Assessing carbon pools in Lemo Nakai community forest Bengkulu

Carbon sequestration and stockpiling in Indonesian community forests become a pressing issue in the context of efforts to mitigate climate change and Indonesia’s contribution to the Sustainable Development Goals. This investigation aimed to determine the carbon stocks at various forest structures within the Lemo Nakai (CF) community forest. The CF encompasses an area between 3°25‘59,588” - 3 27‘57,982” in altitude and 102°19‘25,108” - 102°22‘23,416” in length. The research was conducted between February and July of 2022. The estimated biomass in dense, medium, and sparse forest structures was 601 tons ha-1, 443 tons ha-1, and 241 tons ha-1, respectively, with carbon reservoirs of 276 tons ha-1, 204 tons ha-1, and 111 tons ha-1, respectively. In addition, the estimated CO2eq absorption in dense, medium, and sparse forest structures were 1,013 tons ha-1, 748 tons ha-1, and 406 tons ha-1, respectively.


Introduction
Forests have a crucial role in providing important environmental, social, and economic advantages to nearby people.In contemporary discourse, there is an emerging perspective that emphasizes the multifaceted objectives of forest management, extending beyond the traditional focus on timber and non-timber product extraction.This evolving paradigm recognizes the importance of forests in providing a diverse range of ecosystem services.Forests offer a valuable ecological service by engaging in the process of carbon dioxide sequestration from the atmosphere via photosynthesis, followed by the subsequent storage of this carbon within the forest biomass [1].Moreover, while considering various ecosystems across the globe, it is seen that tropical forests exhibit the most significant capacity for carbon sequestration.This can be attributed to the abundant availability of sunshine and water in these places, which persists consistently throughout the year.These parameters are further corroborated by the climates, specifically the temperature and humidity, which are conducive for the best growth of numerous tree species.Tropical forests fulfill a significant function in the process of global carbon sequestration [2].The entity in question represents a significant carbon sink on a global scale, accounting for approximately 45% of the total terrestrial carbon storage on Earth.Furthermore, it demonstrates the capacity to absorb a substantial amount of atmospheric carbon dioxide, estimated at 2.4 billion tons annually [3].The majority of the carbon that is sequestered by the forest is stored inside the above-ground biomass of the trees.The carbon sequestered inside forest biomass possesses the potential to serve as a mitigating factor for climate change, specifically in relation to the phenomenon of global warming.
IOP Publishing doi:10.1088/1755-1315/1297/1/012090 2 Indonesia is currently confronted with significant challenges pertaining to deforestation [4].Nonetheless, a significant dearth of knowledge persists regarding the intricate mechanisms that contribute to deforestation, encompassing both direct and indirect factors that promote the loss of forests, particularly at the national and regional levels [5].Moreover, a significant portion of the population residing in or in proximity to these forested areas heavily relies on forest resources for their sustenance.However, their means of subsistence are jeopardized due to the detrimental effects of deforestation and the unsustainable use of forested resources.The optimal utilization of the nearby forests, which serve as a valuable national resource, should be prioritized for the benefit of these communities [6].In addition, it is imperative to ensure the equitable distribution of forest utilization by means of community engagement activities, so fostering empowerment and the realization of their full potential.The attainment of maximum advantages would be possible if forest management endeavors were able to generate forests of superior quality and sustainability, with a focus on the populations residing in close proximity to these forested areas.Community forest management has been recognized as a mutually beneficial approach for mitigating deforestation and enhancing the well-being of rural people in Indonesia.
Community forests are designated as state-owned woods that are specifically managed to empower local communities residing in forested areas.The active participation of the community in forest management is vital for the preservation of forest sustainability and the promotion of community well-being [7].Community forest management (CFM) initiatives have been implemented with the primary aim of conserving forests and facilitating the sustenance of local communities, namely in terms of fulfilling their daily need for fuel wood, fodder, timber, and various non-timber forest products.Community forest management programs have become increasingly prevalent as a widely adopted approach, with numerous developing countries currently engaged in the process of formulating and executing policies and pilot initiatives.The initiative was established with the dual purpose of fostering sustainable forest management and mitigating environmental deterioration in order to enhance livelihoods.In this particular scenario, community forests are anticipated to play a crucial role in the stabilization of timber supply and the mitigation of greenhouse gas emissions inside the atmosphere.
The productivity of community forests is a crucial factor in determining their fundamental function in carbon reduction.The accumulation of forest biomass is a key contributor to this process [8].Nevertheless, there has been a limited number of research conducted thus far regarding the carbon dynamics of community forests.In order to assess the strategic role of community forests in aiding climate change mitigation, it is imperative to accurately quantify the biomass and determine the carbon stock present in these forests [9].Previous study was conducted to estimate aboveground carbon stocks based on spatial distribution of the forest structures, and this following study aims to assess carbon pools in the Lemo Nakai community forest, Bengkulu Province.

Materials and methods
The research was carried out between February and July 2022 in the Lemo Nakai community woodlands, located upstream of the Nakai river.This river serves as a water source for irrigating rice fields in Baturaja Village and the surrounding downstream areas of North Bengkulu District, Bengkulu Province, Indonesia.The geographical coordinates of the place are situated between 3°25'59,588" and 3°27'57,982" altitude, and 102°19'25,108" and 102°22'23,416" longitude.The area covered by this location is approximately 1,053.53 hectares, as shown in Figure 1.The forest topologies depicted in Figure 2, as well as the above ground biomass and carbon stocks, were obtained from a prior work that utilized allometric equations.These equations were employed to accurately estimate the biomass of individual trees within the Lemo Nakai community forests.
Root biomass was calculated as follow: RB = (RT) ratio x TB (1) Note: RB = root biomass (kg), RT = root tree ratio, TB = tree biomass (kg) RT ratio depends on tree species, ecosystems, soil conditions, altitude, and climate therefore in this case the RT ratio just followed the value in the tropical rain forests, (0.37).Conversion of the RB to root carbon stock (RC) which used a conversion ratio of 0.46.
The RC calculated as follow: RC = RB x 0.46.
Subsequently, this investigation employed the following calculation to assess the carbon sink to determine the amount of carbon dioxide absorbed by the Lemo Nakai community woods as follow: CO2 = carbon stocks (ton ha-1) x 44/12 (3) The soil sampling technique with purposive method was carried out by a descriptive exploratory survey based on the existing forest structures.The composited disturbed soil samples were taken from 5 point in the plot sample 5 x 5 m 2 .The undisturbed soil samples for bulk density (BD) analysis and disturbed soil samples for analysis carbon soil content were taken from 3 different soil depths involved 0 -10 cm, 11 -20 cm, and 21 -30 cm, and at 3 different forest structures consisted of dense-, medium-, and sparse forest with 2 replications.
To determine BD (g cm -3 ) using an equation as follow: BD = SW/SV in which SW is the soil sample weight (g) and is the soil sample volume (cm -3 ).The determination of total soil carbon, which encompasses both organic and inorganic carbon, has traditionally been conducted through wet combustion analysis of soils using chromic acid digestion.This method has established itself as a standard approach for quantifying total carbon content, and the carbon calculation as follow [10]: Ct = SD x BV x C (gram cm 2 ) which Ct is the total soil carbon (gram/cm 2 ), SD is soil depth (cm), BD is bulk density (g cm -3 ), and C is the percentage of the total soil C analysed (%).The total carbon stocks in the Lemo Nakai community forest in each forest structure within wide area of ha were the in the accumulation carbon determined from the above ground carbon stock and below ground carbon pools both from root carbon and the total soil carbon.

Results and discussion
The Lemo Nakai community forest occupies areas about 1,053 ha relatively well protected by the local people because of this area lying on the upstream of the Nakai sub-watershed as a protection area for maintaining irrigation water supply at the Baturaja village rice fields and the close areas.The forest structure condition from the previous study shown in well maintained involved the dense-, medium-, and sparse forest covered about 753.69 ha, 232.41ha, and 32.49 ha, respectively [11] so about 71.57% from the Lemo Nakai landscape covering with the deciduous tropical rain forest and 22.07% interfered by the local people with agroforestry management.The local population, guided by their traditional belief systems and commitment to conservation, has demonstrated their ability to effectively preserve forested areas.This has resulted in the continued availability of natural resources and ecosystem services that are essential for the well-being of the human population residing in the vicinity [12].Furthermore, the local people considered the forest as a protected area, and it could be accessed or used at certain times only therefore the forest areas maintained its sustainability.
Moreover, utilizing the previously mentioned data, the calculation of the above-ground biomass for the Lemo Nakai resulted in values of 389.74 tons ha-1, 278.88 tons ha-1, and 149.28 tons ha-1 for dense, medium, and sparse structures, correspondingly.The carbon stock values for each comparable area were calculated to be 179.40tons per hectare, 128.29 tons per hectare, and 68.67 tons per hectare, respectively.The Lemo Nakai area, situated adjacent to the Bagdaila Chisapani community forest in the Dang district of Nepal, had an average above-ground carbon (AGC) content of 160.4 tons per hectare (ha-1), when compared to other geographical locations [13].On average, tree biomass accounts for around 60% of the carbon store.Mixed forests have the highest carbon stock, reaching up to 316.64 tons per hectare, followed by plantation forests at 247.19 tons per hectare, and cropland at 51.57 tons per hectare [14].A study was done in Ngoyili forest, situated inside the Lesio-louna protected area in the South-Eastern Republic of Congo, to investigate the quantities of aboveground biomass (AGB) and belowground biomass (BGB).The findings revealed that the average storage of AGB was 273.1 tons per hectare, while BGB accounted for 81% of the total biomass, equivalent to 64.1 tons per hectare, or 19% of the total biomass [15].
Based on the AGB from previous study, the root biomass and the carbon sink in the roots calculated as Table 1.Following the above ground biomass, the total soil carbon contents in the Lemo Nakai community forest with the dense and medium forest structure were also higher than those in the cultivated annual crops lands and the bare lands.The total soil carbon contained in the Lemo Nakai were showed in Table 2. Comparing to other researches, the soil carbon in the Lemo Nakai just equal to the mean SOC observed upto 30 cm soil depth in Ganesh and Ramnagar community forest Nepal containing of 42.55+ 3.10 tons ha -1 and 54.21+ 3.59 tons ha -1 , respectively and the maximum SOC was noticed at 0-10 cm [16] but much lower than the organic carbon stock in soils of Tessala Mount area has an average value of 77.4 tons ha −1 [17].
The mean biomass, carbon pools, and estimated CO2eq at each forest structure in the Lemo Nakai community forest as shown in Table 3.  [20].Similarly, the biomass and carbon stock in Depard community forest, Manahari-6, Makwanpur district of Nepal were 563.12 tons ha-1 and 242.42 tons ha-1, respectively [21].Hence, it can be inferred from this study that the expansion of forests has the capacity to mitigate regional and global atmospheric carbon emissions.Additionally, it is evident that community-based forest management holds promise in terms of generating tree biomass.In order to address the issue of global climate change, active engagement of local communities in the sustainable management of community forests plays a crucial role in enhancing carbon sequestration.

Conclusions
The Lemo Nakai community forest, the upstream of Nakai sub-watershed plays important services for human being in downstream areas mainly as maintaining continuous water supply for the rice fields.The Lemo Nakai areas mostly well forest conditions which is covered about 70% of the virgin forest.Local people only used about 25% areas of the Lemo Nakai for agroforestry systems and no more 5% as unproductive areas.As a virgin forest, the Lemo Nakai stores high biomass and carbon stocks and the Batu Raja Village Communities and closed local people has a role in maintaining the forest in sustainable ecological services such as sources of water supply for irrigation rice fields, camping grounds and tourism areas.Based on the insights gained from the local community, it is evident that the Lemo Nakai community forest possesses the capacity to effectively preserve tree biomass, thereby contributing to the mitigation of carbon emissions inside the atmosphere.The involvement of local communities, specifically those residing in Baturaja village, in the sustainable management of forests contributes to the sequestration process and aligns with strategies aimed at mitigating global climate change.

Table 1 .
The biomass and carbon stock Forest Structure

Table 2 .
Total soil carbon

Table 3 .
[18]mean biomass, carbon pools, and CO3eqThe natural forest covering with the dense structure trees is much more biomass and carbon sink comparing with the agroforestry forest with medium trees cover in the Lemo Nakai community forest.The mean biomass and carbon stock in natural forest were found to be greater in comparison to those observed in agroforestry systems[18].The natural forest in the Lemo Nakai sinks the carbon about 276.48 tons ha-1 which closed to the carbon stock of rich forest in Ba Be National Park, Bac Kan Province Vietnam reaching 273.17 tons ha-1 while at the medium forest, 136.23 tons ha-1 and the poor forest, rehabilitated forest is 42.06 tons ha-1 [19] were much lower than that of in the Lemo Nakai.Furthermore, it is worth noting that the carbon stock in the aforementioned area has a significantly greater magnitude when compared to the carbon stocks found in Suan Phueng Nature Education Park, located in Ratchaburi, Western Thailand.Specifically, the carbon stocks in the dry evergreen + mixed deciduous forest of Suan Phueng Nature Education Park amount to 203.83 ± 82.74 Mg C ha-1, while the carbon stocks in the mixed deciduous forest stand at 145.46 ± 47.90 tons C ha-1