MISTRA DIGITAL FOREST 2019 1
MISTRADIGITALFOREST Laser scanning for estimation
of tree species and growth In the summer of 2019, a multispectral laser scanning of forest test sites in Sweden was carried out from the air, within the framework of Mistra Digital Forest in cooperation with the Swedish University of Agricultural Sciences (SLU). The dense laser scanning (20 points/m2) allows analysis on single tree level, and the use of two laser colours might improve the possibility to detect tree species. Furthermore, since most of the large areas at the test sites were scanned 2009 as well, it will be possible to study growth down to the level of single trees. Three of SLU’s experimental parks were laser-scanned with a new type of high-resolution laser scanning system, using two-colour laser light. In addition, SCA scanned a 50,000 hectare area outside Sundsvall using the same system, Professor Håkan Olsson, at SLU, tells us more about the work. How did the implementation of Mistra Digital Forest’s laser scanning turn out? – Generally very well, I must say. We were lucky with the weather too! How does this laser scan differ from other, earlier scans? – We are testing a scanner that uses two colours of laser light. With the additional information on the amount of reflected laser light in two colours, and not simply the location from where the laser light is reflected, we hope to better distinguish the tree species. We have also scanned at a higher resolution than the National Land Survey’s national scan. – Three of the areas scanned this time – the SLU research parks Asa, Siljansfors and Krycklan – were already scanned ten years ago by SLU’s research park organisation. This also makes it possible to investigate how well growth can be measured, using high-resolution laser scanning from two time points. This part of the research is done in the context of the Future Silviculture Program, which is funded by the Wallenberg Foundations. In addition, Future Silviculture and Stora Enso, have also financed the scanning and associated field inventory, while the initial data processing was carried out by the Department of Forest Remote Sensing at SLU. – The fact that the new national laser scan by Lantmäteriet, the Swedish Mapping, Cadastral and Land Registration Authority, coincides with the program’s own higher-resolution scanning provides us with a gold mine, in the form of data. Being able to access their data in parallel with our own is of great benefit to the program, says Håkan Olsson. How does that benefit the companies within Mistra Digital Forest? – We hope that access to higher-resolution data with information on both tree species and growth can lead to better planning and decision support for forestry. Since, as a forester, you have access to databases where the forest is described in grid boxes, or as individual trees, you can get better support when determining areas in need for thinning, for example. – Up to now, forests have been primarily measured using manual methods, which is expensive. In addition, the forest is constantly changing, so for forest data to be useful it has to be updated regularly. Some forest measurements, such as tree height, timber volume and average diameter, can be well estimated already using laser data. With the development being carried out within Mistra Digital Forest, we hope to improve remote estimation of tree species, and growth too. We also get comprehensive forest-based information at tree level as well. What happens now? – To begin with, we will calculate models for the height of the ground and the height of the canopy. Another important part of our work package is combining laser data with harvest data. We are very much looking forward to undertaking this exciting work. 7 Photo: Opegieka