Rooting Volume Impacts Growth, Coverage and Thermal Tolerance of Green Façade Climbing Plants

Pei-Wen Chung,Stephen J Livesley,John P Rayner,Claire Farrell

doi:10.3390/land10121281

Abstract

Green façades can provide cooling benefits through the shading of walls, evapotranspiration, and insulation. These benefits depend on good plant coverage and tolerance of heat stress. This requires sufficient rooting volume for plant growth and an adequate supply of moisture. On high-rise buildings, plants can be constrained by small rooting volumes due to engineering weight limits and cost. We assessed effects of rooting volume (21, 42, and 63 L) on the growth and coverage of Akebia quinata and Pandorea pandorana and leaf stress (chlorophyll fluorescence) in response to increasing air temperatures. We showed that 42 and 63 L rooting volumes significantly increased early plant growth and the percentage wall coverage for both species. Specific leaf area was significantly greater when grown in 63 L compared with 21 L. Shoot/root ratio did not change with rooting volumes. Regardless of rooting volume, higher air temperatures on west-facing aspects led to afternoon leaf stress. In practice, for each cubic meter of rooting volume, 21 m2 (P. pandorana) and 10 m2 (A. quinata) canopy coverage can be expected within six months.

Highlights

Worldwide, increasing urbanisation and densification continue to have negative environmental impacts in cities, including modification of the urban climate, which leads to urban heat island effects, increased water and energy consumption, and heat-related illness and mortality [1,2]
Our study showed that plant growth and coverage of A. quinata and P. pandorana can be significantly reduced by small rooting volumes
Our results suggested that the smallest rooting volume was not suitable to grow climbing plants for indirect green façades due to the restriction of plant growth and cover

Summary

Introduction

Worldwide, increasing urbanisation and densification continue to have negative environmental impacts in cities, including modification of the urban climate, which leads to urban heat island effects, increased water and energy consumption, and heat-related illness and mortality [1,2]. Vertical greening can potentially provide numerous benefits, including improved air quality, increased plant diversity and habitat provision for wildlife, noise reduction, microclimate improvement, urban heat island mitigation, building thermal performance improvement, and lower energy costs, as well as improved aesthetics and psychological well-being of urban residents [8,9]. While many diverse environmental benefits can potentially be achieved with vertical greening, one of the biggest drivers for their implementation is the cooling benefits they can provide to cities and buildings [6,11]. Vegetation can potentially alleviate the urban heat island effect directly through covering heat-absorbing surfaces and reducing solar gain, and through evapotranspiration, which provides latent heat cooling benefits for the plant and the air surrounding it [12,13,14]

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