Growth Curves for Calcium-tolerant Lichens in the Canadian Rocky Mountains

Abstract

Lichen growth curves have been compiled from measurements of Xanthoria elegans (Link) Th. Fr. and Aspicilia Candida (Anzi.) on tree-ring dated moraines and historically dated structures in the vicinity of Peter Lougheed and Elk Lakes Provincial Parks, Alberta and British Columbia. The newly calibrated growth curve for X. elegans and the previously published growth curve estimate radial growth rates of 0.5 mm yr⁻¹ for the first century. However, the new data show that the growth curve developed by Osborn and Taylor (1975) underestimates radial growth rates and overestimates substrate age beyond 150 yr. It should be replaced by the newly constructed curve.

Aspicilia Candida has lichenometric potential on carbonate-rich moraines in the front ranges of the Canadian Rockies. It has an ecesis of approximately 90 yr, followed by a maximum average growth of 0.9 mm yr⁻¹ for at least 60 yr. It is not known if the species has lichenometric potential beyond approximately 150 yr. More data are needed to better establish whether regional variations in growth and growth rates exist beyond the calibrated period.