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 preci pitation on average during a year in amounts insufficient for plant ge rmination and establishment. Major rainfall events which permit plant germination occur so infrequently that comparatively little is known a bout the relationship between biomass production and precipitation and the fate of biomass in this hyper-arid environment. Plant and inverte brate 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 change s in plant and invertebrate biomass in relation to rain and fog record s. The decline and distribution of biomass was different from that pre dicted by the previous study, most probably because the continued grow th of perennial plants on the dune slopes was not fully anticipated. S tipogrostis sabulicola and Trianthema hereroensis can imbibe fog and c ontinued 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 du ne slip faces and interdunes. (C) 1996 Academic Press Limited