The effect of soil surface litter residue on energy and carbon fluxes in a deciduous forest

The Atmosphere-Land Exchange Surface Energy (ALEX) balance model is an analytical formulation of the energy and mass transport within the soil and the vegetation canopy used for simulating energy, evapotranspiration, and CO2 fluxes in a wide range of vegetation environments. The objective of this study was to evaluate the ability of ALEX to simulate the effect of soil-surface leaf litter residue on soil heat conduction (G), sensible heat (H), evapotranspiration (ET) (or latent heat (LE) when expressed as rate of energy loss) and CO2 fluxes in a deciduous forest. The model was evaluated in a deciduous forest in Oak Ridge, Tennessee where about 550 g m(-2) of dry weight of slow decomposing leaf litter is produced annually during the fall season. Incorporating an explicit formulation of water and energy exchanges within the residue layer in ALEX improved the performance of the model against eddy covariance and G measurements. The discrepancies between model simulations made with and without leaf litter residue were largest during the spring and fall, when soil contributions dominated the energy budget of the forest. During these periods, particularly during the spring, without the inclusion of the residue layer the model overpredicted LE, G, soil temperature and soil moisture, and underpredicted H. The model showed no differences in simulating above-canopy net radiation (RN), with a slight difference in the above-canopy CO2 flux. The largest model improvement for residue effects was in the simulation of G, with the slope of the regression line between predicted and measured values reduced from 2.28 for the model without residue effects to 1.07 when the residue effect was considered. (C) 2012 Elsevier B.V. All rights reserved.