The increase in atmospheric carbon dioxide that has occurred over the past century is well documented, however the long term consequences of this change are not well understood. Experimental manipulations of CO2 concentration have examined individual, population, and ecosystem level responses, however these experiments are limited in size and duration. Long term studies of ecological responses to elevated atmospheric CO2 are needed to understand how changes in ecological processes and feedbacks will drive ecosystem change in the coming decades. This project will test the suitability of two forested sites in Yellowstone National Park for use as long term CO2 enrichment sites. Initial measurements revealed elevated atmospheric CO2 at sites downhill from geothermal sources. Sites are 1-2 km away from the sources, and show no evidence of geothermally altered soils. Tree cores will be analyzed to test how long these sites have been exposed to elevated CO2, soils will be analyzed for cations and compared to potential control sites, and gas samples will be collected throughout the growing season to test for the presence of gases other than CO2 (e.g., hydrogen sulfide, ammonia, methane, gases commonly associated with geothermal activity) that could confound comparison of these sites with adjacent control sites. The intellectual merit of this project is that it has the potential to demonstrate that these sites can serve as long term (50 - 100 year) analogs of existing CO2 enrichment experiments, providing a view much farther into the future than is now possible. The primary broader impact of this project, if it successfully demonstrates the suitability of these sites, will be the identification of a resource that is likely to be used by scientists who are interested in long term consequences of increased atmospheric CO2 on many aspects of terrestrial ecosystems.
