Patterns of bark growth for juvenile trees of six common hardwood species in the eastern United States and the implications to fire-tolerance

Abstract

Bark allocation patterns did not follow fire-tolerance grouping of tree species in all cases; more studies are needed on bark development from juvenile to adult trees. Thick bark is presumed to be a trait of fire-tolerant trees that were historically subjected to frequent surface fires. To be recruited into the forest canopy, a tree must be able to survive fire and grow thick enough bark during the fire-free interval. Previous studies have also suggested that fire-tolerant species grow disproportionately thick bark lower on the stem, where the threat of fire is greatest. The objectives of this study were to quantify how bark develops in six juvenile hardwood species of the Appalachian Piedmont and compare bark allocation between fire-tolerant (Carya tomentosa, Quercus alba, and Quercus velutina) and mesophytic species (Acer rubrum, Fagus grandifolia, and Liriodendron tulipifera). We sampled up to 32 individuals of each species and modeled bark area as a function of wood area and measure height using mixed effect models. Bark area increased approximately 0.4 cm2 for Q. velutina and C. tomentosa, 0.2 cm2, for L. tulipifera and Q. alba, and 0.1 cm2 for A. rubrum and F. grandifolia for each cm2 increase in wood area, holding measure height constant. For Q. velutina, C. tomentosa, and L. tulipifera, the measure height was found to decrease bark area by approximately 0.02, 0.01, and 0.01 cm2 for each cm increase in height, holding diameter constant. A paired sample Wilcoxon test comparing bark:wood ratio at 0 and 140 cm heights yielded similar results. Differences in bark allocation among the six species were not consistent with current groupings of “fire-tolerant” and “mesophytic” species.