**5. Conclusions**

Climate change is rapidly progressing. The most important anthropogenic influences on climate are the emission of greenhouse gases and changes in land use such as urbanization, but the importance of the latter is increasingly being highlighted.

Urbanization is one of the major social changes that have spread around the world. Urbanization is happening rapidly at an unprecedented rate, and the increases in development areas and population growth due to it are causing changes in weather factors and affecting the ecosystem. As phenology is a significant diagnostic tool for the biological impacts from climate change, it could be an indicator for clarifying the effect of urbanization. In this study, the relationship between the phenology response of Mongolian oak and land use intensity was investigated by determining the green-up date of plants through digital camera image and MODIS satellite image analyses. We confirmed that the green-up date of Mongolian oak was advanced due to the temperature rise resulting from urbanization. The change was in proportion to the degree of urbanization and thereby was the largest in the urban center and tended to decrease moving through the rural area to the natural area. By comparing by landscape type according to land use intensity, this showed the biggest difference in the urban center as the difference between the observed date and the expected date of each study site was 11.0 days in the rural area, about 14.5 days in the suburbs, and about 16.3 days in the urban center. If we translate the results into the air temperature based on previous research results, it could be deduced that the air temperature in the urban center, suburbs, and rural area rose by 3.8 to 4.6 ◦C, 3.3 to 4.1 ◦C, and 2.5 to 3.1 ◦C, respectively.

This trend was also identified by AGDD, which determine the physiological activity of the plant depending on the seasonal changes, and the sap flow, one of the physiological responses of the plant. The higher the intensity of land use, the faster the green-up threshold

is reached. From this result, we were able to confirm the availability of AGDD and sap flow in predicting changes in ecosystems due to climate change including phenology.

On the other hand, the change in sap flow was almost consistent with that of the green-up date in the change trajectory as the difference was within one day. As most studies on plant phenology have focused on external changes of plants, observing the seasonal change in plants through this physiological response is meaningful in terms of expanding the scope of research in the field.

Furthermore, the significant difference in the plant phenology response in proportion to land use intensity on the same latitude in the same climate zone can be important evidence for proving the impact of urbanization as a factor in causing climate change. This result is expected to contribute significantly to developing future climate change adaptation strategies.

**Author Contributions:** Conceptualization, A.R.K., C.H.L. and C.S.L.; methodology, A.R.K., C.H.L. and C.S.L.; software, A.R.K. and C.H.L.; validation, B.S.L., J.S. and C.S.L.; formal analysis, A.R.K. and C.H.L.; investigation, A.R.K. and C.H.L.; resources, C.H.L. and C.S.L.; data curation, B.S.L. and J.S.; writing—original draft preparation, A.R.K.; writing—review and editing, C.H.L. and C.S.L.; visualization, A.R.K.; supervision, C.S.L.; project administration, C.S.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** No new data were created or analyzed in this study. Data sharing is not applicable to this article.

**Conflicts of Interest:** The authors declare no conflict of interest.
