Greenspaces 109City and metropolitan area
River corridors typically serve as a major infrastructure conduit for the
city and are squeezed by numerous engineered hard structures. Small gravel
maintenance roads on the floodplain are common. Normal water levels are
low, in part due to groundwater pumping, while peak flows and flood hazard
are higher (Groffmanet al.2003). Pipes carry stormwater, human wastewater,
and industrial pollutants rapidly to the river which becomes severely polluted.
Stagnant pools and wetlands seasonally breed clouds of mosquitoes and midges
(Robinson 1996). Natural vegetation on the floodplain absorbs some floodwater
and supports rich biodiversity. Recreation may be important in river corridors.
Highway corridors are sources of vehicular and road pollutants, which are
washed by stormwater into water bodies. Traffic noise degrades nearby habitat
formany wildlife species. Railway corridors suffer loud intermittent noise, but
still may be rather effective conduits for wildlife movement. Steep slopes cov-
ered by residential developments or squatter settlements have elevated hydro-
logic, erosion, and sedimentation problems, and are more susceptible to periodic
environmental disasters. Coastlines have very little protected area so remnant
natural beach, dune, vegetation, and wetlands along the coast are rare habitats
with concentrations of rare species. Also, the paucity of natural coastal area
means that nearby aquatic ecosystems are severely degraded.
In the metro area a large semi-natural park, as the best facsimile of nature,
commonly has educational and inspirational value, but also may have security
problems. Commonly a few relatively rare species are present. Furthermore a
large semi-natural greenspace (Konijnendijket al.2005): (1) serves as a major
source of species dispersing to other city greenspaces; (2) reduces flood hazard;
(3) cools surrounding downwind built areas for a considerable distance; and
(4) attracts birds migrating across the metro area. A large urban wood-lawn park
also provides the last four benefits. A railway yard tends to be rich in non-native
species mainly transported by trains.
Atafiner scale, tree lines provide continuous cover and cool shade that
enhance movement by people and birds. A shrub line provides cover and move-
ment enhancement for terrestrial animals, and serves as a visual barrier for
people, e.g., between house lots. A row of greenspace stepping stones enhances
directional movement of some species.
Vacant lots often teem with non-native species, and illustrate the process
of succession plus the regeneration power of nature. School yards have deeply
compacted soil, and may serve as roosts for gulls, geese, or ducks on windy
nights. The urban cemetery is usually biologically impoverished, especially due
tothescarcity of shrubs. Finally, green roofs capture and evaporate precipitation