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Paleo Slide Set: Packrat Middens: Vegetation & Climate Variability in the Southwestern United States
Changes in CO2 levels and stomatal density in limber pine during the last 25,000 years.
Packrat middens represent the single richest source of plant macrofossils from the last deglaciation (15-12 ka), when CO2 increased from ca. 180-200 ppmv to ca. 270-280 ppmv. The diagram shows the change in CO2 levels and stomatal density in limber pine during the last 25,000 years. Because every effort was made to hold temperature and relative humidity constant in this time series, the 17% reduction in stomatal density was attributed to CO2 enrichment during deglaciation between 15,000 and 12,000 calendar years ago.

Photo Credits:
Pete Van de Water, Steve Leavitt & Julio L. Betancourt
University of Arizona & U.S. Geological Survey
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Last Modified: 12 October 2001

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