Short- and Long-Term Natural Trends of Scots Pine (Pinus sylvestris, L. ) Radial Growth in North- and Mid-Taiga Forests in Karelia

Abstract

Tree-ring data of Scots pine were collected in north-western Russia, in the Republic of Karelia, between the 62th and 65th latitudes. Due to the remote location and favourable position in regard to prevailing winds, the region is considered relatively free of airborne pollution.

The analysis of the dynamics of radial growth was based on separating of quasiperiodic components and approximating by a polyharmonic model. Forecasting increment dynamics was done by summing up the reliable harmonic constituents for a defined span of time.

In the north taiga, the occurrence of about 18- and 25-year periods is approximately equal. In the eastern mid-taiga subzone, the spectrum expansion shows a decrease in frequency corresponding roughly to a 22-year period. A temporal shift of approximately 30 years between stands in the north- and mid-taiga was observed. A 50-year fluctuation was also evident which coincided with noticeable increment decrease. The most noticeable increment decrease occurs when low- and middle-frequency cyclic components simultaneously reach the minimum. In the present century, a deep increment minimum took place around the year 1960 in the north taiga, and around the year 1990 in the mid-taiga. The lowest levels of increment variability in the mid-taiga subzone are close to the characteristic levels of variation in the north taiga.