Effect of Heat Storage Flux on Energy Balance in a Larch Forest

Sum of sensible and latent heat fluxes measured by the eddy covariance technique is systematically smaller than available energy in many terrestrial ecosystems, which includes forests. This energy imbalance is an essential issue for the flux measurement. In this study, we evaluated heat storage flux and investigated its effect on energy balance in a larch plantation developing on a flat terrain. Above-ground biomass was the largest component producing the heat storage flux of the forest ecosystem; about 70-80% of the heat storage flux was generated in above-ground biomass for summer and fall. Moreover, the heat storage flux of topsoil over heat plates had a considerable bearing on the evaluation of soil heat flux. Adding these heat storage fluxes improved energy balance by 6-10%; it increased the slope of the ordinary least square between eddy energy fluxes and available energy, which was used as an index of energy balance closure, from 0.83 to 0.88 in summer and from 0.93 to 1.03 in fall. This suggests that we have to measure and consider heat storage flux when we investigate the energy balance of forest ecosystems.