Thus the Harlem Railroad transformed Quaker Hill from a community of diversified farming, producing, manufacturing, selling, consuming, sufficient unto itself, into a locality of specialized farming. Its market had been Poughkeepsie, twenty-eight miles away, over high hills and indifferent roads. Its metropolis became New York, sixty-two miles away by rail and four to eight miles by wagon-road.
With the railroad’s coming, the isolated homogeneous community scattered. The sons of the Quakers emigrated. Laborers from Ireland and other European lands, even negroes from Virginia, took their places. New Yorkers became residents on the Hill, which became the farthest terminus of suburban travel.[[47]]
The establishment of a new industry, especially if it displaces the previous economic base, may also make for a more or less complete change of population without greatly modifying the size of the community. This condition is exemplified in many of the small towns of the state of Washington which have changed from lumbering to agriculture or from one type of agriculture to another. In many cases few of the previous inhabitants remained after the invasion of the new economic base.
As a community increases in size, however, it becomes better able to accommodate itself to invasions and to sudden changes in number of inhabitants. The city tends to become the reservoir into which the surplus population drains from the smaller communities round about.
V. ECOLOGICAL PROCESSES DETERMINING THE INTERNAL STRUCTURE OF COMMUNITY
In the process of community growth there is a development from the simple to the complex, from the general to the specialized; first to increasing centralization and later to a decentralization process. In the small town or village the primary universal needs are satisfied by a few general stores and a few simple institutions such as church, school, and home. As the community increases in size specialization takes place both in the type of service provided and in the location of the place of service. The sequence of development may be somewhat as follows: first the grocery store, sometimes carrying a few of the more staple dry goods, then the restaurant, poolroom, barber shop, drug store, dry-goods store, and later bank, haberdashery, millinery, and other specialized lines of service.[[48]]
The axial or skeletal structure of a community is determined by the course of the first routes of travel and traffic.[[49]] Houses and shops are constructed near the road, usually parallel with it. The road may be a trail, public highway, railroad, river, or ocean harbor, but, in any case, the community usually starts in parallel relation to the first main highway. With the accumulation of population and utilities the community takes form, first along one side of the highway and later on both sides. The point of junction or crossing of two main highways, as a rule, serves as the initial center of the community.
As the community grows there is not merely a multiplication of houses and roads but a process of differentiation and segregation takes place as well. Residences and institutions spread out in centrifugal fashion from the central point of the community, while business concentrates more and more around the spot of highest land values. Each cyclic increase of population is accompanied by greater differentiation in both service and location. There is a struggle among utilities for the vantage-points of position. This makes for increasing value of land and increasing height of buildings at the geographic center of the community. As competition for advantageous sites becomes keener with the growth of population, the first and economically weaker types of utilities are forced out to less accessible and lower-priced areas. By the time the community has reached a population of about ten or twelve thousand, a fairly well-differentiated structure is attained. The central part is a clearly defined business area with the bank, the drugstore, the department store, and the hotel holding the sites of highest land value. Industries and factories usually comprise independent formations within the city, grouping around railroad tracks and routes of water traffic. Residence sections become established, segregated into two or more types, depending upon the economic and racial composition of the population.
The structural growth of community takes place in successional sequence not unlike the successional stages in the development of the plant formation. Certain specialized forms of utilities and uses do not appear in the human community until a certain stage of development has been attained, just as the beech or pine forest is preceded by successional dominance of other plant species. And just as in plant communities successions are the products of invasion, so also in the human community the formations, segregations, and associations that appear constitute the outcome of a series of invasions.[[50]]
There are many kinds of intra-community invasions, but in general they may be grouped into two main classes: those resulting in change in use of land, and those which introduce merely change in type of occupant. By the former is meant change from one general use to another, such as of a residential area into a business area or of a business into an industrial district. The latter embraces all changes of type within a particular use area, such as the changes which constantly take place in the racial and economic complexion of residence neighborhoods, or of the type of service utility within a business section. Invasions produce successional stages of different qualitative significance, that is, the economic character of the district may rise or fall as the result of certain types of invasion. This qualitative aspect is reflected in the fluctuations of land or rental values.