Estimation of Carbon Stock Due to Land Cover Change in Small Islands: A Case of Gili Matra Islands, Indonesia’s Marine Tourism Park

As a small island cluster, Gili Matra (Meno, Trawangan, and Air) is the main tourist attraction in West Nusa Tenggara. The trend of population growth in Gili Matra, as well as the trend of tourist visits, continues to increase. It needs to be more balanced between the demand for living space and developing tourism-supporting facilities. As a result, land cover changes are unavoidable, significantly reducing the non-built-up areas. Land cover changes have an impact on ecosystem and climate control functions. The signs of climate change in small islands, such as extreme weather, sea level rise, and coastal abrasion, are starting to be felt. The purpose of this study is to calculate the conversion of carbon stocks based on land cover changes in Gili Matra from 2013 to 2022. The analytical method used to land cover change and analyse carbon stocks. The research showed that the built-up areas increased from 126.84 hectares to 223.55 hectares from 2013 to 2022. Meanwhile, non-built-up areas such as sand beaches, plantations, bare areas, shrubs, and mangrove areas decreased from 576.56 to 479.84 hectares. In addition, mangroves, plantations, and shrubs, three examples of land cover with the highest carbon conversion, have decreased by 28.67%, 11.25%, and 6.36%, respectively. The total carbon stock on Gili Matra in the 2013–2022 period has decreased by 1,802.08 tons C. It indicates increased carbon emissions due to land cover changes in Gili Matra caused by increased demands on space for settlements and tourism support facilities.


Introduction
Gili Meno, Gili Air, and Gili Trawangan (Gili Matra) are a group of islands as well as a Marine Tourism Park (TWP) designated as a National Strategic Area according to the Decree of the Minister of Forestry No. 85/KPTS-II/1993.Then, in 2001, it was designated an Aquatic Nature Conservation Area based on the Decree of the Minister of Forestry No. 99/KPTS-II/2001.In addition, 2009, Gili Matra was also designated as a National Marine Protected Area according to the Decree of the Minister of Maritime Affairs and Fisheries No. Kep.67/MEN/2009.Moreover, administratively, Gili Matra is in Gili Indah Village, North Lombok.It has a total land area of 2,954 hectares [1].As a conservation area with enormous natural resource potential, Gili Matra requires regulations to ensure that its utilization does not exceed its carrying and environmental capacity.The vulnerability of Gili Matra continues to increase over time, despite its natural beauty and abundance of natural resources [2].The vulnerability was measured using the coastal water quality index variables, the degree of relationship between environmental status and tourism, heterogeneity, the spatial connectivity index, biocapacity, the ecological footprint, and a systematic approach to assess capacity and adaptive cycles.In addition, small islands suffer a variety of environmental problems, both directly and indirectly related to land cover changes [3].Small islands with limited carrying capacity, small island size, marginality, and local economic dependence on the mother island make this area vulnerable to environmental demage, especially climate change.Climate change can cause sea level rise, enormous waves, and other disasters [4].
Gili Matra also has a dependency on the tourism industry.The tourism sector in Gili Matra continues to increase.It is evident from the annual increase in the number of tourists.When Gili Matra became widely known to tourists in 1999, the number of tourists reached 25,614 and continued to increase until 2022, totalling 255,701 people [5].Even though there was an earthquake in 2018, followed by the IOP Publishing doi:10.1088/1755-1315/1310/1/012002 2 COVID-19 pandemic in 2020-2021, domestic and foreign tourists were encouraged to visit Gili Matra.The development of the tourism industry does increase the demand for space for tourism-supporting facilities.Furthermore, the growing number of tourists visiting Gili Matra increases the population each year.Over 2000-2022, the ratio of population growth in Gili Matra has increased almost double (2,813 people to 4,848 people) [6].This population growth trend and tourism have resulted in the conversion of non-built-up areas to built-up areas.Land cover changes are a form of human interference with natural and artificial resources referred to as land use [7].Land use in each land cover will continue to change in line with living space demands.If the increasing demand for land for residences and tourismsupporting facilities is not managed, it may threaten environmental sustainability.The problem is that the policies governing space use in Gili Matra overlap.Many things can be more consistent between one procedure and another.As a result, space utilization in protected areas is unavoidable.If this condition is not considered and occurs massively, it will interfere with the balance of the ecosystem, causing environmental degradation on the small islands.Small Islands face challenges in planning, implementing, and controlling space utilization activities for development due to limited area, limited resources, its geographical isolation, and its reliance on nearby larger islands [8].
Non-built-up areas with diverse types of vegetation, such as shrubs, mangroves, plantations, and open land, contribute to the sequestration of carbon released into the atmosphere because of multiple human activities (carbon footprint).The land is a source of greenhouse gas emissions and a carbon sink that stores carbon and prevents it from entering the atmosphere.Therefore, changes in land cover can trigger an increase in GHG emissions [9].If land conversion continues to increase, the vegetation that absorbs carbon will become scarcer, increasing carbon emissions on Gili Matra Island.Therefore, land cover change analysis is essential to determine potential carbon availability [10].The accumulation of carbon emissions in the atmosphere increases the earth's temperature and contributes to climate change.Meanwhile, small islands such as Gili Matra are highly vulnerable to climate change.Therefore, this study aimed to classify land cover types in Gili Matra, describe changes in each land cover class, and measure the potential conversion of carbon absorption capacity based upon the area of land cover type in the 2013-2022 period.This study is critical because reducing carbon emissions is an important thing to focus on in this era of climate change [11].
Many studies on land cover change have been conducted in various locations, including Gili Trawangan.However, there have yet to be studies investigating land cover changes that accommodate three Gilis: Gili Trawangan, Gili Air, and Gili Meno.The previous study on spatial resilience in Gili Matra [2], One part of his research included identifying land cover from 2013 to 2017.The state of the art of this study is: 1) the scope of the research area consisted of three Gilis, allowing comparisons of land cover changes at three location points in the island group unit to be conducted; 2) the researchers used the most recent land cover period, namely the last ten years (2013--2022), which distinguished this study from previous studies; 3) using Sentinel 2-A imagery to double-check the mangrove ecosystem areas that with the highest conversion of carbon stocks; 4) combining land cover change analysis with the potential conversion of carbon absorption of each land cover class in Gili Matra.In addition, in this study, the researchers provide an overview of the dynamics of carbon stocks based on land cover classes that will contribute to climate change on small islands.
Remote sensing methods are one method of monitoring land cover change data [12].The image used Google Earth imagery because it has time series data and a high-resolution image.In addition, Sentinel-2A imagery was explicitly used to observe the distribution of mangroves.The mangrove vegetation in Sentinel Imagery was more clearly visible and could be compared during the image interpretation process from Google Earth.Moreover, land cover maps were used as basic information to determine changes over a predetermined timeframe.Furthermore, the researchers used conversions from the 2012 Directorate General of Forestry Planning standards and the classification from the 2010 National Standardization Agency of Indonesia (BSNI to analyze carbon stocks [13].Knowing the changes in the conditions of land cover and the carbon stocks stored in each type of land cover will provide an overview of the reduced ability of the environment to absorb carbon, causing an increase in Greenhouse Gases (GHG) emissions in the atmosphere.As a result, it will threaten small islands (Gili Matra) vulnerable to climate change.This carbon stock information can become an input for area planning and implementing spatial use according to its function while continuing conservation efforts in protected areas to suppress various bad future possibilities.Moreover, land use planning is also required to be carried out to reduce carbon emissions as a climate change mitigation strategy [14].The consequences of negligence in managing small islands and coastal areas in Indonesia have led to the loss of four islands around the Kepulauan Seribu.Of course, an implemented strategic policy is needed to anticipate such incidents [15].

Methodology
Gili Matra is geographically located between 116°01′34′′ -116°12′11′′ East Longitude and 8°20′02" -8°22′16" South Latitude.This small island is administratively in North Lombok Regency.Gili Matra has a total land area of about 703.4 hectares.The time for conducting research was four months, which was March-June 2023.The stages in carrying out this study consisted of the preparation stage, the initial data collection stage, field observations and ground checks, data management and the preparation of scientific journals.

Figure 1 Research Location
This study used secondary and primary data.Secondary data include 1) satellite imagery (Google Earth and Sentinel 2A), 2) administrative boundary map shapefiles in Gili Matra, 3) population data, 4) tourist visit data, 5) spatial plan documents, and 6) the determination of the Gili Matra area.Moreover, primary data was gathered by conducting field checks between data of land cover obtained from the satellite picture/imagery interpretation and the current conditions on Gili Matra.Furthermore, interviews were also conducted with key actors, consisting of five respondents who knew were knowledgeable about the history of the development of land cover changes in Gili Matra.The primary survey was also carried out to determine the condition of the various types of land cover, take pictures of each land cover, and cross-check the location of land cover changes.
A descriptive method and a satellite image analysis method were used as analytical methods in this study.The descriptive analysis explains the causes and effects of land cover changes and their relationship with carbon stocks [16].The ideal method in question addressed the interpretation of satellite imagery regarding changes in Gili Matra's land cover and the factors and impacts of climate change on small islands.Moreover, satellite imagery analysis used satellite imagery data (Google Earth) from 2013 to 2022.The stages of satellite imagery analysis began with image cropping according to the study area, image sharpening, image interpretation, sample selection using supervised classification, accuracy testing, geospatial analysis, and the creation of map layouts of land cover from 2013 to 2022.The two land cover data sets were overlaid, and then various land cover changes were observed [17].In addition, at the image interpretation stage, the researchers used sentinel 2A imagery as material to double-check land cover, mainly mangroves.The sentinel 2-A image has a higher spatial resolution, allowing for more precise identification of mangrove density.The band combination used is 11-8-4, which was intended for vegetation analysis.Furthermore, band 11 (Shortwave Infrared: 1610 nm) was on the red channel, band-8 (Near Infrared: 842 nm) was on the green-channel, and band 4 (Red: 665 nm) was on the blue-channel.According to the study's result [18], sentinel-2 imagery was the best combination for identifying mangroves.
The ground check stage collected sample points for each land cover class using GPS on each island (Gili Trawangan, Gili Meno, and Gili Air).Ground check results were used as a comparison for accuracy test analysis.The coordinates were determined using a purposive random sampling method, which involved taking random samples of every land cover type.The samples were prioritized for locations that had experienced land cover changes, were easy to access, had a different appearance from the others, and could represent the distribution of land cover on Gili Matra.
The method used in the accuracy test analysis used a confusion matrix.This error matrix aimed to determine deviations or misclassifications in excess or a lack of pixels in each class.Moreover, \ the classification results in the accuracy test were obtained from the the user's accuracy, producer's accuracy, overall accuracy, and Kappa statistics [19].An OA value of more than or equal to 70% indicated that the image was considered accurate [20].In addition, the classification of the level of accuracy was seen from the Kappa coefficient, with a range of coefficient values in Table 1.

Table 1 Kappa Classification
Kappa Value Interpretation 0,00-0,20 Poor 0,21-0,40 Fair 0,41-0,60 Moderate 0,61-0,80 Substantial 0,81-1,00 Almost Perfect The analysis of carbon stocks in each class of land cover used a simple conversion method, namely multiplying the area of land cover type by the carbon stock constant (tons C/Ha), and used the standard from National Standardization Agency of Indonesia [21], which is listed in Table 2 as follows: The following analysis stage is descriptive evaluative, related to what factors cause and what impacts are likely to occur and their relationship to climate change on Small Islands.The factors that influence changes in land cover, the increase in greenhouse gases in the atmosphere, and the impacts that the community on Gili Matra has felt were obtained from the results of in-depth interviews with key stakeholders on the three Gilis.

Accuracy of Land Cover Classification
The types of land cover on Gili Matra consist of 7 categories, including built-up areas, water bodies (lake), shrubs, sand land, plantations, bare areas, and mangroves.Identification of the category of land cover is carried out by carrying out a series of stages of satellite imagery analysis and has gone through an accuracy test.Based on the findings of the accuracy test calculations in Table 1, the OA value is 93.20%.It means that the image classification results are accurate because they have a more than 70% value.The kappa coefficient value obtained is 0.92, which indicates a powerful category as classified in Table 1, which is in the range of 0.81 and 1.00 (0.81 < κ < 1.00).5

Analysis of Land Cover Change in Gili Matra
After the processing of Google Earth satellite imagery from 2013 to 2022 and the interpretation of satellite imagery on Gili Matra, it shows seven land cover classes, including built-up lareas, beach sand, shrubs, mangroves, open land, plantations, and water bodies.In 2013, the most dominant percentage of land cover was the bare areas, with an area of 243.03 ha, or 66.84%.According to the National Standardization Agency of Indonesia (BSN), bare areas is land without any other cover, whether natural, semi-natural, or artificial.Furthermore, On Gili Matra, available land on Gili Matra was in the form of grasslands or a stretch of bare land without vegetation on the surface.Based on Figure 2, the bare areas in 2013 was 35% of the total area of the Gili Matra; however, this has decreased to 25% by 2022.

Figure 2 Distribution of Mangrove in Gili Trawangan
Source: Observation, 2023 Mangroves are a type of land cover that has a protective function on Gili Matra.Unfortunately, the mangroves are declining in number, from 3% to 2%.The identification of mangrove land cover differed from others because it was double-checked using Sentinel-2A Imagery.This check was carried out to reconfirm the area of mangroves in more detail because mangrove land cover has the most excellent conversion of carbon stocks and can impact the contribution of carbon absorption on these small islands.Based on the identification, mangrove land cover was only found in Gili Trawangan and Gili Meno.The total area of mangroves on Gili Trawangan in 2013 was 2.39 hectares in 2013 and has decreased to 1.48 hectares by 2022.The distribution of the mangrove ecosystem on Gili Trawangan was limited, only a few remain at several coastal border points, and several others are adjacent to hotels or resorts.The decrease in the mangrove ecosystem area that is barely left is due to the increase in the development of tourism-supporting facilities that needed to be regulated in the spatial use regulations.Moreover, there were protected areas that should be protected and preserved.However, there needed to be a better use of space with optimal conservation efforts.Furthermore, Gili Meno has the most mangrove ecosystems in Gili Meno, with 15.41 hectares.This area has decreased, whereas in 2013, it had an area of 21,29 hectares.Based on the standard classification of quality degradation of mangrove forests following the Minister of Environment Number 201 Decree of 2004, the mangrove forests around Lake Gili Meno were classified as good or medium.Additionally, population growth and land cover change in cultivation areas were the primary causes of the decrease in mangrove ecosystems [22].
Another non-built-up area is shrubs and plantations.The existence of shrubs decreased from 23% in 2023 to 21% in 2022.The decrease in the shrubs is also one of the triggers for climate change because it consists of trees with tall stands and wide canopies that absorb more carbon.Similarly, land cover in the form of plantations also decreased by 5% over ten years.The plantation is one of the supporting sectors for the local community's economy in Gili Matra, and the types of plants grown include coconut and some horticultural crops such as pineapple.Plantations and green open space have a selling value that can increase the local community's economy.Before the 2000s, land cover in the form of plantations was widely cultivated, such as coconuts, and became one of the economic sources for local communities.However, currently, plantations are only a supporting sector to meet the daily needs of local communities or are sold to tourists.The huge potential of hotels and restaurants in Gili Matra is an opportunity to develop coconut plantations, but the local community still needs to capture this opportunity fully.The other most noticeable change is the conversion of 33.03 ha of shrubs land cover to built-up areas.
The scrub on Gili Matra consists of various vegetation, including trees with tall stands and wide canopies, such as trembesi, ketapang, and coastal pines.These trees have high carbon stocks or absorption.
Research related to landscape patterns on Gili Matra [23] describes changes in land cover in 2014.The most significant changes occurred in bare areas, with a reduction of 17.62% (39.01 ha) for five years.On the other hand, there has been an increase in land use, such as tourism accommodation and settlement areas.This research was then updated with the latest data, namely land cover change from 2013 to 2022, where it is known that there has been an increase in built-up land of 14% over the last ten years.This research also accommodates suggestions from previous research to calculate the carbon stock in each land cover so that carbon loss can be predicted.Changes in land cover from undeveloped land to built-up areas on Small Islands will be at risk of increasing vulnerability.Therefore, controlling land use for settlements, tourism support facilities, or public service facilities is necessary.The maximum limit on land use for development is around 30% [24].This condition contradicts the existing condition in 2012, where the use of built-up land on Gili Matra had reached 32% of the total area.

Analysis of Carbon Stock Change in Gili Matra
Based on data on the land cover area of Gili Matra from 2013 to 2022, conversions were carried out using the carbon stock constants in Table 2.The highest carbon stock constants were land cover for mangroves, plantations, and shrubs.These three land covers have great potential for carbon sequestration in Gili Matra.In 2013, the total available carbon stock was 14,679.84tons C.Meanwhile, in 2022, it decreased to 12,877.77tons C.This decrease was caused by land cover changes, especially mangroves, plantations, and shrubs, which have the most significant potential for carbon stocks.According to (IPCC, 2019), changes in land cover can trigger an increase in GHG emissions.This condition can be explained by changes in land cover on Gili Matra, especially changes in land cover with vegetation to build land cover such as organizations, hotels, restaurants, and other facilities.The decrease in tree stands and vegetation results in a decrease in the ability to absorb carbon in the atmosphere.It increases greenhouse gas emissions.Carbon, as a constituent of greenhouse gases, significantly contributes to global warming, which revolves around climate change.Carbon footprints are not only generated from land cover change activities but also caused by community and tourist activity increasing again after the COVID-19 pandemic.The increase in built-up land on Gili Matra causes an increase in greenhouse gases released into the atmosphere due to excessive use of air conditioning, unwise use of electricity, etc.This change in land cover is a crucial factor in the development of activities that lead to an increase in the carbon footprint of Gili Matra.
Several previous theories and studies stated that Small Islands are vulnerable to climate change.This condition has already happened in Gili Matra.The impacts of climate change seen on Gili Matra are the reduction of the coastline, coastal erosion, which causes several roads to be damaged, water puddles on several roads when it rains, and long dry seasons, which affect water quality.The impact of climate change can reduce the carrying capacity of the environment on Gili Matra, which can threaten economic activities, especially in the tourism sector.Efforts are needed to maintain the balance of the ecosystem on small islands like Gili Matra, specifically by preventing the protected areas from decreasing in size.In addition, concrete steps must be taken to maintain the preservation of protected areas, including: 1) establishing protected areas on Gili Matra, such as forests and mangroves with a high carbon absorption capacity; 2) determining zoning text in protected areas that can limit the use of space for cultivation activities; 3) carrying out conservation and restoring the use of forests and mangroves; 4) enforcing spatial use laws, especially in protected areas; and 5) developing local communities based on the environment, both in terms of institutional strengthening and the development of Human Resources (HR) skills as well as collaboration with various parties for program implementation.
Conservation efforts have been carried out by local governments, academics, local communities, and non-profit organizations engaged in environmental preservation.However, this needs to be done sustainably and continuously.Several activities, such as mangrove rehabilitation, tree planting and reforestation, were only formality with minimal follow-up steps.The environment is increasingly degraded, but efforts to overcome it are minimal.It will threaten the sustainability of small islands from various hazards and impacts of climate change.Hopefully, this study will be the first step in raising awareness for each related actor to provide concrete steps in the future.
Another effort that can be taken to increase carbon stocks that is easy to implement is optimizing private land, such as yards, to carry out reforestation independently [25].This strategy is suitable for implementation on Gili Matra as a group of small islands with high community participation.Greening has been carried out several times, such as activities in collaboration with universities, community service by the academic community, and real work-study programs.Apart from that, Gili Matra has received much attention from the outside world, including various NGOs and significant events that can include environmental-themed activities.Greening can also be done as a condition whenever houses, offices, industry, and supporting infrastructure are constructed.Developers are required to provide green open space on the land they own.

Conclusion
Land cover change impact the dynamics of carbon stocks in Gili Matra.Moreover, the carbon absorption capacity of vegetation decreases when land cover, such as mangroves, plantations, and shrubs consisting of tree stands, is not managed.According to research, carbon stocks in 2022 have decreased by 1,802.08 tons C over the last ten years.It occurred due to the conversion of land cover functions from mangroves, shrubs, and plantations to built-up areas in the form of local community settlements and tourismsupporting facilities.The conversion indirectly impacts increasing carbon emissions in the atmosphere, which raises the risk of climate change.Small islands such as Gili Matra, which are very vulnerable to climate change, should initiate various concrete efforts such as green movement, reducing the carbon footprint of the daily activities of people and tourists, and implementing zoning regulations on Gili Matra based on the regulations that have been set so that the land cover change can be controlled and does not occur massively.In addition, rules regarding space utilization must be emphasized and oriented toward environmental sustainability.Understanding land cover change from 2013 to 2022 in Gili Matra describes various challenges in determining policies regarding future spatial pattern planning to continue to pay attention to ecosystem sustainability.The findings from this research can help various parties take concrete steps to prioritize conservation strategies, increase carbon stocks and mitigate the impacts of climate change.The limitation of this research is that it only uses carbon conversion based on area and type of land cover.Recommendations for further research include conducting comprehensive measurements, for example, measuring soil carbon from each land cover on the 3 Gilis.

Figure 3 .
Figure 3. Land Cover Change (2013-2022)A study of land cover change on Gili Matra was performed using the overlay technique of land cover from 2013 to 2022 to see the distribution of land cover change patterns, followed by manual calculations using MS Excel software.The land cover change map from 2013 to 2022 in Figure3describes the dynamics of land cover on Gili Matra over the last ten years.

Figure 5 .
Figure 5. Example of the Impact of Climate Change on Gili Matra

Table 2 .
Carbon Stock Standard of Land Cover

Table 3
Conversion of Carbon Stock by Land Cover (2013-2022)