BIODIVERSITAS ISSN: 1412-033X Volume 22, Number 4, April 2021 E-ISSN: 2085-4722 Pages: 1996-2004 DOI: 10.13057/biodiv/d220448 Population, habitat characteristic, and modelling of Endangered Orchid, Paphiopedilum javanicum in Mount Lawu, Java, Indonesia MUH. ARIF ROMADLON 1,2, , FATIMAH AZ ZAHRA 2 , GILANG DWI NUGROHO 2 , ARI PITOYO 3 1 Tanah Tinggi Highland Conservation. Jl. Agung Timur, Surakarta 57127, Central Java, Indonesia. ♥ email: arif@tanahtinggi.org 2 Biodiversitas Study Club, Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Sebelas Maret. Jl. Ir. Sutami 36A, Surakarta 57126, Central Java, Indonesia 3 Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Sebelas Maret. Jl. Ir. Sutami 36A, Surakarta 57126, Central Java, Indonesia Manuscript received: 1 January 2021. Revision accepted: 24 March 2021. Abstract. Romadlon MA, Az Zahra F, Nugroho GD, Pitoyo A. 2021. Population, habitat characteristic, and modelling of Endangered Orchid, Paphiopedilum javanicum in Mount Lawu, Java, Indonesia. Biodiversitas 22: 1996-2004. Paphiopedilum javanicum (Reinw. ex Blume) Pfitzer or Java Paphiopedilum is an endangered orchid categorized as appendix I in CITES. In its natural habitat, forest fire, habitat fragmentation, and extreme poaching are considerably the prominent threats for the species. The study aims to assess the population distribution, the habitat characteristics and model the suitable habitat of P. javanicum in Mount Lawu, Java, Indonesia using Maxent (Maximum Entropy) modelling. Eighteen subpopulations of P. javanicum spread across the region with a total number of 104 individuals. The majority of the individuals are in the generative phase (93.3%) and the rest are in the vegetative phase (6.7%). In Mount Lawu, P. javanicum can be found at an elevation of 1,231-1,825 m asl. in a deep shady forest floor with a thick litter and canopy cover between 0-77.4%. The soil has pH between 7-7.1 with 12.5-36.7% of moisture. The air temperature ranging between 21.8˚-29.7˚C, with humidity of 61-78.5%. Based on the Maxent test, annual mean temperature, vegetation cover, type of land use, and elevation are the most influencing factor of P. javanicum distribution in Mount Lawu. The model identifies 6814.75 ha areas in Mount Lawu that are suitable for the species distribution. Lawu Purba, the biggest suitable area for P. javanicum habitat in the southern part of the mountain holds the remaining natural forests in the region. The result is expected to provide recommendations for determining priority areas in the conservation efforts for this threatened orchid. Keywords: Endangered species, habitat modelling, maximum entropy, Maxent, Mount Lawu, Paphiopedilum javanicum INTRODUCTION Orchidaceae is the most diverse plant family with 32,754 accepted species names worldwide (POWO 2021). The diversity of the orchid family is inseparable from the uniqueness of its generative propagation, symbiosis with microorganisms, and various types of habitats where they could grow. However, because it has an association with specific pollinators and microorganisms and limitation of germination, many orchids have limited distribution (Swarts and Dixon 2009; Wani et al. 2021). Some orchids species are becoming threatened by several factors, such as overgrazing, habitat loss, human intrusion, and over-exploitation due to increasing market demand in trading (Pant and Raskoti 2013; Agustini et al. 2016; Warghat et al. 2016). One genus that often traded is Paphiopedilum as known as the slipper orchids (Bänziger et al. 2011). It is particularly popular as an ornamental plant, because it has beautiful flowers and attractive leaves (Vu et al. 2020). The main feature of Paphiopedilum is its pouch-like lip on the flower. Most of the Paphiopedilum species are threatened due to overexploitation, such as P. armeniacum and P. druryi (Bänziger et al. 2011). Many studies on Paphiopedilum have been carried out both in situ and ex situ for conservation purposes, such as P. rothschildianum (Rchb.f.) Stein in Kinabalu National Park, Malaysia (van der Ent et al. 2015), P. fairrieanum (Lindl.) Stein in Bhutan (Samdrup et al. 2020), and P. javanicum (Reinw. ex Blume) Pfitzer in Bali (Tirta 2011). There are 3 species of Paphiopedilum in Java, namely P. lowii, P. glaucophyllum, and P. javanicum (Comber 1990). P. javanicum is one of the endangered species listed by IUCN Redlist (Rankou 2015) and included in the appendix 1 category by CITES (Govaerts et al. 2019). The population of this orchid in nature continues to decline due to various threats, such as habitat fragmentation, unsustainable hunting, and climate change (Rankou 2015). Insight into the population will help determine the number and level of mortality in nature. The distribution of P. javanicum is ranging from West Malesia to the Lesser Sunda Islands. In Java, P. javanicum can be found in the forest of Mount Lawu. The highest peak is at an altitude of 3,265 m asl. and has different environmental characteristics on each side. The forest areas in Mount Lawu are one of the few remaining tropical montane cloud forests (TMCF) in Java. Its vegetation is regularly covered by fogs that often turn to local raindrops (Ray 2013). The dense epiphytic plant communities on the crown of the vegetation are also one of the features of TMCF. TMCF is a rare and fragile ecosystem type but has a high level of species endemicity and has an important role in the hydrological system (Bruijnzeel et al. 2011; Ledo et al. 2012). The forest is also an important habitat for