Measuring Tree Diameter Increment with Terrestrial Laser Scanning

By Philipp Avemaria

Abstract
For the question if tree growth can be accurately determined with terrestrial laser scanning (TLS), a 100-year-old evergreen Scots pine (Pinus sylvestris) forest plot in the Loobos, Netherlands was measured with TLS and the results were compared with manual diameter at breast height (DBH) field measurements. The analysis was performed with historical TLS and field DBH measurements from 10 years prior to retrieve temporal changes. The advantage of repeatability and storage of TLS measurements as digital data creates the possibility for temporal analysis of forest structures. Despite these possibilities, few researchers have explored the potential of temporal forest analysis with laser scanning. It was found that TLS measurements in this study have a diameter measurement precision of +- 1,01 cm when compared with manual measurements. Though, irregularities in the historic DBH values lead to the conclusion that an accuracy of up to 0,5 cm could realistically be achieved. The increment in stem diameter at breast height for one decade at tree level for the Loobos study area was on average 1,55 cm for the field measurements and 1,08 cm for the TLS data. As TLS allows for diameter derivation at different heights, increments were measured at multitudes of breast height up until the crown. The main increment was observed at breast height, closely comparable with heights that were approximating crown formation. The smallest increment was observed in the top part of the trees where the crown is already developing. As the results of this thesis have shown, TLS is a valid method for measuring tree diameter increment and offers many advantages compared to manual field measurements. In the scope of this research, it can be concluded that Terrestrial Laser Scanning is a superior method for making forest inventories compared to conventional field measurements, with the major advantage of traceability.