Terrestrial laser scanning for measuring the solid wood volume, including branches, of adult standing trees in the forest environment

Abstract

This study evaluates the potential of terrestrial laser scanning (TLS) to assess the solid wood volume (i.e., stem and branch diameters of more than 7cm) of adult standing trees in the forest environment. The solid wood volume of 42 trees of different species and size classes was investigated under leafless conditions, both by manual destructive field measurements and by TLS. The trees were first digitised by TLS using a protocol developed to provide fine-scale sampling of trees within acceptable scanning time. TLS data were processed by retro-engineering software using geometric fitting procedures to model tree woody structure and to compute the wood volume. After tree felling, labour-intensive fieldwork was conducted to obtain the solid wood volume of the trees by destructive measurements. The comparison between both methods gave excellent results, regardless of the tree species or size. The relative differences of the TLS estimates remained primarily within a range of ±10% for estimating the volume of the main stem of the trees, and within a range of ±30% for estimating the cumulative branch volumes. Although our semi-automated modelling method makes it possible to overcome the effect of (acceptable) wind, it remains time-consuming and requires further improvement to be used on a large number of trees. However, it demonstrates the appropriateness of laser scanning techniques and simple geometric fitting to characterise the woody structure of a tree in the forest environment and provides new insights for tree growth monitoring, carbon sequestration and bioenergy assessment.