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Inter-annual variation in the response of tree growth and productivity to exposure to elevated [CO2].
Moore, David*,1, Aref, Susanne1, Finzi, Adrien2, Hamilton, Jason3, Pippen, Jeffrey 4, Ho, Moon-ho1, DeLucia, Evan1, 1 University of Illinois - Urbana-Champaign, Urbana, IL2 Boston University, Boston, MA3 Ithaca College, Ithaca, NY4 Duke University, Durham, NC
ABSTRACT- Elevated atmospheric [CO2] enhances growth in plants through an increase in photosynthetic efficiency. Our ability to predict the capacity of future forests to sequester atmospheric carbon depends on understanding how variations in climate will modulate that response at the tree level and forest level. In the longest running experiment of its kind, an intact Pinus taeda forest was exposed to +200 p.p.m. CO2 for 6 years using Free Air Carbon-dioxide Enrichment (FACE). We used a non-linear growth model to determine the initiation and cessation of diameter growth. Stimulation of diameter growth rate, expressed in relative basal area increment (RBAI) was sustained over time (ranging from 17.2- 26.2%) and correlated well with seasonal temperature totals. These results agree with previous modeling and empirical studies of photosynthetic response. There was a sustained increase of productivity caused by the elevated [CO2] treatment (193 gm-2y-1 or 25%). There was no interactive effect of elevated [CO2] and seasonal rainfall; the productivity of both ambient and elevated [CO2] treatments showed a strong parallel reduction in low precipitation years. Predicted rises in [CO2] and temperature will likely stimulate forest growth but water availability will remain a key growth limiting factor.
Key words: loblolly pine, carbon sequestration, FACE, ecosystem