In article ,
writes:

I think we can say more factors than just Bison or no
Bison effect the presence of trees on the great plains or in the
deserts of the Sahara!

Once again, for the geographically challenged, the Great Plains of North
America are not a desert. In fact, they are quite well watered.

Not enough to grow a lot of crops in Colorado without water!


While
the plains get steadily dryer as you move west, the east slope of the
Rockies still gets 18 to 25 inches a year, with more rain falling in the
south.


Is that why it is called the Great American Desert?