Abstract
The three-dimensional forest structure is an important driver of several ecosystem functions and services. Recent advancements in laser scanning technologies have set the path to measuring structural complexity directly from 3D point clouds. Here, we show that the box-dimension (Db) from fractal analysis, a measure of structural complexity, can be obtained from airborne laser scanning data. Based on 66 plots across different forest types in Germany, each 1 ha in size, we tested the performance of the Db by evaluating it against conventional ground-based measures of forest structure and commonly used stand characteristics. We found that the Db was related (0.34 < R < 0.51) to stand age, management intensity, microclimatic stability, and several measures characterizing the overall stand structural complexity. For the basal area, we could not find a significant relationship, indicating that structural complexity is not tied to the basal area of a forest. We also showed that Db derived from airborne data holds the potential to distinguish forest types, management types, and the developmental phases of forests. We conclude that the box-dimension is a promising measure to describe the structural complexity of forests in an ecologically meaningful way.
Highlights
The spatial structure of forests is of great interest to forest scientists as it is related to many ecosystem functions and services [1,2,3,4,5]
We found a significantly (p < 0.05) higher structural complexity (Db) for the investigated deciduous stands when compared to the coniferous stands (Figure 4)
The box-dimension (Db) derived from the airborne laser scanning data was significantly positively correlated with the stand structural complexity measures obtained from the ground-based measurements, namely the stand structural complexity index (SSCI) and structural complexity index (SCI)
Summary
The spatial structure of forests is of great interest to forest scientists as it is related to many ecosystem functions and services [1,2,3,4,5]. Great advances have been made in addressing the three-dimensional (3D) character of forest structure by approaching it with airborne remote sensing as well as ground-based (close-range) remote sensing techniques. Among these techniques, radio detection and ranging (RaDAR; e.g., [6,7,8]), airborne light detection and ranging (LiDAR; e.g., [9,10]), spaceborne LiDAR [11], terrestrial laser scanning (TLS; e.g., [12,13,14]), aerial and satellite imagery (photogrammetry; e.g., [15,16]), or structure-from-motion (SfM, e.g., [17]) can be named as prominent examples. For a comprehensive review of structural indices, the interested reader is referred to [26] and [4]
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