Trees in frequently burned sandhill ecosystems have relatively thicker bark than trees in less frequently burned forest ecosystems. But variation in fire frequency and climate occurs across sandhill ecosystems, which may affect allocation to bark and relative bark thickness (RBT). We investigated differences in RBT of oak species (Quercus chapmanii, Q. geminata, Q. laevis, Q. myrtifolia) in southern ridge sandhills at Archbold Biological Station (ABS) in Florida. We compared RBT between oaks at ABS and oaks (Q. incana, Q. laevis, Q. margaretta, Q. marilandica) in longleaf pine sandhills at Fort Bragg in North Carolina, where fire occurs more frequently. In addition, we investigated intraspecific variation in RBT and inner bark proportion (IBP) of turkey oak (Q. laevis) in five sites along a latitudinal gradient from Florida to North Carolina. We randomly selected individuals of a range of sizes of all oak species and measured stem diameter, total bark thickness, and outer bark thickness. We calculated RBT as the ratio of bark thickness to bole diameter multiplied by 100 percent and calculated IBP as the ratio of inner bark to total bark thickness.
Results/Conclusions
RBT differed among oak species at ABS; turkey oak had the relatively thickest bark and myrtle oak (Q. myrtifolia) had the relatively thinnest bark. Overall, oaks at Fort Bragg had relatively thicker bark than oaks at ABS. This difference could be a consequence of the selective pressure of more frequent fires at Fort Bragg or differences in species composition, with inherently thicker barked species occurring at Fort Bragg. Furthermore, south Florida sandhill oaks also occur in scrub habitats and resprout vigorously after fire, so allocation of resources to resprouting may be more advantageous than allocation of resources to thick bark. Although mean RBT of turkey oak did not differ among sites along the latitudinal gradient, the slope of the relationship between bole diameter and bark thickness varied among sites. In contrast to RBT, mean IBP of turkey oak differed among sites. These results suggest that differences in fire frequency and/or climate affect bark allocation in turkey oaks: allocation to inner bark, which is living tissue involved in conduction, and allocation as stems grow.