Hi,
Well, as that's not always desirable behaviour, by default the
Paint Area isn't linked to the surface.
Anyway, it's easy to bind any Area(s) to the surface with the 3ds Max's
Select and Link function. Optionally, if wanted to not link the whole Forest object, you can use the
Areas -
Convert to Spline feature and
Select and Link just that newly created & assigned spline.
Just take in mind, you'll need to click on the
Update surfaces data button or mark the
Auto check-box (to
Update surface data automatically - this may add a performance hit for complex surfaces) to rebuild the Forest object.
Hope that helps.
Best regards,