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Fig. 1. Location of the study site (black square, 56°27´N, 22°54´E).

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Fig. 2. Weather conditions (monthly mean (solid line), absolute minimum and maximum (dotted lines) temperature and precipitation sums (bars)) from March to November of 2010 (A) and 2011 (B), recorded in meteorological station located at 2 km distance from the study site.

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Fig. 3. Mean height of clones of hybrid aspen with early, intermediate and late leaf flushing phenology in the beginning (17.05.2010, white boxes) and at the end (10.10.2011, grey boxes) of the increment monitoring period. Median is shown by the bold line, box corresponds to lower and upper quartile, whiskers show minimum and maximum values (within 150% of interquartile range from the median) and circles represent outliers of the datasets.

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Fig. 4. Mean daily height increment for growing seasons of 2010 and 2011 for clones of hybrid aspen with early, intermediate and late leaf flushing. Median is shown by the bold line, box corresponds to lower and upper quartile, whiskers show minimum and maximum values (within 150% of interquartile range from the median) and circles represent outliers of the datasets.

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Fig. 5. Mean daily height increment of clones of hybrid aspen with early, intermediate and late leaf flushing phenology, calculated for periods between measurements for growing seasons of 2010 and 2011. Asterisks indicate significance (p-value < 0.05) of differences of height increment among groups of clones with differing phenology of leaf flushing.

Table 1. Significant variables, their coefficients and significance, and main statistics for developed equations of height increment of hybrid aspen based on weather variables and duration of growth (as HI = ax1 + bx2 +...+ intercept, where x1, x2 etc. are the significant parameters and a, b, etc. are coefficient values) showing the best fit to HI. Equations for data of 2010, 2011 and both years are shown. PET – potential evapotranspiration.
Early leaf flushing
2010 2011 Both years
Variable Coeff. p-value Variable Coeff. p-value Variable Coeff. p-value
Intercept 0.142 0.719 Intercept –1.908 0.023 Intercept –0.782 0.060
Mean temp. 0.116 <0.001 Mean temp. 0.274 <0.001 Mean temp. 0.192 <0.001
Temp. sum
( > 5 °C) 		–0.003 0.033 Temp. sum
( > 5 °C) 		–0.007 0.038 Temp. sum
( > 5 °C) 		–0.007 <0.001
Day of growth –0.006 0.032            
AIC –29.2     –19.97     –38.69  
F-statistic 16.51     15.94     24.15  
R-squared 0.81     0.69     0.62  
Adjuster R-squared 0.76     0.65     0.59  
Residual standard error 0.34     0.53     0.53  
Intermediate leaf flushing
2010 2011 Both years
Variable Coeff. p-value Variable Coeff. p-value Variable Coeff. p-value
Intercept –0.684 0.061 Intercept –1.201 0.186 Intercept –1 0.026
Mean temp. 0.159 <0.001 Mean temp. 0.396 <0.001 Mean temp. 0.208 <0.001
Temp. sum
( > 5 °C) 		–0.005 0.002 Solar
radiation 		1.165 0.004 Temp. sum
( > 5 °C) 		–0.007 <0.001
      PET –3.409 0.003      
AIC –27.62     –20.66     –34.62  
F-statistic 21.89     15.47     24.74  
R-squared 0.78     0.77     0.62  
Adjuster R-squared 0.75     0.72     0.6  
Residual standard error 0.36     0.51     0.57  
Late leaf flushing
2010 2011 Both years
Variable Coeff. p-value Variable Coeff. p-value Variable Coeff. p-value
Intercept –1.082 0.009 Intercept –1.169 0.265 Intercept –0.312 0.617
Mean temp. 0.174 <0.001 Mean temp. 0.489 <0.001 Mean temp. 0.337 <0.001
Temp. sum
( > 5 °C) 		–0.005 0.006 PET –4.475 0.002 PET –3.354 0.003
      Solar
radiation 		1.389 0.006 Solar
radiation 		1.038 0.005
AIC –26.02     –12.76     –22.75  
F-statistic 23.6     12.18     12.81  
R-squared 0.8     0.72     0.57  
Adjuster R-squared 0.76     0.66     0.53  
Residual standard error 0.38     0.64     0.67