Urban Ecology - Ecological Systems - page 278

Principle 4 : Urban form is heterogeneous on many scales, and fine-scale heteroge-
neity is especially notable in cities and older suburbs.
The heterogeneous form of contemporary urban systems extends into the sur-
roundings [ 28 ]. The suburban fringe in rapidly growing cities may abut farms,
desert, forest, or whatever landscape constitutes the predominant rural or wild land
cover. Indeed, the adjacencies are often convoluted and complex, leading to
interdigitation of urban elements with the wilder or more rural landscape. In
some wealthy urban regions, individual homes are embedded in what is otherwise
a wild matrix [ 29 ]. An example is the building of suburban houses in chaparral
shrublands in Mediterranean climates, such as Southern California. A similar case
is the construction of houses in the forest fringe of the Pacific Northwest
metropolises, or in forested foothills of the exurban lands of the Southern
Appalachians in the USA. The insertion of households whose financial equity,
lifestyle identity, social connections, and environmental attitudes have been defined
by urban life rather than a life of logging, farming, fishing, or other natural resource
management is perhaps a more significant interdigitation than the mere presence of
their homes. Similar juxtapositions exist for resorts that serve as remote summer or
winter destinations for urban dwellers. The interdigitation of urban with wild or
less-intensively managed lands results not only from the invasion of wild land by
new housing, commercial, or transportation corridors, but also by the afforestation
of foothill developments in arid or semiarid climates in which the lower slopes
would have been savanna or grassland. The well-to-do suburbs of Oakland, CA, are
an example, which now merge to some extent with the ridgetop forests of the Coast
Ranges, and where fire is now a real risk. The fact that urban land cover is growing
more rapidly than urban population in oil-subsidized economies [ 24 ] suggests that
such interdigitation will be the source of increasing conflicts and changing exposure
to natural disturbance regimes [ 29 ]. Recognizing the ongoing interaction of urban
and wild lands suggests this principle:
Principle 5 : Urban land covers and uses extend into and interdigitate with rural or
wild land covers and uses.
Urban form and hence its interaction with less-urbanized landscapes is the result
of a complex of causes. One cause of urban form is conformity to regional plans.
This cause is rare in many countries, such as the USA, but more common in Europe.
Successful constraint on urban sprawl is exemplified in the USA by the metropoli-
tan green line in Portland, OR, or the Urban-Rural Demarcation Line of Baltimore
County, MD [ 30 ]. In Baltimore County, more than 90% of residents live within the
URDL. The line has been in force since the 1970s and is controlled through zoning, the
restriction of sewer infrastructure, and the focusing on urban growth in the county to
specific corridors. However, the rarity of such regional controls is compensated for by
the commonness of the role of developer self-interest in determining urban form.
Indeed, urban planners often lament the predominance of the real estate market as
a driver of urban form. On the social roster of causes of urban form are those that are
described as “push and pull” factors. Persons and households choose to live at specific
places in the metropolis based on such pull factors as attraction to open space,