Local Chronologies and Regional Diversity of Dendrochronological Signal of Douglas Fir in Poland

In Poland, 50 sites of Douglas fir were selected for which tree-ring chronologies were computed. Douglas fir in different parts of Poland has a specific increment rhythm, on the basis of which the four homogeneous dendrochronological zones were distinguished. The first zone (I) comprises Pomerania, Baltic coast, Warmia, and Mazuria (lowlands of northern Poland), the second zone (II) - Great Poland, Lower Silesia (lowlands of central Poland), the third zone (III) - the Sudetes and the Carpathian mountains, and the fourth zone (IV) - foothills of the Carpathians Mts., Roztocze, and the Świętokrzyskie Mts. (uplands of southern Poland). These areas are called the dendroclimatic zones because different thermo-pluvial conditions of the summer season were a cause of diversification of the Douglas fir increment rhythm, and in consequence of its chronology. A high similarity of site chronologies of a given region permitted to construct regional tree-ring chronologies for respective zones. Thermal conditions of the winter season (February - March) were the factor most strongly and similarly affecting radial increment of Douglas fir populations in the entire territory of Poland. This factor caused that all chronologies showed many similar traits in their progress. This fact permitted to construct the supra-regional (all-Polish) tree-ring chronology for this tree species. It comprises the period from 1900 to 2000, and it is a good standard for dating Douglas fir wood samples originating from the area of Poland.