Hi,
I suggest you to create your Forest objects directly from Front / Left view to avoid using of XForm utility.
Generally, we don't recommend to use any modifier over our plug-in to avoid possible issues. The Forest objects are every time while rendering reconstructed based on scene position and coordinates of used splines / surfaces so it shouldn't be transformed or moved.
Anyway by adjusting Rotation parameters under Transform tab you can archive the same. Hope this helps you.
Kind regards,