Growth rates of Rhizocarpon geographicum: a review with new data from Iceland

Bradwell, Tom; Armstrong, R A. 2007 Growth rates of Rhizocarpon geographicum: a review with new data from Iceland. Journal of Quaternary Science, 22 (4). 311-320.

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This paper reviews evidence from previous growth-rate studies on lichens of the yellow-green species of Subgenus Rhizocarpon - the family most commonly used in lichenometric dating. New data are presented from Rhizocarpon section Rhizocarpon thalli growing on a moraine in southern Iceland over a period of 4.33 yr. Measurements of 38 lichen thalli, between 2001 and 2005, show that diametral growth rate (DGR, mm yr-1) is a function of thallus size. Growth rates increase rapidly in small thalli (<10 mm diameter), remain high (ca. 0.8 mm yr-1) and then decrease gradually in larger thalli (>50 mm diameter). Mean DGR in southern Iceland, between 2001 and 2005, was 0.64 mm yr-1 (SD = 0.24). The resultant growth-rate curve is parabolic and is best described by a third-order polynomial function. The striking similarity between these findings in Iceland and those of Armstrong ([1983]) in Wales implies that the shape of the growth-rate curve may be characteristic of Rhizocarpon geographicum lichens. The difference between the absolute growth rate in southern Iceland and Wales (ca. 66% faster) is probably a function of climate and micro-environment between the two sites. These findings have implications for previous lichenometric-dating studies, namely, that those studies which assume constant lichen growth rates over many decades are probably unreliable.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: BGS Programmes > Geology and Landscape Northern
ISSN: 0267-8179
Additional Keywords: lichenometry, Rhizocarpon section Rhizocarpon, climate, dating, Iceland
NORA Subject Terms: Ecology and Environment
Earth Sciences
Date made live: 25 Feb 2008 16:58 +0 (UTC)

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