Short: The Sungai Imbak Virgin Forest Reserve is some 35 km to the north of the better known Maliau Basin, Sabah's "Lost World." The reserve was gazetted 1965 and covers some 18113 hectares of nearly inaccessible mountainous terrain, covered in dense virgin jungle. It belongs to the most important sites in Sabah for virgin jungle conservation and research.

Truly Untouched Rainforest

The Sungai Imbak Virgin Forest Reserve is a Class VI Virgin Jungle Reserve of an area of approximately 18113 hectares, located in central Sabah and divided into six blocks. Some 35 km away is the better known Maliau Basin. Access to the reserve is difficult and only possible by 4x4 over gravelled and dirt roads, and since there is no infrastructure whatsoever the area remains largely pristine.

The Sungai Imbak Virgin Jungle Reserve was initially part of the Sungai Pinangah Forest Reserve, which was gazetted in 1965. In 1984 the reserve was split into two reserves, one being the Sungai Pinangah Forest Reserve (Class II) and the other being Sungai Imbak Virgin Jungle Reserve (Class VI). Both reserves are managed by Yayasan Sabah, though due to its rugged terrain there is no management plan (logging plan or other use) for Sungai Imbak, very fortunately.

The region is mountainous with two main ridges forming two arcs. The highest peak is at 1551 m a.s.l. at the south-eastern-most part of the reserves. The ridge spurs run into the valley where the Imbak River flows. Travelling by foot is best when along spurs rather than traversing. Many hillsides have slopes greater than 25°. The Imbak River which flows into the Kinabatangan River, making the Imbak an important water catchment for the Kinabatangan.

The forest of the Imbak Reserve is pristine in the sense that it has not been logged or affected by any major forms of natural or human disturbance. The Dipterocarpacea is the most dominant tree family in the four general forest types that are recognized in the Imbak area: 1) lowland mix dipterocarp forest, 2) upland mix dipterocarp forest, 3) lower montane kerangas forest, and 4) upper montane kerangas forest.

 

The Dipterocarpacea The dipterocarpaceae, or dipterocarps are one of the main features of Sabah’s forests. Most of them highly valuable hardwoods, the trees are tall (70 meters), with a very long, straight trunk that only branches out at some 50 meters height and forms a close ‘cauliflower’ canopy. In a 10-day survey of the area 58 dipterocarp species from 8 genera were recorded. This accounts for 29 % of the 200 species of dipterocarp known to occur in Sabah. Of these 58 species, 30 are endemic to Borneo, i.e. they occur naturally only on the island of Borneo. For comparison, 48 species have been recorded from the Maliau Basin Conservation Area and 35 from the Kabili-Sepilok Forest Reserve. Dryobalanops beccarii (kapur merah) and Shorea laevis (selangan batu kumus) stand out as being particularly common in the main forest canopy of the mix dipterocarp forest of the Imbak. Large kapur merah trees are often hollow and therefore provide important nesting sites for birds such as hornbills. S. laevis is one of the most important sources of Selangan Batu timber, known for its strength and durability.

Surveys and botanical collection trips were conducted in August of 1992, during a period of mast fruiting. This was done by the Sabah Forestry Department, in collaboration with Yayasan Sabah. However, the collecting activities did not venture into the valley proper and the two main ranges of Sg. Imbak. Prior to this expedition, there were no known botanical explorations of the Imbak area. All collections (150 in total) made during the 1992 botanical expedition are kept for permanent record at the Sandakan Herbarium in Sepilok.

An major expedition was organised by the Sabah Forestry Department in July 2000 and further faunal surveys were carried out during an expedition in 2000 by the Sabah Wildlife Department and the Sabah State Museum. However, information on this survey is not yet available.

 

Biodiversity Conservation Anywhere in Sabah, lowland mixed dipterocarp forests (MFD) represent an extremely important reservoir of biodiversity. At the same time it is the principal source of commercial timbers. For this reason most of the lowland MDF have been heavily exploited, while a large portion have been lost to agricultural development. At present, the Imbak supports one of the few relatively large tracts of pristine dipterocarp forests remaining in Sabah, underscoring its immense value for biodiversity conservation. A major constraint to large scale reforestation efforts in Sabah is the availability of reliable sources and sufficient amounts of planting material. With the ever increasing efforts at reforestation, the Imbak is seen as an important natural source of planting material (or seed production area). Despite those two botanical surveys, much of the Imbak remains unexplored and a lot remains to be studied about the flora of the Imbak. For instance, the highest area of the Imbak (just over 1,500 m a.s.l.) located at the south-eastern corner has yet to be visited botanically. Although the sample plots that were established are not sufficient to provide a comprehensive account of the vegetation, they provide a good indication of the main floristic associations of the Imbak. Such information can be built upon over time as time and resources become available. Considering the current state of forest conservation in Sabah, the protection of the Imbak merits serious consideration.

New species and a new record for Sabah

Two new tree species have been described from the Imbak. Dipterocarpus megacarpus was described by Madani (1992) following the first expedition to the Imbak. The second species to be described was Ceriscoides imbakensis (Azmi, 2000), a very rare tree from the Rubiaceae family. The only two collections of this species are from the banks of the Imbak River. Ruth Kiew, a begonia specialist from the Singapore Botanic Gardens, collected two Begonia species during the 2000 Imbak expedition. These collections have yet to be described and named. Had there been a greater participation from plant specialists on the two expeditions, more new discoveries would have been likely.

How to Get to the Sungai Imbak Forest Reserve & Accommodation

Nearly impossible - plus access is restricted, and probably rightly so if the pristine nature of this part of Sabah is to be totally protected. No accommodation is available, and no other infrastructure has been erected, or is planned.