THE FACE PROGRAM

A large, cooperative, integrated experimental program utilizing free-a ir CO2 enrichment (FACE) is being conducted to expose plants to elevat ed concentrations of CO2. The goals are to evaluate the effects of inc reasing atmospheric CO2 on plants and ecosystems and, in the long run, to contribute to the evaluation of terrestrial plant feedback regulat ion on the rate of change of CO2 in the atmosphere. Having no walls, t he FACE system allows plants to be grown under realistic microclimate and CO2 conditions expected to prevail in the mid-twenty-first century . Data obtained under such conditions are needed for validation of mod els being developed to predict the effects of increasing CO2 and chang ing climate variables on plants, ecosystems, agricultural productivity and water resources. Setup costs for the FACE systems used in these e xperiments are similar to the costs of field chamber systems. Although annual operating costs are about three times the cost of field chambe rs, FACE plots are relatively large, leading to an economy of scale, s o that per unit of treated plant material, FACE systems are the least expensive approach for well-integrated field experiments. These featur es have provided an incentive to conduct comprehensive FACE experiment s with many cooperating scientists working together to measure numerou s plant, soil and micrometeorological parameters, as described in the collection of papers in this special issue of 'Agricultural and Forest Meterology'.