Patch Dynamics

Definition: Patch dynamics refers to the three dimensional structure, changes, causes, and effects of spatial differentiation within ecological systems. 

Examples: Patch dynamics include a wide variety of patterns and processes in socio-ecological systems.  Biological patch dynamics can be seen in the establishment, growth, and demise of a clone of goldenrods in a field, or in the fall of a tree in a continuous forest during a storm, with the subsequent response of younger trees and herbaceous plants in the understory, now exposed to light (Fig 1).  Social patch dynamics occurs when households move through child rearing to “empty nest” status, with changing demands on neighborhood infrastructure and changing political priorities, or when a new highway interchange promotes the establishment of an exurban commercial and business center.  Disinvestment, such as a withholding of insurance rating (Fig 2) shifting tax base, or abandonment of an old neighborhood (Fig 3), also initiate patchy change in biological and social structures and processes in a specific urban locations.  Patch dynamics is sometimes a joint socio-ecological phenomenon.  An example occurs with the maturation of trees planted when a subdivision is initially developed, enhances property values or reduces summer cooling costs. 

Patch Dynamics Figure 1.  A treefall gap in a deciduous forest canopy, looking straight upwards.  Treefalls in forests are an example of patch formation which can alter the structure and the mix of species in the forest.  The light, increased rainfall, and decreased demand for nutrients can release seedlings and saplings from the suppression they had experienced in the intact forest.  Animals may seek out new sources of browse and herbiage in treefall gaps.

 

Patch Dynamics Figure 2.  Patches can result from policy decisions and other social processes.  This map shows the distribution of Home Owners Loan Corporation zones for the security of mortgage loans in Baltimore City in 1930.  Such policies helped alter the dynamics racial and class distributions in the city.

 

Patch Dynamics Figure 3. Changes in the patch structure in West Baltimore between 1938 and 2000.  This example of patch dynamics shows the impact of abandonment and demolition of rowhouses on neighborhood physical structure.  Social changes are also associated with these changes.

Why important:  Urban systems consisting of cities, suburbs, and exurbs are dynamic systems.  The contrast from place to place, often over very short distances, is a conspicuous feature of urban systems.  How these different patches affect one another, and affect the functioning of the entire urban ecosystem is crucial information.  Understanding the historical causes for the spatial structure and how it has changed is important for making plans for the future of urban systems.  In spite of people’s best efforts, combined natural and social disruptions and innovations change urban systems in spatially patchy ways.

For more information:

McGrath, B. 2000. Manhattan timeformations.   www.skyscraper.org/timeformations

McGrath, B.P., V. Marshall, M.L. Cadenasso, J.M. Grove, S.T.A. Pickett, and J. Towers, editors. 2007. Designing patch dynamics. Columbia University Graduate School of Architecture, Preservation and Planning, New York.

Shane, D.G. 2005. Recombinant urbanism: conceptual modeling in architecture, urban design, and city theory. John Wiley & Sons, Hoboken.