Lichen growth may be interrupted or terminated by sudden slope movements, or the encroachment of vegetation.
I investigated its use in the age estimation of relatively recent Austrian Alpine petroglyphs in 1965, but later neglected to develop my experience further. The preferences of geomorphologists are attributable merely to the method’s rather short effective time range: it can only be expected to provide valid data from the most recent millennia, and is particularly precise for ages in the order of up to some centuries.The extensive literature of geomorphic applications of the technique conveys the impression that the applicability of this method is limited to subpolar or alpine conditions, i.e. Although in favourable cases the method has been suggested to be effective to 9000 years BP and possibly even beyond (Miller and Andrews 1972), it is commonly only precise up to 500 or so years (Innes 1985).In geomorphological terms this makes it particularly useful for recent glacial deposits.In the direct approach, growth rates are determined by monitoring individual thalli over several years, typically of yellow-green specimens (subgenus Rhizocarpon geographicum agg.) which have provided the best results and are often abundant.The growth curves predict the thallus size through time.