The Human Ecosystem: What’s Missing?

The human ecosystem concept is one of the most common tools used in the Baltimore Ecosystem Study LTER.  Adopted from a team of social ecologists and sociologists who were involved in community forestry in the Himalayas, the application of such approaches to underserved areas in American cities, and the conservation and management of US National Parks, the concept is remarkably broad and adaptive.  The human ecosystem is not necessarily tuned to emphasizing the intellectual flavor of the week or most current headline issue for cities, urbanization, sustainability, or development.  However, its inclusiveness, nested hierarchical nature, and adaptability makes it well suited to dealing with shifting or even new emphases in social-ecological systems research and application (Figure 1). 
Figure 1.  The Human Ecosystem Framework
(Adapted from Machlis et al. 1997)
What are some of the hot topics that might seem to be missed in our discussions or presentations, but which in fact have a home in the human ecosystem framework?

Political ecology.  
This is at once a scholarly area and a subject of activist attention.  As a scholarly field, it examines the relationships of politics, economics, and environment.  As a social movement, it focuses on the inequitable distribution of benefits and costs of environmental decisions.  The social movement can be seen as a part of a larger social or environmental justice agenda. 
The multidimensional relationships with which political economy is concerned exercise several components of the human ecosystem framework.  Among the bioecological features, catalogued in the “ecosystems pattern and process foundations” component of the framework, many are relevant, including the distribution of energy, water, nutrient, and biomass resources, the kinds and levels of contaminants and pollution of air, water, and soil, and the heterogeneous or mosaic distribution of all of these factors.  Heterogeneity is important because control of access to resources, exposure to hazards, or distribution of benefits is subject to social – that is power and political – control.  Not all persons, groups, or institutions may be uniformly represented across a spatial mosaic.  The social control of access, exposure, and benefit engages many of the components of the human ecosystem framework.  The social ordering by factors of identity, rank hierarchies, and norms are key to the differential power relationships in human ecosystems.  Social rank hierarchy can further be broken down into ranks based on wealth, control of territory, social status, knowledge as a kind of capital, and, tellingly, power.  Among the social and cultural foundations, the distribution of populations, including by race, class, gender, or ethnicity, and the distribution of information by various institutions may reflect power relationships.  Of course the access to or participation in the institutions of sustenance, health, justice, education, etc. are also dependent on power relationships.  Other aspects of the human ecosystem framework (Figure 1) can also be used to investigate and explain, and therefore intervene in, power relationships in the urban social-ecological systems. 

Recently, our colleague N.B. Grimm has emphasized the fact that social-ecological systems have significant technological content.  Grimm at the 2013 Congress of Urban Ecology, the first such international meeting of the Society of Urban Ecology (SURE), introduced the term Social-Ecological Technical System, or SETS to emphasize the role of technology in how people think about urban ecosystems. 
This healthy reminder and highlight does no violence to the human ecosystem framework.  A classical representation of the significance of technology in human environment relationships is the POET model.  Under this general model, environmental change is said to be a function of human population, the way that humans are organized, and the technology available.  Explicit recognition of the role of technology in urban systems appears in the classical work of Borchert (1967), who notes that urban form in the United States shifted with the introduction of new technologies.  
Emphasizing transportation technology, Borchert proposed five epochs of American urban change: 1) sail and wagon (1790-1830), 2) steam powered ships and initial rail roads (1830-1870), 3) national steam rail network (1870-1920), 4) interstates and propeller air transport, and finally 5) satellites and jet propulsion.  American urban transformation continues, with other epochs hypothesized to represent the “slow growth” proposed in the 1970s of the oil embargo (Phillips and Brun 1978), or perhaps an epoch defined by the technology integrating global finance, manufacturing, and consumption.  In any event, the significance of technological innovation, change, and even retrenchment are clearly major components and drivers of urban change.  These latter technologies have a great deal to do with the current global teleconnections of urban systems with each other and with more rural and wild lands (Boone et al 2014).
Baltimore is a prime example of the role of shifting technologies.  For instance, the urban fabric of Baltimore, as described in Hayward and Belfoure (1999), shifted markedly with each transition — from the walking city, through the city of horsedrawn trolleys, through the electric commuter rail, through the automobile era.  The industrial power of Baltimore similarly reflects major technological shifts, from the water power of the “fall line” through wood fueled steam, through coal powered manufacturing and steel production.  Other overlapping shifts, such as the opening up of the American South and Southwest with the availability of air conditioning technology there, and government policy for the location of defense industries away from the vulnerability of the east coast so feared during World War II, played a role in Baltimore’s post-industrial shift to a joint service, tourism, and knowledge footing.
In the Human Ecosystem Framework, technology appears foundationally in such things as the source of energy (e.g. water power, vs. wood, vs. coal), or the path of water flow (the location at the fall line between the Piedmont and the Coastal Plain).  Technology also is reflected in the amassing and deployment of labor, as in the contrast between slavery and voluntary immigration as sources, and the shift in capital investment in water-mill industry and canals versus the creation of America’s first long haul railroad – the Baltimore and Ohio.  
The technologies available and the pursuits different technologies make available have powerful influence on social identity, demographic structure, community and neighborhood cohesion and the like.  For example Baltimore still embraces a historical identity as a seafaring town.  This is shown by the fact that a waterfront neighborhood is still referred to as Canton, in honor of Baltimore’s fast clipper ships that cemented trade between China and the U.S. East Coast.  Or the fact that Fells Point, the location of Baltimore’s first deep water port, still retains the ameities and reputation as a freewheeling entertainment district reflecting its early tradition of hosting sailors on leave.  The coal-fired industrial era is honored in the Middle Class Mythology of Baltimore and its blue collar ethos.  These things are all features that find a home in the human ecosystem framework, for example in cultural myths, social identity, and temporal cycles of change in demography and institutional and organizational structures.

Another hot topic these days is infrastructure.  Strictly speaking, infrastructure is what undergirds the various components of a system.  Infra means below.  It is the supporting structure, linkages, flows in any system.  The human ecosystem may seem to be blind to the built and engineered components of urban ecosystems.  This is because the human ecosystem framework assumes those physical foundations.  In 1997, we worked to refine understanding of the bioecological foundations of the human ecosystem.  The original discussions by Machlis and colleagues certainly included the bioecological and biophysical aspects of human ecosystems in the “resource system” component.  Perhaps because buildings, streets, supply pipes, electrical wires, railroads, sewers, storm drains, and so on are such conspicuous parts of urban ecosystems, we hardly felt the need to call attention to them.  Cities are so often defined based on density of built structures and of human inhabitants that pointing toward buildings and infrastructure could be tacitly assumed.
However, a later description of the human ecosystem as a model template showing major kinds of components and their connections attempted to make this assumption clear.  Cadenasso et al. (2006) is a good example of this integration of built – and hence infrastructural – components into general interactive and classificatory models of urban ecosystems (Figure 2).  There is nothing wrong with pointing to the various components of systems as infrastructure, but in a sense, that seems redundant with saying that an urban place is a human ecosystem comprising social, biotic, built, and physical (e.g. soil, topography, climate) components.  Infrastructure is just another word for components, really.  The big idea is that cities, suburbs, and exurbs are systems that contain many specific features and connections, and that those span and connect biology, physical environment, buildings, social processes and the myriad feedbacks among components.
Figure 2. A process model template of the human ecosystem.
A healthy outcome of the infrastructure label may be helping people to remember the often invisible biological components of cities, suburbs, and towns.  Infrastructure is now often spoken of as gray, blue, and green.  This division suggests that the complex system of the city or more broadly, the urban region, depends on services and structures provided by plants, animals, and microbes, and that these services emerge not only from partly or (almost) entirely engineered features, but also from parks, yards, street plantings, derelict field and lots, open streams, wetlands, and freeflowing atmosphere.  Planning, design, management, policy, and education will be better served, and will better serve the human population when the contributions of biological infrastructures and their components are understood and effectively employed.


The message here is that the human ecosystem framework (Figure 1), a hierarchical enumeration of the kinds of biophysical and social structures, resources, processes, and outcomes that make up not only cities and towns, but also wilderness and production landscapes, is adequate to include contemporary and important concerns of power, justice, technology, and infrastructure.  The human ecosystem framework can be considered a causal hierarchy, in which general causes or factors are broken down into more specific mechanisms and interactions.  Specific models of human (in general) and urban (in particular) ecosystem structure, function, and dynamics will draw upon several to many of the ideas and features included in the human ecosystem framework. 
The framework is complemented by a process model template (Figure 2).  This process model template emphasizes that urban systems are composed of biological components and their interactions, physical environments and their links, social structures and interactions, and built components and the interactions among them.  This model template emphasizes the comprehensiveness of kinds of components of cities, suburbs, and exurbs, as well as the interactions among the various components.
Thus, rather than neglecting important contemporary topics in social, engineering, historical, and political realms, urban ecology has frameworks and model templates that in fact can easily accommodate these features.  Technology is a part of the built environment, Power is an aspect of the social structures, and infrastructure is a way to group various built components, networks, and interactions.


Boone, C. G., C. L. Redman, H. Blanco, D. Haase, J. Koch, S. Lwasa, H. Nagendra, S. Pauleit, S. T. A. Pickett, K. C. Seto, and M. Yokohari. 2014. Reconceptualizing land for sustainable urbanity. Pages 313–330 in K. C. Seto and A. Reenberg, editors. Rethinking urban land use in a global era. MIT Press, Cambridge.

Borchert, J. R. 1967. American metropolitan evolution. Geographical Review 57:301-332.
Cadenasso, M. L., S. T. A. Pickett, and J. M. Grove. 2006. Dimensions of ecosystem complexity: heterogeneity, connectivity, and history. Ecological Complexity 3:1-12.
Hayward, M. E. and C. Belfoure. 1999. The Baltimore rowhouse. Princeton Architectural Press, New York.

Machlis, G. E., J. E. Force, and W. R. Burch. 1997. The human ecosystem. 1. The human ecosystem as an organizing concept in ecosystem manageme

Phillips, P. D., and S. D. Brunn. 1978. Slow Growth: A New Epoch of American Metropolitan Evolution. Geographical Review 68:274–292.