C2_Scientist on Tue Feb 09, 2016 1:39 pm
While I could be wrong, I'm thinking that we shouldn't look at the total faces count, but the total vertex count:
1400 x 1 triangle = 1400 x 3 vertices = 4200 vertices
1000 x 2 triangles = 1000 x 4 vertices = 4000 vertices
640 x 4 triangles = 640 x 6 vertices = 3840 vertices
The numbers don't match
exactly, but that's because the tree counts are really only close estimates.

I think they're in the ballpark anyway.
If you create a triangle, that's 3 vertices. Expanding to a rectangle requires only one additional vertex, so your faces count has become 200%, but the vertex count has only become 133%. Each new face costs only one vertex after the initial cost of 3, as long as they're all connected. That's why single triangle trees aren't very efficient use of the limits we have, but it's unavoidable if you absolutely want to maximize the number of separate trees.
On the other hand, the long, fake forest edges I've used are very efficient, in terms of vertex count, and the number of trees present per vertex cost.
Additionally, remember that the vertex count will increase if you break the UV mapping and/or smoothing groups. In fact, I just tested this with the 100 triangle planes I mentioned above; I selected roughly half of the squares, in a checker pattern, and assigned them their own smoothing group. This reduced the number of visible planes in-game to ~ 28 planes, down from 45. The number of faces (before the disappearance takes place) was the same, but the vertex count had increased due to breaking SGs. The outcome was identical if I broke the UV mapping instead.