Plant functional group responses to fire frequency and tree canopy cover gradients in oak savannas and woodlands

David W. Peterson, Peter B. Reich, Keith J. Wrage

Research output: Contribution to journalArticlepeer-review

66 Scopus citations

Abstract

Questions: How do fire frequency, tree canopy cover, and their interactions influence cover of grasses, forbs and understorey woody plants in oak savannas and woodlands? Location: Minnesota, USA. Methods: We measured plant functional group cover and tree canopy cover on permanent plots within a long-term prescribed fire frequency experiment and used hierarchical linear modeling to assess plant functional group responses to fire frequency and tree canopy cover. Results: Understorey woody plant cover was highest in unburned woodlands and was negatively correlated with fire frequency. C4-grass cover was positively correlated with fire frequency and negatively correlated with tree canopy cover. C3-grass cover was highest at 40% tree canopy cover on unburned sites and at 60% tree canopy cover on frequently burned sites. Total forb cover was maximized at fire frequencies of 4-7 fires per decade, but was not significantly influenced by tree canopy cover. Cover of N-fixing forbs was highest in shaded areas, particularly on frequently burned sites, while combined cover of all other forbs was negatively correlated with tree canopy cover. Conclusions: The relative influences of fire frequency and tree canopy cover on understorey plant functional group cover vary among plant functional groups, but both play a significant role in structuring savanna and woodland understorey vegetation. When restoring degraded savannas, direct manipulation of overstorey tree canopy cover should be considered to rapidly reduce shading from fire-resistant overstorey trees. Prescribed fires can then be used to suppress understorey woody plants and promote establishment of light-demanding grasses and forbs.

Original languageEnglish (US)
Pages (from-to)3-12
Number of pages10
JournalJournal of Vegetation Science
Volume18
Issue number1
DOIs
StatePublished - Feb 2007

Keywords

  • Cedar creek natural history area
  • Disturbance ecology
  • Fire ecology
  • Forb
  • Grass
  • Prescribed fire
  • Savanna restoration
  • Woody plant

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