Diameter increment of beech in relation to social position of trees, climate characteristics and thinning intensity

1Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Prague, Czech Republic 2Forestry and Game Management Research Institute, Jíloviště-Strnady, Opočno Research Station, Opočno, Czech Republic ABSTRACT: We present the results of research on diameter increment in beech stands in the area of Hostýnské and Vsetínské vrchy. The data were collected on three series of permanent research plots (PRP) in middle-aged stands in the property of BFP Forests and Estates of Tomas Baťa, Ltd. established for the evaluation of the effect of different thinning regimes. Each series consists of one control plot and two plots with different treatment intensity. The objective of this paper was to assess the increment response of beech individuals in the first year after a thinning intervention and to evaluate the increment of sample trees in relation to the social position of tree in the stand and the climate trends in the last 30 years. The diameter increment was evaluated on harvested sample trees, after the thinning treatment the growth reaction of standing sample trees of the main stand was evaluated based on their dendrometric characteristics. To calculate the radial growth of beech, the annual ring increment series were cross-dated individually (to eliminate errors caused by missing annual rings) using statistical tests in the PAST4 application software (Knibbe 2007) and then subjected to visual inspection according to Yamaguchi (1991). If a missing annual ring was found, a ring 0.01 mm wide was inserted in its place. The individual curves from PRPs were then detrended and an average annual ring series was created in the ARSTAN software. First a negative exponential spline was used, and then the 30-year spline was applied (Grissino-Mayer et al. 1992). The response of tree radial growth to climatic factors was evaluated using the DendroClim software. The method of single pointer years analysis was used to estimate the influence of extreme climatic events on diameter growth. One year after thinning, the harvest intensity had no significant effect on the radial growth of dominant trees (F(4, 293) = 1.0, P > 0.05), but oppositely, differences in the average diameter increment of co-dominant trees on PRPs were statistically significant (F(4, 362) = 2.6, P < 0.05). The diameter increment of dominant trees in 1978-2013 showed positive correlations with the March temperatures of the current year (r = 0.27) and negative ones with June-September (r = -0.28 to -0.43) and November (r = -0.36) of the last year and April, June and July (r = -0.35 to -0.44) of the current year. Negative correlations of temperature in the growing season of the current year were similar to dominant trees, only the impact was weaker in April to August (r = -0.28 to -0.32). According to the results of the PCA analysis, annual ring width was negatively correlated with temperatures in the vegetation season of the last year and current year, July, April and June temperature of the current year, and with precipitation in January-March of the current year.