Blender Underground

Hello everyone I have made an animation that includes a grass plain made with the particle system. As you can imagine it slows my rendering down quite a bit. My question is after the first 200 frames or so my camera stops at a fixed position, the grass plain is still in the background but that camera does not move anymore, so for the next 2000 frames till the end of the animation that background is the same, is there a way to still have the grass plane background but where the computer doesnt have to calculate everything for every single frame from the point where the camera stops to the end. Thanks for any help.
Gary

Simplest answer: make a picture of the grass background and put it on a vertical plane positioned behind everything so it looks the same to the camera. This only works if the camera is not moving, of course.