Sometimes it might be tricky to get the distribution applied correctly on "rotated" surface and it might require a Reset XForm
operation to be performed. As mentioned in this "Scattering on Vertical Surfaces
" tightly related tutorial:"The most important thing to understand is how to orientate the Axes of the Forest Object, the surface and the scatter geometry. Forest Pack expects the local Z axis of the surface and Forest Pack's local Z axis to be aligned. Any deviation from this and you'll start to encounter issues. In normal use, if you create a new Forest Pack object by selecting a surface, it will inherit the transformation matrix of the selected object. In this case correct alignment is automatic but only if the surface's coordinate system is already oriented correctly, with the local Z axisperpendicular to the plane."
Also, the work-flow described in following "can't propagate things on whole surface
" post would be a good option: "A recommendable way would be to detach a copy of these polygons into a "help surface" which will Forest use for the distribution and remap UVs as wanted to get the correct distribution."
Attaching a modified scene. Hope you'll find it useful.