Population, morphological, and genetic characteristics of pelawan trees on Bangka Island, Indonesia: implications for conservation

Tristaniopsis spp. (pelawan) trees hold great significance in ensuring biodiversity sustainability and supporting the local species within Kepulauan Bangka Belitung Province. Moreover, it plays a crucial role in fostering the social and cultural aspects of the local community. However, the pelawan population has faced great threats due to land conversion, unmanaged forests, and mining. To address these challenges, the local government has shown a commitment to expanding the in-situ conservation areas beyond Namang Biodiversity Park. In order to enhance the conservation status of this species, it is essential to conduct a comprehensive study of the tree’s distribution, morphological characteristics, species delimitation, and genetic diversity. Therefore, this study aimed to obtain information on pelawan distribution, morphological characteristics, species confirmation, and genetic diversity. It was conducted at five natural populations, namely KK (Kota Kapur), BB (Berbura), LAP (Labuh Air Pandan), PN (Pangkal Niur), and LB (Limbung), and the genetic character was observed using ITS and RAPD markers. The first instance of establishing a nucleotide sequence database for pelawan on Bangka Island was also represented, showing the presence of two distinct taxa groups based on ITS sequence nucleotides. Based on morphological characters (bark color and leaves), the two groups were determined to be pelawan merah/orange (Tristaniopsis sp. 1) and pelawan air (Tristaniopsis sp. 2). Significantly, the genetic diversity analysis yielded a range of HE values, from 0.283 (KK) to 0.353 (PN). The PCoA and dendrogram analyses exhibited the formation of a cluster comprising populations from Bangka (KK, BB, LAP, and PN), while LB formed a separate cluster. The result showed significant genetic differentiation between regions and populations, without mixing seeds or seedlings. It was suggested that the conservation strategy for pelawan trees on Bangka Island should be developed with several considerations. In-situ conservation sites should be designated based on the presence of pelawan merah/orange and pelawan air taxa. Additionally, ex-situ conservation plots needed to be established, with at least one location dedicated to each taxonomic group. To preserve the remaining natural genetic resources, KK and LB populations, which had the lowest HE value and different genetic structures should be prioritized. Strategies for ex-situ conservation included KK, LB, and PN. The prioritization of PN for conservation was necessary, and further genetic study of the pelawan should involve larger populations representing the natural distribution of each species.