Paleo Slide Set: Packrat Middens: Vegetation & Climate Variability in the Southwestern United States
1904/1981 comparison at the confluence of the west branch of Santa Cruz River in Tucson, AZ.

Evaluating the effects of natural climate variability and human impact on landscapes is important because 
it affects plant and animal distributions worldwide. The scientific interpretation of these long-term dynamics 
of vegetation change is particularly relevant in the late Quaternary period(circa 150,000 yr.) which encompassed 
several glacial-interglacial cycles. Measuring the direction, magnitude, and rates of these shifts can help scientists 
understand present plant and animal distributions, as well as anticipate how these distributions might change in the 
future.

Vegetation shifts and climatic changes which occurred prior to human observation can be reconstructed by utilizing a 
variety of paleoclimatic proxies (tree rings, fossil pollen, ice and coral cores, lake and ocean sediments). 
Unfortunately, none of these proxy indicators are present in sufficient quantities in the North American deserts 
to allow vegetation cover and climate reconstructions of these regions. 

Photo Credits:
N/A 
Desert Laboratory, U.S. Geological Survey, Tucson, AZ