Estimation and economic valuation of stands carbon in Tubokarto Community Forest, Pracimantoro District, Wonogiri Regency

Climate change mitigation efforts can be carried out by reducing CO2 gas emissions through the use of the forestry sector, which is expected to increase carbon sequestration. Community forests are composed of stands that have the potential to store carbon stocks so that they can play a role in achieving FOLU (Forest and Other Land Use) Net Sink 2030. This study aims to estimate biomass, carbon storage, and carbon economic value in Tubokarto community forest stands, Pracimantoro, Wonogiri. The method in this study used systematic sampling with random start to measure the DBH and tree height with a sampling intensity of 2% and made 50 sample plots measuring 0.04 ha. The carbon storage value is calculated based on the conversion of 47% of biomass estimated by allometric equations. The results showed that the community forest area of Tubokarto has a total biomass potential of 79.69 tons/ha, total carbon storage of 37.45 tons/ha, and a carbon economic value of Rp 14,605,787.19/ha or if multiplied by the total area of the community forest is Rp 1,329,126,634. The potential and economic valuation of carbon storage in community forests provides an opportunity to achieve sustainable development goals and reduction in carbon emissions.


Introduction
Climate change causes major risks to natural resources that impact food and water security, human health, economy and natural disaster.This has caused extreme weather and climate in every region of the world, such as high rainfall, floods, tornadoes, shifting seasons, and prolonged droughts [1].In addition, human activities can increase the concentration of greenhouse gases (GHG), especially carbon dioxide (CO2) in the atmosphere which has caused global warming with an increase in global surface temperature reaching 1.1°C in 2011-2020 [2].Based on data from the Global Carbon Atlas, Indonesia produces carbon emissions of around 1.67% or 619 million tons of the world's total emissions in 2021 and is the ninth largest carbon emitter in the world [3].One of the biggest contributors to carbon emissions is deforestation and conversion of forests into oil palm plantation areas with an average of around 498 thousand hectares of forest lost every year [4].
Based on Indonesia's FOLU Net Sink 2030 Operational Plan for 2022, the forestry and other land use sector, or known as FOLU (Forest and Other Land Use) is expected to continue to increase carbon sequestration than released until 2050.The forestry sector has a major role in efforts to achieve the national Net Zero Emissions target, especially to offset emissions from sectors that are difficult to suppress such as the energy sector [5].One type of forest that has an important role in storing carbon is community forests.
Based on the results of previous research in the community forest of Sambak Village, Magelang, Central Java, the potential for above-ground carbon storage amounts to 24.53 tons/ha with the dominant vegetation composition being Sengon (Falcataria falcata), Mahogany (Swietenia macrophylla), Coconut (Cocos nucifera), and Jackfruit (Artocarpus heterophyllus) [6].The age of fruit trees in the community forest of Sambak Village, Magelang, Central Java is relatively young because they are dominated by the pole phase.Furthermore, the results of research in community forests in Pekon Kelungu, which has an area of 36 ha, shows that the total carbon storage on the surface was 101.61 tons/ha with the highest dominance from the tree phase to the seedling phase, namely durian (Durio zibethinus), cocoa (Theobroma cacao), and cempaka (Michellia champacha) [7].The types of Multi-Purpose Tree Species (MPTS) plants and wood plants in the community forests in Pekon Kelungu are large and long-lived trees.The results of these studies prove that community forest has biomass potential that can be one of the solutions in overcoming global climate change with its ability to absorb, and store carbon stocks to help reduce GHG emissions, especially CO2 in the atmosphere.
Tubokarto is one of the villages in Wonogiri Regency which has a community forest covering an area of 91 ha.The existence of community forests can be a potential store of carbon stocks that have economic value and can be a consideration for the implementation of carbon trading activities in the research area.The carbon potential and economic value in the Tubokarto community forest have never been reported before.Therefore, this research needs to be conducted to find out how much carbon storage potential and economic valuation of Tubokarto community forest.This study aimed to estimate the potential of biomass and carbon storage with the carbon economic value in community forest stands in Tubokarto Village, Pracimantoro District, Wonogiri Regency, Central Java, Indonesia.

Study Area
The location of data collection for research on the estimation and economic valuation of stands carbon is focused on the community forest area, which is located in Tubokarto Village, Pracimantoro District, Wonogiri Regency, Central Java, Indonesia.Tubokarto village is located between 8°01'42"S and 110°49'05"E.The community forest area in Tubokarto Village is 12.96% (0.91 km 2 ) of the total administrative area of 7.02 km 2 .Based on Central Agency of Statistics data for Wonogiri Regency [8], the average annual rainfall is 207.83 mm per month in 2022.The highest rainfall occurs in November, with 19 rainy days and a total rainfall of 486 mm.The average air temperature in Pracimantoro District during the dry season and in the rainy season is a maximum of 35°C and a minimum of 19°C with an average humidity of 92%.

Figure 1. Map of the study area in the Tubokarto community forest
Tubokarto village is including Pracimantoro district which is part of the Gunung Sewu Karst region which stretches from Gunung Kidul Regency in the west to Pacitan Regency in the east [9].The topography of Pracimontoro Karst consists of coral hills, some of which are still covered with trees and more shrubs [10].

Methods
The estimation of standing biomass in this study used a non-destructive method.Sampling locations were determined using a purposive sampling method.Meanwhile, measuring plot points were selected using a systematic sampling method with a random start.Data collection on stands was carried out in the pole phases (diameter 10-19 cm) and tree phases (diameter ≥ 20 cm) because these phases have a longer harvest or cutting time compared to agricultural crops, making it possible to estimate carbon stocks.The data collected included tree species and diameter at breast height (DBH).Data were collected using square plots of 50 sample plots made by nested sampling with the area of each plot being 20 x 20 m for tree-level stands and 10 x 10 m for pole-level stands.The sampling intensity used was 2% of the 91 ha area of Tubokarto community forest.The sampling intensity carried out was based on limited costs and energy used.

Data analysis
The data normality test needs to be carried out as a result of using parametric inferential analysis techniques which require the assumption that the data is normally distributed [11].In this study, the normality test was carried out quantitatively by using the Kolmogorov-Smirnov and qualitatively by using a histogram and normal curve.The Kolmogorov-Smirnov normality test was carried out on the SPSS 16 software with the following criteria [12]: a) Significance (α) = 0.05 b) Significance (α) < 0.05 means the data is not normally distributed c) Significance (α) > 0.05, the data is normally distributed The biomass of community forest stands was calculated using allometric methods [13].This model was chosen because the analysis results by combining the relationship between diameter, tree height, and the average wood density of trees produce a better estimate [14].Allometric equations according to the formula [13] are as follows: Definitions: W = Biomass (kg/tree) ρ = Density of wood (g/cm 3 ) D = Diameter at breast height (cm) The estimation of carbon from stands biomass is calculated using the formula from the National Standardization Agency (SNI 7724) [15]: Cv = Bov × % Organic C (2) Definition: Cv = carbon content of vegetation biomass (kg) Bov = total vegetation biomass (kg) % organic C = percentage value of carbon content of 47% or 0.47 To calculate the economic valuation of forest standing carbon valuation, this study used a price of 25 USD/ton of carbon [16].Based on a study from the International Monetary Fund (IMF), Indonesia is classified as a developing country, so it uses a carbon price of US$ 25/ton.

Result and Discussion
Community forests have an ecological and economic function.Community forests are ecologically capable of storing carbon stocks in the form of biomass, necromass and soil organic matter [6][7].In addition, community forests have a very important role in maintaining water management and soil fertility, minimizing soil erosion, flooding, and landslides, and can contribute to overcoming global warming by absorbing CO2 emissions in the atmosphere [17].Community forests are economically capable of facilitating the process of increasing awareness of the need for sustainable forest management [17] as well as being a guiding tool for public policymakers or decision-makers involved in climate change [18].Thus, community forests are expected to contribute to climate change mitigation efforts by reducing national greenhouse gas emissions [19].

Potential vegetation of the Tubokarto community forest
From the results of research conducted in the community forest area of Tubokarto Village, with a total of 50 observation plots, there are a total of 660 individuals with 18 different species.Overall, in 660 individuals, there are two dominant species, Tectona grandis 62.0% (409 individuals) and Swietenia mahagoni 17.7% (117 individuals) (Table 1).Teak and Mahogany are types of timber plants that are often found in community forests in Java because they are easy to plant, manage, and market and have high economic value [20].Therefore, the people of Tubokarto Village prefer Teak and Mahogany to be planted on their land.The least species found were Artocarpus camansi, Leucaena leucocephala, and Samanea saman with 1 individual each.The stands that composed Tubokarto community forest have a high diversity of species and different numbers.High species diversity shows the level of stability of a community to grow [21].This stability can help an ecosystem in dealing with various existing disturbances [22].The diversity of stand types at different growth phases leads to various diameter distributions.

Normality test
The data normality test needs to be carried out as a consequence of using parametric inferential analysis techniques which require the assumption of normally distributed data [11].In this study, the normality test was carried out quantitatively by using the Kolmogorov-Smirnov and qualitatively by using a histogram and normal curve.Quantitative normality test results are presented in Table 2.The Kolmogorov-Smirnov normality assessment was carried out by comparing the distribution of the data in the samples and the margin of error (α) of 0.05.The data is normally distributed if the significance value is > α (0.05).It can be seen in Table 2, the value of the data distribution in all samples for each variable has a significance of more than 0.05.This indicates that the sample used is normally distributed.To see the qualitative results based on visual analysis of the histogram and normal curve are presented in Figure 2. Based on Figure 2, it can be seen that most of the sample data are in the normal curve.This shows that the sample is normally distributed.Some data appear outside the normal curve range, indicating outlier data or overvalued compared to the overall sample data set.The normal distribution is a certain distribution which, when formed into a histogram, has the characteristic of a bell shape [12].The normality test for the entire stand (Figure 2a) has a bell-shaped curve although it is slightly more skewed to the left, this indicates that the data is normally distributed.Likewise, the normality test for the pole phase (Figure 2b) and the tree phase (Figure 2c), has a bell-shaped normality curve.Samples that have been tested for normality and data significance are expected to represent the original conditions as best as possible.

Diameter distribution of Tubokarto community forest
The diameter distribution and number of individuals are presented in Figure 3.The figure shows that the community forest in Tubokarto Village has variations in diameter class for each species in the pole and tree phases.The diameter distribution of entire stands in Tubokarto community forest is divided into 10 diameter classes (Figure 3a).The first diameter class (10-14 cm) and the second diameter class (14-18 cm) contained 137 and 72 individuals, respectively.This number is less than the third diameter class (18-22 cm), which is 235 individuals.In the fourth diameter class to the ninth diameter class, the number decreases, then increases slightly in the tenth diameter.In the pole phase, there are 9 classes of diameter distribution (Figure 3b).Where, the diameter class with the highest number of individuals was in the first diameter class (10-11 cm), namely 60 individuals and the diameter class with the least number of individuals was in the eighth and ninth diameter classes with 9 individuals each.While in the tree phase, there are 10 diameter distribution classes (Figure 3c).It can be seen that as the diameter increases, the number decrease.Overall, it can be seen that the larger the diameter of the stand, the number of individuals will decrease.Variations in stand diameter distribution are caused by the ability of each tree species to carry out the photosynthesis process, the availability of nutrients in the soil and due to competition between individuals [23].
In Figure 3c, it can be seen that the distribution of diameters in the tree phase has a shape like an inverted J curve.This is supported by the results of a study [24] which stated that the diameter distribution of stands in community forests showed a shape resembling an inverted J.The larger the diameter of the stand, the number will decrease.This situation is close to the characteristics of normal forests in natural forests.The inverted J curve is a feature of natural forests where the distribution of small diameter classes dominates the forest area and decreases in larger diameter classes [25].However, at this time the existence of natural forests has been decreasing due to deforestation and forest degradation which are the main causes of climate change.This is by the FAO statement which states that the area of primary forest worldwide has decreased by more than 80 million hectares since 1990 [26].Thus, reserves and absorption of carbon that could previously be stored by natural forests are reduced.The results of this study indicate that the existence of community forests can be an alternative to mitigating climate change with its potential to store and absorb carbon.

Biomass and carbon storage estimation in Tubokarto community forest
Stand biomass content in this study was calculated based on aboveground biomass, which is the potential biomass in tree trunks.This is because tree trunks have the largest biomass of the total aboveground biomass [24].Table 2 shows the result of biomass and carbon calculation of stands from each species in the Tubokarto community forest.It can be inferred from Table 2, that the Tectona grandis have the highest biomass and carbon storage of 41.28 tons/ha and 19.40 tons/ha, while Leucaena leucocephala has the smallest biomass and carbon storage of 0.11 tons/ha and 0.05 tons/ha.The type of plant affects the biomass and carbon stocks in a stand, this is due to the wood-specific gravity values owned by each tree species [25].Tubokarto community forest has an ecological function in maintaining the balance of the ecosystem, one of its functions is to maintain the climate both inside and outside the area by absorbing CO2 through the process of photosynthesis.Based on Table 2 above, it can be seen that the biomass and carbon stocks in the Tubokarto community forest are respectively 79.69 tons/ha and 37.45 tons/ha.Besides being seen from the species, biomass and carbon can also be seen from the diameter class.An estimate of carbon storage in a unit area (t ha -1 ) of the Tubokarto community forest based on diameter class is shown in Figure 3. From Figure 4, the largest of stands carbon stock is in the third diameter class (18-22 cm) which is 11.13 tons/ha, this is comparable to the number of individuals.Meanwhile, the lowest carbon stock is in the ninth diameter class (42-46 cm), which is 0.32 tons/ha.If it is converted into the area of the Tubokarto community forest, by multiplying the carbon stock per hectare by the area of the community forest (91 ha), the total carbon stock is 3,408.24tons.The value of biomass is directly proportional to the value of carbon storage (Figure 4).If the biomass is large, the carbon stored is also large.The difference in the value of both biomass and carbon in each diameter class is due to the number and diameter of trees at breast height (dbh) in the sample plot.The more CO2 absorbed by plants and stored in the form of carbon biomass, the greater the adverse effect of the greenhouse gas effect that can be controlled [26].

Carbon economic valuation in Tubokarto community forest
Carbon economic assessment is important to do to find out how big the potential of community forests is to participate in climate change mitigation.This is supported by research related to the economic valuation of community forest carbon in Pajangan District, Bantul, DIY which has a carbon economic value of Rp. 2,546,751,882.00 (carbon price = US $ 12/tonne) with an area of 1027,604 ha [27].This proves that an economic assessment of carbon in community forests needs to be carried out.This study used carbon prices of US$ 25 per ton of carbon [16].Based on the USD-Rupiah exchange rate on November 22, 2023 (IDR 15,599), the price of carbon per ton after conversion to Rupiah will be IDR 389,975.The results of calculating the carbon economic value of each species in the Tubokarto community forest are presented in Table 4. Based on Table 3 it can be seen that the economic value of carbon in the Tubokarto community forest with a total area of 91 ha and carbon stocks of 3,408.24tonnes is Rp.1,329,126,634.Even though the potential value of the resulting carbon stock is not very large, this shows that community forests can reduce greenhouse gas emissions in Wonogiri, especially in Tubokarto Village.The results of calculating the economic value of this carbon can be used as an argument regarding the benefits of community forests.One of the benefits is that community forests can store carbon and absorb CO2 so it can be one of the efforts to mitigate climate change.

Conclusion
From the results of the research and discussion that has been described, it can be concluded that the stands of the Tubokarto community forest are dominated by teak (Tectona grandis).The amount of biomass in the Tubokarto community forest is 79.69 tons/ha.The value of this biomass contains carbon stocks of 37.45 tons/ha.The total carbon potential is 3.408,24 ha with an economic value of carbon obtained is Rp.1,329,126,634.The great potential in terms of storing carbon proves that the role of the Tubokarto community forest is quite large in maintaining the climate balance in Wonogiri Regency in particular.To increase and maintain carbon stocks in the Tubokarto community forest, consistency in management is needed for the sustainability of the community forest.The potential and economic valuation of carbon storage in community forests provides an opportunity to achieve sustainable development goals and reduction in carbon emissions.

Figure 2 .
Graph of normality test results for community forest stands in Tubokarto Village.a) Entire stands; b) Pole phase; c) Tree phase

Figure 3 .
Figure 3. Diameter distribution of community forest stands in Tubokarto Village.a) Entire stands; b) Pole phase; c) Tree phase

Figure 4 .
Figure 4. Biomass and carbon storage potential of stands in Tubokarto community forest

Table 1 .
Stands composition of Tubokarto community forest.

Table 2 .
Results of the normality test using the Kolmogorov-Smirnov

Table 3 .
Stands biomass from each species in Tubokarto community forest.

Table 4 .
Carbon economic value of Tubokarto community forest