Lasers digitise forests and measure variation in tree water content

Research collaboration between the Department of Forest Sciences at the University of Helsinki, Hyytiälä Forest Research Station, the School of Forest Sciences at the University of Eastern Finland, the Finnish Geospatial Research Institute FGI and Shinshu University (Japan) has produced novel methods for measuring trees.

Modern remote sensing methods are constantly opening up new possibilities for mapping and tracking forests at different scales, from individual trees, or even needles, to global applications.

The terrestrial laser scanner is an instrument that can measure the detailed 3D structure of the environment and can be used to derive various models that describe the environment. Terrestrial laser scanning (TLS) can be utilised in digitising forests, in which the current situation of the measured forest area is captured nearly as a whole in the microcosm of a single needle. The information can be used to obtain forest characteristics, such as tree structure, biomass, wood quality, the amount of decaying wood and tree vitality.

In addition to the 3D information, the scanner measures the amount of laser light that has reflected from the target. When the laser is adjusted to certain infrared wavelengths that are sensitive to water, we can deduce that if the reflection is changed, the water content of the target has changed. A new method for measuring small diurnal variation in leaf water content was introduced in a recently published research article. Measuring tree or leaf water content manually is extremely laborious, so researchers need novel methods to improve the understanding of tree water dynamics.

“Climate change is a threat to the vitality of the world’s forests largely because the availability of water is altered. Droughts are becoming more intensive and longer, which causes tree mortality. We need more information on tree water dynamics to be able to better understand the effects of the changing environment on our forests”, says postdoctoral researcher Samuli Junttila from the University of Eastern Finland.

“The tree water dynamics research described here is a continuation of the over 20-year collaboration between the University of Helsinki, the Finnish Geospatial Research Institute FGI and Aalto-university. During 2014-2019 the collaboration was supported by the Center of Excellence in Laser Scanning Research funded by the Academy of Finland. Dr. Junttila has expanded his research network to cover the University of Eastern Finland as well. This project is a prime example of research that requires knowledge from several research areas”, notes professor Markus Holopainen from the Department of Forest Sciences at the University of Helsinki.

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