INTRODUCTION

Understanding the reciprocal influences between the land surface and the atmosphere has become a scientific imperative, as human-induced changes in land surface characteristics are impacting the composition of the atmosphere, which in turn is threatening to excite changes in our weather and climate systems. The concentration of efforts to quantify these influences and to develop a predictive framework for them has given birth to the new research field of "land-atmosphere exchange", now populated by a community of scientists and engineers originally trained in a cross-section of disciplines. The field of land-atmosphere exchange research is organized toward the development and use of a comprehensive theory to describe the exchange of mass (e.g. water and CO2), energy, and momentum between the land and atmosphere over a wide range of spatial and temporal scales. The urgency for improved predictive capability in the area of land-atmosphere interaction is underscored by the United States Global Change Research Program's USGCRP recent development of cross-agency Carbon and Water Cycle Science Plan. Both plans independently stress the need to quantify and predict variability in these two cycles over a broad range of space and time scales. My past, present and near future work has focused on developing an understanding of the cycling of water, carbon, and energy within the soil-plant-atmosphere continuum. This topic comprises the core (and intersection) of the USGCRP Carbon and Water Cycle Science Plans.