I wam new to blender. I have a large forest I would like to render. Blender gets extreme lag and usually completely crashes when I display the whole scene. I split the forest into multiple layers. Is there a way to render all the necessary layers without displaying them in the 3d view?
Yes, this is possible, however there might be better ways of handling this.
Disable Lock layers to scene in the 3D view > Header.
Now you can set the Scene layers in Properties > Renderlayers to the layers you want to render (in this case, 1, 2, and 3)
Note that only layer 1 is visible in the viewport.