Predicting the regional impact of ozone and precipitation on the growth of loblolly pine and yellow-poplar using linked TREGRO and ZELIG models

Abstract

To simulate the long-term effects of ozone on forests in the US, we linked TREGRO, a mechanistic model of an individual tree, to ZELIG, a forest stand model, to examine the response of forests to five ozone exposure regimes (0 to ∼100 ppm h SUM06 per year) in 100-year simulations. TREGRO and ZELIG were parameterized using biological and meteorological data from three climate sites in the southeastern US. TREGRO was used to generate 3-year exposure–response relationships between ozone and growth of loblolly pine ( Pinus taeda L.) and yellow-poplar ( Liriodendron tulipifera L.). Ratios (response at ozone exposure: response at base case) of total tree mass, leaf mass, and fine root/leaf mass were calculated and used to modify growth functions in ZELIG. At the end of the ZELIG simulation, the change in basal area of loblolly pine ranged from an increase of 44% to a decrease of 87%, depending on precipitation and ozone exposure. The basal area of yellow-poplar, simulated in competition with loblolly pine was not affected over most of its range. Over the range of the two species, the simulated changes in basal area due to ozone exposure were generally within ±10% of the base case. Competitive interactions between the species were not altered.