Kajian habitat dan estimasi populasi orangutan sumatera (Pongo abelii Lesson, 1872) di kawasan Hutan Toru, Sumatera Utara

Abstract

Kawasan hutan Batang Toru, Sumatera Utara, telah diidentifikasi sebagai salah satu unit habitat orangutan sumatera yang menjadi perioritas utama dengan upaya konservasi. Upaya ini masih terus dikerjakan oleh pemerintah dan semua pihak terkait dengan melibatkan lembaga konsservaasi dan masyarakat setempat dengan maksud untuk menyediakan sebanyak-banyaknya informasi tentang keberadaan populasi orangutan sumatera. Untuk memenuhi kebutuhan tersebut. Maka penelitian habitat dan populasi orangutan di kawasan ini telah dilakukan selama bulan Oktober 2007 sampai dengan Januari 2008 dengan tujuan untuk menganalisis: (1) struktur dan komposisi vegetasi serta sebaran pohon (termasuk pohon sumber pakan dan tempat bersarang); (2) perkiraan jumlah kepadatan dan populasi orangutan ; dan (3) faktor-faktor ancaman bagi keberadaan dan kelangsungan hidup orangutan sumatera di kawasan hutan Batang Toru.

The Batang TofU forest located in North, Center and South of Tapanuli, North Sumatra was recently found as one of Sumatran orangutan population habitat. A survey of trees species, nesting behavior and population of Sumatran orangutan was carried out during October 2007 up to January 2008 and aimed to analyze: (1) the forest structure, composition and trees distribution (including feeding and nesting trees); (2) estimated density and popUlation; and (3) the threat factors influenced the survival of Sumatran orangutan in Batang TofU forest. The results of the inventory of trees with diameter at breast height (DBH) 2: 10 cm in 3.84 ha areal sampling showed that 274 species in 56 families, represented by 1,896 individuals with total basal area of 148.9 m2lha and density of 498 treeslha. This forest was richer in tree species than other lowland forests in North Sumatra, Borneo and the Malay Peninsula and was dominated by Sapotaceae trees. The most prominent species were Tristania maingayi, Casuarina sumatrana, Quercus sumatrana and Ganua motleyana in every types of forest and differenced with Batang Gadis National Park which dominated by Dipterocarps. There were 96 feeding trees species in 25 families, represented by 536 individuals with total basal area of 46.7 m2lha. The prominent heights of feeding trees were below 30 m and distributed abundantly in the old moist secondary forests. The most important feeding trees for orangutans (Diospyros sp., Eugenia sp., Nephelium sp., Lithocarpus sp., Ficus sp., Artocarpus sp., Durio sp., and Garcinia sp.) were abundantly found in the old moist secondary forests, too. Orangutans commonly prefer to nest on the top of tree bar and the main branch of trees (DBH 20-30 cm; heights 15-20 m), especially in the middle canopy (20-30 m). Considering that there were enough feeding trees in this canopy. The most preferred nesting trees genus/species were Quercus sp., Syzygium sp., Shorea sp., Diospyros sp. and Lithocarpus sp. It was also invented 267 orangutan nests along 40.125 km cumulative lengths of line transects or equal with 0.54 percent of study area conducted at 11 sites. Densities were found higher in the old moist secondary forest while it was conversely lower density in the mixed forest. The distributions of nests were tended to clumped, related to the distribution of feeding trees. Orangutan population in 748.86 km2 ha potential habitat was approximately 337-421 individuals. Their distribution was limited by elevation and food availability. Human activities such as land conversion for agriculture purposes had become important factors affecting orangutan distribution. Field fact finding showed that many orangutan direct sightings and nests were located much closer to area human activities and logging concessions. This eventually has become real and concreted threat to their remaining population. It's needed to conduct further research in long-term monitoring and develop a strategic planning which promotes community involvement for the conservation of orangutan.