New allometric models for Eucalyptus tereticornis using terrestrial laser scanning show increased carbon storage in larger trees

Abstract

Accurate aboveground woody biomass (AGB) estimates are crucial for assessing the impact of elevated CO${}_2$ (eCO${}_2$) on net carbon sequestration in trees. Estimating AGB essentially involves developing allometric models using destructively harvested data. Due to the costs and restrictions of harvesting, models from other regions are often used. In the past two decades, terrestrial laser scanning (TLS) has become a widely accepted, non-destructive method for measuring tree structure. We provide new TLS-based allometric AGB models for Eucalyptus tereticornis, the dominant tree species at EucFACE, a replicated, ecosystem-scale mature forest free-air CO${}_2$ enrichment (FACE) experiment in Australia. Based on TLS-derived diameter at breast height (DBH), tree height (H), and crown area (CA) of 116 trees, we developed both an AGB:DBH model and an AGB:(CA$\times$H) model. Our TLS-based AGB:DBH model (uncertainty = 19 %, bias <−1 %), shows substantially larger AGB growth compared to the previously-used allometric model at EucFACE. Although this new model does not change previous conclusions about the impact of eCO${}_2$ on tree-level AGB increments at EucFACE, it does indicate a notable increase in AGB increment, particularly for larger trees. This highlights the need to recalculate net primary productivity and carbon partitioning at EucFACE. Additionally, we present a TLS-based AGB:(CA$\times$H) model (uncertainty = 27 %, bias <1 %). These models improve accuracy in assessing carbon storage at EucFACE and offer scalable methods for monitoring AGB in E. tereticornis across broader landscapes. By enabling reliable, landscape-level carbon estimates, this work supports targeted forest management and conservation strategies under rising CO${}_2$ conditions.