A high‐resolution approach for the spatiotemporal analysis of forest canopy space using terrestrial laser scanning data

Abstract

Forest canopies and tree crown structures are of high ecological importance. Measuring canopies and crowns by direct inventory methods is time‐consuming and of limited accuracy. High‐resolution inventory tools, in particular terrestrial laser scanning (TLS), is able to overcome these limitations and obtain three‐dimensional (3D) structural information about the canopy with a very high level of detail. The main objective of this study was to introduce a novel method to analyze spatiotemporal dynamics in canopy occupancy at the individual tree and local neighborhood level using high‐resolution 3D TLS data. For the analyses, a voxel grid approach was applied. The tree crowns were modeled through the combination of two approaches: the encasement of all crown points with a 3D α‐shape, which was then converted into a voxel grid, and the direct voxelization of the crown points. We show that canopy occupancy at individual tree level can be quantified as the crown volume occupied only by the respective tree or shared with neighboring trees. At the local neighborhood level, our method enables the precise determination of the extent of canopy space filling, the identification of tree–tree interactions, and the analysis of complementary space use. Using multitemporal TLS data recordings, this method allows the precise detection and quantification of changes in canopy occupancy through time. The method is applicable to a wide range of investigations in forest ecology research, including the study of tree diversity effects on forest productivity or growing space analyses for optimal tree growth. Due to the high accuracy of this novel method, it facilitates the precise analyses even of highly plastic individual tree crowns and, thus, the realistic representation of forest canopies. Moreover, our voxel grid framework is flexible enough to allow for the inclusion of further biotic and abiotic variables relevant to complex analyses of forest canopy dynamics.

The shape is more important than we ever thought: Plant to plant interactions in a high mountain community

“…size, shape and orientation) of the individuals of the community are available. Measuring these variables in a fully mapped community could appear as a challenge but the ever-growing development of remote sensing technologies such as LIDAR and digital photogrammetry (Lefsky, Cohen, Parker, & Harding, 2002;Morsdorf et al, 2004;Paris, Kelbe, van Aardt, & Bruzzone, 2017) or terrestrial laser scanning (Hess, Härdtle, Kunz, Fichtner, & von Oheimb, 2018) that enable to map the species canopy would render this a routine task in the near future. In addition, although a high number of simulations has been suggested to be necessary to get reliable inference in Monte Carlo tests (Ruxton & Neuhäuser, 2013), our OAA test could attain enough statistical power in most situations with just 199 simulations.…”

Individual tree measurements in a planted woodland with terrestrial laser scanner

“…As mentioned in the previous section, the most important variable in the process of obtaining the DTM is voxel resolution. At this stage, the voxel resolution was discussed and defined to be 5 cm based on previous studies (Bienert et al, 2006;Hess et al, 2018) and field observations. According to the elevation analysis of raw point cloud data, the maximum tree height was calculated as 22.80 m ( Figure 6).…”

Species and habitat mapping in two dimensions and beyond. Structure-from-Motion Multi-View Stereo photogrammetry for the Conservation Community

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