Vortrag, Gesellschaft für Ökologie (GfÖ), Halle: 08.09.2003 - 12.09.2003
The present study was carried out in the context of the BIOTA Southern Africa project (subprojects S04 and S05.3). The main aim of these subprojects is the assessment of lichen diversity and the characterization of lichen communities forming biological soil crusts at the BIOTA observatories along a climatic gradient from Northern Namibia to the Cape Peninsula. Particular reference is given in this presentation to the observatories of the Knersvlakte in the succulent karoo biome (26 Flaminklavlakte 111, 27 Luiperskop, 28 Moedverloren). These observatories are characterized by a high coverage of quartz pebbles on soil and a particular lichen flora extraordinary rich for semi-arid areas, especially in comparison to that recorded at other observatories along the BIOTA transect. In spite of the low annual average precipitation (about 100-125 mm/year), the area is interested by fog events, which are most favourable for the lichen growth. Lichen specimens were collected for identification throughout the three observatories and soil-growing communities were studied by taking digital images. A comparison of the lichen diversity between the observatories of the Knersvlakte and other BIOTA observatories is presented. The relative frequency occurrence of the various lichen growth-forms is shown. A first characterization of the different lichen communities from the quartz fields is attempted. The main factors conditioning negatively the presence of lichen communities in this area seem to be the coverage degree of quartz pebbles, the high soil salinity, the trampling by animals and the instability of substrates close to and within dry river beds. Trampling by domestic animals has highly disturbing effects on soil-growing lichen communities which, under such conditions, are restricted to sheltered sites under shrubs.