Greenspaces 105(5) Sulfur oxides(SOX), which are especially produced by fossil-fuel burning
industries and power plants, have significant local effects on some plant
species, cause acid precipitation that acidifies certain water bodies, and
forms particles/aerosols in the upper atmosphere.
(6) Nitrogen oxides(NOX), which are produced by vehicles and other high-
compression engines, cause acid precipitation that acidifies certain
waterbodies, blanket the region with nitrogen (noticeably changing
plant species dominance in water, on land, and by highways), and forms
particles/aerosols in the upper atmosphere.
(7) Heavy metals(e.g., zinc, cadmium, copper, nickel), which originate from
wear and chemical breakdown of surfaces such as in vehicles, bridges,
and machinery, inhibit various metabolic processes and therefore at
sufficient levels are toxic to numerous organisms.
(8) Particulate matter(particles), originating from fuel combustion, vehicle
and machinery wear, road dust and wear, fire, and wind erosion from
cropland and construction sites. Particulate matter is commonly classi-
fied as PM10 (small particles) or PM2.5 (very small particles), with the
latter being especially damaging to lung health of people and presum-
ably wildlife. Particulate matter andaerosols(particles or gases combined
with water droplets) also reduce incoming solar radiation.Species, of course, respond differently to different pollutants (Smith 1981).
Thus for ozone, pine (Pinus)andsycamore (Platanus)are very sensitive, but maple
(Acer)andfir (Abies)arenot. Yet for sulfur dioxide, pine and elm (Ulmus)arevery
sensitive, while maple and sycamore are not. Since air pollutants blanket an
urban region, varying from place-to-place in type and concentration, the distri-
bution of urban plants and vegetation is significantly molded by air pollution.
Greenspaces
Greenspaces,asunbuiltareasinan urban region, contain and may sus-
tain natural systems where ecological patterns, processes, and changes are in
most-natural or least-degraded condition. Yet greenspaces, like built areas, are
exceedingly diverse and significant to society. Therefore this section highlights
important greenspace types and illustrates key functions and ecosystem services
provided for the benefit of society.
Agreenspace may be covered by a single natural system or by many, such as
evergreen forest, deciduous woodland, shrubby hilltop, rock outcrop, meadow,
hedgerow, aquifer, pond, stream, wetland, vernal pool, and soil. Periodically the