The ability to predict the likely effects of global change on forest ecosystems is one of the major challenges of ecology at present. The observed increase in the atmospheric CO2 concentration is a direct factor likely to affect the functioning of forest ecosystems, including that of the soil. A diverse range of experimental designs and facilities has been used in attempts to predict the response of forests to forecast concentrations of CO2. They test the reaction of a multitude of organisms and processes, from a single photosynthesising cell to a whole forest, to a CO2 concentration much higher than that of today. As well as scale and system complexity, different lengths of exposure of plants to elevated CO2 were tested. Existing observations vary from only a few days' fumigation, assessing the immediate physiological response, to continuous measurements on trees grown under elevated CO2 conditions for several growing seasons, to measure ecosystem-scale processes. This chapter explains various techniques used to simulate future atmospheric levels of CO2 and then discusses the likely effects of elevated CO2 on forest growth, soil carbon and nitrogen cycles and on forest soil biota functioning and diversity.

Atmospheric CO2 enrichment technology

The concentration of CO2 in the atmosphere has been rising owing to human activity during the past two centuries. The level of CO2 in the pre-industrial period, estimated at 280 ppm, has increased to the present value of approximately 385 ppm and is predicted to rise further during the course of this century.