Arboriculture & Urban Forestry 45(2): March 2019 returns or a continuous waveform for each laser emis- sion (Lim et al., 2003). LiDAR is less susceptible to weather conditions compared to optical sensors and it is effective for measuring objects with complex 3-D structures such as trees and forests (Wulder et al. 2008). Information about the objects hit by the lasers is converted into a large number of point cloud data, which all have x-, y-, and z-coordinate values, as well as attributes such as the intensity and return number. At the forest stand level, the canopy coverage and porosity have been estimated with high accuracies using variables based on the laser canopy hits and laser penetration rate derived from LiDAR data (Sasaki et al. 2008; Hopkinson and Chasmer 2009; Korhonen et al. 2011; Sasaki et al. 2016b). Thus, physical prop- erties of trees such as their crown density and porosity may be estimated by applying these estimation meth- ods at the individual tree level. Furthermore, the health condition of a tree can be estimated if it correlates with these physical indicators. Although many past studies identified individual trees in forests and esti- mated tree characteristics using LiDAR data (Popescu et al. 2003; Holmgren et al. 2008; Ørka et al. 2009), relatively few studies monitored trees outside forests (Schell et al. 2015), and none have associated the LiDAR variables with field-based visual tree health evaluations. In this study, we aimed to verify the effectiveness of using airborne LiDAR data for estimating the indi- vidual tree health condition of Japanese mountain cherry (Cerasus jamasakura) planted in Yoshinoyama, Japan. In particular, we focused on the crown density, which is a visual health indicator, and used the crown porosity data obtained from hemispherical photo- graphs to support the objectivity of the visual health assessment. METHODS Study Site Yoshinoyama (34° 22' N, 135° 52' E), located in Nara Prefecture, Japan, is known for its cultural landscape containing flowering cherry trees. It has been desig- nated as a UNESCO World Heritage Site because of the Sacred Sites and Pilgrimage Routes in the Kii Mountain Range. It has an elevation range of ca. 200 to 850 m above sea level, where cherry trees (mostly Japanese mountain cherry [Cerasus jamasakura]) have traditionally been planted for about 1,300 years (Imanishi et al. 2016). At present, the total planted area is about 50 hectares (0.5 km2 55 ). The four main planted areas are known as Shimosenbon, Nakasen- bon, Kamisenbon, and Okusenbon, in order from the lowest elevation (Figure 1). Recently, local residents have become concerned about declined tree health condition, which is inferred to be caused by multiple factors, including soil water retention ability deter- mined by the topography, infection of fungus, and bark feeding damage by animals (Imanishi et al. 2012). Field Survey We selected 11 clusters comprising a total of 324 cherry trees (Figure 1). We aimed to include trees in various health conditions throughout the entire area of Yoshi- noyama. In August 2011, each tree was visually clas- sified by two experts according to one of four health ranks (1 = good to 4 = poor) taking into account the following eight indicators: tree vigor, tree form, branch growth, crown dieback, crown density, leaf shape and size, leaf color, and bark condition, in accordance with the Japanese traditional method (Shi- bata 2007; Table 1). For each tree, the stem location was measured using differential GPS and total station; the crown projection area was depicted using total station by finding the apexes of branches and connecting them. Each crown projection area on the ground was trans- formed into a polygon with ArcGIS and its area was calculated. We excluded five trees with excessively small crowns that did not produce any meshes when Figure 1. Location of the study site and distribution of C. jamasakura trees tested in the present study. The black border and dots represent the LiDAR data collection area and tested trees, respectively. ©2019 International Society of Arboriculture
March 2019
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