*2.6. Data Correction*

The green-up date of *Q. mongolica* derived from digital camera and MODIS satellite images showed a difference depending on the study site. According to [69], increases in latitude of 1◦ N, longitude of 1◦ E, and altitude of 100 m result in delays of 2.6 ± 0.2 days, 0.6 ± 0.1 days, and 2.1 ± 0.2 days, respectively, in the leaf unfolding date. Based on this information, we corrected the difference in leaf unfolding dates due to differences in latitude, longitude, and altitude among the study areas.

On the other hand, we designated the Mt. Jeombong site as the reference site to clarify the effect of urbanization. Mt. Jeombong maintains a healthy and integrated stand of *Q. mongolica* as it is designated as a reserve by the Korea Forest Service and thereby escapes artificial interferences. Based on the Mt. Jeombong data, the expected dates of green-up were obtained by reflecting the geographic and topographic location of each study site. The effect of urbanization on plant phenology in each study area was determined by comparing the differences between the expected and observed dates of green-up in each site.

#### *2.7. Weather Factor Collection and Analysis*

To analyze the correlation between phenological events and weather factors and identify the weather conditions at the time of major phenological phases, the atmospheric temperature measurement instrument HOBO (HOBO Pro v2 Temp/RH Temp, Onset Computer,

Bourne, MA, USA) was installed. The temperature was measured every 30 minutes every day, and the data measured at 12:30 were used due to compatibility with the digital camera.

Based on the collected weather data, AGDD (accumulated growing degree days) were calculated to analyze the temperature threshold of the plant's green-up period. The formula for calculating AGDD is as follows:

$$\sum\_{\Lambda}^{n} \frac{T\_{\text{max}} + T\_{\text{min}}}{2} - T\_{\Lambda} \left( T \ge 5 \, ^\circ \text{C} \right) \tag{6}$$

where *Tmax* and *Tmin* are the maximum and minimum air temperatures, respectively, and *T*Δ is the temperature below which plant growth is zero. In this study, we assumed a minimum temperature threshold of 5 ◦C for enzymatic activity in *Q*. *mongolica* based on studies of [70,71].
