Micrometeorological conditions at the Forest-Atmosphere Carbon Transfer and Storage (FACTS-II) Aspen FACE facility in northern Wisconsin

The Forest-Atmosphere Carbon Transfer and Storage (FACTS-II) - Aspen Free-Air Carbon Dioxide Enrichment (FACE) Experiment in northern Wisconsin is a multidisciplinary study to assess the effects of increasing tropospheric ozone (O₃) and carbon dioxide (CO₂) levels on aspen forest ecosystems. An important study at this research site is the assessment of the indirect microclimate changes resulting from the altered vegetation characteristics induced by elevated near-surface CO₂ and O₃ concentrations. Forest vegetation changes in response to increasing O₃ and CO₂ concentrations under a changing climate have the potential for altering atmospheric environments and the dynamics of forest-atmosphere interactions in forest ecosystems.

To assess some of these indirect effects on typical forest ecosystems of the northern Great Lakes region of the U.S., a micrometeorological monitoring network has been established at the Aspen FACE facility near Rhinelander, WI. This facility, constructed in 1997-1998, consists of twelve 30 m diameter free-air treatment plots that were each planted with aspen (Populus tremuloides), paper birch (Betula papyrifera) and sugar maple (Acer saccharum) seedlings. The twelve plots represent three replicates of four plots each. Each replicate contains a control plot where CO₂ and O₃ concentrations are not altered, a plot with elevated CO₂ concentrations, a plot with elevated O₃ concentrations, and a fourth plot with elevated CO₂ and O₃ concentrations. Meteorological instrumentation has been installed in all four plots of one replicate as a means of sampling conditions under the different types of fumigation strategies.

This paper describes the meteorological monitoring effort to date and provides an initial overview of some of the atmospheric conditions observed in the instrumented plots during 1998 and part of 1999. Specifically, diurnal and monthly variations in temperature, relative humidity, wind speed, net radiation, photosynthetically-active-radiation, soil temperature, and soil moisture are described in relation to developing vegetation characteristics in a control plot and CO₂-, O₃-, and CO₂+O₃-fumigated plots.