Ozone impacts on loblolly pine ( Pinus taeda L.) grown in a competitive environment

Loblolly pine seedlings in carbon-filtered air open-top chambers, with competition from other plants, behaved differently than those reported in other studies without competition One-year old, bare-root, loblolly pine ( Pinus taeda L.) seedlings grown in an early successional plant community, were exposed to four ozone treatments, 12 h day −1 (09:00–21:59 h CST), 7 day week −1 in east-central Alabama for 2 years (1994–1995). Treatments included AA=ambient air (open plot; no chamber), CF=carbon-filtered air (approximately 0.5×AA), 1X=non-filtered air, and 2X=twice ambient (AA) air. Pine height and diameter were measured monthly for 2 years and total above-ground biomass determined at termination of the experiment. In addition, height, diameter and volume ( d 2 h) growth was modeled for the 2-year study. Trees growing in the CF chambers exhibited the least growth for any variable measured. The predicted height growth rate ( r) was the least for the CF- and 2X-treated pines when compared with the AA and 1X treatments. In addition, percent total vegetative cover was significantly negatively correlated with height, diameter and volume growth in 1994, but not 1995. Our findings regarding the trees growing in the CF treatments, are contrary to previous reports regarding ozone impacts to loblolly pine grown without competition from other vegetation.