What was done
Starting in 1996, three species of scrub-oak (Quercus myrtifolia, Q. chapmanii, and Q. geminata) were grown within sixteen open-top chambers, half of which were maintained at 379 and half at 704 ppm CO2, at the Kennedy Space Center, Florida, USA.  In August, September and October of 2001, the authors counted the numbers of acorns on randomly selected twigs of each species; while in November of that year they counted the numbers of fallen acorns of each species within equal-size quadrats of ground area.  In addition, they evaluated mean acorn weight, acorn germination rate, and degree of acorn infestation by weevils.

What was learned
Acorn germination rate and degree of predation by weevils were unaffected by elevated CO2; while acorn size was enhanced by a small amount: 3.6% for Q. myrtifolia, 7.0% for Q. chapmanii, and 7.7% for Q. geminata.  Acorn number responses, on the other hand, were enormous, but for only two of the three species, as Q. geminata did not register any CO2-induced increase in reproductive output, in harmony with its unresponsive overall growth rate.  For Q. myrtifolia, however, the authors report "there were four times as many acorns per 100 twigs in elevated CO2 as in ambient CO2 and for Q. chapmanii the increase was over threefold."  On the ground, the enhancement was greater still, with the authors reporting that "the number of Q. myrtifolia acorns per meter squared in elevated CO2 was over seven times greater than in ambient CO2 and for Q. chapmanii, the increase was nearly sixfold."

What it means
Stiling et al. say these results lead them to believe "there will be large increases in seedling production in scrub-oak forests in an atmosphere of elevated CO2," noting that "this is important because many forest systems are 'recruitment-limited' (Ribbens et al., 1994; Hubbell et al., 1999)."

References
Hubbell, S.P., Foster, R.B., O'Brien, S.T., Harms, K.E., Condit, R., Wechsler, B., Wright, S.J. and Loo de Lao, S.  1999.  Light-gap disturbances, recruitment limitation, and tree diversity in a neotropical forest.  Science 283: 554-557.

Ribbens, E., Silander, J.A. and Pacala, S.W.  1994.  Seedling recruitment in forests: calibrating models to predict patterns of tree seedling dispersion.  Ecology 75: 1794-1806.