Inconsistent calculation of total_tree_area

[samsrabin]

Originally posted by @ckoven in #1432:

The function currentPatch%UpdateTreeGrassArea() is outside the sope of this PR, but I just realized that the variable currentPatch%total_tree_area is being defined in two subtly different ways in different parts of the code. I don't understand why it should be that way, so unless someone else does, we should align the two definitions.

In currentPatch%UpdateTreeGrassArea(), the total_tree_area and total_grass_area are calculated for both canopy and understory plants, but then clipped so that they cannot exceed the patch area.

Whereas in canopy_summarization, total_tree_areais calculated only for canopy trees (and thus cannot exceed patch area, unless something is wrong).

If PPA logic is strictly rank-ordered and trees are always taller than grasses, then this should not make much of a difference. It seems to me like we should base all of these definitions only on canopy plants, so I'd advocate changing the logic in currentPatch%UpdateTreeGrassArea() to align with the current logic in canopy_summarization. But curious to understand the difference.

UpdateEffectiveWindSpeed should also be changed to ensure weights always sum to 1.

[glemieux]

Consensus per the software engineering meeting today is that we should turn the canopy_summarization code into a procedure call. Change the UpdateTreeGrassArea to be consistent with the current canopy_summarization method. We should rename the procedure name to something to clarify this fact as well.