Empirical and simulated critical loads for nitrogen deposition in California mixed conifer forests

M. E. Fenn, S. Jovan, F. Yuan, L. Geiser, T. Meixner, B. S. Gimeno

Research output: Contribution to journalArticlepeer-review

114 Scopus citations


Empirical critical loads (CL) for N deposition were determined from changes in epiphytic lichen communities, elevated NO3- leaching in streamwater, and reduced fine root biomass in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) at sites with varying N deposition. The CL for lichen community impacts of 3.1 kg ha-1 year-1 is expected to protect all components of the forest ecosystem from the adverse effects of N deposition. Much of the western Sierra Nevada is above the lichen-based CL, showing significant changes in lichen indicator groups. The empirical N deposition threshold and that simulated by the DayCent model for enhanced NO3-leaching were 17 kg N ha-1 year-1. DayCent estimated that elevated NO3- leaching in the San Bernardino Mountains began in the late 1950s. Critical values for litter C:N (34.1), ponderosa pine foliar N (1.1%), and N concentrations (1.0%) in the lichen Letharia vulpina ((L.) Hue) are indicative of CL exceedance.

Original languageEnglish (US)
Pages (from-to)492-511
Number of pages20
JournalEnvironmental Pollution
Issue number3
StatePublished - Oct 2008


  • Atmospheric deposition
  • Biomonitoring
  • Ecosystem protection
  • Epiphytic lichens
  • Harmful effects
  • Nitrogen saturation

ASJC Scopus subject areas

  • Toxicology
  • Pollution
  • Health, Toxicology and Mutagenesis


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