Remote sensing the distribution and spatiotemporal changes of major lichen communities in the Central Namib Desert

Abstract

Biological Soil Crusts (BSCs), composed of lichens, mosses, green algae,microfungi and cyanobacteria are an ecological important part of the perennial landcover of many arid andsemiarid regions (Belnap et al. 2001a), (Büdel 2002). In many arid and hyperarid areas BSCsform the only perennial "vegetation cover" largely due to their extensive resistance to drought(Lange et al. 1975).For the Central Namib Desert (Namibia), BSCs consisting of extraordinary vast lichen communitieswere recently mapped and classified into six morphological classes for a coastal areaof 350 km x 60 km. Embedded into the project "BIOTA" (www.biota-africa.org) financed bythe German Federal Ministry of Education and Research the study was undertaken in theframework of the PhD thesis by Calreadybeen studied concerning their ecology and diversity in the past (Lange et al.1994), (Loris &Schieferstein 1992), (Loris et al. 2004), (Ullmann & Büdel 2001a), (Wessels 1989). Multispectral LANDSAT 7 ETM+ and LANDSAT 5 TM satellite imagery was utilized for anunitemporal supervised classification as well as for the establishment of a monitoring based ona combined retrospective supervised classification and change detection approach (Bock 2003),(Weiers et al. 2003). Results comprise the analysis of the mapped distribution of lichen communitiesfor the Central Namib Desert as of 2003 as well as reconstructed distributions for theyears 2000, 1999, 1992 and 1991 derived from retrospective supervised classification.This allows a first monitoring of the disturbance, destruction and recovery of the lichen communitiesin these arid environments including the analysis of the major abiotic processesinvolved. Further analysis of these abiotic processes is key for understanding the influence ofNamib lichen communities on overall aeolian and water induced erosion rates, nutrient cycles,water balance and pedogenic processes (Belnap & Gillette 1998), (Belnap et al. 2001b), (Belnap2001c), (Evans & Lange 2001), (McKenna Neumann & Maxwell 1999).In order to aid the understanding of these processes SRTM digital elevation model data as well as climate data sets were used as reference. Good correlation between geomorphological form elements as well as hydrological drainage system and the disturbance patterns derived from individual post classification change comparisons between the timeframes could be observed.Conjoined with the climate data sets sporadic foehn-like windstorms as well as extraordinaryprecipitation events were identified to largely affect the distribution patterns of lichen communities.Therefore the analysis and monitoring of the diversity, distribution and spatiotemporal changeof Central Namib BSCs with the means of Remote Sensing and GIS applications proof to beimportant tools to create further understanding of desertification and degradation processes in these arid regions