Abstract
Abstract Quantifying whole branch architecture is critical to understanding tree function, for example, branch surface area controls woody gas exchange. Yet, due to measurement difficulty, branch architecture of small diameter branches (e.g. <10 cm ) is modelled, subsampled or ignored. Methods that use terrestrial laser scanning (TLS) are now being widely applied to analyse tree and plot‐level tree architecture; however, resolving small diameter branches in‐situ remains a challenge. Currently, it is suggested that accurate reconstruction of small diameter branches can only be achieved by harvest and measurement in controlled conditions. Here we present a new TLS workflow for rapid and accurate reconstruction of complete branch architecture from harvested branches. The workflow sets out scan configuration, post‐processing (including a novel reflectance filter) and fitting of quantitative structure models (QSM) to reconstruct topologically coherent branch models. This is demonstrated on 595 branches (scanned indoors to negate the impact of wind) and compared with 65 branches that were manually measured (i.e. with measuring tape and callipers). Comparison of a suite of morphological and topological traits reveals a good agreement between TLS‐derived metrics and manual measurements where RMSE (%RMSE) for total branch length = 0.7 m (10%), volume = 0.09 L (43%), surface area = 0.04 m2 (26%) and N tips = 6.4 (35%). Scanning was faster and invariant to branch size compared with manual measurements which required significantly more personnel time. We recommend measuring a subsample of tip widths to constrain the QSM taper function as the TLS workflow tends to overestimate tip width. The workflow presented here allows for a rapid characterisation of branch architecture from harvested branches. Increasing the number of branches analysed (e.g. many branches from a single tree or branches from many species globally) could allow for a comprehensive analysis of the ‘missing link’ between the leaves and larger diameter branches.
Highlights
Tree architecture is the 3D spatial arrangement, morphology and topology of a tree’s leaves, branches and stem (Barthélémy & Caraglio, 2007; Valladares & Lo Niinemets, 2007)
This paper presents a workflow to rapidly characterise the architecture of harvested branches using a terrestrial laser scanning (TLS)-based workflow
Metrics derived from scanned and modelled branches were correlated with manually measured analogues, demonstrating the method was successful in characterising branch architecture
Summary
Tree architecture is the 3D spatial arrangement, morphology and topology of a tree’s leaves, branches and stem (Barthélémy & Caraglio, 2007; Valladares & Lo Niinemets, 2007). Characterising the architecture of small diameter woody components is difficult given their often non-trivial complexity and in-situ location many metres above the forest floor. This has resulted in traits of higher-order branching being modelled, subsampled or ignored (Lau et al, 2018; Sillett et al, 2015). Capturing and quantifying the architecture of the ‘missing link’ between larger diameter branches and leaves is key to understanding whole tree function, for example, gas exchange and surface area allometry (Chambers et al, 2004), intra-canopy response to light environments (Barthélémy & Caraglio, 2007) or divergence from theoretical predictions of crown architecture (Bentley et al, 2013)
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