interest in a common set of quantities in ecological site studies (quantities such as CO2, trace gas and water fluxes, NPP, nutrient availability, and species composition and diversity), achieving consensus on a core set of measurements, standard methods, and data formats is just beginning. No global-scale experimental design implementing such sites is in place to sample marine and terrestrial ecosystems, although such a design is proposed by the International Geosphere-Biosphere Programme (IGBP), using long baseline transects across ecological gradients. A high priority of global ecosystem science is to develop a network of appropriately sited atmospheric concentration and isotope, flux, and ecological process sites. Both the overall experimental design and the suite of measurements and methods must be decided. Minimally intrusive measurements (e.g., flux measurements) and manipulations (e.g., of CO2 concentration) must be components of such a network design.
Recent advances in hyperspectral measurements made directly and remotely have established that remote sensing of foliar chemistry will be an important element in producing large-scale spatially explicit estimates of forest ecosystem function. During the past decade, a number of studies were conducted to determine if data from the National Aeronautic and Space Administration's 10-nm spectral resolution Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) could be used to make canopy nitrogen and lignin measurements. AVIRIS channels in the visible and infrared regions were correlated to field-measured foliar nitrogen and lignin.6 Estimates of canopy foliar nitrogen were used as input to the primary production model7 to determine ecosystem productivity at the Harvard Forest, in Massachusetts. At Blackhawk Island, AVIRIS-derived foliar lignin was used to determine nitrogen mineralization rates using a relationship observed by Wessman et al. (1998). These and other results suggest that direct measurement of forest canopy chemistry characteristics, based either on field measurements or via remote sensing, may provide simple, direct scalars of current forest productivity potential. In the coming decade, a space-based system will replace AVRIS, and the application of these techniques can be made at research sites globally.
The issue of diversity and species composition changes has emerged as a critical topic for global change in recent years. It is clear that the functional diversity of the Earth's biota is a first-order control over global ecosystem function, but how changes to the biota will affect global ecosystem function still is a young research topic. 8 Designing a global observing system and network of experimental studies, analogous to those described above for biogeochemical fluxes, is premature; the necessary monitoring and manipulations at global scales are currently far from obvious. But a major exploratory effort involving manipulations, studies of ecosystem function in the face of ongoing invasions, extinctions, species range shifts, and global monitoring of species diversity, invasion,