You are here:
Ozone exposure-response curves for tree species in Great Smoky Mountains National Park: A re-evaluation of how potential impacts may have changed over the past 25 years
Citation:
Neufeld, H., EHenry Lee, W. Hacker, S. Huang, AND J. Renfro. Ozone exposure-response curves for tree species in Great Smoky Mountains National Park: A re-evaluation of how potential impacts may have changed over the past 25 years. Presented at Air Pollution Workshop, Portland, OR, June 24 - 27, 2013.
Impact/Purpose:
Tropospheric ozone concentrations in the Great Smoky Mountains National Park (GSMNP) rose sharply from 1988 to 1999, followed by a decline in recent decades, but may still be potentially harmful to ozone-sensitive tree species. A series of exposure-response studies funded by the U.S. Forest Service several decades ago were conducted to determine the potential impacts of elevated ozone concentrations on native tree species in the GSMNP. WED scientists in collaboration with non-Agency scientists have analyzed the experimental data to develop ozone exposure-response relationships with respect to the W126 and SUM06 indices proposed for a secondary national ambient air quality standard (NAAQS). Responses of the tested species ranged from sensitive to moderately sensitive to totally insensitive. We estimate that several tree species could potentially be negatively affected by ozone concentrations for the years 1988-2012. Our findings show that the relative sensitivity of a number of tree species have been misreported in the published literature based on experimental and observational data. Our work is important and timely in filling in the gaps of knowledge in understanding the potential impacts on tree species exposed to elevated ozone concentrations and the development of a future secondary NAAQS for ozone.
Description:
Seedlings of tree species native to Great Smoky Mountains National Park were exposed to ozone in open-top chambers for one or two growing seasons. Species used were red maple (Acer rubrum), chestnut oak (Quercus prinus), black locust (Robinia pseudoacadia), winged sumac (Rhus copallina), yellow buckeye (Aesculus octandra), sycamore (Platanus occidentalis) sweetgum (Liquidambar styraciflua), yellow poplar (Liriodendron tulipifera),Virginia pine (Pinus virginiana), eastern hemlock (Tsuga canadensis) and Table Mountain pine (Pinus pungens) Foliar stipple was measured on two or more leaves/needles per plant and at the end of the exposure period plants were harvested for dry mass. Synthesized diurnal exposure profiles were used in 1988, and modified ambient profiles were used from 1989-1992, with 2.0x ambient being the highest exposures used. Exposure-response curves for biomass were developed using the Weibull function and SUM06 index. Species responses ranged from totally insensitive (no biomass or foliar effects) in Table Mountain pine, hemlock and chestnut oak, to no biomass responses, but elevated foliar stipple in above ambient treatments for Virginia pine, sycamore, and black locust, to both biomass reductions and elevated stipple in above ambient treatments for the remaining species. Ozone exposures in the Park rose sharply from 1988 to 1999, but have fallen since then, with occasional high ozone years interspersed among low ozone years. Using the exposure-response curves for biomass in this study, we estimate which species could potential be negatively affected by ozone for each year from 1988-2012. Among the species in this study, responses range from sensitive to moderately sensitive to totally insensitive. With elevation, seasonal exposures increase and diurnal patterns become flatter, potentially changing species responses. The risk to species was maximal when ozone peaked in the late 1990s, but has dropped dramatically in recent years. However, predictions extrapolated from potted seedlings to mature adult trees should be viewed with caution.