Individual Tree Crown Delineation from Airborne Laser Scanning for Diseased Larch Forest Stands

Abstract

Airborne laser scanning (ALS) can be utilised to derive canopy height models (CHMs) for individual tree crown (ITC) delineation. In the case of forest areas subject to defoliation and dieback as a result of disease, increased irregularities across the canopy can add complications to the segmentation of ITCs. Research has yet to address this issue in order to suggest appropriate techniques to apply under conditions of forest stands that are infected by phytopathogens. This study aimed to find the best method of ITC delineation for larch canopies affected by defoliation as a result of a Phytophthora ramorum infection. Sample plots from two study sites in Wales, United Kingdom, were selected for ITC segmentation assessment across a range of infection levels and stand characteristics. The performance of two segmentation algorithms (marker-controlled watershed and region growing) were tested for a series of CHMs generated by a standard normalised digital surface model and a pit-free algorithm, across a range of spatial resolutions (0.15 m, 0.25 m and 0.5 m). The results show that the application of a pit-free CHM generation method produced improved segmentation accuracies in moderately and heavily infected larch forest, compared to the standard CHM. The success of ITC delineations was also influenced by CHM resolution. Across all plots the CHMs with a 0.25 m pixel size performed consistently well. However, lower and higher CHM resolutions also provided improved delineation accuracies in plots dominated by larger and smaller canopies respectively. The selected segmentation method also influenced the success of ITC delineations, with the marker-controlled watershed algorithm generating significantly more accurate results than the region growing algorithm (p < 0.10). The results demonstrate that ITCs in forest stands infected with Phytophthora ramorum can be successfully delineated from ALS when a pit-free algorithm is applied to CHM generation.

A New Individual Tree Crown Delineation Method for High Resolution Multispectral Imagery

“…Some ITC delineation approaches attempted to improve delineation accuracy by considering scale size [15,24]. For instance, Gaussian filtering has been used to smooth the imagery prior to segmentation, in order to suppress spurious branches, but it is difficult to determine an optimal filter size [25].…”

“…For instance, Gaussian filtering has been used to smooth the imagery prior to segmentation, in order to suppress spurious branches, but it is difficult to determine an optimal filter size [25]. To improve the situation, some multi-scale ITC delineation approaches were proposed, such as identifying tree crown contours at each scale level and selecting seed points from the detected local peak scales [14], choosing three different scales and performing crown extraction at each scale [24], pre-processing the multispectral image using wavelet transform and then delineating tree crowns [26], and adopting nonlinear multi-scale fitting to improve the goodness of fit of tree crowns at different scales [27]. Despite the successes, those algorithms underperform in dense forests, due to the fact that the scales of the tree crowns span a large range, whereas the scales used in these algorithms were sparse and limited, and thus leading to incomplete detection of multi-scale crowns.…”

Drone‐based photogrammetry‐derived crown metrics for predicting tree and oil palm water use

“…Drones equipped with optical detectors such as cameras capturing specific light wave lengths or laser-based approaches offer new opportunities for crown and canopy assessments (Barnes et al, 2017;Díaz-Varela, de la Rosa, León, & Zarco-Tejada, 2015;Thiel & Schmullius, 2016). With the recent development of drone technologies and their application in ecological studies, this might change.…”

“…With the recent development of drone technologies and their application in ecological studies, this might change. Drones equipped with optical detectors such as cameras capturing specific light wave lengths or laser-based approaches offer new opportunities for crown and canopy assessments (Barnes et al, 2017;Díaz-Varela, de la Rosa, León, & Zarco-Tejada, 2015;Thiel & Schmullius, 2016). Crown variables such as crown length (Kallimani, 2016), crown diameter (Lim et al, 2015;Panagiotidis, Abdollahnejad, Surový, & Chiteculo, 2016), or crown volume (Torres-Sánchez, López-Granados, Serrano, Arquero, & Peña, 2015) were calculated using photogrammetric techniques.…”

An Automated Hierarchical Approach for Three-Dimensional Segmentation of Single Trees Using UAV LiDAR Data

“…Forests play a key role in the terrestrial ecosystem and have a large amount of economic, ecological, and social benefits because they regulate the water cycle and carbon cycle on the surface of the Earth [1]. For effective forest management and human activity documentation, the forest inventory for sustainable forest management is usually needed to obtain a great number of single tree-related parameters, such as tree species and tree species distribution, timber volume, increment of timber volume, and mean tree height [2][3][4][5][6][7][8][9]. Traditionally, in practice, most single-tree-level parameters are estimated by manually sampling small plots in a field survey, which is time consuming and labor intensive [10,11].…”