Mechanism of Evapotranspiration from Forest Floor based on Soil Moisture Changes and its Evaluation Method

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This paper examines possible evaluations on the amount of evapotranspiration separately, based on evaporation experiments with an undisturbed soil column.To evaluate the amount of water movement during infiltrating and drying, experiments were performed by using a Kuroboku column picked out under undisturbed conditions on the forest. In the experiments, the pressure heads changes and water balance of the soil column were measured. In comparison with the measured and evaluated amount of water through the upper and lower boundary, the two were in close agreement. To estimate the surface evaporation and the water uptake by pseudo-root system separately, pressure heads in the undisturbed soil column with inserting pseudo-roots on the side were measured. In consequence, the sum of the decrease of volumetric water content in each layer was in good agreement with the loss in weight of the soil column. Evaporation from the top surface of the column was evaluated as the amount of the decrease o … More f volumetric water content in the 1st layer. Water uptake by pseudo-roots was evaluated as a sum of the decrease of volumetric water content from 2nd to 6th layers of the column. Secondly, evaporation from the top surface obtained by solving Richards' equation with the unsaturated flow analysis, was evaluated as the water flux through the top boundary of the column. Water uptake by pseudo-roots was calculated as the difference in the flux between upper and lower layer at the boundary. The sum of estimated amount of evaporation and water uptake by pseudo-roots was in good agreement with the loss in weight of the soil column. Finally, the unsaturated flow analysis applied to the soil moisture changes measured in the southwest slope of Mt. Fuji. As a result, the transpiration rate was evaluated 1.7 mm/day on the average. The evaporation rate from forest floor was evaluated 1.0 mm/day on the average, and the evapotranspiration rate by trees was estimated 2.7 mm/day by adding transpiration rate and evaporation rate. Less