Forest canopy structure is influenced by tree attributes and processes such as forest generation, growth, and mortality. Structural complexity of a tree or a stand has, however, been challenging to assess as comprehensive and quantitative measurements have practically been impossible to produce. Thus, we utilized 3D information provided by terrestrial laser scanning (TLS) in assessing structural complexity of individual Scots pine (Pinus sylvestris L.) trees to better understand of forest systems and especially relationships between structural complexity and crown shape and size. Additionally, we investigated the effects of forest management (i.e. thinning) on structural complexity of individual Scot pine trees. We applied fractal analysis (i.e. box dimension) to provide a measure for structural complexity of individual trees and investigated its relationship between crown dimensions (i.e. width, volume, and projection area). There was a positive relationship between crown characteristics and structural complexity indicating an increased structural complexity when crown shape and size increased. The strongest relationship (correlation coefficient of 0.4-0.7) was found between structural complexity and crown projection area and crown volume. The relationship between structural complexity and all crown attributes was stronger in denser forests (~900 stems/ha) with correlation coefficient 0.6-0.7 compared to sparse forests (~400 stems/ha) with correlation coefficient 0.6. Additionally, it was shown that structural complexity of individual Scots pine trees increased with forest management intensity. Crown characteristics can be considered as drivers of structural complexity of individual trees. Crown shape and size can be expected to characterize vitality of trees. Thus, this study provides an example how crown characteristics can be related to structural complexity of individual trees and how they can be quantitatively assessed. Furthermore, the study affirms the possibilities of TLS as a tool for characterizing forest canopy structure and dynamics.

Tree functional traits together with processes such as forest regeneration, growth, and mortality affect forest and tree structure. Forest management inherently impacts these processes. Moreover, forest structure, biodiversity, resilience, and carbon uptake can be sustained and enhanced with forest management activities. To assess structural complexity of individual trees, comprehensive and quantitative measures are needed, and they are often lacking for current forest management practices. Here, we utilized 3D information from individual Scots pine (Pinus sylvestris L.) trees obtained with terrestrial laser scanning (TLS) to first, assess effects of forest management on structural complexity of individual trees, and second, understand relationship between several tree attributes and structural complexity. We studied structural complexity of individual trees represented by a single scale independent metric called “box dimension”. This study aimed at identifying drivers affecting structural complexity of individual Scots pine trees in boreal forest conditions. The results showed that thinning increased structural complexity of individual Scots pine trees. Furthermore, we found a relationship between structural complexity and stem and crown size and shape as well as tree growth. Thus, it can be concluded that forest management affected structural complexity of individual Scots pine trees in managed boreal forests, and stem, crown, and growth attributes were identified as drivers of it.