Healthy soils for urban sustainability

Healthy soil ecosystems lay the foundation for urban sustainability by providing the basis for ecosystem services such as flood regulation, nutrient cycling and carbon sequestration. Researchers at Future Cities Laboratory (FCL) and collaborators investigate if the soils under different types of urban land cover in tropical Singapore differ in their capacity to provide regulatory ecosystem services associated with the flow of water and nutrients.

In Singapore, soils are typically found beneath five common types of urban land cover: secondary forest, managed grass, shrubs, trees, and trees with shrubs. The researchers collected soil samples from 120 sites in Singapore and analysed them for 15 soil and vegetation properties. In order to determine if land cover affects the capacity of these soils to support litter decomposition and infiltration, they measured these two key ecosystem functions using a standardised tea bag method and a double ring infiltrometer.

They found that urban soils in Singapore are highly heterogeneous. Across the five types of urban land cover, secondary forests best support the two soil ecosystem functions with the highest rates of litter decomposition and infiltration, followed by trees with shrubs, with the lowest rates observed in grass. Parameters such as soil invertebrate activity, leaf litter cover, soil nitrogen content and soil bulk density also influence the capacity of soils to support these ecosystem functions.

The research suggests that city planners should protect remaining fragments of forest and allow natural succession to occur in order to optimise the delivery of soil ecosystem services in tropical cities. Further, multi-layered vegetation with trees and shrubs should be encouraged in non-forested areas, and urban soils can be restored by improving soil nutrients, reducing bulk density, and leaving leaf litter in situ.

This study, led by Fung Tze Kwan, together with Dr Daniel Richards, Rachel Leong, Dr Zuzana Drillet, Prof. em. Peter Edwards and co-authors, was part of the Ecosystem Services in Urban Landscapes research at FCL. The paper external pageLitter decomposition and infiltration capacities in soils of different tropical urban land coverscall_made is published in Urban Ecosystems.