Differential relative bark thickness and aboveground growth discriminates fire resistance among hardwood sprouts in the southern Cascades, California

Abstract

Bark thickness relative to stem diameter and radial stemwood and height growth patterns provided a more accurate discrimination of fire resistance than absolute bark thickness alone in juvenile stems. Thick bark provides thermal protection to cambial tissues and adventitious buds during fires, and thus, is a functional trait associated with more fire-resistant species and species persisting in fire-prone environments. However, bark thickness alone may not provide the best indicator of fire resistance due to differences among species-dependent growth, reproductive, and survival strategies. We measured bark thickness relative to radial stemwood and height growth among five juvenile co-occurring hardwood species following the Chips Fire (2012) in the southern Cascades, California. We found canyon live oak (Quercus chrysolepis) and Oregon white oak (Quercus garryana), the most fire-resistant, did not have the greatest bark thickness (0.7–0.4 mm; 0.8–0.3 mm), but rather had significantly greater relative (to stem diameter) bark thickness (8–18%) at all heights along the stem (p Q. garryana > Q. kelloggii > Pacific dogwood, Cornus nuttallii > A. macrophyllum). Our findings highlight the importance of considering bark thickness relative to stem diameter and aboveground growth patterns in assessing species fire resistance.