An Investigation of the Role of Water (Rain and Dew) in Controlling the Growth Form of Lichens on Cobbles in the Negev Desert

Abstract Dew and rain were measured along the north facing slope (NFS, with epilithic lichens predominating) and the south-facing slope (SFS, with endolithic lichens predominating) in the Negev (P = 95 mm) in order to evaluate the relationships between the abiotic conditions and the lichen growth form. Although insignificant differences characterize the rain and dew amounts with the epilithic growth form, high correlation was obtained between dew duration (r2 = 0.73) and the combined duration of dew and rain (r2 = 0.79). The data imply that daylight wetness duration rather than the amount of precipitation may explain the predominance of epilithic lichens at the shaded NFS. Keywords: dewendolithic and epilithic lichenscobblesNegev Desert ACKNOWLEDGMENTS The study was supported by grant 1358/04 of the Israel Science Foundation (ISF). We would like to thank Shimon Tal for most valuable technical assistance, Michal Kidron for the drawing, Carol A. Kidron for the editing and two anonymous reviewers for their most helpful comments.