A good discussion on scale, Gandy.

Model trees are nearly always made too small by modelers. E.g., a Silver Maple, a relatively common tree around here, and not especially large or small, is about 60-80' tall at maturity. In O scale, that would be 15 - 20" tall. I've never seen anyone do trees that are that big relative to the primary subject of their scenes. (I don't do model RR anymore, mostly figure and vehicle modeling, but the same thing happens in both.) As you note, though, trees are mostly fractal, so they tend to look similar regardless of scale. Interestingly (at least to me), people tend to do cars too large relative to people. (It's common for people to use 1:43 vehicles with figures that are generally scaled at something like 1:64.) I would find it fascinating to see a G scale layout with a couple of hundred 4' tall model trees, though.