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

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. Nomenclature: Barkley (1986).

[1]  P. Reich,et al.  Tree Patches Show Greater N Losses but Maintain Higher Soil N Availability than Grassland Patches in a Frequently Burned Oak Savanna , 2006, Ecosystems.

[2]  Mark A. Davis,et al.  Survival, growth, and photosynthesis of tree seedlings competing with herbaceous vegetation along a water-light-nitrogen gradient , 1999, Plant Ecology.

[3]  B. Raudenbush,et al.  Ratings of Pleasantness and Intensity for Beverages Served in Containers Congruent and Incongruent with Expectancy , 2002, Perceptual and motor skills.

[4]  P. Reich,et al.  FIRE AND VEGETATION EFFECTS ON PRODUCTIVITY AND NITROGEN CYCLING ACROSS A FOREST-GRASSLAND CONTINUUM , 2001 .

[5]  P. Reich,et al.  PRESCRIBED FIRE IN OAK SAVANNA: FIRE FREQUENCY EFFECTS ON STAND STRUCTURE AND DYNAMICS , 2001 .

[6]  P. Reich,et al.  Leaf gas exchange responses of 13 prairie grassland species to elevated CO2 and increased nitrogen supply , 2001 .

[7]  T. Givnish,et al.  GRADIENTS IN THE COMPOSITION, STRUCTURE, AND DIVERSITY OF REMNANT OAK SAVANNAS IN SOUTHERN WISCONSIN , 1999 .

[8]  Judith D. Singer,et al.  Using SAS PROC MIXED to Fit Multilevel Models, Hierarchical Models, and Individual Growth Models , 1998 .

[9]  D. Tilman,et al.  Herbivore effects on plant and nitrogen dynamics in oak Savanna , 1998 .

[10]  Guy R. McPherson,et al.  Ecology and Management of North American Savannas , 1998 .

[11]  J. Blair.  FIRE, N AVAILABILITY, AND PLANT RESPONSE IN GRASSLANDS: A TEST OF THE TRANSIENT MAXIMA HYPOTHESIS , 1997 .

[12]  R. Scholes,et al.  Tree-grass interactions in Savannas , 1997 .

[13]  B. W. Wilgen,et al.  Fire and Plants , 1995, Population and Community Biology Series.

[14]  Martin Kent,et al.  Vegetation Description and Analysis: A Practical Approach , 1992 .

[15]  Anthony S. Bryk,et al.  Hierarchical Linear Models: Applications and Data Analysis Methods , 1992 .

[16]  D. L. White,et al.  Fire regimes for pine-grassland communities in the southeastern United States , 1992 .

[17]  J. Tester.  Effects of fire frequency on oak savanna in , 1989 .

[18]  David Tilman,et al.  Secondary Succession and the Pattern of Plant Dominance Along Experimental Nitrogen Gradients , 1987 .

[19]  T. Barkley,et al.  In: Flora of the Great Plains , 1987 .

[20]  B. Walker,et al.  Interactions of woody and herbaceous vegetation in a southern African Savanna , 1985 .

[21]  C. Owensby,et al.  Long-term effects of annual burning at different dates in ungrazed Kansas tallgrass prairie. , 1984 .

[22]  J. Ehleringer,et al.  Comparative ecophysiology of C3 and C4 plants , 1984 .

[23]  Alan S. White.  The Effects of Thirteen Years of Annual Prescribed Burning on a Quercus Ellipsoidalis Community in Minnesota , 1983 .

[24]  C. E. Lewis,et al.  Shrub and herbaceous vegetation after 20 years of prescribed burning in the South Carolina Coastal Plain. , 1976 .

[25]  Richard J. Vogl,et al.  5 – Effects of Fire on Grasslands , 1974 .

[26]  D. Grigal,et al.  The soils of Cedar Creek Natural History Area , 1974 .

[27]  M. Koelling,et al.  The Influence of Fire on Composition' of Central Missouri Prairie , 1964 .

[28]  J. T. Curtis,et al.  The Vegetation of Wisconsin: An Ordination of Plant Communities. , 1960 .

[29]  J. R. Bray.  THE DISTRIBUTION OF SAVANNA SPECIES IN RELATION TO LIGHT INTENSITY , 1958 .