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The variation of apparent crown size and canopy heterogeneity across lowland Amazonian forests

Authors

  • Nicolas Barbier,

    Corresponding author
    1. FNRS-FWA, Laboratoire de Complexité et Dynamique des Systèmes Tropicaux, Université Libre de Bruxelles, 50 Av. FD Roosevelt, CP 169, B-1050 Bruxelles, Belgium,
    2. Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford OX1 3QY, UK,
      Nicolas Barbier, FNRS-FWA, Laboratoire de Complexité et Dynamique des Systèmes Tropicaux, Université Libre de Bruxelles, 50 Av. FD Roosevelt, CP 169, B-1050 Bruxelles, Belgium. E-mail: nbarbier@ulb.ac.be
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  • Pierre Couteron,

    1. IRD-UMR Botanique et Bioinformatique de l'Architecture des Plantes (AMAP), Boulevard de la Lironde, TA A-51/PS2, 34398 Montpellier Cedex 05, France,
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  • Christophe Proisy,

    1. IRD-UMR Botanique et Bioinformatique de l'Architecture des Plantes (AMAP), Boulevard de la Lironde, TA A-51/PS2, 34398 Montpellier Cedex 05, France,
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  • Yadvinder Malhi,

    1. Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford OX1 3QY, UK,
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  • Jean-Philippe Gastellu-Etchegorry

    1. Centre d'Etudes Spatiales de la Biosphère (CESBIO). Université de Toulouse, UPS, CNRS, CNES, IRD, 18 Av. Ed. Belin, 31401 Toulouse, France
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Nicolas Barbier, FNRS-FWA, Laboratoire de Complexité et Dynamique des Systèmes Tropicaux, Université Libre de Bruxelles, 50 Av. FD Roosevelt, CP 169, B-1050 Bruxelles, Belgium. E-mail: nbarbier@ulb.ac.be

ABSTRACT

Aim  The size structure of a forest canopy is an important descriptor of the forest environment that may yield information on forest biomass and ecology. However, its variability at regional scales is poorly described or understood because of the still prohibitive cost of very high-resolution imagery as well as the lack of an appropriate methodology. We here employ a novel approach to describe and map the canopy structure of tropical forests.

Location  Amazonia.

Methods  We apply Fourier transform textural ordination (FOTO) techniques to subsamples of very high-resolution satellite imagery freely available through virtual globe software (e.g. Google Earth®) to determine two key structural variables: apparent mean crown size and heterogeneity in crown size. A similar approach is used with artificial forest canopy images generated by the light interaction model (discrete anisotropic radiative transfer, DART) using three-dimensional stand models. The effects of sun and viewing angles are explored on both model and real data.

Results  It is shown that in the case of canopies dominated by a modal size class our approach can predict mean canopy size to an accuracy of 5%. In Amazonia, we could evidence a clear macrostructure, despite considerable local variability. Apparent crown size indeed consistently increases from about 14 m in wet north-west Amazonia to more than 17 m for areas of intermediate dry season length (1–3 months) in south and east Amazonia, before decreasing again towards the ecotone with the Cerrado savanna biome. This general trend reflects the known variation of other forest physiognomic properties (height) reported for South America and Africa. Some regions show significantly greater canopy heterogeneity, a feature that may be related to substratum, perturbation rate and/or forest turnover rate.

Main conclusions  Our results demonstrate the feasibility and interest of large-scale assessment of rain forest canopy structure.

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