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Calders, Kim Quantifying forest growth in a free-air CO2 enrichment experiment using terrestrial laser scanning Talk Downloadable
Kim Calders1, Glenn Newnham2, Matthias Boer3, Mathias Disney4,5, David Ellsworth3, Martin Herold6, Belinda Medlyn3, Stuart Phinn6, Pasi Raumonen8, Peter Scarth7, Dan Wu7 and Hans Verbeeck1
(1) CAVElab - Computational & Applied Vegetation Ecology, Faculty of Bioscience Engineering, Ghent University, Belgium(2) CSIRO, Private Bag 10, Clayton South, VIC 3169, Australia(3) Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751 Australia(4) UCL Department of Geography, Gower Street, London WC1E 6BT, UK(5) NERC National Centre for Earth Observation (NCEO), UK(6) Laboratory of Geo-Information Science and Remote Sensing, Wageningen University & Research, Droevendaalsesteeg 3, 6708 PB Wageningen, The Netherlands(7) Remote Sensing Research Centre, School of Earth and Environmental Sciences, University of Queensland, Brisbane 4072, Australia(8) Computing Sciences, Tampere University, Korkeakoulunkatu 7, 33720 Tampere, Finland

Our current knowledge about forest growth is limited, mainly due to the difficulty to accurately measure full tree structure repeatedly and objectively. Techniques using 3D terrestrial laser scanning (TLS) can provide us with a novel and more accurate way to estimate the structure of trees. EucFACE is a free-air CO$_2$ enrichment experiment that consists of six circular 25 m rings in a mature broadleaved evergreen forest. Three rings have been exposed to a CO$_2$ increment of +150 parts per million (i.e. the projected global atmospheric CO$_2$ concentration for 2050) compared to ambient since 2012, with the other three rings serving as control plots. TLS data for the EucFACE rings is available at three timestamps: 2012, 2015 and 2018. The objective of this work is to test the hypothesis "do elevated CO2 concentration levels have an effect on forest growth?". In this presentation, we will show (preliminary) results from estimating tree growth explicitly through 3D TLS data over a six-year period, taking into account the full structure of the tree, and link this to elevated CO$_2$ concentration levels. We will show results from the extraction of tree models from within each EucFACE ring using the TLS point clouds for the three timestamps following a semi-automated approach (treeseg). We will then show the time progression of tree parameters including DBH, tree height and tree volume, as well as their measurement and method uncertainty, through reconstructing QSMs (quantitative structure models) from the individual tree point clouds.