Living Architecture Monitor - Green Roofs for Healthy Cities

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CREATINGHABITAT BYDESIGN RESEARCHERSHAVEDEVELOPEDANEWPROCESSMODEL—USINGTHEDICKCISSELSPIZA AMERICANAATHREATENEDGRASSLANDBIRDASANEXAMPLE—TOHELPGREENROOFERS MAKETHERIGHTDECISIONSWHENTRYINGTORESTOREHABITATFORASPECIFICSPECIES By Dr. Reid Coffman and Allison Thurmond Great Plains grassland bird populations have plummeted in response to fragmented grasslands and a growing presence of agricultural chemicals in surviving habitat. In addition to the restoration and conservation needed to protect grasslands, Michael Rozenweig’s idea of “reconciliation ecology” seeks to pick up where the two leave off, at the edges of development. Preliminary studies indicate strong potential for reconciling habitat on urban rooftops. To further advance the idea, a green roof was proposed as nesting habitat for the Dickcissel (Spiza Americana), a migratory ground-nester (pictured above). The species was chosen for its adaptability, height threshold, and threatened status. From this we designed a new habitat based on the Dickcissel’s environmental needs to demonstrate the ease of applying a habitat template approach to green roof ecological design. Our green roof habitat design is a template which is intended to mimic the environment based on the species-specific information such as soil needs, prey population and nesting behaviors — and provides a model for other designers to consider when designing for ecological restoration. The design process is organized into seven explicit steps, which aid in matching appropriate wildlife species to a functional green roof system. The contextual information is directed to suburbanizing communities practicing bird conservation in the southern Great Plains, while the template concept holds a universal application in ecoroof habitat design. Several constants are locally available materials, and appropriate indigenous species and creation of diverse habitat. One key variable to habitat establishment is matching plant species to substrate mixes. For central Oklahoma, the Permian shale outcroppings found to our west are an ideal example of the drier, windier, hotter, and rockier conditions that a rooftop condition imposes. The Dickcissel’s need for tall vegetation led to a projected substrate depth of 15" to 24": deep enough to support a selection of shallow-rooted native plants with a structure that mimics the archetypical deep-rooted prairie species. Materials like crushed brick, lightweight expanded clay, and cottonseed hulls (lightweight, water-retaining agricultural byproduct) mixed with clean topsoil, sand and gravel are used in different proportions to maintain a diverse environment and lower the overall weight of the roof. Plants are then selected based on several key factors, found in the Plant Rationale Key (see next page). The rational underscore the most important needs of the nesting pair, but may vary by keystone species. LIVING ARCHITECTURE MONITOR WINTER
“The design process is organized into seven explicit steps, which aid in matching appropriate wildlife species to a functional green roof system.” In this case, Elbowbush (Forestiera pubescens), a shallow rooted Plains bush provided structure while Sand Dropseed (Sporobolus cryptandrus) and Idaho Fescue (Festuca idahoensis) served as grassy height and forage. Shale adapted Blue Grama (Bouteloua gracilis) holds soil and native forbs like Evening Primrose (Oenothera speciosa) and Beebalm (Monarda fistulosa) sustain insect populations. Finally, edging the building with trees supplements woody height and eases transition to the roof. The project information is currently being used to educate local officials and designers on the use of a template approach to green roof habitat. It is our hope this step-by-step model will assist you in creating restorative habitats on green roofs and walls. THESEVENDESIGNSTEPS FROMIDENTIFICATIONTOFINALHABITAT STEP identify a threatened bird species in need of nesting habitat STEP locate under-utilized, low slope roof STEP confirm that your roof is adjacent to open land STEP be creative with locally available materials for the growing substrate STEP calculate the substrate’s weight and the structure you’ll need to support it STEP design your base substrate STEP design the nesting habitat, focusing on indigenous plants and biodiversity RECOMMENDEDREADINGS Brenneisen, S. (2003). Biodiversity of European Greenroofs. In conference proceedings of Greening Rooftops for Sustainable Communities Chicago, Illinois. Green Roofs for Healthy Cities. Coffman, R. (2007). Comparing Wildlife Habitat and Biodiversity Across Green Roof Type. In the conference proceedings of Greening Rooftops for Sustainable Conference, Minneapolis, Minnesota, Green Roofs for Healthy Cities. Lundholm, J. (2006). Green Roofs and Facades: A Habitat Template Approach. Urban Habitats Dec. Vol 4, Issue 1, pages 87 — 101. Rozenweig, M. L. (2003) Win-Win Ecology: How the Earth’s Species Can Survive in the Midst of Human Enterprise. Oxford University Press. Dr. Reid Coffman, Ph.D. is an assistant professor of landscape architecture at the University of Oklahoma. He is a founding member of the International Research Committee for Green Roofs for Healthy Cities and a past fellow with the National Wildlife Federation. He holds degrees in urban ecology, environmental horticulture and landscape architecture. Allison Thurmond is a fifth year architecture student at the University of Oklahoma based in Norman, Oklahoma, with a focus on Environmental Studies and Anthropology. She is also a LEED® accredited professional and a National Merit Scholar. PLANTRATIONALEKEY USETHISGUIDETODETERMINEPLANSUITABILITY F/FORAGE produce seeds eaten by the Dickcissel N/NESTING locate under-utilized, low slope roof C/COVER provides height and protection for the Dickcissel and its insects I/INSECTATTRACTOR sustains invertabrate communities needed as a for source for nesting Dickcissel pairs W/EVERGREEN maintains evapotranspiration and insulating plant material year round, improving the performance of the roof E/EROSIONCONTROL helps hold substrate in place, a concern with the additional wind and runoff erosion stresses on an elevated habitat S/SOILFIXER maintains or replaces nitrogen and organic matter in the soil, critical for long-term success for the roof
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Page 5 and 6: THEGROWINGMEDIA&PLANTISSUE Welcome
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Page 11 and 12: Photos courtesy Elisabeth Whitelaw
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