Differential effects of elevated CO2 on acorn density, weight, germination, and predation among three oak species in a scrub-oak forest

Much research on the effects of elevated CO2 on forest trees has focused on quantitative changes in photosynthesis, secondary chemistry, and plant biomass. However, plant fitness responses to rising CO2 should also include quantitative measures of reproduction, since most forest systems are recruitment limited. Until now, it has proved very difficult to grow forest trees to sexual maturity in a CO2-enriched environment. This paper is the first of its kind to address the effects of elevated CO2 on the reproduction of hardwood trees in a natural forest. Beginning in 1996, scrub-oak vegetation, predominantly three species of scrub-oaks, Quercus myrtifolia, Q. chapmanii, and Q. geminata, were grown inside eight chambers with elevated CO2 (704 parts per million (ppm)) and eight with ambient CO2 (379 ppm) at Kennedy Space Center, Florida. In elevated CO2, acorn production increased significantly for the dominant species Q. myrtifolia and for Q. chapmanii, but it did not increase for the subdominant, Q. geminata. Acorn weight, germination rate, and predation by weevils were unaffected by CO2. Thus, recruitment of some forest tree species into the Florida scrub-oak community is likely to be accelerated in an atmosphere of increased CO2. However, because the acceleration of recruitment differs among species, over the long term, Q. myrtifolia and Q. chapmanii will be favored over Q. geminata and this is likely to change patterns of species diversity.