Recollection and conservation of Vatica javanica subsp. scaphifolia, a critically endangered endemic tree species in Southeastern Borneo

Vatica javanica subsp. scaphifolia (Kosterm.) P.S.Ashton (Dipterocarpaceae) is an endemic tree confined to Southeastern Borneo. The International Union for Conservation of Nature (IUCN) Red List classifies the species as Critically Endangered (CR) based on the assessment conducted 25 years ago. The species is not collected yet in any ex-situ conservation areas in the world. After more than 3 decades since the last herbarium specimen was collected in 1991, here this study reported the recollection and new locations of V. javanica subsp. scaphifolia in Bukit Bangkirai Forest, Kutai Kartanegara Regency, East Kalimantan Province. The confirmation of the species involved a comparison between the newest collected specimens and living photos and the specimen type and key to the species in the protologue. The present research provides new information on the morphology of the tree species through photos of the wild living plants. Using an exploration survey method, this research recorded the population in two locations with elevation ranges of 70-95 m. The field survey located a total of 13 immature individuals with height and diameter ranges of 2.1-14.7 m and 1-9.7 cm, respectively. The study observed that forest conversion into rubber plantations (Hevea brasiliensis) and open coal mining are the main threats to the species. Conservation of the species has been done by collecting plant materials to serve as the first ex-situ living collection at the Bogor Botanic Gardens BRIN.


Introduction
Dipterocarpaceae is a tree family mainly distributed in the tropical lowland rainforest of Southeast Asia, a region that supports an essential proportion of the world's biodiversity [1,2].According to Plants of the World Online (POWO) [3], Dipterocarpaceae comprises 21 genera and 540 species with approximately 67.4% (364 species) at risk of extinction in the 2 wild [4].Borneo is the heart of Indonesia's tropical rainforests and home to 1,433 endemic plant species, including 218 genera and 65 families.Dipterocarpaceae is recorded as the family with the most endemic species (171 species), followed by Euphorbiaceae (147 species), Myrtaceae (123 species), Myristicaceae (80 species), Guttiferae (55 species), and Ebenaceae (51 species) [5,6].In Kalimantan, Dipterocarp is locally known as Meranti, Keruing, Kapur, Mersawa, and Resak.These trees are important in the rainforest ecosystem and are known for their valuable timber, camphor, resins, oleoresins, and oils for the construction and cosmetic industry [5,7].In addition to their commercial value, dipterocarp forests play a significant role in regulating environmental services and climate, and in maintaining soil fertility of the ecosystem.Some species can grow up to 88.3 m tall, making them one of the tallest trees in Sabah Malaysia [8].
Vatica Linnaeus, commonly known as resak tree, comprises 79 species and is the third largest genus of the Dipterocarpaceae family after Shorea and Hopea [3].It can be distinguished from others by the absence of looped intra-marginal nerves on the leaves, the winged fruits cover with the size of less than half of the nut, glabrous anthers, and stout style [9,10,11,12,13].Ranging from understory to main canopy trees, this genus is frequently found in lowland dipterocarp primary forests and rarely in hill forests [11].In Southeast Asia, it ranges from small to medium-sized trees with timbers specifically used for house posts and small construction materials [11].According to the IUCN Red List, approximately 79% of Vatica (63 species) are threatened with the Critically Endangered status (19 species), Endangered (29 species), and Vulnerable (15 species) [4].
Vatica javanica Slooten comprises two subspecies: Vatica javanica subsp.javanica and Vatica javanica subsp.scaphifolia (Kosterm.)P.S.Ashton [9].While the first subspecies is known only from Central and West Java [9,14,15,16,17], V. javanica subsp.scaphifolia is distributed only in Southeastern Borneo [9].The tree species is currently under threat and listed as Critically Endangered (CR) According to the IUCN Red List, based on an assessment conducted a quarter-century ago [18].The species' habitat has been under continuous decline due to various threats, such as deforestation and forest degradation.A vast area of forest in the region has been converted into agricultural land (oil palm, rubber, acacia plantations), settlements and commercial development, mining, and vacant land [8,19,20,21].Furthermore, the habitat of V. javanica subsp.scaphifolia is situated near the new capital city of Indonesia.Consequently, the development activities will potentially alter the landscape and ecosystem of its surrounding environment, including the habitat of V. javanica subsp.scaphifolia [22,23].Currently, neither collection nor ex-situ conservation has been performed on this species [24].
In the current research, we report the re-collection of V. javanica subsp.scaphifolia after more than three decades from the last collection.This study is able to verify the characteristics of morphological specimen, capture the first actual image of living plants in the wild, estimate the population size and structure, inform threats to the habitat, and initiate exsitu conservation.The research findings can be used as a baseline to develop a comprehensive conservation strategy and action plan for the species and its natural habitat.

Exploration and plant collection
Both herbarium specimens and living materials were obtained during the exploration of V. javanica subsp.scaphifolia in two lowland mixed dipterocarp forests in Kutai Kartanegara Regency of East Kalimantan Province, namely Bukit Bangkirai and at KM 5 of Wanariset Samboja (Figure 1), from October to November 2022.An exploration survey method was employed to explore threatened plant species [25], while GPS was used to record the coordinates of the targeted individuals.The survey involved the activities of counting the number of individuals and classifying them based on their maturity.Measurement included the tree height (m) and diameter at breast height (dbh; cm) of each individual, as well as site elevation (m above sea level (m asl)) and degree of steepness (⁰).The collected ripe fruits, seeds, small wildings, and shoot cuttings were sent to the Bogor Botanic Gardens for ex-situ conservation purposes.While conducting the field surveys, we observed the potential threats to the individual species and its natural habitat.

Identification of collected specimens
The specimens were preserved on sheets and subsequently oven-dried at the herbarium of Research Center for Plant Conservation, Botanic Gardens and Forestry BRIN.In addition to the herbarium, as a complementary resource, digital photos of the living plants were also taken.We used digital camera and ruler or other objects to serve as a dimensional comparison [26].We were able to identify and confirm the most recent specimens by deep examining their characteristics of morphology and comparing to the newest herbarium and the type specimen [27], description in the protologue [9], and other subspecies from living specimen images of V. javanica subsp.javanica [14,16,17].

Morphological observation
The identification of the newest herbarium specimen as V. javanica subsp.scaphifolia (Kosterm.)P.S.Ashton was confirmed by examining the morphological characteristics of both living material and voucher specimen (Table 1).Most of their morphological characteristics are in accordance with the protologue description, except for buttresses and resins.The documented immature living specimens showed the buttress of 25 cm tall, while based on the notes of digital herbarium photos accessed via GBIF, the buttress of a mature tree (80 cm dbh) reaches 4.5 m tall [9,27].We found that the bark yielded clear, pale resin (Figure 3c), while previous herbarium recorded opaque resin.Different colors are possibly caused by different coagulation time periods.While we presumed that this trait is highly subjective and less significant, we still pointed it out for additional examination.Ashton [9] distinguished V. javanica subsp.scaphifolia from V. javanica subsp.javanica by leaf shape and nerve characters (Table 1).The former has elliptic-oblong to obovate, prominently (boat shaped) with a concave of abaxial surface, bullate between nerves, the nerves and tertiary nerves channeled above (Table 1) (Figure 2b, 3d-g) [9].Meanwhile, the leaves of V. javanica subsp.javanica are applanate/pressed flat to each other (Table 1) (Figure 2a).The exploration activities could not find any single flower or fruit.Nevertheless, fruit is not a major parameter to distinguish these two species, but the vegetative characteristic specifically leaf shape is [9].The field surveys recorded the living photograph of the species (Figure 2b, 3a-i).

Population structure
During the surveys in Bukit Bangkirai and Wanariset Samboja km 5, a total of 13 individuals of V. javanica subsp.scaphifolia were located (Figure 4a-b).All the individuals were at an immature stage with a height range of 2.1-14.7 m and a dbh range of 1-9.7 cm.Mother trees or mature trees around the population could not be found.The population was found in a clump at 94 m altitude on a relatively flat primary forest (15°).Plant species with small population size or a limited number of mature individuals implies a 7 serious threat to the population.Such species are highly vulnerable to extinction, especially those located in the area with high human activities [28].

Threats to the species
Kalimantan is one of the main islands in Indonesia with a large area of tropical rainforests and high plant diversity.However, the primary forest in Kalimantan undergoes rapid deforestation and land degradation [29], which seriously threaten plant habitats.Therefore, it is necessary to conserve and protect threatened and endemic plant species and habitats from extinction.Moreover, the development of East Kalimantan as the new capital city potentially accelerates habitat loss.Many endemic and threatened plants had not been either assessed or re-assessed, and ex-situ conservation had not been initiated yet.During the field surveys, we observed that many areas of forest habitat of V. javanica subsp.scaphifolia in Bukit Bangkirai have been converted into rubber plantations (Figure 5a) and open coal mining (Figure 5b).Rubber plantations are established in the lowland to hilly areas in Kalimantan [30].The plantations most often change an area dramatically from high species diversity to monoculture since they usually involve intensive management practices, i.e., clearcutting during site preparation and herbicide application.The effect is exacerbated by open coal mining activities that eliminates the existing vegetation and is responsible for acid mine drainage that adversely affects the habitat and hinders plant growth [31].This highlights the severity of deforestation and habitat in the location.

Ex-situ conservation program
Given the dangers posed by deforestation and degradation, a conservation action is urgently required to reduce the risk extinction of the species in the natural habitat.To support the insitu conservation program of V. javanica subsp.scaphifolia, the rediscovery of this endemic and critically endangered species has been reported to the Forest Management Unit (Inhutani I UMHTI) Balikpapan, the forest management authority of the forest areas where V. javanica subsp.scaphifolia was located.For ex-situ conservation of the species, 20 shoot cuttings were collected from immature individuals in the field and subsequently sent to the Bogor Botanic Gardens.Shoot-cutting trials of this species showed only a 10% survival rate without any roots developed.This low survival rate was allegedly caused by the high amount of resin on cut surfaces of the shoots, and prolonged transport time from the field to Bogor Botanic Gardens.We propose the ex-situ conservation programs are conducted at Balikpapan Botanic Gardens, a local ex-situ conservation area located near the species' habitat.

Conclusion
The current research provides new information on the morphological characteristics of V. javanica subsp.scaphifolia equipped with photos of living plants.This result study provide new locations of species and highlight the potential threats to the individual species and forest habitat.Information on the current population in the wild is essential to support in-situ conservation strategy.Conservation efforts for this species are crucial considering that V. javanica subsp.scaphifolia is the only protected Dipterocarpaceae species under the Regulation of the Minister of Environment and Forestry of Indonesia.Therefore, researches on propagation and cultivation are required to enhance the in-situ population of this species.This endemic plant species of V. javanica subsp.scaphifolia should be developed and utilized for mining land reclamation by companies, as well as for enrichment planting in plantations by local people.

Figure 1 .
Figure 1.The locations and specimen collection year of V. javanica subsp.scaphifolia based on the recent field survey in Bukit Bangkirai, East Kalimantan Province (yellow circles-line) and previous herbarium records (red circles-line).

Figure 5 .
Figure 5. Threats to the population of V. javanica subsp.scaphifolia observed in the study areas: (a) forest conversion into rubber (Hevea brasiliensis) plantations; (b) open coal mining.