Assessing forest area fragmentation potential in Bali, Nusa Tenggara and Maluku islands, Indonesia

Forest fragmentation has emerged as an important driver of habitat loss and biodiversity degradation, but research on this topic has been limited, particularly in island areas. The aim of this study is to address this research gap by investigating forest fragmentation in the islands of Bali, Nusa Tenggara and Maluku. To identify the potential for forest fragmentation in these regions, Simmon’s Index was used. Land cover maps derived from the Sentinel-2 dataset for the period 2017-2022 were obtained from Google Earth Engine. They were combined with forest area maps to generate the fragmentation index. Our results show that Maluku has the highest fragmentation index with an average of 0.32. This is followed by East Nusa Tenggara with 0.31, North Maluku with 0.21, West Nusa Tenggara with 0.13 and Bali with 0.04. During the period 2017-2022, the average number of developed land, expressed in polygons, was 2533 in Maluku, and 3706, 1412, 1878, and 637 in East Nusa Tenggara, North Maluku, West Nusa Tenggara, and Bali, respectively. The development of a methodology to quantify the potential extent and drivers of forest fragmentation is essential to inform policy makers and guide strategies to protect forest areas and prevent further habitat loss.


Introduction
The fragmentation of forests has become an important issue in many parts of the world, including Indonesia, due to massive development.In general, forest fragmentation refers to the breaking up or fragmenting of a large area of forest into smaller patches of forest habitat.This change is mainly caused by human activities.Examples include logging, conversion of forest into agricultural land, settlements and other infrastructure.The definition of forest fragmentation is not only related to the creation of patches, but also emphasises the effects on habitat isolation, patch size and number of patches [1].Fragmentation has led to a discontinuity in the resources and conditions of the ecosystem [2].Several studies emphasise the need to distinguish between habitat loss and forest fragmentation, particularly as they affect biodiversity.However, many of them agreed that these concepts are so closely intertwined that habitat loss can be considered to be a component of fragmentation [1].
Biodiversity loss is one of the most important effects of forest fragmentation.For plant species, fragmented populations due to habitat fragmentation will lead to increased genetic drift and inbreeding, reduced availability of mates, changes in interactions with pollinators and changes in habitat conditions.[3].In addition, the creation of habitat patches also has an impact on species richness and plant species composition [4].Landscape changes due to forest fragmentation pose significant risks to plant, bird, mammal and insect diversity.Fragmented areas also have a negative impact on the ecosystem services they provide to local communities.These include reduced agricultural productivity and increased incidence of domestic pets [5].The number of patches can also reflect spatial diversity.This can affect species interactions and influence the spread of habitat disturbance.Furthermore, the extent of forest fragments is related to species diversity, with larger areas having higher numbers of tree species and rarer species [6].
The terrestrial forest area in Indonesia is 120.5 million ha.This is 63.5% of the total area.It consists of several forest statuses: Conservation forest, Production forest, Limited production forest, Convertible production forest and Protected forest [7].Indonesia is among the tropical countries with the highest rate of deforested area [8].However, studies on forest fragmentation based on the current status of forest cover in Indonesia remain limited.This is especially true for small islands, where the extent of forest cover is smaller than that of insignificant islands.The aim of this study is to identify forest fragmentation in island areas, with the islands of Bali, Nusa Tenggara and Maluku as a case study for assessment.The result of this study is expected to be used as initial development of the methodology to generate robust estimates of fragmented forest areas, as well as preliminary information for policy makers to improve forest management based on their status to prevent habitat and biodiversity loss in the region.

Data collection
The study covers all the areas in the islands of Bali, Nusa Tenggara and Maluku.To identify fragmented areas, his study used two datasets, including a land cover map from the Sentinel-2 dataset derived from Google Earth Engine with a spatial resolution of 10m from 2017-2022, and a forest area map issued by the Ministry of Environment and Forestry with a spatial resolution of 10 x 10m.The data sources of this study are presented in Table 1.

Data analysis
Spatial data analysis was carried out using the LecoS plug-in to QGIS [9].In this study, the Simmons index was used to assess forest fragmentation, which represents the variation of land cover in a polygon.The equation used to calculate the Simmons index is as follows: Where a is the extent of polygon I in forest areas and A is the extent of forest area.If the total value of ai is close to the value of A, the actual A area covered by the polygon is minimal.This indicates a low variation in land cover or a low potential level of fragmentation of the forest area [10,11].Therefore, if the value of the Simmons index is close to 0, the potential fragmentation of the forest area is smaller.

Results and Discussion
The result shows that the Simmon index values are constant in all regions from 2017 to 2022.Maluku has the highest Simmons index with 0.32, followed by East Nusa Tenggara (0.31), North Maluku (0.21) and 3 West Nusa Tenggara (0.13).Meanwhile, Bali has the lowest Simmons index of 0.03 (Table 2).This indicates that Maluku has the highest potential for forest fragmentation compared to other provinces.The fragmented forest area in this study was identified based on the built-up areas in a polygon, although the number of polygons does not represent the extent of fragmented forest areas.The result shows that East Nusa Tenggara has the highest number of polygons, with an average polygon of 3706.Maluku is the second highest with 2533 polygons, followed by West Nusa Tenggara with 1878 polygons and North Maluku with 1412 polygons.In terms of the Simmons index value, Bali has the lowest number of polygons with 637 (Figure 1).

Figure 1. Number of polygons with built-up area
The figure above shows that the highest number of polygons was found in East Nusa Tenggara.This province has >4000 patches of built-up areas in 2022.Based on the land cover map for 2017-2022, the number of patches tends to be constant.This trend is similar to other provinces such as Maluku, North Maluku and West Nusa Tenggara.Meanwhile, in Bali, the number of patches shows an increasing trend between 2017 and 2022.
The extent of forest cover in Maluku, Bali and Nusa Tenggara is smaller than in other major islands.The total terrestrial forest area in these regions is 9.1 million ha, or about 7.5% of Indonesia's total terrestrial forest area.This area is spread over several forest types.About 1 million ha (11%) is classified as conservation forest, 2.4 million ha (27%) as protection forest and 5.5 million ha (62%) as production forest [7].The effects of forest fragmentation can vary depending on the forest area status.Conservation forests, where one of the main functions is to protect biodiversity, may be severely affected.The effects may be exacerbated as these areas are considered to be highly endemic.Reduced habitat size and isolation lead to a decline in species diversity.In addition, fragmentation can also amplify edge effects, making species and their habitats in the edge areas more vulnerable.As a result, fragmentation promotes further habitat degradation in the region and can exacerbate biodiversity loss.The effects are expected to be gradual and could affect endemic species [12].Habitat isolation has been shown to shift wildlife communities.Variations in vegetation composition have different effects.Wildlife species are more likely to decline in monocultures where plant species are homogeneous.Most species found in monoculture areas also have the conservation status of least concerned, suggesting that generalist species can survive in fragmented regions [13].However, homogeneous plant species in fragmented areas still provide essential habitat for wildlife.While fragmented natural forests may not effectively conserve the intact forest species previously found in the area, they can serve as habitats for resilient species that can survive environmental changes.In areas where extensive forest cover has been almost completely lost, these fragmented forests play a crucial role in conserving biodiversity [14].
In the long term, forest fragmentation can also lead to extinction, particularly for species with large home ranges [15].One of the most notable effects is the reduction of species genetic diversity.A study of the effects of forest fragmentation on the genetic diversity of species by [16] showed that larger-bodied species are disproportionately affected by fragmentation, with terrestrial and arboreal mammals being more affected than flying species.In addition, herbivores also consistently show negative effects on genetic diversity.In general, larger animals require larger areas and more resources to survive.They therefore naturally occupy larger home ranges.However, when their habitat is reduced, the availability of resources is also reduced.As a result, large mammals are more vulnerable to the negative effects of forest fragmentation.
Fragmentation rates may also differ according to the status of the forest area.Rulli et al [17] pointed out that concession areas have higher fragmentation than non-concession areas.Logging concessions have less fragmented areas compared to oil palm and pulpwood concessions.According to this study, the initial forest cover in concession areas was more than 70% in 2000.In particular, there was a significant decrease in forest cover in concession areas in 2014.Among these, forest conversion to oil palm plantations has been a key driver of land use change in Indonesia.Further analysis is needed to investigate whether the drivers and patterns of forest fragmentation in Bali, Nusa Tenggara and Maluku Islands are similar to those at the national level.
Although the Indonesian government has introduced regulations to protect primary forests from deforestation by imposing a moratorium on the issuance of new permits, there is still a need for supportive regulations to prevent forest fragmentation within forest areas.In addition, massive infrastructure development in recent years, including road expansion, is likely to create additional forest mosaics.Therefore, minimisation of environmental impacts through appropriate mitigation measures should be a priority in infrastructure development.For example, the establishment of new protected areas along road corridors is recommended to further protect wildlife habitats [18].

Conclusion
This study shows that Maluku has the highest potential for forest fragmentation, especially among other island areas.Understanding and identifying forest fragmentation in island areas is essential due to their high endemism, which makes them more vulnerable to species extinction.Developing a reliable methodology to quantify the potential extent and underlying drivers of forest fragmentation is essential to inform policy makers and formulate effective strategies to protect forest areas and mitigate further habitat loss.

Table 2 .
Simmons index of study areas in 2017-2022