Comparison of two models of forest transpiration

Two transpiration models were tested in the paper, one is with plant control, and another without plant control. Principle of the (1) model with plant control was, that physical mechanism of transpiration is evaporation actively controlled by plants. The supposed mechanism is: part of the heat (heat equivalent of the energy absorbed from solar radiation), which would cause overheating the plant above 25 ºC is dissipated by evaporation. The model has five physical parameters, which are in principle measurable. (2) The model without plant control is based on the assumption, that transpiration dissipates a constant fraction of the heat from the heat equivalent of absorbed solar radiation (about 45 %). The model needs only one measurable physical parameter. Both models were tested by comparing their results with results actually measured daily totals of transpiration (via sap flow) in the floodplain forest Pohansko (near the town of Břeclav, southernmost Moravia), which was typical with almost non-limiting soil water supply over the period May 1 to Sept. 30, 1998. Results of both models were almost equal. We discussed their physical differences evaluating their goals and weak points and specified a program for further testing the physical mechanism of transpiration