Macro to Micro: Scalable Urban Habitat
In 1998 Leslie Sauer Jones wrote The Once and Future Forest: A Guide to Forest Restoration Strategies. Embedded within the book’s forward, landscape architect Ian McHarg implored: “We must participate, with action and all the experience we can bring” in order to attempt to reverse environmental degradation and we can no longer expect our actions to be reversed with inaction. He further suggested that we embrace, “important havens, such as the interstices of cities” as critical canvasses for habitat enhancement and expansion for our native plants and animals.
Within our cities, large, contiguous tracts of vegetation, such as urban forests and riverfront corridors, offer critical ecological value potential. However, in more densely developed fragments of the city, where landscape design increasingly occurs, researchers are discovering that purposely selected woody plants can similarly provide animal species with viable urban habitat. Conceptualizing the ecological value of these urban interstices may be a function of perspective, or scale.
Surprisingly, many land-dwelling mammals, birds, and invertebrates occupy a relatively small territory during their life cycle. Research by Yasuda and Koike (2009) suggests that the bark of an isolated urban tree can serve as micro-habitat for a variety of arthropods, particularly ant species. The study investigated arthropod occupancy on trees in isolation, linear corridors, and patches, and found that tree species was the most important determinant of occupancy, followed by tree size. These findings indicate that landscape architects can use individual tree species selection as a tool to support invertebrate populations that perform ecosystem services and attract desirable predators.
Scaling up from isolated trees to wooded streetscapes, research by Fernandez-Juricic (2000) found that corridors are valuable to certain songbird species that ground-feed and nest in trees. The study, which investigated bird species richness, temporal persistence, and density of feeding and nesting guilds, found that wooded streetscapes can be particularly adept at supporting songbirds when connected to a larger habitat area, such as an urban park. Habitat quality further influences songbird species richness, particularly when native plant species (White, et al. 2005), large trees, berries, and favorable water quality are present (Melles, et. al 2003). These findings suggest that conceptualizing a streetscape design as a habitat system, within a particular eco-region, is paramount in promoting biodiversity. Landscape architects are adept at this type of systems thinking, and fostering interlinked networks of ecologically-rich urban environments should be a primary design goal.
To no surprise, ecologists have found that urban forest supports even more biodiversity (Alvey 2006). Research by The Ohio State University (2010) found that, “even tiny patches of woods in urban areas seem to provide adequate food and protection for some species of migrating birds as they fly between wintering and breeding grounds.” Larger segments of urban forest can meaningfully contribute to species diversity of certain pollinators (Matteson, et. al 2008) and migratory birds (Lynch & Whigham 1984). Other species, such as interior-forest dwelling mammals, require large-scale, uninterrupted habitat that may be less common in cities. When the creation of these contiguous habitats are not possible, landscape architects should deploy their knowledge of spatial dynamics to provide effective micro-habitats for key species.
As landscape architects, we have the opportunity to create urban ecologies that are ideally self-sustaining, and breed richness and resilience over time. Research shows that these ecosystems, no matter how small, can enhance the biodiversity of our cities while filtering the air and sequestering carbon.
Want to Learn More?
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Fernandez-Juricic, E. (2000). Avifaunal Use of Wooded Streets in an Urban Landscape. Conservation Biology, 14(2), 513-521.
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The Ohio State University (2010). Even small patches of urban woods are valuable for migrating birds. ScienceDaily. Retrieved November 2, 2013
White, J.G., Antos, M.J., Fitzsimons, J.A., & Palmer, G.C. (2005). Non-uniform bird assemblages in urban environments: the influence of streetscape vegetation. Landscape and Urban Planning, 71 (2-4), 123-135.
Yasuda, M. & Koike, F. (2009). The contribution of the bark of isolated trees as habitat for ants in an urban landscape. Landscape and Urban Planning, 92(3-4) 276-281.