This is a collection of information about our rainforest.

  • Questions on Primary Forest
  • Ecosystem Services


Questions about our Primary forest?

There is only 2.01 km2 (201 ha) of Primary Forest left in Singapore today and it covers 0.28% of our total land area.

Singapore has 17 golf courses occupying 1,500ha of land, about 2% of our total land area.

Q: What is a Primary forest?

  • Simply put, it is a forest untouched by human activities or natural disturbance, and has matured naturally. It is hence a pristine forest, never been significantly altered.
  • Unlike Secondary forest, it has a mature, thick canopy which allows little light to reach the forest floor. This results in little vegetation on the forest floor.
  • Because of its age, a Primary forest has many mature and thick trees, with a distinct broad-crowned emergent layer.
  • It has a multi-layered forest structure that confers its variety of niches, habitats and biodiversity. Hence, between different forests, Primary forests host the greatest species richness.
  • Certain species of fauna or flora are so rare that they can only be found within Primary forests.

Q: Why should we be bothered about Primary forests? Isn’t Singapore already very green?

Different forests are different shades of green. Primary forests are our most scarce and precious forests – valuable in many aspects including benefits to us. Here, a simple comparison table illustrates the unique contribution of Primary forests.


Q: Ok, so Primary forests are special. But can’t we ‘cultivate’ or create Primary forests?

Unlike human structures, we cannot create these special forests. Moreover, even with time, scientists are unable to determine whether Secondary forests can ever attain the structure and biodiversity of Primary Forests.

The Marina Bay Sands has become an icon of Singapore; with resources, it can be demolished and rebuilt again at any location. However, our natural crown jewel, the Central Catchment Nature Reserve (with its Primary forests), cannot be rebuilt even with resources. It took thousands of years to attain its maturity, support rich biodiversity, and provide great benefits and services to us.

In short, Primary forests are irreplaceable. Once disturbed (by the site investigations for the CRL), the Primary forests will cease to exist, and the process is irreversible.

Albert Liu

Lee Kong Chian Natural History Museum –
Rainforest Journal –
Mongabay –
Nature Society Singapore – Feedback on the Updated URA Master Plan (November 2013)

You can read more about our Nature Reserve – It is ANCIENT, It is FRAGMENTED, It is RICH, It is SMALL

Ecosystem Services

  • Tropical rainforests have the highest total leaf area per unit area (leaf area index)
  • Diversity of plants that live in the various layers in the forest
  • Nature reserves serve as a catchment area for the surrounding reservoirs
  • Forest soil acts like a sponge to absorb rainwater
  • Transpiration and evaporation of water in the soil cools the forests


Even though Singapore has outstanding urban greenery, there is no doubt that our tropical rainforest nature reserves are Singapore’s true green lungs. Among the different land ecosystems, tropical rainforests have one of the highest total leaf area per unit ground area (aka. leaf area index) on earth.

Leaves are the powerhouses of photosynthesis, the process that purifies our air by converting carbon dioxide into oxygen. Leaves also trap dusts and other air pollutants, which are washed off to the ground with the next downpour.

Enter the rainforests and you would see that forests have such high leaf area, because plants of different forms and structures maximize use of the three dimensional space to capture every bit of sunlight.

Crane your head upwards and you will see giant trees that protrude above the forest canopy. Beneath the canopy are understory trees that are adapted to photosynthesize even under shade conditions. The trees in turn play hosts to climbers, epiphytic ferns, lichens, mosses, etc. Thus the total area of leaves per unit ground area in the rainforests easily surpasses that from a single row of trees lining the roadside. Unsurprisingly then, when you walk into our nature reserves, the air is that much fresher and cleaner, a boon to your lungs and spirits.

Our forest nature reserves also serve as a catchment area for the surrounding reservoirs. Bukit Timah Hill was also first declared as a forest reserve in late 1880s for “climatic purposes”, as the British were alarmed over the rapid rate of deforestation and its impact on the island’s climate – by late 1880 about 90% of our forests were gone.

But really, how do rainforests impact water catchment or moderate the local climate? Intuitively one notices the high humidity within the rainforest. The air just seems to be laden with water vapour.

Plant transpires, a process of pulling water from the soil up to the leaves. Some of this water is used in photosynthesis, while some of it “leaks” into the atmosphere via the same entrance (“stomata”) for carbon dioxide.

At the same time, the forest soil, which is a few meters deep, acts like a sponge to absorb rainwater. Water then evaporates from the soil surface during non-rainy days. Both transpiration and evaporation uses incoming energy from the sun to change water from liquid to vapour. This means that less energy goes into heating the earth surfaces, and thus a cooler environment!

Research has shown that in the rainforests, this “evapo-transpiration” process actually absorbs a whooping 45% of the total incoming radiation from the sun (Malhi et al. 2002), hence significantly cooling the ground surface. With a more water-laden atmosphere, there is thus more rainfall in forested areas. Moreover, water that is not evaporated flows through the soil and enters the waterways, in this case, the reservoirs, to be used by us.

These ecosystem services that are provided by the forests – air purification, moderating the local climate, sustaining the water catchment, is dependent on the health of the forests. A look at our forests today shows that the forests are still recovering very slowly from past deforestation. Some areas of the Central Catchment Nature Reserve appear to stagnant as forest patches with low species diversity and poor forest structure. Poor seed dispersal from tiny fragments of primary forests, degraded soil that slows forest succession, are part of the reason….

Chua Siew Chin

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