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.
Hope this helps you, but in case of any further questions or doubts please don't hesitate to contact us. Have a nice day.