Pollen production by Pinus taeda growing in elevated atmospheric CO 2

Summary1 Rising concentrations of atmospheric CO 2 may have important consequences for reproductive allocation in forest trees. Changes in pollen production could influence population dynamics and is likely to have important consequences for human health. This is the first study to evaluate pollen production by forest trees in response to rising atmospheric CO 2 . 2 Our research objective was to quantify pollen production by Loblolly Pine ( Pinus taeda L.) trees growing in elevated CO 2 (ambient + 200 µl l −1 ) since 1996. 3 Trees grown in high‐CO 2 plots first began producing pollen while younger and at smaller sizes relative to ambient‐grown trees. Pollen cone and airborne pollen grain abundances were significantly greater in the fumigated stands. We conclude that the greater number of mature trees in high‐CO 2 plots resulted in greater pollen production at the stand level. 4 Precocious pollen production has important implications for fertilization and pollen dispersal from young, dense stands. Increasing levels of airborne pollen raise concerns for escalating rates of human respiratory disease.