Like most people, full-time national serviceman John Tan used to pay little attention to the trees and shrubs when he walked by the gardens and parks in his neighbourhood.

But he learnt yesterday during a guided tour of the Yishun Nature Way that certain plants are grown in various green corridors for a reason.

"For instance, host plants of butterflies are planted in areas so that they can congregate and breed," said the 19-year-old. "On a day-to-day basis, these are things that you don't appreciate."

The guided tour was one of two organised by the National Parks Board (NParks) as part of this year's Clean and Green Singapore campaign.

Yesterday's tour took participants along a green corridor that connects Yishun Park and Mandai Nature Reserves. It was the first time NParks was running free guided tours for the public. It attracted about 30 people.

Another tour, which takes place today, will see participants visiting the Tampines Nature Way, which stretches from Pasir Ris Park to Bedok Reservoir Park.

Nature ways are routes planted with specific trees and shrubs to facilitate the movement of animals like birds and butterflies between two green areas. NParks hopes to use these routes to bring biodiversity closer to residents.

There are four nature ways - in Yishun, Tampines, Admiralty and Kheam Hock - that cover a total distance of 21km in Singapore. NParks aims to expand that network to about 60km by 2015.

Both tours offered by NParks were fully booked, with many people put on a waiting list.

NParks said it will consider organising more of such guided tours in the future.

One of the participants on the Yishun Nature Way tour, Ms Cheng Lian Chee, was thrilled to spot the leopard butterfly at Yishun Avenue 4.

The retiree in her 50s said: "Such tours create greater awareness that we can co-exist with plants and animals. It is not one or the other."