Paleo Slide Set: Packrat Middens: Vegetation & Climate Variability in the Southwestern United States
Plant zonation with elevation on the Colorado Plateau from the last glacial to the present.

In mountainous regions, vegetation varies dramatically with elevation, which affects temperature, 
precipitation and even the partial pressure of carbon dioxide. Many of the changes documented in the 
midden record can be described as displacements of the elevation range of a species through time. 
During the last glacial period, areas above tree line were more extensive while boreal and mixed-conifer 
forests occurred 800-m lower than they do today on the Colorado Plateau. Not all changes, however, can 
be described as simple elevation displacements. For example, the ponderosa pine forests and pinon-juniper 
woodlands that characterize intermediate elevations today were missing during the last glacial period, 
displaced far to the south. 

Photo Credits:
Julio Betancourt 
U. S. Geological Survey