D3000: Internal tree stem damage alters aboveground biomass estimates across a tropical rainfall gradient in Queensland, Australia

Woody biomass is an important component of the carbon storage capacity of terrestrial ecosystems. In calculating biomass via allometry, tree stems are assumed to be solid structures, however internal stem damage may lead to overestimating the amount of carbon trees store. Decomposer agents such as microbes and insects (especially termites) have been identified to cause stem damage by targeting heartwood to instigate decay and substrate removal. However, it is less well understood how this stem damage varies across tree stem-level and site-level factors. In this study, we investigated four predictors of stem damage: wood density and stem size (stem-level predictors), as well as precipitation and relative damage by termites of downed deadwood (site-level predictors) to explore the amount of C missing from living trees. We measured these predictors across five sites in tropical Northern Queensland, Australia, spanning multiple forest types (rainforest, sclerophyll, and savannah) and a precipitation gradient (~800mm/yr to ~4,500mm/yr). We observed that stem damage increased with both increasing tree DBH and wood density. Our stem damage model showed a strong interactive effect between site-level predictors and wood density, likely a result of shifting decomposer communities and their differing responses to changes in wood construction. Ultimately, we show that aboveground biomass estimates are considerably altered when stem damage is incorporated, especially at drier sites. This finding has knock-on consequences for accurately estimating carbon across woody plant communities while taking into account the effect of changes in decomposer communities and abiotic conditions.