Self-thinning/mortality

[Rasilgon]

The origin of this is issues is #65.

The self-thinning / density-dependent mortality regulates how many trees remain in the stand based on the maximum stem mass of as:

where wSx1000 defines the maximum stem mass of a tree, when n=1000 trees; and nm, aka thinPower, is the exponent of the self-thinning rule. "When the mean individual tree stem mass ws (WS/N) is greater than wSx the N will be reduced and hence wSx will increase. his is done following an iterative procedure until ws < wSx." (Forrester and Tang 2016)

This mortality does not always work optimally. For low tree densities, the value of wSx (biom_tree_max) is very high and translates into very high, even unrealistic, stand biomass (biom_stem). For (very) high stem numbers, the wSx is so low that many trees die in the first years of a simulation.

These problems could be addressed by tuning/calibrating the parameters wSx1000 and thinPower, although it is not fully clear, to my knowledge, whether this mortality could always keep stand biomass within realistic ranges. Besides, there are trade-offs when doing so, and a better fit for low tree densities, might be not solve the problem with high tree densities, and vice versa.

[trotsiuk]

Hi @Rasilgon and @DavidForrester was not sure whether we aim to develop something in this direction or it is more a comment?