Brookhaven National Laboratory free-air carbon dioxide enrichment forest prototype -- Interim report

Abstract

A variety of approaches have been used in fumigation experiments to quantify the effects of increasing atmospheric carbon dioxide concentration ([CO{sub 2}]{sub atm}) on plants. Mot of these approaches, reviewed elsewhere (Allen 1992), entail some type of enclosure or chamber. Chambers provide containment of the CO{sub 2}-enriched air and in this way reduce the amount of CO{sub 2} required for the experiment. At the same time, chambers alter microclimate conditions in a variety of ways so that there is a significant chamber effect on the plants within. Free-air carbon dioxide enrichment (FACE) is an alternative experimental strategy in which CO{sub 2}-enriched air is released into the ambient environment in such a way as to provide effective experimental control over [CO{sub 2}]{sub atm} without causing any change in other environmental variables. Early types of free-air exposure systems were built in the Netherlands and England for exposing vegetation to elevated concentrations of atmospheric trace gases. The FACE Program at Brookhaven National Laboratory (BNL) considered these original ideas in designing the BNL FACE systems. The purpose of the current BNL project in the Duke Forest is to develop a FACE system that can provide adequate control over [CO{sub 2}]{sub atm} in a tall forest setting. This report is a preliminary overview of the data and much remains to be done in the analysis.