CLIMATIC-CHANGE EFFECTS ON THE PHYSIOLOGY AND GROWTH OF PINUS-PONDEROSA - EXPECTATIONS FROM SIMULATION MODELING

The TREGRO model was used to simulate the growth response of mature Pi izus ponderosa Dougl. ex Laws. to the interacting effects of changes i n CO2 (+200 mu L/L), temperature (+4 degrees C), and O-3 (0.5x, 1x, an d 2x ambient). Relative to simulated growth under the base-line climat e in Corvallis, Oregon, elevated CO2 and temperature individually incr eased total-tree biomass gain by 29% and 13%, respectively, but when c ombined increased biomass gain by 49%. Ozone at all exposures reduced total-tree biomass gain by 1%, 19%, and 39%, respectively, as compared with simulated base-line conditions. Elevated CO2 increased photosynt hesis and reduced stomatal conductance and partially offset growth red uctions due to 2 x O-3. Elevated temperature, however, increased both photosynthesis and stomatal conductance and was less effective at miti gating growth reductions due to 2x O-3. Growth at 2x O-3 in elevated C O2 and temperature conditions had little effect on total-tree growth, but decreased fine-root growth by 61%. The simulated changes in stomat al conductance and fine-root biomass are expected to interact with the availability of soil resources to affect tree growth and possibly alt er the distribution of Pinus ponderosa.