It’s undoubtedly a buzzword of sustainable development, but what does it really refer to? I’ve identified two main “schools” of green infrastructure thought: the city-centric school and the natural resource-centric school. These two schools focus on different, yet complementary aspects of sustainable development. In the former, green infrastructure refers to the action of “greening” existing infrastructure that serves cities. The emphasis is on city resource, material, energy, and even economic flows. In the latter school, green infrastructure refers to the the action of “infrastructuring” greenness, or the systematization and rationalization of natural and working open space planning. Here, the emphasis is on acknowledgment and protection of ecological services and natural resources that support humans from outside urban areas.

The Tehachapi Wind Farms in California are an example of city-centric green infrastructure. They are replacing fossil fuel energy sources needed as an input to urban environments with renewable wind energy. They improve urban systems by reducing their impact on the environment. Image source: www.visittehachapi.com
The Tehachapi Wind Farms in California are an example of city-centric green infrastructure. They are replacing fossil fuel energy sources needed as an input to urban environments with renewable wind energy. They improve urban systems by reducing their impact on the environment. Image source: www.visittehachapi.com

The first school–the “city-centric” school– focuses on greening existing city systems. Due to the US EPA’s formal acceptance and promotion of Green Infrastructure (GI) as a desirable technology to mitigate stormwater runoff in urban areas, GI is often understood as vegetated stormwater best management practices, or Low Impact Development landscape features, but this is only one aspect of city-centric GI. In addition to stormwater runoff, GI can also refer to the “greening” of other urban infrastructures in ways other than through vegetation. In these applications, “green” takes on the meaning of promoting economic, environmental and social sustainability. For example, solar panels and wind turbines are green energy infrastructure. Bike racks and clean fuel public transit fleets are green transportation infrastructure. To take it beyond just hardware infrastructures, you could also say that the addition to inter-departmental sustainability teams within city government is greening governance infrastructure. The commonality between these seemingly unrelated types of infrastructure is that they all start with the intent to improve upon already existing functions of urban systems by making them “greener”. The concept of “green” is often associated with the triple bottom line values of sustainable development: economics, social equity, and environment. In contrast, natural resource-centric GI starts from the other direction. Natural open space is already “green”; GI is a framework by which this “green” can be actively planned.

Maryland's statewide green infrastructure network plan is an example of the natural resource-centric school of green infrastructure. Its focus is on strategic conservation of ecological areas in concert with urban development. Image source: www.dnr.state.md.us
Maryland’s statewide green infrastructure network plan is an example of the natural resource-centric school of green infrastructure. Its focus is on strategic conservation of ecological areas in concert with urban development. Image source: www.dnr.state.md.us

The natural resource-centric GI is the GI that Benedict and McMahon write about in their seminal work, Green Infrastructure: Linking Landscapes and Communities. In it, the authors argue that conventionally, natural open space conservation is planned in a piecemeal fashion that is reactive to encroaching development, and therefore suffers in ecological quality. The GI approach that Benedict and McMahon advocate for is to elevate natural open space planning to level of rational and preemptive planning and financing equal to that of conventional infrastructures necessary for development. Natural resource-centric GI is an acknowledgment that natural areas– forests, streams, wetlands– and working lands–farms, managed forests– are critical to urbanized areas and necessitate an adequate amount of planning if they are to effectively provide us with the eco-services we expect of them. Since the city relies on natural open space to purify our water, provide us with food, stabilize our soil, and be a source of recreation and inspiration to humans, it serves a multitude of critical purposes. This school of GI refers more to ecological land use planning outside urban areas for the functions that are often overlooked, but that are just as critical to healthy human development. It relies on a rationalized decision-making system with value rankings, and characterization of areas as links or hubs within the network.

Is it a problem that “green infrastructure” can refer to everything from urban bioswales and rain gardens, to a clean fuel bus fleet, to a statewide farm preservation program, to a wind farm? There is the fear that with ever-broadening meaning, “green infrastructure” could begin to lose meaning. But maybe, the pervasiveness of the term is evidence that its underlying values are “catching” in society. Similar to how Stephen Campbell said in his 1996 article “Green Cities, Growing Cities, Just Cities” of the broadening understanding of the term “sustainability”, perhaps “green infrastructure” is also shifting from being a variable of the debate to being the parameter of the debate. I think the effects of expanding meaning of green infrastructure still remains to be seen.

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