30 November 2013

Silent Voices in the Wilderness

Silent Voices in the Wilderness
Butterflies in MacRitchie Forest 

A female Plane (Bindahara phocides phocides) a rare Lycaenid that is found only in our forested nature reserves

When the Land Transport Authority (LTA) announced in Jan this year, that a proposed new 50km MRT line that starts from Changi and ends in Jurong will be ready by 2030, it raised more than just eyebrows amongst the nature community.  The new east-west MRT line's alignment will bring it right across the MacRitchie Forest, which falls within the boundaries of what is traditionally known as Singapore's "nature reserves". Although the LTA clarified that the line will be well below ground, it did not manage to convince the nature community that in the process of constructing the line, there will be no impact to the environment and delicate habitats within the nature reserves.

The proposed alignment of the Cross Island MRT line cutting through a narrow 'neck' of the Central Catchment Nature Reserves

A lot of questions were raised, many of which were valid and technically relevant. How would the soil investigation activities, which some estimated at having a bore hole at intervals of at least 20m apart, affect the forested areas? Would there be utility structures and penetrations above ground that serve the tunnel beneath that would be located within the nature reserves? What would LTA do to mitigate impact to the flora and fauna during the tunnelling process? What kind of maintenance regime and access to the forests would be needed after the line is completed and in operation? And so on...

The proposed alignment of the CRL showing approximately where it will run under the MacRitchie Forest, including two patches of primary forest. (Source : Nature Society Singapore)

From the viewpoint of the engineers and the economists, the alignment of the Cross Island Line (CRL) will take the most technically efficient and economically pragmatic route, which will cut across the narrowest portion of the Central Catchment Nature Reserves (see map). As the line will be completely below ground, it was also assumed that the impact to the forest habitats above would be "minimal".

The Common Faun (Faunis canens arcesilas) a forest denizen that is not found outside of the nature reserves nor is seen in urban parks and gardens.

Much has been debated about the potentially damaging and irreversible impact to the flora and fauna that may be caused by the CRL, so I won't delve into the details of those arguments. We have been asked about how butterflies could be affected by habitat changes that may be caused by the CRL and the construction activities that are associated with the line. As butterflies are mobile and can fly to other areas, why would any changes in the MacRitchie Forest environment threaten them?

Arhopala trogon a rare Oakblue that is found in only a few locations in the nature reserves, one of which is in the MacRitchie Forest

The host plant specificity of the early stages of butterflies makes them particularly vulnerable to changes in plant diversity due to changes in land use and loss of their host plants. The information on the host plants of butterfly species in Singapore is largely incomplete.

The Malay Gem (Poritia philota philota) a rare forest butterfly of which the MacRitchie Forest is one of a couple of locations that this species can be found

As Koh et al. (2004a) pointed out, “the preservation of whole habitats is urgently needed if we are to avoid the possible cascading effects of species (co-)extinctions, especially in ecological communities, such as tropical rainforests, where different species are inextricably dependent on one another.”

The Dark Blue Jungle Glory (Thaumantis klugius lucipor) a large Morphinae that lurks in heavily shaded forested areas in the nature reserves

Although butterflies are able to fly from location to location in search of their caterpillar host plants, it is not known for certain why certain species have gone extinct. Some species may go extinct sooner than their host plants when the relative rarity, and not absolute disappearance, of certain host plants reduce butterflies to below their minimum viable populations. Coupled with predation, environmental factors and loss of habitats, some species of butterflies may have gone extinct long before their host plants actually disappear from our forests.

Cover of RMBR's Expose of Singapore's Rainforests showcasing the amazing diversity in our nature reserves and rainforests in Singapore

The unpredictability of the extent of damage that starts with the soil investigation works and how the plant diversity and the associated habitats will change and adapt through the construction period, tunnelling and eventual changes in water table will form the major part of the risk of undertaking the CRL. Whilst the tunnelling work is assumed to have minimal visible impact at the ground level within the nature reserves, very little is known about how the water table changes when an impervious concrete tube is built - spanning up to 20m across and running a few kilometres across the nature reserve, some 40m or more below the surface.

Two pages about forest butterflies from RMBR's Expose of Singapore's Rainforests

Many of the larger trees may suffer due to the changes in the water table, and if they die out, the drying out of the forest in that area will spread unpredictably, and may cause damage of untold proportions. Such changes in the forest may threaten some of the host plants and hence the related butterfly caterpillars that feed on them.

A male Archduke (Lexias pardalis dirteana) another forest-dependent butterfly

It is estimated that at least 60% of Singapore's butterfly fauna are forest-dependent. Whilst the increase of urban planting and landscaping strategies to attract butterflies in urban areas have begun to bear fruit, the same cannot be said for forest butterflies. Many of the forest-dependent species will not come out to the urban butterfly gardens. Most of the butterfly species featured in this article are rarely seen in urban parks and gardens.

The Harlequin (Taxila haquinus haquinus) that may now be extinct on Singapore island due to the destruction of its habitat in the north-western part of Singapore.  Attempts to translocate it to other sites have not been successful.

Even if their caterpillar host plants are available, these butterflies' preferred habitats have to be conducive to support a sustainable population. Not enough is known about why certain species prefer particular locations whilst other similar habitats elsewhere do not attract the same species. An earlier attempt by ButterflyCirle to translocate the Harlequin (Taxila haquinus haquinus) at a forested site that was threatened by development was unsuccessful. Whilst a few sites were chosen, that were similar in terms of habitats and availability of host plants, there were no signs that Harlequin survived in the new locations after a period of monitoring.

The Lesser Harlequin (Laxita thuisto thuisto) a relative rare Riodinid that survives only in our forested areas in Singapore

Around the MacRitchie Forest area, there are records of some rare species of butterflies that are found in the forested area and a few have only been observed in that area and nowhere else. If their habitats or host plants are affected, there is a high risk that these species may face extinction in Singapore.

The very rare Storey's Palmer (Zela storeyi) which is found in our forested nature reserves

It is encouraging that the LTA has confirmed that an Environmental Impact Assessment study will be carried out over the next two years, starting in early 2014 to assess the potential environmental impact caused by the CRL. Will the study recommend that the CRL be realigned outside the Nature Reserves? Or will it support the current alignment but with strict mitigation measures be put in to minimise damage to the MacRitchie Forest?

A 3D topographical map of the MacRitchie Forest area. (Source : Nature Society Singapore)

How deep should the tunnels be constructed, where it will not cause any changes or damage to the forest ecology? We have to acknowledge that we do not know. But a general rule of thumb in tree biology points out that the tap roots of large trees like Dipterocarps can reach as deep as the height of the tree itself. That would mean that a 30m tree would have roots reaching 30m or more below ground. Would a tunnel that runs below such trees affect the health of the forest? Has it been done elsewhere before? Should we even try?

The Five Bar Swordtail (Pathysa anthiphates itamputi) a forest-dependent butterfly that is found regularly in the nature reserves of Singapore

As to the fate of our forest butterflies, if the CRL were to proceed as planned, we cannot say for sure - we do not know enough. The CRL appears to be a rare project that has breached the previously-assumed impenetrable gazetted nature reserves in Singapore. True, there have been other structures like the military facilities or water treatment plants sited within the nature reserves, but none so recent nor extensive as to generate quite a bit of controversy and grab the attention of the nature community in Singapore like the CRL.

The Purple Duke (Eulaceura osteria kumana) - common but forest dependent.  Can such a butterfly be attracted to urban habitats like our parks and gardens with judicious planting of its host plants?  Apparently not.

Are there no other alternatives to the alignment that LTA has proposed? The NSS has come up with a position paper that says otherwise. Will the alternative route be still technically possible but will come at a great financial cost to the government? How would that expenditure stack up against the nature reserves which some consider as 'priceless' and it would be futile to even put a value to? Are there any compromises that can be made?  Both sides will have to keep an open mind to options.

The Central Catchment Nature Reserves - our "Green Heart" of Singapore

Are we courageous enough to gamble with a part of the 'green heart' of Singapore and stand to lose a part of our natural heritage and sacrifice a legacy to our future generations? We should know the recommendations of the EIA in early 2016, and the fate of MacRitchie Forest then. At that point in time, we hope that we will make a wise decision for the greater good of all Singaporeans and the flora and fauna that share our little island with us.

Text by Khew SK : Photos by Sunny Chir, Khew SK, Koh CH, Nelson Ong & Horace Tan

Further Reading

References :

  • Koh, L.P. & Sodhi, N.S. 2004. Importance of reserves, fragments and parks for butterfly conservation in a tropical urban landscape. Ecological Applications, 14, 1695–1708.
  • Koh, L.P., Sodhi, N.S. & Brook, B.W. 2004a. Co-extinctions of tropical butterflies and their hostplants. Biotropica, 36, 272–274.