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Official Magazine of the Nature Society (Singapore)
  Rainforest Rojak
Rainforest Rojak | Will the animals return too?

This 'rojak' of plants is exciting and important, for within this mixture are trees and climbers that are typical of the primeval rainforest that once covered almost all of Singapore island ... the rainforest is returning, says Shawn Lum as he walks the old rubber 'trail' in the Central Catchment area. All photos by Shawn Lum.

Peirce Reservoir seen from
atop Bukit Timah
Biology is the study of living things, yet many students find this subject deadly boring. Isn't this ironic? Maybe that's why, in a recent Biology Speech contest for junior college students, the most popular topic by far was, "How biology classes should be conducted".
Every speaker on this subject urged teachers to incorporate field trips into the curriculum to breathe life into the subject. Good idea—but the field trip destinations they suggested were either Bukit Timah and/or Sungei Buloh. Not a single mention was made of other nature areas in Singapore! No wonder there are throngs of school children at Bukit Timah on a Saturday morning but the MacRitchie Nature Trail is relatively empty and tranquil!

In my opinion, the MacRitchie Nature Trail is the best "value-added" field trip destination anywhere on the island.

Less than two hundred years ago, primary rainforest covered most of Singapore, including the area we know of today as MacRitchie Reservoir. Then the British colonists arrived (1819) and in their wake, immigrant settlers. Soon farmers and loggers were felling the magnificent hardwoods that had taken hundreds of years to grow. Worse was to come. Later almost all of this forest was clear-felled to make way for cash crops—mostly rubber and gambier.

More years passed and sometime late last century the plantations, first gambler and then later rubber, were abandoned. With the abundant rainfall on the island, the forest soon grew back. But it was a different kind of forest and became impenetrable with the tangle of undergrowth characteristic of secondary forest. .

Giant rattan
(Plectocomia sp.)

This "ocean" of secondary forest now surrounds MacRitchie Reservoir, the island's oldest water catchment store (it also stretches up to border Upper and Lower Peirce Reservoir and Mandai)

But even today, on the MacRitchie Nature Trail, it is easy, to spot those old rubber trees: even more exciting, this trail offers a vast array of flora and fauna (though the latter isn't as easily seen), that vividly demonstrates that the original rainforest is coming back ... And we are afforded a glimpse—through living things—into the history of this island nation.

The MacRitchie Nature Trail is a three-kilometre stretch connecting the Singapore Island Country Club ("Island" location on Upper Thomson Road) with the MacRitchie Reservoir Park. You can enter either end but at the entrance that is near the Little Sisters of the Poor, you can spot a few rubber trees and they immediately betray this forest's past.

While the history of rubber cultivation in British Malaya (which includes Singapore), with its beginnings in our Botanic Gardens, is itself a remarkable story, the tales these old rubber trees in the Catchment Area tell are no less fascinating. For these remnant patches of rubber (Hevea brasiliensis), the offspring of seeds that had been brought over from Brazil, South America, were planted, nurtured and tapped by early Chinese and Indian immigrants who laboured hard to eke out a living from what must have been inhospitable surroundings. Remember, just a century ago tigers freely roamed here and those areas, where now stand the modern high rises of Bishan and Ang Mo Kio. And the lonely tapper working his patch in the dimness of dawn, was very vulnerable.

So how does one spot a rubber tree in an "ocean" of secondary forest trees? Well, naturalists often speak of creating a "search image" of an animal or plant that they are looking for. What this means is that you enter a mental zone (i.e., visualise) and the desired object will make itself visible, no matter how well-concealed it may have been or how quickly it zooms by.

So, create a "search image" for rubber trees as you begin to walk the trail. Look for trees with trifoliate leaves that hang limply and are reddish when young. The old trees are often about 20 metres tall or more so you may need to crane your neck and use a pair of binoculars. It is easier to look for the rubber saplings; they indicate that the rubber is self-perpetuating, long after cultivation has ceased.

The very old trees bear the faint scars of tapping (diagonal cuts) and these very same trees helped develop the economy of the British settlement in their youth. But while the once highly prized milky sap has long run dry in the old trees, they give life and vigour to rubber saplings; and it is these saplings that teach us about the ecology of a forest in its adolescent stage.

As one walks the trail and the "search image" works its magic it becomes easy to pick out the rubber trees, and these indicate the extent of former rubber plantations within the Central Catchment area. Look more carefully wherever rubber is found and you will see that in some patches there is a profusion of other kinds of trees, a sign that the original inhabitants of this area have begun to re-establish their hegemony.

The take-over is not at random and it appears that certain kinds of plants are more suited to returning to disturbed sites than others. In areas that have experienced the most exploitation (or disturbance), trees are often absent. The ground here is covered instead by a fern known locally as resam (Dicranopteris linearis). But there are signs on this trail that the patches of resam are gradually being shaded out and tree saplings are growing in their place.

Seedlings emerging
from a resam fern patch

Ecologists call the gradual replacement of one set of species by another "succession", and such succession is easily observed along the Nature Trail.

For example, in the midst of some stands of abandoned rubber, one can find trees that are "typical" secondary forest species; these are generally the first to reclaim the abandoned plantations. These include silverback (Rhodamnia cinerea), kayu manis (Cinnamomum iners), jambu laut (Eugenia grandis), and fishtail palm (Caryota mitis). In these secondary forests the canopy is fairly even and roughly 20-30 metres high. The girth of these trees is not massive, at least not when compared to the larger trees of the "primary" forest.

Now we move to look at those species which indicate the primary forest is beginning to stake its claim. The most telling are the mature terentang (Campnosperma auriculatum) with their unmistakably large and spirally-arranged leaf clusters. These are indicative of areas which were cleared or disturbed a long time ago.

Plants in Transition
Look more closely at the larger clumps of terentang and you will be surprised at the variety of saplings present. These saplings or invaders are plants in transition; the typical secondary forest species were the early colonists of the vacated plantations. Now they are gradually being supplanted by species which signal that the primary forest is returning. Once again these areas may be covered by the mighty big trees and their associated species the rattans and woody climbers.

This transitional type of forest is most interesting. Not only does it show that a degraded forest can recover, given sufficient time, but it also illustrates that not all species (we refer to plants only) return to their original sites at the same time. Scattered along many parts of the trail are representative species such as bintangor (Calophyllum spp.), terap (Artocarpus spp.), rambai (Baccaurea parviflora), mahang (Macaranga triloba), bat laurel (Prunus polystachya), gaharu (Aquilaria malaccensis), pulai (Alstonia spp.) and Gironierra spp. (tropical members of the elm family), among many others. Also present is the treelet Anisophyllea disticha, a good indicator of the "recovering" forest, as is the small understorey fan palm of the genus Licuala.

These plants mentioned above are distinctive and varied in their appearance and they all bear fruits which are easily dispersed (usually via wind or small animals). Other trees are not so good at getting around. They may require larger animals (now rare or extinct in Singapore) to disperse their seeds, or have large fruits that don't travel a long way on their own.

Patches of Primary Forest—The Big Trees
As the trail winds towards the Island Country Club, some two kilometres from the starting point, the forest abruptly changes its appearance. You now encounter some trees of stupendous proportions. Notice too the great variety of shapes and sizes of the trees and shrubs. Palms and climbers are everywhere and at your feet are some placate leaves; that is, they are folded like a paper fan. These leaves belong to several species of keruing (Dipterocarpus) found in the area and together with their cousins in the genus Shorea (known as meranti) they make up the dominant species of the Indomalayan primary forests which once proudly stood where now stand shopping centres, factories and housing estates.

Dipterocarps are good indicators that elements of primary forests have returned. They are also a cinch to identify with their twisted leaf stalks and diagnostic leaf venation. Look carefully as you walk the trail and you will also see keruing and meranti seedlings by the hundreds. But besides the dipterocarps, there are other plant species of the primary forest. There are Dysoxylum cauliflorum with their fascinating fruits, Scaphium macropodum (source of the jelly used in the local dessert cheng t'ng), the shrub Thottea grandiflora (larval food plant for some beautiful papilionid butterflies), wild nutmegs and hundreds of others.

Young Terentang

Anisophyllea disticha

Gaharu seedlings
(Aquilaria malaccensis)

Licuala palm

Keruing fruits

Dysoxylum cauliflorum

Scaphium macropodum

In fact, there are more species of trees in the Catchment forests than there are at Bukit Timah. This was the findings of Mr Wong Yew Kwan, Ms Chew Ping Ting and Mr Ali Ibrahim who surveyed the area. Of course Bukit Timah Nature Reserve covers a much smaller area but this shows that MacRitchie should not be overlooked, as it often is.

From Noah's Ark to the Promised Land
Dare we dream of the Central Catchment forests becoming the principal (but not the only) refuge of primary forest flora and fauna in Singapore? There's no reason why it cannot become such a sanctuary—not if we choose to help nature and spread the seeds.

And nature needs not just protection but in this instance, a helping hand. You see, some of the plants, like keruing, are not very adept at moving their seeds about; this was shown when some biology teachers and I made a quick survey of keruing seedlings and saplings. The teachers found that the young keruing are at most only a few metres away from the edges of their mothers' crowns. For this primary rainforest tree species to naturally replenish the entire Central Catchment forest would take hundreds, perhaps even thousands, of years.

It may well be possible to re-establish these trees throughout the catchment area with a little human help and a source of seedlings. Already the National Parks Board have made some replanting efforts but these represent a first step in a long process which even concerned nature lovers could someday be involved in. Perhaps we could think of Bukit Timah as Noah's Ark while the Catchment Area is the Promised Land (to use an apt but admittedly clichéd Biblical analogy). The Catchment Area is our best hope for terrestrial biodiversity as it is the largest contiguous expanse of natural habitat on the island.

Dr. Shawn Lum is a biologist from NTU and the co-author (with Ilsa Sharp) of A View from the Summit. The Story of Bukit Timah Nature Reserve.

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