16 8Built systems, built areas, and whole regions
of these, movement of people, produces varied effects, such as tree cutting,
overfishing, livestock grazing, road construction, soil erosion, damaging sensi-
tive habitats and disturbance of wildlife (Lucket al.2004). Each of the diverse
effects often has a major degradation effect, generally extensively analyzed in
theliterature, on an adjoining natural ecosystem, whether terrestrial or aquatic.
More modest interactions go in the opposite direction, from natural to built
area. Here positive effects include cooling during hot periods and a source of
species and biodiversity. A natural area adjacent to a built area can absorb and
break down pollutants, and provide ready access to nature and nature-related
recreation for residents. Negative interactions of natural areas on built areas
include being a source of mosquitoes and other insects as pests and disease
vectors, floodwater, wildfire in dry climates, pest animal populations, and dan-
gerous large predators.
If everyone lived in an enormous skyscraper and the rest of an urban region
were nature, people would have ready access to a small area around their build-
ing, and natural systems would be the best ever. Conversely, if the homes of every-
one were evenly distributed across the region, natural systems would be exten-
sively degraded, probably the worst possible design. The planning trick then is
tocreate a land with people aggregated enough to sustain widespread natural
systems, in order that their uses for society remain vibrant for the long term.
Withall urban regions little-planned and urbanization ongoing, one could
focus on mitigation or restoration. Yet those approaches have usually been piece-
by-piece site-by-site activities. While valuable, especially for the most sensitive or
strategic places, a differenttwo-step planning approachseems more promising.
First plan the region for big areas, then mold small places to fit the big vision.Built systems
Keypatterns and results identified in the figures are grouped into the
following categories: (1) ring highways; (2) radial highways, ring highways, and
commuter-rail lines; (3) airports and aircraft noise; (4) shipping/ferry ports, air-
ports, and development corridors; and (5) wildlife underpasses and overpasses.Ring Highways
[S1]Half of the urban regions have no external ring highway, only radial high-
ways(Figures7. 2and7. 3).
In these cases, strip (ribbon) development tends to spread along and near
theradial highways producing car-dependent communities, interrupting stream/
river corridors, and forming a barrier to regional wildlife movement. However,