Seasonal variability of energy and carbon fluxes in an oak openings forest

Background/Question/Methods Climate change projections predict an intensifying hydrologic cycle and an increasing frequency of droughts, yet quantitative understanding of the effects on energy and carbon flux remains limited. Energy fluxes, including latent heat (LE) and sensible heat (Hs) fluxes, carbon flux (Fc) were examined from January 2004 to December 2009 in a 70-yr-old mixed oak forest in northwestern Ohio, USA, based on direct measurements from an eddy-covariance tower. Our objectives were to determine if there were significant seasonal differences in these fluxes during the 6-year study period.

Results/Conclusions We found that LE, Hs and Fc were significantly different for seasons among six years: (1) effects of years on LE, Hs and Fc were significantly different (P<0.0001), except for Hs in autumn (P=0.0808), Fc in summer (0.0022) and winter (P=0.1917); (2) effects of months on LE, Hs and Fc were significantly different (P<0.0001) , except for Hs in autumn (P=0.0034); (3) effects of the years × months interaction on LE, Hs and Fc were significantly different (P<0.0001), except for Fc in summer (P=0.0839) and Hs in autumn (P= 0.0072). Over the study period, Hs increased gradually, while LE and Fc fluctuated.