The rain forest covers almost 65% of the island of Siberut. This forest is a palace for the life of flora and fauna by providing a source of food and shelter as well as forest also serves as a supporter of the traditional life of the Mentawai people, especially as traditional medicine. Botanical collection was first created by Ridley (1924) and produces a description of 33 new species. Some speceis plants have evolved unique characteristics to form an unusual morphology. For example Xanthophyllum villarii (Rubiaceae), an extraordinarily high in Siberut. This species is known only in the Philippines. Chloranthus officinalis (Chloranthaceae) grows very large when compared with each of these species in other areas. Phaeomeria minor (Zyngiberaceae) has the smallest size in the genus. LIPI (1995) has managed to record about 846 species, 390 genera and 131 families of a group of trees, shrubs, herbs, liana and ephypit. Also identified 18 species of ferns and 5 species of mosses and fungi. The most important families are Euphorbiaceae (24 genera, 100 species), Orchidaceae (41 genera, 67 species), Rubiaceae (25 genera, 54 species) and Lauraceae (11 genera, 39 species). Dipterocarpaceae group which successfully accounted for as many as 20 species including 6 species of Dipterocarpus, 2 species of Hopea, 8 species and 4 species of Shorea Vatica. An estimated 15% of plants in Siberut is an endemic species. Among others who have found is that as many as 6 species of endemic plants are: Mesua cathairinae (Clusiaceae), brevicalyx Diospyros (Ebenaceae), Aporusa quadrangularis (Euphorbiaceae), Baccaurea dulcis (Euphorbiaceae), subsymmetrica Drypetes (Euphorbiaceae) and Horsfieldia macrothyrsa (Myristicaceae). As a result of the isolation of P. Siberut, other forms of endemic flora found in changing its form from the mainland of Sumatra such as sago is a staple food in the Mentawai which has more height and large that is the largest sago areas in Southeast Asia.
Rattan is one of non-timber forest commodities are of significance for the economy in Siberut. In addition to producing cash, many types of rattan are very useful in daily life of society as a means to bind, wrap the leaves for a roof or traditional foods of sago (kapurut). From the results of the inventory SNP (1999) found 15 species of rattan-rotanan in Siberut which consists of 3 genera are: Calamus 10 species, and Korthalsia Daemonorops 3 types of 2 types. From these types of wicker-rattan Calamus Calamus scipionum comfort and is a valuable economic, where rattan-cane is widely available in mixed primary forest.
Wild orchids found in the area of SNP of 25 species included in 13 genera comprising 22 species of epiphytic orchids and 3 types of ground orchid (LIPI, 2002). Orchids are well known from Siberut is the White Moon (Phalaenopsis amabilis), white flowers thick fleshy leaves, long flowering 3-4 months with the number of florets 7-15 in one stalk. Other orchids that can be found is Coelogyne incrasata , Eria nutans, Dendrobium paphyllum etc.
- Hylobates klossii (Bilou or Little Gibbon)
Bilou is the most famous primate species in the Mentawai. Anatomically including agile gibbon species oldest surviving with a rare feathers dusky black, and the membrane between the second and third fingers. Screeched screeches Bilou simplest among agile gibbon, longer, varied and not conducted by the agile gibbon and other. Bilou live in groups consisting of male and female parent with children who are minors. Bilou including animal monogamy with an average family of three to four individuals, while the number of members in one group can be reached 11 individuals.Bilou is a primate species that spend most time on top of tall tree (over 20 meters)
- Presbytis potenziani (Joja or monkey Mentawai)
Joja have the most beautiful forms of primates endemic, with shiny black, the abdomen dark brown, white around the face and neck and long tail and black as silk. Although included in a large genus of tropical Asia and spread widely, Joja is unique in many ways. Adult female and male partners participated in the demonstration shriek and a challenge to other groups, unlike other agile gibbon, and langur species, because only males who do both. Joja usually made sounds before dawn and taken as a sign the group territory so that other animal groups to avoid. Joja most of his life living in trees and seldom come down to the ground.
- Simias concolor (simakobu)
This includes family bekantan monkey (the same group are in Kalimantan). Simakobu very different from bekantan and all other forms of monkeys because of the short tail-like pig tails, body fat and body members of the same length and there are two types of coat color of dark grey and golden. Simakobu live in trees and eat leaves. Simakobu live in a group consisting of 1 female, 1-5 male adults and children. Adult males have larger size of adult females and have canine teeth more than twice the length of an adult female canines.
- Macaca pagensis (Bokkoi or monkey Mentawai)
Bokkoi very closely related to the monkey that is in Sumatra, Kalimantan and Southeast Asian continent, but has a darker coat color that contrast with the white cheeks and yelled unique. Monkey usually live on large islands, and very unusual turns Bokkoi live on small islands such as Pulau Siberut. Bokkoi also made sounds before dawn but did not show shriek territories. Bokkoi male repeatedly cries out so keep in touch with group members who also responded with screams and the sounds they used to spend to keep in touch one another in dense forest. Bokkoi group consisted of 30 individuals, usually consisting of 80-10 individuals with a male alone in the lead. The group was divided into small groups to find food and re-join the group at the time each night.
Species that are most attracted the attention of the fauna on the island of Siberut are mammals. There are about 28 species of mammals, 65% of them are endemic at the genus level, species and subspecies. Among the 28 species of mammals, the group of primates is a major concern because there are four types of primates that are endemic in the Mentawai. Found as many as 7 species of squirrels, 5 of which are endemic species are: Callosciurus melanogster, Sundasciurus fraterculus, Lariscus obscurus, Iomys Sipora and Hylopetes Sipora. Three species of rats in Siberut is a subspecies endemic to the Mentawai islands namely Rattus tiamonicus mentawi (commonly found in homes and forest edge), Rattus surifer pagensis (live in primary forest, colorful body and brown around the neck, black back, abdomen white and both sides of the upside-down and the legs dark yellow), Ratus sabanus siporanus (found in primary forest, black top and white on the bottom). Siberut has only three carnivores, two species of civet is endemic at the subspecies and one species of otter (Aonyx cinerea). Weasel who lived on Siberut are very different than the weasel which are common in Sumatra. None of the features found in civet that lives in Siberut so-called primitive ferret. Marine mammals in the waters of Siberut island consists of whales, spotted dolphins (Stenella longirostris, Delphinus sp and Grampus sp) which is often seen around the east coast of Siberut and dugongs (Dugong-dugon), which is very rarely found in waters east coast.
Siberut Island there are many birds. From 106 species of birds are, 13 species (12%) of them including endemic subspecies level. The only bird species endemic to this island is Celepuk Mentawai (Otus Mentawai ). SNP inventory (2000) recorded 134 species of birds in Siberut. Birds that occupy forest stratification profile, in which the main canopy tree-dwelling (> 25 m) among other hornbills, eagles, crows, parrots, etc
Reptil, Fish and Amphibians
According to the article A. Whitten, J. Dring and Mitchell (1982), there are 21 types of amphibians on the island of Siberut and one of them is endemic frog species of Rana signata Siberut. While there are 62 types of reftil and 3 of them are endemic species of snakes and Oligodon Calamaria klossii sp. of the tribe and Boiga nigriceps brevicauda Colubrinae of interest Boiginae. s, Viperidae / 5 species of poisonous snakes, Testudinidae / 2 species of turtles, Cheloniidae / 2 species of sea turtles, Sibynophinae / snake species and Pareinae 1 / 2 snake species.