In article ,
writes:

The old explanation for the Great American Desert that I recall was wind -
too much evapotranspiration to allow broadleaved trees except in valleys and
on streams but ideal for grass. I wouldn't discount long term effects of
fire, plowing or grazing either. Restoration experts have managed to bring
back small parcels of pre-settlement plant communities just by fencing OUT
the cattle. Pioneer graveyards usually held reservoirs of original plants
that stopped abruptly at the fenceline.

I'm sorry I jumped from discussing desert and sage brush to the great
plains. It confused the issue. The part about the advance of forests
into the plains had nothing to do with desert areas. Cattle are nowhere
near as destructive of trees as bison. I think fire suppression has a
lot to do with it too, since burning is a great way to maintain
grasslands.

I don't know what area they are talking about clearing in Colorado, but
there is a good chance that some of it was not historically forested.
Mountain bison were a separate, somewhat smaller strain than the plains
bison that inhabited the mountain states.

If juniper is advancing is it because of less grazing, less fire, less
management or a change in climate? Succession should follow the usual
rules.

I think less fire is the biggest reason. Juniper has a very oily wood
that burns like a candle. There is an article that gives some mention of
juniper clearing at

http://www.nv.blm.gov/bmountain/fore...front_page.htm

It's a Nevada BLM site, but the difference between Nevada desert and
Oregon desert is just a line on a map. The juniper discussion is about
halfway down the page.

--
http://home.teleport.com/~larryc