Temperatures and Yields
If one looks at a vegetation map of the biggest country on Earth (yes that’s still Russia) one will quickly find out that most of the surface is hard to use or straight unusable for the habitation of all but the hardiest lifeforms. There is a narrow band that’s the Russian wheat belt where life is pleasant enough because it’s not so cold that body parts fall off in deep winter. Cold weather is very bad for all life – that’d why there is such a stark difference between the tropics and the arctic. One teeming with life, the other almost lifeless.