I made of trees of different species with the sapling tree generator. I put them into a particle system to populate a forest with trees. The particle system wants to animate the trees being emitted and dying. This is an animated project so I can't just pick a frame to keep. I want the trees to belong to a location and stay. How do I make the particle system permanent so the trees stay in the same arrangement?
Set the Frame start and End frame to 1, and the lifetime to the length of frames for the whole the animation.
You can convert the particle system Modifier. This will create linked copies of them all. (The particle system will still be there so you will probably need to move that out of the way)
The other alternative is to let all trees spawn at frame 1 to 1 and then give them a live time that works for your project.