Hi,
It can be done setting
Display->Render->Mode to
Meshes. That disables the instancing engine, generating a mesh for the Forest object.
If you also need a mesh for the viewport as, set
Viewport Mode to
Mesh, and adjust the faces limit in
Max.Faces (just at the bottom of the rollout).
Please note this may generate an huge mesh for complex objects. There are two ways to optimize it:
a) Collapse Forest to Editable Mesh once generated. You can keep a copy of the FP object as 'Disabled', to modify it if needed.
b) Create a separated FP object using low-poly geometry, just to be used as surface and keep it hidden.
Displacement Map Effect uses the map to compute the height. Unfortunately this case is different and cannot be implemented with Effects.