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Keywords:

  • allometry;
  • basal area increment;
  • elevated CO2;
  • forest productivity;
  • free-air CO2 enrichment (FACE);
  • global change;
  • Liquidambar styraciflua (sweetgum);
  • tree growth

Summary

  •  In a free-air CO2 enrichment (FACE) study, above-ground growth of Liquidambar styraciflua (sweetgum) trees was measured in a closed-canopy stand to test hypotheses about long-term effects of rising [CO2] in a deciduous forest.
  •  Allometric relationships were established between above-ground dry mass and basal area, height, taper and wood density for all trees in the 314-m2 plots. Leaf area index was calculated from leaf litter mass.
  •  In the first year of exposure, elevated [CO2] stimulated stand-level aboveground dry matter increment by 33%, but in the second year the growth stimulation was reduced to 15% and was no longer statistically significant. Leaf area index was not affected by CO2 enrichment in either year.
  •  These results indicate that large trees that are no longer in an exponential growth phase retain the capacity to respond to elevated [CO2]. The combined 2-yr response of a 24% increase in growth per unit leaf area is consistent with predictions from earlier studies. A longer-term data set is needed to resolve the reason for different responses in the 2 years.