Tuesday, August 3, 2010 - 9:50 AM

OOS 11-6: Determinants of oak savanna ground layer composition and richness

Noel B. Pavlovic and Ralph Grundel. US Geological Survey


While oak savannas and woodlands are defined by their canopy structure and cover, it is their diverse groundlayer vegetation and the factors that contribute to this diversity that have been the focus of research.  We examine the variation in oak savanna groundlayer composition scaling up from canopy gaps to the local and regional levels.  We address the following questions:  What is the relationship between fire history and groundlayer species richness and how does this relationship vary with increasing scale?  How does groundlayer vegetation vary with size of canopy gaps in woodland and how does this relate to models of savanna herbaceous vegetation studied elsewhere? What are the effects of disturbance and fire suppression on oak savanna groundlayer composition and richness?  What role does fire season play in the groundlayer dynamics?  We develop a model to examine

Results/Conclusions Groundlayer diversity increases with increasing fire frequency at both the meter squared level and larger scales.  Variation in composition is correlated with gradients of soil structure and composition, light levels and topographic moisture gradients.  These gradients are also reflected in groundlayer variation within and adjacent to canopy gaps and at the regional scale.  Fire, irrespective of season, diminishes shrub flowering for at least a year.  Fire season also influences the timing of herbaceous plant flowering.  The relative roles of fire regime, canopy structure, hydrology, soil nutrients, light gradients, and disturbance on oak savanna groundlayer diversity will determine the pathways by which climate change will impact oak savannas.  Climate change will shift groundlayer composition relative to the degree it alters canopy cover through changes in fire regime, and moisture topographic gradients through changes in seasonal precipitation.