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Terrestrial laser scanning reveals convergence of tree architecture with increasingly dominant crown canopy position

Martin-Ducup O., Ploton P., Barbier N., Momo Takoudjou S., Mofack G.I., Kamdem N.G., Fourcaud T., Sonké B., Couteron P., Pélissier R.. 2020. Functional Ecology, 34 (12) : p. 2442-2452.

DOI: 10.5061/dryad.10hq7

DOI: 10.1111/1365-2435.13678

To fulfil their growth and reproductive functions, trees develop a three-dimensional structure that is subject to both internal and external constraints. This is reflected by the unique architecture of each individual at a given time. Addressing the crown dimensions and topological structure of large tropical trees is challenging considering their complexity, size and longevity. Terrestrial laser scanning (TLS) technology offers a new opportunity for characterising and comparing these properties across a large number of individuals and species. In the present study, we specifically developed topology and geometry metrics of crown architecture from TLS data and investigated how they correlated with metrics of tree and crown form, crown position and shade tolerance. Fifty-nine trees belonging to 14 coexisting canopy species in semideciduous forests of Cameroon were scanned with TLS and reconstructed using quantitative structural models (QSMs). The species belonged to different shade-tolerance groups and were sampled in different crown positions. Crown-form metrics and branch topology metrics were quantified from the TLS data, and principal component analysis (PCA) was used to study how the 59 sampled trees were distributed along axes of architectural diversity. Allometric scaling parameters derived from West Brown and Enquist (WBE) metabolic theory were also quantified from the QSMs, and their correlations with the PCA axes were evaluated. The results revealed that the branch topology and crown-form metrics were not correlated since similar topologies could lead to contrasting crown forms. Crown form, but not branch topology, changed with tree shade tolerance, while convergence in tree topology and towards expected WBE parameters was observed for all trees reaching dominant crown positions independent of species shade tolerance. This convergence is interpreted as resulting from a liberation effect of canopy trees from side-shading constraints, leading to crown development processes through sequential reiteration.

Mots-clés : laser; allométrie; morphologie végétale; couvert forestier; croissance; cameroun; architecture végétale; architecture des arbres; canopée

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