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Flora & Fauna

Forest Types

Sarawak's rainforests are amongst the richest and most diverse on the planet.

This page provides an introduction to the major forest types in Sarawak.

Flora & Fauna
Forest Types
> Introduction
> Mixed Dipterocarp Forest
> Kerengas Forest
> Mangrove Forest
> Beach Vegetation
> Peatswamp Forest
> Riverine Forest
> Montane Forest
> Limestone Forest
Trek Locations
> Bako NP
> Gunung Gading NP
> Kubah NP & Matang
> Lambir Hills NP
> Mulu NP
> Niah NP
> Santubong
> Tanjung Datu NP
Introduction

Sarawak's forests display an extraordinary diversity - both in vegetation types, and in species richness.

There is some disagreement as to the exact classification of the different forest types, and any distinctions are necessarily artificial. However, there are 8 broadly accepted categories of vegetation or forest type in Sarawak, which are described on this page.

Understanding the general nature of the forest types provides a good context for understanding the individual species living within them - specific flora and fauna are described in more detail in other pages.

The location and of the different forest types is dependent on a number of factors, especially geology - the nature of the underlying soils and rocks, how fertile (or infertile) they are, how well water is retained, how steep slopes are, as well as variations in rainfall, etc. Some forest types are very specific - eg limestone forest only occurring where there is limestone, beach forest only growing in a narrow strip behind beaches.

A map showing the distribution of the major forest types in Sarawak is shown below:

Map (c) Sarawak Forest Department

All the different forest types can be experienced in Sarawak's national parks, although some national parks will not include all forest types.

Bako National Park includes almost all, other than limestone forest. Limestone forest can be found at Mulu and Niah. Most of the other National Parks include a mix of dixed dipterocarp forest, kerengas forest, montane forest, and some also have riverine forest.

Each forest type has its own unique features and attractions. These are explored in turn in the following sections.

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Mixed Dipterocarp Forest
Description: Mixed dipterocarp forest is the richest of Sarawak's major forest types, the archetypal "tropical rainforest". Mixed dipterocarp forest is the most significant forest in Sarawak, both in terms of area covered and commercial importance for logging. Its name derives from the towering dipterocarp trees (Dipterocarpaceae) which dominate this forest type.

The canopy formed by these great trees can be as high as 60m, excluding most light from the forest floor. As a result, the forest floor (or "understory") can be quite open and easy to pass through. However, a number of plants specially adapted to low-light do grow on the forest floor, along with young canopy trees - trying to break through, or waiting for an old giant to topple, leaving enough of a gap (and sunlight) to fill.

Sarawak's mixed dipterocarp forest is amongst the most diverse on the planet, with up to 1500 tree species alone (compared with only about 175 tree species in the whole of North America, and 75 in Europe!) . In addition to the dipterocarps these forests contain a huge array of palms, fruit trees such as figs, durians and mangoes, ferns, orchids, liana vines, and numerous other plant types. Many of the large trees are literally covered in various other epiphytic and parasitic plants. The famous giant rafflesia flower is one type of parasitic plant found in mixed dipterocarp forests.

This huge diversity results in an extremely complex ecosystem, with species of plants and animals adapted to living at different levels in the canopy or on the forest floor, or only on certain trees (for example most fig trees are pollinated by their own unique associated species of wasp, not even found on other fig species!).

Another consequence of the huge diversity of tree species within mixed dipterocarp forests is that any single given species may be very rare (if there are 500 tree species found within 1 hectare, that means most of them only occur once in that area). Many of the plants found in Sarawak's mixed dipterocarp forests are only found in Borneo, some only in Sarawak, and some only in certain national parks within Sarawak.

The diversity of plants in mixed dipterocarp forests is also reflected in the diversity of animals, birds, and insects found there. For example, Sarawak has an estimated 185 mammal species, 530 bird species, and 154 snake species (don't worry - they're mostly harmless), plus more than 5000 beetle species, 3000 moth species, and 900 butterfly species! Many of these are found primarily in the rich dipterocarp forests.

Various subtypes of mixed dipterocarp forest have been described, including lowland dipterocarp forest, hill dipterocarp forest, summit ridge forest and submontane forest. However, these types are not all clear-cut, and the borders between dipterocarp forest types (and borders with other forest types as well) may be diffuse and not obvious.

Best places to see: Primary mixed dipterocarp forest can be seen at most of the national parks described in this website. Lambir Hills National Park has potentially the most diverse mixed dipterocarp rainforest in Sarawak, and possibly one of the most diverse forests in the world. It is also only a 1/2 hour drive from Sarawak's second city, Miri! The facilities there (including an observation tower) also make Lambir Hills one of the better places to see into the canopy itself. In the immediate vicinity of Kuching, the mixed dipterocarp forest of Gunung Santubong is hard to beat; and because part of the trail runs along a ridge it also allows a good opportunity to see into the canopy of the trees whose bases are far below. But for sheer size and the pristine condition of the forests, Mulu National Park and Batang Ai National Park are probably the richest remaining areas of mixed dipterocarp rainforest in Sarawak.

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Kerengas Forest
Description: Kerengas is an Iban term meaning a place where rice can't be grown. Kerengas forests occur where the soil is very sandy and nutrient-poor. Because of the sandy soil, kerengas forest usually drains quickly, so it is often dry as well. Kerengas is typically found in areas where the underlying rock is sandstone (such as Bako National Park), and along exposed ridges on mountain slopes (it can be difficult to distinguish from "ridge-top forest", with which it shares many characterisitcs).

The poor quality of soils and harsh conditions mean that kerengas forest is generally much smaller and less diverse than mixed dipterocarp rainforest. Trees in kerengas forest (even dipterocarps) generally do not grow to be more than 30m tall, and the vegetation is usually much scrubbier - with lots of small trees growing closely together, and a more dense understory than in mixed dipterocarp rainforest. Kerengas forest has been described as "pole forest" because of the large number of small trees.

Because of the harsh conditions, certain species of tree grow better in kerengas forest than others - typically hardier tree species such as casuarinas. However, a number of dipterocarps are commonly found in kerengas forests, and in the more sheltered and damper areas (such as creek beds), palms proliferate as well.

The poor nutrient levels in kerengas forest also means that some plants have to supplement their "diet". Pitcher plants (Nepenthes sp) are common in kerengas forest. These amazing plants have special pitcher-shaped leaves which are full of digestive fluids. The pitchers are designed to trap and digest insects, providing nutrients to the plant which it cannot get from the poor soils. These pitcher plants come in a huge variety of shapes and sizes, probably most easily seen at Bako National Park. (Shown here is an aerial pitcher of a Nepenthes rafflesiana.) There are other carniverous plants as well, including the sticky sundews, which catch their prey like flypaper.

Some other plants in kerengas forest have adapted to live with insects, rather than devouring them. These include the so-called "ant plants", which provide shelter and food for ants in especially developed growths, chambers or leaves. In exchange, the ants protect the plant from other insects, and also provide nutrients through their waste products. (This picture shows a vine called Dischidia raflesiana, which is wrapped around the branch of a small tree. The big pyramidal yellow growths are specially modified hollow leaves, in which ants live.)

As with other vegetation types, there is rarely a clear deliniation between kerengas and other forest types, which tend to gradually blend into each other around the edges. Different sub-categories of kerengas forest have also been identified.

In Bako National Park there is a particular kind of kerengas which is even more fragile and impoverished than kerengas forest found elsewhere in Sarawak. It is commonly known as fire padang (padang means "field" in Malay), and is thought to occur in areas which had been burned at some stage. (Water runs off or through the sandstone of Bako very quickly, leaving it very dry and susceptible to fire.) In fire padang, the vegetation is very scrubby and there are very few trees at all. These areas are very dry and nutrient poor, and resemble scrubby impoverished Australian bushland more than the lush tropical rainforest which you expect to find in Borneo.

Because of the tough scrubby vegetation (and absence of fruit trees), mammals and birds are not common in kerengas forest. However, a few skinks scurry about, and you will notice the odd bird or squirrel jumping about in the branches of bigger trees in some areas.

Best places to see: Bako National Park has probably the most accessible and obvious kerengas forest (and fire padang), and is also probably the best place to see nepenthes (pitcher plants). However, patches of kerengas forest can also be seen in many of the other national parks, including Kubah National Park & Matang, Lambir Hills National Park and Gunung Santubong.

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Mangrove Forest
Description: At first glance, mangrove forests are unappealing and unwelcoming places - muddy, smelly, wet, hard to move through because of deep mud, tides and tangled roots, and infested with millions of mosquitoes and sandflies (and if you're unlucky, crocodiles too). Despite this, mangroves can in fact have a certain haunting beauty.

Mangroves are also extremely important. One of the most important roles mangroves play is as a breeding ground for fish - without mangroves, fish-stocks would be drastically reduced. This is important for the health of the oceans, but is also significant because of the economic importance of commercial fishing. Mangroves are also a prime habitat for many edible crabs.

In addition, mangroves play an important role in stabilizing coastlines and river mouths, protecting them from erosion. A number of mangrove plants also have traditional medicinal uses, as well as practical applications.

Mangrove forests are not nearly as diverse in tree species as mixed dipterocarp rainforests, probably because of the high degree of specialisation which the harsh mangrove habitat requires - the trees must be able to grow in salty water, cope with rapid changes in water levels from tides, and cope with storms and hot sunshine. Many of the trees have adapted special mechanisms for coping with these conditions, including stilt-roots for support, breathing roots which stick up out of the dense mud, and ways to pump out excess salt!

Plants: The most important plant species include the various mangrove trees themselves - pioneering Sonneratia sp, as well as Avicennia sp, and Rhizophora sp. The trees of the first two genus grow breathing roots called pneumatophores, the third is recognisable from its extensive stilt-roots. Trees from the genus Avicennia are locally known as api api ("fires" or "lights") trees, because they attract large numbers of fireflies at night. The versatile Nipah palm grows in brackish, swampy areas behind mangroves. Many mangrove trees also support large numbers of epiphytes, such as ferns and orchids.

Animals: Key animals include monitor lizards, scavenging in the shallows, and proboscis monkeys, which venture in to look for succulent leaves to eat. Macaques occasionally venture into the mangroves looking for shellfish, and otters play in river mouths lined with mangroves. Estuarine habitats (especially where rivers and streams run through tidal mangroves) are also important for the large potentially man-eating estuarine crocodiles. Crabs are abundant and all around at low tide - especially fiddler crabs, with their one oversized claw; and bumbling hermit crabs in their clumsy borrowed homes. The loud popping sound at low tide, made by certain mud-burrowing bivalves (similar to mussels and clams), is a typical mangrove sound.

Insects: The most noticeable insects in mangroves are the mosquitoes and sandflies, which can be quite a nuisance at times. Fireflies are also noticeable at night.

Best places to see: The best place to see Mangrove in Sarawak is Bako National Park. A beautifully made boardwalk winds through mangroves alive with fidler crabs, mudskippers, garfish, kingfishers, and if you're lucky, monitor lizards and proboscis monkeys. It is especially beautiful and lively at dusk and dawn. At low tide, you can also walk through the more open mangrove forest in other parts of the Park. A small patch of mangrove can also be seen on the walk to Tanjung Datu National Park, from Telok Melano. There is also a mangrove boardwalk at Similajau National Park.

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Beach Vegetation
Description: Beach vegetation is highly specialised and adapted to growing in a very particular habitat - the thin strip of land between the sea and the hills and forests behind. Because it only occupies such a narrow strip of land, beach forest is one of the rarer forest types in Sarawak.

The plants in beach forest have to be able to cope with storms and high tides, as well as the salt water. Like mangroves, this vegetation plays a critical role in protecting and stabilising the coastline. Lack of fresh water and salty winds have meant that the plants have had to adapt to avoid water loss, by developing thick bark and leathery leaves. The conditions also mean that many have very strong and hardy wood as well.

Many of the plants found along the beaches have a range of traditional medicinal uses as well.

Plants: Commonly encountered beach plants include the beautiful sea-almond or pagoda tree (Terminalia catappa, katapa in Malay), which gets rid of excess salt by shedding all its leaves twice a year.

Sea hibiscus (Hibiscus tiliaceus) grows into medium sized bushy trees, and has beautiful yellow flowers - romanticised in films of polynesian beauties wearing one behind the ear.

Barringtonia asiatica, a medium-sized tree produces very fragrant flowers which resemble giant pink puffballs. The Malay name for this tree is putat laut, and it was traditionally used for poisoning fish in streams, which could then be easily collected for eating.

Cycads, such as Cycas rumpii, are "living fossils" which resemble small palm trees or ferns, but are in fact primitive plants, related to trees living 200 million years ago.

A tree-like pandan (screw pine), Pandanus odoratissimus, grows along beaches and in some of the touger rockier coastal areas.

Morning glory (Ipomea pes-caprae) is a creeper which grows across the sand, holding it in place against the eroding forces of rain, wind and tide. It has pretty purple flowers.

A type of hardy casuarina, Casuarina equisetifolia (rhu laut in Malay), also plays an important role in stabilising coastlines, and are a protected species because of this.

Best places to see: The best places to see beach forest (covered in this website) are at Bako National Park and Tanjung Datu National Park. It can also be seen at other beach locations, including Similajau National Park.

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Peatswamp Forest
Description: Peatswamp forest develops after mangroves have "reclaimed" land from the sea or river estuaries. Mangrove-mud is typically very oxygen-poor (and salty and often sulfur-rich), and as a consequence plant matter which drops to the floor of a mangrove forest decays only very slowly. Over thousands of years, deep layers of organic matter made up of partly decomposed leaves and trees, build up. This is called "peat". As the peat builds up, the ground becomes more stable, drier and less prone to flooding from the ocean, and the mangroves eventually give way to other trees. In some places, the peat may be as much as 15 metres deep, and over 5,000 years old at the bottom.

Peat is rich in organic material, so it can burn; and because of the lack of oxygen, it burns quite slowly. Peat fires burning in logged peat-swamp (which is prone to drying out) are almost impossible to put out, and can burn for years - much like burning coal seams. A significant amount of the pollution causing the famous "hazes" which periodically blanket southeast Asia is thought to come from burning peat forests in Kalimantan.

Peatswamp forests were once very common and quite widespread in Sarawak and Borneo generally (see map at top of page), but have been quite extensively logged.

Because of their unique development, and the fact that they are prone to flooding and have acidic soils, peatswamp forests have a unique ecology and composition.

Plants: There are several types of peatswamp forest, which depend on the age of the forest. The youngest parts of the forest are those closest to the ocean and directly behind the mangroves. The oldest are futher back. The soils in old peatswamp forest are poor, all the nutrients having been washed away by millennia of rainwater. Despite this, peatswamp forests manage to support some very rich forest, including some huge trees. A number of the trees have a local name ending in the word paya, which simply means "swamp". These include rengas paya (Gluta beccarii), related to mango and cashews and with a nasty blister-causing sap, kapur paya (Dryoblanops rappa) a giant dipterocarp and sepetir paya (Copaifera palustris), which have large scented pods and were traditionally considered good for making boats. Huge alan trees (Shorea albida) dominate away from rivers. These can grow to 66m high and 6m in diameter. In the oldest parts of the peatswamp, with the most infertile soils, small trees related to the estuarine mangroves can be found.

Animals: Peatswamp forests are not rich in fruit-trees, and as a result, they generally cannot support much animal life, although various primates, including proboscis monkeys, are occasionally found in peatswamp forests. Despite the general absence of larger mammals, squirrels, bats and numerous bird species occur in abundance in peatswamp forests.

Best places to see: The best accessible peatswamp forest in Sarawak is found at Loagan Bunut National Park, near Miri.

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Riverine Forest
Description: Riverine forest occurs in the bottom of Sarawak's river valleys, and along the edges of the rivers. These valleys have fertile soils, deposited by aeons of flooding. As a consequence, these areas are often cleared for farmland. However, a thin strip will often be left on the river banks themselves, so that they don't get washed away.

Engkabang (Shorea spp) trees are common in this forest. These species (from the Dipterocarp family), have large winged seeds which are rich in oils. These seeds were an important food source for Indigenous peoples. They were also once an important export commodity - the thick butter-like oil is said to have made excellent chocolate.

Large ensurai (Dipterocarpus oblongifolius) trees overhang many of the rivers, often supporting an unbelievable weight of ferns, vines and other saprophytes (passing underneath can be quite unnerving). These trees are protected under Sarawak law because of the important role they play in protecting the river-banks for erosion

Riverine forests are also the habitat of proboscis monkeys (Nasalis lavartus), amongst other animals. Although proboscis monkeys may travel away from rivers, into mangroves or even up coastal hills, they always come back to nest alongside the river. In fact they often cross rivers as well, and are strong swimmers.

Best places to see: Bako National Park, Mulu National Park, Niah

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Montane Forest
Description: Montane forest is essentially just forest that grows (not surprisingly) on mountains. In Sarawak, three distinct varieties are found: lower montane forest, upper montane forest and summit zone forest.

Lower Montane Forest - Lower montane forest gradually emerges from lowland mixed dipterocarp forest as you start heading up the hillsides. The massive dipterocarp trees gradually become fewer; eventually giving way to smaller trees belonging to the chestnut and oak families. (The oaks have gigantic acorns - they look like they are made for 100kg squirels.) Hill sago (Caryota no), a type of spiny palm, is an important food source for Indigenous peoples living in lower montane forests - notably the Penan. Some fruit trees also occur in lower montane forest - primarily members of the mangosteen and myrtle family.

Upper Montane Forest (Moss Forest) - Above 1200m, the vegetation is markedly different. The forest is dense and stunted, growing to a maximum height of only about 15m. Thick layers of damp mosses and lichens cover everything, soaking you as you brush past. It's also very quiet in moss forest - the cicadas, which provide a constant background buzz in the lowlands, are absent, and there are fewer birds. And the thick carpets of moss absorb most other sounds. Ferns are very common in upper montane forest because of the frequent cloud formation and constant dampness. The trees hidden under the moss include oaks, chestnuts, conifers, and rhododendrons. Smaller flowering begonias and orchids are also common.

Summit Zone - This only occurs on the very top of the highest of Sarawak's mountains. On the summit of Gunung Mulu, the vegetation is very stunted and windswept, consisting of myrtles and rhododendrons, as well as some very specific pitcher plants (Nepenthes muluensis, Nepenthes lowii). Contrasting with the thousands of species of plants found in lowland mixed dipterocarp rainforest, only 26 species of plants have been recorded in summit zones.

Best places to see: Mulu National Park - the walk up Gunung Mulu gives an amazing experience of the transition from riverine and lowland mixed dipterocarp rainforest, all the way through the three zones of montane forest. The variety and change is extraordinary.

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Limestone Forest
Description: Lowland Limestone forest In lowland areas with limestone soils, Dipterocarps are also the predominant tree family, but the canopy height is shorter than LMDF. There is also less understory and palms are generally rare. At ground level, there are some intriguing limestone-specific plant species, including Monophyllea sp with a single, broad leaf, some very hairy begonias, and slipper orchids, including Paphiopedilum sanderianum with very long, ringleted tendrils.

Best places to see: Mulu National Park

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