Lichenometric dating (lichenometry) and the biology of the lichen genus rhizocarpon: challenges and future directions

Richard A. Armstrong*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Lichenometric dating (lichenometry) involves the use of lichen measurements to estimate the age of exposure of various substrata. Because of low radial growth rates and considerable longevity, species of the crustose lichen genus Rhizocarpon have been the most useful in lichenometry. The primary assumption of lichenometry is that colonization, growth and mortality of Rhizocarpon are similar on surfaces of known and unknown age so that the largest thalli present on the respective faces are of comparable age. This review describes the current state of knowledge regarding the biology of Rhizocarpon and considers two main questions: (1) to what extent does existing knowledge support this assumption; and (2) what further biological observations would be useful both to test its validity and to improve the accuracy of lichenometric dates? A review of the Rhizocarpon literature identified gaps in knowledge regarding early development, the growth rate/size curve, mortality, regeneration, competitive effects, colonization, and succession on rock surfaces. The data suggest that these processes may not be comparable on different rock surfaces, especially in regions where growth rates and thallus turnover are high. In addition, several variables could differ between rock surfaces and influence maximum thallus size, including rate and timing of colonization, radial growth rates, environmental differences, thallus fusion, allelopathy, thallus mortality, colonization and competition. Comparative measurements of these variables on surfaces of known and unknown age may help to determine whether the basic assumptions of lichenometry are valid. Ultimately, it may be possible to take these differences into account when interpreting estimated dates.

Original languageEnglish
Pages (from-to)183-206
JournalGeografiska Annaler: Series A
Issue number3
Early online date30 May 2016
Publication statusPublished - Sept 2016

Bibliographical note

This is the peer reviewed version of the following article: Armstrong, R. A. (2016). Lichenometric dating (lichenometry) and the biology of the lichen genus rhizocarpon: challenges and future directions. Geografiska Annaler: Series A, Early view., which has been published in final form at This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.


  • competition
  • development
  • growth rate/size curve
  • lichenometry
  • mortality
  • rhizocarpon
  • senescence


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