Format: ORAL

Julieta A. Rosell1, Karen Vzquez1, Mark E. Olson2, Susanne Vetter3, Carmen R. Marcati4, Guillermo ngeles5

1 Instituto de Ecología, Universidad Nacional Autónoma de México, Mexico City, Mexico 2 Instituto de Biología, Universidad Nacional Autónoma de México, Mexico City, Mexico 3 Rhodes University, Makhanda, South Africa 4 Faculdade de Ciências Agronômicas, Universidade Estadual Paulista (UNESP), Botucatu, Brasil. 5 Instituto de Ecología AC, Xalapa, Mexico

Bark is a conspicuous part of woody stems, but a poorly understood one, especially in comparison with wood. Bark includes the tissues outside the vascular cambium and can be divided, from a functional point of view, into an inner mostly living region (inner bark, IB) and an outer dead region (outer bark, OB). There has been a recent surge of interest in bark functional ecology, but biologists are still far from understanding why some woody plants invest more or less carbon in IB and OB. Bark and wood thickness or cross-sectional areas are good proxies of relative carbon investment, because the density of both tissues covaries strongly. We review the main drivers of IB and OB thickness and area across species and ecosystems at the global level, integrating across-species and ontogenetic approaches. Across mature individuals, across species and environments, woody species allocate more carbon to IB in more seasonal environments in which higher storage of water, non-structural carbohydrates, and nutrients is of selective importance, whereas they allocate more carbon to OB as fire frequency increases. In turn, ontogenetic approaches (along stems or across conspecifics of differing sizes) underscore the role of storage but also of metabolic demands as crucial drivers of allocation in the secondary phloem, a tissue that includes the photosynthate-translocating tissue and a large fraction of axial and radial parenchyma. Regarding OB, ontogenetic approaches show that very frequent fire drives an isometric pattern of carbon allocation to OB along stems. Ontogenetic approaches have not only confirmed across-species patterns, but have also contributed to disentangling the functional roles of poorly-understood bark regions such as the phelloderm and the cortex. Further understanding of the remarkable diversity of bark demands a combination of ontogenetic and across-species approaches to the measurement of structural and functional traits.