Climate change is expected to increase regional variations in extreme weather events, such as drought, and the frequency of spring drought is increasing in Korea. The effect of spring drought on forest carbon dynamics may vary depending on species composition, especially the presence of leaves during spring drought. Since the leaf habit (evergreen vs. deciduous) is closely related to the change of evapotranspiration, rainfall crown interception, and soil moisture in forest, forest carbon uptake under drought and its recovery afterward could be different. In the present study, we explored linkage between leaf habit and forest carbon and water cycle during and after drought from 2015 to 2018 at two nearby forests in Korea, a Korean pine (Pinus koraiensis) plantation, which is an evergreen coniferous forest, and a deciduous Quercus forest. We compiled the data including net ecosystem production (NEP) and evapotranspiration (ET) measured by eddy covariance (EC) system, soil water content, and canopy conductance (gc) in both stands.
Results/Conclusions
The responses of pine and oak forests during and after drought had remarkable differences in carbon and water balance. In terms of carbon, growing season NEP had significantly reduced in the evergreen pine stand during the severest drought period in 2017, while it was not detected in the deciduous oak stand. Furthermore, recovery of growing season NEP after drought in 2018 was much greater in the oak stand than the pine stand. During the severest drought, soil moisture in the pine stand decreased close to its wilting point, which caused substantial reduction in gc, whereas it didn’t happen in the oak stand even though soil type was the same in both stands. Our analysis revealed the major reason for these differences in two stands was derived from the higher winter and spring evapotranspiration of the pine stand than the leafless oak stand, which resulted in the serious shortage of soil water in the pine stand during spring and early summer. We conclude that carbon assimilation by deciduous oak forests may not be affected by future drought events as much as evergreen pine forests, and it would accelerate the succession from conifer to broadleaved in temperate forests.