Tree Root System Characterization and Volume Estimation by Terrestrial Laser Scanning and Quantitative Structure Modeling

Abstract

Abstract:The accurate characterization of three-dimensional (3D) root architecture, volume, and biomass is important for a wide variety of applications in forest ecology and to better understand tree and soil stability. Technological advancements have led to increasingly more digitized and automated procedures, which have been used to more accurately and quickly describe the 3D structure of root systems. Terrestrial laser scanners (TLS) have successfully been used to describe aboveground structures of individual trees and stand structure, but have only recently been applied to the 3D characterization of whole root systems. In this study, 13 recently harvested Norway spruce root systems were mechanically pulled from the soil, cleaned, and their volumes were measured by OPEN ACCESSForests 2014, 5 3275 displacement. The root systems were suspended, scanned with TLS from three different angles, and the root surfaces from the co-registered point clouds were modeled with the 3D Quantitative Structure Model to determine root architecture and volume. The modeling procedure facilitated the rapid derivation of root volume, diameters, break point diameters, linear root length, cumulative percentages, and root fraction counts. The modeled root systems underestimated root system volume by 4.4%. The modeling procedure is widely applicable and easily adapted to derive other important topological and volumetric root variables.

Analysis of Geometric Primitives in Quantitative Structure Models of Tree Stems

“…The average volume error for all models was below 5%, and using, e.g., the circular cylinder model on extremely elliptic stems, resulted in a maximum volume error below 14%. These ties well with the field-calibrated studies of [16,23], as the volume and length errors are similar in all studies. In [16], it is shown that a hybrid version of polyhedral and cylindrical modelling is accurate, even for the highly complex shapes of stump-root systems.…”

“…These ties well with the field-calibrated studies of [16,23], as the volume and length errors are similar in all studies. In [16], it is shown that a hybrid version of polyhedral and cylindrical modelling is accurate, even for the highly complex shapes of stump-root systems. Furthermore, [24] shows that using allometric equations to predict the volume of eucalyptus trees results in a 36.6% average error with the species-specific equation and a 29.9% error with the generic eucalyptus equation, while circular cylinder structure models produce an error of 9.7%.…”

“…None of the tested approaches could accurately model complex cross-sections, such as flanges. On the other hand, the polyhedron method has been shown to give a good representation of complicated stump shapes that are not well represented by the other primitives [16,22].…”

“…In addition, we use polyhedral cylinder surfaces (trian), which are triangulated meshes, to reconstruct tree stems. Similar triangulated surfaces have been previously used for reconstruction with data collected with a digitizer from tree stems [14] and root systems [15] and for TLS data and root systems [16].…”

Terrestrial Structure from Motion Photogrammetry for Deriving Forest Inventory Data

“…Furthermore, in addition to the regular tree attributes measured in practical field inventories, more detailed tree attributes, such as the stem curve or taper curve (stem diameter as a function of height), which reveal the wood productivity and quality, can be derived from TLS with high degrees of accuracy [9]. Studies have explored the use of TLS at the plot level for assessing stem volume and biomass components [10][11][12][13] for individual tree reconstruction, including branches, twigs, and leaves [3,14,15], in order to improve the physiological understanding of tree growth [16]. Moreover, TLS has been used for determining the stem curve [17,18], which is not easily measurable using conventional tools.…”