Spawning 2x2 large trees (4 saplings in total) will not work. I have not tested to see if the biome affects the ability to spawn, but I'd assume not. I have tested the dark oak and the spruce trees and neither will grow; I am growing them in a plains biome. My tickspeed is set at 9, which may affect this problem, but again, I am not sure. The areas around the four saplings are bare of any vegetation, etc.