Research Projects

Project at a Glance

Project Status: complete

Title: Ambient ozone patterns and ozone injury risk to Ponderosa and Jeffrey pines in the Sierra Nevada.

Principal Investigator / Author(s): Arbaugh, Michael J.

Contractor: USDA Forest Service

Contract Number: 98-305


Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Ecosystem Impacts, Impacts


Abstract:

Spatially explicit estimates of ambient ozone exposure to the Sierra Nevada were developed using data from an extensive survey of passive ozone monitors. The study area included the Sierra Nevada subregion, and extended from the Sequoia National Forest in the south through the Lassen National Forest in the north. Both Westside and Eastside forests were included in the ambient ozone survey. This survey provided data at a total of 94 locations across the Sierra Nevada, of which nine were collocated with active ozone monitors. In addition digital elevation maps, and spatial maps of temperatures and precipitation were developed as part of the analysis.

The unique data set generated from the passive monitor network elicited widespread interest. As a result three analysts were given the data set to develop relationships and estimate spatial patterns of ambient ozone for the Sierra Nevada. Spatial models of biweekly and seasonal ozone distribution were constructed by each group using topographical, weather and other information.

Modeling efforts resulted in a spatial model with an estimated of R2=0.58 and with an average standard deviation of 6.68 ppb-hour. Futher improvements in the accuracy of predictions are possible because residual analysis indicates unexplained spatial patterns in the data.

The results of these studies also suggest that almost 94% of the study area was reliably estimated for the Sierra Nevada, although the distribution of the measurement sites could still be improved (there was clearly insufficient number of sites on the eastern side of the mountain range). The availability of the weather data and presence of strong correlations between maximum temperatures and elevation with ozone contributed to low sampling site densities being needed to obtain reliable spatial surface estimates in the Sierra Nevada.

Along with monitoring ambient ozone, evaluations of crown injury were performed at 25 sites. Eight Project FOREST sites and 15 other sites located near selected passive monitor sites were evaluated using the Forest Pest Management (FPM) method. All sites were located along the western side of the Sierra Nevada in Jeffrey, ponderosa or mixed conifer forest types.

The number of sites sampled for this study was low, and the distribution of the sample sites did not represent the distribution of the pines. In spite of these deficiencies, patterns of ozone injury generally followed patterns of ozone exposure risk. Although the design of the FPM survey portion precluded a detailed spatial comparison with the ambient ozone samplers, it was of great value for development of future long-term ozone injury monitoring system for the Sierra Nevada.


 

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