Invasion–Succession

The terms invasion and succession in human geography reflect the influence of Charles Darwin and evolution as well as the influence of Ernst Haeckel and Frederick Clements and ecology. Important 19th-century thinkers such as Herbert Spencer adapted their principles to explain the changing social order. Social arrangements became the outcome of competition for advantageous locations. New entrants into an area disturbed old forms, setting off competition for dominance and generating a new set of land uses and new social organization.

Such explanations permeated understandings of American geography. Historian Frederick Jackson Turner incorporated invasion and succession into his influential frontier thesis developed in 1893. According to Turner, successive waves of settlement (or invasion), each pushing the frontier farther west, created a distinctive American personality—buoyant, self-reliant, and enterprising. Each group recapitulated the experience of those groups that came before, with each stage ultimately leading toward mature settlement (or succession).

Turner drew directly on the work of the U.S. Bureau of the Census's Francis Walker and Henry Gannett, who tracked America's population growth and viewed it as inexorably progressive. According to Walker's Statistical Atlas of the United States, published in 1874, the country was composed of three major settlement categories: wilderness, frontier, and fully settled. Wilderness would turn to frontier after invasion by early entrants, scouts, and trappers. Ranchers followed, and then farmers followed after that. Ultimately, cities would sprout—the final phase (or, in ecology terms, the climax phase) of human settlement. Each density level signaled a specific social configuration and associated economic form.

In urban geography, invasion–succession is most closely associated with the 1920s work of Chicago School urbanists Robert Park, Ernest Burgess, and Roderick McKenzie. The period was one of dynamic urban growth. The Chicago School used empirical methods to analyze urban spatial patterns. The researchers drew explicit analogies between behavior and processes shaping plant and human communities. Cities were composed of distinctive interdependent areas comparable to ecological communities, each dominated by its own characteristic land use and population. The city's zones ranged in function (e.g., central business district, residential zone) and desirability (e.g., better residences, slum areas). Invasion–succession was the process that explained change. Burgess's concentric zone model of the city placed the central business district at the center, the site for the most successful economic competitors. New immigrant groups had to vie for space with more advantaged groups; therefore, opportunistically, they could invade only the less desirable areas near their jobs—the vacant lots of ecology. Each new immigrant group would be followed by others like it, creating a mosaic of ethnic neighborhoods over time.

Invasion–succession explanations for development have been critiqued and changed. Turner's America never became fully settled in terms of density, yet high-tech cities are located in the midst of low-density settlement. Urban patterns are driven by capital flows in discussions of gentrification and abandonment, and the processes are viewed as anything but natural.