Wind drives drought responses of green roof vegetation in two substrates

The multifunctionality and delivery of ecosystem services from green roofs is improved by biological diversity of the roof vegetation. However, the frequency and intensity of drought episodes on extensive green roofs may limit the use of non-succulent species and the potential functional and phylogenetic diversity of the vegetation. Wind accelerates water use by plants and desiccation of the green roof substrate, and may be a key factor in selection of non-succulent plant species for green roofs. In this study, we tested wind interactions with green roof substrate composition and the effects on plant and substrate water balance, overall plant performance, and wilting and survival of three non-succulent species (Plantago maritima L., Hieracium pilosella L., and Festuca rubra L.) under realistic prolonged water deficit conditions. We found that, regardless of species or substrate tested, wind accelerated drought response. Drought-stressed plants exposed to wind wilted and died earlier, mostly due to more rapid desiccation of the growth substrate (critical substrate moisture content was 6-8%). The moderate wind levels applied did not affect plant performance when not combined with drought. Species with contrasting growth forms showed similar responses to treatments, but there were some species-specific responses. This highlights the importance of including wind to increase realism when evaluating drought exposure in non-succulent green roof vegetation.

Download Full-text

Substrate Depth Influences Sedum Plant Community on a Green Roof

HortScience ◽

10.21273/hortsci.44.2.401 ◽

2009 ◽

Vol 44 (2) ◽

pp. 401-407 ◽

Cited By ~ 45

Author(s):

Kristin L. Getter ◽

D. Bradley Rowe

Keyword(s):

Plant Community ◽

Plant Stress ◽

Green Roof ◽

Green Roofs ◽

Plant Performance ◽

Blue Spruce ◽

Waterproofing Membrane ◽

Substrate Moisture ◽

Substrate Depth

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’.

Download Full-text

Influence of Temperature and Moisture Content on Thermal Performance of Green Roof Media

Energies ◽

10.3390/en14092421 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2421

Author(s):

Bohan Shao ◽

Caterina Valeo ◽

Phalguni Mukhopadhyaya ◽

Jianxun He

Keyword(s):

Thermal Conductivity ◽

Moisture Content ◽

Green Roof ◽

Green Roofs ◽

Power Functions ◽

Thick Substrate ◽

Different Temperatures ◽

Test Cells ◽

Substrate Moisture ◽

Phase Transition Zone

The influence of moisture content on substrate thermal conductivity at different temperatures was investigated for four different commercially available substrates for green roofs. In the unfrozen state, as moisture content increased, thermal conductivity increased linearly. In the phase transition zone between +5 and −10 °C, as temperature decreased, thermal conductivity increased sharply during the transition from water to ice. When the substrate was frozen, thermal conductivity varied exponentially with substrate moisture content prior to freezing. Power functions were found between thermal conductivity and temperature. Two equally sized, green roof test cells were constructed and tested to compare various roof configurations including a bare roof, varying media thickness for a green roof, and vegetation. The results show that compared with the bare roof, there is a 75% reduction in the interior temperature’s amplitude for the green roof with 150 mm thick substrate. When a sedum mat was added, there was a 20% reduction in the amplitude of the inner temperature as compared with the cell without a sedum mat.

Download Full-text

Plant performance on Mediterranean green roofs: interaction of species-specific hydraulic strategies and substrate water relations

AoB Plants ◽

10.1093/aobpla/plv007 ◽

2015 ◽

Vol 7 ◽

Cited By ~ 22

Author(s):

Fabio Raimondo ◽

Patrizia Trifilò ◽

Maria A. Lo Gullo ◽

Sergio Andri ◽

Tadeja Savi ◽

...

Keyword(s):

Water Relations ◽

Green Roofs ◽

Plant Performance ◽

Species Specific

Download Full-text

Site Conditions, Maintenance Costs, and Plant Performance of 10 Extensive Green Roofs in the Research Triangle Area of Central North Carolina

HortTechnology ◽

10.21273/horttech04565-20 ◽

2020 ◽

Vol 30 (6) ◽

pp. 761-769

Author(s):

Julieta Trevino Sherk ◽

Wenyan Fu ◽

Joseph C. Neal

Keyword(s):

North Carolina ◽

Plant Cover ◽

Green Roof ◽

Green Roofs ◽

Economic Benefits ◽

Plant Performance ◽

Site Conditions ◽

Maintenance Costs ◽

Research Triangle ◽

Highly Correlated

Compared with traditional roofing, green roofs (GRs) have quantifiable environmental and economic benefits, yet limited research exists on GR plant survival, maintenance practices, and costs related to plant performance. The objective of this study was to assess plant cover, site conditions, and maintenance practices on 10 extensive GRs in the Research Triangle Area of North Carolina. Green roof maintenance professionals were surveyed to assess plant performance, maintenance practices, and maintenance costs. Vegetation cover on each site was characterized. Relationships among plant performance and environmental and physical site characteristics, and maintenance practices were evaluated. Survey respondents ranked weed control as the most problematic maintenance task, followed by irrigation, pruning, and debris removal. No single design or maintenance factor was highly correlated with increased plant cover. Green roof age, substrate organic matter, and modular planting methods were not correlated with greater plant cover. Results showed a trend that irrigation increased plant cover. Plants persisting on GRs included several species of stonecrop (Sedum sp.), but flame flower (Talium calycinum) and ice plant (Delosperma basuticum) were also present in high populations on at least one roof each. Green roof maintenance costs ranged from $0.13/ft2 to $3.45/ft2 per year, and were greater on sites with more weeds and frequent hand watering.

Download Full-text

Role of drainage layer on green roofs in limiting the runoff of rainwater from urbanized areas

Journal of Water and Land Development ◽

10.2478/jwld-2019-0022 ◽

2019 ◽

Vol 41 (1) ◽

pp. 12-18 ◽

Cited By ~ 2

Author(s):

Anna M. Baryła

Keyword(s):

Moisture Content ◽

Green Roof ◽

Initial Moisture Content ◽

Green Roofs ◽

Climatic Conditions ◽

Column Studies ◽

Initial State ◽

Drainage Layer ◽

Urbanized Areas ◽

Substrate Moisture

Abstract Green roofs play a significant role in sustainable drainage systems. They form absorbent surfaces for rainwater, which they retain with the aid of profile and plants. Such roofs therefore take an active part in improving the climatic conditions of a city and, more broadly, the water balance of urbanized areas. One of the factors influencing the hydrological efficiency of green roofs is the drainage layer. In the article, column studies were carried out under field conditions involving the comparison of the retention abilities of two aggregates serving as the drainage layer of green roofs, i.e. Leca® and quartzite grit. The average retention of the substrate was 48%; for a 5 cm drainage layer of Leca® retention was 57%, for a 10 cm layer of Leca average retention was 61%. For a 5 cm layer of quartzite grit average retention was 50%, for 10 cm layer of quartzite grit 53%. The highest retention was obtained for the column with the substrate and 10-centimeter layer of Leca®. At the same time, it was shown that Leca® is a better retention material than quartzite grit. The initial state of substrate moisture content from a green roof appears to be a significant factor in reducing rainfall runoff from a green roof; the obtained values of initial moisture content made for a higher correlation than the antecedent dry weather period.

Download Full-text

No neighbour-induced increase in root growth of soybean and sunflower in mesh divider experiments after controlling for nutrient concentration and soil volume

AoB Plants ◽

10.1093/aobpla/plab020 ◽

2021 ◽

Author(s):

Bin J W Chen ◽

Li Huang ◽

Heinjo J During ◽

Xinyu Wang ◽

Jiahe Wei ◽

...

Keyword(s):

Root Growth ◽

Nutrient Concentration ◽

Ideal Free Distribution ◽

Plant Performance ◽

Root Competition ◽

Individual Level ◽

Key Factor ◽

Promising Solution ◽

Soil Volume ◽

Ideal Free

Abstract Root competition is a key factor determining plant performance, community structure and ecosystem productivity. To adequately estimate the extent of root proliferation of plants in response to neighbours independently of nutrient availability, one should use a setup that can simultaneously control for both nutrient concentration and soil volume at plant individual level. With a mesh-divider design, which was suggested as a promising solution for this problem, we conducted two intraspecific root competition experiments one with soybean (Glycine max) and the other with sunflower (Helianthus annuus). We found no response of root growth or biomass allocation to intraspecific neighbours, i.e. an ‘ideal free distribution’ (IDF) norm, in soybean; and even a reduced growth as a negative response in sunflower. These responses are all inconsistent with the hypothesis that plants should produce more roots even at the expense of reduced fitness in response to neighbours, i.e. root over-proliferation. Our results suggest that neighbour-induced root over-proliferation is not a ubiquitous feature in plants. By integrating the findings with results from other soybean studies, we conclude that for some species this response could be a genotype-dependent response as a result of natural or artificial selection, or a context-dependent response so that plants can switch from root over-proliferation to IDF depending on the environment of competition. We also critically discuss whether the mesh-driver design is the ideal solution for root competition experiments.

Download Full-text

Seismic Performance of a Green Roof Structure

Sustainability ◽

10.3390/su13084278 ◽

2021 ◽

Vol 13 (8) ◽

pp. 4278

Author(s):

Svetlana Tam ◽

Jenna Wong

Keyword(s):

Green Roof ◽

Time History ◽

Green Roofs ◽

Moment Frame ◽

Steel Moment Frame ◽

Roof Structure ◽

Nonlinear Time History Analyses ◽

Vegetated Roofs ◽

Nonlinear Time History ◽

The Impact

Sustainability addresses the need to reduce the structure’s impact on the environment but does not reduce the environment’s impact on the structure. To explore this relationship, this study focuses on quantifying the impact of green roofs or vegetated roofs on seismic responses such as story displacements, interstory drifts, and floor level accelerations. Using an archetype three-story steel moment frame, nonlinear time history analyses are conducted in OpenSees for a shallow and deep green roof using a suite of ground motions from various distances from the fault to identify key trends and sensitivities in response.

Download Full-text

Addressing the Water–Energy–Food Nexus through Enhanced Green Roof Performance

Sustainability ◽

10.3390/su13041972 ◽

2021 ◽

Vol 13 (4) ◽

pp. 1972

Author(s):

Jeremy Wright ◽

Jeremy Lytle ◽

Devon Santillo ◽

Luzalen Marcos ◽

Kristiina Valter Mai

Keyword(s):

Climate Change ◽

Performance Optimization ◽

Urban Areas ◽

Stormwater Management ◽

Green Roof ◽

Green Roofs ◽

Management Tool ◽

Contributing Factors ◽

Rainwater Runoff ◽

Rain Events

Urban densification and climate change are creating a multitude of issues for cities around the globe. Contributing factors include increased impervious surfaces that result in poor stormwater management, rising urban temperatures, poor air quality, and a lack of available green space. In the context of volatile weather, there are growing concerns regarding the effects of increased intense rainfalls and how they affect highly populated areas. Green roofs are becoming a stormwater management tool, occupying a growing area of urban roof space in many developed cities. In addition to the water-centric approach to the implementation of green roofs, these systems offer a multitude of benefits across the urban water–energy–food nexus. This paper provides insight to green roof systems available that can be utilized as tools to mitigate the effects of climate change in urbanized areas. A new array of green roof testing modules is presented along with research methods employed to address current issues related to food, energy and water performance optimization. Rainwater runoff after three rain events was observed to be reduced commensurate with the presence of a blue roof retention membrane in the testbed, the growing media depth and type, as well as the productive nature of the plants in the testbed. Preliminary observations indicate that more productive green roof systems may have increasingly positive benefits across the water–energy–food nexus in dense urban areas that are vulnerable to climate disruption.

Download Full-text

Hydrologic Performance of an Extensive Green Roof under Intensive Rain Events: Results from a Rain-Chamber Simulation

Sustainability ◽

10.3390/su13063078 ◽

2021 ◽

Vol 13 (6) ◽

pp. 3078

Author(s):

Elena Giacomello ◽

Jacopo Gaspari

Keyword(s):

Water Retention ◽

Green Roof ◽

Green Roofs ◽

International Standards ◽

Dimensionless Number ◽

Runoff Coefficient ◽

Retention Performance ◽

Extensive Green Roof ◽

Rain Events ◽

Hydrologic Performance

The water storage capacity of a green roof generates several benefits for the building conterminous environment. The hydrologic performance is conventionally expressed by the runoff coefficient, according to international standards and guidelines. The runoff coefficient is a dimensionless number and defines the water retention performance over a long period. At the scale of single rain events, characterized by varying intensity and duration, the reaction of the green roof is scarcely investigated. The purpose of this study is to highlight how an extensive green roof—having a supposed minimum water performance, compared to an intensive one—responds to real and repetitive rain events, simulated in a rain chamber with controlled rain and runoff data. The experiment provides, through cumulative curve graphs, the behavior of the green roof sample during four rainy days. The simulated rain events are based on a statistical study (summarized in the paper) of 25 years of rain data for a specific location in North Italy characterized by an average rain/year of 1100 mm. The results prove the active response of the substrate, although thin and mineral, and quick draining, in terms of water retention and detention during intense rain events. The study raises questions about how to better express the water performance of green roofs.

Download Full-text

Green roof hydrologic performance and modeling: a review

Water Science & Technology ◽

10.2166/wst.2013.770 ◽

2013 ◽

Vol 69 (4) ◽

pp. 727-738 ◽

Cited By ~ 77

Author(s):

Yanling Li ◽

Roger W. Babcock

Keyword(s):

Peak Flow ◽

Green Roof ◽

Field Measurements ◽

Green Roofs ◽

Economic Benefits ◽

Design Parameters ◽

Technical Literature ◽

Factors Affecting ◽

Model Soil ◽

Runoff Volume

Green roofs reduce runoff from impervious surfaces in urban development. This paper reviews the technical literature on green roof hydrology. Laboratory experiments and field measurements have shown that green roofs can reduce stormwater runoff volume by 30 to 86%, reduce peak flow rate by 22 to 93% and delay the peak flow by 0 to 30 min and thereby decrease pollution, flooding and erosion during precipitation events. However, the effectiveness can vary substantially due to design characteristics making performance predictions difficult. Evaluation of the most recently published study findings indicates that the major factors affecting green roof hydrology are precipitation volume, precipitation dynamics, antecedent conditions, growth medium, plant species, and roof slope. This paper also evaluates the computer models commonly used to simulate hydrologic processes for green roofs, including stormwater management model, soil water atmosphere and plant, SWMS-2D, HYDRUS, and other models that are shown to be effective for predicting precipitation response and economic benefits. The review findings indicate that green roofs are effective for reduction of runoff volume and peak flow, and delay of peak flow, however, no tool or model is available to predict expected performance for any given anticipated system based on design parameters that directly affect green roof hydrology.

Download Full-text