Landscape green spaces in apartment complexes are mostly determined based on the shape and layout of buildings. As buildings have risen high, the distance ratio between buildings has decreased, but the distance between buildings has increased to protect residents’ right to light, which has led to wider green spaces between buildings. In terms of the shape of buildings, flat-type structures are used more for the straight layout of buildings and tower-type structures are used to save spaces and flexibly lay out buildings, which affects the flow of human traffic in apartment complexes and the direction of buildings. Changes in the shape of apartment buildings and underground parking lots have led to the expansion of landscape spaces in apartment complexes (Shin, 2010). People’s interest in the duration of daylight and the growth of trees in apartment complexes increases, but only few studies have been conducted to identify the correlation between the environment of daylight - the most fundamental and important factor for the growth of trees - and the growth of trees or essential daylight conditions for the growth of trees (Jung et al., 2015). Outdoor landscape spaces in apartment complexes are designed after planning the block layout and the flow of emergency vehicles. In this process, microclimate that is created under fixed conditions such as the duration of daylight and insolation and other various factors such as the growth conditions of trees need to be analyzed and reflected in planting design, but they have not been done so in reality. If planting is designed and performed without analyzing the growth conditions of trees, trees will grow poorly and the defect rate of trees will also increase over time, resulting in the continuous repair of defects and an increasing burden on constructors and residents. Therefore, the environment of daylight (duration of daylight, insolation, etc.) that directly affects the growth of trees and permanently shaded areas must be considered before selecting trees suitable for the environment in order to lower the defect rate of trees and continuously maintain a good landscape of trees in the stage of completion.

The recent layout of apartment complexes has mainly adopted the method of laying out L-shaped buildings (flat + tower) repeatedly in order to efficiently utilize spaces considering economic feasibility. Compared to the early flat-type layout, the shape and layout of buildings have become complex, and thus has created many permanently shaded areas that can hinder the growth of trees in outdoor spaces. Recent trends in studies on defects in trees in apartment complexes were examined. Yoon and Ahn (1996) surveyed the current size and planted location of four landscape trees within apartment complexes and analyzed the time of shadows of each building to identify the relationship between the time of shading and the growth of trees. Han et al. (2015) calculated the range of illumination intensity in spaces for planting for biodiversity in landscape spaces in apartment complexes and provided basic data for planting shrubs and flowering plants according to it. Park (2019) simulated daylight in study sites, checked whether the conditions of daylight that were measured at each point on site coincided with the simulated conditions of daylight, and utilized the results in selecting locations for trees considering the amount of solar radiation according to solar altitude. Park, Jeong, et al. (2015) utilized Ecotect Analysis to simulate daylight conditions according to the layout shape of apartment complexes and selected flowering plants that are applicable to each illumination intensity in each area (shady, sunny, complex areas) categorized by analyzing the conditions of daylight. Han et al. (2016), Lee et al. (2017) and Park, Han, et al. (2015) surveyed the light distribution in the lower part of trees based on the results of analysis of light requirements for ground-cover plants for multi-layer planting in order to utilize the results as basic data for planting shrubs and flowering plants. Han and Lee (2018) examined the effects of shadows created by buildings on the roadsides - physical elements in urban spaces - and the appropriateness of planting roadside trees. Kim et al. (2014) analyzed the duration of daylight in spaces for planting by the type of apartment complexes to provide data for gardeners in apartment complexes to select plants suitable for the location of planting. Moon (2014) analyzed the growth conditions of trees and ground-cover flowering plants according to the amount of daylight in the lower parts of overpasses. The amount of daylight was analyzed using Google Sketchup program and the amount of chlorophyll content and soil moisture were analyzed to examine the growth status in the study. It was found that the growth of plants was affected not only by the amount of daylight, soil moisture and the height of overpasses, but also by other environmental factors. Most of earlier studies simulated daylight to suggest flowering plants applicable to each light condition or to increase the production of plants and many studies have been conducted on ground-cover plants planted in permanently shaded areas. However, databases for each species of plants applicable to permanently shaded areas have not been established through basic research on trees.

This study aimed to survey the growth status of trees in the outdoor spaces of apartment complexes according to the conditions of daylight in order to analyze the defect rate of trees and to provide basic data on trees for utilizing in planting design and execution. To do so, daylight simulations were conducted on recently constructed apartment complexes to analyze the conditions of daylight and the defect rate of trees planted in permanently shaded areas and those planted in green spaces of which daylight conditions were good were compared through time series analysis. Specific species of trees that are applicable to permanently shaded areas were suggested in this study, which is differentiated from earlier studies.

This study aimed to compare and analyze the growth status of trees in outdoor spaces of apartment complexes according to the conditions of daylight, and to identify species that can be utilized in planting design and execution in permanently shaded areas. To do so, daylight simulations were performed on recently constructed apartment complexes to analyze the conditions of daylight, and the defect rate of trees planted in permanently shaded areas and those planted in green spaces of which daylight conditions were good were compared through time series analysis.

To examine the ratio of shadows by hour and the environment of daylight according to the location of the sun from sunrise to sunset in study sites, simulations were conducted utilizing Solar Access Analysis of Ecotect Analysis. The results of analysis showed that permanently shaded areas were formed in the rear part of buildings that faced north. Permanently shaded areas were also found to be affected not by the height of buildings, but by the length of buildings. When the length of buildings increases due to a higher number of houses on the same floor and the length of the long side was similar to the length of the short side from the corner at the center of buildings, the area of permanently shaded areas was relatively wider. When the shape of buildings was identical, permanently shaded areas near those located within apartment complexes were wider than those located along the border of apartment complexes.

The image of study sites analyzed through daylight simulations was overlapped with their as-built drawing, and permanently shaded areas and green spaces of which daylight conditions were good were distinguished to survey the growth status of trees. The first tree survey was conducted between November 18, 2019 and February 15, 2020 focusing on trees planted in permanently shaded areas and the growth and withering status of trees that could be identified with the naked eye were surveyed. The second tree survey was conducted between March 16, 2020 and March 30, 2020, and the conditions of all the trees planted in study sites including those planted in permanently shaded areas were surveyed. Considering that the selected study sites were built by the same constructor, their physical conditions and management such as standards of landscape soil and drainage facilities were equal, and thus the growth conditions of trees planted within study sites were also assumed to be equal. Under the assumption, the growth status of trees planted in permanently shaded areas and green spaces of which daylight conditions were good was compared and analyzed. The defect rate of Study Site-1 was highest, followed by Study Site-2, Study Site-3 and Study Site-4, and the order of the defect rate of trees in permanently shaded areas was the same. The overall defect rate in study sites tended to gradually increase over time after completion and the defect rate in permanently shaded areas also increased. Among the trees planted in permanently shaded areas, evergreen tall-tree species that are categorized as shade intolerant trees including Pinus densiflora, American arborvitae and Thuja occidentalis showed a higher defect rate over time, and species that are categorized as shade tolerant trees and shade moderate trees including Taxus cuspidata, Zelkova serrata, Cornus kousa, Chionanthus retusus and Chionanthus retusus showed the good growth status and a low defect rate, which indicates that they can be utilized in designing planting for permanently shaded areas in apartment complexes. Sorbus commixta and Cornus officinalis can be also utilized although they were excluded from analysis due to their small number of samples. The daylight simulation technique utilized in this study to analyze permanently shaded areas can be used as an analysis tool at the stages of design and execution considering the environment of daylight.

This study distinguished green spaces in the outdoor spaces of apartment complexes based on daylight conditions, analyzed the defect rate of trees planted in permanently shaded areas and thus suggested specific species of trees that are applicable to permanently shaded areas, which differentiates this study from earlier studies, but there are still some limitations. First, as this study utilized the data of one constructor for collecting accurate as-built drawings and quantity data, the number of samples was small. Second, this study focused on tall trees planted in permanently shaded areas, and thus it will be necessary to conduct follow-up studies on shrubs and ground-cover flowering plants. Defects in trees are affected by daylight conditions but they are also caused by the combination of multiple factors that give stress to trees such as climate change, the selection of unsuitable trees, poor planting foundation, poor construction management, and poor maintenance. Therefore, it will be necessary to conduct additional studies on the growth of trees according to the conditions of daylight through data accumulation and monitoring by managing the records of trees that can occur in the process of planting and maintaining trees across the entire life cycle of trees.