Light and water competition
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Competition for light and water represents one of the most relevant factors influencing biomass allocation. To simulate light competition, the 3D-CMCC-CNR model considers a modified version of the Lambert-Beer law, approximated by Monsi-Saeki formulation of exponential attenuation, and coupled with the “Big-Leaf” approach for a multi-layered model. This approach allow to scale the physiological processes from leaf to canopy level, considering the exchanges between upper and lower layers. Each canopy storey intercepts and absorb a fraction of the receiving light. The remain fraction reaches the understoreys determining different light conditions and growth rates.
The 3D-CMCC-CNR considers water competition as an asymmetric competition, although to a different degree. Water competition is simulated by computing iteratively the soil water balance and modifiers. The calculation is occurred for each forest layers, starting from the dominant level to the dominated ones.
With an high availability of water, trees located into the dominant layers grow with more efficiency, but they increase respiration and suffer this disadvantageous. When a low level of water availability occurs, dominant trees reduce growth rates.