Introduction
Singapore has undergone rapid transformation in the past 200 years before becoming the bustling hub that it is today. Have you wondered what most of Singapore was like prior to 1819? Perhaps the answer is closer than you think.
One would not have to look beyond our own Bukit Timah Nature Reserve, the most prominent example of a primary lowland forest vestige left in Singapore. In the early 19th century, almost 82% of Singapore was covered in lowland dipterocarp rainforest, a type of primary vegetation which grows mainly on dry land1. By the end of the 19th century, however, over 90% of the lowland dipterocarp forest had been cleared, mainly for agricultural purposes2.
What are lowland dipterocarp forests?
As the name suggests, such forests tend to be dominated by dipterocarp trees. Dipterocarps are generally tall emergent trees with winged seeds to facilitate wind dispersal1. Some of the more prominent genera in the Dipterocarp family include Shorea, Hopea, Dipterocarpus and Dryobalanops1.
In Singapore, lowland dipterocarp forests are restricted to small patches in the Central Catchment Nature Reserve, with the most sizeable patch found in Bukit Timah Nature Reserve3.
On Bukit Timah itself, the more accurate term to use would be “Hill Dipterocarp Forest”4. While it is very similar to lowland dipterocarp forests in terms of the botanical composition, hill dipterocarp forests tend to have stands of Seraya (Shorea curtisii) growing on the drier ridge tops1, a species that is generally absent from forests on flat ground. Of course, being a very rich and diverse ecosystem, the forest contains many other plant species apart from the Dipterocarps!
Forest Structure and Vegetation Characteristics
In general, the forest can be divided into five layers, namely emergent, canopy, sub-canopy, understorey, and forest floor3. In Singapore, not all the vegetation layers are present in our lowland dipterocarp forests due to heavy deforestation in the past3. Moreover, a study conducted on hill dipterocarp forests in Peninsular Malaysia showed that vegetation structures within the forests can be rather diverse, depending on the topography5. Despite this, many of the forest trees mast or fruit in synchrony in response to major climatic events, such as the El-Nino phase of the El-Nino Southern Oscillation3. The images below show some of the plants which occupy the various layers as outlined above.
- Emergent Layer and Main Canopy
The trees in this layer tend to be dominated by the Dipterocarps in the genus Shorea and Dipterocarpus. Other tree families which occupy these two layers as well, such as those from the bean family (Fabaceae).
One example of an emergent legume would be the Petai (Parkia speciosa), source of the Petai beans commonly used in regional cuisines such as sambal petai prawns.
- Sub-canopy
Plants in this layer are smaller and shorter in stature compared to the emergent and canopy trees. Some of these tree genera include Calophyllum, Horsfieldia and Syzygium.
- Understorey and Forest Floor
These two layers consist of smaller shrubs, herbaceous plants, and tree seedlings. They are likely to be more tolerant of the deep shade formed by the intervening layers of tree canopies above them.
Ecosystem Services
Now that we have some knowledge about the structure and dynamics of lowland forests, you may be wondering how they benefit human beings. One perspective would be to look at the ecosystem services provided by lowland forests.
Ecosystem services are defined as the “benefits people reap from the ecosystem”, and they can either be extrinsic or intrinsic6. One of the most obvious would be provisioning services or resources extracted directly from forests. Forests serve as a source of raw materials, such as commercially important timbers. For instance, the famous Malaysian tualang honey is harvested from hives built precariously on massive Tualang trees (Koompassia excelsa)7.
In Singapore, the regulating and cultural aspects are more pertinent. The former refers to ecological processes which alleviate extreme environmental conditions while the latter refers to the intangible benefits that nature offers to humans6. Our local forests help maintain the water quality in several reservoirs while serving as venues for people to seek respite from city life.
Threats to the ecosystem
In the parts of Southeast Asia where lowland dipterocarp forests are found, they continue to face pressures from human activity. These include plantation expansion, logging, mining, and road construction8. While the lowland dipterocarp forests in Singapore are relatively well protected due to their location within existing nature reserves, the small populations of primary forest tree species could lead to the risk of inbreeding and thus loss of adaptability in the long run 3 . Moreover, high visitorship to nature areas such as Bukit Timah Nature Reserve threatens to ruin sensitive ecosystems through disturbance9.
What you can do
While you may think that your actions as an individual are powerless in the face of challenges afflicting tropical forests, this is not the case. For a start, you could start to learn more about the forests around you by joining nature walks and gaining a deeper appreciation of the flora and fauna.
With this new knowledge, you could educate the people around you about the importance of conservation. Buying products with sustainably sourced oil palm could also help to reduce the pressures faced by tropical forests in the face of expanding plantations. Of course, this is not exhaustive and there are many more ways that you as an individual can make a difference.
Hopefully, you have gained a better picture about the significance of lowland dipterocarp forests after reading this article!
Glossary
Topography: Terrain and prominent features of a particular area, commonly depicted on maps in the form of contour lines.
El-Nino Southern Oscillation: Periodic variations in sea surface temperatures and wind patterns over the tropical eastern Pacific Ocean which affects the global climate.
Online References
[2]: https://www.sciencedirect.com/science/article/abs/pii/S0006320720309058
[5]: https://www.frim.gov.my/v1/jtfsonline/jtfs/v29n2/137-150.pdf
[7]: https://www.nparks.gov.sg/florafaunaweb/flora/2/9/2983
[8]: https://www.worldwildlife.org/ecoregions/im0146
Non-Online References
[1]: Ashton, P. S. (1988). DIPTEROCARP BIOLOGY AS A WINDOW TO THE UNDERSTANDING OF TROPICAL FOREST STRUCTURE. Ann. Rev. Ecol. Syst, 19, 347–370. https://doi.org/annurev.es.19.110188.002023