Lichenometry

Abstract

Developed approximately 50 yrs ago [2], lichenometry has mainly been used by earth cientists to estimate the timing of (and hence monitoring) prehistoric glacial advances, landslides and other geomorphological events. The technique has been especially useful in monitoring polar and alpine environments where eyewitness or documentary accounts are lacking and other methods of dating (e.g. ¹⁴C analysis, dendrochronology) are unavailable or yield ambiguous results. When critically applied, lichenometry can provide quick, accurate, reproducible minimum ages for surfaces over a period of the last three centuries. However, because lichenometric ages are not always close estimates of actual age, they are termed as such and require verification using documentary sources or independent dating techniques to relate them to real time. There is no formula or standard practice that will ensure accurate lichenometric ages under all circumstances. Prior to field work, potential users should review and tentatively select one of the many sampling strategies that are described [9, 10, 11]. They should also examine the assumptions and criticisms of the technique recently reviewed by McCarthy [12]. Three methods are set out below. The first is based on the biodiversity of lichens which occur on surfaces, and because some species are late colonisers they are also indicators of long term exposure of a surface. The second and third are based on the growth rates of individual lichen thalli which are presumed to have colonised the surface when, or soon after, it was first exposed.