Theory
There are three different ways to represent the vegetation in the model. (1) The simplest representation is the implicit big leaf model, where transpiration and soil evaporation are treated as a common flow (no soil evaporation is calculated). In this case the distribution of water uptake from soil layers have to be specified. Potential evapotranspiration is used as a driving variable. (2) The vegetation can also be represented explicitly as one big leaf. Transpiration and soil evaporation are then treated as separate flows and potential transpiration is calculated with the Penman-Monteith equation. (3) Finally vegetation may also be represented by an array of plants, multiple canopies and root systems may also be represented (See Structure of Models, switch “PlantType”).
The “multiple plants” option is similar to the explicit big leaf model. The major difference is that the use of multiple plants makes it possible to assume different properties for different stands covering the same area, and it therefore enables the user to account for competition within a plant community. On the other hand the explicit big leaf option gives the user more alternatives when simulating for example potential transpiration than the multiple plants option.
Distribution of roots with depth