Please see the attached file for a possible solution. It uses ForestLOD to change patch sizes and Distance Density Falloff to reduce the density based on camera distance. A few notes:
- You can use Forest LOD to pick patches instead of single trees. The procedure is the same as shown in the tutorial
- For both LOD and Distance Falloff I've activated Use Environment Range. This means that both these controls are linked to the camera's Environment Range > Near/Far settings.
- In this example I've switched LODs at 33% intervals.
- To match this, step the Density Falloff curve as shown in the image below.
I hope that helps, please let me know if you have any further questions.