Abstract
The growth of a lichen, Trapelia ornata (Sommerfelt) Hertel, exposed to variations of chronic gamma irradiation stress throughout its life was studied. Tracings of lichen colonies were made on plastic sheets and the average radial growth was determined for each of 52 colonies. Two regressions analyses were performed, the first one for maximum annual radial growth and the second for average annual radial growth. A minimum average annual growth rate of 4·02 mm for non-irradiated T. ornata colonies was extrapolated from the first regression analysis while a mean average annual radial growth rate for non-irradiated colonies of 2·58 mm was extrapolated from the second regression line. The general effects of chronic ionizing radiation stress on T. ornata were a decrease in growth rate and a reduction in growth rate variability.
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