Siberut Conservation Programme: The Habitat of Siberut Island (Sundaland, rainforest, swamp forest, mangroves, logging, land conversion)

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	Habitat

Situated on the western margin of the Sundaland Hotspot of biodiversity, the Mentawai Archipelago is of special conservation interest. Comprising the four main islands of Siberut, Sipora and N and S Pagai, the archipelago has been separated from “mainland” Sumatra for more than 500 000 years. Mentawai fauna and flora have thus evolved in isolation since the mid-Pleistocene and this process has resulted in an unusually high number of endemic animal and plant species. Some species are considered to be relicts of early Sundaland communities, whereas others have evolved into forms clearly distinct from the representatives on the Asian mainland.

Today Siberut’s flora is reported to consist of 846 species out of 390 genera belonging to 131 families, but it is generally assumed that the list of plant species known to be endemic is incomplete, and that over time new species will be identified (UNESCO MAB 2004).

Primary rainforests represent the principal refuge for almost all of the unique species of the Mentawai archipelago, but unfortunately many forests have been lost over the last few decades due to relentless pressure from timber logging and land conversion. Only small fragments of primary rainforest are left in the 3 southern islands and although approximately 50% of Siberuts rainforest cover is thought to remain, the threats posed by non-sustainable forms of land use continue and several major logging companies currently hold concessions to legally operate within Siberuts forests.





		About 50% of Siberut is still covered by primary rainforest, the canopy of which is home to the majority of the islands endemic species. Most of these remain either poorly studied or have yet to be described.



The Peleonan forest in northern Siberut is one of the few remaining undisturbed primary forest areas on the Mentawai islands and home to a wide diversity of unique animal and plant life. This forest still contains relatively high densities of all four Siberut primate species.



	Where these dense forests are pervaded by small or medium sized rivers, ground dwelling flowers receive just enough sunlight to bloom.



In the North of Siberut a 3-4 km wide belt of peat swamp forest separates the rain forest from the sandy coast. As SCP scientists have recently shown, peat swamp forest provides a suitable habitat for many different species including Siberut’s four primate species


			The coastal areas of eastern Siberut are dominated by mangrove swamps, another valuable and irreplaceable habitat for numerous species – both above and below the water surface. Like the coral reefs, the mangroves, represent important breeding areas for tropical fish species, but are under serious threat of destruction.




	Giant tropical trees are a highly important resource and have been sustainably used by the local people for hundreds of years. For several decades however, they have also been the target of professional logging companies serving the international timber trade.


	Together with land conversion for oil palm plantations, logging activities have already permanently removed about 75% of the forest cover on the Mentawai archipelago, causing large scale soil erosion and loss of agricultural potential.


	Shrinking forests lose their ability to buffer water levels in the rivers throughout the year, resulting in extreme fluctuations from water shortage during drier periods to severe flooding after rainfall. Frequent flooding creates large expanses of standing water which in turn results in a marked increase in the incidence of malaria.


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