Ecosystems and problems of measurement at large spatial scales

Both the structure and function of terrestrial ecosystems have significant impact on atmosphere-biosphere dynamics. Analyzing and predicting their roles in global environmental change present a major challenge to ecosystem scientists. Measurements at landscape, regional, and global scales are both necessary and difficult because they incorporate the full complexity of interacting system components, variations inherent in resource and climate constraints, and the effects of land-cover or land-use change. Our objective in this chapter is to identify the large-scale measurements that will most effectively further our understanding of regional and global ecology. To do this, our discussion expands from present-day measurements of biophysical structure and function to the areas in which new measurements can span our knowledge gaps. Although today's observation strategies are conducted at several scales, they tend to address either structure (e.g. vegetation-type distribution) or function (e.g. trace-gas fluxes) and rarely link the two. They lack integration as a result of several gaps, the most significant of which may be knowledge of dynamic carbon allocation processes and changing land-cover and land-use distributions. Continued development of dynamic global vegetation models is needed to couple ecosystem redistribution with biogeochemistry. However, because allocation is not mechanistically simulated by present-day ecosystem process models, remote sensing of aboveground allocation patterns will be required to constrain simulations for the foreseeable future. We contend that a stronger effort to link the physical structure to the function is critically needed to advance our understanding and predictive capability at large scales, and that quantitative remote sensing will provide important measurements to make those links.