The best place for biodiversity to thrive is within primary or secondary forests of a certain size and undisturbed by human presence.

Before the various housing and commercial developments sprang up, Singapore was almost completely covered in thick jungle.

Now, there is little biodiversity in the carefully manicured parks and gardens here.

The presence of people also drives away most wild fauna.

Bukit Timah Nature Reserve is home to more than 840 species of flowering plants and more than 500 species of animals. However, it is a far cry from the plant and animal populations in the Amazon or even parts of Malaysia.

In Singapore, a big portion of land is occupied by above-ground expressways. These expressways cut across the nature reserves, and are hazards for animals crossing these roads to get to the other side of the forest.

If these expressways could go underground, we could substantially extend the size of our primary forests. Additional trees forming the canopy layers of the forest would be more able to mop up excess carbon dioxide, helping to reduce the concentration of greenhouse gas in the atmosphere and lower temperatures.

I have travelled several times through existing underground expressways and find that it is a cooler ride, with no glare from the tropical sun beating down.

The cost of moving our expressways underground will be substantial, but it is possible if carried out in stages.

Lee Kay Yan (Miss)