Annual rings of birch (Betula pubescens ssp tortuosa (Ledeb) (Nyman)), climate and defoliation: an exploratory study

The suitability of mountain birch as a subject for tree ring analysis was explored in a study near Jankajarvi based on a small number of samples and published monthly summaries of climatic data. Examination of the distribution of annual wood formation along the stem, in the form of annual growth layer profiles, gave inconclusive results, but significant correlations were obtained between climatic variables and ring indices derived from horizontal ring-width sequences. Simple correlations were significant only with measures of temperature, of which maximum temperature wss the most important. Highest correlations were with average maximum temperature of June and July of the year of ring formation and August of the previous year. Discussion of the results in relation to independent observations of birch growth in general, to defoliation and to the sub-arctic environment leads to the general conclusion that ring analysis could make a significant contribution to the study of birch - climate - defoliaton interactions, but relationships with climate and with defoliation require to be examined in more detail than in the present study.