The effects of meteorological phenomena upon forest produc­ tivity and forestry operations have been of concern for many years. With the evolution of system-level studies of forest eco­ system structure and function in the International Biological Program and elsewhere, more fundamental interactions between forest ecosystems and the atmosphere received scientific atten­ tion but the emphasis on meteorological and climatological effects on forest processes remained. More recently, as recogni­ tion has developed of potential and actual problems associated with the atmospheric transport, dispersion, and deposition of airborne pollutants, the effects of forest canopies upon boundary-layer meteorological phenomena has come under scientific scrutiny. Looking to the future, with rising atmospheric con­ centrations of C02 and increasing competition for the finite fresh-water resources of the earth, interest in the role of forests in global C02 and water balances can also be expected to intensify. Thus, the nature of forest canopy-atmosphere interac­ tions, that is to say, the meteorological phenomena occurring in and above forest canopies, are of importance to a wide variety of scientific and social-issues. Demands for forest meteorological information currently exceed levels of knowledge and given the economic constraints of science in general and environmental sciences in particular, chances for major improvements in scien­ tific support in the near future are slim. Unfortunately, studies of environmental phenomena in and above forests are costly and logistically difficult. Trees, the ecological dominants of forest ecosystems, are the largest of all terrestrial organisms.