 15.09.2007
The main aim of our work, carried out in the context of the BIOTA Africa project, is to assess the diversity of lichens forming biological soil crusts at BIOTA observatories in Southern Africa, to analyze diversity shifts due to differences in climate, soil type and land use, to identify the indicator value of lichen taxa, morphological groups and lichen characters, and finally to develop a long-term monitoring approach of environmental changes using lichens as bioindicators. Studies on soil lichens in Namibia have been hitherto restricted to the Namib desert, while the lichen-mycota of other parts of Namibia is mostly unexplored. The diversity of soil lichens has been compared at different observatories located in central Namibia. Most of them host no lichens, mostly due to unfavourable climate and soil conditions. Hitherto, it was known that lichen diversity decreases from the coast of central Namibia to inland due to increasing xerophytic conditions. In this study it was however observed that the observatories richest in species are Wlotzkasbaken (placed along the coast of the central Namib) and Duruchaus and Narais (inland, close to Rehoboth). The richness at Duruchaus and Narais appear to be mainly due to the presence of calcareous soils. Along the coast, relative air humidity is also an important factor influencing lichen richness. In both cases, different kinds of human impact can reduce lichen richness. In Duruchaus and Narais 13 taxa of soil lichens are remarkably found: 4 of them are recorded as new to southern Africa, and 7 reported for the first time from Namibia. Even if the observatory of Wlotzkasbaken and the two close to Rehoboth have similar number of taxa, the composition of lichen mycota and the distribution of lichen characters are quite different. Squamulose and peltate lichens are dominant at Duruchaus and Narais, while foliose and fruticose lichens are very rare and only show reduced forms. On the contrary, crustose, large foliose and fruticose lichens are abundant in Wlotzkasbaken. Cyanobacteria are the dominant photobiont type (75% of taxa) at Duruchaus and Narais, while green algae are the only photobionts occurring in the lichen mycota of Wlotzkasbaken. Lichens have fairer and multicoloured thalli along the coast of the Namib Desert in comparison to the up-country observatories, where lichens are mostly dark coloured. These differences denote a clear adaptation to different environmental conditions.