The effect of different stand density on diameter growth response in Scots pine stands in relation to climate situations

The effect of stand density on the resistance of Scots pine (Pinus sylvestris L.) to climatic stress and subsequent response of diameter increment were investigated using data gathered from six long-term experimental series located in the typical pine regions of the Czech Republic (sandy nutrient-poor soils on the Pineto-Quercetum oligotrophicum-arenosum). Diameter growth of dominant individuals (with the largest diameter at the age before the first thinning) was measured in all variants of experimental series (control and thinned). Monthly average temperature and total precipitation were taken from the nearest climatological stations and, additionally, three climatic factors (precipitation and temperature ratio in different periods) were calculated. Diameter growth responses were analyzed in connection with long-term deviations of climatic characteristics. The effect of different stand density on diameter growth response in relation to climate situations was evaluated by cluster analysis and the variability of diameter growth response to climate situations was interpreted by the variance of correlation coefficients in groups of sample trees. The investigation confirmed the significant negative effect of meteorological drought on diameter increment of studied pine stands in the period of the last 30 years. At the same time, we observed a significant positive influence of higher spring (February, March) air temperatures on the annual diameter growth of dominant trees. The effect of stand density (in thinned stands) on the relation between diameter growth and climatic characteristic was not significant.