Precipitation and biomass changes in the Namib Desert dune ecosystem

Parts of the Namib Desert receive 19 mm of rain and 35 mm of fog precipitation on average during a year in amounts insufficient for plant germination and establishment. Major rainfall events which permit plant germination occur so infrequently that comparatively little is known about the relationship between biomass production and precipitation and the fate of biomass in this hyper-arid environment. Plant and invertebrate biomass sampling has previously been conducted in 1975 and 1976 preceding and following an exceptionally wet period when over 80 mm of rain fell in a few weeks. We used the same study area and equivalent methods to repeat the sampling in 1985 and 1991 and examine the changes in plant and invertebrate biomass in relation to rain and fog records. The decline and distribution of biomass was different from that predicted by the previous study, most probably because the continued growth of perennial plants on the dune slopes was not fully anticipated. Stipogrostis sabulicola and Trianthema hereroensis can imbibe fog and continued to contribute biomass to the system while nothing else could grow; in addition, the presence and structure of these plants probably trapped detritus which otherwise would have been blown between the dune slip faces and interdunes.