Grantee Research Project Results
1999 Progress Report: Modeling Ozone Flux to Forests Across an Ozone Concentration Gradient in the Sierra Nevada Mountains, CA.
EPA Grant Number: R826601Title: Modeling Ozone Flux to Forests Across an Ozone Concentration Gradient in the Sierra Nevada Mountains, CA.
Investigators: Goldstein, Allen H. , Panek, Jeanne A.
Institution: University of California - Berkeley
EPA Project Officer: Chung, Serena
Project Period: August 1, 1998 through October 31, 2002
Project Period Covered by this Report: August 1, 1998 through October 31, 1999
Project Amount: $621,367
RFA: Ecological Indicators (1998) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration
Objective:
Tropospheric ozone is a pollutant that is responsible for forest damage worldwide. Currently, extensive ozone-monitoring networks measure ozone concentrations throughout the United States and Europe; however, the physiologically relevant measure of ozone effects on forest health is not concentration, but ozone flux, the amount of ozone that actually enters the foliage. We are developing a model that estimates ozone flux from ozone concentration by utilizing routinely measured ozone and meteorology. It is anticipated that this model will be adapted for monitoring networks. We also are exploring the utility of 13C as a proxy for stomatal conductance in the estimation of ozone deposition. To develop the model and the proxy, four sites have been selected along a well-documented ozone injury gradient in the Sierra Nevada Mountains of California (Table 1). The results of this research will contribute to the current state of knowledge regarding ozone stress effects on California forest ecosystems.Progress Summary:
In 1998, we conducted an initial study at the Blodgett Forest site to investigate the influence of typical Mediterranean summer drought on the uptake of ozone and general physiological response of ponderosa pine, and to test results from the model being developed against directly measured ozone fluxes. Fluxes of ozone, CO2, water, and energy were measured by eddy covariance from May through October 1998. Using this eddy flux data, we also compared typically reported ozone metrics SUM0, SUM06, SUM08, and W126 against direct measurements of ozone deposition to document that ozone metrics are poor predictors of ozone uptake in California pine ecosystems. The field campaign began in May 1999. We established sites at four locations along the ozone injury gradient in the Sierra Nevada, CA (Table 1), to take advantage of existing ozone monitoring (National Park Service and California Air Resources Board Environmental Protection Agency) and an ongoing forest damage assessment project. Year-round continuous measurements of ecosystem scale ozone, carbon dioxide, and water and energy fluxes were begun in May at the Blodgett Forest site. Measurements of physiology that were made monthly at each site from May through September, included: diurnal net photosynthesis, stomatal conductance and transpiration; predawn and afternoon water potential; photosynthesis response curves to light and carbon; and dark respiration. Foliage was collected for starch 13C analysis every month. At the end of the season, foliage samples were collected for cellulose 13C measurement.
Table 1. Site locations and characteristics.
| Site | Location | Slope | Elevation (m) | OII1 | Ozone2 (ppb) |
| Sequoia/King's Canyon National Park | N36?33'55" W118?46'36" | 30% | 1920 | 41.3 | 63a |
| Yosemite National Park | N37?42'43" W119?42'19" | 10% | 1220 | 14.7 | 41a |
| Blodgett Forest Res. Sta. Control Site | N38?53'43" W120?37'58" | 2% | 1315 | N/A | 49b 57c |
| Watered Site | N38?53'43" W120?37'58" | 1% | 1315 | N/A | Same as control |
| White Cloud | N39?19'00" W120?50'45" | 10% | 1326 | 27.3 | 62a |
1. Ozone Injury Index (OII) is derived from a combination of the primary effects of ozone on pine (Arbaugh et al. 1998)
2. 24-hour mean ozone concentration (ppb) from June 1 - October 31, (a) from Arbaugh et al. 1998: (b) from our measurements in 1998, (c) from our measurements in 1999.
We completed a study at Blodgett Forest that was intended to gain further insights into the limitations imposed by typical summer drought on the uptake of carbon and ozone in the ponderosa pine ecosystem. Two sites were set up?one control, one watered?in a ponderosa pine plantation. Although the 1998 growing season was abnormally wet, a pronounced drought effect was seen at the control site. Carbon uptake in 1-year old control foliage was reduced compared to the watered treatment during the 3 measurement days following treatment by 39 percent, 35 percent, and 30 percent, respectively, per unit leaf area. Stomatal conductance was lower at the control site leading to a reduction in estimated ozone deposition (ozone concentration times stomatal conductance) of 36 percent, 46 percent, and 41 percent that of the watered site, respectively. This controlled experiment demonstrated that site moisture is the most important factor controlling ozone uptake in California forests. Expected changes in climate will profoundly affect the ozone uptake by California forest ecosystems.
The metrics that are currently employed throughout the United States to estimate ozone exposure for forest trees are derived from atmospheric concentrations and assume that the forest is physiologically active at all times of the growing season. This may be inaccurate in regions with a Mediterranean climate, such as California, where peak physiological activity occurs early in the season to take advantage of high soil moisture and does not correspond to peak ozone concentrations. Direct measurements of ozone flux into a ponderosa pine canopy were compared with a suite of the most common ozone exposure metrics to determine which one best correlated with actual ozone uptake by the forest. Of all the metrics that were used, SUM0, the sum of all ozone concentrations > 0, best corresponds to ozone uptake by the ponderosa pine, but only at times when the stomata are unconstrained by site moisture conditions. Early in the growing season?May and June in a typical year?SUM0 is an adequate metric for forest ozone uptake. Later in the season, when stomata are constrained by water availability, SUM0 overestimates ozone uptake. These results suggest that in California, a better metric would be one that incorporates forest physiological activity, either through mechanistic modeling or by weighting ozone concentrations by stomatal conductance, or by weighting concentrations by site moisture conditions.
Future Activities:
The field campaign will continue in growing seasons 00 and 01. We will compare models that estimate stomatal conductance and ozone flux into foliage and evaluate them for their appropriateness in the Sierra Nevada ponderosa pine ecosystem. We will further develop the selected model to apply to our specific needs, and compare modeled ozone deposition with direct measurements of canopy scale ozone deposition at Blodgett Forest. Measurements of ecosystem scale fluxes at Blodgett Forest will continue year round.Journal Articles on this Report : 2 Displayed | Download in RIS Format
| Other project views: | All 19 publications | 10 publications in selected types | All 8 journal articles |
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Goldstein AH, Hultman NE, Fracheboud JM, Bauer MR, Panek JA, Xu M, Qi Y, Guenther AB, Baugh W. Effects of climate variability on the carbon dioxide, water, and sensible heat fluxes above a ponderosa pine plantation in the Sierra Nevada (CA). Agricultural and Forest Meteorology 2000;101(2-3):113-129. |
R826601 (1999) R826601 (2000) R826601 (Final) |
Exit Exit |
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Panek JA, Goldstein AH. Response of stomatal conductance to drought in ponderosa pine: implications for carbon and ozone uptake. Tree Physiology 2001;21(5):337-344. |
R826601 (1999) R826601 (2000) R826601 (2001) R826601 (Final) |
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Supplemental Keywords:
ozone damage, modeling forest response, carbon isotopes, forest physiological processes, carbon cycling, water cycling, ozone deposition, pollution stress, forest health monitoring., RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Air, Geographic Area, Ecological Indicators, State, Ecosystem Protection, Forestry, Ecology, Environmental Chemistry, Ecosystem/Assessment/Indicators, tropospheric ozone, Ecological Effects - Environmental Exposure & Risk, California (CA), pine trees, carbon storage, stressors, meteorological fluctuations, ecosystem indicators, forests, Sierra Nevada Mountains, atmospheric contaminants, ozone flux, meteorology, ozoneRelevant Websites:
http://www-cbe2.ced.berkeley.edu/panek/research
http://www.cnr.berkeley.edu/~ahg
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.