Nature in urban regions 149Ban*
Ban*
Cut•Nai+Nai+Ula•
Por•San*
San*
Sto+Sto+
Ott+Ott+Seo* Sap+
Mos*Eas• Mex*
Mos*
Bar+Iqu•Ber+Ber+Teg•Kua+Kag•Edm•Edm•Atl•
Atl•Number of gaps between natural landscapes in urban regionNumber of gaps near metro area and natural landscapesisolated by a single gap02
1
2
3
4
5
46 8
Sdt+Sdt+
Te h*Te g*
Keg*
Bei*
Cai*
Cai*
Rom+Bra+Bar+Erz•
Abe•Rah• Can• Cut•= Gap ≤ 50 km from city center
= Isolated natural landscape
≤
≥Figure 6.6Number of gaps near cities and number of isolated natural landscapes
relative to total number of gaps between natural landscapes. Vegetation gaps or
breaks separate natural landscapes (>100 km^2 and compact in shape) and are
caused by human clearing, not an intervening ridge, river, or valley. Isolated
landscapes are those whose only connection to another natural landscape has been
cut, leaving a vegetation gap; this also considers possible connections outside the
urban region. See Chapter5 fornatural vegetation types, Figure 6.3 caption for
landscape types, and Figure 6.2 caption for city information.Wetlands
[N14]Major wetlands are absent in urban regions with cities of >8 million
population, generally scarce in regions with cities of 2 to 8 million, and sometimes frequent
around cities of <0.5 million(Figure6.7).
Wetlands in urban regions were often drained or filled long ago for farming
purposes. As the human population rose, wetlands disappeared under roads and
buildings, and often to reduce mosquito and other insect populations as pests
and disease vectors. However, wetlands provide many benefits to society, such
as reducing floodwaters, absorbing and breaking down chemicals, supporting
many special wetland species, and providing recreational sites.