Research Note 89-5: Topic = Ozone Risks to California Forests (A Data Base and Ranking of Forest Sensitivity

 California Environmental Protection Agency

Air Resources Board

 No. 89-5

May 1989


Brief Reports to the Scientific and Technical Community

 Research Division, John R. Holmes, Ph.D., Chief

P.O. Box 2815, Sacramento CA 98512

Ozone Risks to California Forests
(A Data Base and Ranking of Forest Sensitivity)

The purpose of this study was to collect ambient particle samples in Riverside, California, and measure levels of polycyclic aromatic hydrocarbons with identified carcinogenic potency for which there is a lack of ambient air concentration data. The data permit distinction between direct emission and atmospheric formation of these compounds. The results may be used with potency equivalency factors to estimate potential cancer risks from these compounds. The study was conducted by the Statewide Air Pollution Research Center at the University of California, Riverside.



Significance and Application:

Related Projects:

Approximately 33 million acres in California, one-third of the state's land area, are classified as forest land.  California forests are the source of about 85 percent of the state's water supply; timber for the forest products industry; animal and plant habitat; forest recreation; and revenue and employment in rural mountain counties.

There is evidence that air pollution is damaging trees and other vegetation in California.  Ozone damage has been observed in the forests of southern California and in the southern and mid-range of the Sierra Nevada mountains.  This study is a step in expanding our understanding of the nature and extent of that air pollution damage.

This project collected, calculated and synthesized biological, economic, geographic and ozone monitoring data into  a forest resources data base.  Current and potential ozone risks to forest areas of California were then estimated.  Over 50 percent of the forested areas in 12 California counties,  five out of 19 national forests and 13 California watershed designation areas were found to be at high risk to ozone using a .045 ppm, 12 hour seasonal ozone standard.

The data are organized into a computerized data base consisting of over 90 descriptive variables.  The data base and forest ozone risk assessment are described below:

  • Estimates of Ambient Ozone Levels.  Ambient ozone concentrations were averaged over the growing season for  four different averaging times:  7, 9, 12, and 24 hours.  The means and variances for each day were used to estimate a growing season average and standard deviation at each of the stations for the 1977-1981 period.  The ozone monitoring data set consisted of data from 104 stations scattered relatively uniformly throughout California.  A limited quality assurance review was conducted.
  • Tree Species Sensitivity Ranking.  Seventy different California forest tree species were ranked for sensitivity to ozone damage.
  • Tree Species Volume Estimates.  Tree volumes for up to 17 different tree species were estimated for each grid cell in the data base containing US Forest Service land.  In grid cells with non-Forest Service lands, tree volume estimates were developed for 14 different species groups.
  • Data Base Construction.  A data base was constructed containing about 3500 grid cells including about 30,000 acres each.  The grid cell data includes:  location, elevation at center, area, soil type, hydrologic drainages, estimated seasonal ozone concentrations, vegetative cover, tree species volume, forest ownership, county and air basin designations, recreational use, and estimates of ozone vulnerability of tree species in the cell.
  • Ozone Risk Assessment.  The vulnerability to ozone damage of the tree species in each forested grid cell was estimated.   Forest risk rankings were then examined by air basin, county, ownership code, national forest, and watershed. 
  • Benefits of Forest Protection.  The economics literature on the benefits of ozone protection of California forests was reviewed.  One study assessed the costs of soil erosion damage caused by ozone in the San Bernardino mountains to be $27 million per year.  A second estimated that residents of the South Coast Air Basin counties would be willing to pay up to $143 million annually to prevent ozone degradation to the San Bernardino and Angeles National Forests.  A third California study estimated that recreators would be willing to pay $9 million per year to prevent ozone damage to trees in the San Bernardino National Forest.     

The data base allows researchers to identify which species at which locations are most at risk to ozone damage and will be used in forest research planning. It will assist controlled exposure studies and in locating field plot experiments. The qualitative risk assessment can be used to support an ambient ozone standard to protect forests from damage. The risk analysis is also available to support appropriate emission control rules. The data base and risk assessment provide uniquely synthesized data for multi-use planning and evaluation activities.

The Air Resources Board is planning a series of forest research projects. This study will provide input to those projects.

This research was conducted under contract with RCG/Hagler, Bailly, Inc. (formerly: Energy and Resource Consultants, Inc.), (ARB Contract No: A6-049-32). Comments or questions can be directed to the Research Division, by mail, FAX (916) 322-4357, e-mail, or phone (916) 445-0753.

Copies of the research report upon which this Note is based can be ordered from:

National Technical Information Service
5285 Port Royal Rd
Springfield VA 22161
Request NTIS No. (pending)

Title: Risks to California Forests Due to Regional Ozone Pollution

Authors: Donald C. Peterson, Jr.