Tree biodiversity in Bornean lowland forest: What are the key species for forest city development in the new capital city of Indonesia?

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 1 / 19 OPEN ACCESS Citation: Atmoko T, Sitepu BS, Adinugroho WC, Mukhlisi, Sayektiningsih T, Setyawati T, et al. (2025) Tree biodiversity in Bornean lowland forest: What are the key species for forest city development in the new capital city of Indonesia?. PLoS ONE 20(4): e0320489. https://doi.org/10.1371/journal.pone.0320489 Editor: Gandhiv Kafle, Agriculture and Forestry University, Nepal Received: May 5, 2023 Accepted: February 17, 2025 Published: April 8, 2025 Copyright: © 2025 Atmoko et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data availability statement: All relevant data on tree species characteristics are within the paper and its Supporting Information files. Funding: The authors received no specific funding for this work. Competing interests: The authors have declared that no competing interests exist. RESEARCH ARTICLE Tree biodiversity in Bornean lowland forest: What are the key species for forest city development in the new capital city of Indonesia? Tri Atmoko1☯, Bina Swasta Sitepu 2☯, Wahyu Catur Adinugroho 2☯, Mukhlisi1☯, Tri Sayektiningsih3☯, Titiek Setyawati2☯, Francis Q. Brearley 4☯*, Ishak Yassir5☯ 1 Research Center for Applied Zoology, Research Organization for Life Sciences and Environment, National Research and Innovation Agency (BRIN), Bogor, Indonesia, 2 Research Center for Ecology

and Ethnobiology, Research Organization for Life Sciences and Environment, National Research and Innovation Agency (BRIN), Jakarta, Indonesia, 3 Makassar Environment and Forestry Standard Instrument Implementation Institute, Ministry of Environment and Forestry (BPSILHK Makassar), Makassar, Indonesia, 4 Department of Natural Sciences, Manchester Metropolitan University, Manchester, United Kingdom, 5 Samboja Environment and Forestry Standard Instrument Implementation Institute, Ministry of Environment and Forestry (BPSILHK Samboja), Samboja, Indonesia ☯ These authors contributed equally to this work. * f.q.brearley@mmu.ac.uk Abstract The national capital of Indonesia is in the early stages of relocation from the island of Java to East Kalimantan; Indonesia’s new capital city (Ibu Kota Negara; IKN) will be called Nusantara. The development of IKN will utilise the concept of a forest city representing the lowland forest of Borneo containing its rich biodiversity. To realize this concept, sufficient data and information regarding the status of tree diversity in this area is required. To provide this information, research was conducted in sample plots totaling 20.75 ha spread over eight locations in East Kalimantan. The selection of priority tree species for reha- bilitation was carried out by using the Analytical Hierarchy Process (AHP) method with the criteria of conservation status, endemicity, climax species, distribution, food poten- tial, ethnobotanical potential, animal food, and tree growth rates. In the sample plots, we

found 5,745 trees representing 571 species with the family Dipterocarpaceae dominating, followed by Euphorbiaceae, Phyllanthaceae, Malvaceae and Annonaceae. Based on the priority categories of restoration, most of the species proposed for planting belong to the Dipterocarpaceae, in the genera Anisoptera (2 species), Anthoshorea (2 species), Cotyle- lobium (1 species), Dipterocarpus (3 species), Dryobalanops (1 species), Hopea (3 species), Richetia (3 species), Rubroshorea (7 species), Shorea (4 species), and Vat- ica (4 species). Hopea rudiformis is a Critically Endangered and Borneo endemic species with the highest score, and the only species included in 1st priority, followed by 14 species in 2nd priority, 62 species in 3rd priority, and the remainder in 4th priority. About 18% of tree species with potential food sources can be planted to meet the 10% target of forest cover to contribute to food security in IKN. Samboja Research Forest, Sungai Wain Protection

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 2 / 19 PLOS ONE Tropical urban tree selection Forest, and Bangkirai Hill are forested areas with high tree species diversity and can act as a source of seeds for the IKN nursery. Introduction Borneo is one of the world’s richest areas for plant diversity [1] and home to up to 15,000 spe- cies of flowering plants [2] of which more than 1,400 are thought to be endemic [3]. Middle- ton et al. [4] noted that there are 3,936 endemic species in Kalimantan (Indonesian Borneo), and based on [5] it is estimated that endemic species in Borneo reach 7,000 species. Woody plant species are dominated by tree species from the Dipterocarpaceae family, which are the key family in intact forest areas [2,6–8]. The distribution of plants on the island of Borneo is strongly influenced by various environmental conditions, including the history of past climate change and current edaphic conditions [6,9,10] with the greatest plant species richness recorded in lowland forest areas [2,6]. Jakarta, Indonesia’s capital city, has become one of the most densely populated areas on the island of Java, with a population density approaching 15,978 individuals km-2 in 2021 [11]. Apart from being the center of government, Jakarta is also the most prominent economic center and, as with many large and developing cities, faces many environmental and social problems. These include flooding which occurs almost every year [12], piles of garbage [13], traffic jams and air pollution [14], limited supplies of clean water [15] and crowded buildings

and slum settlements [16]. In addition, Jakarta is also prone to natural hazards such earth- quakes, volcanoes, and even tsunamis [17]. Plans to move the Indonesian capital city from Java to Borneo have been proposed since 1957 by the first Indonesian President, Sukarno [18], and this has recently been declared by President Joko Widodo in August 2019. East Kalimantan province was chosen as the loca- tion for the new capital city because it is located centrally in the Indonesian archipelago, and this allows the change of perspective from Java-centric to Indonesia-centric. The new capital city will be called Ibu Kota Negara Nusantara or IKN. The area that has been delineated to become IKN is located in North Penajam Paser and Kutai Kartanegara regencies and is one of the hotspots of diversity for lowland plant species on the island of Borneo, especially in forest areas that are still protected [6,19–21]. Ibu Kota Negara’s land area of around 256,000 ha is currently dominated by forest cover (39%), plantations (29%), mangrove forests (2.2%), and swamp forests (1.2%) [22]. It is proposed that the new capital city will be developed by retaining the existing forest function, maintaining biodiversity, and reducing the negative impact on the environment. Ibu Kota Negara is also designated as a forest city (a city inside a forest). In the absence of a model of how to implement the forest city concept in other areas, this requires that the principles of managing biodiversity and the environment be carried out carefully [23]. The Indonesian

government has set key performance indicators (KPIs) as long-term directions that guide the development and management of IKN in line with green development. One of the KPI prin- ciples is to design the city in harmony with nature, namely by developing 75% of the area with green cover (65% as protected areas and 10% to support the provision of food sources) [24]. To realize the concept of the nation’s new capital, the government will revitalize green open spaces in the core area of the capital, which is currently occupied by an industrial eucalyptus (Eucalyptus sp.; Myrtaceae) plantation. These non-native species will be replaced by native and local species so that they return to a landscape with a forest cover resembling native Kalimantan lowland ecosystem types. The green space target will be fulfilled through rehabil- itation and reforestation, including roof gardens, subsistence farming, and botanical gardens

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 3 / 19 PLOS ONE Tropical urban tree selection [24]. The IKN forest rehabilitation and restoration efforts also support the international agenda to combat forest degradation and deforestation declared at the Convention on Biologi- cal Diversity COP11 in Hyderabad, India, in 2012 [25]. Rehabilitation and restoration efforts require supporting an adequate number of seed sources of species originating from the intact forest and surrounding forest areas [26]. First, we need to consider genetic diversity because it relates to forest city sustainability in the future. Low genetic diversity reduces a forest's ability to cope with diseases and extreme weather [27]. The use of local indigenous species is expected to restore the structure and com- position of IKN forest tree species to mimic their original condition, especially in degraded or restored areas. Moreover, tree species to be planted must be carefully selected to create a forest with a structure and composition close to the natural conditions of Kalimantan’s existing forests. Species selection is, therefore, based on understanding the reference species found in the surrounding forest areas. The condition of some forest areas in and around IKN remains relatively good and many studies have been carried out on their floristic structure and composition, such as the Sun- gai Wain Protection Forest [28], the Samboja Research Forest [19,20,29,30], Bukit Soeharto Grand Forest Park [21], PT. ITCIKU [31], and Bangkirai Hill [32,33].

Based on the above, this research aims to determine the key tree species for the develop- ment of IKN according to the concept of a forest city. The selected tree species are prioritised based on various criteria such as native species, rarity, protected status, animal food, food source, and growth rates. Materials and methods Study sites The research was conducted in forested areas within a radius of 30 km from the centre (zero point) of IKN. A total of eight sampling areas were selected from forests around IKN (Fig 1; Table 1). In each sampling area, a number of square or rectangular plots of 0.04 to 0.1 ha in size were sampled for trees ≥ 10 cm diameter at breast height (dbh) (except Sotek Garden where a single plot large plot was surveyed). Field surveys in forest areas were conducted in the period 2018–2021 in the context of research activities organised by the Ministry of Envi- ronment and Forestry, Indonesia. This area remains forested (S1 Fig), although there was an area of Bangkirai Hill that experienced a fire in 1998 [33]. The current landscape around IKN includes lowland forests, plantation forests, karst, mangrove forests, agriculture, coal mines and settlements. The topography is undulating, with elevations ranging up to 300 meters above sea level. Climatic conditions based on meteoro- logical data collected from Sepinggan Airport, Balikpapan, show that mean annual rainfall (2001–2021) in the study location is 2,820 mm and the temperature ranges from 21.7 ºC to 35.7 ºC. Tree diversity

The flora recorded in the sample plots were woody trees with a diameter of more than 10 cm dbh that were identified at the Herbarium Wanariset (WAN) where needed. Relative fre- quency (RF), relative density (RD), and relative dominancy (Rdom) were calculated and then summed to calculate the importance value index (IVI) [34] (Eqn. 1). The vegetation in Sotek Garden was cultivated trees so, to avoid bias, the data from this location were not included in the IVI calculation; however, they were used in determining priority species. IVI RF RD Rdom = + + (1)

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 4 / 19 PLOS ONE Tropical urban tree selection Density (D) is the ratio of the number of individuals to the total area sampled, while frequency (F) is the ratio of the number of quadrats in which a species occurs to the number of quadrats observed. Thus, relative density (RD) is the density of a given species (D) divided by the den- sity of all species (multiplied by 100) and relative frequency (RF) is the frequency of a given species (F) divided by the frequency of all species (multiplied by 100). Relative dominance (Rdom) is the basal area of a given species expressed as a percentage of the total basal area of all species present (maximum value of 100). These three measures, RF, RD, and Rdom, are summed to calculate the Importance Value Index (IVI), which lies between 0 and 300 [34]. The diversity of tree species was calculated as the Shannon-Wiener Index (H’). This diver- sity metric was calculated using R v. 3.6.3 [35] package vegan [36], provided in Eqn. 2. Fig 1. Map of research locations around Ibu Kota Negara Nusantara (Nusantara Capital City), East Kalimantan, Indonesia. https://doi.org/10.1371/journal.pone.0320489.g001

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 5 / 19 PLOS ONE Tropical urban tree selection ′ = − = ∑ H pi log pi i n ( ) ( ) 2 1 (2) Where pi is the proportional abundance of species i. Habitat clustering Habitat clustering used the hierarchical clustering “ward.D” method using R v. 3.6.3 [35] package vegan [36]. Cluster distance was calculated based on the Jaccard index using the rela- tive abundance of tree species in each location. Species selection The selection of tree species for rehabilitation was carried out by scoring and weighing the criteria based on the Analytical Hierarchy Process (AHP) multi-criterion decision-making technique [37]. The publication of AHP articles is growing markedly over time with the great- est increase in the total number of articles concerning the subject area Environmental Science, probably related to the increasing interest in environmental issues in the world. However, AHP in the subject area of Ecology and Ecosystems is relatively new [38]. We applied the AHP technique using the following steps: (1) Problem Identification refers to the identification of the problem (choices) and the criteria that influence these choices, (2) Pairwise Compari- son involves a pairwise comparison of the different criteria of the constructed hierarchy; the relative priorities of the criteria are calculated. (3) Eigenvector Construction and Ranking of Alternatives is the final stage in AHP. Selection was only made on trees identified to the

species level (74% of all individuals). We considered eight criteria for decision making: (i) conservation status, (ii) endemicity, (iii) climax species, (iv) distribution, (v) food potential, (vi) ethnobotanical potential (mainly medicinal or cultural), (vii) animal food, and (viii) tree growth rates. Weighting of criteria used the AHP method by conducting a comparison of paired criteria [39]. Each criterion was scored against the other criteria by assigning a relative dominance value between 1 and 9 (least important to most important) based on expert opin- ion. Five experts in ecology, silviculture, wildlife, botany, and the environment were involved in the analysis (names provided in the Acknowledgments). In addition, these experts were also Table 1. Description of research locations around Ibu Kota Negara Nusantara, East Kalimantan, Indonesia. Location Coordi- nates Elevation (m.a.s.l) Number of plots Total plot area (ha) Date of collection Forest type Arsari Forest S00°54’ E116°34’ 385 22 1.27 2021 Secondary forest Bangkirai Hill S01°02’ E116°52’ 80 48 1.92 2021 Secondary forest Bhirawa S00°52’ E116°28’ 565 42 1.68 2019 Old secondary forest Kenangan S01°03’ E116°44’ 5 39 2.14 2018 & 2021 Secondary forest Parung-Tembinus S00°49’ E116°47’ 180 30 1.32 2021 Karst, old secondary forest Samboja Research Forest S00°59’ E116°57’ 50 16 1.60 2021 Lowland tropical forest, sec- ondary forest, swamp forest Sotek Garden S01°12’ E116°37’ 20 1 10.0 2021 Old secondary forest Sungai Wain Protection Forest S01°09’ E116°50’

15 20 0.80 2019 Lowland tropical forest https://doi.org/10.1371/journal.pone.0320489.t001

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 6 / 19 PLOS ONE Tropical urban tree selection familiar with the area, the project, and the local species. Weight values were determined using the Super Decisions 2.10 program. The weight of each criterion generated from the AHP is presented in Table 2 with a consistency ratio (Cr) of 0.086 which is below the recommended maximum threshold (Cr < 0.1) [39]. The total score of each species was the sum of the eight criteria scores resulting from multiplying the weight of each criterion by the parameter scores. The list of tree species was ranked based on the total score and grouped based on the Likert scale with four categories (Priority 1st, 2nd, 3rd, and 4th) based on quartile values. Results Diversity of tree species A total of 5,745 trees were recorded in the sample plots covering 571 (morpho)species, 238 genera and 81 families (Table 3). As many as 420 taxa were identified at the species level. The three locations with greatest tree densities were Parung-Tembinus, Samboja Research Forest and Bangkirai Hill, which had more than 500 trees ha-1. However, even though the density Table 2. Criteria weighting and scoring parameters used for the selection of tree species for rehabilitation of Ibu Kota Negara, East Kalimantan, Indonesia. Criterion Weight Parameter Score Description Source Conservation status 0.292 EW, CR 3 Listed in IUCN Red List: EW (Extinct in the Wild), CR (Critically Endangered), EN (Endangered), VU (Vulnerable), NT (Near Threatened), LC (Least Concern), DD (Data

No 0 https://doi.org/10.1371/journal.pone.0320489.t002

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 7 / 19 PLOS ONE Tropical urban tree selection at Parung-Tembinus was slightly higher than in the Samboja Research Forest, the number of species found was much lower. Shannon-Wiener diversity indices for each location ranged from 1.98 to 2.87 (Table 3) with the greatest diversity found in Samboja Research Forest. Clustering by location The eight study locations are divided into two main clusters (Fig 2). Sotek Gardens formed a separate cluster because it is a former community settlement that has not been occupied for a long time, and has developed into an old secondary forest dominated by large-diameter fruit trees. The other seven locations are natural and old secondary forests, and some are burnt areas. The forests in the Bhirawa and Sungai Wain Protection Forests had similar tree species. The Bhirawa sample plot was a production forest area protected by the company as a source of Shorea (and other Dipterocarpaceae) seeds. Sungai Wain was also a protected forest area, so both are relatively safe from disturbances. The forests in Bangkirai Hill and Samboja Research Forest had similar tree species composition because they were relatively close together and the Table 3. Tree species richness and diversity in the eight sample locations within 30 km of Ibu Kota Negara, East Kalimantan, Indonesia. Location Number of trees Density (trees ha-1) Number of species Number of genera Number of families Species diversity (H’) Arsari Forest 619 487 230 128 56 2.31 Bangkirai Hill 962 501 179 108 50 2.50

Bhirawa 435 258 126 84 48 2.12 Kenangan 719 332 128 82 40 1.98 Parung-Tembinus 701 531 137 91 41 2.22 Samboja Research Forest 843 526 212 137 53 2.87 Sotek Garden 1,080 108 83 56 32 2.47 Sungai Wain Protection Forest 386 482 155 95 41 2.63 All locations 5,745 277 571 238 81 2.39 https://doi.org/10.1371/journal.pone.0320489.t003 Fig 2. Habitat cluster dendrogram based on binary data on the presence of tree species in eight forest locations within 30 km of Ibu Kota Negara, East Kalimantan, Indonesia. https://doi.org/10.1371/journal.pone.0320489.g002

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 8 / 19 PLOS ONE Tropical urban tree selection sample plots included areas of forest that were still in good condition, in addition to forests that had been burnt. Species composition The results showed that the family with the greatest number of species found in the forests around IKN was the Dipterocarpaceae, followed by Euphorbiaceae, Malvaceae, and Phyllan- thaceae (Fig 3). Four hundred and fifty-eight individual trees (40 species) were within the Dipterocarpaceae from 11 genera, namely: Anisoptera (2 species), Anthoshorea (2 species), Cotylelobium (1 species), Dipterocarpus (5 species), Dryobalanops (1 species), Hopea (4 spe- cies), Parashorea (1 species), Richetia (3 species), Rubroshorea (8 species), Shorea (4 species), and Vatica (8 species). Jambu-jambu (Syzygium sp.; Myrtaceae) and large-leaved mahang (Macaranga gigantea; Euphorbiaceae) had the greatest IVI values among 571 species found at the study location although it is quite likely that Syzygium sp. included more than one species (Table 4). These spe- cies are common in lowland secondary forest habitats as pioneer species along with laban (Vitex pinnata; Lamiaceae) and Strobocalyx arborea (Asteraceae). Three species of Rubroshorea were recorded among the ten species with the greatest IVI values. Rubroshorea also occupied the top Fig 3. The families and number of species in each family at eight forest locations within 30 km of Ibu Kota Negara, East Kalimantan, Indonesia. https://doi.org/10.1371/journal.pone.0320489.g003

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 9 / 19 PLOS ONE Tropical urban tree selection position among the IVIs for genera. These results showed that the study location is comprised of a mix of secondary forests (from various histories) as well as areas that are less disturbed and are typical lowland evergreen rain forest, a.k.a. mixed dipterocarp forest (MDF). Species categories Most tree species were fast-growing and are a source of animal food (S1 Table). One hundred and twenty-three tree species were known to have potential social and economic functions for the people of Borneo, both as a source of food and medicine. Based on the IUCN Red List categorisa- tion, 11.7% of the species were threatened, one of which (Mangifera casturi; Anacardiaceae) was declared Extinct in the Wild. This species was only found as a cultivated fruit tree at Sotek Gar- den. All Critically Endangered species (8) belonged to the Dipterocarpaceae, namely Anthoshorea lamellata, Dipterocarpus cornutus, D. kunstleri, Hopea mengarawan, H. rudiformis, Rubroshorea johorensis, Shorea inappendiculata, and Vatica venulosa. The Dipterocarpaceae also dominated as the climax species by contributing 40 species out of a total of 97 climax species found at the study site. A total of seven Endangered species were found: Agathis borneensis (Araucariaceae), Anisoptera costata (Dipterocarpaceae), Dipterocarpus grandiflorus (Dipterocarpaceae), Santiria rubiginosa (Burseraceae), Rubroshorea pauciflora (Dipterocarpaceae), Shorea dasyphylla (Dip-

terocarpaceae), and Syzygium scortechinii, while there were 33 species in the Vulnerable category. Only one species was found which is legally protected under Indonesian regulations, namely bandang (Borassodendron borneense; Arecaceae), as one of the endemic palms of Borneo. Species selection for rehabilitation Species selection for rehabilitation was based on criteria including conservation status, ende- mism, climax species, distribution, potential as a food source, ethnobotanical uses, key animal food sources, and fast-growing species. Among 420 species (S1 Table), we found one species as the first priority for rehabilitation followed by 15 species, 89 species, and 315 species for the second, third, and fourth priorities, respectively (Table 5). Discussion Status of tree species diversity Biodiversity is crucial to support human well-being and to provide life-supporting services such as clean water, food, pollination, climate control, and flood prevention. It also plays roles in Table 4. The top ten species, genera and families based on IVI in the forest locations in the vicinity of Ibu Kota Negara, East Kalimantan, Indonesia. Species IVI Genus IVI Family IVI Syzygium sp. 6.52 Rubroshorea 28.32 Dipterocarpaceae 34.57 Macaranga gigantea 5.29 Macaranga 15.98 Euphorbiaceae 21.81 Rubroshorea parvifolia 5.12 Syzygium 11.99 Lauraceae 15.55 Eusideroxylon zwageri 4.60 Artocarpus 7.76 Myrtaceae 14.05 Strobocalyx arborea 4.49 Litsea 5.21 Moraceae 11.94 Rubroshorea ovalis 4.08 Lithocarpus 4.91 Phyllanthaceae 9.67

Rubroshorea smithiana 3.57 Eusideroxylon 4.85 Annonaceae 9.12 Vitex pinnata 3.20 Madhuca 4.80 Myristicaceae 9.04 Madhuca kingiana 3.07 Pternandra 4.71 Malvaceae 9.01 Schima wallichii 3.04 Strobocalyx 4.71 Sapotaceae 8.90 https://doi.org/10.1371/journal.pone.0320489.t004

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 10 / 19 PLOS ONE Tropical urban tree selection Table 5. The top fifty priority tree species for rehabilitation and reforestation of Ibu Kota Negara, East Kaliman- tan, Indonesia based upon eight criteria included in an AHP analysis. Rank Species Total Score Priority 1 Hopea rudiformis 2,043 1st 2 Mangifera casturi 1,835 2nd 3 Durio kutejensis* 1,549 2nd 4 Anthoshorea lamellata, Hopea mengarawan, Rubroshorea johorensis 1,473 2nd 5 Rubroshorea smithiana 1,459 2nd 6 Santiria rubiginosa 1,432 2nd 7 Dipterocarpus cornutus, Dipterocarpus. kunstleri, Shorea inappendiculata, Vatica venulosa 1,424 2nd 8 Anthoshorea ochracea, Richetia macrobalanos, Richetia mujongensis, Vatica sarawakensis 1,410 2nd 9 Artocarpus tamaran 1,300 3rd 10 Palaquium sericeum 1,295 3rd 11 Pentace laxiflora 1,293 3rd 12 Ficus variegata* 1,260 3rd 13 Durio dulcis, Mangifera pajang 1,251 3rd 14 Eusideroxylon zwageri* 1,240 3rd 15 Durio lanceolatus 1,220 3rd 16 Dracontomelon dao, Pometia pinnata 1,209 3rd 17 Pentace erectinervia 1,193 3rd 18 Durio zibethinus 1,185 3rd 19 Dipterocarpus grandiflorus 1,181 3rd 20 Dipterocarpus confertus, Dryobalanops lanceolata*, Rubroshorea parvistipulata 1,167 3rd 21 Pterospermum javanicum 1,160 3rd 22 Scorodocarpus borneensis 1,134 3rd 23 Agathis borneensis, Anisoptera costata, Rubroshorea pauciflora, Shorea dasyphylla 1,132 3rd 24 Richetia patoiensis, Vatica oblongifolia 1,118 3rd 25 Alseodaphne elmeri 1,063 3rd

26 Artocarpus anisophyllus 1,054 3rd 27 Borassodendron borneense 1,008 3rd 28 Dialium platysepalum 0,987 3rd 29 Aquilaria microcarpa* 0,964 3rd 30 Parkia timoriana 0,962 3rd 31 Horsfieldia reticulata, Sandoricum borneense 0,959 3rd 32 Myristica simiarum 0,942 3rd 33 Shorea seminis 0,936 3rd 34 Gonystylus consanguineous, Horsfieldia gracilis 0,912 3rd 35 Aporosa nitida, Litsea umbellata 0,897 3rd 36 Madhuca kingiana 0,896 3rd 37 Shorea laevis* 0,889 3rd 38 Madhuca motleyana, Payena acuminata, Pterospermum diversifolium 0,887 3rd 39 Syzygium tawahense 0,846 3rd 40 Anisoptera marginata, Hopea beccariana, Rubroshorea balangeran, Vatica pauciflora 0,840 3rd 41 Dyera costulata, Lagerstroemia speciosa, Peronema canescens 0,821 3rd 42 Artocarpus integer, Nephelium lappaceum 0,809 3rd 43 Cotylelobium melanoxylon, Rubroshorea ovalis 0,795 3rd 44 Gymnacranthera farquhariana, Litsea elliptica 0,774 3rd (Continued)

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 11 / 19 PLOS ONE Tropical urban tree selection improving quality of life and human health and prosperity [40,41,42]. Therefore, biodiversity should become the main indicator for successful forest city development in IKN. This research found that the landscape around the proposed IKN contained high tree species richness, particu- larly in less-disturbed forested areas such as Samboja Research Forest and Sungai Wain Protec- tion Forest. Previous research also found that Samboja Research Forest had the second highest plant diversity across forests in Indonesia with 553 identified tree species [20]. Of the 13 Dip- terocarpaceae genera found in Kalimantan, only the monospecific genera Neohopea and Upuna were not found in this study area. However, there are records from Kartawinata et al. [20] of the presence of Upuna at Samboja Research Forest based on an inventory in 2004. Whilst the Dipterocarpaceae was the dominant family as expected [6,7,8], the Euphorbia- ceae, Malvaceae and Phyllanthaceae were also abundant in the landscape. These families are known to be characteristic of lowland evergreen rain forest in Kalimantan. In a rehabilitation context, fast-growing pioneer tree species (such as members of the Euphorbiaceae) can make the micro-climate shadier, thus allowing better growth of shade-tolerant species [43,44]. The pioneer tree species with short lifespans live up to around 30 years [45], then allowing shade-tolerant species to form the subsequent canopy. Priority species

The development of IKN is within the framework of a forest city, namely a city designed on a landscape basis placing forest ecosystems at the centre of urban spatial planning and facilitat- ing the life of urban communities [46]. To revitalize green open areas and to implement the forest city concept, replacement of Eucalyptus spp. with native species from Borneo is needed. The high score given to conservation status and endemicity shows the spirit of IKN develop- ment by prioritizing rare and endangered tree species to support recovery of Borneo’s tropical forests. To rehabilitate forest ecosystems, appropriate species selection is fundamental to its success. Species selected should be native [47,48,49] and have high survival rates [50]. In addi- tion, fast-growing species can be added to the species selected, but we should pay attention to the trade-offs related to life-history strategies since fast-growing species have short lifespans [51]. The advantage of planting fast-growing species in the initial step of rehabilitation is the ability of these species to rapidly form canopy cover [47], thereby creating microclimates suitable for the growth of shade-tolerant species as noted above. Several studies recommend combining trees with a diversity of traits in rehabilitation, such as pioneer species and climax species [52], or fast-growing native tree species and slow-growing native tree species [49]. There is also increasing recognition that tree selection should be not only be considered in

terms of ecosystem recovery but also for local communities. Therefore, selected trees should have economic benefits and improve local livelihoods [27,53,54]. Rank Species Total Score Priority 45 Knema pallens, Knema percoriacea, Myristica villosa, Palaquium stenophyllum 0,771 3rd 46 Artocarpus rigidus 0,762 3rd 47 Lithocarpus gracilis 0,750 3rd 48 Macaranga beccariana 0,744 3rd 49 Durio oxleyanus 0,730 3rd 50 Rubroshorea leprosula* 0,723 3rd Remarks: *Seed sources are available in IKN. https://doi.org/10.1371/journal.pone.0320489.t005 Table 5. (Continued)

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 12 / 19 PLOS ONE Tropical urban tree selection The overlap of tree species that produce food for humans and food for animals has the potential to cause conflict if not managed properly. This is because all potential species pro- viding food sources for humans also provide food sources for animals, especially primates. Some primates present in the study area that have the potential to cause conflict with humans are long-tailed monkeys (Macaca fascicularis), macaques (Macaca nemestrina), proboscis monkeys (Nasalis larvatus) and orangutans (Pongo pygmaeus). The first three species have natural distribution in the study area, while orangutans have been introduced to Sungai Wain Protection Forest and Gunung Beratus Protection Forest. The prioritization of species to be planted based on the regional spatial plan of IKN [55] must be adjusted to the characteristics and suitability of the growing area. Our study did not include mangrove or wetland habitats, and tree selection was based on the terrestrial charac- teristics of the study area. Emphasis on the right trees for the right place and the right pur- poses is the main underlying challenge that needs to be tackled to make restoration through tree-based interventions successful [56]. Species in priority 1 and 2 can be used for species enrichment or collection gardens (S1 Table) as a demonstration for the use of key species in the IKN region. Due to the complexity of environments and site diversity, testing tree species

under local biotic and management conditions to identify their adaptations to site variables is essential. We recommend that future studies or restoration plans in the region include soil assessments (soil physico-chemical properties) to guide species selection and improve the success of rehabilitation efforts. Seed source availability Seed source availability is essential to developing the forest city [57,58]. There are seven seed sources currently available, which includes the Rubroshorea leprosula seed source at Samboja Research Forest with a total production of 5 ha, plus Dipterocarpus humeratus (5 ha) and Eusideroxylon zwageri (Lauraceae) (30 ha). Other seed sources are available for Aquilaria microcarpa (Thymelaeaceae) (5 ha), Agathis borneensis (5 ha) and Durio kutejensis (Mal- vaceae) (2.5 ha) [59], whilst Ficus variegata (Moraceae) (5 ha), Tengkawang (Rubroshorea stenoptera) (3 ha), Rubroshorea ovalis (1 ha), Tengkawang (Rubroshorea beccariana) (6 ha), Kapur (Dryobalanops beccarii) (5 ha) and Shorea laevis (5 ha) have been growing since 2015 (Nanang Riana, Manager of Samboja Research Forest, pers. comm.). Another approach to obtain seeds is buying from seed industries or local communities’ nurseries. Seeds used for rehabilitation should have good performance, so it is important to understand the seeds’ origin. Indeed, seeds derived from seed industries have to be accompanied by a seed certificate [60]. Furthermore, buying seeds from local communities is another option to supply the seed

requirements for rehabilitation. Some people living in the Samboja area have developed seed nurseries for personal and commercial purposes, and supporting these growers will provide economic benefits to them. This activity can stimulate the local economy by creating job opportunities such as seed collectors and nursery caretakers, increasing communities’ income. For rehabilitation purposes, the government has established a large nursery that produces 15 million seeds per annum in Mentawir, Penajam Paser Utara district. An obstacle emerges to provide seed sources for high-scoring rare species where there is limited information on their ecology and thus silvicultural techniques. There are some efforts to overcome this challenge by natural collection and vegetative propagation. Vegetative propagation, tissue culture and shoot cuttings may be alternatives to supply seeds through generative techniques [61–65]. We therefore suggest that future restoration efforts incorpo- rate propagation research and the development of local nurseries to ensure that the selected species can be effectively propagated and thus out-planted.

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 13 / 19 PLOS ONE Tropical urban tree selection Rehabilitation strategies The development of IKN needs to integrate environmental and forestry issues, including wild- life home ranges and habitat protection within the landscape. Currently, forest plantations of Eucalyptus spp. cover a considerable proportion of the landscape within IKN. Nevertheless, they will be replaced by native and endemic species of lowland tropical forest of Kalimantan as we discuss here. There are four strands encompassing successful strategies for rehabilitation in order to achieve the target of green cover of 75%, which are forest rehabilitation, land rehabilitation, reclamation, and social forestry (Table 6). Rehabilitation and reclamation are defined accord- ing to Peraturan Pemerintah No. 26/2020 [66] on Forest Rehabilitation and Reclamation. Initially, forest rehabilitation aims to recover degraded forest. This can then be expanded to other issues, since factors contributing to forest degradation are complex. Forest rehabilitation is now not only considered from the point-of-view of forest recovery but also that of local prosperity. Nawir et al. [67] offer recommendations in implementing successful rehabilitation: (1) good knowledge on rehabilitation sites (soils, topography, local culture, local wisdom), (2) seed source availability, (3) local community participation, (4) project sustainability, and (5) clear land tenure. The development of IKN needs to integrate environmental and forestry issues, including

wildlife home range and habitat protection within the landscape. Based on Law No. 3 of 2022 concerning the National Capital, 75% of the area will be maintained as green space (65% forest + 10% food source plants). The regional spatial plan of IKN [53] allocates protected areas in IKN as a component of the forest city implementation. The five types of protected areas in the spatial plans are: environmental buffer areas and food security; local protected areas (protec- tion to coastlines, riverbanks, and around lakes or reservoirs); green open areas (urban forest, Table 6. Rehabilitation strategies in the proposed Ibu Kota Negara area, East Kalimantan, Indonesia. Strategy Objective Coverage Implementation Forest Rehabilitation Restore, preserve, and increase forest function to improve car- rying capacity, productivity, and functions to maintain life support systems Conservation forest (except Nature Reserve and National Park core zone), Production Forest, and Protection Forest - Intensive reforestation (Crit- ical land with zero commu- nity activity) - Agroforestry (Critical land with community activity) Land Rehabilitation Restore, preserve, and increase land function to improve carrying capacity, productivity, and functions to maintain life support systems Outside forest area with forest cover or land area Revegetation with the scheme: - Private forest - Environmental revegetation - Urban Forest (Settlement area, industrial area, rec- reation area, biodiversity sanctuary area, protection area) Forest Reclamation To improve or restore the

degraded forest area to functioning optimally and according to the designation Degraded forest with land and vegetation change due to utilization Revegetation with tree planta- tions and maintenance in the post-use forest to restore and recover degraded vegetation Social Forestry Local communities as a principal element in the sustainable forest management to improve prosper- ity, environmental balance, and social/cultural dynamics State Forest, Private Forest, and Indigenous Forest Village Forest, Indigenous Forest, Community Forest, Community Plantation Forest, and Forestry/Conservation Partnership Source: [66]. https://doi.org/10.1371/journal.pone.0320489.t006

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 14 / 19 PLOS ONE Tropical urban tree selection city park, sub-district park, village park, green belt, burial ground); conservation area; and mangrove ecosystems. The Urban Forest covers an area of 64,618 ha, most of which will be developed from the former concession area of plantations of Eucalyptus spp. Not all parts of the site will be used to build infrastructure facilities; however, most will be rehabilitated to restore the Eucalyptus plantation to the original tropical rain forest using the native and endemic species of the low- land tropical forest of Borneo. The urban forest also includes two wildlife corridors that will be built in the IKN area, namely the northern corridor connecting Bukit Suharto Grand Forest Park (GFP) with the Production Forest and the southern corridor connecting Bukit Suharto GFP with Sungai Wain Protection Forest. Bukit Suharto GFP is the only conservation area in IKN that covers lowland forest areas to the coast, including the unique heath forest ecosystem. The area of 64,255 ha is not entirely forest; forest fires have damaged part of it, and some of it has been converted into agricultural fields and is occupied by the local community. This area will be maintained and restored to become a key part of the identity of the forest city. Hajjar et al. [68] stated that community participation will improve their responsibility and commitment to preserve the forest. This involvement should start from the project plan and design to the program’s implementation,

including the methods used in forest management and species selection for rehabilitation activities. In Indonesia, Safe’i et al. [69] demonstrated that a social forestry program with a community forest scheme in Tanggamus Regency, Lampung (Sumatra), contributed to the economic improvement of the forest farmer group by about 15%. Another community’s forest scheme also contributed to the recovery of the forest area of about 29.3% from 40 ha of the project area in Gunung Kidul Regency, Yogyakarta [70]. Several factors that contribute to social forestry programs’ success include technical and financial assistance for forest farmers in forest management and product processing [71], and their capacity building [72]. Land rehabilitation, forest reclamation, and social forestry could all use species as food source trees to meet 10% of the targeted green cover in IKN. Nevertheless, the choice of food source trees needs to be considered with the involvement of local communities who have knowledge of the species’ attributes in terms of economic benefits, medicinal use, and social/ cultural values [73]. The introduction of poorly-known species in community participation projects is possible as long as this is followed by supporting activities in the appropriate plant- ing techniques, maintenance, harvesting, post-harvest production, and marketing strategies. As 10% of the green cover is allocated for food security, the zoning of species planted in land rehabilitation activities is important to avoid animal-human conflict. Planting animal

food source species should be done in forest edge areas or restored forest areas. The species selected for planting in these areas are those with potential for animals but low preference for humans. Meanwhile, human food source species should be planted away from forest boundaries or around settlements. To mitigate the risk of conflict, we propose a spatial zoning approach in the city forest design where trees that serve as animal food sources are planted in areas further from human settlements and city centers, creating natural buffers and wildlife corridors. This would encourage wildlife to remain in designated forest areas while mini- mizing direct interactions with the urban population. Additionally, as part of the forest city planning, monitoring and management strategies should be developed to address potential human-wildlife interactions proactively. Forest rehabilitation in the IKN area also could be conducted via natural regeneration [74] or secondary forest succession. In particular, for the Eucalyptus plantations, the canopy cover could be opened to facilitate the climax species seed germination and initiate appropriate microclimate conditions as shown by Brancallion et al. [75] in Brazil. Removal of Eucalyp- tus close to the natural forest border is also essential to facilitate the natural regeneration

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 15 / 19 PLOS ONE Tropical urban tree selection of natural forest plant species. There are some examples of this processes in other tropical regions, but limited guidance for restoration of Eucalyptus plantations into natural diptero- carp forest leads to a challenging opportunity. Conclusions Rehabilitation activities in the IKN area towards natural ecosystem conditions can be fulfilled by selecting and using priority tree species based on the natural habitats of these species in Bor- neo. Species selection should be further conducted according to the availability of seeds and the availability of rehabilitation areas in order to support the formation of the lowland evergreen (mixed dipterocarp) rain forest ecosystem as the original and natural ecosystem in the IKN area. This ecosystem recovery strategy requires several critical stages considering the area’s biophysical conditions and the surrounding communities’ socio-economic conditions. Choosing the right rehabilitation strategies will help achieve the goals of developing the IKN within the forest city concept and have a positive impact on the surrounding community during urban development. Supporting information S1 Data. Data IKN. (XLSX) S1 Fig. Land use/land cover map (2023) around Ibu Kota Negara Nusantara (Nusantara Capital City), East Kalimantan, Indonesia. (JPG) S1 Table. List of trees in 20.75 ha of plots in eight locations around Ibu Kota Negara, East Kalimantan, Indonesia. (DOCX) Acknowledgements

The authors would like to express their sincere gratitude to the following experts for their invalu- able contributions to the Analytic Hierarchy Process (AHP) analysis: Prof. Raden Garsetiasih from the National Research and Innovation Agency Indonesia, for her expertise in conservation and biodiversity; Dr. Henti Hendalastuti Rachmat from the National Research and Innovation Agency Indonesia, for her expertise in silviculture; Dr. Onesimus Patiung, Director of Environ- mental Management and Disaster Mitigation at the Nusantara Capital City Authority, for his expertise in environmental management; Dr. Medi Hendra from Mulawarman University, for his expertise in botany; and Dr. Sofian Iskandar from Nusa Bangsa University, for his expertise in wild animal ecology. We also acknowledge the kind support of the Management Units of Sungai Wain Protection Forest, Bangkirai Hill - PT. Inhutani I, PT ITCI Kartika Utama, and the Balai Penerapan Standar Instrumen Lingkungan Hidup dan Kehutanan (BPSI LHK) Samboja - Minis- try of Environment and Forestry, for their support in the implementation of research activities. Author contributions Conceptualization: Tri Atmoko, Bina Swasta Sitepu, Wahyu Catur Adinugroho, Mukhlisi, Tri Sayektiningsih, Titiek Setyawati, Ishak Yassir. Data curation: Tri Atmoko, Bina Swasta Sitepu, Mukhlisi, Tri Sayektiningsih. Formal analysis: Tri Atmoko, Bina Swasta Sitepu, Wahyu Catur Adinugroho, Mukhlisi, Titiek Setyawati.

PLOS ONE | https://doi.org/10.1371/journal.pone.0320489 April 8, 2025 16 / 19 PLOS ONE Tropical urban tree selection Investigation: Tri Atmoko, Bina Swasta Sitepu, Wahyu Catur Adinugroho, Tri Sayektiningsih. Methodology: Tri Atmoko, Bina Swasta Sitepu, Wahyu Catur Adinugroho, Mukhlisi, Tri Sayektiningsih, Titiek Setyawati, Francis Q. Brearley, Ishak Yassir. Project administration: Wahyu Catur Adinugroho, Mukhlisi, Tri Sayektiningsih, Ishak Yassir. Resources: Titiek Setyawati, Ishak Yassir. Software: Wahyu Catur Adinugroho. Supervision: Titiek Setyawati, Francis Q. Brearley, Ishak Yassir. Validation: Bina Swasta Sitepu, Mukhlisi, Tri Sayektiningsih, Titiek Setyawati, Ishak Yassir. Visualization: Tri Atmoko, Wahyu Catur Adinugroho. Writing – original draft: Tri Atmoko, Bina Swasta Sitepu, Wahyu Catur Adinugroho, Mukhlisi, Tri Sayektiningsih, Titiek Setyawati, Ishak Yassir. Writing – review & editing: Tri Atmoko, Bina Swasta Sitepu, Wahyu Catur Adinugroho, Mukhlisi, Tri Sayektiningsih, Titiek Setyawati, Francis Q. Brearley, Ishak Yassir. References 1. Neo L, Wong K, Tan H. A synopsis of the endemic plant genera of Borneo. Nordic J Botany. 2020;38(9):e02871. 2. MacKinnon K, Hatta G, Halim H, Mangalik A. The ecology of Kalimantan. Singapore: Periplus Editions (KH) Ltd; 1996. 3. Sidiyasa K. Jenis-jenis pohon endemik kalimantan. Samboja, Indonesia: Balai Penelitian Teknologi Konservasi Sumber daya Alam, Kementerian Lingkungan Hidup dan Kehutanan; 2015. 4. Middleton D, Armstrong K, Baba Y, Balslev H, Chayamarit K, Chung R. Progress on Southeast Asia’s

flora projects. Gardens’ Bulletin Singapore. 2019;71(2):267–319. 5. Van Welzen P, Slik J, Alahuhta J. Plant distribution patterns and plate tectonics in Malesia. Biologiske Skrifter. 2005;55:199–217. 6. Slik J, Poulsen A, Ashton P, Cannon C, Eichhorn K, Kartawinata K. A floristic analysis of the lowland dipterocarp forests of Borneo. J Biogeogr. 2003;30(10):1517–31. 7. Brearley F, Banin L, Saner P. The ecology of the Asian dipterocarps. Plant Ecol Divers. 2016;9(5–6):429–36. 8. Ashton PS, Morley RJ, Heckenhauer J, Prasad V. The magnificent dipterocarps: précis for an epi- taph?. Kew Bulletin. 2021;76(2):87–125. 9. Raes N, Roos MC, Slik J, van Loon E, ter Steege H. Botanical richness and endemicity patterns of Borneo derived from species distribution models. Ecography. 2009;32(1):180–92. 10. de Bruyn M, Stelbrink B, Morley RJ, Hall R, Carvalho GR, Cannon CH, et al. Borneo and Indochina are major evolutionary hotspots for Southeast Asian biodiversity. Syst Biol. 2014;63(6):879–901. 11. Badan Pusat Statistik Indonesia. Statistical yearbook of Indonesia 2022. Jakarta, Indonesia: Badan Pusat Statistik Indonesia; 2022. 12. Amira R, Surjandari I, Laoh E. Jakarta flood risk mapping using index-based approach and spatial analysis. Proceedings of the International Conference on ICT for Smart Society (ICISS). 2020. https:// doi.org/10.1109/ICISS50791.2020.9307583 13. Muhashiby MI, Hasibuan HS, Wahyono S. Waste management in Jakarta recycle centre: case study of Pesanggrahan, Jakarta. IOP Conference Series: Earth and Environmental Science. 2021; 940:012034.