Something else interesting I found out by accident. If you make a neighborhood, using a terrain, and then make another neighborhood using the same terrain (either deleting the old or keeping it) the trees will often import into different Sims 2 tree types.
ooooo! That's something worth playing around with - thanks! I have so many terrains now but most of them are my own rejects that never got uploaded because they're just...wrong - guess it's time to clean out
that file.