10 6Natural systems and greenspaces
central ecological and natural-systems values elucidated will be supplemented by
pointing out other issues, such as economics, social meeting places, aesthetics,
and public health.
Aglimpse of the urban region as a whole is useful before focusing in on spe-
cific greenspace types. Many ecological patterns and processes have been com-
pared between urban and rural or suburban areas (Gilbert 1991, Birdet al.1996).
Added insight is often gained by analyzingurban-to-rural gradients,fromcity
center to the outer urban-region ring dominated by natural vegetation and/or
agriculture. For example, studies of over 200 urban areas show that lichens
decrease sharply from rural to urban sites, presumably largely due to the combi-
nation of desiccation and air pollution (Schmid1975,Gilbert 1991 ). Spatial pat-
terns and plant species change along the gradient (Steinberget al.1997, Williams
et al.2005,Hahs and McDonnell2007). Soil characteristics such as hydropho-
bic conditions, fungi, heavy metals, organic matter, and mineral nutrients also
change markedly from rural to urban greenspaces (McDonnellet al.1997,Pouyat
et al.1997). The presence of rare species and many wildlife characteristics also
sharply decrease along this gradient (Gilbert 1991 , Birdet al.1996,vander Ree
and McCarthy2005). The number of native species decreases, but the number
of non-native species often increases more, so semi-natural city-center sites may
have the greatest number of total species (Kowarik and Langer2005). Landscape
ecology patterns also change along an urban-to-rural gradient (Luck and Wu
2002, McGarigal and Cushman 2005). Discontinuities in response curves may be
expected along urban-to-rural gradients, such as a drop in temperature at the
metro-area border (Spirn 1984). Ecological measurements along numerous radii
of an urban region might be expected to have the highest variability in the
vicinity of the metro-area border or inner urban-region ring.
In Northern and Central Europe, plant species richness has been correlated
with a city’s area and population (Klotz1990). Species number increased steeply
up toacityofabout130km^2 and 100 000 inhabitants. Plant species number
remained essentially constant from about 130 to 420 km^2 (50 to 160 mi^2 ) and
population 100 000 to 1 300 000, beyond which the curves noticeably rose. The
smallest cities measured (Ballensted and Schmalkalden, Germany), both in area
and population (1.5 and 2.5 km^2 ;10000 and 17 000 inhabitants), had about 350
plant species and the largest city, West Berlin (481 km^2 ;1900 000 inhabitants),
had approximately 1400 species.
Where would you go in your city to find the lowest, and highest, species
richness? Ignore the zoo. In Dusseldorf, Germany, five groups of species (plants,
butterflies, grasshoppers, landsnails, and woodlice) were measured in 38 habitat
types (Goddeet al.1995). Overall, six habitat types had the fewest species, though
considerable variation from group to group existed (in order, beginning with