Understanding the Relationship Between Crown Shape and Size and Structural Complexity of Individual Trees

Abstract:

Forest canopy structure is influenced by tree attributes and their relationships as well as 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 Scots pine (Pinus sylvestris L.) trees to better understand of forest systems and especially relationships between structural complexity and crown shape and size. 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 surface 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 0.5-0.7) was found between structural complexity and crown surface area. 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 0.4-0.5. Crown characteristics can be used for assessing structural complexity of individual trees, especially crown surface area showed strong relationship between the structural complexity. Crown surface area, on the other hand, can be expected to characterize photosynthetically active surface which again affects respiration and 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.