Living Architecture Monitor - Green Roofs for Healthy Cities

CREATINGHABITAT
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RESEARCHERSHAVEDEVELOPEDANEWPROCESSMODEL—USINGTHEDICKCISSELSPIZA
AMERICANAATHREATENEDGRASSLANDBIRDASANEXAMPLE—TOHELPGREENROOFERS
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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.
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