Hi ,
Unfortunately this started to get out of my area of knowledge, so I pulled over several of our rendering team members and found a potential solution. In each LOD outside of LOD 0 for your trees, set EnableCollision to No Collision. Enable collision only on the trees closest to your individual actors by utilizing LOD 0’s collision settings. This is why I suggested the imposter sprites, though I have a bit more understanding now of how they work, you’d still have to set the Enable Collision to NoCollision and ensure that they are only set up on your final LOD setting for the objects in question. They drastically reduce the amount of verts that are being utilized, freeing up more processing power for the meshes that do have collision. This will still help as the CPU is storing the data for where the objects are in the world, so it is still handling half the work of the LOD, the other half being rendering itself which, as you said, is handled by the GPU.