Its not like it would take lots of extra memory or even design time...
just make the area (at least) 4 times larger and plonk down a few dozen extra trees...
a very simple object placer would be nice
1/ select height field.(possibly from image)
2/ select prefab model (park bench / tree / race gate etc)
3/ select X,Z ground coordinate, app places it on ground (Y)
4/ if not finished goto step 2