Hi,
It looks as though some of the objects in that scene have been scaled disproportionately. To fix it you'll need to reset the XForm's by following these steps:
1 - Select the Surface floor plate 
2 - Open the 
Utilities Panel. 
3 - Select the
 Reset XForm utility and click 
Reset Selected.  This will "reset" it's local coordinates / scale and should fix the issue.

4 - Create a 
new  Forest object using the surface.
I hope that helps, please let me know if you have any further questions.
Many thanks!
Paul.
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