Variations in Lichen Growth from Direct Measurements: Preliminary Curves for Alectoria Minuscula from Eastern Baffin Island, N. W. T., Canada

Abstract

Direct measurement of thallus area of the subfruticose lichen Alectoria minuscula from eastern Baffin Island allows construction of preliminary lichen growth curves for this area. The tracing method of determining thallus diameters is accurate within ±0.5 mm, whereas the photogrammetric method is accurate within ±0.1 mm and is capable of even greater precision. The form of the growth curve for A. minuscula is sigmoidal with an average diameter increase ranging from 0.6 to 1.0 mm year-1. Previously published curves for this species are similar to the empirically derived curve presented here. There appears to be a decrease in the rate of growth with elevation which underlines the immediate necessity of establishing growth stations in selected localities for areas in which lichenometry is employed. With the accuracy of the photogrammetric technique, growth of even the slowest growing species (i.e. Rhizocarpon geographicum) should be detectable within a decade (0.3 mm diameter increase) and within two to three years for faster growing species.