The data has been collected from northern Finland between about 64th and 68th north latitudes, excluding the polar tree line areas. The sample plots have been selected to represents greatest variation of the habitats in altitude, rainfall and other site factors. The selected trees were cut, their age, height, and diameter at various heights examined and possible signs of forest fires noticed. The age of the trees was examined also with microscope. The age class distribution of the sample plots was studied. The determination of historical seed years was based on age class distribution of the sample plots.
Grouping of the trees into different age classes was too weak a method to make any conclusions about the periodicity or even less about the frequency of the seed years. There were also noticeable differences in determining the age of the trees between macroscopic and microscopic age examination. There are also differences in the amount of seedlings between different forest types.
The growth of pines in northern Finland is very slow particularly in the young ages but the growth increases after they reach 1,3 meters, which may take up to 30 years. The development of the forest has been similar through last centuries