Identifying architectural characteristics that determine tree structural complexity

Key message: We found structural complexity can best be predicted from a combination of measures that relate to the horizontal and vertical, as well as the internal branching pattern of the trees (range of branch angles). Abstract: Forest structure is related to several ecosystem services and functions provided by forests. To support a management for structural complexity, which is considered to have beneficial effects on most forest functions and services, it is crucial to understand how tree and stand structural complexity are created. We used fractal analysis to describe the structural complexity of trees and investigated how it depends on a tree architectural properties using a combination of measures that relate to vertical, horizontal and internal branching characteristics. Across a large range of tree sizes, we found that the structural complexity can best be predicted from a combination of conventional measures that relate to the horizontal and vertical extent as well as to the internal branching pattern of the trees (R² = 0.73). Our findings also indicate that large trees tend to possess a greater structural complexity than small trees, which is not due to their size per se but due to a more complex architecture.