Tip-to-base bark cross-sectional areas contribute to understanding the drivers of carbon allocation to bark and the functional roles of bark tissues

Abstract

• Along their lengths, stems experience different functional demands. Because bark and wood traits are usually studied at single points on stems, it remains unclear how carbon allocation changes along tip-to-base trajectories across species.
• We examined bark vs wood allocation by measuring cross-sectional areas of outer and inner bark (OB and IB), IB regions (secondary phloem, cortex, and phelloderm), and wood from stem tips to bases of 35 woody angiosperm species of diverse phylogenetic lineages, climates, fire regimes, and bark morphologies. We examined how varied bark vs wood allocation was and how it was affected by precipitation, temperature, soil fertility, leaf habit, and fire regime.
• Allocation to phloem (relative to wood) varied little across species, whereas allocation to other tissues, strongly affected by the environment or shed in ontogeny, varied widely. Allocation to parenchyma-rich cortex and phloem was higher at drier sites, suggesting storage. Higher allocation to phloem and cortex also occurred on infertile soils, and to phloem in drought-deciduous vs cold-deciduous and evergreen species. Allocation to OB was highest at sites with frequent fires and decreased with fire frequency.
• Our approach contextualizes inferences from across-species studies, allows testing functional hypotheses, and contributes to disentangling the functional roles of poorly understood bark tissues.