SEASONAL GROWTH OF FOLIOSE LICHENS IN SUCCESSIVE YEARS IN SOUTH GWYNEDD, WALES

The aim of this study was to test the hypothesis that differences in the pattern of seasonal growth in foliose lichens from year to year were determined by yearly differences in the distribution of rainfall, shortwave radiation and temperature. Hence, the radial growth of Parmelia conspersa (Ehrh. ex Ach.)Ach., P. glabratula ssp. fuliginosa (Fr. ex Duby) Laund. and Physcia orbicularis (Neck) Poetsch. was studied on slate fragments over 34 successive months in an area of South Gwynedd, Wales, U.K. Similarities and differences were observed in the pattern of seasonal growth in the three species. Periods of maximum growth of a species occurred in different seasons in successive years. Correlation and multiple regression analyses suggested that total rainfall per month was the most important climatic variable positively correlated with monthly growth. Significant positive correlations were found in some growth periods with number of raindays per month, average windspeed and maximum and minimum temperature. Total number of sunshine hours per month and the frequency of ground frosts were negatively correlated with monthly growth in some growth periods. For each species, monthly radial growth was correlated with different climatic variables in each growth period. Hence, the results support the hypothesis in that periods of maximum growth can occur in any season in South Gwynedd and depend on (1) the distribution of periods of high total rainfall and (2) whether or not these periods coincide with periods of maximum sunlight.