IMPORTANT ECOLOGICAL PROCESSES AND MODELS OF LAND USE

{NOTE: THESE PROCESSES ARE OFTEN RELATED TO TEMPORAL AND SPACIAL DIMENSIONS OF THE IMMIGRANT ADAPTION PROCESS. HOWEVER, THE ORIGINAL FOCUS WAS ON THE COMPOSITION CHANGES BETWEEN BLACKS AND WHITES IN AMERICAN NEIGHBOURHOODS.}

CONCENTRATION // DECONCENTRATION: REFERS TO THE MASSING AND OUTWARD MOVEMENT OF "CLUSTERS" OF PEOPLE -- E.G., "WHITE FLIGHT" FROM THE CITY TO THE SUBURBS.

SEGREGATION: THE PRIMARY FACTOR LEADING TO THE DEVELOPMENT OF "NATURAL AREAS", IS THE TENDENCY FOR VARIOUS GROUPS AND INSTITUTIONS TO LOCATE IN SEPARATE AND DISTINCT PARTS OF THE CITY -- E.G., SIMILAR "ECOLOGICAL UNITS" LIKE ETHNIC GROUPS HAVE A TENDENCY TO CLUSTER NEAR ONE ANOTHER.

COMPETITION: SORTS OUT VARIOUS ECOLOGICAL UNITS OF GROUPS, AND THE ORGANIZATION OF THE CITY IS IN CONSTANT FLUX . (THE CITY IS A LIVING BREATHING ORGANISM) -- E.G., SOME MINORITY GROUPS ARE LESS ABLE TO COMPETE AND THEREFORE FORCED TO TAKE UP RESIDENCE IN LESS DESIRABLE SECTIONS OF THE CITY.

INVASION: REFERS TO A SITUATION IN WHICH ONE GROUP OR INSTITUTION ENCROACHES ON THE TERRITORY HELD BY ANOTHER GROUP OR INSTITUTION -- E.G., THE ARRIVAL OF A NEW IMMIGRANT GROUP INTO A NEIGHBOURHOOD AND ITS GRADUAL PUSHING OUT OF THE RESIDENT IMMIGRANT GROUP (BLACK-JEW HOSTILITY IN N.Y.).

SUCCESSION: REFERS TO THE COMPETED PROCESS OF INVASION, IN WHICH AN AREA IS COMPLETELY CONVERTED FROM ONE USE TO ANOTHER. THE IDEA OF SUCCESSION IS TEMPORAL AS WELL AS TERRITORIAL. IT ENTAILS THE REPLACEMENT OF OLD POPULATION GROUPS BY NEW ONES AND THE APPEARANCE OF NEW INSTITUTIONS IN A GIVEN AREA.

THEREFORE, SUCCESSION IMPLIES AND REQUIRES CONTINUOUS AND STEADY CHANGE.

__________________________________________________________

(THE CONCEPTS ARE DESCRIPTIVE, SO THE NEXT STEP WAS TO):

INTEGRATE CONCEPTS INTO THEORIES-MODELS OF ECOLOCIAL DEVELOPMENT AND URBAN GROWTH

THREE MODELS OF LAND USE:

Figure 1 Three Generalizations of Urban Structure Upper Left: Burgess' Concentric Zone Model; Upper Right: Hoyt's Sector Model; Bottom Left: Harris and Ullman Multiple Nuclei Model.  Graphic repared by Department of Geography and Earth Sciences, University of North Carolina at Charlotte.

(1) THE CONCENTRIC ZONE MODEL -- ERNEST W. BURGESS, I925 =è THE CONCENTRIC ZONE MODEL WAS AMONG THE EARLY DESCRIPTIONS OF URBAN FORM, AND ONE OF THE EARLIEST MODELS DEVELOPED TO EXPLAIN THE SPATIAL ORGANIZATION OF URBAN AREAS ===è THE MODEL WAS BASED ON BURGESS’S OBSERVATIONS OF CHICAGO DURING THE EARLY YEARS OF THE 20TH CENTURY ===è ONE CENTRE THAT RADIATES OUTWARD -- PRINCIPLES OF "INVASION AND SUCCESSION" ===èTHE CONCENTRIC ZONE MODEL DEPICTS THE USE OF URBAN LAND AS A SET OF CONCENTRIC RINGS WITH EACH RING DEVOTED TO A DIFFERENT LAND USE (SEE FIGURE 1). MAJOR ROUTES OF TRANSPORTATION EMANATED FROM THE CITY’S CORE, MAKING THE CBD THE MOST ACCESSIBLE LOCATION IN THE CITY. BURGESS IDENTIFIED FIVE RINGS OF LAND USE THAT WOULD FORM AROUND THE CBD. THESE RINGS WERE ORIGINALLY DEFINED AS THE (1) CENTRAL BUSINESS DISTRICT, (2) ZONE OF TRANSITION, (3) ZONE OF INDEPENDENT WORKERS’ HOMES, (4) ZONE OF BETTER RESIDENCES AND (5) ZONE OF COMMUTERS.

CITY GROWS OUT IN A SERIES OF CIRCULAR AREAS OR ZONES, EACH WITH A DIFFERENT TYPE OF LAND USE, THAT DEVELOPS FROM THE CENTRAL BUSINESS DISTRICT (CBD), THE LOCATION OF THE HIGHEST LAND VALUES.

(A) "ZONE 1" IS THE CENTRAL BUSINESS DISTRICT AND CULTURAL CENTRE (RETAIL STORES, FINANCIAL INSTITUTIONS, HOTELS, AND THEATRES, FOR EXAMPLE) IN WHICH HIGH LAND PRICES CAUSE VERTICAL GROWTH IN THE FORM OF SKYSCRAPERS.

(B) "ZONE 2" IS THE ZONE OF TRANSITION. AS THE CITY EXPANDS, HOUSES FORMERLY OCCUPIED BY WEALTHY FAMILIES WERE DIVIDED INTO ROOMS THAT NOW ARE RENTED TO RECENT IMMIGRANTS AND THE POOR; THIS ALSO CONTAINS WHOLESALE LIGHT MANUFACTURING AND MARGINAL BUSINESSES (SUCH AS, SECONDHAND STORES, PAWNSHOPS, AND TAVERNS).

(C) "ZONE 3" CONTAINS WORKING-CLASS RESIDENCES AND SHOPS AND ETHNIC ENCLAVES, SUCH AS LITTLE ITALY.

(D) "ZONE 4" IS COMPOSED OF HOMES FOR AFFLUENT FAMILIES, SINGLE-FAMILY RESIDENCES OF WHITE-COLLAR WORKERS, AND SHOPPING CENTRES.

(E) "ZONE 5" IS A RING OF SMALL CITIES AND TOWNS POPULATED BY PERSONS WHO COMMUTE TO THE CITY TO WORK AND BY WEALTHY PEOPLE LIVING ON ESTATES.

THE TWO IMPORTANT ECOLOGICAL PROCESSES INVOLVED IN THE CONCENTRIC ZONE THEORY ARE "INVASION" AND "SUCCESSION".

HOWEVER, THE MODEL IS MOST APPLICABLE TO OLDER CITIES THAT EXPERIENCED HIGH LEVELS OF IMMIGRATION EARLY IN THE TWENTIETH CENTURY.

_______________________________________________________________

(2) "THE SECTOR MODEL" -- HOMER HOYT, 1939, STUDIED 142 CITIES -- SOON AFTER BURGESS GENERALIZED ABOUT THE CONCENTRIC ZONE FORM OF THE CITY, HOMER HOYT RE-CAST THE CONCENTRIC RING MODEL. WHILE RECOGNIZING THE VALUE OF THE CONCENTRIC RING MODEL, HOYT ALSO OBSERVED SOME CONSISTENT PATTERNS IN MANY AMERICAN CITIES. HE OBSERVED, FOR EXAMPLE, THAT IT WAS COMMON FOR LOW-INCOME HOUSEHOLDS TO BE FOUND IN CLOSE PROXIMITY TO RAILROAD LINES, AND COMMERCIAL ESTABLISHMENTS TO BE FOUND ALONG BUSINESS THOROUGHFARES ==è HOYT'S SECTOR MODEL IS SIMPLY A CONCENTRIC ZONE MODEL MODIFIED TO ACCOUNT FOR THE IMPACT OF TRANSPORTATION SYSTEMS ON ACCESSIBILITY.

(EXPLAINS A WIDER RANGE OF SETTINGS -- SIGNIFICANCE OF "TERRAIN AND TRANSPORTATION ROUTES" IN LAYOUT OF CITY);

RESIDENCES OF A PARTICULAR TYPE AND VALUE TEND TO GROW OUTWARD FROM THE CENTRE OF THE CITY IN WEDGE-SHAPED SECTORS --

(A) RECALL THAT MOST MAJOR CITIES EVOLVED AROUND THE NEXUS OF SEVERAL IMPORTANT TRANSPORT FACILITIES SUCH AS RAILROADS, SEA PORTS, AND TROLLY LINES THAT EMINATED FROM THE CITY'S CENTER. RECOGNIZING THAT THESE ROUTES (AND LATER METROPOLITAN EXPRESSWAYS AND INTERSTATE HIGHWAYS) REPRESENTED LINES OF GREATER ACCESS, HOYT THEORIZED THAT CITIES WOULD TEND TO GROW IN WEDGE-SHAPED PATTERNS, OR SECTORS, EMINATING FROM THE CBD AND CENTERED ON MAJOR TRANSPORTATION ROUTES. HIGHER LEVELS OF ACCESS TRANSLATE TO HIGHER LAND VALUES.

(B) MORE EXPENSIVE RESIDENTIAL NEIGHBOURHOODS LOCATED ALONG THE HIGHER GROUND NEAR LAKES AND RIVERS OR ALONG CERTAIN STREETS THAT STRETCH IN ON DIRECTION OR ANOTHER FROM DOWNTOWN AREA.

(C) (BY CONTRAST) INDUSTRIAL AREAS TEND TO BE LOCATED ALONG RIVER VALLEYS AND RAILROAD LINES

(D) MIDDLE-CLASS RESIDENTIAL ZONES EXIST ON EITHER SIDE OF THE WEALTHIER NEIGHBOURHOODS.

(D) (FINALLY) LOWER-CLASS RESIDENTIAL AREAS OCCUPY THE REMAINING SPACE, BORDERING THE CENTRAL BUSINESS AREA AND THE INDUSTRIAL AREAS.

(3) "THE MULTIPLE NUCLEI MODEL" -- CHANCEY HARRIS AND EDWARD ULLMAN, 1945 -- BY MID-TWENTIETH CENTURY, IT WAS CLEAR TO CHAUNCY HARRIS AND EDWARD ULLMAN THAT MANY CITIES DID NOT FIT THE TRADITIONAL CONCENTRIC ZONE OR SECTOR MODEL. CITIES OF GREATER SIZE WERE DEVELOPING SUBSTANTIAL SUBURBAN AREAS AND SOME SUBURBS, HAVING REACHED SIGNIFICANT SIZE, WERE FUNCTIONING LIKE SMALLER BUSNIESS DISTRICTS. THESE SMALLER BUSINESS DISTRICTS ACTED AS SATELLITE NODES, OR NUCLEI, OF ACTIVITY AROUND WHICH LAND USE PATTERNS FORMED. WHILE HARRIS AND ULLMAN STILL SAW THE CBD AS THE MAJOR CENTER OF COMMERCE, THEY SUGGESTED THAT SPECIALIZED CELLS OF ACTIVITY WOULD DEVELOP ACCORDING TO SPECIFIC REQUIREMENTS OF CERTAIN ACTIVITIES, DIFFERENT RENT-PAYING ABILITIES, AND THE TENDENCY FOR SOME KINDS OF ECONOMIC ACTIVITY TO CLUSTER TOGETHER. AT THE CENTER OF THEIR MODEL IS THE CBD, WITH LIGHT MANUFACTURING AND WHOLESALING LOCATED ALONG TRANSPORT ROUTES. HEAVY INDUSTRY WAS THOUGHT TO LOCATE NEAR THE OUTER EDGE OF CITY, PERHAPS SURROUNDED BY LOWER-INCOME HOUSEHOLDS, AND SUBURBS OF COMMUTERS AND SMALLER SERVICE CENTERS WOULD OCCUPY THE URBAN PERIPHERY.

(CITIES DO NOT HAVE ONE CENTRE FROM WHICH ALL GROWTH RADIATES -- BUT RATHER – SPECIALIZED CELLS OF ACTIVITY WOULD DEVELOP ACCORDING TO SPECIFIC REQUIREMENTS OF CERTAIN ACTIVITIES, DIFFERENT RENT-PAYING ABILITIES, AND THE TENDENCY FOR SOME KINDS OF ECONOMIC ACTIVITY TO CLUSTER TOGETHER) ===è CITIES HAVE A NUMBER OF CENTRES OF DEVELOPMENT BASED ON SPECIFIC URBAN NEEDS OR ACTIVITIES -- CITIES GROWTH ANNEXES OUTLYING TOWNSHIPS WITH VARIOUS NUCLEI (GOV CENTRES, EDUCATION, MEDICAL COMPLEX, ETC.,. HEAVY INDUSTRY WAS THOUGHT TO LOCATE NEAR THE OUTER EDGE OF CITY, PERHAPS SURROUNDED BY LOWER-INCOME HOUSEHOLDS, AND SUBURBS OF COMMUTERS AND SMALLER SERVICE CENTERS WOULD OCCUPY THE URBAN PERIPHERY.

(A) IN ADDITION TO THE CENTRAL BUSINESS DISTRICT, OTHER NUCLEI DEVELOPED AROUND ACTIVITIES SUCH AS AN EDUCATIONAL INSTITUTION, A MEDICAL COMPLEX, OR A GOVERNMENT CENTRE.

(B) RESIDENTIAL NEIGHBOURHOODS MAY EXIST CLOSE TO OR FAR AWAY FROM THESE NUCLEI. A WEALTHY RESIDENTIAL AREA MAY BE LOCATED NEAR A HIGH-PRICED SHOPPING CENTRE, FOR INSTANCE, WHILE LESS EXPENSIVE HOUSING MUST LOCATE CLOSER TO INDUSTRIAL AND TRANSITIONAL AREAS OF TOWN.

THIS MODEL FITS SOME URBAN AREAS SUCH AS TORONTO, WHICH HAS LARGE NUCLEI SUCH AS THE BUSINESS DISTRICT OF NORTH YORK.

IT ALSO APPLIES TO A NUMBER OF COMMUNITIES SUCH AS EDMONTON, WHICH HAVE NUCLEI AROUND UNIVERSITIES.

HOWEVER, CRITICS SUGGEST THAT IT DOES NOT PROVIDE INSIGHTS ABOUT UNIFORMITY OF LAND USE PATTERNS AMONG CITIES AND RELIES ON A MATTER-OF-FACT EXPLANATION OF WHY CERTAIN ACTIVITIES ARE LOCATED WHERE THEY ARE.