Leaf trait plasticity means green facades are a flexible nature-based solution for vertical greening under full-sun and heavy shade conditions

Abstract

Climbing plants that cover building walls (indirect green façades) are a nature-based solution for urban greening in dense urban areas. Green facades can provide important ecosystem service benefits such as cooling, biodiversity habitat and visualamenity and screening. However, as new buildings are constructed the urban form changes and this can create heavy shade that impacts the growth, health and function of existing green façade climbing plants. Climbing plants may respond to increased shade through plasticity in some leaf traits (e.g. specific leaf area, photosynthetic rate or leaf chlorophyll content). However, deciduous climbing plant species are likely to be more plastic than evergreen species as they have less conservative resource strategies.In this study we measured morphological, physiological and biochemical leaf traits of seven mature climbing plant species growing in full-sun and in response to the addition of heavy shade (via shade cloth). All seven climbing plant species significantly increased specific leaf area; whilst physiological traits relating to light compensation and thermal tolerance remained unchanged in response to heavy shade. Other physiological, biochemical or morphological traits only changed in response to heavy shade for certain species. There was a very similar level of phenotypic plastic response to shade by both deciduous and evergreen climbing plant species, except for photosynthetic capacity which was significantly more plastic (greater reduction) in deciduous species.Our results suggest most climbing plant species can maintain growth and physiological function when light conditions change from full-sun to heavy shade. These green façade plants are likely to maintain building wall coverage, healthy function and delivery of ecosystem service benefits in cities. In areas experiencing densification and new building shadows, deciduous climbing plant species appear to respond slightly better to heavy shade and may be more suitable for green façades that may become shaded by future building.