Microclimate control upon sand microbiotic crusts, western Negev Desert, Israel

Approximately 208 of the world's arid zones are covered by eolian sand. Par ts of the sand are occupied by microbiotic crusts or have the potential of sustaining microbiotic crusts, which may have a great impact upon geomorpho logical processes and the ecology of the ecosystem. Any attempt to understa nd the distribution of microbiotic crusts inevitably necessitates knowledge concerning the microclimate within these ecosystems and in particular mois ture, temperature, and eolian input. In the Hallamish dune field in the wes tern Negev Desert, Israel, cyanobacterial crusts with a chlorophyll a conte nt of 15-20 mg m(-2) characterizes the south-facing footslopes, whereas a m oss-dominated crust with a chlorophyll a content of 50-60 mg m(-2) covers t he north-facing footslopes. Since the entire dune field was re-stabilized c oncurrently, following the 1982 peace treaty with Egypt, it was hypothesize d that physical conditions, rather than time duration, may account for the differences observed. Microclimatological data, which included temperature, rainfall, runoff, dew and fog, surface moistness and eolian input were mon itored. The differences in crust type could not have been attributed to rai nfall, dewfall, temperatures, or eolian input. Although lower amounts of in cident rain, lower temperatures and lower eolian input characterized the mo ss-dominated north-facing footslope, moss-dominated crusts were also found in restricted areas of high temperatures and eolian input at the interface between the mobile and the encrusted dune section of the south-facing aspec t. High variability in daytime moisture duration following rain was however monitored with surface moisture duration being approximately 2.5 times lon ger at the moss-dominated habitat. These differences are seen responsible f or crust-type distribution within the ecosystem, which may affect, in turn, variable geomorphological processes. (C) 2000 Elsevier Science B.V. All ri ghts reserved.