I don't know how many nukes are headed for the middle of the Amazon or the jungles of Indonesia. I suspect interior Africa will be one of the safest places on Earth, simply because its so far down the list of places with infrastructure worth bombing. And while radioactive waste will be a problem for animal life, plant life is significantly more resilient. No shortage of trees growing up around Chernobyl and Fukushima.

I wouldn't want to be a land-bound apex predator during nuclear winter. Or any kind of commercial agricultural crop, like livestock or rice. But Yellowstone will do just fine.