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 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