A multilayer numerical model has been developed for the simulation of heating and evapo-transpiration processes in the plant canopy. The model takes into account all complex and up-to-date knowledge of plant physiology and dynamic processes in the soil, the plant canopy and the air. Heat and moisture fluxes at the soil surface are evaluated by solutions of equations coupling subsurface heat and moisture transfer, and the evaporation at the ground surface. The heating and transpiration processes in the plant canopy are computed using a model coupling the foliage heating and water transport in the soil-plant system. The plant canopy is divided into layers with LAI in each layer equal or less than 0.1; and stomatal conductance and photosynthesis of leaves in each layer were simulated with account for environmental factors such as PAR, air temperaturem, air humidity, and available water in the tree. The model for transpiration in the plant canopy includes a submodel for the absorption of water in the soil by root, a submodel for the transport of water in the stem, and a submodel for the transpiration at the leaves. Details of the air temperature, specific humidity and wind velocity inside the plant canopy are also investigated.
Field observations has been carried out to investigate the influence of various environmental factors such as solar radiation, air temperature, air humidity, wind velocity etc. to the heating and evapo-transpiration processes at the plant canopy. The observational site is located in a forest in Tsukuba City, Ibaraki, Japan. There are many plant species such as Cyptomeria japonica, Chamaecyaris obtusa, Querucus acuisima, Oak, Fagus crenata, Prunus, and others. The dominant species are Cyptomeria japonica and Chamaecyaris obtusa. A tower with the height of 10 m was set up inside a Cyptomeria japonica area with a canopy height of 12m. A perch was mounted on the tower, which enables the measurement of wind velocity, air temperature and relative humidity at the height of 15m. During the observations, wind velocity was measured by anemometers; air temperature and relative humidity at some heights from the ground surface were measured by thermo-hygrometer; solar radiation and albedo of the canopy top were measured by pyranometer and albedometer, respectively; and soil temperature at the surface and different depths in the soil were also measured. Foliage surface temperature at some levels was measured using hand thermography (thermoflow). The LAI of the canopy was measured by a plant canopy analyzer. The chosen observational site provides favorable conditions for the application of the one-dimensional model.
Comparison between field observational data and computational results reveals that the model can simulate satisfactorily the mass and heat transfer processes in the plant canopy. Due to its general type, the model can be used to predict the heating and evapo-transpiration processes in plant canopies with any plant species. Further development of the model with account for plant growth can enable the model investigating infeluence of different environmental factors the growth of the plants.