The resilience of the carbon cycles of temperate coniferous and broadleaved forests to drought

Abstract

Abstract Climate change is expected to increase regional variations in extreme weather events including drought, which will significantly affect forest ecosystem carbon cycles. Although studies on the resilience of forests to drought have been increasing, the resilience of carbon flux components and its underlying biophysical mechanism during and after drought are still poorly understood. In the present study, changes in carbon exchange in adjacent evergreen Korean pine and deciduous oak forests were investigated to compare the resilience of the two forests to drought from 2016 to 2018 using an eddy covariance technique. A severe drought occurred in spring and early summer 2017 due to substantially low rainfall since August 2016. Although there were no major differences in other environmental factors between both sites during the drought, soil moisture content (θ) in the pine site was up to 8.7% lower than that in the oak site. The drought resulted in a temporary net carbon source in the pine stand with 38% increase in ecosystem respiration (Reco) and 45% reduction in net ecosystem production (NEP). These changes were more conspicuous than the changes in the oak stand (+30% of Reco, −17% of NEP). Although Reco and NEP recovered in 2018 when θ at both sites was replenished by large amounts of precipitation, they did not fully recover to their 2016 level due to drought legacies with reduced leaf area and enhanced Reco. We conclude that evergreen Korean pine stands could be more vulnerable than deciduous oak stands to intense and frequent droughts in the future, and this may accelerate succession from coniferous to broadleaved species in temperate forests.