If you can give me the details that I requested then I should be able to look into it for you and fix it if it is an issue of Nature Renderer. What is the size of the terrain? And how many terrains do you have? If you disable the Nature Renderer component on the terrain, do you still have the same issue? Can you open the profiler in Unity and share the stats from the frame when you remove a tree. That should show what part of the code is taking up so much time. Just to clarify, is the grass on your terrain currently added on the terrain as detail objects or as trees?