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Net Primary Productivity at the Duke Forest FACE Facility
McCarthy, H.R., Oren, R., Johnsen, K.H., Gallet-Budynek, A., Pritchard, S.G., Cook, C.W., LaDeau, S.L., Jackson, R.B. and Finzi, A.C. 2010. Re-assessment of plant carbon dynamics at the Duke free-air CO2 enrichment site: interactions of atmospheric [CO2] with nitrogen and water availability over stand development. New Phytologist 185: 514-528.

The Duke Forest Free-Air CO2-Enrichment or FACE study is a long-term experiment that was designed to investigate the effects of an extra 200 ppm of atmospheric CO2 on the growth and development of a plantation of loblolly pine (Pinus taeda) trees with an understory of various broadleaf species (Liriodendron tulipifera, Liquidambar styraciflua, Acer rubrum, Ulmus alata, Cornus florida) plus various other trees, shrubs and vines, all of them growing on a soil that Finzi and Schlesinger (2003) have described as being in "a state of acute nutrient deficiency that can only be reversed with fertilization," which fertility deficiency many people had long thought would stifle the ability of the extra aerial supply of CO2 to significantly stimulate the forest's productivity on a continuing basis.

What was done
Working with data for the years 1996-2004, the team of nine researchers write that "net primary productivity [NPP] for pines, hardwoods and the entire stand was calculated as the sum of the production of coarse wood (stems, branches, coarse roots), leaf litter (lagged for pines), fine roots and reproductive structures."

What was learned
McCarthy et al. state that "elevated CO2 increased pine biomass production, starting in 1997 and continuing every year thereafter," that "the CO2-induced enhancement remained fairly consistent as the stand developed," that "elevated CO2 increased stand (pine plus all other species) biomass production every year from 1997 onwards with no trend over time [italics added]," while noting that the average yearly increase in NPP caused by the approximate 54% increase in the air's CO2 content was 28%.

What it means
In spite of the original belief of many scientists that low levels of soil nitrogen -- especially an acute deficiency -- would preclude any initial growth stimulation provided by atmospheric CO2 enrichment from long persisting, the suite of trees, bushes and shrubs that constitute the Duke Forest has continued to maintain the extra CO2-enabled vitality that it exhibited right from the start of the study, with no sign of it even beginning to taper off.

Finzi, A.C. and Schlesinger, W.H. 2003. Soil-nitrogen cycling in a pine forest exposed to 5 years of elevated carbon dioxide. Ecosystems 6: 444-456.

Reviewed 31 March 2010