Biological Invasions

, Volume 12, Issue 2, pp 313–324 | Cite as

Introduced ungulate herbivore alters soil processes after fire

  • Michelle L. Stritar
  • Jennifer A. SchweitzerEmail author
  • Stephen C. Hart
  • Joseph K. Bailey
Original Paper


Ungulate herbivory can have profound effects on ecosystem processes by altering organic inputs of leaves and roots as well as changing soil physical and chemical properties. These effects may be especially important when the herbivore is an introduced species. Utilizing large mammal exclosures to prevent access by introduced elk at multiple sites along a fire chronosequence, we examined the effects of elk herbivory and fire on soil microbial activity and nutrient availability. Using time since fire as a co-variate and herbivore exclosures, paired with areas outside of the exclosures, we hypothesized that reductions in plant biomass due to herbivory would reduce organic inputs to soils and impact soil microbial activities and nutrient storage. We found three major patterns: (1) when elk were excluded, surface mineral soils had higher soil organic carbon (C), total nitrogen (N), microbial N pools, and increased extra-cellular enzyme activity of a C-acquiring enzyme across a gradient of time since fire. (2) When introduced elk are present, the activity of some extracellular enzymes as well as NO3 availability are enhanced in the soil but the post-fire patterns described above with respect to nutrient accrual over time are delayed. (3) Herbivory by an introduced ungulate upsets the trajectory of ecosystem “recovery” after wildfire and delays soil C and N dynamics by an estimated 14.5–21 years, respectively. These results suggest that introduced, browsing herbivores significantly decelerate ecosystem processes but herbivory by exotics may also result in unpredictability in specific soil responses.


Aspen Decelerated nutrient cycles Elk Fire Introduced herbivores Populus 



We thank Dan Guido, Paul Selmants, Nashelly Meneses, Clara Pregitzer and Bob Barbour for help in the field or laboratory and Rick Lindroth, Tad Theimer and Martin Nuñez and anonymous reviewers for comments that significantly improved the manuscript. Funding was provided to MLS by a Henry Hooper Undergraduate Research Award from NAU; additional funding was provided by the National Science Foundation, Frontiers in Integrated Biological Research program (DEB-0078280).


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Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  • Michelle L. Stritar
    • 1
  • Jennifer A. Schweitzer
    • 2
    Email author
  • Stephen C. Hart
    • 3
  • Joseph K. Bailey
    • 2
  1. 1.School of Forestry and Merriam-Powell Center for Environmental ResearchNorthern Arizona UniversityFlagstaffUSA
  2. 2.Department of Ecology and Evolutionary BiologyUniversity of Tennessee, KnoxvilleKnoxvilleUSA
  3. 3.School of Natural Sciences and Sierra Nevada Research InstituteUniversity of CaliforniaMercedUSA

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