Air pollution impacts in the mixed conifer forests of southern California

Abstract

Air pollution, principally in the form of photochemical ozone and deposition of nitrogen compounds, has significantly affected mixed conifer forests in the mountains of southern California. Foliar injury, premature needle abscission, crown thinning, and reduced growth and vigor have been well documented, particularly for ponderosa (Pinus ponderosa Laws.) and Jeffrey (P. jeffreyi Grev. and Balf.) pines on the western side of the pollution deposition gradient in the San Bernardino Mountains. Tree mortality of the more ozone-susceptible ponderosa and Jeffrey pines has led to alterations in stand composition, in favor of increased dominance by more ozone-resistant species such as incense cedar (Calocedrus decurrens [Torr.] Florin), white fir (Abies concolor [Gord. & Glend.] Lindl.), and sugar pine (P. lambertiana Doug.). Increased rates of litter deposition, alterations in C/N ratios in litter and soil, and reductions in fine root biomass of trees have also altered the dynamics of biogeochemical processing in stands impacted by ozone and excess N deposition. Research into the effects of atmospheric deposition across the mixed conifer forests of the San Bernardino Mountains continues to provide insights into the complex interactions among anthropogenic and natural stresses in a forest ecosystem.

Parent Publication

• Planning for biodiversity: bringing research and management together; Proceedings of a Symposium for the South Coast Ecoregion

Citation

Temple, Patrick J.; Bytnerowicz, Andrzej; Fenn, Mark E.; Poth, Mark A. 2005. Air pollution impacts in the mixed conifer forests of southern California. In: Kus, Barbara E., and Beyers, Jan L., technical coordinators. Planning for Biodiversity: Bringing Research and Management Together. Gen. Tech. Rep. PSW-GTR-195. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture: 145-164