Resprouting by American hazel (Corylus americana) in response to experimental clipping in a restored oak savanna and adjacent oak woodlands

Oak savannas, which once occupied millions of hectares between Manitoba and Texas, have been reduced to approximately 0.02% of their pre-1850 range due to land use change (conversion to agriculture or sub/ex/urban) and fire suppression (conversion to woodlands). Conversion to woodlands involves both shrub and tree expansion that alter light heterogeneity, a defining feature related to high biodiversity of oak savanna ecosystems.  Our research seeks to inform land managers about effective control of woody expansion in remnant oak savanna.  While tree canopy cover consistently declines with fire and mechanical removal, it is unclear how shrub cover is affected.  We sampled one prevalent shrub, American Hazel (Corylus Americana), in frequently burned oak savanna and unburned oak woodland at Cedar Creek Natural History Area. We measured resprout stem number, length, diameter, and biomass on individual shrubs under four clipping frequencies (0,2,4 or 8 times during one 16 week season.) We hypothesized that resprouting of C. americana would be negatively related to clip frequency and positively related to fire treatment (e.g. shrubs will resprout more in open, burned savanna than in unburned woodlands). We found a significant, negative relationship between resprout biomass and clipping frequency and five-fold higher resprout biomass in burned savanna.  Shrubs clipped once (e.g. same frequency as prescribed burning) resprouted profusely, gaining 30 times more biomass than more frequently clipped individuals.  However, we found diminishing effects of clipping; there was no significant difference between the shrub resprout biomass after 8 clip treatments versus 4 clip treatments in either burned or unburned areas.  Our results suggest that fire-dependant ecosystems may be more vulnerable to shrub expansion, due to the resprout capabilities of shrubs after single disturbances and high light availability. We recommend monthly clip treatments during the growing season to effectively manage C. americana expansion, either with or without prescribed burning.