Potential of carbon storage and sequestration in the Heroes Park City Forest , Purworejo Regency , Central Java

Heroes Park City Forest has a high vegetation density in Purworejo Regency, Central Java province, absorbing and storing carbon from the atmosphere. This study analyzes the value of carbon stock, sequestration, and tree composition in the Heroes Park City Forest. Data collection was carried out in February 2021, using three randomly distributed 20 x 100 m plots. Analysis of carbon stock data, important value index, and diversity index was carried out quantitatively descriptively. The results showed that the carbon stock value of trees was 116.84 tons ha-1, which according to Reducing Emissions from Deforestation and Forest Degradation or REDD+, was included in the high carbon stock category. The value of carbon sequestration in Heroes Park urban forest is 428.80 tons ha-1, which is higher than some city forests in Indonesia. The sampling location is covered with 157 tree species, dominated by Acacia auriculiformis, and has a moderate level of tree diversity. Vegetation dominated by Acacia auriculiformis from Fabaceae contributed 43 percent of the total carbon stock in Heroes Park. Abiotics such as rainfall, air temperature, and humidity in Purworejo City support the growth of plants from the Fabaceae. Therefore, Heroes Park City Forest in Purworejo Regency has high carbon storage or carbon stock and sequestration values and needs to be monitored annually to maintain this potential.


INTRODUCTION
Dynamic urban areas with physical development in various sectors result in disturbances in green open space (GOS) conditions [1,2,3,4]. On the other hand, GOS such as city forests plays a role in maintaining the quality of the urban environment, as city lungs, dust filters, groundwater storage, noise suppression, ecosystem preservation, and global warming mitigation [5,6]. Motorized vehicles, the discharge of industrial waste into the atmosphere, and other anthropogenic activities in urban areas account for seventy-five percent of global carbon dioxide emissions [7,8,9,10]. Disruption to urban forests will reduce vegetation that can absorb and store greenhouse gases such as carbon [11].
The absorption or sequestration of carbon carried out by plants through photosynthesis describes the amount of carbon dioxide (CO2) absorbed from the atmosphere [12,13,14]. In addition, plants also can store a certain amount of carbon or known as carbon stock, in the form of biomass by forty-six percent in their body [15]. According to the Intergovernmental Panel on Climate Change (IPCC), carbon sequestration will be stored in the form of above-ground biomass, below-ground biomass, necromass, litter, and soil organic [16].
Trees, as woody plants, are the significant sinks in absorbing and storing carbon [17]. After the tree died as a necromass, the carbon stored in the biomass will enter the food chain or into the soil as soil carbon [18]. Tree biomass above ground level is influenced by tree size at maturity, life span and growth rate [19], land type, soil type, land management [20], composition, and diversity of tree vegetation [21].
One way to monitor changes in vegetation structure and composition is through vegetation analysis [22]. Changes in vegetation have an essential effect on stability, productivity, trophic structure, movement of ecosystem components, and abiotic factors such as temperature and humidity [23]. The parameters of density, dominance, frequency, species composition, and level of diversity will be measured [24]. Vegetation analysis also analyzes the relationship between changes in vulnerable communities such as green open spaces to micro and macro climates [25].  [28] or city forests in Jambi obtained the value of carbon stock is 164.78 ton ha -1 . Carbon sequestration is 604.20 ton ha -1 [29]. The diversity of carbon stock values in various urban parks is influenced by several parameters, such as plant species diversity, individual density, forest type, vegetation type, climate, rainfall, and topography [30].
Heroes Park City Forest is expected to help optimize the role of urban forests as carbon sinks in the Purworejo Regency. Analysis of vegetation composition, diversity, and monitoring of potential carbon storage needs to be carried out regularly as a database for local governments to monitor environmental conditions. This study analyzes the value of carbon stocks and sequestration and tree composition in the Heroes Park City Forest, Purworejo Regency, Central Java Province. The results of this study can be used as information and input for the Dinas Lingkungan Hidup Purworejo Regency in planning conservation or protection efforts for tree communities in urban GOS.

Research Design
This research is a descriptive quantitative study comparing data on carbon stock and diversity in Heroes Park with similar studies in other city forests in Indonesia. Primary data collection was carried out in February 2021 in the Heroes Park City Forest, Purworejo Regency, Central Java Province. Forest City Heroes Park is geographically located at 7º43'29.91" S 110°00'45.10" E.

Materials and Equipment
The tools used in this research are roll meter, sewing meter, thermohygrometer, laptop, camera, Google Earth Pro application for making sampling maps, Flora of Java identification book, PlantNet application, GPS, label paper, thread, paper, insulation, press, 70% alcohol to preserve specimens.

Data Collection
Measurement of carbon stock and analysis of tree vegetation in Heroes Park was carried out on a plot measuring 20x100 m [20] in three plots randomly distributed over an area of 60,044 m² ( Figure 1). The three plots with a total area of 0.6 ha or 6,000m 2 have been adapted to forest groups with an area of 1,000 hectares with a sampling intensity of ten percent [31].
Tree carbon stock was obtained from forty-six percent of total tree biomass [15,20]. The tree biomass value was acquired by a non-destructive method by measuring the diameter at breast high (DBH), which was entered into the allometric equation (1) [32]. In contrast, the carbon sequestration was obtained by calculating carbon storage multiplied by 3.67 [33].
The trees in the three plots were then identified and validated using an identification book, and a herbarium was made. After that, all trees were analyzed for Importance Value Index or IVI (2) and Shannon Wiener Diversity Index or H' (3) [24].  The criteria for the Shannon Wiener Diversity Index (H') according to Haryadi (2017) are H' < 1 is categorized as low diversity, 1 ≤ H' < 3 is categorized as moderate, and H' ≥ 3 is ranked as high [34].
Abiotic parameters such as air temperature, humidity, and rainfall (obtained from measurement data from the Dinas Pekerjaan Umum dan Penataan Ruang Purworejo Regency) were measured by repeating three times in each plot (except for rainfall data). The abiotic data were then analyzed with tree vegetation biotic data.

Data Analysis
Data on carbon stock, carbon sequestration, composition, and diversity of tree vegetation were analyzed descriptively. This data is compared with the results of similar research in the last five years in the period 2017 to 2021 at city forest locations in other Regencies in Indonesia. Specifically for carbon stock data, it will be validated with the categories issued by Reducing Emissions from Deforestation and Forest Degradation or REDD+ such as low carbon stock (< 35 ton ha -1 ), medium carbon stock (35 -100 ton ha -1 ), and high carbon stock (> 100 ton ha -1 ) [35]. The absorption of pollutants in urban areas is closely related to carbon sequestration by vegetation in the urban forest. The most significant proportion of carbon storage on land is generally found in the tree component [20]. Therefore, optimizing the carbon sequestration process in urban forest areas is a crucial climate change mitigation measure at this time. Each type of plant can grow, and the number of stomata as a way of carbon absorption is different and can affect the process of carbon sequestration [29]. Increasing carbon sequestration in urban forests can also be done by increasing biomass growth by maintaining trees and increasing wood reserves by planting incredibly fast-growing tree species. However, this carbon sequestration will be insignificant if anthropogenic CO2 emissions are not controlled.

Carbon Storage and Sequestration
The tree with the highest carbon stock value in Heroes Park is Acacia auriculiformis from the Fabaceae family. A. auriculiformis trees have a carbon stock value of 50.56 tons ha -1 or 43 percent of the total carbon stock in Heroes Park (Table 2). Compared to other plants of the genus Acacia, Acacia mangium has potential carbon storage of 52.10 tons ha -1 and carbon sequestration of 191.20 tons ha -1 [41]. The advantages of trees from the genus Acacia are that they grow fast, adapt to acidic pH and minimal water sources, and live in various soil types [41]. In forest areas near Purworejo Regency, such as in the Mount Merapi National Park in Sleman Regency the Pinus Mangunan Forest in Bantul Regency, the genus Acacia also dominates in terms of carbon storage compared to other tree species [21,42]. Other tree species with high carbon stock values include Senna siamea (19.27 ton ha -1 ), Pterocarpus indicus (14.14 ton ha -1 ), Tectona grandis (11.74 ton ha -1 ), and Samanea saman (10.43 ton ha -1 ) ( Table 2). The five tree species with the highest carbon stock values have a high total Diameter at the Breast High (DBH), because DBH is the most crucial variable in the allometric equation for biomass measurement [43].

Vegetation Composition and Diversity
The sampling location found 157 individual trees from 19 species (Figure 2) and 11 families. The tree species with the highest importance value was Acacia auriculiformis (88.19%), followed by Tectona grandis (48.15%), Swietenia macrophylla (34.89%), Senna siamea (31.75%), Samanea saman (18.08%) (Figure 2). A. auriculiformis species has the highest carbon stock value and has the highest important value index in Heroes Park City Forest. The basal area and frequency of A. auriculiformis are very high, indicating mastery of the sampling area, and its distribution is very high [24]. The type of T. grandis, known as Teak, actually has the highest density or number of individuals per area but has not outperformed the frequency and dominance values of A. auriculiformis. The IVI value of A. auriculiformis and T. grandis was classified as high according to Fachrul (2007), with an IVI value above 42.66 [44]. Species with a high IVI category have a dominant number of individuals, the level of distribution and control over the soil surface compared to other species [24,45]. If the IVI value of a species of vegetation type is high, then that type significantly affects the stability of the ecosystem [44]. The species T. grandis dominate the city forest in Gresik Regency with the highest IVI value and carbon stock [28]. S. macrophylla or mahogany is the third-highest dominant tree in Heroes Park. The same thing was also reported in the Taman Margasatwa Ragunan City Forest, which was dominated by S. macrophylla [39]. The Meliaceae family can reduce air pollution by about 47 to 69 percent. Senna siamea or Johar and Sennea saman or Trembesi come from the Fabaceae family that dominates in Heroes Park City Forest. The Fabaceae family has a wide distribution, especially in the tropics [46]. The abiotic measurements of air temperature and humidity at the time of sampling were 28.85 °C and 64.82%. Rainfall recorded in February 2021 around Heroes Park was 436.5 mm month -1 because it was entering the peak of the rainy season [47]. During the dry season, such as June to August, the temperature ranges from 25 to 32 °C with rainfall reaching 0 mm month -1 [48]. Environmental conditions with these abiotic factors affect the dominance of A. auriculiformis and T. grandis to maximize growth and development. The Acacia species can grow in the air temperature range between 12 °C to 34 °C, humidity 53%-85%, and optimum rainfall at 2,000 mm year -1 [49,50,51]. The optimal type of T. grandis grows in environmental conditions with rainfall between 1,200-3,000 mm year -1 , temperatures ranging from 22-31 °C, and humidity between 60-80% [52,53].
Based on the calculation results, the tree vegetation Diversity Index (H') in the Heroes Park City Forest, Purworejo Regency is 1.08. These results indicate that the Heroes Park City Forest tree has a moderate level of tree diversity. The species diversity index is essential information about a community. The wider the sample area and the more species found, the higher the species diversity index value. Relatively low diversity index values are common in communities that have reached climax [45]. To maintain high diversity, communities require regular and random disturbances [24]. Usually, after the disturbance has passed, there will be an increase in species diversity to a point where the community reaches a climax. Furthermore, after the climax, there is a tendency for the diversity index to decrease again.

CONCLUSION
The conclusions in this study are as follows: 1. Heroes Park City Forest, Purworejo Regency, Central Java, has a carbon stock and carbon sequestration value of 116.84 ton ha -1 and 428.80 ton ha -1 , which are included in the high category to REDD+. 2. At the sampling location in the Heroes Park City Forest, Purworejo Regency, 19 tree species from 11 families were found, with the dominant species being Acacia auriculiformis.
In addition, Heroes Park City Forest has a moderate level of tree diversity with an H value of 1.08.