The Chequamegon National Forest in north-central Wisconsin is the site of extensive observations of forest-atmosphere exchanges of carbon dioxide and energy. Long-term measurements have been made from a 450m TV tower since the spring of 1995, including a six-level carbon dioxide profile, and eddy-covariance flux measurements at 30, 122 and 396 meters above ground. In 1998 the experiment has expanded to include component carbon dioxide flux measurements, airborne sampling of atmospheric carbon dioxide profiles, small-tower (30 m) eddy-covariance flux measurements, radar remote-sensing of boundary-layer development, validation of satellite remote-sensing of ecological parameters, leaf physiology measurements, and numerical simulations forest-atmosphere interactions. We will present a summary of these efforts whose overall goal is understanding forest-atmosphere interactions and carbon dioxide exchange in this region, and possible responses to climatic change.
We will also present preliminary comparisons of the net ecosystem exchange of carbon dioxide as observed from the 450m WLEF TV tower versus the 30m Willow Creek flux tower and ground-based component carbon flux measurements. The WLEF tower is located in a very heterogeneous region composed of upland hardwoods and pines, and lowland conifers and shrubs. The height of the measurements results in flux measurements that are an integration of net ecosystem exchange over this region. The Willow Creek tower is located nearby in a fairly uniform, upland hardwood forest. This location will also be the site of frequent component carbon flux measurements, including soil flux chambers and leaf enclosures. We will show a preliminary study of the relationship between the WLEF tower fluxes, the Willow Creek fluxes, and the component fluxes which make up the net ecosystem exchange. We will discuss sources of variability among these observations as a function of spatial scale,time, and carbon-exchange mechanisms.