The plants model#
Model overview#
The Plant Model works by using the cohort data within each cell to generate the heights and vertical canopy profiles of all individuals. These are then used to build a community wide canopy structure under the perfect-plasticity approximation model (Purves et al., 2008). The area of the grid cell is used to constrain the community-wide distribution of crown area into closure layers: as the canopies of taller trees use up the available space in the top most layer, shorter trees then fill up lower canopy layers until all of the community crown-area is allocated to a canopy layer.
These canopy layers then define the vertical light profile through the canopy. The photosynthetic photon flux density (PPFD) is partially intercepted by each canopy layer, giving the eventual PPFD reaching ground level.
The P Model (Prentice et al., 2014) is then used to estimate the light use efficiency for each individual across their canopy contributions to each canopy layer. The specific canopy conditions of air temperature, vapor pressure deficit, atmospheric pressure and \(\ce{CO2}\) concentration define the optimal trade-off between carbon uptake and water loss for the leaves in each canopy layer. The PPFD flux intercepted by each layer can then be used to scale the light use efficienct up to the gross primary productivity (GPP) of each layer, and these can be summed across layers to generate per stem GPP.
The Virtual Ecosystem then uses the T model (Li et al., 2014) to estimate the increase in diameter at breast height from the GPP. The T model estimates maintenance and respiration costs for a given stem and then allocates the resulting net-primary productivity (NPP) to growth, generating an expected change in diameter at breast height given the wood density, stem geometry and NPP. These calculated increments are then applied to the cohorts and the larger stems are used for the next update.
Mortality and reproduction have not yet been implemented.
Required array variables#
In addition to the definition of the plant communities, the plants model needs some additional array data to be set. These provide values that can be easily structured as arrays by grid cell id and by plant functional type name:
Generated variables#
The calculations described above result in the following variables being calculated and saved within the data object, and then updated
Updated variables#
The link below provides the complete set of model variables that are updated at each model step.