The use of lichen growth rings in lichenometry: Some preliminary findings

Citation

Armstrong RA & Bradwell T (2010) The use of lichen growth rings in lichenometry: Some preliminary findings. Geografiska Annaler: Series A, Physical Geography, 92 (1), pp. 141-147. https://doi.org/10.1111/j.1468-0459.2010.00383.x

Abstract
Certain species of crustose lichens have concentrically zoned margins which probably represent yearly growth rings. These marginal growth rings offer an alternative method of studying annual growth fluctuations, establishing growth rate–size curves, and determining the age of thalli for certain crustose species. Hence, marginal growth rings represent a potentially valuable, unexploited, tool in lichenometry. In a preliminary study, we measured the widths of the successive marginal rings in 25 thalli ofOchrolechia parella(L.) Massal., growing at a maritime site in north Wales. Mean ring widths of all thalli varied from a minimum of 1.02 mm (the outermost ring) to a maximum of 2.06 mm (the third ring from the margin). There is some suggestion that marginal ring width and thallus size are positively correlated; and hence that growth rates increase in larger thalli in this small population. In a further study on recently exposed bedrock adjacent to Breiðarlon, SE Iceland, we examined the potential for using marginal growth rings to estimate thallus age of a lichen tentatively identified as aRhizocarpon(possiblyR. concentricum(Davies) Beltram.) and thus confirm the timing of surface exposure (c.50 years). Collectively, these results suggest: 1) the measurement of marginal rings is a possible alternative method of studying the growth of crustose lichens; 2)O. parellamay grow differently to other crustose species, exhibiting a rapidly increasing radial growth rate in thalli >40 mm; 3) where lichens with marginal rings grow on recently exposed surfaces (<60 yrs), minimum age estimates can be made using growth rings as anin situindication of lichen growth rate; 4) it is suggested that this phenomenon could provide a valuable, previously unexploited,in situlichenometric-dating tool in areas lacking calibration control.

Keywords
Ochrolechia parella (L.) Massal.; Rhizocarpon; marginal growth ring; radial growth rate; age–size curve; lichen-dating

Journal
Geografiska Annaler: Series A, Physical Geography: Volume 92, Issue 1