Klimešová J., Klimeš L. & Kyncl J. 1997. Věková struktura olše a břízy v olšině „Na bahně" [Age structure of Alnus glutinosa and Betula pubescens in the alder carr „Na bahně" (E. Bohemia, Czech Republic)]. Příroda 11: 83-91
Vegetation changes in the Natural Monument „Na bahně“ in the past 75 years were recorded in phytosociological literature: in 1924 the peat bog in the centre of the protected area was surrounded by an alder carr. From 1924 to 1962 the peat bog was overgrown by Alnus glutinosa. We aimed at verifying the literature data on vegetation chages by tree-ring analysis. Along a transect across the alder carr which was about 140 m long, two cores were taken from randomly selected trees with Pressler increment borer at cca 1.3 m height. In Alnus glutinosa we counted 34 to 97 tree rings. Age distribution showed two peaks with maximum at about 34 and 90 years (n = 80). The age of Betula pubescens varied between 54 and 99 years (n = 16). It follows from the results of the age structure of Alnus glutinosa that the establishment of the alder carr was not a continuous process. There were two periods of Alnus establishment, corresponding to the two peaks of the age-distribution. In 1880s the current forest margins was established. The centre of the locality was overgrown by the alder carr between 1930 and 1940. The regression line describing the relationship between trunk girth and tree age has the same slope for Alnus glutinosa and Betula pubescens. However Betula pubescens had smaller trunk girths than Alnus glutinosa at the same tree age. It was probably caused by suppressed growth of young Betula trees. The increments of Alnus glutinosa depended on summer temperatures. Betula pubescens showed a high mortality. If the canopy of the alder carr is opened due to mortality of old trees little changes in tree composition are expected as neither light nor moisture conditions are suitable for establishment of Alnus glutinosa seedlings.