Studies on the growth of Rhizocarpon geographicum in NW Scotland, and some implications for lichenometry

Citation

Bradwell T (2010) Studies on the growth of Rhizocarpon geographicum in NW Scotland, and some implications for lichenometry. Geografiska Annaler: Series A, Physical Geography, 92 (1), pp. 41-52. https://doi.org/10.1111/j.1468-0459.2010.00376.x

Abstract
Scotland, a maritime subpolar environment (55–60°N), has seen relatively few applications of lichenometry – even though it offers much potential. Perhaps surprisingly, direct measurements ofRhizocarpon geographicumgrowth rates in Scotland are so far lacking. This study reports on the growth of this crustose areolate species from two sites in Assynt, NW Scotland, between 2002 and 2009. Repeat photography of 23 non-competing thalli growing under identical environmental conditions on a single vertical surface over 5 years at Inchnadamph showed growth rates to be a function of size – with larger thalli (10–30 mm) growing significantly faster than the smallest thalli (<10 mm). Mean diametral growth rates in thalli >10 mm are 0.67 mm yr−1(s.d. = 0.16). Studies on a second vertical surface near Lochinver, over 7 years, yielded complex growth data on a more mature population ofR. geographicumthalli (<50 mm in diameter). Here, mean diametral growth rates in the larger thalli (>10 mm) are slower (0.29 mm yr−1; s.d. = 0.12) than those at Inchnadamph. However, at this site, competition with other species rules out any meaningful comparison of growth rates between the two sites. Other growth processes were monitored over the five to seven-year study period, including hypothallus growth, areolae development, thallus coalescence, and inter-species competition – all have important implications for the use ofRhizocarponspecies in lichenometry.

Keywords
lichenometry; direct measurement; growth rate; Assynt

Journal
Geografiska Annaler: Series A, Physical Geography: Volume 92, Issue 1