Huge amount of Meshes (Actors) performance?

Hi,
I want to make a landscape level with a forest.
However the level is kind of big and to make it look realistic i have to spawn 6000 or more trees.
I used the speedtree conifer, which comes with LOD and the framerate drops to under 10.
My problem is that this is only with trees and i would like to have a lot more meshes like rocks etc.
Is there a solution to keep the performance up even with that much actors?

-plan your map carefully → hills
-when the trees are behind a hill you could cull them
-I dont have experience with speedtree, but a very low poly 3rd LOD channel would increase the performance
-create your own low poly trees → e.g the ones for our game have around 2000 tris in LOD0 (it even goes down to 1000 tris)
-cull small plants like grass, bushes,…

Billboards are also commonly used for far away trees, especially if they are “outside” the playable part of the level.