canopy spread issues

[ckoven]

A thing occurred to me recently that I am not sure about how we should deal with. Since #279 the canopy spread logic has been at the site rather than the patch level. In the case of a nocomp configuration, if the total area in which woody PFTs can grow is less than the canopy closure threshold parameter on a given gridcell, then the trees will always remain in the high-crown-area state. This doesn't seem ideal to me but I am not sure what the best alternative is. We could change the canopy spread parameter when in nocomp configuration to make it a vector of length nocomp PFTs and evaluate it separately on patches of each nocomp PFT. Or maybe we could leave as-is. Curious if others see this as a problem in the current scheme or if anyone sees a better solution.

[ckoven]

Also noting that this will also apply when and if we have managed land-use types that exclude woody plants: if their total area approaches one minus the canopy closure threshold, then that would change the crown area allometry of trees in the unmanaged land-use types.