Declining Orangutans Population in the Unprotected Forest of Batang Toru
Main Article Content
Abstract
Habitat loss and hunting are major threats to the long-term survival of the viable orangutan population in Batang Toru. East Batang Toru Forest Block (EBTFB) is the most threatened area due to low forest cover and high encroachment. Based on a preliminary survey in 2008, Hopong forest which is located in EBTFB, had the highest orangutan density (0.7 ind/km2). However illegal logging and hunting of protected species were occuring in this unprotected forest. Since this location has been gazetted as unprotected forest from the first survey until this study was conducted, it is important to assess orangutans population trends. This study aims to provide an updated density of orangutan in Hopong forest. The study included the location of the original survey but covered a wider overall area. The line transect method was used to record orangutan nests, ficus and trees bearing fruits. A quadrat method was used to record vegetation. The encounter rate of orangutan declined from 0.7 ind/km2 to 0.4 ind/km2 between 2008 and 2015. Forest cover has also changed in the seven years between surveys and this has influenced orangutan and orangutan nest encounter rates in Hopong. Since unprotected forest is at more risk in comparison with protected forest, allocation status of the Hopong forest is critical to reduce the threats it faces.
Article Details
This work is licensed under a Creative Commons Attribution 4.0 International License.
References
Buckland S T, Anderson D R, Burnham K P and Laake J L. (1993). Distance sampling: Estimating abundance of biological populations. London: Chapman and Hall.
Campbell-Smith G, Simanjorang H V, Leader-Williams N and Linkie M. (2010). Local attitudes and perceptions towards crop-raiding by orangutans (Pongo abelii) and other non-human primates in northern Sumatra, Indonesia. American Journal of Primatology 72: 866–876. https://doi.org/10.1002/ajp.20822
Campbell-Smith G, Campbell-Smith M, Singleton I and Linkie M. (2011). Apes in space: Saving an imperilled orangutan population in Sumatra. Plos ONE 6(2): e17210. https://doi.org/10.1371/journal.pone.0017210
Carne C, Semple S and Lehmann J. (2015). Investigating constraints on the survival of orangutans across Borneo and Sumatra. Tropical Conservation Science 8(4): 940–954. https://doi.org/10.1177/194008291500800405
Estrada A, Garber P A, Rylands A B, Roos C, Fernandez-Duque E, Di Fiore A, Nekaris K A et al. (2017). Impending extinction crisis of the world’s primates: Why primates matter. Science Advances 3: 1–16. https://doi.org/10.1126/sciadv.1600946
Fredriksson G. (2008). Orangutan and mammal surveys of the East Batang Toru Forest Block, Tapanuli, North Sumatra, Indonesia (Unpublished report). Yayasan Ekosistem Lestari - Sumatran orang-utan Conservation Project, Medan, Indonesia.
Gaveau D L A, Curran L M, Paoli G D, Carlson K M, Wells P, Besse-Rimba A, Ratnasari D and Leader-Williams N. (2012). Examining protected area evectiveness in Sumatra: importance regulations governing unprotected land. Conservation Letters 5(2): 142–148. https://doi.org/10.1111/j.1755-263X.2012.00220.x
Gregory S D, Brook B W, Goossens B, Ancrenaz M, Alfred R, Ambu L N and Fordham D A. (2012). Long-term field data and climate-habitat models show that orangutan persistence depends on effective forest management and greenhouse gas mitigation. PLoS ONE 7(9): e43846. https://doi.org/10.1371/journal.pone.0043846
Johns A G and Johns B G. (1995). Tropical forest primates and logging: Long-term coexistence? Oryx 29(3): 205–211. https://doi.org/10.1017/S0030605300021141
Meijaard E. (1997). A survey of some forested areas in south and central Tapanuli, North Sumatra; New chances for orangutan conservation. Bogor, Indonesia: The International MOF Tropenbos Kalimantan Project and The Golden Ark Foundation.
Nater A, Nietlisbach P, Arora N, van Schaik C P, van Noordwijk M A, Willems E P, Singleton I et al. (2011). Sex-biased dispersal and volcanic activities shaped phylogeographic patterns of extant orangutans (genus: Pongo). Molecular Biology and Evolution 28(8): 2275–2288. https://doi.org/10.1093/molbev/msr042
Nater A, Mattle-Greminger M P, Nurcahyo A, Nowak M G, de Manuel M, Desai T, Groves C et al. (2017). Morphometric, behavioral, and genomic evidence for a new orangutan species. Current Biology 27: 1–12. https://doi.org/10.1016/j.cub.2017.09.047
Onrizal and Perbatakusuma E A. (2011). Potensi pohon sumber pakan orangutan Sumatera untuk kegiatan rehabilitasi di Blok Barat dan Blok Timur Hutan Batang Toru, khususnya kawasan koridor orangutan Batang Toru, Sumatera Utara (Unpublished Report). Conservation International Indonesia, Medan, Indonesia.
Odum E P. (1993). Dasar-dasar ekologi. (Translated from Tjahjono Samingan). 3rd ed. Yogjakarta: Gadjah Mada University Press.
Prasetyo D, Ancrenaz M, Bernard H M, Utami-Atmoko S S, Wich S A and van Schaik C P. (2009). Nest building orangutans. In Wich S A, Utami S S U, Setia T M and van Schaik C P (eds.). Orangutans: Geographic variation in behavioral ecology and conservation. New York: Oxford University Press, 226–227.
Rao M and van Schaik C P. (1997). The behavioral ecology of Sumatran orangutans in logged and unlogged forest. Tropical Biodiversity 4(2): 173–185.
Rijksen H D. (1978). A field study of Sumatran orangutans (Pongo pygmaeus abelii, Lesson 1827). PhD dissertation, Wageningen University, the Netherlands.
Singleton I, Wich S A, Husson S, Stephens S, Utami-Atmoko S S, Leighton M, Rosen N, Traylor-Holzer K, Lacy R and Byers O. (eds). (2004). Orangutan population and habitat viability assessment: Final report. Apple Valley, MN: IUCN/SSC Conservation Breeding Specialist Group.
Strum S C. (1994). Prospects for management of primates pest. Revolution Ecology 49: 295–306.
Susanto T W, Basalamah F and Siswanto I. (2008). Survei mamalia dan orangutan di kawasan Hutan Batang Toru Blok Timur, Sumatera Utara (Unpublished Report). Yayasan Ekosistem Lestari - Sumatran orang-utan Conservation Project, Medan (ID).
van Schaik C P, Azwar and Priatna A. (1995). Population estimates and habitat preferences of orangutans based on line transects of nests. In Nadler R D, Galdikas B M F, Sheeran L K and Rosen N. (eds.). The neglected ape. New York: Plenum Pr.
Wich S A, Meijaard E, Marshall A J, Husson S, Ancrenaz M, Lacy R C, van Schaik C P, Sugardjito J, Simorangkir T, Taylor-Holzer K et al. (2008). Distribution and conservation status of the orangutan (Pongo spp.) on Borneo and Sumatra: How many remain? Oryx 42(3): 329–339. https://doi.org/10.1017/S003060530800197X
Wich S A, Fredriksson G M, Usher G, Peters H H, Priatna D, Basalamah F and Susanto W. (2011). Hunting of Sumatran orang-utans and its importance in determining distribution and density. Biology Conservation 146: 163–169. https://doi.org/10.1016/j.biocon.2011.12.006
Wich S A, Usher G, Peters H H, Khakim M F R, Nowak M G and Fredriksson G M. (2014). Preliminary data on the highland Sumatran orangutan (Pongo abelii) of Batang Toru. In NB Grow et al. (ed.). High altitude primates, development in primatology: Progress and perspective. New York: Springer Science+Business Media, 265– 283. https://doi.org/10.1007/978-1-4614-8175-1_15
Wich S A, Singleton I, Nowak M G, Utami Atmoko S S, Nisam G, Arif S M, Putra R H, Ardi R, Fredriksson G, Usher G, Gaveau D L A and Kühl H S. (2016). Land cover changes predict steep declines for the Sumatran orangutan (Pongo abelii). Sciience Advance 2(3): e1500789.