An Experimental Study in Simulated Greenroof in Mediterranean Climate

Antonio Vestrella,Robert Savé,Carmen Biel

doi:10.5539/jas.v7n4p95

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..

Highlights

The remarkable growth of green roofing in Central and Northern Europe in recent years has not been followed by similar developments in nearby Mediterranean countries
It can be seen that the mortality rate of Asteriscus maritimus, Drosanthemum floribundum and Lotus creticus was above 81% in winter, regardless of the irrigation protocol applied
The remaining species to which water was supplied artificially resulted in a mortality rate ranging from 0% to 38%, whereas the species in the rain fed group showed mixed results: Asteriscus maritimus, Drosanthemum floribundum, Lotus creticus and Dymondia margaretae had an almost 100% mortality rate; Frankenia laevis and Limonium virgatum had a mortality rate of 70% and 74% respectively; Thymus serpyllum 48%; Helichrysum stoechas 37%; the mortality rates of Armeria maritima, Centranthus ruber, Iris lutescens and Santolina rosmarinifolia were between 14% and 18%

Summary

Introduction

The remarkable growth of green roofing in Central and Northern Europe in recent years has not been followed by similar developments in nearby Mediterranean countries. Green roof experiments first took place in Germany in 1950, and other countries followed during the 1970s (Köhler, 2006). In 1982, the German Landscape Research, Development and Construction Society (FLL) published regulatory guidelines for green roofing (FLL, 2008). Urban ecology studies have looked at the impact of green roofs in terms of urban biodiversity (Lundholm, 2006; Bass, 2009; Lundholm & Peck, 2008; Oberndorfer et al, 2007), energy consumption (Andersson, 2006; Carter & Butler, 2008; Abram, 2011; Spala et al, 2008) and the psychological and social impact on individuals and small communities (Samangooei, 2006; So-Young et al, 2008). Over the past few years the use of green roofs has spread to Italy and Spain and other areas with continental and atlantic climates, but only very recently have green roofs begun to spread to Mediterranean coastal areas (Abram, 2006; Briz Escribano, 2004; Neila et al, 2008; Damas et al, 2010)

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