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Casella, Eric Sensing the growth of oak trees from an eight-year TLS survey period Poster
Eric Casella1, Pasi Raumonen2 and Markku Åkerblom2
(1) Centre for Sustainable Forestry and Climate Change, Forest Research Agency of the Forestry Commission, Farnham, GU10 4LH, UK(2) Mathematics, Tampere University, FI-33014 Tampere University, Finland

Terrestrial laser scanners (TLS) have been demonstrated to be reliable for non-destructive and accurate measurements of the above ground volume (AGV) and biomass (ABG) of trees. A novel and automated processing chain for extracting tree metrics from TLS data has been applied in this study to detect changes in AGV and AGB of 80-year-old English oak trees during an eight year survey. This analysis was based on data recorded by a Leica HDS-6100 during winters of 2012-19. Eight trees were recorded over time from nine scan positions across a 15 m radius plot at a TLS sampling resolution of 0.018°. Prior to scanning, the stem diameter at breast height (DBH) of each tree was measured and its position marked with a highly reflective plastic band. The 3D geometry of the scanned trees was reconstructed and stratified into lower stem (Ls) and branch (B) sections. TLS inferred AGBs were derived from these volume estimates and nominal specific gravity. Site-specific empirical relationships, developed from 20 harvested trees and explaining AGBs as a function of DBH, were used for data comparison. The volume of Ls was found to increase consistently in all trees (r²>0.9, p<0.01) at a rate ranging from about 5 (for supressed trees) to 30 l per year (for dominant trees) ca. 3-17 kg of dry mass per year. By contrast, the B section showed contrasting patterns with negative, nil and positive rates ranging from about -4 to 50 l per year. This demonstrates the contribution of the canopy to the non-leaf litter production.