Vegetation resilience to absorbing carbon dioxide emissions in the Gajahmada Street

Abstrak. Gajahmada Street is one of the main streets in the city of Semarang. The location is very strategic, which connects the Golden Triangle Region in Semarang City which is the center of the city. As a city center, transportation activities in the area are very high. Transportation activities produce carbon dioxide emissions. The accumulation of carbon dioxide emissions is dangerous for health and the environment. Semarang City Government provides green open space along the road section to reduce carbon dioxide emissions. The purpose of this study was to determine the vegetation resilience to absorbing carbon dioxide at that location. The data collection method uses literature collection and field observations. The results showed the ability of green open space to absorb carbon dioxide emissions is 1.218,7 tons/ha/year. While the emissions produced are 6.832 tons/year, meaning that there is residual carbon dioxide that is not absorbed, that is 5.613,3 tons/year.


Introduction
Global warming is an increase in the earth's average temperature due to the concentration of greenhouse gases (GHGs) [1]. Increase in average temperature -based on increasing concentrations of GHGs [2]. GHGs consists of CO2 , N2O, NO2, CH4, CFC, etc. The gas will accumulate in the earth and form a transparent layer in the earth's atmosphere which is likened to the glass layer. As a result, sunlight cannot be reflected and becomes trapped on earth. This causes an increase in the temperature of the earth.
Carbon dioxide is the gas that can last the longest in the atmosphere. CO2 can last 50-200 years, N2O for 114-120 years, CH4 and CFC substitutes for 12 years [3]. Basically, carbon dioxide is an important gas for photosynthesis. However, excessive levels can be dangerous for the environment, which triggers global warming, acid rain, etc. For health, exposure to low levels of carbon dioxide gas can cause dizziness, hyperventilation, eye and throat irritation, minor lung disorders, central nervous system injuries, etc. While exposure to high levels can cause oxygen supply to be obstructed, which can cause seizures -even death.
Based on IPCC data at 2007, from 1970 to 2004 there has been an increase in carbon dioxide equivalent of 77%, from 21 Gt of CO2-eq to 31 Gt of CO2-eq [2]. In Indonesia, based on the 2018 Greenhouse Gas inventory report by the Ministry of Environment and Forestry, during the last 17 (seventeen) years there was an increase in carbon dioxide of 124,879 Gg (124,879,000 Tons). Transportation activities were the second largest contributor to the increase in carbon dioxide, which amounted to 17.20%.
For modern urban society, transportation is a vital means of movement that cannot be separated from daily activities. Especially in Indonesia, almost all of the cities are developed based on the pattern of land transportation networks. This creates a dilemma, on the one hand the land transportation system has become a dependency for the community, but on the other hand land transportation is suspected to threaten urban ecological conditions. Green open space is one solution to reduce global warming [4]. Green open space is an area that extends or lines and or groups, the use of which is more open, a place to grow plants, both naturally and intentionally planted. The provision of green open space is suspected to reduce carbon dioxide [5]. Green open space has an important role to improve the quality of life in urban areas, one of them as a very effective air purifier [6]. Green vegetation, especially trees, has the ability to absorb large amounts of carbon dioxide. One tree has the ability to absorb carbon dioxide of 569 tons / ha / year.
Trees are vegetation that have an important role in the process of reducing the concentration of CO2 in the air through the process of photosynthesis. Trees have the highest CO2 absorption compared to other types of vegetation (shrubs and groundcovers), because they have greater biomass compared to other vegetation. The part of the tree in charge of absorbing CO2 is the leaves through the stomata. Then the carbon will be stored in the biomass, namely in the stems and leaves. Compared to leaves, stems can deviate far more carbon [5]. Even 50% of the total dry stem consists of carbon. The amount of carbon stored in biomass is called carbon storage. While the ability of plants to absorb carbon is called carbon sequestration [7].
Based on the Spatial Planning Law, the green space requirements that must be met by the City are 30% of the total area, with the provisions that 20% are public and 10% are private. Semarang City is one of the cities in Indonesia that has fulfilled the provision of public green open space [8]. Based on information from the City of Semarang Department of Commerce, the number of green open space in the city of Semarang is 35%, which means it has exceeded the recommended minimum. Viewed in quantity, the presence of green open space in the city of Semarang has met the provisions. However, judging from its function, is the presence of green space effective enough to reduce the CO2 emissions produced? For this reason, this study aims to determine the ability of CO2 absorption by vegetation. Case study was carried out on the Jl. Gajah Mada. The location was chosen because transportation activities on the road section are quite high, resulting in considerable CO2 emissions. Gajahmada Street is one of the main streets in the city of Semarang. Its location is very strategic, which connects the Golden Triangle Region in Semarang City which is the center of the city. In addition, the use of land on these roads is also very complex, giving rise to high generation and pull 2 Method

Data collection methods
Data collection methods used in this study are literature studies, observations and interviews. Literature study is carried out by gathering literature related to the topic to be studied. Observations were made by observing daily traffic and inventorying the types of vegetation on Gajah Mada Street. Interviews were conducted with relevant agencies responsible for managing green open spaces on Gajah Mada Street.

Data analysis method
To find out the adequacy of green open space in absorbing CO2 emissions in Gajahmada Street, it is done by: 1) calculating the CO2 absorption by vegetation, 2) calculating CO2 emissions resulting from transportation activities on Jl. Gajahmada, 3) analysis of the adequacy of green space to absorb emissions.

Analysis of vegetation resilience (carbon stocks by trees)
Plants need CO2 to carry out photosynthesis. The results of the absorption of CO2, will be converted into carbohydrates which will then be spread and piled up in the body of the plant. The process is called C-sequestration. Therefore, measuring carbon still stored in the body of living plants (biomass) can describe the amount of CO2 that can be absorbed by plants. According to the [9], half the biomass of trees is CO2. Calculation of CO2 deposits in plant biomass is carried out using a formula developed by [9]:

Analysis of the adequacy of green open space to absorb CO2 emissions
An analysis of the adequacy of green space to absorb CO2 emissions is done by comparing the carbon stock of green space on Gajahmada Street with CO2 emissions resulting from transportation activities.

Type of vegetation in green open spaces pedestrians on Gajahmada Street
Gajahmada street is located in Sekayu Village, Central Semarang District. The location is very strategic, which is located in the city center and connects the golden triangle of the City of Semarang.

Analysis of vegetation resilience (carbon stocks by trees)
Vegetation Resilience of carbon absorption is the ability of trees to absorb CO2 in their bodies. The following is presented the potential for carbon uptake in the pedestrian green space on Gajahmada Street.  Table 3, potential CO2 uptake on Gajahmada Street is 1,218.7 tons/ha/year. Basically, plants need CO2 gas for photosynthesis. Plants need CO2 to carry out photosynthesis. The results of the absorption of CO2 will be converted into carbohydrates which will then be spread and piled up in the body of the plant. Each type of vegetation has the ability to absorb different CO2. According to Hidayati et al (2013), the ability of carbon dioxide uptake from each tree is influenced by the number of stomata and the ability of stomata to open a plant. The greater the opening of the stomata, the greater the ability of carbon dioxide absorption. In addition, the size of the rod also affects the carbon storage capacity. Because 50% of the carbon stock is stored in the trunk.

CO2 emissions on Gajahmada Street
CO2 emissions on Gajahmada Street is sourced from transportation activities. Gajahmada Street is the main road that connects the Golden Triangle Region of Semarang City. In addition, the use of surrounding land is quite complex, namely: settlement, trade and services, education, and worship. As a result, the generation and pull of traffic in this area is quite high. The rise and pull of traffic can be seen from the high volume of vehicles passing through this road section. The following is the vehicle volume on Gajahmada Street: Table 4, vehicles passing through Gajahmada Street consist of long vehicles, heavy vehicles, motorbikes, and public transportation. The types of vehicles that pass this road are 2253 units of motorbikes and 1142 private cars. Of the many vehicles that pass through these roads cause exhaust gases that contain emissions, in the form of: Carbon monoxide (CO), Sulfur (SOx), Nitrogen oxide (Nox), Hydro carbon (HC), dust (TSP) and lead (PB). CO gas when oxidized in the earth's atmosphere can turn into CO2 gas which is a greenhouse gas, triggering global warming.
Based on the calculation results, CO emissions are generated from vehicles passing through Jl. Gajahmada of 4,346.4 tons/year. If converted into CO2 it becomes 6,832 tons/year. This figure is quite high, and can continue to increase given the trend in the number of vehicles in the city of Semarang is exponential.

Adequacy of green open space to absorbing CO2 emissions on Gajahmada Street
Adequeacy of green open space : CO2 absorption -CO2 emissions :

Conclusions and recommendations
The ability of CO2 absorption by vegetation on Gajahmada Street of 1,218.7 tons / ha / year. While emissions resulting from transportation activities at these locations are 6,832 tons / year. It can be concluded that there are residual emissions as large as 5,613.3 tons / year, so that the presence of vegetation is not optimal in reducing CO2. Suggestions given, it is necessary to add vegetation to the pedestrian green space on Gajahmada Street. It is very possible, seeing the density of trees is still low. In addition, the proposed selection of trees with high carbon absorption: such as trembesi.