USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Research Topics Air Quality

Interactive Effects of Air Pollution and Climate Change on Forest Ecosystems

Smoke obscures the sun across a mountainous landscape with vegetation  shadowed in the foreground.
Forest health monitoring plot in a mixed conifer stand affected by the long-term interactive effects of air pollution, climate change and fires (Camp Paivika, the San Bernardino Mountains, southern California). (U.S. Forest Service/Andrzej Bytnerowicz)

Research is done through detection, monitoring and evaluation of impacts of interactive abiotic (non-living factors that affect ecosystems, such as water, temperature, landforms, and the gases in the atmosphere) and biotic (living factors that affect ecosystems, including the organisms that inhabit the area) stressors on forests in California, Mexico, Canada, Spain, and central European countries. Through collaboration with environmental chemists, hydrologists, ecophysiologists, lichenologists, forest inventory analysts, we investigate and explain complex changes in forest environment and forest ecosystems function and health.

To evaluate the effects of air pollution on ecosystem health, a network of forest plots have been established and periodically observed since the 1960s. The San Bernardino Mountains network has been currently revised so that long-term effects of multiple stressors (elevated ambient ozone, nitrogen (N) deposition, drought, fires, bark beetle infestations) can be re-evaluated. We conducted an inventory of trees and evaluate their health at the low (Camp Osceola) and high (Camp Paivika) N deposition sites on the air pollution gradient caused by emissions from the Los Angeles Basin.

Little is known of the dose response for tree growth and mortality to the combined exposure of ozone and N deposition under ambient conditions in the largely Mediterranean climate of California. We analyze changes in tree growth (dbh and height) and mortality in response to these pollutants for 13 species across California based on data from the US Forest Service, Forest Inventory and Analysis (FIA) program. Because available ozone exposure data does not cover the entire state of California, separate models of tree response to air pollution will include N deposition only and where possible, both pollutants. Ozone exposure data consists of two-week average concentrations from a monitoring network equipped with Ogawa passive samplers. N deposition data is from the EPA's Community Multi-scale Air Quality (CMAQ) modeling system for air quality management in which simulated annual N deposition data have been adjusted with empirical throughfall N deposition data. Tree evaluations are based on 10-year plot revisit intervals for the 2001-2003 to 2011-2013 censuses. Early results show that nitrogen deposition in California forests causes increased soil N, tree growth (threshold ca. 15 kg N/ha/yr) and possibly mortality. Preliminary analyses also suggest that ozone modifies the growth response, particularly at lower N deposition levels.

Smoke obscures the sun across a mountainous landscape with vegetation  shadowed in the foreground.
Estimated effect of total nitrogen deposition on relative basal area increment (BAIrel; basal area growth per year relative to basal area at time 1) for conifer and hardwood species in California forests. Units on the y-axis are expressed as multiplicative change in BAIrel relative to BAIrel at average nitrogen deposition
  • Monitoring air quality in Southeast Alaska’s National Parks and Forests: Linking atmospheric pollutants with ecological effects. D. Schirokauer, L. Geiser, A. Bytnerowicz, M. Fenn, K. Dillman. 2014.
  • Evaluation of forest growth and health changes cause by long-term effects of air pollution, climate change and fires in the San Bernardino Mountains. M. Fenn, A. Bytnerowicz and R. Lopez, 2013-2015.
  • Nitrogen deposition and ozone exposure effects on tree growth and mortality in California forests. M. Fenn, J. Fried, H. Preisler, A. Bytnerowicz, S. Jovan, S. Schilling. 2014-2015.
Last Modified: Nov 30, 2018 12:16:45 PM