230 Basic principles for molding land mosaics
(C) Metapopulation arrangement.Human activities in the urban region often
subdivide a large natural population into spatially separate small pop-
ulations with few individuals moving among them (a metapopulation),
in which case a few large natural patches, each surrounded by small
patches, is an excellent design for sustaining metapopulations.
(D) Metapopulation dynamics.Species disperse outward from a large patch,
providing genetic variation and reducing local extinction in nearby
small patches, whereas species that disappear from a small patch are
less likely to return or recolonize, if the patch is isolated or surrounded
by an inhospitable matrix.
(E) Movement among small patches.Foraspecies that inhabits and moves
among a few small patches, loss of a patch tends to reduce population
size, movement, and stability.
(F) Straightand convoluted boundaries.Astraight boundary tends to have
more species movement along it, whereas a convoluted boundary with
lobes and coves provides diverse wildlife habitat and facilitates bound-
ary crossing between adjacent habitats.Wat er f lows
(A) Surface runoff.Rainwater washing surfaces and soils of a land mosaic
carries dissolved chemicals, erodes surface particles containing chemi-
cals, and rapidly flows as stormwater into and along channels to cause
apulse of flooding, and to deposit its contents in gullies, streams, lakes,
and other water-bodies (Figure9.1).
(B) Groundwater f lows. Surfacewater carries dissolved chemicals down into
theground where they may accumulate and contaminate the typi-
cally slow-moving water of an aquifer, or groundwater may be partially
cleaned by flowing through soil or wetlands to water bodies on the
surface such as streams and lakes.
(C) Streamcorridor.A(‘‘ blue-green”) ribbon of dense natural vegetation that
covers the floodplain, both hillslopes, and a strip of interior habitat on
both adjoining upland areas will normally provide protection against
erosion, dissolved mineral nutrients, and toxic chemicals from the
matrix, especially if the vegetation widens to surround entering inter-
mittent channels.
(D) Vegetation along small channels.Vegetation protecting intermittent chan-
nels and small (first-order) streams is especially important for minimiz-
ing downstream peak flows and flooding.
(E) Floodplain or riparian vegetation.Dense floodplain vegetation, especially
shrub cover, provides friction to reduce downstream flooding, pro-
vides shade, dead leaves and wood to enhance fish and other aquatic