Rotten to the core? Drivers of the vertical profile and accumulation of internal tree stem damage

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Abstract Trees are important above‐ground carbon sinks in savanna ecosystems, yet consumption of internal wood by decomposers (e.g. termites and microbes) creates uncertainties in tree biomass accounting. It remains unclear whether internal stem damage is constant or variable throughout the tree, making it uncertain if a single sample reflects damage through the tree. Furthermore, total damage and damage location are likely influenced by external damage pressures (i.e. termites, microbes and fire), tree species and tree traits (i.e. diameter at breast height [DBH], wood density) and their interactions. We sampled internal damage in the lower stem (<2 m) of savanna trees in North Queensland, Australia to examine the vertical profile of proportional and absolute amounts of damage. We compared damage estimates from a single‐sample method, assuming constant damage, with a multi‐sample method, assuming variable damage, to test how well one sample represented the lower stem. We investigated if tree species accumulated damage differently due to DBH, wood density or susceptibility to external damage pressures (i.e. fire scarring and termite presence). Finally, we tested if external damage pressures differentially affected tree species and if this was mediated by DBH or wood density. The absolute amount, but not proportion, of damage decreased with higher vertical position on the stem. There was no difference in total stem damage between the single‐sample and multi‐sample methods. Species‐specific variation in internal stem damage was influenced by DBH and wood density. Total damage was greatest in large trees, particularly those with external termite presence. Finally, external termite presence, but not fire scarring, differed among tree species and was most likely to occur on large, dense trees. We demonstrated that a single sample effectively captured total internal damage in the lower stem. Although species differed in total damage, damage accumulation rates with increasing height on the stem were consistent, suggesting a general relationship. By integrating the influence of external damage pressures and tree traits, our findings underscore the importance of considering these elements for accurately estimating carbon stored in above‐ground tree biomass. Read the free Plain Language Summary for this article on the Journal blog.