The current tmodel submodule provides the T Model of GPP allocation and growth. It takes in a productivity estimate and returns the change in stem diameter, given respiration and maintenance costs.

This needs to be reworked to wrap it up into a demographic model framework:

• A better plant functional type (PFT) representation. The TModelTraits constants class does this at the moment, and may not need much changing. It is unusual though - all the other constants classes only have a single instance for any one analysis, but the demographic model will need a Flora object containing a set of trait instances for different PFTs.
• A representation of a cohort - a number of stems of a specific PFT, with a specific size.
• A representation of a community: a set of cohorts of possibly mixed plant functional types and sizes that occupy an area.
• Functionality to convert a community into the canopy model for the area.
• Functionality to calculate light extinction through the canopy and hence allow the P Model to be used to predict average GPP for each stem in a cohort.