A study on the effects of species, plant density, population size and species mixture on the morphological, physiological and thermal performance of six woody shrubs growing on rooftops in Sheffield, UK

Urbanisation destabilises natural environments and causes the loss of ecosystem services. Green roofs are engineered structures that allow vegetation growth on rooftops and contribute to the recovery of ecosystem services, including temperature abatement for building energy savings. The present study evaluated the morphological, physiological and thermal performance of six woody shrubs growing in 300-mm substrate in containers placed on two campus building rooftops at the University of Sheffield, UK. Temperature sensors placed on bare substrate and above and beneath shrub canopies measured temperatures between January 2016 and August 2018 to assess the cooling and insulating ability of each species in the summer and winter, respectively, compared to bare substrate. Plant morphological and physiological parameters were measured in the summer to observe the effects of species, plant density, population size and species mixture on plant fitness and survival. The study also observed the same effects on the temperature profiles of the different species to evaluate shrub thermal performance.