The different shades of green

SINGAPORE — Cultivated greenery is a poor substitute for natural greenery when it comes to sustaining richness of biodiversity, a local study has found.

A higher percentage of natural vegetation cover supports richer and diverse communities of bird and butterfly species. In contrast, cultivated greenery was found to support a homogenous community of species — albeit a higher number than areas of low greenery.

Part of a National University of Singapore (NUS) biological sciences graduate’s doctoral thesis, the findings have implications on the management of green spaces here. It is a first step towards quantifying trade-offs in biodiversity levels when natural green spaces make way for development, as well as how the effects of development could be mitigated, said Mr Chong Kwek Yan, the study’s author.

The research was funded by the Ministry of National Development’s Research Fund for the Built Environment.

Vegetation covers about 56 per cent of Singapore’s land area — 27 per cent is cultivated greenery and 29 per cent is natural greenery. Common bird species found in low greenery areas are mynas, pigeons and sparrows, while in high cultivated greenery areas, species like the Asian koel and sunbirds can be sighted.

Mr Chong analysed surveys of 42 plots of land islandwide measuring 500m by 100m.

Twenty-three plots in places like the city and newer heartlands like Tampines were classified as that with low greenery, nine were of high cultivated greenery and 10 — such as along Changi Coast Road and Bukit Batok Nature Park — were of high natural greenery. The areas were classified based on factors including percentage cover of cultivated trees and natural shrub and grassland.

Areas with 80 per cent natural vegetation cover had an average of about 45 bird species and 25 butterfly species, while areas with 20 per cent natural vegetation cover averaged 35 bird species and fewer than 20 butterfly species.

While the authorities already know cultivated greenery is not a replacement for natural greenery, the study, with its quantitative findings, helps measure the trade-offs when certain actions are undertaken, said Mr Chong, 29.

NUS Associate Professor Hugh Tan, Mr Chong’s thesis supervisor, said: “If our objective is to have a diverse urban wildlife, we must explicitly make plans for natural greenery.”

The research also found that big trees were the component of cultivated greenery that support rich urban wildlife. Hence, it is important to keep as many healthy large trees as possible when land plots are developed, said Assoc Prof Tan. Another option is to have minimal maintenance of cultivated landscapes to achieve a more semi-natural state for these areas.

Comparing latest findings with surveys done in 2000 and 2001, Mr Chong also found that numbers for 14 of the 20 most common bird species here, such as the Javan myna and brown-throated sunbird, had increased. But whether this is at the expense of rarer bird species is unclear, as different surveyors were used in the older and newer surveys.

Going forward, more research can be done on the interplay between traffic and greenery on biodiversity, as well as on the status of the species found, suggested Mr Chong.