PS 34-230 - Effects of prescribed fire on planted oak growth and survival in restored savannas

Abstract: The majority of oak savannas in the Midwestern United States have been lost to agriculture and habitat degradation. Because of their rarity and their ability to support high plant and animal diversity, savannas are often a target for restoration. Oak savanna restoration frequently relies on direct planting of oak seedlings to establish the necessary tree canopy. Returning fire to the system is critical to the herbaceous component of the savanna, but managers risk damaging or killing trees if burning is introduced too soon. We studied growth and physiological responses of three oak species (Quercus alba, Q. macrocarpa, and Q. velutina) to prescribed fire to determine impacts on previously planted trees. This study utilized two restored oak savanna units that were planted in 1992 and 1998, each with burned and unburned areas. Trees in these areas ranged from 0.9 to 29.8 cm in diameter. We followed trees to determine the size threshold above which top kill is unlikely, and documented differences in leaf structure and extension growth between burned and unburned portions of each area. No trees larger than 4 cm diameter at breast height (dbh) were top killed by the fire and there was no mortality observed. Fire responses in leaf mass per unit area and chlorophyll content were small and inconsistent across species and units. However, all oak species grew more in burned areas than trees in adjacent unburned areas. Therefore, the addition of low intensity prescribed fire to an oak savanna planting may increase the growth rate of planted trees with minimal risk of mortality, especially if the trees are greater than 5 cm dbh.