PARENT SESSION
Oral Session 81: Forest Ecology IV: Seeds, Growth, and Recruitment.
Presiding: J Kush
Wednesday, August 4, 1:30 PM to 5:00 PM, Meeting Room C 120.

Differential growth of understory hardwood species in a Loblolly pine plantation exposed to elevated CO₂.

Moore, David^*,1, Pippen, Jeffrey ^*,2, DeLucia, Evan^{*,1, 3}, ¹ Program in Ecology and Evolutionary Biology, Urbana, IL, USA² Botany Department, Durham, NC, USA³ Department of Plant Biology, Urbana, IL, USA

ABSTRACT- Rising CO₂ is predicted to increase forest productivity and may potentially change future species composition. We used repeated measures of diameter growth to determine the effect of free air carbon dioxide enrichment on the growth of both understory hardwood species and the dominant canopy species (Pinus taeda) in a rapidly growing plantation exposed to elevated CO₂ for 7 years. Elevated CO₂ increased individual tree relative basal area increment (RBAI) in some species more than others. Responses of understory hardwoods were dependent on their size and proximity to their neighboring canopy trees. For the dominant P. taeda the growth stimulation was only observed in trees in two intermediate size classes. The smaller, suppressed pines did not respond nor did the largest pines indicating a shift in the competitive interactions among individuals. The loss of responsiveness by the largest pines suggests that the stimulation in growth rate by elevated CO₂ may be confined to early stages of stand development. Changes in the structure and relative species abundance in forests are likely to complicate efforts to predict the role of future forests in the global carbon cycle.

Key words: community ecology, relative growth rate, face, pinus taeda