Abstract:
Lichenologists and users of lichenometry have long used calipers or
photogrammetry to measure the growth of crustose lichens. Now, digital photography
and popular computer software provide methodological alternatives. This thesis
developed and tested a new methodology for tracking change and growth of the lichen,
Rhizocarpon geographicum. Adobe Photoshop CS3 Extended software and a
photographic time series (1996,2003,2006 and 2007) were used to measure thallus
diameter, area, prothallus width and areolae area in 115 small R. geographicum thalli
(0.53-1049.88 mm2
). Measures of 8 diameters per thallus showed that change in diameter
was highly variable and is a weak index of growth. Thallus area was a reliable measure of
growth (power correlation, R2 = 0.89). Rapid, highly irregular growth occurred in small
thalli «30 mm2
), and steady, uniform growth occurred in larger thalli (>30 mm2
). This
new methodology is tedious but can potentially generate accurate and precise measures
for even the tiniest of lichens.
