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Does shallow substrate improve water status of plants growing on green roofs? Testing the paradox in two sub-Mediterranean shrubs

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... Water is an additional limited natural resource within many cities, particularly in semiarid and arid locations such as the Mediterranean, and especially during the summer months [8]. Furthermore, in Mediterranean regions, high temperatures make the development of green roofs more difficult [9]. Under the increasing threat of climate change, water conservation is a priority. ...
... A balance among species of water and substrate is needed to address the adverse environmental conditions of green roofs and the effect of temperature extremes [19]. Therefore, plant selection and the improvement of the available amount of water to plants are key research aims [9]. Plant survival on green roofs with shallow substrates and low water availability is not easily understood, and is determined by a combination of drought avoidance physiological processes [10] such as the decline of stomatal conductance, and hydraulic conductivity [20] expressed by species in various ways that include dormancy, drought deciduousness and stomatal regulation [10]. ...
... High substrate temperatures can limit root nutrient and water uptake and transport to leaves [53][54][55][56]. Also, the water in the substrate is susceptible to rapid evaporation [9]. In the current study, for all species and both irrigation treatments, the substrate cover from the vegetation within the surface area of each simulated extensive green roof system container was not complete (data not shown), and the meteorological data confirmed the presence of high air temperatures and moderate relative humidity (Figure 1). ...
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In green roofs, the use of plant species that withstand dry arid environmental conditions and have reduced water requirements is recommended. The current study presents the effect of irrigation amount on the growth of four different species of lavender; Lavandula angustifolia, Lavandula dentata var. candicans, Lavandula dentata var. dentata, and Lavandula stoechas established on an extensive green roof system and used in urban agriculture. Two irrigation treatments (high and low) determined by the substrate hydraulic properties were applied. Plant growth studied at regular intervals included measurements of plant height, shoot canopy diameter, plant growth index, shoot dry weight and stomatal conductance. The results were consistent and showed that low irrigation reduced plant growth. With the exception of L. stoechas, the appearance of plants watered with the low irrigation treatment was satisfactory, and their use under low water amount irrigation is supported. Interspecies differences among lavender species were present in both irrigation treatments. Overall, L. dentata var. candicans showed the greatest growth, followed in descending order by L. dentata var. dentata and L. angustifolia. In parallel, for stomatal conductance, L. dentata var. candicans showed the lowest value, similar to L. dentata var. dentata, and L. angustifolia the largest. Differences in plant characteristics and size among the latter three species can be considered in the design of extensive green roof systems. The use of substrate hydraulic properties was shown to be important for irrigation management on extensive green roof systems.
... Mediterranean green roofs to improve their performance. These include modifications of substrate composition to increase water retention and available water content (WC) (Raimondo et al., 2015;Xue & Farrell, 2020) and the use of soil conditioners to improve water holding capacity (Papafotiou et al., 2013;Savi et al., 2014Savi et al., , 2015. Still, adequate selection of plant species to vegetate green roofs and proper irrigation management appear as the most promising strategies for further implementation of green roofs in harsh climates. ...
... Selection of drought-tolerant plants including succulents (e.g., Sedum Spp.), grasses, herbs and shrubs reduces water requirements of green roofs. In particular, shrubs are very good candidates for EGRs in Mediterranean climates (Raimondo et al., 2015;Savi et al., 2015) as they generally have a better stomatal control of transpiration (Farrell et al., 2013) and at the same time higher water use rates than herbaceous plants, ensuring higher storm water retention capacity (Brandão et al., 2017). However, studies on plant performance and trait-based selection on EGRs are still scarce (Du et al., 2019a). ...
Article
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Irrigation management in extensive green roofs (EGRs) is crucial in Mediterranean and semi‐arid climates, as it should guarantee efficient water use while ensuring plant survival and vegetation cover. However, benefits of maintaining moderately low substrate water potential (Ψs) have not been adequately investigated to date. An irrigation control unit based on Ψs thresholds for irrigation (MWS) was compared to a common irrigation timer maintaining Ψs ⁓ 0 MPa (CTR) in shrub‐vegetated Mediterranean EGR modules. The effect of the different irrigation regimes on substrate temperature, plant water relations (leaf conductance to water vapour, midday water potential, turgor loss point) and root vulnerability to heat stress via electrolyte leakage was tested in four shrub species. Decreasing Ψs thresholds to ‐0.4 MPa reduced irrigation volumes by 68% in 3 summer months. However, the MWS unit neither influenced plant water status and vegetation cover, nor induced physiological acclimation responses. Brief irrigation cycles imposed by MWS in the warmest hours reduced substrate surface temperature by 3 °C compared to CTR. Plant water status dynamics and root vulnerability to heat were species‐specific. Progressive stomatal closure and plant decline occurred only in Ceanothus thyrsiflorus and were associated to high root vulnerability to heat. Mortality occurred only in some Ceanothus plants in the CTR module, where higher Ψs favoured the expansion of Hyperucum x moserianum. The results suggest that selecting proper Ψs thresholds for irrigation could optimize EGR benefits, guaranteeing substantial water savings and proper plant establishment. Moreover, we claim root resistance to heat as a key parameter for plant selection in Mediterranean EGRs.
... Generally, plants growing in deeper green roof substrates are expected to have a greater survival and better growth, as deeper substrates store more water and provide more room for roots (Dunnett et al., 2008;Kazemi and Mohorko, 2017;Eksi and Rowe, 2019). Nevertheless, some studies have also demonstrated that plants can survive equally well or better in shallow substrates (Thuring et al., 2010;Zhang et al., 2014), which may be due to roots in shallow substrates accessing water in retention layers beneath substrates more quickly after planting (Savi et al., 2015). For example, Zhang et al. (2014) showed that the survival of some herbs (e.g. ...
... This has also been demonstrated for non-succulent life-forms in green roof studies in other climates, including oceanic (Dunnett et al., 2008) and humid continental (Zhang et al., 2014) climates. The fact that some species surviving better in shallower substrates did not have greater survival in deeper substrates may be because roots in shallow substrates can access water in retention layers beneath substrates (Savi et al., 2015). The external utilisable water for these plants in shallower substrates can be the same or greater than in deeper substrates due to their root lengths. ...
Article
The many ecosystem services that green roofs can provide rely on good plant coverage and plant survival, which is challenging in hot and dry climates. While true succulents like Sedum spp. have been shown to survive well on green roofs, there are limited studies relating individual traits or trait combinations to survival in other life-forms. Succulence is a rarely studied trait that describes plant water storage in leaves, stems and roots, regardless of life-form. This means that succulence can occur in plants which are not considered to be true succulents like Sedum or Crassula species. Improving water availability through succulence may improve survival on unirrigated green roofs, but succulence, as a trait, has rarely been investigated in plants which are not true succulents. We investigated whether succulence or trait combinations can relate well with survival and could be used to improve plant selection for different substrate depths on hot and dry green roofs. We conducted two experiments with the same 11 Mediterranean species (five herbs, three sub-shrubs and three shrubs); (1) a pot experiment to determine traits under well-watered conditions including: succulence, leaf lethal temperature, water use, root:shoot ratio and leaf area. These individual traits and the combinations of all these traits were used in the analyses of this experiment; and (2) a green-roof module experiment to determine survival in four substrate depths (10, 15, 20, and 25 cm). Survival was not related to succulence, indicating that increased internal water storage in non-succulent plants does not per se lead to greater survival in extreme conditions. Survival was also not related to individual traits relating to water use and leaf heat tolerance or trait combinations. Nevertheless, plants in the same functional groups had similar survival, which suggests plants with similar trait combinations can have similar survival on green roofs.
... This natural selection process must be pre-empted by designers and landscape architects for green roof systems, informed by site-specific research. Appropriate plant species selection tailored to the engineered environment is fundamental to achieving the objectives of the designed soil plant system (Michael et al., 2007;Savi et al., 2015;Williams et al., 2021;Michael, 2010). Additionally, following the principles of biodiversity sensitive urban design, the inclusion of native plant species to create habitat should be considered during the design process (Brenneisen, 2003;Garrard et al., 2017;Gedge and Kadas, 2005). ...
... The highly significant positive correlation be- tween Ψ tlp or π 0 and g L further points to symplastic drought resistance as a good predictor of plant water use over green roofs. In fact, low g L values displayed by species with low Ψ tlp translates into low evapo- transpiration rates and a more conservative water use, which repre- sents a desirable feature of plants selected for green roofs to be installed in drought-prone regions ( Savi et al., 2015). Similarly, low water use under drought conditions has been recently reported for granite outcrop shrubs capable to tolerate substantial Ψ leaf drop under drought (Farrell et al., 2013). ...
Article
Green roofs are gaining momentum in the arid and semi-arid regions due to their multiple benefits as compared with conventional roofs. One of the most critical steps in green roof installation is the selection of drought and heat tolerant species that can thrive under extreme microclimate conditions. We monitored the water status, growth and survival of 11 drought-adapted shrub species grown on shallow green roof modules (10 and 13cm deep substrate) and analyzed traits enabling plants to cope with drought (symplastic and apoplastic resistance) and heat stress (root membrane stability). The physiological traits conferring efficiency/safety to the water transport system under severe drought influenced plant water status and represent good predictors of both plant water use and growth rates over green roofs. Moreover, our data suggest that high substrate temperature represents a stress factor affecting plant survival to a larger extent than drought per se. In fact, the major cause influencing seedling survival on shallow substrates was the species-specific root resistance to heat, a single and easy measurable trait that should be integrated into the methodological framework for screening and selection of suitable shrub species for roof greening in the Mediterranean.
... I quattro cluster ottenuti classificando gli habitat naturali di riferimento comprendono 1) vegetazione di gariga tipica dei pavimenti calcarei con molte specie annuali ed un mosaico di diverse forme biologiche; 2) vegetazione basofila ricca in terofite (piante annuali), muschi e licheni; 3) praterie mesofile su suoli calcari con poche terofite e geofite (erbe perenni con gemme sotterranee); 4) vegetazione mesofila e xerofila di gariga e praterie con poche terofite. Dal dataset iniziale sono state escluse le specie con apparato radicale maggiore di 20 cm, restrizione che potrebbe essere valutata in maniera specifica poiché le stesse specie sui tetti sviluppano apparati radicali e caratteristiche morfologiche peculiari (Savi et al., 2015), e.g. specie nane, maggiore superficie radicale complessiva ed andamento plagiotropo (costretto dal ridotto spessore del substrato, dalle guaine impermeabili antiradice e dalla struttura portante). ...
Article
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Cities are defined as heterotrophic systems (Odum, 1983) as they depend mainly on external resources and cause habitat loss and fragmentation. Green roofs represents a fundamental means of ecological compensation within the built environment, i.e. in highly altered and disturbed places by humans. In particular, green roofs for biodiversity (or biodiversity green roofs), being characterised by different but contiguous microhabitat (habitat mosaics or patches), can host several species with different mor- phological and functional traits (Brenneisen, 2003). The method known as the habitat template consists of choosing suitable plant species for green roofs from among the one that live in nature under similar conditions e.g. shallow and nutrient poor substrate, drought resistant (Lundholm, 2006). The phytosociological approach applied to green roofs considers the habitat analogue not only as a species pool, but also as a model to group plants in specific associations.
... The pots were filled with a lightweight substrate designed for green roof systems settled in Mediterranean areas (SEIC, Verdepensile, Harpo). The substrate consists of a porous, slightly acid growing medium of volcanic origin, with high drainage capacity and low organic content (for additional details, see Savi et al. 2015). Substrate characteristics were similar to those on which these species grow in the wild. ...
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Key message Easily measurable functional traits can be used as proxies in the selection of drought-tolerant saplings for reforestation in Mediterranean ecosystems. Abstract Heat and drought events—increasing both in frequency and severity—have led to forest decline, and are a serious threat for the Mediterranean biome. Whereas drought tolerance of adult trees of different Mediterranean species has been widely investigated, this is not the case for saplings and young trees. We analysed correlations and trade-offs among leaf (water potential at the turgor loss point, Ψtlp, modulus of elasticity, ε, osmotic potential at full turgor, π0, leaf capacitance, Cleaf_dw, leaf venation, VLA, leaf mass per area, LMA) and stem (wood capacitance and wood density, Cwood and Dwood, stem-specific conductivity and water potential inducing 50% loss of hydraulic conductance) functional traits of saplings for 14 woody species of the Mediterranean flora. The results support previously reported correlations among functional traits known to confer drought tolerance to plants. In particular, Ψtlp was positively correlated to π0, Cleaf_dw and VLA, while negatively correlated to ε and LMA. A highly significant correlation was highlighted between Cwood and Dwood. Overall, we observed surprisingly low symplastic and apoplastic resistance. We identify some easily measurable traits (π0 and LMA), which evidence seedlings’ ability to cope with drought, and which therefore could be used as proxies in the selection of drought-tolerant saplings for reforestation in Mediterranean areas.
... Our results are consistent with these in that the featureless shallow microsites had the lowest seedling densities, the highest temperatures but not the lowest moisture contents. While some recent work shows that deeper substrates may promote poor survival in drought due to high biomass production during wet periods (Savi et al., 2015), in our study, the shallowest treatments (2 cm) were too extreme to support seedlings without the mitigating influence of pebble piles. While microsites under pebble piles may not represent the wettest conditions on a green roof soon after a rain event, they appear to play a more important role by slowing water loss during drought and reducing temporal moisture variability, making ultrathin (2-3 cm substrate) green roofs more hospitable to seedlings when hot, dry weather prevails. ...
Article
Urban areas benefit from the ecosystem services provided by low input green roofs. However, limited substrate depth on these green roofs creates challenging conditions for plant establishment and survival, leading to industry reliance on non-native succulents. Through a green roof and glasshouse study, we assessed the impact of simple design modifications to the green roof surface, including redistribution of substrate and addition of logs and pebble piles, on both substrate temperature and moisture content. We added seeds of 26 native species and quantified seedling density, species richness and composition over a single growing season. Overall effects of microsite heterogeneity on species diversity were assessed using species accumulation curves. The modifications altered substrate temperature and moisture. Deep substrate (10–12 cm) and the presence of surface features reduced the temperature by 14.6°C and, while surface features had mixed effects on substrate moisture on the green roof, pebble piles slowed moisture loss during a 6-week drought in the glasshouse. Following drought conditions, seedling density and species richness were greatest, relative to seeded controls, where substrate was deep on the green roof and where pebbles were present in glasshouse modules, despite high mortality overall. Design modifications did not result in differentiation of seedling communities among different microsite types. Species accumulation curves showed no difference in species richness between aggregates of modified vs. unaltered microsites. Synthesis and applications. Redistribution of green roof substrate and the addition of logs and pebble piles altered microsite conditions and created habitat heterogeneity on a green roof. These design modifications represent a minimalist strategy to ameliorate growing conditions, improve seedling survival and decrease species loss on shallow substrate green roofs. © 2017 The Authors. Journal of Applied Ecology
... Water potential (Ψ) measurements were performed using a dew point water potential meter (WP4, Decagon Devices, Inc.) as the average of three subsequent values in the range below the error of the instrument (0.1 MPa) and coupled with measurements of sample fresh weight (FW). The cumulative water loss of colonies (Wl = TW − FW) was plotted versus −1/Ψ, and experiments were concluded when this re- lationship became linear (R 2 > 0.98) ( Savi et al., 2015). Ψ tlp was es- timated as the flex point transition between the curvilinear and linear parts of the relationship (Tyree and Hammel, 1972;Bartlett et al., 2012). ...
Article
The relation between water status and expression profiles of desiccation -related genes has been studied in the desiccation tolerant (DT) aeroterrestrial green microalga Trebouxia gelatinosa, a common lichen photobiont. Algal colonies were desiccated in controlled conditions and during desiccation water content (WC) and water potential (Ψ) were measured to find the turgor loss point (Ψtlp). Quantitative real-time PCR was performed to measure the expression of ten genes related to photosynthesis, antioxidant defense, expansins, heat shock proteins (HSPs), and desiccation related proteins in algal colonies collected during desiccation when still at full turgor (WC > 6 g H2O g-1 dry weight), immediately before and after Ψtlp (-4 MPa; WC ∼ 1 g H2O g-1 dry weight) and before and after complete desiccation (WC < 0.01 g H2O g-1 dry weight), quantifying the HSP70 protein levels by immunodetection. Our analysis showed that the expression of eight out of ten genes changed immediately before and after Ψtlp. Interestingly, the expression of five out of ten genes changed also before complete desiccation, i.e. between 0.2 and 0.01 g H2O g-1 dry weight. However, the HSP70 protein levels were not affected by changes in water status. The study provides new evidences of the link between the loss of turgor and the expression of genes related to the desiccation tolerance of T. gelatinosa, suggesting the former as a signal triggering inducible mechanisms.
... Interestingly, peak plant heights did not occur at the same sampling time point as peak canopy density by city or by species. Recent research suggests that where drought is a significant source of mortality, lower substrate depths can actually result in higher survivorship as plant growth is constrained in shallower substrates leading to reduced mortality rate during drought (Savi et al., 2015), but we did not see this result in the more benign Canadian climates studied here. ...
Article
Green rooftops are installed in many climates worldwide to support urban ecosystem services. Across North America, green roofs often make use of the same limited set of plant species, but the effects of regional climates on the survival and growth of a core set of plant species has seldom been investigated. To identify the impact of climate on green roof plant performance, we installed an identical green roof system in three Canadian cities that experience different climate conditions: Calgary, Alberta; London, Ontario; and Halifax, Nova Scotia. The green roofs were monitored across three growing seasons for plant survival, plant height, and canopy density of three species grown in monoculture: Aquilegia canadensis, Sporobolus heterolepis, and Sedum spurium, and a mixture planting with all three species. Green roof vegetation canopy density, plant height and growth rates differed by city, plant species, substrate depth and planting type (monoculture or mixture treatment). Between sites, plant species exhibited different growth phenologies. Mixture treatments performed slightly better than monoculture plantings at each site in canopy density measures but were not significantly greater in plant height measures. The growth rate between years two and three was greatest for the mixture treatment, indicating greater potential for long term survival and performance of mixture plantings. The London, Ontario site, with a relatively moderate climate, supported the best green roof growth and performance compared to the cooler and drier Calgary and the rainier Halifax.
... Whilst this strategy can be achieved by some plant functional types, woody plants exhibit a trade-off between drought response and water use ( Du et al. 2018): drought resistant shrubs tend to have a low water use, whereas shrubs that have a high transpiration rates are not drought tolerant. Consequently, to select shrubs or other woody plants for future green roofs under water-deficit it will be more important to select species with high drought resistance and conservative water use ( Savi et al. 2015;Savi et al. 2016). ...
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Aims Green roofs are important novel urban ecosystems, but their shallow substrates can create plant water deficits in dry climates. Physiological approaches can improve green roof plant selection, and shrubs with high drought tolerance and conservative water use under water-deficit should perform well. The water potential at turgor loss point (Ψtlp) has been used to predict drought resistance. Therefore we aimed to determine whether Ψtlp could be used as a screening tool to assess drought resistance for green roof plant selection. Methods We evaluated 20 shrub species, originating from ecosystems varying in water availability, quantified by heat moisture index (HMI) and mean annual precipitation. We conducted a water-deficit experiment to measure Ψtlp, the degree of iso-anisohydry (△ΨMD) and water use (ET) in response to drought. Results Shrubs with lower Ψtlp were more anisohydric (greater △ΨMD) and had a more conservative water use (lower ET). However, Ψtlp, ΔΨMD and ET were not related to HMI. Conclusions These results suggest that Ψtlp could be used to select shrubs for green roofs, as species with lower Ψtlp tended to be more drought tolerant, more anisohydric and used less water under water-deficit. However, species with higher Ψtlp could also potentially survive through drought avoidance.
... Furthermore, this study was conducted during a relatively dry summer in 2018 with only 1.2 mm rainfall in February, which likely exacerbated plant mortality, as drought duration and severity would potentially influence the physiological impact of drought on plants (Choat et al., 2018;McDowell et al., 2018;McDowell et al., 2008). Additionally, the substrate depth would also influence plant mortality, as Savi et al. (2015) showed that plants with deeper substrate depth had higher survival under water-deficit because of high biomass accumulation during wet seasons and higher plant water availabilities (Savi et al., 2016). Consequently, there would be a combination of multiple factors influencing plant survival, rather than merely one. ...
... As concern the substrate depth, Savi et al. [94] investigated the performance of two sub-Mediterranean shrubs (Cotinus coggygria and Prunus mahaleb) grown over green roofs with extremely shallow substrate depths and identified the impact of substrate thickness on shrubs water status, survival, and growth in a sub-Mediterranean climate. The results confirmed the possibility to install extensive green roofs vegetated with stress-tolerant shrubs in sub-Mediterranean areas using 10 cm deep substrate. ...
Article
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In order to consider green roofs as an environmentally friendly technology, the selection of efficient and sustainable components is extremely important. Previous review papers have mainly focused on the performance and advantages of green roofs. The objective of this paper is to examine the primary layers: The waterproof and anti-root membranes; the protection, filter, and drainage layers; the substrate; and the vegetation. First, the history, modern applications, benefits and classification are analyzed in order to present a well-defined state of the art of this technology. Then, the roles, requirements, characteristics, and materials are assessed for each green roof layers. This technology was compared to a conventional roof technology, Mediterranean climate conditions and their influence on green roof design were assessed, also comparing them with Tropical area and focusing on irrigation systems, examples about the commercial materials and products available in the market were provided and innovative materials coming from recycled sources were analyzed. Future research should evaluate new materials for green roof technologies, in order to enhance their performance and increase their sustainability. The information provided in this review paper will be useful to develop Mediterranean green roof guidelines for selecting suitable components and materials during the design and installation phases.
... Hydrogels have been shown previously to prolong survival times and increase plant morphological and physiological characteristics in drought conditions (Orikiriza et al., 2013;Tomadoni et al., 2020). Accordingly, there are studies that have assessed the effects of hydrogel mixed substrates and their relationship to plant growth (Farrell et al., 2013;Olszewski et al., 2010;Savi et al., 2015). However, these studies`have focused mainly on the physicochemical properties of the substrates and drought-resistant plants, including succulents, grasses, legumes, and shrubs. ...
Article
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Agricultural hydrogels improve water retention in a variety of substrates. However, little is known about their impact on herb cultivation in rooftop farming. To identify the optimal substrate and hydrogel concentration for the growth and flowering of spearmint ( Mentha spicata ) in rooftop gardens, coir and perlite were mixed in three different ratios of 80% to 20% (v/v; referred to as C 4 P 1 ), 50% to 50% (C 1 P 1 ), or 20% to 80% (C 1 P 4 ). Hydrogels were added into different substrates at different concentrations including 0 (control), 0.25, 0.5, 1.0, or 2.0 kg⋅m –3 . Substrate composition significantly affected the growth ( P < 0.001) and flowering ( P < 0.05) properties of spearmint. The addition of hydrogels into substrates resulted in a significant ( P < 0.05) increase in growth parameters for spearmint during the dry season. However, plants grown in C 4 P 1 , which has the highest ratio of coir, displayed inferior growth and flowering compared with those of the other two substrates during the rainy season. Therefore, a perlite-based substrate, such as C 1 P 4 with added hydrogel, provides a suitable environment for the cultivation of spearmint in rooftop gardens regardless of seasonal rainfall patterns.
... It is also of great importance for medicine [10]. Having a number of decorative features and high drought resistance, C. coggygria is used in landscape construction, including the landscaping of roofs [8,[11][12][13]. ...
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Due to the deterioration of the environmental situation, the requirements for the assortment of woody plants for landscaping territories for various purposes are constantly growing. To form a stable assortment of woody plants with the specified characteristics, it is necessary to use introduced species in the breeding process. The genetic collection of the VNIISPK Arboretum includes more than 310 species, forms and varieties of woody plants, including the Anacardiaceae family R.Br. All representatives of this family are introduced species, one of which is Cotinus coggygria . The purpose of the research is a comprehensive assessment of the ecological and biological features of Cotinus coggygria and its varieties to justify the use in breeding to obtain varieties with economically valuable traits in the conditions of the Central part of Russia. According to the research results, the most promising for use in breeding in order to obtain new varieties is C. coggygria cv. ‘Follis Purpureis’, which has a number of economically valuable features: winter hardiness, resistance to diseases and pests, complex of decorative qualities. C. coggygria cv. ‘Royal Purple’ can only be used as a source of resistance to diseases and pests and decorative coloring of leaves.
... This natural selection process must be pre-empted by designers and landscape architects for green roof systems, informed by site-specific research. Appropriate plant species selection tailored to the engineered environment is fundamental to achieving the objectives of the designed soil plant system (Michael et al., 2007;Savi et al., 2015;Williams et al., 2021;Michael, 2010). Additionally, following the principles of biodiversity sensitive urban design, the inclusion of native plant species to create habitat should be considered during the design process (Brenneisen, 2003;Garrard et al., 2017;Gedge and Kadas, 2005). ...
... We need to know the recommended substrate depth for optimal rainfall retention relative to the cost and weight loading on the roofs (e.g. Seidl et al., 2013;Savi et al., 2015). ...
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Cities are defined as heterotrophic systems as they mainly depend on external resources and cause habitat loss and fragmentation. Green roofs represent a fundamental means of ecological compensation within the built environment, i.e. in places that are heavily altered and disturbed by humans. In particular, green roofs for biodiversity (or biodiverse green roofs), being characterized by different but contiguous microhabitats (habitat mosaics or patches), can host several species with different morphological and functional traits. The method known as the habitat template consists of choosing suitable plant species for green roofs by selecting them among those that live in the wild under similar conditions, e.g. shallow, nutrient-poor, drought-prone substrates. The phytosociological approach applied to green roofs considers habitat analogues not only as species pools but also as models of the way plants should be grouped to form specific associations.
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Green roofs are expected to contribute to the mitigation of multiple environmental issues that affect urban areas. Owing to their composition, organization, and external factors, the performances of green roofs have been demonstrated to be overall positive but strongly variable. Our work first aims at proposing consensual definitions and a frame adapted to these biotic-abiotic systems. It also aims at shedding light on the qualitative relations between various internal properties and external factors of green roofs on their hydrological and thermal performances. One hundred relevant study papers were filtered from 395 papers as per our defined search criteria based on originality and precision. The expectations were to be capable of hierarchizing factors and properties that would influence the performances of green roofs. The main findings highlighted that most factors and properties have a positive influence on the performances of green roofs, showing there are many existing levers to enhance the green roof performances and tackle some of the main urban environmental issues. However, even if previous research has already explored various relations, in the final filtered consideration of 6 performances and 30 factors and properties, there was a possibility of 180 combined factor–property–performance relations studies overall. Out of these possibilities, only 82 have been studied at least once, leaving the other 98 relations (54%) unexplored. Considering that these lists were far from exhaustive, a huge potential in determining green roof performances remains unearthed. In this regard, various proposals have been made regarding: (i) identification of levers to enhance the performances of green roofs; (ii) filling the gaps: the exploration of the unstudied relations; (iii) promotion of deeper and innovative experimental approaches for research on green roof performances; and (iv) the shift from mono to transdisciplinary research about green roofs.
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To reduce water consumption and construction weight of green roofs, the synergistic effect of the type and depth of substrate layer and irrigation frequency was investigated on the growth performances of six xerophytic, aromatic Mediterranean species, Helichrysum italicum Roth., H. orientale L., Origanum majorana L., O. dictamnus L., Santolina chamaecyparissus L., Artemisia absinthium L. Rooted cuttings were planted in plastic boxes, with a green roof infrastructure (substrate moisture retention and protection of the insulation, drainage element and filter sheet), placed in a fully exposed second floor roof at the Agricultural University of Athens. Two types of substrate were used, peat: soil: perlite (2:3:5, v/v) and marc compost: soil: perlite (2:3:5, v/v) as well as two substrate depths, 7.5 (shallow) and 15 cm (deep). Two irrigation frequencies, sparse (every 5 or 7 d in shallow and deep substrate respectively) and normal (every 3 or 5 d in shallow and deep substrate respectively) were investigated for the substrates. Increased contents in macro elements especially P and K were recorded in the compost substrate, while substrates differed slightly in physical properties. The use of compost and the deep substrate gave plants with higher dry weight of the aerial part in all species except for O. dictamnus; the latter grew better in low depth peat substrate with sparse irrigation. A remarkable result was that low depth compost substrate with sparse irrigation resulted in similar or even superior growth in all species, except for O. dictamnus, than high depth peat substrate with normal irrigation. So the replacement of peat by marc compost helps to reduce the water needs of plants, as well as the depth of the substrate layer, thus reducing the weight of the construction of a green roof.
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Introduction: Since their development in the late 1970s in Germany, extensive green roofs (EGR) have become increasingly popular as mitigation tools for urban environmental issues around the world. EGRs are planted with select species, which ensure consistent cover and performance over time. This research presented herein is part of a systematic re-evaluation of EGR technology since the German industry began. Methods: Given the opportunity to access a small sample of old EGRs installed over 20 years ago in south-west Germany, this research surveyed the vegetation and substrate with an interest in describing these parameters with time-through-space substitution. Results: Similar to previous studies, this preliminary work found correlations between roof age with vegetation (cover abundance and species diversity) and substrate properties (e.g., depth, organic content, pH, and nutrients). Roof age had positive relationship with soil organic content (Corg), and negative relationships with substrate depth and soil pH. These soil variables are inter-related, as shallow acidic substrates create unfavourable conditions for decomposition and thereby the accumulation of duff. Substrate variables correlated with EGR vegetation, suggesting a trend of simplified species composition over time. Indeed, Corg had a negative relationship with cover and species diversity of most life forms; only Sedum species had positive associations with Corg. Conclusions: Considering the dynamics associated with shallow mineral substrates, and the greater floristic diversity of younger roofs, simple Sedum-based vegetation may represent a steady state for conventional EGRs.
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ADDITIONAL INDEX WORDS. winter dam-age, low-temperature injury SUMMARY. A green roof system was installed on an existing 35-year-old building. The purpose of the study was to evaluate the effect of three substrate depths on low-temperature injury of six herbaceous perennials: bugleweed (Ajuga reptans), sandwort (Arenaria verna 'Aurea'), sea pink (Armeria maritima), whitlow grass (Draba aizoides), creeping baby's breath (Gypsophila repens), and stonecrop (Sedum xhybridum). Plants in 4-inch (9-cm) pots were trans-planted into three substrate depths: 2, 4, and 6 inches (5, 10, and 15 cm) and evaluated over a 3-year period. The analysis of the results showed that the species have different winter hardiness, therefore some species were subject to more freezing injury than others. Stonecrop had significantly more damage at 2-inch than 4-or 6-inch depths during the two winters. Bugleweed and creeping baby's breath showed more damage at 2 inches in 1996–97, not in 1995–96. Substrate temperatures were measured from Oct. 1995 to May 1997. Low temperature injury was more pro-nounced at 2 inch than at 4 or 6 inch depths. Minimum daily temperature and temperature variations measured in fall and spring of these 2 years were also higher at 4-and 6-inch depths.
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Green roofs are generally seen as a desirable building element, providing numerous benefits where water availability does not restrict their implementation. However, most Mediterranean locations have long, dry summers, requiring irrigation to sustain vegetation throughout extended dry periods. The cooling effect and water use of several types of plants suitable for extensive green roof systems were assessed using small test cells, which were insulated and equipped with internal thermal mass to provide a thermal response comparable to that of real buildings. The water requirements of the plant species tested ranged from 2.6 to 9.0 L/m2 per day. Aptenia cordifolia was the most efficient in its use of water, providing the highest cooling benefit per unit water required for irrigation. However, the cooling efficiency of all roof variants studied was very low, and the reduction in the sensible heat load of the model building attributed to the green roof system was less than 5% of the latent heat content of the water lost to evapotranspiration. In this context, it is hard to justify green roofs in such environments on the basis of their contribution to building energy conservation, although other benefits may nevertheless make green roofs attractive.
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With the aim of selecting physiological tests for the screening of drought tolerant species, we have studied the behaviour of bean leaf discs treated with PEG 600 (−1.13 MPa) for 4 h. The kinetics of electrolyte and Pi leakages and of soluble sugar and starch content were studied during 24 h rehydration of the leaf discs. These four tests were related, respectively, to cell and chloroplast membrane integrity and to photosynthetic or sugar mobilization ability. The results obtained showed that stress caused by PEG induced an increase in the leakage of electrolyte of 4 to 7 times and of Pi up to 10 and 28 times, and a decrease in soluble sugar and starch content. These phenomena were stimulated by darkness. The magnitude of the physiological responses varied according to the species but correlated well with each other. Therefore, the tests used are indicators of cell and membrane integrity and they allowed us to propose a classification of the species according to their cell sensitivity to water deficit. The sequence obtained was: Phaseolus vulgaris, sensitive, Phaseolus acutifolius and Vigna radiata moderately tolérant and Vigna unguiculata, tolerant. This classification agrees well with that of drought resistance of these species when grown in the field.
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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 200mm) 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 150mm 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. KeywordsGreen roof-Substrate depth-Mediterranean flora-Dry tolerance-Biodiversity
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Urban areas are hot spots that drive environmental change at multiple scales. Material demands of production and human consumption alter land use and cover, biodiversity, and hydrosystems locally to regionally, and urban waste discharge affects local to global biogeochemical cycles and climate. For urbanites, however, global environmental changes are swamped by dramatic changes in the local environment. Urban ecology integrates natural and social sciences to study these radically altered local environments and their regional and global effects. Cities themselves present both the problems and solutions to sustainability challenges of an increasingly urbanized world.
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Evapotranspiration (ET) is a key parameter that influences the stormwater retention capacity, and thus the hydrological performance, of green roofs. This paper investigates how the moisture content in extensive green roofs varies during dry periods due to evapotranspiration. The study is supported by 29 months continuous field monitoring of the moisture content within four green roof test beds. The beds incorporated three different substrates, with three being vegetated with sedum and one left unvegetated. Water content reflectometers were located at three different soil depths to measure the soil moisture profile and to record temporal changes in moisture content at a five-minute resolution. The moisture content vertical profiles varied consistently, with slightly elevated moisture content levels being recorded at the deepest substrate layer in the vegetated systems. Daily moisture loss rates were influenced by both temperature and moisture content, with reduced moisture loss/evapotranspiration when the soil moisture was restricted. The presence of vegetation resulted in higher daily moisture loss. Finally, it is demonstrated that the observed moisture content data can be accurately simulated using a hydrologic model based on water balance and two conventional Potential ET models (Hargreaves and FAO56 Penman–Monteith) combined with a soil moisture extraction function. Configuration-specific correction factors have been proposed to account for differences between green roof systems and standard reference crops.
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The use of turfgrasses might provide an additional solution for establishing green roofs in urban environments. The aim of the present study was to determine Manilagrass [Zoysia matrella (L.) Merr. 'Zeon'] drought tolerance when grown under green roof conditions and under two different irrigation regimes. Treatments included: 1) two extensive green roof substrates {locally produced substrate [3 sandy loam soil:8 pumice:4 perlite:4 compost:1 zeolite (by volume)] and a commercially available substrate based on crushed tiles}; 2) two substrate depths (7.5 cm or 15 cm); and 3) two irrigation regimes (3 mm or 6 mm of irrigation every 3 days). Substrate characteristics (particle size distribution, saturated and dry bulk density, total porosity, water potential curves, in situ substrate moisture, pH, electrical conductivity, and nutrient analysis), turfgrass growth, and physiological status [green turf cover (GTC), normalized difference vegetation index (NDVI), and leaf relative water content (RWC)] were determined. During moisture deficit periods, GTC, NDVI, and RWC were most affected by substrate depth; moderately affected by irrigation regime; and, to a lesser extent, by substrate type. Turfgrass growth and physiological status were best during moisture deficit conditions in the deeper profile (15 cm) using the higher amount of irrigation (6 mm) and the locally mixed substrate.
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Negative hydrostatic pressure can be measured in plants.
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Green roofs have received increased interest as a result of their environmental, social, and economic benefits. The present study aims to evaluate suitable, lightweight substrates for the installation of semi-intensive-type green roofs and their effects on Lavandula angustifolia growth and physiological status under Mediterranean climatic conditions. The study was conducted in field containers (1.2 × 1.2 m), and treatments included the use of two depths (20 cm or 30 cm) and three different substrates: 1) pumice (Pum) mixed with peat (P) and zeolite (Z) in a volumetric proportion of 65:30:5 (Pum65:P30:Z5); 2) pumice mixed with compost (C) and zeolite in a volumetric proportion of 65:30:5 (Pum65:C30:Z5); and 3) sandy loam soil (S) mixed with perlite (Per) and zeolite in a volumetric proportion of 30:65:5 (S30:Per65:Z5). Each experimental plot was planted with four plants of L. angustifolia. The physical and chemical characteristics of the substrates and the in situ substrate moisture levels were determined. Plant growth was determined by the growth index and root dry weight, whereas the plant physiological status during the stressful summer period was determined by chlorophylla+b content and stomatal resistance. It was found that the bulk density of all of the substrates was less than 0.8 g-cm-3, whereas the water retention of substrate S30:Per65:Z5 was greater than the other two substrates at all tensions. Substrate depth was the most influential factor; therefore, the deeper substrates (30 cm) provided higher growth indices and root dry weight, increased total chlorophyll content, and reduced leaf stomatal resistance compared with the shallower substrate depth of 20 cm. Differences between substrate types were smaller compared with those of substrate depth. In spring, the growth index in substrate Pum65:C30:Z5 was larger but not in the summer when the growth index of substrates S30:Per65:Z5 and Pum65:P30:Z5 exceeded that of the substrate amended with compost until the end of the study. In late summer, the plant total chlorophyll content decreased in all substrates, whereas substrate Pum65: C 30:Z5 exhibited increased stomatal resistance compared with the other two substrates at the same period. It was concluded that L. angustifolia could be grown successfully in semi-intensive Mediterranean green roofs at a substrate depth of 20 cm, but its growth and tolerance to the harsh summer conditions would improve at a substrate depth of 30 cm.
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The need of planning more sustainable cities leads to a wider use of extensive green roofs (EGRs) as they provide significant advantages to the urban environment (e.g., energy conservation and increase of biodiversity). In Central and North Europe, as well as in North America and Asia, EGRs are generally included in new building designs, whereas they are still uncommon in Mediterranean countries. The adaptations of many Mediterranean plants to drought stress and their floristic diversity constitute, however, positive elements in finding solutions for them. This research proposes a methodological approach to select wild species for EGRs based on ecological characteristics (using natural ecosystems as templates for green roof design). An extensive bibliographic search on plants proposed for EGRs in Mediterranean countries has led to the creation of a wide database. Other plants were selected considering their synecological, structural, and autoecological characteristics. All the data were integrated in a comprehensive database of 138 taxa potentially suitable for setting EGRs according to their syntaxonomical classification and their ecological behavior (fitting both the Mediterranean and EGR environmental conditions). The selected taxa could enlarge the pool of species for EGRs in Mediterranean cities, increasing urban biodiversity.
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Climate features of the Mediterranean area make plant survival over green roofs challenging, thus calling for research work to improve water holding capacities of green roof systems. We assessed the effects of polymer hydrogel amendment on the water holding capacity of a green roof substrate, as well as on water status and growth of Salvia officinalis. Plants were grown in green roof experimental modules containing 8 cm or 12 cm deep substrate (control) or substrate mixed with hydrogel at two different concentrations: 0.3 or 0.6%. Hydrogel significantly increased the substrate's water content at saturation, as well as water available to vegetation. Plants grown in 8 cm deep substrate mixed with 0.6% of hydrogel showed the best performance in terms of water status and membrane integrity under drought stress, associated to the lowest above-ground biomass. Our results provide experimental evidence that polymer hydrogel amendments enhance water supply to vegetation at the establishment phase of a green roof. In particular, the water status of plants is most effectively improved when reduced substrate depths are used to limit the biomass accumulation during early growth stages. A significant loss of water holding capacity of substrate-hydrogel blends was observed after 5 months from establishment of the experimental modules. We suggest that cross-optimization of physical–chemical characteristics of hydrogels and green roof substrates is needed to improve long term effectiveness of polymer-hydrogel blends.
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Evapotranspiration (ET) is a key parameter that influences the stormwater retention capacity, and thus the hydrological performance, of green roofs. This paper investigates how the moisture content in extensive green roofs varies during dry periods due to evapotranspiration. The study is supported by 29 months continuous field monitoring of the moisture content within four green roof test beds. The beds incorporated three different substrates, with three being vegetated with sedum and one left unvegetated. Water content reflectometers were located at three different soil depths to measure the soil moisture profile and to record temporal changes in moisture content at a five-minute resolution. The moisture content vertical profiles varied consistently, with slightly elevated moisture content levels being recorded at the deepest substrate layer in the vegetated systems. Daily moisture loss rates were influenced by both temperature and moisture content, with reduced moisture loss/evapotranspiration when the soil moisture was restricted. The presence of vegetation resulted in higher daily moisture loss. Finally, it is demonstrated that the observed moisture content data can be accurately simulated using a hydrologic model based on water balance and two conventional Potential ET models (Hargreaves and FAO56 Penman–Monteith) combined with a soil moisture extraction function. Configuration-specific correction factors have been proposed to account for differences between green roof systems and standard reference crops.
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Competition for water among multiple tree rooting systems is investigated using a soil-plant model that accounts for soil moisture dynamics and root water uptake (RWU), whole plant transpiration, and leaf-level photosynthesis. The model is based on a numerical solution to the 3D Richards equation modified to account for a 3D RWU, trunk xylem, and stomatal conductances. The stomatal conductance is determined by combining a conventional biochemical demand formulation for photosynthesis with an optimization hypothesis that selects stomatal aperture so as to maximize carbon gain for a given water loss. Model results compare well with measurements of soil moisture throughout the rooting zone, of total sap flow in the trunk xylem, as well as of leaf water potential collected in a Loblolly pine forest. The model is then used to diagnose plant responses to water stress in the presence of competing rooting systems. Unsurprisingly, the overlap between rooting zones is shown to enhance soil drying. However, the 3D spatial model yielded transpiration-bulk root-zone soil moisture relations that do not deviate appreciably from their proto-typical form commonly assumed in lumped eco-hydrological models. The increased overlap among rooting systems primarily alters the timing at which the point of incipient soil moisture stress is reached by the entire soil-plant system.
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The research focused on the experimental evaluation of Photovoltaic (PV) – green roofs under Mediterranean climate summer conditions. Two autochthonous plants, Gazania rigens and Sedum clavatum, were selected for the PV-green systems while a PV-gravel configuration was used as the reference roof. The above mentioned roofing systems were developed and tested at the University of Lleida, in Spain. Research focused on electrical differential performances. In addition, thermal and irradiance analysis were also conducted. The results obtained for a sunny, five-day time period revealed an average increase of the maximum power output of the PVs (ranging from 1.29% to 3.33% depending on the plant), verifying the positive synergy between the PVs and the plants. Another positive effect of the plant/PV interaction was the fact that the PV-green systems showed considerably lower roof surface temperature in comparison with the PV-gravel configuration. Conclusively, the present work demonstrates the benefits of the PV-green roofs and fills the gap which exists in the literature in terms of the experimental evaluation of PV-green systems, especially under Mediterranean climatic conditions.
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Green roofs as one of the components of water-sensitive urban design have become widely used in recent years. This paper describes performance monitoring of four prototype-scale experimental green roofs in a northern suburb of Adelaide, South Australia, undertaken over a 1-year period. Four species of indigenous Australian ground cover and grass species comprising Carpobrotus rossii, Lomandra longifolia 'Tanika,' Dianella caerula 'Breeze' and Myoporum parvifolium were planted in extensive and intensive green roof configurations using two different growing media. The first medium consisted of crushed brick, scoria, coir fibre and composted organics while the second comprised scoria, composted pine bark and hydro-cell flakes. Plant growth indices including vertical and horizontal growth rate, leaf succulence, shoot and root biomasses, water use efficiency and irrigation regimes were studied during a 12-month period. The results showed that the succulent species, C. rossii, can best tolerate the hot, dry summer conditions of South Australia, and this species showed a 100% survival rate and had the maximum horizontal growth rate, leaf succulence, shoot biomass and water use efficiency. All of the plants in the intensive green roofs with the crushed brick mix media survived during the term of this study. It was shown that stormwater can be used as a source of irrigation water for green roofs during 8months of the year in Adelaide. However, supplementary irrigation is required for some of the plants over a full annual cycle.
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Living, or green roofs, are increasingly built in cities for their environmental benefits, however there is little evidence about how to maximise their aesthetic appeal. Because preferences for landscapes can be determined by vegetation characteristics we surveyed the preferences of 274 Australian office workers using 40 living roof images which systematically manipulated plant life-form, foliage colour, flowering, diversity and height. These preferences were compared to those for a bare concrete roof. The potential restorativeness of the most preferred living roof and the concrete roof were also assessed. Results showed that all living roofs were preferred over the concrete roof; however preferences differed according to vegetation characteristics. The most preferred and restorative living roof had taller, green, grassy and flowering vegetation, while lower-growing red succulent vegetation was least preferred. Participants preferred a productive landscape, with green foliage and flowering consistently preferred. Participants with a stronger connection to nature consistently assigned higher preferences to taller, compared to lower-growing, vegetation. Increasing diversity was associated with higher preferences overall, but decreasing preferences for highly preferred vegetation. This research makes an important contribution to understanding employee preferences in the unique context of urban living roof landscapes
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Because the waterproofing membrane beneath green roofs is estimated to last at least 45 years, long-term plant performance beyond initial establishment is critical. Plants that survive initially on a green roof may not exist in the long term because of variability in climate and other factors. This study evaluated the effect of green roof substrate depth on substrate moisture, plant stress as measured by chlorophyll fluorescence, and plant community development and survival of 12 Sedum species over 4 years in a midwestern U.S. climate during 4 years of growth. Plugs of 12 species of Sedum were planted on 8 June 2005 and evaluated biweekly for absolute cover (AC). Most species exhibited greater growth and coverage at a substrate depth of 7.0 cm and 10.0 cm relative to 4.0 cm. For the species evaluated, substrate depths of at least 7.0 cm are highly recommended. AC of Sedum was significantly greater at this substrate depth than at 4.0 cm. Mean volumetric moisture content of the three substrate depths followed the same pattern as AC. When averaged over time, the 4.0-cm substrate depth held less moisture than depths of 7.0 or 10.0 cm, whereas the 7.0- and 10.0-cm substrate depths were statistically the same. Species exhibiting the greatest AC at all substrate depths were S. floriferum, S. sexangulare, S. spurium ‘John Creech’, and S. stefco. In general, species that are less suitable at these substrate depths are S. ‘Angelina’, S. cauticola ‘Lidakense’, S. ewersii, S. ochroleucum, and S. reflexum ‘Blue Spruce’.
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Green roofs have been proposed for sustainable buildings in many countries with different climatic conditions. A state-of-the-art review of green roofs emphasizing current implementations, technologies, and benefits is presented in this paper. Technical and construction aspects of green roofs are used to classify different systems. Environmental benefits are then discussed mainly by examining measured performances. By reviewing the benefits related to the reduction of building energy consumption, mitigation of urban heat island effect, improvement of air pollution, water management, increase of sound insulation, and ecological preservation, this paper shows how green roofs may contribute to more sustainable buildings and cities. However, an efficient integration of green roofs needs to take into account both the specific climatic conditions and the characteristics of the buildings. Economic considerations related to the life-cycle cost of green roofs are presented together with policies promoting green roofs worldwide. Findings indicate the undeniable environmental benefits of green roofs and their economic feasibility. Likewise, new policies for promoting green roofs show the necessity for incentivizing programs. Future research lines are recommended and the necessity of cross-disciplinary studies is stressed.
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The relative contribution of substrate depth and vegetation type on temperature mitigation and stormwater runoff reduction was studied in an experimental green roof in North eastern Italy. Two substrate depths (120 and 200 mm) and two vegetation types (herbaceous plants and shrubs, respectively) were used, and compared to control modules with similar substrate depths but left bare of vegetation. Experimental observations showed that: a) green roofs substantially reduce thermal load over the rooftop, with significant effects of substrate depth and no apparent impact of vegetation type; b) thermal effects are strongly influenced by substrate water content; c) green roofs strongly reduce water runoff with significant substrate x vegetation effects. Our data suggest that green roof design addressed to optimization of the thermal functions should take into account adequate planning of substrate depth. Moreover, our data show that vegetated modules out-competed medium-only ones in terms of runoff reduction capacity, in accordance with some previous studies. Both shrub-vegetated and herbaceous modules intercepted and stored more than 90% rainfall during intense precipitation events, with no significant difference between the two vegetation types despite different substrate depths.
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The influence of different green roof layering types on the amount of water available to plants was investigated in the specific climatic context of the Mediterranean region. Water status, productivity and survival rate of Salvia officinalis L. plants growing in experimental green roof modules were monitored between early spring and late summer. Experimental data showed that: (a) substrate and water retention layer retained respectively 34% and 90% in volume of water potentially available to plants; (b) water retention layer had a positive effect on plant water status and survival; (c) the design of the overall green roof system, and in particular the characteristics of the drainage layer, influenced the amount of water transferred between different green roof elements, thus significantly influencing the amount of water available to plants. In particular, significant amounts of water were shown to be transferred from the retention layer into the cavities of the plastic drainage layer in response to temperature fluctuations, leading to day/night cycles of water evaporation/condensation. Targeted modifications of the geometrical and technical features of drainage elements were shown to be potentially useful to improve plant survival during intense and/or prolonged drought events.
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The purpose of this research was to determine the phenomenological parameters that impact the sound transmission of vegetated roofs. A reverse indoor-to-outdoor testing method involving propagating sound from an interior diffuse field to an exterior free field was first implemented at an existing field site. The findings from the field work supported the development of a purpose-built field laboratory specifically designed and commissioned as part of this research. Transmission loss measurements were completed on 2 non-vegetated reference panels, on gradients of substrate depth (25-mm increments), and on 2 plant communities established in 150 mm of substrate depth. Increased transmission loss, resulting from the installation of vegetated roof material layers on the reference roof, at the field site (wood frame construction) and at the field laboratory (light-weight metal) generally aligned in the low and mid frequency ranges. The increased transmission loss of the wood frame roof was 5–13 dB in the 50–2000 Hz frequency range, and up to 8 dB above 2000 Hz. For the light-weight metal deck, the increased transmission loss was up to 10 dB, 20 dB, and >20 dB in the low, mid, and high frequency ranges, respectively. Field mass law, using an effective mass to describe the composite roof deck, predicted the transmission loss of non-vegetated reference roofs. A gradient increase in substrate depth (equated in terms of mass) incrementally increased transmission loss, but not as predicted by mass law. A variation in the moisture content of the substrate did not translate to a measurable change in transmission loss. The deep roots of the coastal meadow community contributed to an increase in transmission loss relative to the shallow-rooted sedums community. The results of this research confirm that vegetated roofs increase transmission loss over non-vegetated roofs and have a beneficial application towards architectural situations requiring high transmission loss and specifically mitigation of low frequency noise.
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Low impact development (LID) is generally regarded as a more sustainable solution for urban stormwater management than conventional urban drainage systems. However, its effects on urban flooding at a scale of urban drainage systems have not been fully understood particularly when different rainfall characteristics are considered. In this paper, using an urbanizing catchment in China as a case study, the effects of three LID techniques (swale, permeable pavement and green roof) on urban flooding are analyzed and compared with the conventional drainage system design. A range of storm events with different rainfall amounts, durations and locations of peak intensity are considered for holistic assessment of the LID techniques. The effects are measured by the total flood volume reduction during a storm event compared to the conventional drainage system design. The results obtained indicate that all three LID scenarios are more effective in flood reduction during heavier and shorter storm events. Their performance, however, varies significantly according to the location of peak intensity. That is, swales perform best during a storm event with an early peak, permeable pavements perform best with a middle peak, and green roofs perform best with a late peak, respectively. The trends of flood reduction can be explained using a newly proposed water balance method, i.e., by comparing the effective storage depth of the LID designs with the accumulative rainfall amounts at the beginning and end of flooding in the conventional drainage system. This paper provides an insight into the performance of LID designs under different rainfall characteristics, which is essential for effective urban flood management.
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This paper presents field monitoring results from a 235 m(2) extensive living roof in Auckland New Zealand (NZ) The extent of stormwater control is quantified by comparing three different substrate types (Pumice Zeolite and Expanded Clay all pumice based but named for their distinguishing components) at two different substrate depths (50 and 70 mm) in a side-by-side comparison No statistically significant differences in runoff response were found between the three substrate types tested or the two different depths The cumulative retention efficiency of the living roof was 66% based on 12 months of continuous monitoring On an event basis the living roof demonstrated reductions in both volume and peak flow rates regardless of the rainfall and climatic characteristics The living roof retained a median of 82% of rainfall received per rainfall event with a median peak flow reduction of 93% compared to rainfall intensity The hydrologic response of a living roof is controlled by multiple parameters such as rain depth rain intensity climatic variables and antecedent dry days Detailed analysis indicates that antecedent dry days have the greatest influence on retention Seasonal differences do not influence runoff response living roofs will effectively moderate runoff hydrology year round in Auckland s sub-tropical climate (C) 2010 Elsevier B V All rights reserved
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The increase of peak and energy demand during the cooling season is becoming a crucial issue, as well as the intensification of the urban heat island effect. This trend is observed at several latitudes, including areas where overheating was unknown at building and urban levels. This phenomenon involves different issues: reduction of greenhouse gases, quality and comfort in outdoor and indoor environment, security of energy supply, public health. The building sector is directly involved in this change and adequate solutions can provide great benefit at energy and environmental levels. Roofs in particular are envelope components for which advanced solutions can provide significant energy savings in cooled buildings or improve indoor thermal conditions in not cooled buildings. Cool materials keep the roof cool under the sun by reflecting the incident solar radiation away from the building and radiating the heat away at night. Roofs covered with vegetation take benefits of the additional thermal insulation provided by the soil and of the evapo-transpiration to keep the roof cool under the sun. These two technologies are different in: structural requirements, initial and lifetime maintenance costs, impact on the overall energy performance of buildings. This paper presents a numerical comparative analysis between these solutions, taking into account the several parameters that affect the final energy performances. By means of dynamic simulations, the paper depicts how cool and green roofs can improve the energy performance of residential buildings in different localities at Mediterranean latitudes.
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Plant water status and hydraulics were measured in six woody angiosperms growing in a karstic woodland, during an extreme summer drought. Our aim was to take advantage of an unusual climatic event to identify key traits related to species-specific drought damage. The damage suffered by different species was assessed in terms of percentage of individuals showing extensive crown desiccation. Stem water potential (Ψstem ) and percent loss of hydraulic conductivity (PLC) were measured in healthy and desiccated individuals. Vulnerability to cavitation was assessed in terms of stem water potential inducing 50% PLC (Ψ50 ). Stem density (ρstem ) was also measured. Species-specific percentage of desiccated individuals was correlated to Ψ50 and ρstem . Crown desiccation was more widespread in species with less negative Ψ50 and lower ρstem . Desiccated individuals had lower Ψstem and higher PLC than healthy ones, suggesting that hydraulic failure was an important mechanism driving shoot dieback. Drought-vulnerable species showed lower safety margins (Ψstem - Ψ50 ) than resistant ones. The Ψ50 , safety margins and ρstem values emerge as convenient traits to be used for tentative predictions of differential species-specific impact of extreme drought events on a local scale. The possibility that carbohydrate depletion was also involved in induction of desiccation symptoms is discussed.
Article
The availability of soil water, and the ability of plants to extract it, are important variables in plant research. The matric potential has been a useful way to describe water status in a soil-plant system. In soil it is the potential that is derived from the surface tension of water menisci between soil particles. The magnitude of matric potential depends on the soil water content, the size of the soil pores, the surface properties of the soil particles, and the surface tension of the soil water. Of all the measures of soil water, matric potential is perhaps the most useful for plant scientists. In this review, the relationship between matric potential and soil water content is explored. It is shown that for any given soil type, this relationship is not unique and therefore both soil water content and matric potential need to be measured for the soil water status to be fully described. However, in comparison with water content, approaches for measuring matric potential have received less attention until recently. In this review, a critique of current methods to measure matric potential is presented, together with their limitations as well as underexploited opportunities. The relative merits of both direct and indirect methods to measure matric potential are discussed. The different approaches needed in wet and dry soil are outlined. In the final part of the paper, the emerging technologies are discussed in so far as our current imagination allows. The review draws upon current developments in the field of civil engineering where the measurement of matric potential is also important. The approaches made by civil engineers have been more imaginative than those of plant and soil scientists.
Article
Green roofs in hot and dry climates are frequently exposed to drought due to shallow depth and low water holding capacity (WHC) of substrates (growing media). Water-retention additives have the potential to increase substrate water availability leading to greater plant growth and survival, expanding the range of plant species suitable for green roofs. We determined whether two different water-retention additives (silicate granules and hydrogel) increased substrate WHC, plant available water (PAW), days until permanent wilting and growth of winter wheat (Triticum aestivum L.) and white lupin (Lupinus albus L.) grown in green roof substrates. Two substrates were compared; one based on scoria, the other based on crushed terracotta roof-tiles. Without additives both substrates had similar WHC (40–43%) but PAW was lower in scoria than in roof-tile due to greater air-filled porosity (AFP) and lower bulk density in scoria. Silicates increased WHC in both scoria and roof-tile substrates, but hydrogel only improved scoria WHC. The effects of additives on PAW differed between plant species, with additives increasing PAW in both substrates for wheat but only in roof-tile for lupins. PAW was not significantly different between hydrogel and silicates. Although hydrogels increased substrate WHC and PAW there was no increase in time until wilting in either substrate. Silicates on the other hand, increased time until wilting and total and root biomass for wheat growing in scoria and for lupins in both substrates. While there was a species effect on the efficiency of water-retention additives which requires further study, the addition of silicates is more likely to enhance species capacity to tolerate periods of low water availability on green roofs.
Article
Although weed research in maize has broadened from an emphasis on herbicide technology to include studies of weed- maize competition, many studies only consider competition descriptively (e.g. defning the critical period for weed control). Furthermore, studies of the mechanisms of weed competition in maize have considered only competition for resources such as soil moisture, nutrients and light. Physiological ecologists have recently recognized the signi®cance of early detection of neighbouring plants through the far-red/red (FR/R) signal as an important mechanism affecting plant±plant interactions. In this review, we have indicated the importance of integrating the concept of the mechanism of early detection of neighbours with the resource-limiting approach in reassessing weed competition in maize during the critical time for weed control. Hypothetical integration of early detection of neighbours into the existing concepts of critical time for weed control and weed thresholds led us to view maize±weed competition as a series of complex processes, which is triggered by the FR/R signal and followed by the development of shade avoidance characteristics accompanied by a reduction in the plant's ability to absorb nutrients and water, and to photosynthesize. However, due to lack of research on effects of weeds on light quality impinging corn plants as well as corn response to an increase in FR light during critical time for weed control, our conclusions remain to be speculative. We believe that incorporation of early detection of neighbours through the FR/R ratio as a primary signal during the critical period for weed control would open a new approach for future studies on weed competition in maize. We recognize that resource limitation occurs in a maize±weed association, however, this may be more of an effect rather than a cause of competition.
Article
Summary • It has been claimed that, compared with plants grown without competition, plants competing for a common pool of soil-based resources overproduce roots at the expense of reproduction (known as the tragedy of the commons). However, experiments on this phenomenon have manipulated not only the presence/absence of neighbours, but also substrate volume. Restricted substrate volume can itself affect plant growth, possibly through chemical self-inhibition of root growth. We conducted an experiment with oats (Avena sativa) to examine whether the experimental design used in previous studies on the tragedy of the commons in root competition might have confounded the effects of detection of neighbours and substrate volume. • Six treatments combined two factors, namely the presence or absence of activated carbon, and either the presence of a plastic or a mesh partition, or the absence of a partition, between two plants in a pot. Activated carbon was used to adsorb root exudates and reduce their potential effects on root growth. In a seventh treatment, plants were grown alone in pots with half the substrate volume replaced by gravel, to fragment the distribution of available resources. • We observed no tragedy of the commons in a comparison of the performance of plants grown with and without partitions; plants performed equally well in the presence and absence of root competition. • In the treatment with gravel, plants displayed reduced tillering and shoot growth per unit root mass, and an earlier switch to reproduction. • Pot partitioning was associated with inhibition of root growth that was mediated by root exudates. When activated carbon was present, plants in partitioned pots performed better than plants growing with a root competitor. • We conclude that two processes could determine plant growth in the experimental design used in studies of the tragedy of the commons: (i) greater root self-inhibition in the more limited space of partitioned pots, and (ii) inefficient root placement in larger substrate volumes in unpartitioned pots that are shared with roots of a competitor. These findings provide a new challenge for experimental designs attempting to demonstrate the role of self/non-self discrimination in root competition. Journal of Ecology (2007) 95, 252ndash;260 doi: 10.1111/j.1365-2745.2007.01210.x
Article
Recently there has been a surge in the number of green roofs and façades (vegetation on the roofs & walls of a building) installed in the UK, with advocation of their use by policy-makers and claims that they are aesthetically pleasing and promote restoration. But these claims rely on generalisations from different landscapes, raising concerns about validity. The present study examined whether houses with vegetation would be more preferred than those without, be perceived as more beautiful and restorative, and have a more positive affective quality. Differences between types of building-integrated vegetation were also examined. Two studies were conducted: an online survey in which participants (N = 188) rated photographs of houses with and without vegetation on each of these measures, and interviews (N = 8) which examined preference and installation concerns. Results showed that houses with (some types of) building-integrated vegetation were significantly more preferred, beautiful, restorative, and had a more positive affective quality than those without. The ivy façade and meadow roof rated highest on each. These findings are consistent with other areas of landscape research and the claims of those in the industry, and suggest that building-integrated vegetation would be a valuable addition to the urban environment.Research highlights► Houses with building-integrated vegetation are more preferred than those without. ► Vegetated houses are more beautiful & restorative compared to non-vegetated houses. ► Vegetated houses have a more positive affective quality than non-vegetated houses. ► Ivy façades and meadow roofs are most restorative, beautiful and preferred.
Article
Green roofs are engineered ecosystems that rely on vegetation to provide services such as reduction of roof temperatures. Drought resistance is critical for plant survival on shallow-substrate green roofs, but potential trade-offs exist between water-use efficiency and ecosystem functions like transpirative cooling. Water loss from simulated green roof systems (microcosms) each containing 1 of 14 plant species belonging to 4 growth forms (succulents, herbaceous dicots, grasses and woody creeping shrubs) was quantified for 3 watering treatments (watering to field capacity every 4, 11 and 24 days). After 2 months only succulents survived the dry treatment. The dry treatment was the only treatment in which planted microcosms showed consistently greater water loss (∼30% greater) than the controls (soil-only microcosms). Microcosms planted with Poa compressa lost the most water in all moisture treatments but in the wet and intermediate treatments, respectively, native species Rhodiola rosea and Campanula rotundifolia had equivalent performance to P. compressa. The mat-forming Sedum acre retained more water than controls and other species in the wet and intermediate treatments suggesting that its growth form impeded evaporation from the soil surface. Performance differences among growth forms and species across soil moisture gradients suggest that optimal water loss and roof surface cooling could be enhanced by planting multiple species.
Article
Ecology Letters (2012) 15: 393–405 Increasing drought is one of the most critical challenges facing species and ecosystems worldwide, and improved theory and practices are needed for quantification of species tolerances. Leaf water potential at turgor loss, or wilting (πtlp), is classically recognised as a major physiological determinant of plant water stress response. However, the cellular basis of πtlp and its importance for predicting ecological drought tolerance have been controversial. A meta-analysis of 317 species from 72 studies showed that πtlp was strongly correlated with water availability within and across biomes, indicating power for anticipating drought responses. We derived new equations giving both πtlp and relative water content at turgor loss point (RWCtlp) as explicit functions of osmotic potential at full turgor (πo) and bulk modulus of elasticity (ε). Sensitivity analyses and meta-analyses showed that πo is the major driver of πtlp. In contrast, ε plays no direct role in driving drought tolerance within or across species, but sclerophylly and elastic adjustments act to maintain RWCtlp, preventing cell dehydration, and additionally protect against nutrient, mechanical and herbivory stresses independent of drought tolerance. These findings clarify biogeographic trends and the underlying basis of drought tolerance parameters with applications in comparative assessments of species and ecosystems worldwide.
Article
This paper attempts to evaluate the positive effects of vegetation with a multi-scale approach: an urban and a building scale. Monitoring the urban heat island in four areas of New York City, we have found an average of 2 °C difference of temperatures between the most and the least vegetated areas, ascribable to the substitution of vegetation with man-made building materials. At micro-scale, we have assessed the effect of surface albedo on climate through the use of a climatological model. Then, using the CO(2) equivalents as indicators of the impact on climate, we have compared the surface albedo, and the construction, replacement and use phase of a black, a white and a green roof. By our analyses, we found that both the white and the green roofs are less impactive than the black one; with the thermal resistance, the biological activity of plants and the surface albedo playing a crucial role.
Article
Three woody species typically encroaching the Karstic region of Trieste ( Northeastern Italy) i.e. Cotinus coggygria L., Prunus mahaleb L. and Fraxinus ornus L., have been measured for diurnal and seasonal time courses of leaf conductance to water vapour, transpiration and water potential (Psi(L)), as well as whole-plant, shoot and root hydraulic resistance (R-plant, R-shoot and R-root, respectively) in view of investigating the impact of plant hydraulics on water stress resistance. F. ornus suffered the highest Psi(L) drop in July and September due to the high R-plant measured in this species. Positive significant relations were found of R-plant and Psi(L) to R-root in all three species studied, thus suggesting that root hydraulics is a major determinant of plant hydraulics and water stress resistance. The increasing R-root (and R-plant) from C. coggygria to P. mahaleb to F. ornus provided a possible explanation for the typical temporal sequence of expansion of the three species into degraded areas.
Article
The infrastructure (roads, sidewalk, commercial and residential structures) added during the land development and urbanisation process is designed to collect precipitation and convey it out of the watershed, typically in existing surface water channels, such as streams and rivers. The quality of surface water, seepage water and ground water is influenced by pollutants that collect on impervious surfaces and that are carried by urban storm water runoff. Heavy metals, e.g. lead (Pb), zinc (Zn), copper (Cu), cadmium (Cd), polycyclic aromatic hydrocarbons (PAH), mineral oil hydrocarbons (MOH) and readily soluble salts in runoff, contribute to the degradation of water. An intensive literature search on the distribution and concentration of the surface-dependent runoff water has been compiled. Concentration variations of several pollutants derived from different surfaces have been averaged. More than 300 references providing about 1300 data for different pollutants culminate in a representative concentration matrix consisting of medians and extreme values. This matrix can be applied to long-term valuations and numerical modelling of storm water treatment facilities.
Flora vascolare spontanea di Trieste
  • F Martini
Martini, F., 2009. Flora vascolare spontanea di Trieste. Edizioni Lint, Trieste.
La diversità vegetale del carso fra Trieste e Gorizia. Guide alla flora-IV
  • L Poldini
Poldini, L., 2009. La diversità vegetale del carso fra Trieste e Gorizia. Guide alla flora-IV. Edizioni Goliardiche, Trieste.