Nature in urban regions 145Natural and wooded landscapes close to a metropolitan area are subject
todiverse and often intense human impacts, which are likely to increase as
urbanization proceeds. Thus flood-control benefits, nature conservation, cooling
sources reducing urban heat-island effects, and so forth in these important land-
scapes represent a particular challenge. Indeed wooded landscapes are especially
valuable for diverse recreational activities in proximity to a city. In the outer
portion of an urban-region ring, natural and wooded landscapes are normally
less subject to degradation, and hence are a particularly good investment for
maintaining aquifer/water-supply protection, nature conservation, clean surface
waterbodies, and many other environmental and socioeconomic benefits for
society.
[N4]Forhalf the regions, the largest natural patches present (outside of natural landscapes)
are relatively small (median sizes 0--12 km^2 )(Figure6.3).
This suggests lower biodiversity, lower connectivity, more degraded habitat,
and more risk of patch shrinkage and disappearance, than if these ecologically
critical patches were larger.
Stability related to number and types of natural landscapes
[N5]Most regions have 3--12 natural landscapes, 8 % have only one or two, and
another 8 % have no natural landscapes remaining(Figure6.3).
Alownumber indicates little stability plus high risk for the many ecological
values of large natural landscapes. Also few natural landscapes suggest some
diversity of types may be present, but little stability exists due to the low redun-
dancy of types. A higher number of natural landscapes should provide both a
diversity of types and reasonable stability.
Regional connectivity for nature
[N6]Afully connected emerald network of natural landscapes, with no major
gaps separating them, is present in a quarter of the urban regions(Color Figures1--39).
Theemerald networkis one of the most important patterns in this book. Effec-
tively it is a set of large natural interconnected patches, in this case natural
landscapes of >100 km^2. These landscapes are large enough to provide the range
of large-patch benefits, such as protection of aquifers, large-home-range species,
and viable populations of interior species. Also they are numerous enough to
provide some diversity and some redundancy of types, and therefore stability.
The connections or corridors permit effective movement of species and walkers
throughout the network. Multidirectional corridors for movement also provide
stability, for example, in the face of global climate change or the spread of a