Size Variation of Rhizocarpon on Moraine Slopes in Southern Norway

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Abstract
The Rhizocarpon green zone hypothesis states that maximum thallus diameters of the yellow species in this taxon are largest at the foot of the proximal slopes of moraine ridges. The hypothesis is tested by data from 2 glacial forelands: Storbreen in the Jotunheimen and Nigardsbreen in the Jostedal, Norway. The results support the green zone hypothesis and suggest that the phenomenon is mainly due to the behavior of R. geographicum. It is generally presumed that the proximal slope of any 1 moraine is of a uniform age. Therefore, the existence of a zone where mean maximum thallus diameters are larger than elsewhere on the proximal slope is considered to have important implications for the use of this species group for lichenometric dating.