g->pr does not reflect "extra" resources

[kpalmqui]

g->pr is a parameter calculated at the functional group level in rgroup_PartResources that reflects whether a functional group is resource limited or not:

/* Calculate PR at the functional group level: resources required/resources available */
        g->pr = ZRO(g->res_avail) ? 0. : g->res_required / g->res_avail;

Values > 1 indicate resource limitation for the functional group. It is then utilized within the mortality due to resource limitation implementation:

/* kill plants if low resources for consecutive years */
    /* increment yrs_neg_pr if pr > 1, else zero it. */
    /* one good year cancels all previous bad years. */
    if ( GT(g->pr, 1.0) ) {
       if (++g->yrs_neg_pr >= g->max_stretch)
          _no_resources( rg);

    } else {
      g->yrs_neg_pr = 0;
    }

g->pr is set every year based on "normal" resource partitioning - i.e. how much each functional group receives based on root-water matching and space. However, it does not reflect additional "extra" resources that a functional group receives if there are remaining resources left over after "normal" resource partitioning (see _res_part_extra and rgroup_ResPartIndiv). Thus, this could occasionally potentially kill individuals within a functional group that is not resource limited.

Simple solution:

1. incorporate g->res_extra into g->res_avail and then re-calculate g->pr
2. move the calculation of g->pr from line 103 of ST_resgroups.c to line 149 of ST_mortality.c right before the parameter is used (this is the only place it is actually used and there is no need to calculate it twice unnecessarily)

[kpalmqui]

I did some testing with the above solution implemented and made some comparison figures to the old implementation. I did this for one site with specific climate and climate-specific space parameters.

This issue does impact mortality, particularly for sagebrush. With the fix implemented, fewer individuals are killed when they are young and more individuals approach their maximum age before killing.

Figures here (1ter and 100 iters results shown, old = black, new = yellow):

Site868.mort.sagebrush.pcoolgrass.pdf
Site868.mort.pwarmgrass.pforb.pdf

The outcome is increases in big sagebrush biomass and density. Impacts on perennial grasses and perennial forbs is minimal.

Figures here (1ter and 100 iters results shown on each panel, old = black, new = blue):
SIte868.sagebrush.pcoolgrass.pdf
Site868.pwarmgrass.pforb.pdf

@dschlaep

[dschlaep]

That looks very promising! The old sagebrush individuals are getting heavier too.

[kpalmqui]

resolved by f9264f3