Seasonal Variability in the Effect of Elevated CO sub(2) on Ecosystem Leaf Area Index in a Scrub-Oak Ecosystem

In a scrub-oak ecosystem on Merritt Island, FL, which had regenerated after fire in both ambient and elevated atmospheric carbon dioxide concentrations in open-top chambers, the seasonal variability in the effect of elevated CO sub(2) on leaf area index was examined. The 2-yr study was performed prior to canopy closure, 3 5 yr into the fire regeneration cycle. Leaf area index determined from photosynthetically active radiation transmission through the canopy was compared with that determined by the normalized different vegetation index, hemispherical photography, and allometric relationships. Results showed that elevated atmospheric CO sub(2) increased leaf area index prior to canopy closure, with the stimulation highest during spring, when leaf area expansion was faster, and lowest in winter, when leaf fall was greater. Good measures of leaf area index were achieved with all techniques except for the allometric relationship between stem diameter and leaf area.