Abstract

The use of green roofs in the Mediterranean area is becoming more widespread. Use of the species which are most commonly used across the world can be limited by the specific conditions of the Mediterranean climate. An experimental green roof simulation tested the performance of 12 species divided into three groups according to growth form (ground cover, sub-shrub, rhizomatous-herbaceous). Different irrigation criteria were applied to each group: in two sections potential evapotranspiration (ET0) levels of 20% and 40% were applied, while the third section was rainfed. Mortality, green coverage, blooming and final biomass were measured.

The amount of water received and the low winter temperatures affected plant mortality. Significant differences in coverage were observed when comparing the rainfed section with the two irrigated areas. Ground cover plants in the irrigated sections achieved the best results in terms of coverage. Significant differences in biomass were observed only when comparing the irrigated plots with the rainfed plot. The influence of different irrigation protocols on flowering was observed in five species only.

The growth form groups responded in different ways to drought stress: rhizomatous-herbaceous developed slowly and consistently; ground cover developed quickly and relied more on the water supply; sub-shrubs showed lower resistance to drought stress under the present experimental conditions. Of the 12 plants tested for green-roof adaptation in a Mediterranean climate, those which performed best were: Centranthus ruber (L.) DC., Santolina rosmarinifolia L., Helichrysum stoechas (L.) Moench, Iris lutescens Lam..

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