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Carbon reduction and planning strategies for urban parks in Seoul
Urban Forestry & Urban Greening 41 (2019) 48–54
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Carbon reduction and planning strategies for urban parks in Seoul a
b,⁎
Hyun-Kil Jo , Jin-Young Kim a b
, Hye-Mi Park
b
T
Department of Ecological Landscape Architecture Design, Kangwon National University, Chuncheon 24341, Republic of Korea Department of Landscape Architecture, Graduate School, Kangwon National University, Chuncheon 24341, Republic of Korea
ARTICLE INFO
ABSTRACT
Handling Editor: N Nilesh Timilsina
This study quantified carbon storage and uptake for urban parks in Seoul, the capital of the Republic of Korea. A total of 38 study parks were selected using a systematic random sampling method and all the trees in the parks were field-inventoried. Carbon storage and uptake by the park trees were estimated applying a quantitative model for urban open-grown trees of each species. Mean carbon storage per unit of park area, basal area, and crown cover by the trees was 38.5 ± 3.0 t/ha, 27.3 ± 0.8 kg/100 cm2, and 7.4 ± 0.4 kg/m2, respectively. Annual carbon uptake per unit area and cover by the trees averaged 3.5 ± 0.2 t/ha/yr, 2.5 ± 0.1 kg/100 cm2/ yr, and 0.7 ± 0.0 kg/m2/yr, respectively. The major determinants of the levels of carbon storage and uptake were species, density, sizes, and layering structures of the planted trees. The trees across all urban parks in Seoul were estimated to store 222.3 kt of carbon and to annually sequester 20.2 kt of carbon. The trees in these parks played an important role in annually offsetting carbon emissions from gasoline consumption by approximately 2.3% of the total population of the city. The economic value of the annual carbon uptake, which was $7.1million/yr, equaled 15.1% of the annual maintenance budget of the parks in the city. However, the role of study parks as a source of carbon uptake was limited due to the distribution of large grass and impervious areas, the single-layered structures, and the dominance of small trees. Planning strategies were explored to enhance carbon reduction effects of the parks. They included the expansion of tree planting spaces through the minimization of unnecessary grass and paving areas, the active tree planting in the potential planting spaces, the multi-layered planting grouped with larger trees, and the planting of tree species having satisfactory growth rates. This study puts an emphasis on finding out the present carbon offset levels of urban parks on which information is limited and suggesting a future direction of park planning based on a detailed actual survey.
Keywords: Indicator Offset Planting Storage Uptake
1. Introduction Climate change from the greenhouse effect is one of the serious environmental issues faced by the current generation. Recently, the nations which are members of the UNFCCC have agreed to a greenhouse gas emissions reduction goal to limit an increase in atmospheric carbon concentrations and global temperatures (UNFCCC, 2015). The Republic of Korea has also set a national goal to reduce greenhouse gas emissions by 37% of its estimated business as usual (BAU) emissions by the year 2030 and has established the first basic plan on responding to climate change (Cheongwadae, 2016). The average level of global CO2 concentration in 2016 was about 403 ppm, which was a 45% increase compared to the levels prior to the industrial revolution (WMO, 2017). The level of CO2 concentration in the Republic of Korea measured at approximately 410 ppm, which was 7 ppm higher than the global average (KMA, 2017). According to the (IEA (2017), the average per capita CO2 emissions of OECD member countries reduced from 10.3 t in
⁎
1990 to 9.2 t in 2015, but the CO2 emissions of the Republic of Korea increased by approximately 2.1 times from 5.4 to 11.6 t. Increases in atmospheric carbon concentrations are typically induced by fossil fuel consumption and greenspace destruction. Trees can play an important role as a source of carbon sequestration that delays or mitigates the adverse effects of climate change, because they sequester atmospheric carbon during the growth process and contribute to the accumulation of carbon in the soil. The carbon neutralization and offsetting programs of countries across the globe have included the planting of trees as a key carbon-reducing activity and are increasingly emphasizing its importance. Efforts to reduce atmospheric carbon concentrations have evoked diverse studies that explore the effects of urban trees (Jo, 1993; Nowak et al., 1994; Jo and Cho, 1998; McPherson, 1998; McPherson and Simpson, 1999; Jo and Ahn, 2001; Nowak and Crane, 2002; Jo, 2002; Jo et al., 2003; Yang et al., 2005; Davies et al., 2011; Jo and Ahn, 2012; Liu and Li, 2012; Nowak et al., 2013; Jo et al., 2013, 2014; Gratani et al., 2016; Jo et al., 2017a,b). Jo
Corresponding author. E-mail address: [email protected] (J.-Y. Kim).
https://doi.org/10.1016/j.ufug.2019.03.009 Received 4 June 2018; Received in revised form 24 January 2019; Accepted 12 March 2019 Available online 15 March 2019 1618-8667/ © 2019 Published by Elsevier GmbH.
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(2002) quantified the carbon storage and uptake by urban greenspace of several cities in the Republic of Korea and proposed a greenspace planning strategy to improve the efficiency of carbon reduction. Nowak et al. (2013) computed the carbon sequestration by urban trees across 34 cities and states in the United States and estimated the total carbon sequestration effects of urban trees across the country. Jo and Ahn (2012) and Jo et al. (2013, 2014) studied the carbon reduction effects of urban landscape tree species through a direct harvesting method including root digging. Gratani et al. (2016) estimated the carbon sequestration by vegetation and its economic value in four urban parks in Rome. The quantification of carbon reduction by urban greenspace requires the development and application of indicators of carbon estimates per unit greenspace area and per unit crown cover that are relevant to each type of greenspace such as parks, streets, and gardens. However, studies that quantitatively analyze carbon reduction effects by each type of greenspace are still rarely pursued. Carbon reduction by urban parks and appropriate design guidelines are, in particular, critical, because urban parks have the potential to create a substantially large greenspace area within the limited openspace of cities, and can largely contribute to the securing of carbon uptake sources (Davies et al., 2011; Gratani et al., 2016) and carbon emissions credits. However, there is currently little information on carbon reduction via trees planted in urban parks and low carbon design of the parks, not only in the Republic of Korea but also globally. The objectives of this study were to quantify carbon storage and uptake for urban parks in Seoul, the capital of the Republic of Korea, and to explore planning strategies to improve carbon reduction effects of the parks. For urban parks, no information is available regarding a carbon storage and uptake indicator per unit of tree cover, even though the indicator is significant to carbon estimates associated with tree density and sizes. This study could be of usefulness in internationally sharing the information regarding indicators to estimate carbon reduction effects of urban parks and desirable planning strategies associated with tree planting. In this study, carbon storage refers to total carbon accumulated by tree growth over time and carbon uptake indicates the annual rate of carbon absorption.
area of each park and areal distribution of land cover types were measured. The survey of tree planting included species, height, crown width, stem diameter at a breast height of 1.2 m (dbh) for trees and at a height of 15 cm above ground for shrubs (2 cm or less in dbh), and layering structures. The potential planting space was also surveyed to obtain a realistic estimate of carbon reduction through a new tree planting. This potential planting space included only the permeable area over which trees of 3 m or more in height and 2 m or more in crown width could be grown without interfering with various facilities such as utility lines, manholes, and septic tanks. The surveyed data on tree planting were used to analyze structural characteristics such as dbh distribution, density and cover per unit area, and importance values of species. The data were also applied to estimate carbon storage and uptake by trees in each study park. 2.3. Estimation of carbon storage and uptake Carbon storage and uptake by urban trees could significantly differ from those by forest-grown trees due to different growth environments, including management practices and competing conditions. Therefore, this study estimated carbon storage and uptake by park trees by using a quantitative model developed for urban open-grown trees of each species (Jo and Cho, 1998; Jo, 2001, 2002; Jo and Ahn, 2001, 2012; Jo et al., 2013, 2014). That is, the carbon storage and uptake for each species were computed applying the stem diameter of each tree as the major independent variable to the quantitative models (Table 1), which were derived from seasonal CO2 exchange rate measurements or a direct harvesting method of urban trees. For a particular species without a quantitative model available, the models for the same genus or group were substituted to average carbon estimates. Mean carbon storage and uptake per unit of park area, per unit of basal area, and per unit of crown cover were calculated based on park area, stem diameters, and tree cover surveyed. The carbon indicator per unit of park area was applied to estimate total carbon storage and uptake of the entire park area in the study city (Seoul, 2017a), excluding urban nature parks and cemetery parks. 3. Results and discussion
2. Methods
3.1. Areal distribution of study parks and land cover types
2.1. Study parks
Seoul is located in the central western region of the Korean Peninsula at 126°–127 °East and 37 °North. The east-west and northsouth distances of the city are 36.8 km and 30.3 km, respectively, and its total area measures 60,520 ha. In 2017, total population and the number of households in the city were 10,124,579 people and 3,784,705 households, respectively, and its population density was 167 people/ha (Seoul, 2017a). Of all land categories in the city, land plots comprised the largest proportion (36%). This category was followed by forests (23%), roads (13%), rivers (9%), schools (4%), and parks (3%) (Seoul, 2017a). The area of study parks ranged from a minimum of 0.1 ha to a maximum of 91.9 ha (Table 2). The study parks of less than 0.5 ha accounted for approximately 73.7% of all the parks. The total area of the study parks surveyed was 215.0 ha or approximately 5.2% of that of urban parks in Seoul, excluding urban nature parks and cemetery parks. Of the study parks, Boramae Park (P6), Seoul Children’s Grand Park (P33), Seoul Forest Park (P34), and Seonyudo Park (P32) were identified as large parks having an area of 11 ha or more. The ratio of land cover types in the study parks averaged 49.6 ± 2.4% for trees and shrubs, 47.0 ± 2.5% for pavements and facilities, and 3.4 ± 0.8% for grass and bare soils (Table 2). The impervious areas of facilities and pavements were almost similar to the areas covered by trees and shrubs. Nowak et al. (2012) found that the impervious areas of parks in Toronto, Canada were approximately 10%. Compared to their estimate, the areas covered by pavements and
This study sampled urban parks in Seoul, the city with the largest area and the highest population density in the Republic of Korea. A total of 38 sample study parks was selected applying a systematic random sampling method to a 1:1000-scale aerial photograph (Fig. 1): 8 straight lines radiating from the center of the study city were drawn in the equidistant direction and looping circles were plotted at 40 cm intervals; at least 25% of all the points at which the lines and circles crossed was randomly sampled in each direction; urban parks located at the crossing points or at the shortest distances from the points were selected as study parks. This sampling design is a new approach to sample the parks randomly at a city-wide scale, avoiding a selection bias. Urban parks selected were neighborhood parks and children’s parks, as stipulated in the Korea Urban Park and Greenspace Act, which are easily accessible and daily used by citizens. This study excluded urban nature parks and cemetery parks that were considerably different from study parks in land cover distribution, because the former is dominated by natural vegetation in mountainous areas and the latter, by grass with little tree planting. The number of samples was determined upon a compromise between the conflicting concerns for a large sample size and the availability of labor and budget. 2.2. Survey and analysis of tree planting All the trees in study parks selected were field-surveyed, and total 49
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Fig. 1. Depiction of systematic sampling method used in this study and location of study parks sampled.
facilities in the study parks were about 5 times higher. These large nonpermeable areas and grass areas absent of specific purpose of use could limit an area considered useful for tree planting and decrease the role of carbon offset by the parks.
Ahn, 2010). The vertical planting structures of the study parks revealed that a single layer of trees, shrubs, or grass comprised 51.5% of the total planted area, while multi-layered structures in which tree, shrub, and herb layers overlap occupied 48.5%. Of the total single-layered area, the area planted only with grass accounted for 48.4%, which indicated a relatively high ratio of the grass area. The remaining ratios of the single-layered area were composed of planting only with trees (42.9%) and planting only with shrubs (8.7%). The single-layered planting could be unfavorable to an increase of carbon storage and uptake per unit area (Jo, 2002).
3.2. Tree planting structures Planting density of trees ranged from 1.2 to 8.9 trees/100 m2 depending on the study parks (Table 3). The density of 3–5 trees/100 m2 accounted for 68.4% of all study parks, which was the most, followed by ≥6 trees/100 m2 (18.4%) and < 3 trees/100 m2 (13.2%). The tree density averaged 4.1 ± 0.3 trees/100 m2 across all study parks, which was slightly lower than 5.0 trees/100 m2 of some parks in Toronto, Canada (Nowak et al., 2012). The basal area of the planted trees ranged from 504.1 to 2,746.8 cm2/100 m2 with an average of 1,3111311.8 ± 86.6 cm2/ 100 m2. The basal area of 1,000–2,000 cm2/100 m2 comprised 44.7% of all study parks, followed by < 1,000 cm2/100 m2 (42.1%) and > 2,000 cm2/100 m2 (13.2%). The dbh of trees averaged 18.1 ± 0.6 cm across all study parks. Trees with a dbh of < 20 cm occupied 59.8% of all the planted trees, which was the most, followed by 20–30 cm (21.5%) and > 30 cm (18.7%) (Fig. 2). The dbh of trees planted in some parks of Italy averaged 45 cm (Gratani et al., 2016). The average dbh of the trees in the study parks was approximately 60% smaller than that in Italy. The cover of the planted trees and shrubs averaged 50.9 ± 1.8%, ranging from a minimum of 32.4% to a maximum of 90.3%. The tree and shrub cover of 30–50% and > 50% accounted for 52.6% and 47.4% of all study parks, respectively. The tree cover of some parks in the United States, Canada, and Italy was reported to range from 49 to 57% (Nowak and Heisler, 2010; Nowak et al., 2012; Gratani et al., 2016). Compared to this report, the tree cover of the study parks (46.9% excluding shrubs) was similar or lower by 17.5%. The total number of tree and shrub species in the study parks was 148, which indicated a relatively diverse composition of species. The top 10 species in importance values included Pinus densiflora (7.8%), Pinus koraiensis (6.9%), Zelkova serrata (6.6%), Prunus yedoensis (6.3%), Acer palmatum (5.5%), Rhododendron yedoense var. poukhanense (5.1%), Ginkgo biloba (4.5%), Pinus strobus (3.2%), Platanus occidentalis (2.3%), and Metasequoia glyptostroboides (2.2%). These are the key landscape species that also typically presented a relatively high dominance in other cities of the Republic of Korea (Jo et al., 1998; Jo and Ahn, 2006;
3.3. Carbon storage and uptake The carbon storage by the planted trees per unit area of the study parks ranged from a minimum of 12.2 t/ha to a maximum of 111.1 t/ha with an average of 38.5 ± 3.0 t/ha (Table 4). The carbon uptake per unit area ranged from 1.2 to 8.4 t/ha/yr with an average of 3.5 ± 0.2 t/ha/yr. Gratani et al. (2016) found that the mean carbon uptake per unit area of some parks in Italy was about 6.6 t/ha/yr. The average carbon uptake of the study parks was significantly lower, compared to their estimate. This difference could be due to the variations in density, sizes, and growth rates of the planted trees. The carbon storage per unit of basal area of the planted trees averaged 27.3 ± 0.8 kg/100 cm2, ranging from 15.2 to 40.2 kg/ 100 cm2 depending on the study parks. The carbon uptake per unit of basal area ranged from 1.7 to 3.3 kg/100 cm2/yr with an average of 2.5 ± 0.1 kg/100 cm2/yr. The mean dbh of the trees in the study parks was, as mentioned above, approximately 18 cm and the basal area of this tree size was 254.3 cm2. Based on the average carbon storage and uptake per unit of basal area, a single tree of the size is capable of storing 69.4 kg of carbon and annually sequestering 6.4 kg of carbon. The carbon storage per unit of cover of the planted trees averaged 7.4 ± 0.4 kg/m2, ranging from 2.9 to 12.3 kg/m2 depending on the study parks. The carbon uptake per unit of cover ranged from 0.4 to 1.0 kg/m2/yr with an average of 0.7 ± 0.0 kg/m2/yr. As an urban land average of the Republic of Korea, the carbon storage and uptake per unit of tree cover were 4.8 kg/m2 and 0.5 kg/m2/yr, respectively (Jo, 2002). In the case of the United States, these figures averaged 7.8 kg/ m2/yr and 0.3 kg/m2/yr, respectively (Nowak et al., 2013). The average carbon uptake per unit of tree cover in the study parks was found to be 50
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Table 1 Regression model sources of tree and shrub species used to compute carbon storage and uptake in study parks. Carbon
Species
Storage
Tree
Shrub
Uptake
Tree
Diameter rangea (cm)
Reference
Abies holophylla Acer palmatum Chionanthus retusus Cornus officinalis Ginkgo biloba Pinus densiflora Pinus koraiensis Prunus armeniaca Prunus yedoensis Taxus cuspidata Zelkova serrata Lespedeza bicolor Pinus spp. Quercus spp. Rhododendron spp. General hardwoods
5–19 5–20 3–11
Jo et al. (2014) Jo and Ahn (2012) Jo et al. (2014)
3–15 5–25 5–25 5–31 4–14 5–23 2–15 5–28 0.4–2.5 0.6–3.5 0.5–4.0 0.4–3.4 0.4–4.0
Jo et al. (2014) Jo and Ahn (2012) Jo et al. (2013) Jo et al. (2013) Jo et al. (2014) Jo and Ahn (2012) Jo et al. (2014) Jo and Ahn (2012) Jo (2002) Jo, (2002) Jo, (2002) Jo, (2002) Jo (2001, 2002)
Abies holophylla Acer palmatum
5–19 7–27 5–20 3–11
Jo Jo Jo Jo
Pinus densiflora
3–15 6–31 5–25 5–29
Pinus koraiensis
5–33
Platanus occidentalis Prunus armeniaca Prunus yedoensis Taxus cuspidata Zelkova serrata
10–58
Jo et al. (2014) Jo and Cho (1998) Jo and Ahn (2012) Jo and Ahn (2001), Jo et al. (2013) Jo and Ahn (2001) Jo et al. (2013) Jo and Cho (1998)
4–14 5–23 2–15 6–34 5–28 0.4–2.5 0.6–3.5 0.5–4.0 0.4–3.4 0.4–4.0
Jo Jo Jo Jo Jo Jo Jo Jo Jo Jo
Chionanthus retusus Cornus officinalis Ginkgo biloba
Shrub
Lespedeza bicolor Pinus spp. Quercus spp. Rhododendron spp. General hardwoods
Table 2 Percentage of land cover types in study parks. Parka
Baebatgol (P1) Bangadari (P2) Banghyeon (P3) Bansu (P4) Bareum (P5) Boramae (P6) Buntogol (P7) Cheonho (P8) Dongnimmun (P9) Eunhasu (P10) Gakkul (P11) Gangbyeon (P12) Gangnam (P13) Geumho (P14) Gongneung-dong (P15) Gyeonghak (P16) Gyodae (P17) Hakdong (P18) Itaewon (P19) Jangan (P20) Keungol (P21) Kkachi (P22) Mongnyeon (P23) Mugunghwa (P24) Mukjeong (P25) Nari (P26) Nodeullnaru (P27) Nogosan (P28) Pureundongsan (P29) Sarok (P30) Seonangdang (P31) Seonyudo (P32) Seoul Children’s Grand (P33) Seoul Forest (P34) Somdari (P35) Usangak (P36) Wooram (P37) Yeongmal (P38) Mean
et al. (2014) and Cho (1998) and Ahn (2012) et al. (2014)
et al. (2014) and Ahn (2012) et al. (2014) and Cho (1998) and Ahn (2012) (2002) (2002) (2002) (2002) (2001,2002)
Area (ha)
Land cover type (%) Tree/Shrub
Grass/Bare soil
Paving/Facility
0.09 0.15 0.18 0.13 0.09 42.41 0.10 2.67 0.33 0.20 0.08 0.18 0.09 1.35 0.70
78.2 32.4 53.2 39.1 52.8 20.9 44.1 59.2 29.8 59.1 43.7 43.3 43.0 46.4 72.9
0.0 0.0 0.0 0.0 0.0 15.6 0.0 1.9 0.0 6.7 0.0 0.0 0.0 1.4 5.8
21.8 67.4 46.8 60.9 47.2 63.5 55.9 38.9 70.2 34.2 56.3 56.7 57.0 52.2 21.3
0.25 0.10 0.16 0.29 0.09 0.17 0.11 0.10 0.10 0.35 0.40 4.46 0.10 0.09 0.10 1.02 11.04 53.61
66.5 51.8 63.0 59.2 39.7 64.5 51.7 44.4 37.0 42.0 77.9 40.3 67.4 67.6 46.9 49.3 20.3 48.7
15.0 0.0 0.0 1.7 0.0 0.0 0.0 0.0 0.0 2.8 7.2 0.8 7.9 0.0 0.0 2.8 16.8 16.3
18.5 48.2 37.0 39.1 60.3 35.5 48.3 55.6 63.0 55.2 14.9 58.9 24.7 32.4 53.1 47.9 62.9 35.0
91.89 0.19 0.45 1.07 0.09 5.66
31.0 74.7 52.3 28.2 42.1 49.6 ± 2.4
4.7 7.4 4.7 11.3 0.0 3.4 ± 0.8
64.3 17.9 43.0 60.5 57.9 47.0 ± 2.5
a Abbreviation of each park name is expressed in parenthesis (the same with subsequent tables).
a
Stem diameter at breast height of 1.2 m for trees and diameter at 15 cm above ground for shrubs.
0.57 kg/L (GIR, 2019). The trees in the urban parks played an important role in annually offsetting gasoline consumption-induced carbon emissions by approximately 2.3% of the total population of the city (230,000 people). The cost of carbon capture and storage was reported to be approximately $351/t (GCCSI, 2017). Based on this cost, the economic value of the carbon uptake by the urban park trees was equivalent to about $7.1million/yr, 15.1% of the annual maintenance budget of the urban parks in the city (Seoul, 2017b).
greater than their estimates for entire cities. This result might be largely associated with smaller hardscape area (e.g., pavements, buildings) and higher tree density in the study parks. The carbon storage and uptake per unit of park area, per unit of basal area, and per unit of tree cover were variable depending on the study parks. This was attributed to differences in species, density, sizes, and layering structures of the planted trees. That is, the carbon storage and uptake were relatively greater in the parks having fast-growing species, higher density, larger sizes, and multi-layered structures than in those having slow-growing species, lower density, smaller sizes, and single-layered structures. The carbon storage and uptake per unit area and cover from the study parks can be used as the indicators to estimate carbon reduction effects for other urban parks. Based on the carbon storage and uptake estimates per unit area of the study parks, the planted trees in all urban parks of Seoul, excluding urban nature parks and cemetery parks, were found to be capable of storing a total of 222.3 kt of carbon and annually sequestering 20.2 kt of carbon. The per capita carbon emissions of the city from gasoline consumption were 88.0 kg/yr when applying a gasoline consumption of 154.3 L/yr (Seoul, 2017a) and a carbon emissions coefficient of
3.4. Planning strategies Limitations of tree planting structures regarding the carbon reduction in the study parks were represented by the distribution of large grass and impervious areas absent of a specific purpose of use, the single-layered structures of only trees, shrubs, or grass, and the dominance of small trees. Urban parks are a key resource that can be used to enhance carbon reduction effects, because they have a high potential for the planting of trees in cities that have limited areas for greenspace. Park trees also can provide other diverse ecosystem services such as air pollution abatement, microclimate amelioration, rainfall interception, wildlife inhabitation, and property value improvement (Konijnendijk et al., 2013; Miller et al., 2015). 51
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potential planting areas was estimated to sequester an additional 70 t/ yr, approximately 10% of the existing carbon uptake in the study parks. This potential planting space included only the permeable area. If the impervious area is added (nearly 50% of study park area), the carbon uptake potential would be much greater. This study suggests multi-layered and clustered planting techniques, instead of avoiding the single-layered planting, because they are more effective to increase tree density and carbon sequestration per unit area. In addition, it is recommended to plant larger trees rather than small trees and tree species having satisfactory growth rates (e.g., Zelkova serrata, Prunus yedoensis, Pinus koraiensis). A park ordinance of stipulating the above-mentioned strategies of land uses and tree planting is required to create a low carbon park as one of theme parks.
Table 3 Density, basal area, and cover of trees planted in study parks. Park
Density (tree/100 m2)
Basal area (cm2/100 m2)
Covera (%)
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 P31 P32 P33 P34 P35 P36 P37 P38 Mean
2.7 7.5 2.0 3.4 4.2 1.6 2.0 3.8 1.2 4.0 3.1 5.0 4.0 3.2 2.6 3.0 5.8 3.2 2.8 5.1 7.7 4.6 5.1 2.5 7.3 3.1 4.3 4.1 6.8 3.6 4.8 1.8 4.1 4.0 8.9 5.2 3.1 6.4 4.1 ± 0.3
1,543.9 757.5 1,135.1 940.2 846.5 885.1 839.7 971.1 646.6 955.3 1,191.0 1,838.4 2,324.2 865.9 806.2 1,814.5 1,877.9 1,841.7 877.7 1,479.2 1,766.3 2,013.5 1,156.2 999.5 1,626.7 1,547.6 703.6 2,746.8 952.9 1,308.5 923.7 666.6 2,028.3 1,467.3 2,026.7 1,405.8 504.1 1,565.1 1,311.8 ± 86.6
42.1 51.4 46.6 43.8 43.5 40.3 47.3 58.9 33.5 43.7 41.9 54.8 65.4 54.0 40.8 53.5 52.0 51.8 50.1 50.8 55.2 48.9 48.1 42.7 55.4 70.1 43.2 90.3 50.6 49.3 52.3 32.4 63.6 60.8 73.1 46.9 38.7 47.0 50.9 ± 1.8
a
4. Conclusions Reducing atmospheric carbon levels and delaying climate change require greenspace enlargement, including tree planting as well as fossil fuel savings. Urban parks provide a sizable greenspace for tree planting and have a high potential to contribute to carbon reduction and other ecological services such as microclimate amelioration, rainfall interception, and wildlife inhabitation. However, little is currently known regarding carbon reduction of trees planted in urban parks and desirable low carbon design of the parks throughout the world. This study quantified the carbon storage and uptake for urban parks in the capital of the Republic of Korea, Seoul and explored planning strategies to enhance carbon reduction effects of the parks. The cover of trees and shrubs planted in the study parks averaged approximately 51%. Mean carbon storage and uptake per unit of cover were 7.4 kg/m2 and 0.7 kg/m2/yr, respectively, which were higher than the estimates for the entire city. The planted trees across all urban parks in Seoul played an important role in offsetting gasoline consumptioninduced carbon emissions by about 2.3% of the total population of the city. The economic value of carbon uptake was equivalent to 15.1% of the annual maintenance budget of the urban parks in the city. However, the role of the parks as a source of carbon uptake was limited due to the distribution of large grass and impervious areas, the single-layered structures of tree planting, and the dominance of small trees. That is, the mean dbh of the planted trees was approximately 18 cm, the singlelayered structures accounted for about 52% of the total planted area, and the impervious areas of facilities and pavements comprised 47% of the total park area. The carbon storage and uptake levels were relatively greater in the study parks having higher density, larger sizes, and multi-layered structures, and fast-growing species of the planted trees. Thus, it is not the best way just to establish many parks. Desirable planning strategies, including land uses and tree planting structures, should be applied to enhance the capacity of urban parks to reduce atmospheric carbon levels. Such strategies include the areal enlargement of tree planting through the minimization of unnecessary grass and non-permeable areas, the multi-layered planting clustered with larger trees, and the planting of tree species with better growth rates. This study pioneers, in the Republic of Korea, in acquiring indicators of carbon estimates per unit of park area, basal area, and tree cover, and also exploring practical planning strategies for urban parks. These results were based on an actual survey of land cover distribution and tree planting characteristics over the considerable area of the study parks. The detailed field survey to attain reliable results was a new challenge as one of the most difficulties in this study. The above-mentioned structural limitations of land uses and tree planting in the study parks would exist in other parks throughout the world (e.g., grassdominant landscape) and the planning strategies suggested could be internationally applied to creating a low carbon park. The carbon storage and uptake per unit area and cover by trees from the study parks, on which information is limited, also could be of usefulness as the indicators to assess carbon offset levels for other urban parks.
Cover includes shrubs.
Fig. 2. Dbh distribution of trees planted in study parks.
Thus, the carbon uptake capacity of the parks can be improved by planting trees in grass and vacant areas that currently do not support trees. Davies et al. (2011) also mentioned that planting trees on public lands dominated by grass could significantly increase tree carbon storage. The potential planting space in the study parks was measured at a total of 20 ha in which about 63,000 trees with a crown width of 2 m can additionally be planted. The active planting of the trees in the 52
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Table 4 Carbon storage and uptake by trees and shrubs planted in study parks. Park
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 P31 P32 P33 P34 P35 P36 P37 P38 Mean
Per basal area (100 cm2)
Per park area (ha)
Per tree cover (m2)
Storage (t)
Uptake (t/yr)
Storage (kg)
Uptake (kg/yr)
Storage (kg)
Uptake (kg/yr)
36.7 15.1 38.2 29.5 29.0 29.0 32.2 28.5 19.8 30.1 34.1 50.1 71.1 27.3 22.8 46.0 47.9 49.8 31.4 35.6 46.7 56.3 31.2 29.5 48.3 56.9 16.6 111.1 24.3 41.1 24.8 19.8 68.8 40.0 51.0 36.1 12.2 45.7 38.5 ± 3.0
3.5 1.9 3.0 2.6 2.7 3.0 2.7 2.7 1.6 2.9 3.5 4.0 6.1 2.6 2.1 3.4 4.6 4.6 2.7 3.6 4.4 4.8 2.8 2.7 3.7 4.0 1.9 8.4 2.8 3.5 2.7 2.1 6.4 3.7 5.4 3.5 1.2 3.9 3.5 ± 0.2
23.1 15.2 32.2 24.3 33.4 32.1 36.1 28.7 22.3 27.4 27.7 25.9 30.2 26.9 27.9 23.2 25.1 26.4 33.7 23.8 25.5 27.8 23.6 24.1 29.6 34.7 21.7 40.2 23.8 26.9 24.2 27.5 33.1 25.9 25.0 25.2 22.4 27.4 27.3 ± 0.8
2.2 1.9 2.5 2.1 3.1 3.3 3.0 2.7 1.8 2.6 2.8 2.1 2.6 2.5 2.6 1.7 2.4 2.4 2.9 2.4 2.4 2.4 2.3 2.2 2.3 2.5 2.5 3.1 2.7 2.3 2.7 2.9 3.1 2.4 2.6 2.5 2.3 2.3 2.5 ± 0.1
8.7 2.9 8.2 6.7 6.7 7.2 6.8 4.8 5.9 6.9 8.1 9.1 10.9 5.1 5.6 8.6 9.2 9.6 6.3 7.0 8.5 11.5 6.5 6.9 8.7 8.1 3.8 12.3 4.8 8.3 4.7 6.1 10.8 6.6 7.0 7.7 3.6 9.7 7.4 ± 0.4
0.8 0.4 0.6 0.6 0.6 0.7 0.6 0.5 0.5 0.7 0.8 0.7 0.9 0.5 0.5 0.6 0.9 0.9 0.5 0.7 0.8 1.0 0.6 0.6 0.7 0.6 0.4 0.9 0.6 0.7 0.5 0.7 1.0 0.6 0.7 0.8 0.4 0.8 0.7 ± 0.0
The maintenance of park trees could help ensure their normal growth and carbon uptake, even though it releases carbon back to the atmosphere (Jo and McPherson, 1995; McPherson et al., 2015). The carbon flux associated with tree maintenances was not considered in this study. More research regarding life cycle assessment of carbon for park trees is needed to combine the planning strategies from this study with an appropriate maintenance decision to enhance net carbon uptake. Related studies about carbon reduction effects of different urban greenspace types such as streets and gardens are also required to compare their effects with the case of parks and to provide appropriate planning and management guidelines for each greenspace type.
Davies, Z.G., Edmondson, J.L., Heinemeyer, A., Leake, J.R., Gaston, K.J., 2011. Mapping an urban ecosystem service: quantifying above-ground carbon storage at a city-wide scale. J. Appl. Ecol. 48 (5), 1125–1134. GCCSI (Global carbon capture and storage institute), 2017. Global Costs of Carbon Capture and Storage. Retrieved March 29nd, 2018 from. https://hub. globalccsinstitute.com/sites/default/files/publications/201688/global-ccs-costupdatev4.pdf. GIR (Greenhouse Gas Inventory and Research Center), 2017. National Greenhouse Gas Inventory Report of Korea. Retrieved March 29nd, 2018 from. . http://www.gir.go. kr/home/index.do?menuId=36. Gratani, L., Varone, L., Bonito, A., 2016. Carbon sequestration of four urban parks in Rome. Urban For. Urban Green. 19, 184–193. IEA (International Energy Agency), 2017. CO2 emissions from fuel combustion highlights. Paris. Jo, H.K., 1993. Landscape Carbon Budgets and Planning Guidelines for Greenspaces in Urban Residential Lands. Ph.D. Thesis. University of Arizona, Tucson. Jo, H.K., 2001. Indicator for CO₂ Uptake and Atmospheric Purification Evaluation of Vegetation. Development of Eco-indicators for Sustainable Development. Ministry of Environment, Seoul. Jo, H.K., 2002. Impacts of urban greenspace on offsetting carbon emissions for middle Korea. J. Environ. Manag. 64, 115–126. Jo, H.K., Ahn, T.W., 2001. Annual CO2 uptake and atmospheric purification by urban coniferous trees: for Pinus densiflora and Pinus koraiensis. Korean J. Environ. Ecol. 15 (2), 118–124. Jo, H.K., Ahn, T.W., 2006. Structural conditions of greenspace in a rural region and strategies for its functional improvement: in the case of Yanggu, Gangwon Province. Korean J. Environ. Ecol. 20 (4), 493–502. Jo, H.K., Ahn, T.W., 2012. Carbon storage and uptake by deciduous tree species for urban landscape. J. Korean Inst. Landsc. Archit. 40 (5), 160–168. Jo, H.K., Cho, D.H., 1998. Annual CO2 uptake by urban popular landscape tree species. J. Korean Inst. Landsc. Archit. 26 (2), 38–53. Jo, H.K., McPherson, E.G., 1995. Carbon storage and flux in urban residential greenspace. J. Environ. Manag. 45, 109–133. Jo, H.K., Lee, K.E., Yun, Y.H., Seo, O.H., 1998. Land use and greenspace structure in
Acknowledgements This study was carried out with the support of the ‘R&D Program for Forest Science Technology (Project No. 2017043B10-1919-BB01)’ provided by the Korea Forest Service (Korea Forestry Promotion Institute). References Ahn, T.W., 2010. A Study on Establishment of Greenspace Planning Indicators to Accomplish Low Carbon Green City: in the Case of Chuncheon. Ph.D. Thesis. Kangwon National University, Chuncheon. Cheongwadae, 2016. Plan to Counteract Climate Change I. Seoul. Retrieved February 30nd, 2018 from. http://www.moef.go.kr/nw/nes/detailNesDtaView.do? searchBbsId=MOSFBBS_000000000028&menuNo=4010100&searchNttId=MOSF_ 000000000006696.
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H.-K. Jo, et al. several cities of Kangwon Province. J. Korean Inst. Landsc. Archit. 25 (4), 171–183. Jo, H.K., Cho, Y.H., Ahn, T.W., 2003. Effects of urban greenspace on improving atmospheric environment: focusing on Jung-gu in Seoul. J. Korean Inst. Landsc. Archit. 31 (3), 83–90. Jo, H.K., Kim, J.Y., Park, H.M., 2013. Carbon storage and uptake by evergreen trees for urban landscape: for Pinus densiflora and Pinus koraiensis. Korean J. Environ. Ecol. 27 (5), 571–578. Jo, H.K., Kim, J.Y., Park, H.M., 2014. Carbon reduction effects of urban landscape trees and development of quantitative models: for five native species. J. Korean Inst. Landsc. Archit. 42 (5), 13–21. Jo, H.K., Kim, J.Y., Park, H.M., 2017a. Carbon sequestration by urban forests and planning strategies in Seoul. Annu. Int. Symp. Kangwon National Univ. Inst. Forest Sci. XX. Jo, H.K., Kim, J.Y., Park, H.M., 2017b. Carbon uptake by urban forests and planning strategies in Chuncheon. Proc. Korea Environ. Sci. Soc. Conf. 26, 181. KMA (Korea Meteorological Administration), 2017. Global CO2 Concentration Increases Rapidly in 2016. Retrieved March 27nd, 2018 from. http://web.kma.go.kr/notify/ press/kma_list.jsp?bid=press&mode=view&num=1193439. Konijnendijk, C.C., Annerstedt, M., Nielsen, A.B., Maruthaveeran, S., 2013. Benefits of Urban Parks: A Systematic Review. Retrieved January 20nd, 2019 from. https:// www.worldurbanparks.org/images/Newsletters/IfpraBenefitsOfUrbanParks.pdf. Liu, C., Li, X., 2012. Carbon storage and sequestration by urban forests in Shenyang. China. Urban For. Urban Green 11, 121–128. McPherson, E.G., 1998. Atmospheric carbon dioxide reduction by Sacramento’s urban forest. J. Arboricult. 24 (4), 215–223. McPherson, E.G., Simpson, J.R., 1999. Carbon Dioxide Reduction Through Urban Forestry: Guidelines for Professional and Volunteer Tree Planters. General Technical Report PSW-GTR-171. USDA Forest Service, Pacific Southwest Research Station, Albany, CA. McPherson, E.G., Kendall, A., Albers, S., 2015. Life cycle assessment of carbon dioxide for different arboricultural practices in Los Angeles, CA. Urban For. Urban Green. 14,
388–397. Miller, R.W., Hauer, R.J., Werner, L.P., 2015. Urban Forestry: Panning and Managing Urban Greenspaces, 3rd ed. Waveland Press, Inc. Nowak, D.J., Crane, D.E., 2002. Carbon storage and sequestration by urban trees in the USA. Environ. Pollut. 116, 381–389. Nowak, D.J., Heisler, G.M., 2010. Air Quality Effects of Urban Trees and Parks. National Recreation and Parks Association Research Series Monograph, Ashburn, VA. Nowak, D.J., 1994. Atmospheric carbon dioxide reduction by chicago’s urban forest. In: McPherson, E.G., Nowak, D.J., Rowntree, R.A. (Eds.), Chicago’s Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. General Technical Report NE-186. USDA Forest Service, Northeastern Forest Experiment Station, Radnor, PA. Nowak, D.J., Endreny, T.A., Hoehn, R.E., Yang, Y., Bodine, A.R., Zhou, T., Greenfield, E.J., Henry, R., Ellis, A., 2012. Assessing Urban Forest Effects and Values: Toronto’s Urban Forest. USDA Forest Service, Northern Research Station Resource Bulletin NRS-79, Newtown Square, PA. Nowak, D.J., Greenfield, E.J., Hoehn, R.E., Lapoint, E., 2013. Carbon storage and sequestration by trees in urban and community areas of the United States. Environ. Pollut. 178, 229–236. Seoul, 2017a. Seoul Statistics Service. Retrieved February 26nd, 2018 from. http://data. seoul.go.kr/dataService/boardList.do#none. Seoul, 2017b. Annual Budget Information. Retrieved March 20nd, 2018 from. http:// finance.seoul.go.kr/archives/category/budget/data_budget/data_info_budget-n2. UNFCCC (United Nations Framework Convention on Climate Change), 2015. The Paris Agreement. Retrieved February 15nd, 2018 from. http://bigpicture.unfccc.int/# content-the-paris-agreemen. WMO (World Meteorological Organization), 2017. Greenhouse Gas Bulletin No 13. Retrieved February 15nd, 2018 from. https://public.wmo.int/en/resources/library/ wmo-greenhouse-gas-bulletin. Yang, J., McBride, J., Zhou, J., Sun, Z., 2005. The urban forest in Beijing and its role in air pollution reduction. Urban For. Urban Green 3, 65–78.
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Carbon reduction and planning strategies for urban parks in Seoul a
b,⁎
Hyun-Kil Jo , Jin-Young Kim a b
, Hye-Mi Park
b
T
Department of Ecological Landscape Architecture Design, Kangwon National University, Chuncheon 24341, Republic of Korea Department of Landscape Architecture, Graduate School, Kangwon National University, Chuncheon 24341, Republic of Korea
ARTICLE INFO
ABSTRACT
Handling Editor: N Nilesh Timilsina
This study quantified carbon storage and uptake for urban parks in Seoul, the capital of the Republic of Korea. A total of 38 study parks were selected using a systematic random sampling method and all the trees in the parks were field-inventoried. Carbon storage and uptake by the park trees were estimated applying a quantitative model for urban open-grown trees of each species. Mean carbon storage per unit of park area, basal area, and crown cover by the trees was 38.5 ± 3.0 t/ha, 27.3 ± 0.8 kg/100 cm2, and 7.4 ± 0.4 kg/m2, respectively. Annual carbon uptake per unit area and cover by the trees averaged 3.5 ± 0.2 t/ha/yr, 2.5 ± 0.1 kg/100 cm2/ yr, and 0.7 ± 0.0 kg/m2/yr, respectively. The major determinants of the levels of carbon storage and uptake were species, density, sizes, and layering structures of the planted trees. The trees across all urban parks in Seoul were estimated to store 222.3 kt of carbon and to annually sequester 20.2 kt of carbon. The trees in these parks played an important role in annually offsetting carbon emissions from gasoline consumption by approximately 2.3% of the total population of the city. The economic value of the annual carbon uptake, which was $7.1million/yr, equaled 15.1% of the annual maintenance budget of the parks in the city. However, the role of study parks as a source of carbon uptake was limited due to the distribution of large grass and impervious areas, the single-layered structures, and the dominance of small trees. Planning strategies were explored to enhance carbon reduction effects of the parks. They included the expansion of tree planting spaces through the minimization of unnecessary grass and paving areas, the active tree planting in the potential planting spaces, the multi-layered planting grouped with larger trees, and the planting of tree species having satisfactory growth rates. This study puts an emphasis on finding out the present carbon offset levels of urban parks on which information is limited and suggesting a future direction of park planning based on a detailed actual survey.
Keywords: Indicator Offset Planting Storage Uptake
1. Introduction Climate change from the greenhouse effect is one of the serious environmental issues faced by the current generation. Recently, the nations which are members of the UNFCCC have agreed to a greenhouse gas emissions reduction goal to limit an increase in atmospheric carbon concentrations and global temperatures (UNFCCC, 2015). The Republic of Korea has also set a national goal to reduce greenhouse gas emissions by 37% of its estimated business as usual (BAU) emissions by the year 2030 and has established the first basic plan on responding to climate change (Cheongwadae, 2016). The average level of global CO2 concentration in 2016 was about 403 ppm, which was a 45% increase compared to the levels prior to the industrial revolution (WMO, 2017). The level of CO2 concentration in the Republic of Korea measured at approximately 410 ppm, which was 7 ppm higher than the global average (KMA, 2017). According to the (IEA (2017), the average per capita CO2 emissions of OECD member countries reduced from 10.3 t in
⁎
1990 to 9.2 t in 2015, but the CO2 emissions of the Republic of Korea increased by approximately 2.1 times from 5.4 to 11.6 t. Increases in atmospheric carbon concentrations are typically induced by fossil fuel consumption and greenspace destruction. Trees can play an important role as a source of carbon sequestration that delays or mitigates the adverse effects of climate change, because they sequester atmospheric carbon during the growth process and contribute to the accumulation of carbon in the soil. The carbon neutralization and offsetting programs of countries across the globe have included the planting of trees as a key carbon-reducing activity and are increasingly emphasizing its importance. Efforts to reduce atmospheric carbon concentrations have evoked diverse studies that explore the effects of urban trees (Jo, 1993; Nowak et al., 1994; Jo and Cho, 1998; McPherson, 1998; McPherson and Simpson, 1999; Jo and Ahn, 2001; Nowak and Crane, 2002; Jo, 2002; Jo et al., 2003; Yang et al., 2005; Davies et al., 2011; Jo and Ahn, 2012; Liu and Li, 2012; Nowak et al., 2013; Jo et al., 2013, 2014; Gratani et al., 2016; Jo et al., 2017a,b). Jo
Corresponding author. E-mail address: [email protected] (J.-Y. Kim).
https://doi.org/10.1016/j.ufug.2019.03.009 Received 4 June 2018; Received in revised form 24 January 2019; Accepted 12 March 2019 Available online 15 March 2019 1618-8667/ © 2019 Published by Elsevier GmbH.
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(2002) quantified the carbon storage and uptake by urban greenspace of several cities in the Republic of Korea and proposed a greenspace planning strategy to improve the efficiency of carbon reduction. Nowak et al. (2013) computed the carbon sequestration by urban trees across 34 cities and states in the United States and estimated the total carbon sequestration effects of urban trees across the country. Jo and Ahn (2012) and Jo et al. (2013, 2014) studied the carbon reduction effects of urban landscape tree species through a direct harvesting method including root digging. Gratani et al. (2016) estimated the carbon sequestration by vegetation and its economic value in four urban parks in Rome. The quantification of carbon reduction by urban greenspace requires the development and application of indicators of carbon estimates per unit greenspace area and per unit crown cover that are relevant to each type of greenspace such as parks, streets, and gardens. However, studies that quantitatively analyze carbon reduction effects by each type of greenspace are still rarely pursued. Carbon reduction by urban parks and appropriate design guidelines are, in particular, critical, because urban parks have the potential to create a substantially large greenspace area within the limited openspace of cities, and can largely contribute to the securing of carbon uptake sources (Davies et al., 2011; Gratani et al., 2016) and carbon emissions credits. However, there is currently little information on carbon reduction via trees planted in urban parks and low carbon design of the parks, not only in the Republic of Korea but also globally. The objectives of this study were to quantify carbon storage and uptake for urban parks in Seoul, the capital of the Republic of Korea, and to explore planning strategies to improve carbon reduction effects of the parks. For urban parks, no information is available regarding a carbon storage and uptake indicator per unit of tree cover, even though the indicator is significant to carbon estimates associated with tree density and sizes. This study could be of usefulness in internationally sharing the information regarding indicators to estimate carbon reduction effects of urban parks and desirable planning strategies associated with tree planting. In this study, carbon storage refers to total carbon accumulated by tree growth over time and carbon uptake indicates the annual rate of carbon absorption.
area of each park and areal distribution of land cover types were measured. The survey of tree planting included species, height, crown width, stem diameter at a breast height of 1.2 m (dbh) for trees and at a height of 15 cm above ground for shrubs (2 cm or less in dbh), and layering structures. The potential planting space was also surveyed to obtain a realistic estimate of carbon reduction through a new tree planting. This potential planting space included only the permeable area over which trees of 3 m or more in height and 2 m or more in crown width could be grown without interfering with various facilities such as utility lines, manholes, and septic tanks. The surveyed data on tree planting were used to analyze structural characteristics such as dbh distribution, density and cover per unit area, and importance values of species. The data were also applied to estimate carbon storage and uptake by trees in each study park. 2.3. Estimation of carbon storage and uptake Carbon storage and uptake by urban trees could significantly differ from those by forest-grown trees due to different growth environments, including management practices and competing conditions. Therefore, this study estimated carbon storage and uptake by park trees by using a quantitative model developed for urban open-grown trees of each species (Jo and Cho, 1998; Jo, 2001, 2002; Jo and Ahn, 2001, 2012; Jo et al., 2013, 2014). That is, the carbon storage and uptake for each species were computed applying the stem diameter of each tree as the major independent variable to the quantitative models (Table 1), which were derived from seasonal CO2 exchange rate measurements or a direct harvesting method of urban trees. For a particular species without a quantitative model available, the models for the same genus or group were substituted to average carbon estimates. Mean carbon storage and uptake per unit of park area, per unit of basal area, and per unit of crown cover were calculated based on park area, stem diameters, and tree cover surveyed. The carbon indicator per unit of park area was applied to estimate total carbon storage and uptake of the entire park area in the study city (Seoul, 2017a), excluding urban nature parks and cemetery parks. 3. Results and discussion
2. Methods
3.1. Areal distribution of study parks and land cover types
2.1. Study parks
Seoul is located in the central western region of the Korean Peninsula at 126°–127 °East and 37 °North. The east-west and northsouth distances of the city are 36.8 km and 30.3 km, respectively, and its total area measures 60,520 ha. In 2017, total population and the number of households in the city were 10,124,579 people and 3,784,705 households, respectively, and its population density was 167 people/ha (Seoul, 2017a). Of all land categories in the city, land plots comprised the largest proportion (36%). This category was followed by forests (23%), roads (13%), rivers (9%), schools (4%), and parks (3%) (Seoul, 2017a). The area of study parks ranged from a minimum of 0.1 ha to a maximum of 91.9 ha (Table 2). The study parks of less than 0.5 ha accounted for approximately 73.7% of all the parks. The total area of the study parks surveyed was 215.0 ha or approximately 5.2% of that of urban parks in Seoul, excluding urban nature parks and cemetery parks. Of the study parks, Boramae Park (P6), Seoul Children’s Grand Park (P33), Seoul Forest Park (P34), and Seonyudo Park (P32) were identified as large parks having an area of 11 ha or more. The ratio of land cover types in the study parks averaged 49.6 ± 2.4% for trees and shrubs, 47.0 ± 2.5% for pavements and facilities, and 3.4 ± 0.8% for grass and bare soils (Table 2). The impervious areas of facilities and pavements were almost similar to the areas covered by trees and shrubs. Nowak et al. (2012) found that the impervious areas of parks in Toronto, Canada were approximately 10%. Compared to their estimate, the areas covered by pavements and
This study sampled urban parks in Seoul, the city with the largest area and the highest population density in the Republic of Korea. A total of 38 sample study parks was selected applying a systematic random sampling method to a 1:1000-scale aerial photograph (Fig. 1): 8 straight lines radiating from the center of the study city were drawn in the equidistant direction and looping circles were plotted at 40 cm intervals; at least 25% of all the points at which the lines and circles crossed was randomly sampled in each direction; urban parks located at the crossing points or at the shortest distances from the points were selected as study parks. This sampling design is a new approach to sample the parks randomly at a city-wide scale, avoiding a selection bias. Urban parks selected were neighborhood parks and children’s parks, as stipulated in the Korea Urban Park and Greenspace Act, which are easily accessible and daily used by citizens. This study excluded urban nature parks and cemetery parks that were considerably different from study parks in land cover distribution, because the former is dominated by natural vegetation in mountainous areas and the latter, by grass with little tree planting. The number of samples was determined upon a compromise between the conflicting concerns for a large sample size and the availability of labor and budget. 2.2. Survey and analysis of tree planting All the trees in study parks selected were field-surveyed, and total 49
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Fig. 1. Depiction of systematic sampling method used in this study and location of study parks sampled.
facilities in the study parks were about 5 times higher. These large nonpermeable areas and grass areas absent of specific purpose of use could limit an area considered useful for tree planting and decrease the role of carbon offset by the parks.
Ahn, 2010). The vertical planting structures of the study parks revealed that a single layer of trees, shrubs, or grass comprised 51.5% of the total planted area, while multi-layered structures in which tree, shrub, and herb layers overlap occupied 48.5%. Of the total single-layered area, the area planted only with grass accounted for 48.4%, which indicated a relatively high ratio of the grass area. The remaining ratios of the single-layered area were composed of planting only with trees (42.9%) and planting only with shrubs (8.7%). The single-layered planting could be unfavorable to an increase of carbon storage and uptake per unit area (Jo, 2002).
3.2. Tree planting structures Planting density of trees ranged from 1.2 to 8.9 trees/100 m2 depending on the study parks (Table 3). The density of 3–5 trees/100 m2 accounted for 68.4% of all study parks, which was the most, followed by ≥6 trees/100 m2 (18.4%) and < 3 trees/100 m2 (13.2%). The tree density averaged 4.1 ± 0.3 trees/100 m2 across all study parks, which was slightly lower than 5.0 trees/100 m2 of some parks in Toronto, Canada (Nowak et al., 2012). The basal area of the planted trees ranged from 504.1 to 2,746.8 cm2/100 m2 with an average of 1,3111311.8 ± 86.6 cm2/ 100 m2. The basal area of 1,000–2,000 cm2/100 m2 comprised 44.7% of all study parks, followed by < 1,000 cm2/100 m2 (42.1%) and > 2,000 cm2/100 m2 (13.2%). The dbh of trees averaged 18.1 ± 0.6 cm across all study parks. Trees with a dbh of < 20 cm occupied 59.8% of all the planted trees, which was the most, followed by 20–30 cm (21.5%) and > 30 cm (18.7%) (Fig. 2). The dbh of trees planted in some parks of Italy averaged 45 cm (Gratani et al., 2016). The average dbh of the trees in the study parks was approximately 60% smaller than that in Italy. The cover of the planted trees and shrubs averaged 50.9 ± 1.8%, ranging from a minimum of 32.4% to a maximum of 90.3%. The tree and shrub cover of 30–50% and > 50% accounted for 52.6% and 47.4% of all study parks, respectively. The tree cover of some parks in the United States, Canada, and Italy was reported to range from 49 to 57% (Nowak and Heisler, 2010; Nowak et al., 2012; Gratani et al., 2016). Compared to this report, the tree cover of the study parks (46.9% excluding shrubs) was similar or lower by 17.5%. The total number of tree and shrub species in the study parks was 148, which indicated a relatively diverse composition of species. The top 10 species in importance values included Pinus densiflora (7.8%), Pinus koraiensis (6.9%), Zelkova serrata (6.6%), Prunus yedoensis (6.3%), Acer palmatum (5.5%), Rhododendron yedoense var. poukhanense (5.1%), Ginkgo biloba (4.5%), Pinus strobus (3.2%), Platanus occidentalis (2.3%), and Metasequoia glyptostroboides (2.2%). These are the key landscape species that also typically presented a relatively high dominance in other cities of the Republic of Korea (Jo et al., 1998; Jo and Ahn, 2006;
3.3. Carbon storage and uptake The carbon storage by the planted trees per unit area of the study parks ranged from a minimum of 12.2 t/ha to a maximum of 111.1 t/ha with an average of 38.5 ± 3.0 t/ha (Table 4). The carbon uptake per unit area ranged from 1.2 to 8.4 t/ha/yr with an average of 3.5 ± 0.2 t/ha/yr. Gratani et al. (2016) found that the mean carbon uptake per unit area of some parks in Italy was about 6.6 t/ha/yr. The average carbon uptake of the study parks was significantly lower, compared to their estimate. This difference could be due to the variations in density, sizes, and growth rates of the planted trees. The carbon storage per unit of basal area of the planted trees averaged 27.3 ± 0.8 kg/100 cm2, ranging from 15.2 to 40.2 kg/ 100 cm2 depending on the study parks. The carbon uptake per unit of basal area ranged from 1.7 to 3.3 kg/100 cm2/yr with an average of 2.5 ± 0.1 kg/100 cm2/yr. The mean dbh of the trees in the study parks was, as mentioned above, approximately 18 cm and the basal area of this tree size was 254.3 cm2. Based on the average carbon storage and uptake per unit of basal area, a single tree of the size is capable of storing 69.4 kg of carbon and annually sequestering 6.4 kg of carbon. The carbon storage per unit of cover of the planted trees averaged 7.4 ± 0.4 kg/m2, ranging from 2.9 to 12.3 kg/m2 depending on the study parks. The carbon uptake per unit of cover ranged from 0.4 to 1.0 kg/m2/yr with an average of 0.7 ± 0.0 kg/m2/yr. As an urban land average of the Republic of Korea, the carbon storage and uptake per unit of tree cover were 4.8 kg/m2 and 0.5 kg/m2/yr, respectively (Jo, 2002). In the case of the United States, these figures averaged 7.8 kg/ m2/yr and 0.3 kg/m2/yr, respectively (Nowak et al., 2013). The average carbon uptake per unit of tree cover in the study parks was found to be 50
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Table 1 Regression model sources of tree and shrub species used to compute carbon storage and uptake in study parks. Carbon
Species
Storage
Tree
Shrub
Uptake
Tree
Diameter rangea (cm)
Reference
Abies holophylla Acer palmatum Chionanthus retusus Cornus officinalis Ginkgo biloba Pinus densiflora Pinus koraiensis Prunus armeniaca Prunus yedoensis Taxus cuspidata Zelkova serrata Lespedeza bicolor Pinus spp. Quercus spp. Rhododendron spp. General hardwoods
5–19 5–20 3–11
Jo et al. (2014) Jo and Ahn (2012) Jo et al. (2014)
3–15 5–25 5–25 5–31 4–14 5–23 2–15 5–28 0.4–2.5 0.6–3.5 0.5–4.0 0.4–3.4 0.4–4.0
Jo et al. (2014) Jo and Ahn (2012) Jo et al. (2013) Jo et al. (2013) Jo et al. (2014) Jo and Ahn (2012) Jo et al. (2014) Jo and Ahn (2012) Jo (2002) Jo, (2002) Jo, (2002) Jo, (2002) Jo (2001, 2002)
Abies holophylla Acer palmatum
5–19 7–27 5–20 3–11
Jo Jo Jo Jo
Pinus densiflora
3–15 6–31 5–25 5–29
Pinus koraiensis
5–33
Platanus occidentalis Prunus armeniaca Prunus yedoensis Taxus cuspidata Zelkova serrata
10–58
Jo et al. (2014) Jo and Cho (1998) Jo and Ahn (2012) Jo and Ahn (2001), Jo et al. (2013) Jo and Ahn (2001) Jo et al. (2013) Jo and Cho (1998)
4–14 5–23 2–15 6–34 5–28 0.4–2.5 0.6–3.5 0.5–4.0 0.4–3.4 0.4–4.0
Jo Jo Jo Jo Jo Jo Jo Jo Jo Jo
Chionanthus retusus Cornus officinalis Ginkgo biloba
Shrub
Lespedeza bicolor Pinus spp. Quercus spp. Rhododendron spp. General hardwoods
Table 2 Percentage of land cover types in study parks. Parka
Baebatgol (P1) Bangadari (P2) Banghyeon (P3) Bansu (P4) Bareum (P5) Boramae (P6) Buntogol (P7) Cheonho (P8) Dongnimmun (P9) Eunhasu (P10) Gakkul (P11) Gangbyeon (P12) Gangnam (P13) Geumho (P14) Gongneung-dong (P15) Gyeonghak (P16) Gyodae (P17) Hakdong (P18) Itaewon (P19) Jangan (P20) Keungol (P21) Kkachi (P22) Mongnyeon (P23) Mugunghwa (P24) Mukjeong (P25) Nari (P26) Nodeullnaru (P27) Nogosan (P28) Pureundongsan (P29) Sarok (P30) Seonangdang (P31) Seonyudo (P32) Seoul Children’s Grand (P33) Seoul Forest (P34) Somdari (P35) Usangak (P36) Wooram (P37) Yeongmal (P38) Mean
et al. (2014) and Cho (1998) and Ahn (2012) et al. (2014)
et al. (2014) and Ahn (2012) et al. (2014) and Cho (1998) and Ahn (2012) (2002) (2002) (2002) (2002) (2001,2002)
Area (ha)
Land cover type (%) Tree/Shrub
Grass/Bare soil
Paving/Facility
0.09 0.15 0.18 0.13 0.09 42.41 0.10 2.67 0.33 0.20 0.08 0.18 0.09 1.35 0.70
78.2 32.4 53.2 39.1 52.8 20.9 44.1 59.2 29.8 59.1 43.7 43.3 43.0 46.4 72.9
0.0 0.0 0.0 0.0 0.0 15.6 0.0 1.9 0.0 6.7 0.0 0.0 0.0 1.4 5.8
21.8 67.4 46.8 60.9 47.2 63.5 55.9 38.9 70.2 34.2 56.3 56.7 57.0 52.2 21.3
0.25 0.10 0.16 0.29 0.09 0.17 0.11 0.10 0.10 0.35 0.40 4.46 0.10 0.09 0.10 1.02 11.04 53.61
66.5 51.8 63.0 59.2 39.7 64.5 51.7 44.4 37.0 42.0 77.9 40.3 67.4 67.6 46.9 49.3 20.3 48.7
15.0 0.0 0.0 1.7 0.0 0.0 0.0 0.0 0.0 2.8 7.2 0.8 7.9 0.0 0.0 2.8 16.8 16.3
18.5 48.2 37.0 39.1 60.3 35.5 48.3 55.6 63.0 55.2 14.9 58.9 24.7 32.4 53.1 47.9 62.9 35.0
91.89 0.19 0.45 1.07 0.09 5.66
31.0 74.7 52.3 28.2 42.1 49.6 ± 2.4
4.7 7.4 4.7 11.3 0.0 3.4 ± 0.8
64.3 17.9 43.0 60.5 57.9 47.0 ± 2.5
a Abbreviation of each park name is expressed in parenthesis (the same with subsequent tables).
a
Stem diameter at breast height of 1.2 m for trees and diameter at 15 cm above ground for shrubs.
0.57 kg/L (GIR, 2019). The trees in the urban parks played an important role in annually offsetting gasoline consumption-induced carbon emissions by approximately 2.3% of the total population of the city (230,000 people). The cost of carbon capture and storage was reported to be approximately $351/t (GCCSI, 2017). Based on this cost, the economic value of the carbon uptake by the urban park trees was equivalent to about $7.1million/yr, 15.1% of the annual maintenance budget of the urban parks in the city (Seoul, 2017b).
greater than their estimates for entire cities. This result might be largely associated with smaller hardscape area (e.g., pavements, buildings) and higher tree density in the study parks. The carbon storage and uptake per unit of park area, per unit of basal area, and per unit of tree cover were variable depending on the study parks. This was attributed to differences in species, density, sizes, and layering structures of the planted trees. That is, the carbon storage and uptake were relatively greater in the parks having fast-growing species, higher density, larger sizes, and multi-layered structures than in those having slow-growing species, lower density, smaller sizes, and single-layered structures. The carbon storage and uptake per unit area and cover from the study parks can be used as the indicators to estimate carbon reduction effects for other urban parks. Based on the carbon storage and uptake estimates per unit area of the study parks, the planted trees in all urban parks of Seoul, excluding urban nature parks and cemetery parks, were found to be capable of storing a total of 222.3 kt of carbon and annually sequestering 20.2 kt of carbon. The per capita carbon emissions of the city from gasoline consumption were 88.0 kg/yr when applying a gasoline consumption of 154.3 L/yr (Seoul, 2017a) and a carbon emissions coefficient of
3.4. Planning strategies Limitations of tree planting structures regarding the carbon reduction in the study parks were represented by the distribution of large grass and impervious areas absent of a specific purpose of use, the single-layered structures of only trees, shrubs, or grass, and the dominance of small trees. Urban parks are a key resource that can be used to enhance carbon reduction effects, because they have a high potential for the planting of trees in cities that have limited areas for greenspace. Park trees also can provide other diverse ecosystem services such as air pollution abatement, microclimate amelioration, rainfall interception, wildlife inhabitation, and property value improvement (Konijnendijk et al., 2013; Miller et al., 2015). 51
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potential planting areas was estimated to sequester an additional 70 t/ yr, approximately 10% of the existing carbon uptake in the study parks. This potential planting space included only the permeable area. If the impervious area is added (nearly 50% of study park area), the carbon uptake potential would be much greater. This study suggests multi-layered and clustered planting techniques, instead of avoiding the single-layered planting, because they are more effective to increase tree density and carbon sequestration per unit area. In addition, it is recommended to plant larger trees rather than small trees and tree species having satisfactory growth rates (e.g., Zelkova serrata, Prunus yedoensis, Pinus koraiensis). A park ordinance of stipulating the above-mentioned strategies of land uses and tree planting is required to create a low carbon park as one of theme parks.
Table 3 Density, basal area, and cover of trees planted in study parks. Park
Density (tree/100 m2)
Basal area (cm2/100 m2)
Covera (%)
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 P31 P32 P33 P34 P35 P36 P37 P38 Mean
2.7 7.5 2.0 3.4 4.2 1.6 2.0 3.8 1.2 4.0 3.1 5.0 4.0 3.2 2.6 3.0 5.8 3.2 2.8 5.1 7.7 4.6 5.1 2.5 7.3 3.1 4.3 4.1 6.8 3.6 4.8 1.8 4.1 4.0 8.9 5.2 3.1 6.4 4.1 ± 0.3
1,543.9 757.5 1,135.1 940.2 846.5 885.1 839.7 971.1 646.6 955.3 1,191.0 1,838.4 2,324.2 865.9 806.2 1,814.5 1,877.9 1,841.7 877.7 1,479.2 1,766.3 2,013.5 1,156.2 999.5 1,626.7 1,547.6 703.6 2,746.8 952.9 1,308.5 923.7 666.6 2,028.3 1,467.3 2,026.7 1,405.8 504.1 1,565.1 1,311.8 ± 86.6
42.1 51.4 46.6 43.8 43.5 40.3 47.3 58.9 33.5 43.7 41.9 54.8 65.4 54.0 40.8 53.5 52.0 51.8 50.1 50.8 55.2 48.9 48.1 42.7 55.4 70.1 43.2 90.3 50.6 49.3 52.3 32.4 63.6 60.8 73.1 46.9 38.7 47.0 50.9 ± 1.8
a
4. Conclusions Reducing atmospheric carbon levels and delaying climate change require greenspace enlargement, including tree planting as well as fossil fuel savings. Urban parks provide a sizable greenspace for tree planting and have a high potential to contribute to carbon reduction and other ecological services such as microclimate amelioration, rainfall interception, and wildlife inhabitation. However, little is currently known regarding carbon reduction of trees planted in urban parks and desirable low carbon design of the parks throughout the world. This study quantified the carbon storage and uptake for urban parks in the capital of the Republic of Korea, Seoul and explored planning strategies to enhance carbon reduction effects of the parks. The cover of trees and shrubs planted in the study parks averaged approximately 51%. Mean carbon storage and uptake per unit of cover were 7.4 kg/m2 and 0.7 kg/m2/yr, respectively, which were higher than the estimates for the entire city. The planted trees across all urban parks in Seoul played an important role in offsetting gasoline consumptioninduced carbon emissions by about 2.3% of the total population of the city. The economic value of carbon uptake was equivalent to 15.1% of the annual maintenance budget of the urban parks in the city. However, the role of the parks as a source of carbon uptake was limited due to the distribution of large grass and impervious areas, the single-layered structures of tree planting, and the dominance of small trees. That is, the mean dbh of the planted trees was approximately 18 cm, the singlelayered structures accounted for about 52% of the total planted area, and the impervious areas of facilities and pavements comprised 47% of the total park area. The carbon storage and uptake levels were relatively greater in the study parks having higher density, larger sizes, and multi-layered structures, and fast-growing species of the planted trees. Thus, it is not the best way just to establish many parks. Desirable planning strategies, including land uses and tree planting structures, should be applied to enhance the capacity of urban parks to reduce atmospheric carbon levels. Such strategies include the areal enlargement of tree planting through the minimization of unnecessary grass and non-permeable areas, the multi-layered planting clustered with larger trees, and the planting of tree species with better growth rates. This study pioneers, in the Republic of Korea, in acquiring indicators of carbon estimates per unit of park area, basal area, and tree cover, and also exploring practical planning strategies for urban parks. These results were based on an actual survey of land cover distribution and tree planting characteristics over the considerable area of the study parks. The detailed field survey to attain reliable results was a new challenge as one of the most difficulties in this study. The above-mentioned structural limitations of land uses and tree planting in the study parks would exist in other parks throughout the world (e.g., grassdominant landscape) and the planning strategies suggested could be internationally applied to creating a low carbon park. The carbon storage and uptake per unit area and cover by trees from the study parks, on which information is limited, also could be of usefulness as the indicators to assess carbon offset levels for other urban parks.
Cover includes shrubs.
Fig. 2. Dbh distribution of trees planted in study parks.
Thus, the carbon uptake capacity of the parks can be improved by planting trees in grass and vacant areas that currently do not support trees. Davies et al. (2011) also mentioned that planting trees on public lands dominated by grass could significantly increase tree carbon storage. The potential planting space in the study parks was measured at a total of 20 ha in which about 63,000 trees with a crown width of 2 m can additionally be planted. The active planting of the trees in the 52
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Table 4 Carbon storage and uptake by trees and shrubs planted in study parks. Park
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 P31 P32 P33 P34 P35 P36 P37 P38 Mean
Per basal area (100 cm2)
Per park area (ha)
Per tree cover (m2)
Storage (t)
Uptake (t/yr)
Storage (kg)
Uptake (kg/yr)
Storage (kg)
Uptake (kg/yr)
36.7 15.1 38.2 29.5 29.0 29.0 32.2 28.5 19.8 30.1 34.1 50.1 71.1 27.3 22.8 46.0 47.9 49.8 31.4 35.6 46.7 56.3 31.2 29.5 48.3 56.9 16.6 111.1 24.3 41.1 24.8 19.8 68.8 40.0 51.0 36.1 12.2 45.7 38.5 ± 3.0
3.5 1.9 3.0 2.6 2.7 3.0 2.7 2.7 1.6 2.9 3.5 4.0 6.1 2.6 2.1 3.4 4.6 4.6 2.7 3.6 4.4 4.8 2.8 2.7 3.7 4.0 1.9 8.4 2.8 3.5 2.7 2.1 6.4 3.7 5.4 3.5 1.2 3.9 3.5 ± 0.2
23.1 15.2 32.2 24.3 33.4 32.1 36.1 28.7 22.3 27.4 27.7 25.9 30.2 26.9 27.9 23.2 25.1 26.4 33.7 23.8 25.5 27.8 23.6 24.1 29.6 34.7 21.7 40.2 23.8 26.9 24.2 27.5 33.1 25.9 25.0 25.2 22.4 27.4 27.3 ± 0.8
2.2 1.9 2.5 2.1 3.1 3.3 3.0 2.7 1.8 2.6 2.8 2.1 2.6 2.5 2.6 1.7 2.4 2.4 2.9 2.4 2.4 2.4 2.3 2.2 2.3 2.5 2.5 3.1 2.7 2.3 2.7 2.9 3.1 2.4 2.6 2.5 2.3 2.3 2.5 ± 0.1
8.7 2.9 8.2 6.7 6.7 7.2 6.8 4.8 5.9 6.9 8.1 9.1 10.9 5.1 5.6 8.6 9.2 9.6 6.3 7.0 8.5 11.5 6.5 6.9 8.7 8.1 3.8 12.3 4.8 8.3 4.7 6.1 10.8 6.6 7.0 7.7 3.6 9.7 7.4 ± 0.4
0.8 0.4 0.6 0.6 0.6 0.7 0.6 0.5 0.5 0.7 0.8 0.7 0.9 0.5 0.5 0.6 0.9 0.9 0.5 0.7 0.8 1.0 0.6 0.6 0.7 0.6 0.4 0.9 0.6 0.7 0.5 0.7 1.0 0.6 0.7 0.8 0.4 0.8 0.7 ± 0.0
The maintenance of park trees could help ensure their normal growth and carbon uptake, even though it releases carbon back to the atmosphere (Jo and McPherson, 1995; McPherson et al., 2015). The carbon flux associated with tree maintenances was not considered in this study. More research regarding life cycle assessment of carbon for park trees is needed to combine the planning strategies from this study with an appropriate maintenance decision to enhance net carbon uptake. Related studies about carbon reduction effects of different urban greenspace types such as streets and gardens are also required to compare their effects with the case of parks and to provide appropriate planning and management guidelines for each greenspace type.
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