Green walls

On land, too, researchers are finding ways to improve biodiversity by using human-made vertical greenery systems in which vegetation is incorporated into vertical surfaces such as walls.

Such green walls could help mitigate rising temperatures and loss of biodiversity, which are the results of climate change and urbanization, said a report published in the international journal Building and Environment in November.

The study was a collaboration between Utrecht University in the Netherlands, Nanyang Technological University in Singapore and Bio-SEA, a company in Singapore that specializes in ecological design.

The temperature regulation of green walls has been studied before, but the biodiversity benefits these walls deliver are not well researched, especially in tropical climates, said Katharina Hecht of Utrecht University, the lead researcher.

The study compares the green walls with their natural counterparts such as natural cliffs, which Hecht said is a novel approach to evaluate whether building walls perform to their full potential in providing ecosystem services.

A total of eight green walls on buildings, four climber and four foliage, as well as four natural cliffs and eight non-vegetated building walls, were studied between August 2022 and March 2023.

A total of 280 animal species were recorded across all 20 walls — foliage walls, climber walls and walls with no vegetation. Of these, natural cliffs hosted the most number of species, with 115 recorded, including the Asian hermit spider. Foliage green walls hosted 111, such as the yellow-vented bulbul, while climber green walls hosted 77 species, such as the pond wolf spider. Walls without any vegetation had only about 20 to 39 species.

The researchers also found that animal diversity increases when there is more surrounding vegetation, such as trees within 10 meters of a wall, which can act as stepping stones for creatures to move from other nearby green spaces to the walls.

The research also supported the findings of earlier studies that showed that green walls can act as temperature buffers for the building during the day and at night. They can help to cool the building in the day while providing insulation from cooler temperatures at night.

Green walls can help lower the temperature around the building wall by an average of 0.6 C to 0.7 C, the study showed.

On the implications of the study, Anuj Jain, director and principal ecologist at BioSEA and the study's senior author, said he hopes the collection of such data can be useful for decision-makers, such as building developers, to make more informed decisions in the built environment.

This can help to ensure regenerative, meaning having more nature than its original state, and multifunctional building designs that are hospitable to wildlife.

On green walls, Jain said: "Green walls cannot replace a natural cliff, they cannot replace a forest, but they are attracting a decent diversity of animals, particularly insects, where the details depend on the configuration and the complexity of the wall itself.

"That itself is already a very good starting point to incorporating biodiversity in urban environments."

The Straits Times, Singapore