A Gardener's Influence on Urban Soil Quality

Simon Tresch,Renée-Claire Le Bayon,David Frey,Andreas Fliessbach,Andrea Zanetta,Paul Mäder,Marco Moretti

doi:10.3389/fenvs.2018.00025

Abstract

Gardens are hot spots for urban biodiversity and provide habitats for many plant and animal spe- cies, both above- and below-ground. Furthermore, gardens provide a wide range of ecosystem services, including carbon (C) storage and nutrient cycling. Although the soil is the foundation of sustainable gardens providing those ecosystem services, very little is known about the conseque- nces of garden management on soil quality. Here we present a comprehensive assessment of urban garden soil quality, including biotic and abiotic site characteristics combined with land-use history and garden management information in a multivariate evaluation. A set of 44 soil quality indicators was measured at 170 sites of 85 gardens in the city of Zurich, Switzerland, comprising contrastingly managed garden habitats along a gradient of urban density. Taken together, our results show that garden management was the driving factor that inﬂuenced soil quality and soil functions. Eco-physiological soil quality indices were useful to identify differences in disturbance and intensity of soil use, showing highest microbial (microbial biomass (Cmic)/soil organic carbon (SOC)) and lowest metabolic (qCO2) quotients in perennial grass sites compared to annual vegetable sites. Despite the intensity of soil disturbance in annual vegetable and ﬂower beds, the highest endogeic earthworm biomass and diversity were found in those habitats. Whereas decomposition of green tea bags was higher in grass sites. Soil heavy metal contents varied considerably and could not be linked with garden management practices, but with spatial patterns of industry and trafﬁc. We conclude that understanding soil quality in urban ecosystems needs multi-indicator frameworks to capture the complexity of soil characteristics and the inﬂuencing factors in space and time. This study contributes to a better understanding of urban gardens and enhances the development of sustainable soil management strategies aimed at long-term improvement of soil quality and related ecosystem services in cities.

Highlights

Urban gardens are hot spots of urban biodiversity, serving as fertile islands for plants and animals in increasingly densified cities (e.g., Gilbert, 1989; Owen, 2010)
Urban garden soils are an important part of urban green spaces, they are still poorly investigated
Garden management was identified as the main driver of the differentiation of gardens according to soil quality

Summary

Introduction

Urban gardens are hot spots of urban biodiversity, serving as fertile islands for plants and animals in increasingly densified cities (e.g., Gilbert, 1989; Owen, 2010). Besides their importance as ecological niches for many species (Smith et al, 2006), they increase the connectivity of urban landscapes (Rudd et al, 2002) and provide multiple ecosystem services (Elmqvist et al, 2015). Urban garden soils are important for regulating the micro-climate by providing shade and allowing water to infiltrate and evaporate (Bowler et al, 2010). In many cities the sealed area is expanding tremendously with negative consequences for these ecosystem services (Sachs, 2015), especially for contested urban green spaces like allotment gardens (Tappert et al, 2018), due to the need for accommodation and infrastructure of growing urban populations

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