Map to join Singapore's green dots

Many people enjoy getting around on well-lit and paved paths, but shy, wild animals favour quiet and leafy routes when travelling from one forest patch to another.

To help native animals get around in Singapore, where development has fragmented forests into isolated patches of green, experts here are developing a map that aims to join up the green dots.

The idea for the connectivity map was first mooted by National Development Minister Desmond Lee in February. Last week, Singapore witnessed the first outcomes of the endeavour when plans for the Dover Forest were revised.

Instead of the entire 33ha plot being developed for residential use, only the eastern half will be developed for now, the Housing Board said. The western half, which another study had found to be richer in wildlife, will be set aside and reviewed again in about a decade.

But a nature park will be carved from it, the authorities have assured, as the mapping exercise had shown that a conserved green plot there could be a "stepping stone" for wildlife moving between the Bukit Timah Nature Reserve north of the site and the Southern Ridges farther down.

The scientific effort is led by the National Parks Board (NParks), in consultation with local biodiversity experts, and is known as an ecological profiling exercise.

It is the technical name for an effort that aims to identify where forests can be safeguarded as homes for rare species or habitat types; where wildlife corridors or "stepping stones" can be planned; and how development can be planned in a way that will not disrupt wildlife movement.

This is key to ensuring that Singapore's native wildlife can find food and mates in other forest patches to preserve their genetic diversity. If not, isolated populations could become inbred, reducing their resilience to stressors like disease.

"The ecological profiling exercise allows Singapore to take a long-term view and plan more holistically," said Mr Ryan Lee, group director of NParks' National Biodiversity Centre.

"Singapore is not very large, and being the size we are, planning at a landscape level for conservation will help Singapore best strike a balance between development and nature preservation."

There are six indicator species that the connectivity map is based on: three mammals - the Annandale's rat, Sunda pangolin and treeshrew - and three birds, the hill myna, blue-winged leafbird and white-rumped shama.

NParks said these species were selected as they are sensitive forest dwellers that prior studies have shown can be coaxed to use wildlife corridors, provided a suitable habitat is created for them there.

Their movement pathways would provide a conservative estimate for the routes that other animals will take, said Dr Tan Puay Yok, NParks' chief science and technology officer, who was part of the team that first explored the use of the methodology.

On the one hand, choosing a species that is urban-adapted, such as hornbills, would yield a much wider corridor that more sensitive species will not use.

On the other hand, choosing forest specialists, such as the Asian fairy-bluebird, which have not been found in disturbed forests, would not be realistic either, Dr Tan added.

After satellite data is used to locate existing forested sites, researchers plot out the routes that wildlife are likely to take from patch to patch using a method known as "least-cost modelling". This assumes the animal takes the path of least resistance.

To calculate this, researchers first identify the surface structures between the green dots - for example, roads, forests, buildings and open fields - and then assign each one a numerical value. A lower value indicates a surface structure that is conducive for an animal, while a higher value indicates a structure that it would find much harder to cross.

When these are plotted out, they resemble pixels on a map.

For example, ground-dwelling pangolins may be more hesitant to cross a road than a leafbird, which can simply fly across. A road is therefore assigned a higher value for the pangolin model, compared with the leafbird model.

This value is assigned based on discussions with experts, NParks said. The eventual movement pathway for each species is then plotted out by selecting a route comprising pixels of the lowest value.

The movement pathways of the six species are combined for the overall map.

National University of Singapore mammal scientist Marcus Chua said the choice of target species is key as it underpins the model and decisions made for ecological connectivity. "Well-selected species and models would benefit a host of other species as well," he said.

Bird scientist David Tan, from the University of New Mexico in the United States, said the hill myna, for instance, is not the best choice of indicator species as it is a fruit eater capable of "flying from Sentosa to Pulau Ubin without breaking a sweat".

"I think the striped tit babbler would make more sense as a connectivity indicator," said Mr Tan, who has studied the genetic diversity of the woodland-dependent songbird in Singapore.

He added: "As the babblers have short wings and sedentary lifestyles, they don't disperse far and they live largely in the mid-to-lower part of the forest, making them better indicators of wildlife connectivity compared with hill mynas that may be better at dispersing in search of fruit trees."

The connectivity maps are being drafted regionally, with the one for south-western Singapore prioritised owing to discussions over the fate of Dover Forest.

NParks' Mr Lee said the aim is to piece together an islandwide connectivity map by the end of the year, although this will be regularly fine-tuned to take into consideration new urban and scientific developments.