SINGAPORE is helping develop a grading system to measure how cities worldwide are conserving their plant and animal species.

More than half the world's population now lives in cities, which poses threats to biodiversity in the form of development, pollution, and competing land use.

Yet a wide range of plants and animals is essential even to cities - for instance, plants absorb carbon dioxide and prevent flooding and soil erosion, and bats pollinate the fruit trees in gardens and roadsides.

For more The Straits Times stories, click here.