GROWTH-RESPONSES OF 7 MAJOR COOCCURRING TREE SPECIES OF THE NORTHEASTERN UNITED-STATES TO ELEVATED CO2

Examined how elevated CO2 affected growth of American beech Fagus grandifolia, paper birch Betula papyrifera, black cherry Prunus serotina, white pine Pinus strobus, red maple Acer rubrum, sugar maple Acer saccharum and eastern hemlock Tsuga canadensis. Seedlings and transplants were grown in 1 of 4 plant growth chambers for 60 d (beech, paper birch, red maple, black cherry) or 100 d (white pine, hemlock, sugar maple) under CO2 levels of 400 or 700 μL.L-1. The biomass of beech, paper birch, black cherry, sugar maple and hemlock significantly increased in elevated CO2, but that of red maple and white pine only marginally increased. There were large differences in the magnitude of growth enhancement by increased levels of CO2 between species, so one consequence of rising levels of CO2 may be to increase the competitive ability of some species relative to others. The species exhibiting the largest increase in growth with increased CO2 concentrations were shade-tolerant (beech, sugar maple, hemlock). Thus, elevated CO2 levels may enhance the growth of relatively shade-tolerant forest trees to a greater extent than growth of shade-intolerant trees. -from Authors