change where stem_biomass is set

[ekluzek]

These are changes that @olyson is running with for the PPE work. Because stem_biomass should be set to zero in the InitCold method, I think it's equivalent to what's currently being done. But I need to check for sure. This moves the setting of stem_biomass as well as the if woody statement up to where leaf_biomass is set. It also clearly sets stem_biomass to zero there. So it looks like this...

            ! calculate vegetation physiological parameters used in biomass heat storage
            if (use_biomass_heat_storage) then
               ! Assumes fbw (fraction of biomass that is water) is the same for leaves and stems
               leaf_biomass(p) = max(0.0025_r8,leafc(p)) &
                    * c_to_b * 1.e-3_r8 / (1._r8 - fbw(ivt(p)))

               if (woody(ivt(p)) == 1._r8) then
                  stem_biomass(p) = (spinup_factor_deadwood*deadstemc(p) + livestemc(p)) &
                       * c_to_b * 1.e-3_r8 / (1._r8 - fbw(ivt(p)))
               else
                  stem_biomass(p) = 0._r8
               end if
            else
               leaf_biomass(p) = 0._r8
               stem_biomass(p) = 0._r8
            end if

[ekluzek]

Here's a suggestion from @swensosc to make the code easier to read...

the only thing I don't like about the first version is all the if-blocks, which I think makes it harder to read. If it just started with
leaf_biomass(p) = 0._r8
stem_biomass(p) = 0._r8 before the 'if use bhs' block, we could get rid of the extra else statements and make it cleaner.

leaf_biomass(p) = 0_r8
stem_biomass(p) = 0_r8
if (use_biomass_heat_storage) then                              
                  ! Assumes fbw (fraction of biomass that is water) is the same for leaves and stems 
               leaf_biomass(p) = max(0.0025_r8,leafc(p)) &                      
                    * c_to_b * 1.e-3_r8 / (1._r8 - fbw(ivt(p)))                                                                                            
            if (woody(ivt(p)) == 1._r8) then                                                          
                  stem_biomass(p) = (spinup_factor_deadwood*deadstemc(p) + livestemc(p)) &                       * c_to_b * 1.e-3_r8 / (1._r8 - fbw(ivt(p)))                                                   
               end if
endif

[ekluzek]

For code efficiency it's better to use "else" statements rather than set something and then overwrite it for most cases. And actually we should be able to get away with setting biomass to zero just at initialization when use_biomass_heat_storage is off.

[ekluzek]

We talked about this a bit, and for this case really the best thing to do is to make sure when BHS is off that biomass is set to zero at initialization. Then it doesn't need to be updated each time-step. There's no real reason we should set this to zero each time-step. That will simplify the code a bit.

As a general philosophy we agreed with the following statement

"Our #1 priority should be code readability, unless we have a strong reason to think that efficiency matters for that part of the code."