I’d suggest disabling everything from view except the foliage, isolating sections of it, converting them to meshes, merging actors, snapping an impostor of the merged actor, and using the impostor insted of foliage by setting a more aggressive render distance.
This works in so long as you don’t allow zoom/scopes and your terrain/foliage cannot be modified - while also taking several hours of dedicated work for each “flange” of forest you isolate.
Results can be really good looking if you bump up the quality of the impostor and use octhedral impostors for them.
It actually works well for replacing foliage on landscape tiles as well.
You won’t find tutorials for anything like it.