Burton Lab FACE

Northern Forest Ecosystem Experiment/ Aspen FACE (free air CO2 enrichment)


  • There is evidence beyond dispute that modern society is causing the concentration of atmospheric CO2 to rise dramatically and ozone levels in the troposphere are approaching toxic levels (to plants) in areas exposed to heavy industry, air traffic and auto-exhaust.

  • Clearly, humans are having an ever-increasing impact on the quality of the environment for plant growth, and we are just beginning to realize this may have important consequences for the future climate and habitability of the planet. Since 1998, we have examined the interacting effects of elevated CO2 and O3 on ecosystem processes in an aggrading northern forest ecosystem. This study utilized a free-air carbon dioxide enrichment (FACE) facility in Rhinelander, Wisconsin to compare the responses of rapid-growing shade intolerant species (trembling aspen [Populus tremuloides Michx.] and paper birch [Betula papyrifera Marsh.]) to that of a slower growing shade tolerant species (sugar maple [Acer saccharum Marsh.]). Throughout the experiment, photosynthesis has increased with elevated CO2 and decreased with elevated O3, compared to the control, and stomatal conductance has decreased under elevated CO2. Treatment effects on photosynthesis have contributed to CO2 stimulation of aboveground and belowground growth that was species and genotype dependent, with birch and aspen being most responsive and maple least responsive. The addition of O3 tended to completely eliminate the positive CO2 effect in early years, but in later years only dampened it. Other investigators have examined impacts of the treatments on insect and disease interactions, belowground processes and C storage, nutrient cycling, plant physiology and biochemistry, gene expression, hydrology, and soil microbial communities, as well as interactions between treatment responses and interannual variations in climate. The Aspen FACE Experiment is a multidisciplinary study involving collaboration between scientists from 8 countries, and we now have over 110 Aspen FACE scientific users, who have worked together for more than a decade. Research at the Aspen FACE Experiment has been funded jointly by the the Department of Energy, USFS North Research Station, the National Science Foundation, the National Council on Air and Stream Improvement (NCASI), the USFS Global Change Program, and Michigan Technological University, resulting in more than 120 publications to date.

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