Even-aged multispecies harvesting algo

[gowachin]

The present function that use even-aged harvest does work with multiple species but each species is harvested on their own like it's two different forests. This is caused by the computation of the density index ratio ($RDI$).

The aim of the issue is to compute a forest scale $RDI$ and harvest each species in order to get to the targetRDI of the forest.

A solution could be to compute $RDI_t$ and optimise $Kg$ like we do for single species forest. We would have following equations :

• compute total $RDI$ $$RDI = \sum_{s=1}^S RDIs = \sum{s=1}^S \frac{N_s}{Nmax_s}$$

• optimise $Kg$ and $RDI$ where $$Dg^2 = \frac{ \sum_{s=1}^S mesh_s \cdot xs }{ \sum{s=1}^S tx_s }$$

This method may not help for favoured species during even harvest.

[gowachin]

I implemented a version in the commit linked above and here are the results. The code is present in vignettes/Harvestings.Rmd within the branch dev.

To compare, this was the previous result where each species where harvested by their own RDI (with a shorter time period)

Next goal will be to plot the RDI and Kg along time to check if the new implementation follows the targets. This will augment the package as well because I think this kind of functions will help future harvest analysis.

[gowachin]

I'm working on computing RDI and Kg on simulations results, for assessing if the harvesting algortihm is working fine for multi species even management.

@kunstler noticed that RDI should not be computed with individual below the minimal size (individual of size 0 due to the lag in the mesh). This is a present issue with single and mutli specific even simulations.

[gowachin]

Implementation is done on the dev branch and ready to be added for a new stable version.

Examples are present in Harvesting vignette.

Functions are present in R/harvest.R

I added a function for computing $RDI$ and $Kg$ after the simulation. This help to check that targets are reached.

Here is an example of output :