Figure 1. Examples of objects with box dimension ranging from one (cylindrical pole) to three (solid cube) in between two real-life trees and a Menger sponge (box dimension = 2.72).
Box dimension is a relatively new measure for assessing structural complexity of trees and forests in relation to TLS. Seidel et al. (2019b) studied the relationship between structural complexity (i.e. box dimension) and horizontal and vertical architectural characteristics (i.e. tree height and volume, crown radius and surface area, branching angles) of deciduous trees (Fagus sylvatica, Fraxinus excelsior, Acer pseudoplatanus, Carpinus betulus ) of varying size. They concluded that structural complexity was related to crown radius and surface area of deciduous trees. Dorji et al. (2019) studied how competition affects structural complexity of European beech (Fagus sylvatica L.) trees and concluded that their crowns were influenced by competition, as measured through box dimension. Seidel et al. (2019a), on the other hand, reported decreasing structural complexity when competition (i.e. light availability) increased for deciduous trees. Previous work (Seidel et al. 2018, 2019a, b) demonstrated the potential of box dimension as a meaningful measure for structural complexity of individual trees. However, how this measure can be used to quantify forest structure of conifers and how it can expand our understanding about effects of anthropogenic activities (e.g. forest management) on tree structure is largely unexplored.
Although forest management affects growing conditions of trees as well as their size and shape (Mäkinen & Isomäki 2004, Saarinen et al. 2020), it is unclear how forest management affects structural complexity of conifers. This study aims at identifying relationships between a variety of attributes (e.g. characterizing stem, crown, and competition) and structural complexity of individual Scots pine (Pinus sylvestrisL.) trees in even-aged and single-layered managed boreal forest conditions. We aim to understand how structural complexity is driven by forest management and underlying structural attributes. We hypothesize that thinning intensity affects structural complexity of Scots pine trees (H1). It is also hypothesized that horizontal and vertical measures (e.g. stem and crown dimensions) are related to structural complexity of Scot pine trees (H2). Finally, we hypothesize (H3) that there is a relationship between structural complexity and i) crown dimensions, ii) architectural benefit-to-cost ratio (i.e. surface-to-volume ratio), iii) tree growth (i.e. DBH, height, volume, and Δheight/DBH), and iv) the availability of light (i.e. competition). In other words, structural complexity of individual Scots pine trees can be explained by these attributes.