Much that happens in cities -- urban areas more broadly -- is not obvious to the naked eye or to casual observation. The invisible things in urban social-ecological systems represent four key dimensions: social processes and their legacies; the built and technological structures and infrastructures; ecological structures and processes; and influences and events that arrive from a distance. These ordinarily invisible features of urban systems can become visible when something goes awry, or when some long-forgotten decision rears its head as a legacy shaping current conditions or options. The invisible becomes visible when something "breaks" or is unexplainable based only on current or local conditions.
Social legacies take myriad forms. This blog has presented several examples, from the clashing street grids in Baltimore arising from orientation to different shorelines around a complex harbor, to the mortgage redlining that mirrors the concentrated abandonment in city neighborhoods.
The "break" of the clashing grids is revealed in several layers of attempts to knit the city's traffic flow more seamlessly. The disjunction between the north-south grid of the Mount Vernon neighborhood and the north-west to southeast orientation of the Madison neighborhood reflect differences between the orthogonal north-south/east-west orientation of the monument-studded downtown grid, and the more organic flow following the old market road on the high ground of the divide between the Gwynns Falls and Jones Falls watersheds, which trends northwestward.
|The 1890 map of Baltimore City, showing the multiple, incongruent street grids.|
The break of redlining is actually part of a longer-term and persistent system of racial, ethnic, and class segregation that has characterized Baltimore since at least the demise of post-Civil War Reconstruction and the rise of Jim Crow laws, customs, and conventions. Given that the primary source of wealth of most Americans is investment in a house, the denial of mortgage security put the residents of neighborhoods judged by the federal Home Owners Loan Corporation to be less than mortgage worthy at a significant and lasting disadvantage in the accumulation of wealth. Other local ripples of this situation extend to property tax revenue flow, educational resources, and through a complex cascade to access to such things as gainful employment in a post-industrial economy and grocers purveying fresh vegetables.
|The 1930s redlining map of Baltimore city, with green, yellow, and red overlays indicating high, medium, and low mortgage desirability based on factors such as race, national origin, and housing stock.|
Much built infrastructure is literally out of sight. Fresh water and gas mains are buried beneath streets and sidewalks, as are sanitary sewers and storm drains. The drainage infrastructure exemplifies the complexity of build infrastructure. In row house neighborhoods in old Baltimore, the stormwater drainage system extends from roofs sloping from the street sides of houses toward the back yards, with downspouts draining into alley gutters, which conveyed water to storm drain catch basins in the streets. So the infrastructure was not just the pipes, but also the roofs, downspouts, gutters, and then the buried drain pipes. Many of the underground stormwater pipes were, in actuality, buried and piped streams. The breakage of this stormwater system is seen in the collapse of roofs of long abandoned houses, and the puddling of rainwater in cellar holes and elsewhere where debris collects or obstructs the flow of rain water.
|Water main break at Gay and Lombard Streets.|
Other forms of breakage are the common leaks that unintentionally connect the remaining surface streams, the sanitary sewers, and the storm drains. The pressurized drinking water system also leaks, adding flow to streams and the two sewer systems, and in some cases adding an avoidable burden to sanitary treatment facilities.
Perhaps the least visible component of urban systems is the ecological structures and processes they contain. Of course, the large green spaces in cities, suburbia, and exurbs are obvious. Signature parks, golf courses, cemeteries, and the green campuses of private and public institutions are often recognized as ecosystems, a designation that clearly acknowledges their ecological content, and facilitates their inclusion in designs and plans. However, such large and often socially valued properties are not the only venues for biophysical processes in urban systems. Yards, volunteer vegetation along fencelines, slivers of lightly managed areas along rights-of-way also contribute to the ecological processes. Hidden riparian strips behind shopping malls, or at the backs of factories, or transportation corridors can also be seen as ecosystems. Clearly, there are many ecological processes that occur in these sites: nutrients are cycling, carbon is being processed, decomposition of organic matter is under way.
However, these quintessential ecological processes are also occurring in urban soils, in surface streams, and in largely ignored wetlands. Biodiversity -- native and introduced birds, medium sized mammals, and an impressive complement of microbes -- are active throughout the urban system. Some of these help retain potentially polluting nutrient compounds, sequester some of the climate-changing carbon that economic processes release, help control disease agents, or simply give pleasure to urban residents. Some of these organisms release contaminating byproducts, and others are themselves disease agents or vectors. But together they constitute a web of interactions and influences that generate amenities and hazards in urban areas. Harnessing the positive outputs of urban biota, conserving native biodiversity, and limiting the risks that some organisms pose, requires making them and their interactions visible features of the city.
Invisible from a Distance or from the Past
Not all things that influence the social-ecological structure and processes in a given urban area constantly reside or originate within it. This is especially true of socially-generated influences, which arrive in the form of new migrants at airports, appear as redistribution of financial capital via investment, disinvestment, or personal remittance, or exist as cultural products such as fashion, movies, or music. Political movements can be seeded from a distance, and opportunities for trade, migration, or commuting determine population densities, economic activities, or cultural vitality. Social influences, either personified or electronically mediated, are extraordinarily mobile in the globalized, urban world.
|A tornado over Baltimore in June 2013|
Other, seemingly more concrete effects also arise from outside a given urban area. Biophysical agents of disturbance, those events that can disrupt the physical structure of a city, often arrive from elsewhere. Hurricanes, with strong winds, coastal flooding, or torrential inland rains are a familiar example. So to are storm fronts that unleash snow, ice, or tornados. Climate change, with the potentials for obvious change in average temperatures, seasonal distributions of heat, cold, wet, and dry, is a prime and increasingly widely appreciated action from outside. Ironically, the high energy demands of urban systems contribute to these global changes, which come back to haunt, in some form or another, virtually every urban area on the planet. Notably, many of the changes associated with climate change are already well developed in urban areas. Heat islands, heat stress, drought, and extreme storm events are phenomena that urban policy makers, managers, and citizens are planning for and adapting to at present.
The Invisible as Personal
Given that humans seem to give greatest credence to events and things that they have themselves experienced, it may be that a great deal of what characterizes urban social-ecological-technical systems remains invisible. The experience of individual persons, or even a nuclear family, is constrained. Human memory is powerful and poignant, but it is temporally quite limited.
On the scale of a human life span, or the span of two or three generations' memory, many important ecological events can be missed. Fires in uninhabited chaparral -- shrubland in the mediterranean climates of the American west -- may recur about once every 70 years on average. A single generation, or even two, may not have seen a big chaparral fire. Chaparral vegetation is made up of species that are adapted to reproduce after fire. Indeed, without fire for long periods, other species can replace the chaparral dominants. Add short human life spans to the fact that the majority of residents in American mediterranean climates are likely to be new arrivals who lack a personal access to multi-generational memory, and the possibility of chaparral fires to be invisible parts of suburbs and exurbs in California or Colorado is enhanced. Many vegetation types are affected naturally by fire, such as many pine forests in the south and eastern U.S. Others are affected by periodic catastrophic wind storms, albeit on a time interval of several centuries. Extreme floods also periodically affect many riverine areas. However, if people have never experienced such a flood, or if they are lulled into security by a floodwall built to contain the last most catastrophic flood plus a foot or two, the risk is essentially invisible. In such situations, floods "to worry about" are virtually invisible.
This is a common phenomenon. Reporting on urban disasters driven by otherwise invisible ecological events often includes this kind of sentiment: "I've lived here all my life, and I have never seen anything like this before." The "this" can be a wind storm, blizzard, hurricane, huge tornado, or outbreak of some native insect. Add to this list new invasive pest or disease organisms, intensifying storms due to climate change, shifting and deepening of drought prone pockets, and so on, and the list of the invisible in the city becomes longer still.
The invisible in the city points toward the need for humility -- individual memory often misses rare weather events, social legacies no longer much spoken about, or catastrophic infrastructure failures of the past. Even family or communal memory seems fallible. The invisible is a key part of cities and urban systems. Urban social-ecological-technical research helps to lift the veil. Maybe the old New Englander suggests how to operationalize humility in the face of the invisible: The question was asked, "Have you lived here all your life?" The droll reply was, "Not yet." One hopes the answer suggests an openness to the invisible in that lived place. Seeking the invisible in the city is one of urban ecology's primary tasks.