Forest uses local coordinates of the surface, so it's rotated as well. Please, try this:
1) With the surface selected apply Pivot->Affect Pivot Only->Align to World.
2) Utilities->Reset XForm.
3) Optionally, collapse surface to editable mesh.
4) Create a new Forest picking the surface.
If that doesn't work, check flipped faces and normals as MH4288 suggested.