I set up an Adaptive tree family that used the scaling method, linked through some parameters, Repeated it on a Divided Surface, and then used Randomizer - this random forest is so easy :-) With the scaling method working, we can even just drop some imported Sketchup trees into the most deeply nested family (the one that gets scaled), reload it through the hosts back to the project, and even these imported CAD files will scale correctly.
This is the simple tree randomizer (height only):
Next, I added an X and Y offset so I could randomize the position from the grid slightly, resulting in this...
Tree randomizer with move parameter:
Here are the sample files for download. Enjoy!
(this is the Sketchup tree that I used for the example above)