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Catalyzing Design-Science Feedback Loop in Green Roof Optimization for Hot Climates
Native prairie species have been both promoted and questioned in their ability to serve as vegetative covers for green roofs. The green roof environment with its exposure to intense sun and wind and limited moisture restricts the capacity for a large diversity of species. The result has been, in many cases, a standard, low-diversity mix of Sedum species often focused on ornament and minimizes the potential for wider environmental benefits. We reviewed the ecological literature on prairie and grassland communities with specific reference to habitat templates from stressed environmental conditions and examined analogs of prairie-based vegetation on twenty-one existing green roofs. We found that many, but not all prairie and grassland species will survive and thrive on green roofs, especially when irrigated as needed or given adequate growing medium depth. We raise several important questions about media, irrigation, temperature, biodiversity and their interactions needing more study.
Green roofs are still often seen as a pure aesthetical element in architecture, as a spleen of some “greenies”. In fact green roofs already contribute, to some extent, to a better microclimate through evaporation, filtering of dust from the air and a decrease in temperatures at the rooftop. In cities like Berlin and Munich many green roofs have already been realised. Coupled with this microclimate improvement, is the thermal comfort improvement under such roofs by more mass, dry or wet substrate, and shading through the plants. Besides improving the microclimate and the indoor climate, the retention of rainwater is another important advantage. That means an important reduction of the rainwater input in the sewage system during rainfalls, cutting the peak load, avoiding an overload of the system, which might cause flooding and serious health problems. The risk of flooding in cities, which is increasing in many cities due to a ground sealed by buildings, asphalt and concrete, can be diminished. One recent example of the use of green roofs with this purpose is the Potsdamer Platz in the centre of Berlin, where 100 percent of the rainwater has to be evaporated or used for toilet flushing on the building site. Scientific knowledge on green roofs is still limited to temperate climates, due to a development which took place in central Europe. Since 2000 a scientific project in Rio de Janeiro is checking local parameters, like possible vegetation, which can be used and substrate composition. Parallel to this, four prototype roofs, three greened and one blank, are used to measure the retention rate of the rain water and the temperature on the underside of the roofs in order to analyse the possible improvement of the thermal comfort in buildings. This paper will describe the scientific results of Germany and discuss the practicability on a larger scale under tropical conditions.
A green roof is a vegetated roof or deck designed to provide urban greening for buildings, people, or the environment. Made popular across Europe over the past few decades, green roofs are now becoming more familiar to North Americans as some cities have built green roof pilot projects and adopted incentives for using green roofs or even require their use. Green roof standards and guidelines are also emerging to be used for governance and project specification. Although much is known about the application of green roofs across Europe, much less is known about their application across North America's diverse ecological regions. When considering the many decisions required in applying green roof technology to a specific place, there are few choices more critical to their success than the selection of appropriate vegetation. We conducted a review of green roof research to investigate what is known about the application of plants on green roofs across North America and their ecological implications. Results indicate that investigation sites across ecoregions begin to reveal differences in plant survival. Although ecological investigations are limited, their results show improved plant performance and ecological services with diverse green roofs. We conclude that as green roofs continue to become regulated and adopted in policy, further development of standards and guidelines is needed. To date, there is no common ground for reporting of green roof research, and we make recommendations for facilitating such efforts for improved research, policy development and their management across North America's diverse ecological regions.
Landscape ecological science has produced knowledge about the relationship between landscape pattern and landscape processes,
but it has been less effective in transferring this knowledge to society. We argue that design is a common ground for scientists
and practitioners to bring scientific knowledge into decision making about landscape change, and we therefore propose that
the pattern–process paradigm should be extended to include a third part: design. In this context, we define design as any
intentional change of landscape pattern for the purpose of sustainably providing ecosystem services while recognizably meeting
societal needs and respecting societal values. We see both the activity of design and the resulting design pattern as opportunities
for science: as a research method and as topic of research. To place design within landscape ecology science, we develop an
analytic framework based on the concept of knowledge innovation, and we apply the framework to two cases in which design has
been used as part of science. In these cases, design elicited innovation in society and in science: the design concept was
incorporated in societal action to improve landscape function, and it also initiated scientific questions about pattern–process
relations. We conclude that landscape design created collaboratively by scientists and practitioners in many disciplines improves
the impact of landscape science in society and enhances the saliency and legitimacy of landscape ecological scientific knowledge.
Green roofs have the potential to retain stormwater on the roof surface and lower the thermal loading on buildings. Because
of this, the greatest environmental benefits from green roofs might be achieved in subtropical climates characterized by high
temperatures and intense rain events. There is, however, little research to support this. In a replicated study in Texas,
we compared the performance of six different extensive green roof designs vegetated with native species, to non-reflective
(black) roofs, and reflective (white) roofs. Preliminary hydrologic and thermal profile data indicated not only differences
between green and non-vegetated roofs, but also among green roof designs. Maximum green roof temperatures were cooler than
conventional roofs by 38°C at the roof membrane and 18°C inside air temperature, with little variation among green roofs.
Maximum run-off retention was 88% and 44% for medium and large rain events but some green roof types showed very limited retention
characteristics. These data demonstrate indicate that: 1. Green roofs can greatly affect the roof temperature profile—cooling
surface layers and internal space on warm days. 2. Green roofs can retain significant amounts of rainfall, this is dependent
on the size of the rain event and design and can fail if not designed correctly. We suggest that as green roofs vary so much
in their design and performance, they must be designed according to specific goals rather than relying on assumed intrinsic
attributes.
Microorganisms have critical roles in the functioning of soil in nutrient cycling, structural formation, and plant interactions,
both positive and negative. These roles are important in reestablishing function and biodiversity in ecosystem restoration.
Measurement of the community indicates the status of the system in relation to restoration targets and the effectiveness of
management interventions, and manipulation of the community shows promise in the enhancement of the rate of recovery of degraded
systems.
Green roof systems have been developed and adopted in the temperate and cool-temperate climates of Europe and North America. Although these regions can get extreme weather, they generally do not experience climatic extremes of high temperatures, prolonged drought, and intense rainfall events of tropical and subtropical regions. This presents challenges for green roof design to not only provide adequate growing conditions for plants, but also to improve roof performance with respect to intrinsic (e.g. cooling building, extension of roof membrane lifetime) and extrinsic (e.g. flash flood mitigation, building cooling, reduction of heat island effect) benefits. Therefore, the components of conventional green roof including plant palette, growing media composition and the other synthetic layers need to be modified. The characteristics of green roof water retention, plant water availability, plant selection, and thermal properties are all critical factors which need to be adapted to help address the harsher environmental conditions and performance demands of hot climates. If these problems can be overcome, the combined environmental, ecological and sociological benefits suggest green roofs could be an imperative technology for towns and cities in tropical and subtropical regions of the world.
The ecosystem services green roofs provide are influenced by both the engineered and biotic components of green roof systems. This chapter focuses on how the functioning of green roofs is controlled by plant species and the synthetic vegetation communities created by them. Plant species can differ greatly in their ability to provide services such as roof cooling and stormwater retention. Newer work, emphasizing less-well-characterized benefits such as reduction of heat loss in winter, air pollution mitigation and carbon sequestration (Chap. 2), also shows significant effects of plant species. The species that best perform a particular service differ between services; other research shows performance advantages in combining species or functional groups of plants into communities. Optimizing green roof benefits thus requires close attention to plant properties, and even superficially similar plant groups (e.g. succulents) can show large performance differences among species. Characterizing green roof vegetation by plant traits, such as leaf area, leaf thickness and photosynthetic pathway, could be a useful way to select green roof species, allowing rapid screening of regional floras for potential species. Plant traits are often directly linked to ecosystem processes that provide economically and environmentally valuable services. Consequently a trait-based approach can help elucidate the relationships among the performance of individual species, the role of plant diversity and the ecosystem services provided by green roofs. This should allow the design of purpose-specific green roofs that provide higher levels of ecosystem services.
Soil from four native prairie remnant sites was used as inoculum in pot culture to achieve vesicular–arbuscular mycorrhizal (VAM) infection of Sudangrass [ Sorghum sudanense (Piper) Stapf]. The prairie sites varied in their management histories and degradation levels. Sudangrass plants that became infected with VAM grew better than those grown in standard pasteurized greenhouse mix or those grown in a pasteurized greenhouse–prairie soil mix. Soil from prairie remnants may serve as a beginning source of inoculum that can be increased via Sudangrass pot culture for inoculation of prairie plant seedlings in nursery production.
As forests, agricultural fields, and suburban and urban lands are replaced with
impervious surfaces resulting from development, the necessity to recover green space is
becoming increasingly critical to maintain environmental quality. Vegetated or green
roofs are one potential remedy for this problem. Establishing plant material on rooftops
provides numerous ecological and economic benefits, including stormwater management,
energy conservation, mitigation of the urban heat island effect, and increased
longevity of roofing membranes, as well as providing a more aesthetically pleasing
environment in which to work and live. Furthermore, the construction and maintenance
of green roofs provide business opportunities for nurseries, landscape contractors,
irrigation specialists, and other green industry members while addressing the issues of
environmental stewardship. This paper is a review of current knowledge regarding the
benefits of green roofs, plant selection and culture, and barriers to their acceptance in the
United States. Because of building weight restrictions and costs, shallow-substrate
extensive roofs are much more common than deeper intensive roofs. Therefore, the
focus of this review is primarily on extensive green roofs.