Table 1.
The symbols and units of the variables and parameters used in the equations of the studied models.
Figure 1.
Frequency distribution of budburst dates of the experimental trees for the three studied species.
Frequency distribution of budburst dates of the experimental trees for the three studied species. The number of saplings for a given budburst date is presented on the Y-axis. The small photos on the upper right part of each panel visually show the stage of leaf development when we considered budburst to have occurred.
Figure 2.
Budburst response to different warming treatments.
Budburst response to different warming treatments: W0S0: no warming; W6S6: winter and spring warming; W6S0: winter warming only, and W0S6: spring warming only (winter is from December 1 2009 to February 22 2010 and spring from February 22 to budburst date). The delta temperature was calculated as the average difference between treatments and outside controls from December 1st to the day of observed budburst for three warming treatments. Because the period with warming in spring was shorter than the period with warming in winter, the W0S6 treatment experienced less warming on average than the W6S0 treatment. Especially for birch, the earliest flushing species, this difference was pronounced. The different letter close to the symbols denote a significant difference (at P<0.05) among treatments for each species, separately.
Table 2.
Root mean square error (RMSE), model efficiency (ME) and Akaike's Information Criterion (AIC) of model validation for the five models and the three study species.
Figure 3.
Comparison of the observed budburst dates with the predicted values for five models.
Comparison of the observed budburst dates with the predicted values for five models fitted on the whole observation dataset. Data are for three species. The diagonal line is the 1∶1 line, whereas RMSE is the Root Mean Square Error.
Figure 4.
Modeled against observed budburst dates for different warming treatments.
Modeled against observed budburst dates for different warming treatments (W0S0: no warming; W6S6: winter and spring warming; W6S0: winter warming only, and W0S6: spring warming only; winter is from December 1 2009 to February 22 2010 and spring from February 22 to budburst date) when using the Sequential model and the Thermal time model for each species. The models were fitted on the whole observation dataset. The observed budburst dates are represented by open symbols and the predicted budburst dates are represented by solid symbols.