Toomas Tarmu defended his doctoral thesis on more accurate methods for assessing Estonian forests

The doctoral thesis was supervised by Professor Diana Laarmann and Professor Andres Kiviste. The opponent was Professor Jari Hynynen from the Natural Resources Institute Finland (Luke).

When assessing forests, it is important to obtain information that is as accurate as possible about both stand growth conditions and the condition of individual trees. Advances in measurement technologies and modelling methods are providing an increasing range of new possibilities for this purpose. In his doctoral thesis, Tarmu investigated two approaches: dominant-height-based site index models and the use of acoustic tomography to detect stem decay in trees.

The doctoral thesis was based on four studies using data from the Estonian Network of Forest Research Plots as well as separately collected measurement data from Norway spruce stands. Tarmu investigated the effects of thinning on mean and dominant stand height and developed dominant-height-based site index models for pine, spruce and birch stands.

The results showed that dominant height is less sensitive to thinning than mean stand height. It therefore provides a more stable basis for site index modelling in managed stands. The models developed as part of the doctoral thesis can be applied under Estonian conditions, although their use should take into account the ages and conditions of the stands represented in the permanent sample plot data.

In the second part of the thesis, Tarmu assessed the potential of acoustic tomography for detecting stem decay in Norway spruce. Acoustic tomography provides information about the internal condition of a tree based on the propagation of sound through the stem. The study showed that the method can detect hidden stem decay when the damage is severe enough to affect sound propagation within the stem. Decay was more extensive in the lower part of the stem and decreased with increasing height.

However, the dataset studied did not confirm any associations between the occurrence of decay and the proportion of spruce, previous thinning or forest site type. The wider use of acoustic tomography in practical forest management is currently also limited by the time required for measurements, the cost of the equipment and the specialist knowledge needed to interpret tomograms.

Toomas Tarmu’s doctoral thesis demonstrates how new measurement technologies and modelling methods can be used to improve the accuracy of forest assessment in Estonia. The results contribute to more accurate assessments of stand growth conditions and the internal condition of trees and provide a basis for the further application of these methods in forest management.

The doctoral thesis is available in the Estonian University of Life Sciences digital repository, EMÜ DSpacelink opens in new page.