Thermodynamics of transpiration in heavy forest during active snowmelt

The thermodynamic relationships involved in forest transpiration in snow covered areas during non-advective weather are analyzed using data from the 1949 melt season (May 9-13) in the Willamette Basin Snow Laboratory and assuming that net advection, net basin energy change, and net moisture content change of the air and soil are nil. The energy used for transpiration is computed as the difference between the net all-wave energy change with space and the energy required for melting snow. The transpiration loss is found to consume about 50% of the net input energy to the basin, amounting to an average of 0.14 inches/day (about 10% of melt) for the period investigated. Condensation water undergoes a repeated cycle of evaporation and condensation, aiding the transpiration process by supplying water to vegetation and aiding the transpiration process by supplying water to vegetation and aiding melt by returning some of the total transpiration energy to the snow. Data on the magnitude of the processes involved in the transpiration loss, including melt components are tabulated.