Increasing CO2 and tree growth: drawing conclusions from observational data
1996
Reams, G.A. (USDA Forest Service, New Orleans (USA). Institute for Quantitative Studies) | Noejd, P.J.
Strong evidence from numerous sources indicates that the concentration of atmospheric CO2 is steadily rising. It is common knowledge from controlled experiments that growth of tree seedlings and saplings is enhanced by increased CO2. Whether these experimental results based on juvenile trees subjected to a short period of treatment can be extrapolated to forests is unknown. The available data for such an evaluation is largely based on observational studies. Observational studies are defined as such because the researcher cannot use controlled experimentation. The type of observational studies used to investigate CO2 effects includes forest surveys, long-term growth and yield plots, and long-term individual tree radial growth rates. The problem facing the researcher in all observational studies is the establishment of methods of control. Because control can usually be attempted on a limited number of variables that can influence growth, control is likely to be only partially effective. It is therefore incumbent upon researchers to think carefully about what biases are most likely, and what the sources, direction, and possible magnitudes these sources may have. This paper reviews and suggests a number of control methods that have been or could be used by forest researchers investigating the CO2 growth enhancement hypothesis
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