The effects of heavy winter rains and rare summer rains on biological soil crusts in the Negev Desert

Biological soil crusts (BSCs) abound in the Hallamish dune field in the western Negev Desert, Israel. While their abundance may imply high adaptability to environmental change, such as fluctuations between wet and dry conditions following winter rains, summer rains, although rare, may also occur in the Hallamish dune field. The aim of the present paper is to examine crust responses to winter and summer rains, focusing particularly on its biomass components, chlorophyll and carbohydrate. In addition, species composition, during summer and winter was examined. Analysis took place during an exceptionally wet winter (1994/95 with 172. mm) and a summer rainstorm (12.5.93 with 9.7. mm). The data showed a 2-3 fold increase in chlorophyll a and total carbohydrates and a much richer species composition following the heavy winter rains of 1994/95. Yet, the data also showed ~. 15-30% decrease in the chlorophyll content of the crust (with no concomitant significant decrease in total carbohydrates) following the summer rainstorm. Intense weathering by the summer rain coupled with cell mortality may explain the decrease in the chlorophyll content following the summer rainstorm, suggesting possible changes in the BSC following a potential change in the precipitation regime due to global climate change.