PARENT SESSION
Oral Session #58: Elevated CO₂. Presiding: A. Finzi.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Madison Ballroom C.

Leaf phenology of saplings growing in the understory of a forest exposed to elevated CO₂.

Hartz-Rubin, Jennifer¹, DeLucia, Evan¹, ¹

ABSTRACT- Elevated atmospheric CO₂ may stimulate the growth of trees by increasing the longevity of foliage and thus the active period for photosynthesis. We monitored leaf phenology (emergence, duration, abscission, survival) of six hardwood species growing in a forest exposed to elevated CO₂. Leaf births and deaths were recorded on shoots of Cercis canadensis, Acer rubrum, Carya glabra, Quercus velutina, Ulmus alata, and Liquidambar styraciflua for two growing seasons. Mean leaf area duration (LAD) differed significantly among species (p<0.001) and among leaf cohorts (p<0.001). There was a pronounced effect of elevated CO₂ on leaf phenology, but it varied among species and interacted strongly with the year of measurement. By increasing survivorship and decreasing the rate of senescence, elevated CO₂ increased LAD for L. styraciflua (both years; p<0.04) and Ce. canadensis (1998; p<0.001). For U. alata and Q. velutina, LAD was increased by elevated CO₂ in one year but decreased in the other, and there was no effect on LAD of A. rubrum. Interannual variation in precipitation may exert a strong influence on the responsiveness of leaf phenology to elevated CO₂. Species with increased LAD, such as Ce. canadensis and L. styraciflua, may show greater stimulation of growth in response to elevated CO₂. In the long-term, wide-ranging variation in species' leaf phenology could alter patterns of forest regeneration and species composition.

KEY WORDS: longevity, phenology, senescence, survivorship