Initial agronomic performances of Mediterranean xerophytes in simulated dry green roofs

Abstract

The growing desire to make the urban environment more sustainable from an ecological point of view has stimulated research on the architectural and agronomic aspects of green roofs. The practical realisation of green roofs, is however limited by economic and ecological issues. More specifically, water availability is the most limiting factor, and is likely to be ever more so in the future in the light of climate change. For this reason, we evaluated the agronomic performance of several xerophytes in a simulated dry green roof. Seeds of 20 species were collected in typically dry habitats (abandoned quarries, rocky soils, dunes, etc.) and studied in the laboratory for germination ecology. In cases of strong dormancy, methods were tested to stimulate germination and their germination ecology was studied. The resulting seedlings were transplanted in spring 2008 in two green roof types that differ in substrate depth (150 and 200 mm) made up of lapil, pumice, zeolites and peat, resting on a drainage layer of hydroperlite. Temperature and humidity in the substrate and drainage layer were measured during the whole test period. Survival of the seedlings in both substrate depths was almost 100%, favoured by a rainy spring. Most of the tested species showed an excellent performance during the hot and dry summer months in terms of survival rates, growth, and vegetation cover dynamics, notwithstanding the difficult ecological conditions (temperatures around 50°C; hydric potential Ψ -15 bars). Furthermore, most of the species had a long flowering stage in the first year of growth. Plants in the green roof with the deeper substrate depth produced, for most of the tested taxa, a significantly higher vegetation cover and growth compared to when they were placed in the 150 mm substrate. The results of this study show that some Mediterranean xerophytes have biological characteristics suitable for their use in dry green roofs, although an irrigation system for emergency use seems advisable. To conclude, further research should focus on long term evaluation of green roof vegetation in terms of plant survival and flowering dynamics.

Effect of green roof media depth on Crassulacean plant succession over seven years

“…General conclusions regarding depth agree with many previous studies on succulents, as well as herbaceous perennials and grasses (Benvenuti & Bacci, 2010;Dunnett, Nagase, & Hallam, 2008;Durhman et al, 2007;Thuring et al, 2010). Deeper media depths allow for greater diversity in plant material and generally encourage healthier plants with greater biomass.…”

“…Regardless of species, media depth influences how well plants perform (Benvenuti & Bacci, 2010;Dunnett, Nagase, & Hallam, 2008;Dunnett & Nolan, 2004;Durhman, Rowe, & Rugh, 2007;Rowe et al, 2006;Thuring et al, 2010). Deeper media depths are beneficial for both increased water holding capacity (VanWoert et al, 2005a(VanWoert et al, , 2005b and as a buffer in fluctuating winter temperatures (Boivin, Lamy, Gosselin, & Dansereau, 2001).…”

Substrate Composition and Depth Affect Soil Moisture Behavior and Plant-Soil Relationship on Mediterranean Extensive Green Roofs

“…Research on green roofs currently focuses on cold climates, and may not take into account prolonged periods of drought, extreme temperatures or heavy precipitation, the future climatic conditions due to global changes [3,[13][14][15]. In the Mediterranean context, such severe conditions impose severe restrictions on plant growth and on plant survival [16]. Water is one of the most common limiting factors for the development of plants [17][18][19].…”

“…It is therefore important to establish plant selection criteria prior to implementation [22]. In the case of Mediterranean green roofs, the main criteria are drought tolerance, their indigenous nature, aesthetic characteristics (to ensure acceptance by the general public) and low maintenance requirements [3,16,23,32]. Regional plant communities can thus serve as a model for the recruitment and installation of seeds on green roofs [22,32,33], being composed of stress-adapted species and ruderal species that have the capacity to maximize resources.…”

Growth of the Chilean plants Haplopappus macrocephalus and Selliera radicans on an extensive modular green roof system under three irrigation regimes

“…In most cases extensive green roofs are planted with succulent species mainly from the genus Sedum (Durhman et al, 2007;Snodgrass and Snodgrass, 2006;Nektarios et al, 2015) which is also the case for Chilean extensive green roofs. However, there is a significant worldwide trend to utilize native species that are better adapted to the local conditions and pests, provide better aesthetics and avoid the problems of monocultures (Benvenuti and Bacci, 2010;Nektarios et al, 2012Nektarios et al, , 2015Kokkinou et al, 2016;Kotsiris et al, 2012b). The task is challenging due to minimal substrate depth of the extensive green roof systems, exacerbated by the harsh environmental conditions that prevail on the roofs of buildings and the need for minimal maintenance requirements.…”