Provision of ecosystem services by hedges in urban domestic gardens: focus on rainfall mitigation

Abstract

In the UK urban context, domestic gardens are an important resource, taking up to 25% of an urban area, with hedges being their popular and widespread features. Garden hedges are able to provide a number of ecosystem services, including mitigation of rainfall, trapping of particulate pollution, local temperature regulation etc. Using hedges as a model, we argue that differences in plants’ capacity to provide environmental benefits should be taken into account, in addition to their suitability for particular conditions, ornamental appeal and cost, when choosing plants for green spaces. The overarching aim of our project is to quantify the simultaneous provision of multiple services by several widely used hedge species and cultivars. In this paper, we are focusing on the provision of rainfall capture by the hedges. The following species and cultivars, differing in the leaf and canopy structure and size, and in some physiological parameters, were chosen for the study: Photinia x fraseri 'Red Robin', Thuja plicata ‘Atrovirens’, Taxus baccata, Ligustrum ovalifolium ‘Aureum’ and ‘Argenteum’ and Cotoneaster franchetii. The experiments were conducted June-July 2015 in glasshouses at the University of Reading, UK. We measured the water use of different species/cultivars (6 plant ‘treatments’ and bare substrate as a control, in 10 L containers, with 6-8 replicates each) and their ability to hold water within the canopy. Plants’ leaf and root biomass and leaf area (LA) were also measured. Species/cultivars differed in the capacity of canopies to retain water after a simulated rainfall event. Ligustrum ‘Aureum’ held significantly more water within the canopy than other species/cultivars, despite not having the largest LA. Furthermore, when differences in LA were taken into the account, Cotoneaster, Thuja, Taxus and Ligustrum ‘Argenteum’ lost most water per unit leaf area suggesting that they have the greatest potential to restore soil’s capacity to receive subsequent rainfall. Our initial findings confirm the hypothesis that differences in plant structure and function lead to different capacities for rainfall capture. This could inform our planting choices and help to manage/reduce problems associated with excess rainfall.