Assessing Forest Vitality and Forest Structure Using 3D Data: A Case Study From the Hainich National Park, Germany

Abstract

The adaptation of forest management to changing environmental conditions due to climate change relies on information on the current forest and tree vitality. In common practice, the percentage of crown defoliation is used as a proxy for tree vitality, an approach that has several drawbacks. By performing laser scanning on a forest plot in the Hainich National Park, we tested a new approach to quantifying tree vitality. Based on the difference in structural complexity measured between summer and winter, assessed via the box-dimension, the new approach provides an objective and reproducible method that does not only allow the quantification of the defoliation, but also includes the effects of branch diebacks. In addition, we assessed the change in box-dimension and branch lengths between 2013 and 2021 and studied the overall structural development of the trees to analyze the alteration of their vitality. On average, we found a decrease in overall structural complexity, as well as in branch lengths for most trees in the investigated forest. Further, the mean difference in box-dimension (summer minus winter) decreased with ascending vitality class. We conclude that the vitality of the trees was negatively affected over the period of 8 years, and we argue the newly proposed method based on the box-dimension holds potential to be used as a measure for tree vitality in deciduous forests.

What Are We Missing? Occlusion in Laser Scanning Point Clouds and Its Impact on the Detection of Single-Tree Morphologies and Stand Structural Variables

“…To us, a voxel size of 20 cm seems to be an appropriate size to reduce the effect that occlusion has on the data and still provide enough detail at the forest stand level. The same conclusion was also made by Heidenreich and Seidel [21].…”

“…Additionally, difficulties arise in obtaining detailed tree structures due to canopy occlusion [19]. Mobile laser scanners, on the other hand, are well suited for scanning forest stands and individual trees with a high level of detail, e.g., [20,21].…”

TreeArchTraits: an R package to analyse the architectural traits of trees using TLS data

“…Box-dimension parameter ( Db ) is an integrative measure of tree architecture firstly suggested by Mandelbrot (Mandelbrot 1982). Considering the TLS technology potential for a 3D detailed analysis, Db was recently re-introduced by some authors (Seidel et al 2019; Heidenreich and Seidel 2022; Neudam, Annighöfer, and Seidel 2022). Db is a measure sensitive to both outer shape and internal structure of a tree.…”

Towards a causal understanding of the relationship between structural complexity, productivity and adaptability of forests based on principles of thermodynamics

“…Today, it is possible to quantify the complexity of forest structures objectively, holistically, and efficiently based on light detection and ranging (LiDAR) technology (e.g. Ehbrecht et al 2021, Heidenreich andSeidel 2022). Structural complexity in general was shown to have beneficial effects on various ecosystem functions and services provided by forests (Lindenmayer et al 2000, Knoke and Seifert 2008, D'Amato et al 2011, Neill and Puettmann 2013.…”