Litter decomposition and infiltration capacities in soils of different tropical urban land covers

Healthy soil ecosystems are important for urban sustainability, because they provide the basis for ecosystem services such as flood regulation, nutrient cycling and carbon sequestration. We investigated the soils beneath five types of urban land cover in the tropical city of Singapore—secondary forest, managed grass, shrubs, trees, and trees with shrubs. We quantified the capacity of these soils to support two key ecosystem functions: litter decomposition, which we measured using a standardised tea bag method, and infiltration, which we measured using a double ring infiltrometer. Soil samples (0–20 cm depth) were collected from 120 sites and were analysed for 15 soil and vegetation properties including pH, soil organic matter content, particle size, bulk density and soil nitrogen, phosphorus and potassium. The forest sites had significantly higher leaf litter cover and canopy leaf area index than the other land cover types. Rates of litter decomposition and infiltration were highest in secondary forest, followed by trees with shrubs, and lowest in grass. Litter decomposition rates were positively related to soils with presence of soil invertebrate activity, leaf litter cover and soil nitrogen content. Infiltration rates were negatively related to soil bulk density. To optimise the delivery of soil ecosystem services in tropical cities, city managers and planners should protect any remaining fragments of forest, allow natural succession to occur, plant multi-layered vegetation with trees and shrubs, and restore urban soil by improving soil nutrients, reducing bulk density, and leaving leaf litter in situ.