Study on the Optimization of Street Tree Management Strategies for Enhancing Growth and Carbon Storage Capacity

Abstract

Average global temperatures have risen by approximately 1.1 °C above pre-industrial levels, prompting South Korea and many other countries to set a carbon neutrality goal by 2050. Expanding green spaces has been proposed as a landscape-based approach to achieving urban carbon neutrality. However, the dense development of urban areas presents spatial and economic constraints in securing new green spaces. As a result, street trees, an existing urban green infrastructure, are increasingly regarded as a practical solution to enhancing carbon storage. Nevertheless, concerns have been raised that street trees planted without a systematic management plan may suffer from reduced vitality, leading to diminished carbon storage capacity. Ultimately, these conditions can result in increased tree mortality, turning what should be carbon sinks into sources of emissions. Such tree mortality not only results in the loss of carbon storage but also degrades the urban landscape, making systematic street tree management essential. This study aimed to address these challenges by developing an effective diagnostic approach to assess street tree growth conditions and identify methods to improve their carbon storage capacity. The methodology included identifying diagnostic indicators through a review of prior research and conducting field surveys on 72 Ginkgo biloba in Dalseo-gu, Daegu Metropolitan City. Correlation and regression analyses were performed, taking into account both growth diagnostic indicators and environmental variables. The results revealed that traffic volume and service population were the main environmental factors affecting the carbon storage capacity of Ginkgo biloba. Among the individual growth characteristics, tree height (β = 0.514), chlorophyll content (β = 0.26), and stem vigor (β = 0.216) were found to have significant influences. Based on these findings, this study proposed a management strategy to enhance the growth and carbon storage potential of urban street trees. These results are expected to serve as a vital foundational resource, contributing to the development of practical street tree management guidelines that support sustainable urban environments and climate change mitigation efforts.

1. Introduction

The issue of climate change stands as one of the most critical challenges of our time, driving growing demands for reducing carbon dioxide (CO₂) emissions and increasing carbon sinks. This global demand has even led to the establishment of a target to limit the rise in average global temperatures to 1.5 °C above pre-industrial levels [1]. South Korea has likewise declared its commitment to achieving carbon neutrality by 2050, aiming to balance CO₂ emissions and absorption and ultimately reach net-zero emissions.

Among the various approaches to achieving this goal, the field of landscape architecture can contribute through urban greening projects [2,3,4]. However, creating additional large-scale green spaces such as urban parks within highly urbanized cities presents significant challenges [5]. In response, the importance of street tree planting and management has steadily increased. Street trees have been recognized as a practical and cost-effective alternative for addressing urban climate challenges, including reducing carbon emissions and mitigating urban heat islands [6].

However, planting street trees alone is insufficient to effectively address climate change, as inadequate management often leads to tree mortality. Consequently, existing carbon storage and CO₂ absorption sources continue to decline [7]. This underscores the critical importance of managing already-planted street trees before initiating new planting efforts. To achieve this, it is essential to identify the factors that influence tree growth and carbon storage. Numerous studies have been conducted in this area to deepen our understanding.

Key domestic and international studies on street tree management can be categorized as follows. First, a significant number of studies have evaluated the growth conditions and planting environments of street trees. In South Korea, research has examined the impact of physical and chemical soil properties on tree vitality [8,9], the effects of heavy metal contamination on tree growth [10], and the chemical characteristics of soils in which street trees are planted [11]. Studies have measured stem resistance to assess tree health [12,13] and compared visual assessments of tree condition with more precise diagnostic evaluations [14]. Internationally, researchers have explored the influence of meteorological factors and soil stress on street tree growth [15], examined the relationships between planting space and tree health through visual assessments [16], and studied the impact of paving materials on tree growth and ecosystem services [17]. Additionally, research on the carbon storage function of street trees and their role in addressing climate change has significantly increased both domestically and internationally. In South Korea, studies have estimated the carbon storage and CO₂ absorption rates for street trees [18], evaluated the carbon storage capacity of major tree species [19], and used relative growth equations to predict carbon storage [20]. Globally, researchers have employed tools such as the i-Tree Planting Tool to evaluate tree carbon sequestration, combined biochar with soil carbon storage modeling to quantitatively assess urban green spaces carbon sequestration potential [4] and utilized UFORE models and biomass equations to measure urban street trees carbon storage and sequestration capacity [21].

Despite the numerous studies conducted, significant limitations remain in enhancing the growth and carbon storage capacity of street trees. Most studies diagnosing street tree growth have primarily relied on visual assessments, making it difficult to ensure reliability. For instance, Moon [14] analyzed street tree growth based on visual assessments alone, without accompanying precise diagnostic evaluations, which resulted in limitations for quantitatively evaluating growth conditions. Furthermore, many studies have focused primarily on soil contamination levels as a key factor influencing tree growth. In the field of carbon storage, while there are numerous studies that have developed formulas for estimating carbon storage capacity and diagnosing carbon storage, relatively few have quantitatively identified the factors affecting carbon storage capacity.

In this study, we have established quantitative diagnostic indicators that influence the growth of street trees and applied them to precisely measure the growth conditions of Ginkgo biloba, a representative street tree species in South Korea. In addition, this study statistically clarified the effects of these diagnostic indicators and growth environments on tree growth levels and ultimately focused on exploring systematic management measures to improve the diameter growth rate and carbon storage capacity of urban street trees.

2. Materials and Methods

2.1. Scope of Research

This study quantitatively diagnosed the growth conditions of street trees and focused on enhancing their efficient management and carbon storage capacity. The spatial, thematic, and temporal scopes of the study are as follows. The key features of the study site, Dalseo District in Daegu Metropolitan City, are as follows.

Dalseo District in Daegu Metropolitan City is characterized by having the largest industrial and manufacturing area [22] and the highest population among administrative districts [23]. Additionally, the annual average temperature in Dalseo District has increased by 0.5 °C, from the long-term average of 12.6 °C to 13.1 °C. Annual precipitation has decreased by 22.9 mm compared to the average of 1148.0 mm over the past 10 years [24]. Furthermore, a review by Kim et al. [5] shows that air pollution has been worsening in the area (Figure 1). In Dalseo District, the specific spatial scope of the study was set to three main roads planted with Ginkgo biloba: Guma-ro (0.37 km), Dalgubeol-daero (2.71 km), and Dalseo-daero (3.3 km). Regarding the thematic scope, while establishing effective street tree management plans requires a comprehensive analysis of numerous factors, the factors considered vary depending on the research institution and researcher. This study focused on the quantitative diagnosis of street tree growth conditions and the calculation of carbon storage. Finally, the temporal scope of the research spanned approximately three months from August to October 2024, a period of peak tree vitality, including preliminary surveys and detailed field investigations.

2.2. Procedure for Conducting the Study

The research process of this study is divided into five major stages (Figure 2). First, the fundamental data necessary for the study were established, including the selection of survey sections and tree species. Second, previous studies related to street tree management and growth condition assessment were analyzed to derive indicators for diagnosing tree growth conditions. Third, the derived management indicators were applied to the study area, and a detailed field survey was conducted. Fourth, the carbon storage capacity of the trees was measured using the diameter at breast height (DBH), estimation equations, and carbon emission coefficients. Finally, the key management indicators for improving carbon storage were derived based on the analysis results. The specific research methods for each step are as follows.

2.3. Constructing Basic Data for Analysis

The establishment of fundamental data for analysis is broadly divided into two aspects—tree species selection and survey section selection. First, for tree species selection, the major street trees planted in Daegu Metropolitan City and Dalseo-gu were examined. The selection process primarily considered factors such as the planting ratio, ease of management, and carbon storage capacity. The analysis utilized nationwide street tree creation data as well as street tree management data specifically managed by Dalseo-gu, Daegu Metropolitan City.

Next, for the selection of survey sections, key factors such as traffic volume and land use have been identified by Kim et al. [5] as influencing street tree growth conditions by region and species. Based on these findings, four aspects—traffic volume, service population, land use, and estimated tree age—were considered in this study. A prior study by Han and Lee [9] also indicated that street tree vitality tends to improve as the distance from urban centers increases. In this regard, the traffic volume was analyzed using the 2023 Basic Traffic Survey Report published by Daegu Metropolitan City in 2024 [25]. Regarding the service population, it includes not only the resident population but also individuals who temporarily visit the area for purposes such as tourism, shopping, medical services, and education. Service population data are collected through a big mobile data system based on base stations operated by the Korean telecommunications company SK Telecom. The data were obtained from the Daegu Metropolitan City Service Population Analysis Information System [26].

For example, as shown in Figure 3, in October, the resident population of Jinchon-dong was approximately 50,000, while the average service population was significantly higher at around 480,000, indicating that a large number of people visit Jinchon-dong for various purposes.

Furthermore, in the selection of survey sections, areas in Dalseo-gu with Ginkgo biloba aged 20 years or older were categorized based on land use to assess the growth conditions. The selected areas were divided into sections where land use falls under general residential areas and central commercial areas with both the highest and lowest traffic volumes, as well as sections designated as general industrial areas. The reason for selecting areas with trees older than 20 years is based on Ahn’s study [27], which has found that trees achieve successful establishment and stable growth after 10 to 15 years of development.

2.4. Derivation of Street Tree Growth Diagnostic Indicators

The derivation of diagnostic indicators for assessing street tree growth conditions is of great importance, and a thorough review of previous studies and reports was conducted. The diagnostic indicators were broadly classified into general condition indicators and precise diagnostic indicators using specialized equipment. General condition indicators consist of survey data related to tree characteristics or the surrounding environments, which do not require precise measurements but were utilized for statistical analysis when establishing management plans. On the other hand, precise diagnostic indicators were derived based on measurable numerical data that can accurately assess tree growth conditions. To achieve this, international journals such as Sustainability and Landscape and Urban Planning were extensively reviewed. Domestically, studies related to street tree management published in journals such as the Journal of the Korean Institute of Landscape Architecture and the Journal of Environmental Restoration Technology over the past decade were closely examined. Additionally, legal frameworks, including municipal street tree master plans and various research reports, were also reviewed [8,9,11,28,29,30,31,32,33]. For example, the study by Go et al. [11] reported that areas with high traffic volumes and industrial complexes exhibited higher concentrations of Fe, Cd, Cu, Zn, and Pb in the soil compared to areas with low traffic volumes and general residential zones, which negatively impacted tree growth.

2.5. Field Survey

The field survey methodology utilizing the derived diagnostic indicators for street tree growth conditions was based on the survey method used in the study by Xiaoyang Tan and Shozo Shibata [16]. Specifically, approximately 10% of the total street tree samples within the selected survey sections were systematically selected at regular intervals for a detailed field investigation of Ginkgo biloba. The analysis was divided into two main categories—growth condition analysis and diameter at breast height (DBH) measurement for carbon storage estimation. A team of three individuals conducted the survey based on the selected indicators.

The growth condition analysis was conducted in the following two phases: the first phase involved a general survey, while the second phase focused on a detailed assessment of tree growth conditions. The first phase of the survey covered general aspects such as road name, tree species, specifications and estimated age, sidewalk width, and annual average service population. The estimated age of the trees was calculated using the planting year data provided by the Park and Greenery Division of Dalseo-gu, Daegu Metropolitan City. However, since there were no available data on the initial DBH of the street trees at the time of planting, the street tree selection criteria provided by the Korea Forest Service were utilized. According to these criteria, street trees planted in general areas must have an initial DBH of at least 6 cm, while those in areas with high traffic and pedestrian volume must have an initial DBH of at least 8 cm. Accordingly, an average value of 7 cm was applied in this study to estimate the tree age. Based on this, the study by Jo and Park [34] provided an estimated annual diameter growth rate of 0.73 cm/year for Ginkgo biloba over a 30-year period, which was used to estimate the initial age of the street trees. The estimation formula is presented below (Equation (1)).

Estimated Tree age = Survey Year − Planting Year + Initial DBH/Diameter Growth Rate

(1)

The second-phase survey involved precise measurements using analytical tools. A total of five evaluation parameters were assessed, including chlorophyll content, soil acidity (pH), soil hardness, soil electrical conductivity, and stem vitality. Additionally, to calculate the carbon storage capacity, diameter at breast height (DBH) measurements were conducted using a diameter tape (Figure 4). To ensure accurate values, DBH measurements were taken from trees without branching at the measurement height.

The description of the main evaluation factors and measurement criteria used for the analysis of the previously mentioned tree growth conditions is as follows (

Table 1. Measurement methods and reference materials for the evaluation of items of street tree management conditions.

Evaluation Items		Measurement Methods and Criteria
General Information	Height	The measurements were carried out using a Suunto PM5/1520PC Heightmeter (Suunto, Vantaa, Finland). Measurements were taken from a distance of 15 or 20 m away from the tree, aiming the device at both the top and base of the tree. The readings from the scale were then combined [35].
	Sidewalk width	The width of the pedestrian paths (in meters) was recorded [36].
	Annual average service population	The relevant road sections and administrative regions were selected, along with the corresponding dates, prior to conducting the analysis [26].
Precision Diagnosis	Chlorophyll content	Chlorophyll was measured using a SPAD-502plus Chlorophyll Meter (Konica Minolta, Tokyo, Japan). Leaves without yellowing or browning were selected, with eight leaves sampled per individual tree, and the average value was recorded [14].
	Soil pH	pH was measured using a HI99121 Direct Soil Measurement pH Portable Meter (Hanna Instruments, Woonsocket, RI, USA). After removing 5 cm of the surface soil, pH was measured at three locations near the target tree, and the average value was calculated [11].
	Soil hardness	Soil hardness was measured using an Soil Hardness Meter (Yamanaka Standard Type, Daiki Rika Kogyo Co., Ltd., Tokyo, Japan). Measurements were taken five times near the target tree, and the average value was determined [36].
	Electrical conductivity	Soil moisture, electrical conductivity (EC), and temperature were measured using a WT-1000H Soil Moisutre/EC/Temperature Sensor (Mirae Sensor, Seoul, Republic of Korea). Measurements were repeated three times near the target tree, and the average value was calculated [37].
	Stem vigor	Cambial electrical resistance was measured using a JunsMeter (PurumBio, Suwon, Republic of Korea). Measurements were taken at breast height (1.2 m) on the north, south, east, and west sides of the tree, once for each direction, and the average value was recorded [38].

).

As an example, the JunsMeter, used for measuring stem vigor, is a widely utilized diagnostic tool for assessing tree vitality in South Korea. A previously commonly used instrument, the Shigometer, has a measurement range of 0–200, where lower values indicate higher tree vitality. In contrast, the JunsMeter has a measurement range of 0–100 and employs a principle where higher values indicate greater tree vitality, making it more intuitive for assessing tree health. Additionally, it can increase the readings for healthy trees by up to 1.5 times and decrease the readings for declining trees by up to threefold, allowing for a more accurate evaluation of tree health. Measurement images for the precision instruments, including the JunsMeter, are shown in Figure 5.

2.6. Calculation of Carbon Storage Capacity

The estimation of carbon storage based on the measured DBH utilized the National Institute of Forest Science (NIFoS) estimation formula proposed by Kim et al. [39]. This estimation formula has been adjusted to better suit urban trees by applying the Urban Tree Conversion Factor (UCF). However, a limitation of the aforementioned study is that the same carbon fraction (CF = 0.5) was applied to both coniferous and broadleaf trees. Therefore, to improve accuracy, this study applied the carbon fraction values suggested in the 2006 IPCC Guidelines for National Greenhouse Gas Inventories (CF = 0.51 for coniferous trees and CF = 0.48 for broadleaf trees) [40].

Furthermore, it was observed that there are inconsistencies in the coefficients of the relative growth equations used to estimate the aboveground volume by tree species across previous studies. In this study, the relative growth equations proposed by Yoon et al. [41], which were conducted in the same study area, Daegu Metropolitan City, were applied to estimate the aboveground volume of representative street tree species. Based on this, the appropriate carbon emission coefficients and carbon storage estimation formulas were applied to calculate the carbon storage capacity of street trees in Daegu Metropolitan City. The estimation formula and species-specific carbon emission coefficients are presented in Equation (2) and Table 2.

Carbon storage(kg C) = (a(DBH)^b)D∙BEF∙UCF∙(1 + R)∙CF

(2)

where

• a and b represent the volume equation constants.
• D represents the basic wood density.
• BEF represents the biomass expansion factor.
• UCF represents the urban tree conversion factor.
• R represents the root-to-shoot ratio coefficient.
• CF represents the carbon fraction coefficient, with values of 0.51 for coniferous trees and 0.48 for broadleaf trees.

Table 2. Carbon emission factor of Ginkgo biloba.

Species	D (kg/m3)	BEF	UCF	R	V (m3) = aDBH (cm)b		CF
					a	b
Ginkgo biloba	460	1.46	0.8	0.51	0.0000453	2.656	0.51

Table 2. Carbon emission factor of Ginkgo biloba.

Species	D (kg/m3)	BEF	UCF	R	V (m3) = aDBH (cm)b		CF
					a	b
Ginkgo biloba	460	1.46	0.8	0.51	0.0000453	2.656	0.51

2.7. Deriving Key Management Indicators for Improving Tree Growth Rate and Carbon Storage

Key management indicators were established using DBH and various diagnostic indicators. DBH serves as an indirect measure of growth conditions because its growth rate increases under favorable conditions. Therefore, the SPSS 29 program was used for correlation and regression analyses to identify the factors affecting DBH. Among the various diagnostic indicators, soil pH was excluded from the statistical analysis due to its nonlinear relationship with carbon storage. According to Go et al. [11], the optimal soil pH range for the healthy growth of Ginkgo biloba is reported to be 5.6–6.5. Additionally, the soil pH evaluation criteria presented in the Act on the Creation and Management of Urban Forests, etc. [42], classify soil pH as follows: 6.0–6.5 as superior, 5.5–6.0 and 6.5–7.0 as moderate, 4.5–5.5 and 7.0–8.0 as inferior, and less than 4.5 or greater than 8.0 as poor. Due to this nonlinear relationship, the statistical analysis focused on diagnostic indicators other than soil pH. Prior to the analysis, all diagnostic indicators were standardized.

3. Results

3.1. Constructing Basic Data for Analysis

The distribution of street trees in Daegu Metropolitan City shows that Ginkgo biloba, Zelkova serrata, Platanus occidentalis, and Prunus serrulata are among the most commonly planted species (

Table 3. Street tree distribution status in Daegu metropolitan city.

Category	Ginkgo biloba	Zelkova serrata	Platanus occidentalis	Prunus spp.	Chionanthus retusus	Acer spp.	Others
239,394	51,456	49,269	30,831	30,692	27,862	16,392	32,892
100 (%)	21.47	20.59	12.88	12.83	11.64	6.85	13.74

Source: Daegu Metropolitan City (as of 31 December 2023) [43].

). Similarly, the distribution of street trees within Dalseo-gu, Daegu, reveals that Ginkgo biloba accounts for the largest proportion, at 39.8% of the total street trees, followed by Zelkova serrata, Platanus occidentalis, and Acer palmatum (Table 4).

Various species, such as Ginkgo biloba and Zelkova serrata, have been widely planted in South Korea due to their ease of management and carbon storage capacity, as indicated by numerous prior studies [18,19,20,44]. Despite these advantages, complaints regarding the unpleasant odor from the fruit of Ginkgo biloba in the autumn have led to a decrease in its planting frequency or its replacement with other species [45]. Nonetheless, Ginkgo biloba remains resistant to disease and exhibits a strong coppicing ability. It is also highly tolerant of pollution and is known for its efficient nitrate reductase activity, which helps reduce atmospheric nitrogen oxide concentrations [46]. However, its adaptability to climate change is relatively low, necessitating systematic management to maintain its original functions. Accordingly, this study selected Ginkgo biloba as the focal species for analysis, recognizing its many advantages as a street tree and its need for structured management.

Table 4. Status of street trees in Dalseo-gu, Daegu Metropolitan City.

Category	Ginkgo biloba	Zelkova serrata	Platanus occidentalis	Acer spp.	Chionanthus retusus	Prunus spp.	Others
39,854	15,836	9590	7388	2994	1010	846	2190
100 (%)	39.8	24.1	18.5	7.5	2.5	2.1	5.5

Source: Parks and Greenery Division, Dalseo-gu District Office, Daegu Metropolitan City (as of 24 May 2024) [47].

Table 4. Status of street trees in Dalseo-gu, Daegu Metropolitan City.

Category	Ginkgo biloba	Zelkova serrata	Platanus occidentalis	Acer spp.	Chionanthus retusus	Prunus spp.	Others
39,854	15,836	9590	7388	2994	1010	846	2190
100 (%)	39.8	24.1	18.5	7.5	2.5	2.1	5.5

Source: Parks and Greenery Division, Dalseo-gu District Office, Daegu Metropolitan City (as of 24 May 2024) [47].

The survey sections selected for analysis are Guma-ro, Dalgubeol-daero, and Dalseo-daero. In the case of Guma-ro, the surrounding land use was identified as general residential, with an average traffic volume of approximately 35,000 vehicles over a 12 h period and an annual average service population of 4899. In contrast, Dalgubeol-daero recorded a higher average traffic volume of around 50,000 vehicles and featured a mix of residential and commercial land uses. Notably, the service population was significantly higher than that of Guma-ro, reaching 117,220, indicating a large number of visitors to the section. Dalseo-daero, on the other hand, is an area where Ginkgo biloba was relatively recently planted. This section recorded an annual average service population of 93,520 and was identified as having general industrial land use (

Table 5. Study area and subjects.

Division	Name of the Street	Tree Planting Count in the Surveyed Section	Number of Surveyed Trees (Units)	Year of Establishment (Year)	Traffic Volume (Vehicles/12 h)	Average Annual Service Population	Land Use
Ginkgo biloba	Guma-ro	38	10	1989	34,959	4899	General Residential Area
	Dalgubeol-daero (in front of Seongseo Keimyung University)	337	32	1987	49,694	117,220	General Residential Area and Central Commercial Area
	Dalseo-daero	229	30	1999	-	93,520	General Industrial Area
Total	-	604	72	-	-	-	-

).

3.2. Derivation of Street Tree Growth Diagnostic Indicators

To assess the growth conditions of street trees, a total of eight diagnostic indicators were selected, with three general condition indicators, including tree height and sidewalk width, and five precise diagnostic indicators, including soil pH and stem vigor. For the five precise diagnostic indicators, the grading criteria are shown in

Table 6. Evaluation grade criteria for precision measurement devices used in street tree vitality assessment.

Evaluation Items	Evaluation Criteria		References
Chlorophyll Content (SPAD)	Excellent	Above 40	Moon [14], Kim [36].
	Good	30 to less than 40
	Fair	20 to less than 30
	Poor	Below 20
Soil pH (pH)	Excellent	6.0–6.5	According to the Act on the Creation and Management of Urban Forests, etc., the evaluation criteria for soil chemical properties are outlined within the standards for creating and managing urban forests, living forests, and street trees [42].
	Good	5.5–6.0 or 6.5–7.0
	Fair	4.5–5.5 or 7.0–8.0
	Poor	Below 4.5 or above 8.0
Electrical Conductivity (dS/m)	Excellent	Less than 0.2
	Good	0.2–1.0
	Fair	1.0–1.5
	Poor	Above 1.5
Soil Hardness (mm)	Excellent	Less than 21	According to the Act on the Creation and Management of Urban Forests, etc., the evaluation criteria for soil chemical properties are outlined within the standards for creating and managing urban forests, living forests, and street trees [42].
	Good	21–24
	Fair	24–27
	Poor	Above 27
Stem Vigor (JunsMeter)	Excellent	100–86	JunsMeter evaluation grade criteria.
	Good	85–76
	Fair	75–55
	Poor	Less than 55

. For the chlorophyll content, the growth conditions were diagnosed by dividing the content into four grades based on the criteria proposed in previous studies. In the case of soil hardness, the evaluation referred to standards outlined in relevant regulations, a value below 21 was considered favorable, while a value of 27 or higher was deemed very poor. For stem vigor, the evaluation was based on the following officially defined grading standards: a mean score between 100 and 86 indicated very favorable growth conditions, whereas a score below 75 was judged as poor.

3.3. Field Survey

The field survey results for each section are as follows (

Table 7. Average results by evaluation indicator for the study sites of Ginkgo biloba.

Division	Name of the Street	Height (m)	Sidewalk Width (m)	Annual Service Population (People)	Estimated Age	Chlorophyll Content (SPAD)	Soil pH (pH)	Soil Hardness (mm)	Electrical Conductivity (dS/m)	Stem Vigor (Juns Meter)
Ginkgo biloba	Guma-ro	9.79	2.68	4899	45	42.13 (A)	7.56 (C)	21.69 (B)	0.41 (B)	81.51 (B)
	Dalgubeol-daero	5.94	4.25	117,220	47	28.69 (C)	7.19 (C)	13.31 (A)	0.48 (B)	71.62 (C)
	Dalseo-daero	9.37	2.42	93,520	35	37.69 (B)	8.91 (D)	11.82 (A)	0.54 (B)	76.04 (B)

A: excellent; B: good; C: fair; D: poor.

). First, in the case of Guma-ro, the average tree height was the highest among the sections. The diagnostic indicator chlorophyll content was graded as A (Excellent), while stem vigor and soil hardness were both graded as B (Good). However, soil pH was graded as C (Fair), indicating conditions unsuitable for growth. In the case of Dalgubeol-daero, the average tree height was the lowest, but the soil hardness value was assessed as A (Excellent), indicating relatively healthy conditions. Conversely, the chlorophyll content, stem vigor, and soil pH were graded as C (Fair), suggesting overall poor growth conditions. Finally, in Dalseo-daero, located in an industrial area, soil pH was graded as D (Poor), the lowest among all sections, while chlorophyll content, stem vigor, and soil hardness were graded as B (Good), indicating relatively favorable conditions for these indicators.

The field survey results for the Ginkgo biloba in Dalgubeol-daero, including the section with the poorest growth conditions, are summarized in

Table 8. Results of the general information analysis on the growth condition of Ginkgo biloba.

Tree Photographs	General Information
	Name of the street	Dalgubeol-daero
	Survey section	Gangchanggyo Bridge to Sindang intersection
	Date	7 September 2024
	Estimated age	47
	Species	Ginkgo biloba
	Height (m)	4.8
	DBH (cm)	15.98
	Sidewalk width	2.62
	Annual average service population	117,220

and

Table 9. Results of the tree growth condition analysis for Ginkgo biloba.

Evaluation Items	Measurement Methods and Criteria
① Chlorophyll Content	32.8
② Soil pH	7.43
③ Soil Hardness	8.0
④ Electrical Conductivity	0.53
⑤ Stem Vigor (JunsMeter)	73.55

. The estimated age of the trees was 47 years, and their average height was 4.8 m. Regarding the diagnostic indicators, the chlorophyll content was graded as B (32.8), indicating an average level, while the soil hardness was graded as A (8.0), showing excellent conditions. However, the stem vigor was graded as C (73.55), indicating poor conditions. Considering the estimated tree age, the overall growth condition was found to be very poor.

3.4. Calculation of Carbon Storage Capacity

The results of the carbon storage calculations for each survey site, based on the DBH and the estimation formula, are shown in

Table 10. Average DBH and carbon storage for each survey site.

Name of the Street	DBH (Average)	Carbon Storage (kg C)
Guma-ro	27.77	130.72
Dalgubeol-daero	16.91	36.97
Dalseo-daero	23.81	104.27

. At Guma-ro, the average DBH was the highest among the sites at 27.77 cm, and the average carbon storage was analyzed as 130.72 kgC. In contrast, at Dalgubeol-daero, where the growth condition of Ginkgo biloba was poor, the average DBH was 16.91 cm, and the average carbon storage was 36.97 kgC—significantly lower than that at Guma-ro.

Finally, in the case of Dalseo-daero, despite being an industrial area, the average DBH was 23.81 cm, and the resulting average carbon storage was 104.27 kgC, which was higher than the average carbon storage in Dalgubeol-daero.

3.5. Deriving Key Management Indicators for Improving Tree Growth and Carbon Storage

Before selecting the key management indicators, the correlations among the indicators used were analyzed (Appendix A). The results revealed a strong negative correlation (−0.75) between tree height and sidewalk width, which suggests that these variables represent independent factors reflecting growth conditions and individual physiological growth characteristics. Sidewalk width functions as an environmental factor linked to spatial constraints and management conditions, while tree height serves as an indicator of the physiological growth and photosynthetic potential of individual trees. Thus, while a correlation exists between these two variables, they can complement each other in a comprehensive analysis of growth conditions. Meanwhile, no significant correlations were observed among soil health indicators (soil hardness and soil electrical conductivity), indicating that these variables may act independently. However, correlations alone cannot fully confirm the independence of these variables. Variance inflation factor (VIF) analysis is considered a more appropriate method for diagnosing multicollinearity in multiple regression models [48,49].

Subsequently, a regression analysis was performed between DBH and the diagnostic indicators of 72 Ginkgo biloba (

Table 11. Regression analysis results between the DBH of Ginkgo biloba (dependent variable) and evaluation indicators.

Dependent Variable	Independent Variable	B	β	t	p	VIF
DBH	(Constant)	0.130		1.394	0.168
	Height	0.442	0.442	3.676	0.000	2.972
	Sidewalk width	−0.068	−0.068	−0.579	0.564	2.864
	Service population	0.046	0.046	0.385	0.701	2.941
	Chlorophyll content	0.216	0.302	3.337	0.001	1.688
	Soil hardness	0.116	0.119	1.273	0.207	1.791
	Electrical conductivity	−0.004	−0.002	−0.029	0.977	1.486
	Stem vigor	0.197	0.197	2.026	0.047	1.951
F = 20.198 (p < 0.001), R2 = 0.688, adjR2 = 0.654, D-W = 2.127

). The analysis yielded an R² value of 0.688, demonstrating a relatively high explanatory power. The VIF analysis confirmed that all variables had values below 10, indicating no multicollinearity issues. Among the diagnostic indicators, tree height, chlorophyll content, and stem vigor were found to significantly influence DBH. In other words, trees with higher chlorophyll content and greater stem vigor tended to have better growth conditions and larger DBH values. These findings align with the results of Park et al. [38], who reported that tree height and stem vigor affected DBH, as well as the analyses of Kim et al. [8] and Moon [14], who found higher DBH values in areas with superior photosynthetic capacity.

In summary, tree height, chlorophyll content, and stem vigor can be considered key variables that independently influence DBH, regardless of the growth conditions. On the other hand, variables such as soil hardness and service population did not show statistically significant effects.

4. Discussion

Street trees in urban areas serve a range of functions, such as providing shade, enhancing the quality of the urban landscape, and regulating microclimates. As climate change intensifies, managing street trees becomes increasingly critical, especially in cities where expanding green space is difficult. In light of this, the current study identified key management indicators that influence tree growth and carbon enhancement. The management strategies for each key indicator are summarized as follows (Table 12).

First, the excessive pruning of street trees is a prevalent issue in South Korea (Figure 6). This is largely due to safety concerns related to overhead power lines and the cost of labor. To address these issues, efforts are underway to adjust pruning intensity by undergrounding power lines and through legal and institutional improvements [50]. Additionally, high traffic volumes or industrial areas cause significant particulate matter to adhere to leaves, adversely affecting photosynthesis. This study found that the chlorophyll content values in areas with these environmental characteristics—such as Dalgubeol-daero and Dalseo-daero—were lower than those in Guma-ro. This trend is consistent with the findings of Kim et al. [8] and Moon [14], who reported that the chlorophyll content was lower in areas with poor growth or higher air pollution levels. In summary, maintaining the chlorophyll content requires regular watering. This is particularly critical in Daegu, where the annual rainfall has been decreasing due to climate change, underscoring the importance of managing this indicator.

Table 12. Key management strategies for enhancing the carbon storage of Ginkgo biloba.

Diagnostic Indicators	Management Strategies
Tree Height	- Implement minimal pruning practices that do not affect tree height growth. - Promote underground power line projects to eliminate unnecessary height adjustment and avoid severe pruning caused by overhead lines.
Chlorophyll Content	- In areas with high traffic or industrial zones, maintain photosynthetic efficiency through periodic leaf washing (e.g., leaf surface cleaning) and regular watering. - Preserve leaf vitality by managing pests and diseases.
Stem Vigor	- Maintain stem vigor through regular monitoring, pest and disease control, and ensuring soil pH remains between 5.6 and 6.5. Remove topsoil layers that negatively impact root respiration [51].
General Management	- In areas with narrow sidewalks and high service populations, install protective covers to maintain proper soil compaction. - Enhance crown ventilation through periodic pruning. - Maintain appropriate soil temperature through irrigation systems and mulching. - Utilize biochar to facilitate soil improvement [4,52].

Table 12. Key management strategies for enhancing the carbon storage of Ginkgo biloba.

Diagnostic Indicators	Management Strategies
Tree Height	- Implement minimal pruning practices that do not affect tree height growth. - Promote underground power line projects to eliminate unnecessary height adjustment and avoid severe pruning caused by overhead lines.
Chlorophyll Content	- In areas with high traffic or industrial zones, maintain photosynthetic efficiency through periodic leaf washing (e.g., leaf surface cleaning) and regular watering. - Preserve leaf vitality by managing pests and diseases.
Stem Vigor	- Maintain stem vigor through regular monitoring, pest and disease control, and ensuring soil pH remains between 5.6 and 6.5. Remove topsoil layers that negatively impact root respiration [51].
General Management	- In areas with narrow sidewalks and high service populations, install protective covers to maintain proper soil compaction. - Enhance crown ventilation through periodic pruning. - Maintain appropriate soil temperature through irrigation systems and mulching. - Utilize biochar to facilitate soil improvement [4,52].

Continuing with stem vigor, Kim [12] found that vigor values differ according to the planting environment, highlighting the importance of management conditions and environmental factors. Similarly, this study also considered factors such as urban land use and service population, revealing variations in vigor and growth depending on environmental conditions. However, to obtain statistically significant results, it will be necessary to consider more detailed environmental factors and measure stem vigor across a larger sample size.

Furthermore, promoting growth and increasing carbon storage will require improvements beyond indicators such as chlorophyll content and stem vigor. In high foot traffic areas, tree protection coverings should be installed to minimize damage from soil compaction. Additionally, a systematic approach to monitoring and responding to pests and diseases is essential for restoring tree vigor. Soil improvement also plays a critical role in enhancing street tree growth and vitality. Previous studies by Kim and Kim [53] and Lee [54] have shown that thorough soil management has a positive effect on tree growth. Recent research has further suggested that soil amendments, such as biochar, can contribute to improved tree growth and enhanced carbon storage potential [4,55]. This study’s analysis of DBH and carbon storage at different survey sites revealed significant differences compared to normal growth conditions at the estimated tree age (Figure 7). These findings highlight the necessity for more systematic street tree management and suggest that incorporating soil improvement techniques, such as biochar, could enhance growing conditions.

Additionally, legal and institutional improvements as well as increased financial support must be accompanied. First, the content regarding street tree management within existing laws and regulations should be more detailed. The Act on the Creation and Management of Urban Forests, etc., includes criteria for the creation and management of urban forests, living forests, and street trees according to their functions. However, these criteria primarily specify evaluation items and standards related to the soil depth and the physical and chemical properties of the soil, without addressing management methods for maintaining and enhancing tree carbon storage capacity in detail. Furthermore, examining ordinances on street tree management in major metropolitan cities such as Seoul, Daegu, and Busan revealed that Daegu and Seoul specified measures for tree replacement, replanting, pruning, pest control, tree surgery, topography and soil protection, and protective tree covers. Seoul also provides more specific guidelines on pruning standards, targets, timing, and methods through its enforcement regulations. In contrast, Busan’s ordinances offer only brief descriptions of pest control, tree surgery, and pruning measures. As such, current regulations generally outline basic management methods for street trees but fail to present quantitative evaluation indicators or measurement methods. Moreover, among the various functions of street trees, particularly those related to carbon storage capacity, the content is severely lacking. Therefore, future legal and institutional improvements must include the introduction of quantitative evaluation methods, the presentation of clear management standards, and a more comprehensive focus on carbon storage capacity.

Second, establishing a systematic street tree management system is essential. In most cities in South Korea, information such as planting locations, tree species, and tree quantities is relatively well recorded. However, critical data—such as the planting year, tree age at the time of planting, and diameter at breast height (DBH)—is often not documented. This lack of information makes it challenging to assess the current growth status of trees or measure their carbon storage capacity based on their original planting conditions. To resolve these issues, it is essential to establish a detailed management system that includes both the current state and the original characteristics of the trees at the time of planting, along with ongoing updates to the data. Based on the results of this study, the expected DBH and carbon storage of Ginkgo biloba under normal growth conditions are shown below (

Table 13. Predicted DBH and carbon storage of Ginkgo biloba based on the initial diameter and years since planting.

Initial DBH	After 10 Years		After 20 Years		After 30 Years		After 40 Years		After 50 Years
	DBH (cm)	Carbon Storage (kg C)	DBH (cm)	Carbon Storage (kg C)	DBH (cm)	Carbon Storage (kg C)	DBH (cm)	Carbon Storage (kg C)	DBH (cm)	Carbon Storage (kg C)
6 cm	11.68	12.82	18.98	46.56	26.28	110.5	33.58	211.89	40.88	357.29
7 cm	12.41	15.06	19.71	51.47	27.01	118.84	34.31	224.35	41.61	374.49
8 cm	13.14	17.53	20.44	56.69	27.74	127.57	35.04	237.25	42.34	392.19

). Using these figures, priority management plans should be developed for trees in poor health whose DBH falls short of the standard during regular monitoring.

Finally, securing adequate funding and skilled personnel for the management of street trees and green spaces is essential. Despite the increasing urgency of global climate change, the budget for climate change response and environmental management in South Korea has been declining. In fact, in Daegu Metropolitan City, the budget for climate and environmental policies dropped significantly from approximately 70.1 billion KRW to 54.4 billion KRW in 2025. Furthermore, funding for urban green space development and street tree maintenance has also seen substantial reductions, reflecting a lack of recognition of the importance of green spaces, including street trees.

5. Conclusions

Street trees serve as a vital component of the urban landscape, offering habitats for small organisms, filtering air pollution, and moderating microclimates. Effective management of these trees relies on quantitative assessments and ongoing monitoring to ensure that they are growing appropriately. In this regard, the present study contributes by exploring diagnostic indicators that can help evaluate the growth conditions of street trees and by proposing management strategies to increase carbon storage. However, while the study found that growth conditions and carbon storage capacity differ depending on the surrounding environment of planted street trees, statistically significant results require the future analysis of a larger sample size. Additionally, this research is limited to examining only Ginkgo biloba, among various street tree species. Future studies should expand the scope to include multiple tree species and develop methodologies based on measured data that can be directly applied to citywide legal frameworks, such as comprehensive urban and green space plans.